Source: UNIV OF MINNESOTA submitted to
OVERSTORY AND UNDERSTORY EFFECTS ON TREE REGENERATION: EXPERIMENTS EXPLORING THE IMPORTANCE OF ABOVE- VERSUS BELOWGROUND COMPETITION
Sponsoring Institution
National Institute of Food and Agriculture
Project Status
TERMINATED
Funding Source
Reporting Frequency
Annual
Accession No.
0010804
Grant No.
(N/A)
Project No.
MIN-42-074
Proposal No.
(N/A)
Multistate No.
(N/A)
Program Code
(N/A)
Project Start Date
Oct 1, 2005
Project End Date
Sep 30, 2010
Grant Year
(N/A)
Project Director
Montgomery, R. A.
Recipient Organization
UNIV OF MINNESOTA
(N/A)
ST PAUL,MN 55108
Performing Department
FOREST RESOURCES
Non Technical Summary
In many Minnesota forests, shrub densities are rising. Suppression of fire has been implicated in current high shrub densities in many Minnesota forests and in S. Minnesota forests, invasive shrubs (e.g. buckthorn/) /also contribute. Thick shrub understories deter forest regeneration through slow growth and increased mortality of seedlings. Removal of competing vegetation through brushing or herbicide is a common management practice. Although we know that shrub competition can have negative impacts on tree regeneration we know little about the mechanisms by which shrubs and trees interact. To what extent is competition for light versus water or nutrients? Do the effects of shrubs differ among species? This project furthers our understanding of the mechanisms by which shrubs interact with tree seedling regeneration in two Minnesota ecosystems of ecological and economic importance, red pine forests and oak savannas.
Animal Health Component
50%
Research Effort Categories
Basic
50%
Applied
50%
Developmental
(N/A)
Classification

Knowledge Area (KA)Subject of Investigation (SOI)Field of Science (FOS)Percent
1230610107060%
1230620107040%
Goals / Objectives
(1)determine the impact of competition from shrubs and other understory vegetation on survival and growth of tree seedlings; (2) understand the mechanisms by which shrubs and tree seedlings compete for resources and, in particular, the relative importance of above- versus belowground competition; and (3) test hypotheses related to species differences in response to competition.
Project Methods
Data will be collected annually on growth, survival and physiology of Pinus resinosa, P. banksiana, P. strobus, Acer rubrum, Quercus rubra, and Betula papyrifera planted in eight experimental treatments that manipulate above and belowground competition from both trees and shrubs. The experiment is located in red pine forest in the Chippewa National Forest in North Central Minnesota. A comparative project is in the planning process for work at the Cedar Creek Natural History area in oak savanna. In addition, effects of the experimental treatments will be monitored through measurements of the resource environment, including light, water and nutrient availability.

Progress 10/01/05 to 09/30/10

Outputs
OUTPUTS: MIN-42-074 was initiated July 1, 1956 as project 1917 led by D.P. Duncan and colleagues. It initially focused on understanding suitability of southern MN farmlands for tree planting. In 1962, E.I. Sucoff assumed leadership of the project, which he led until 1999. Over those 37 years, Dr. Sucoff focused on the physiology of tree growth. From 2000-2003, Eileen Carey led the project and focused on net primary productivity and carbon sequestration of Lake States forests. Rebecca Montgomery took over leadership in 2004 and has focused on the physiology of competitive interactions that influence tree regeneration and on the interaction of tree physiology and climate change. PARTICIPANTS: Nothing significant to report during this reporting period. TARGET AUDIENCES: Nothing significant to report during this reporting period. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.

Impacts
Sucoff's early work on the project made important contributions to the cohesion-tension theory of the ascent of water in xylem. Studies examined physiological bases for tree growth exploring manipulations to improve yields (e.g. fertilization, irrigation). Sucoff also examined root function, plant water balance, mineral nutrition and related all to patterns of tree regeneration and growth in Minnesota Forests. Later focus was on net primary productivity and carbon sequestration of Lake States forests and the physiology of competitive interactions that influence tree regeneration and on the interaction of tree physiology and climate change.

Publications

  • No publications reported this period


Progress 01/01/09 to 12/31/09

Outputs
OUTPUTS: (1) Shrub-tree interactions: Analyzed data and drafted a manuscript on results from research on the effects of above- and below-ground interactions between tree seedlings and shrubs in a red pine ecosystem. Additionally, field studies of this topic in closed canopy red pine forests have been continued. We now have seedlings that have spent seven years in experimental manipulations of plant-plant interactions. (2) Warming: Continued experiments on climate warming and how it may modify plant-plant interactions. Specifically, the project continued a study that uses open top chambers to elevate temperature in a range of light environments and examine effects of warming on seedling growth and survival. The effects on productivity of associated vegetation have also been measured to examine indirect effects of warming on plant-plant interactions. In addition, a greenhouse warming and shading experiment on temperate and boreal tree seedlings common in Minnesota was also analyzed. The project has also involved mentoring one graduate student. The above results are being developed as journal publications. One important manuscript in review is entitled "Untangling positive and negative biotic interactions: views from above and below ground." Preliminary results have been presented at the North American Forest Ecology Workshop and in presentations in the Harvard Forest seminar series and in the Department of Forestry at the University of Toronto seminar series. Finally, during a summer site review of the Cedar Creek LTER, I co-led a field tour that visited experimental plots that manipulate shrub-seedling-forb-grass interactions in oak savanna. Graduate Student Years = 0.5. PARTICIPANTS: Researchers: Brian Palik (Northern Research Station, USDA Forest Service), J.M. Cheeseman (Department of Biology, University of Illinois), Kala Peebles and Chris Buyarski (Department of Forest Resources, University of Minnesota). Organizations: USDA Forest Service Northern Research Station, Chippewa National Forest, and University of Minnesota Cloquet Forestry Center, Hubachek Wilderness Research Center, and Cedar Creek Ecosystem Science Center. TARGET AUDIENCES: Researchers in the fields of forest ecology and silviculture and forestry professionals in industry, federal, state and county agencies--notably forest management professionals and silvicultural specialists. Additionally, the study areas have provided important learning sites for University of Minnesota students in FR3104/5104 Forest Ecology classes. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.

Impacts
Change in knowledge. (1) Shrub-tree interactions: Study results indicated that shrubs either suppress or facilitate seedling survival and growth depending on the seedling species, source of interaction (e.g. above- or belowground), and ecological context (e.g., gap or forest interior). In general, shrubs strongly influenced seedling survival and growth in gaps, with more modest effects in the forest interior. In gaps, the presence of shrub roots markedly decreased tree seedling growth and survival whereas shrub shade effects were neutral for three species (jack pine, red pine and red oak) and facilitative for the other three (white pine, red maple, paper birch). In the forest interior, shrub shade negatively affected tree seedling survival for the most shade intolerant species (jack and red pine). For several species the net effect of shrubs masked the existence of both positive and negative interactions above- and belowground (red maple, white pine, paper birch). These results highlight the complexity of plant-plant interactions in forested ecosystems, demonstrate that outcomes of these interactions vary with the nature of resource limitation and the ecophysiology of the species involved, and suggest that ecological theory should incorporate simultaneous positive and negative interactions occurring above and below ground. (2) Warming: We found that warming in the field increases herbaceous and shrub plant biomass and can increase or decrease tree seedling survival and growth depending on species. In associated greenhouse work, warming seedlings by 5C in extremely low light led to more rapid mortality. We further showed that some boreal species are more sensitive than temperate species. These findings are important to forestry professionals in choosing the type of silvicultural system and practices for various covertypes and stand conditions and notably the choices made in harvesting in order to foster effective regeneration of desired species now and under changing climatic conditions.

Publications

  • Powers, J.S., R.A. Montgomery, E.C. Adair, F.Q. Brearley, S.J. DeWalt, C.T. Castanho, J. Chave, E. Deinert, J.U. Ganzhorn, M.E. Gilbert, J. Antonio-Gonzalez, S. Bunyavejchewin, H.R. Grau, K.E. Harms, A. Hiremath, S. Iriarte-Vivar, E. Manzane, A.A. de Oliveira, L. Poorter, J.B. Ramanamanjato, C. Salk, A. Varela, G.D. Weiblen, and M.T. Lerdau. 2009. Decomposition in tropical forests: a pan-tropical study of the effects of litter type, litter placement and faunal exclusion across a precipitation gradient. Journal of Ecology: 97:801-811. http://10.1111/j.1365-2745.2009.01515.x


Progress 01/01/08 to 12/31/08

Outputs
OUTPUTS: Activities - During this reporting period work continued on the effects of dense shrub understories in red pine and oak savanna ecosystems in MN and the mechanisms that underlie these effects. Field studies continued on the affects of above and below ground competition from shrubs for seedling in red pine forests. New experiments began on climate warming and how it may modify these interactions. Finished processing biomass of >1500 individuals harvested in Fall 2006. Mentored one graduate student (Kala Peebles) in work related to this project. Numerous undergraduate students worked on processing tree biomass as part of this project. Events - Attended the annual meeting of the Ecological Society of America. Products - Gained new knowledge on effects of hazel on oak savanna biodiversity and tree seedling growth. Dissemination - Presentation on work related to the project at the annual meeting of the Ecological Society of America. Participated in an educational video by the Minnesota Christmas Tree Growers Association. Graduate student years = 1. PARTICIPANTS: Rebecca Montgomery, PI. - provided leadership in data collection and processing related to the project. Partner organizations: USDA Forest Service Northern Research Station, Cedar Creek Ecosystem Science Center, Chippewa National Forest. Training and professional development: Kala Peebles - graduate student TARGET AUDIENCES: Nothing significant to report during this reporting period. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.

Impacts
Change in knowledge - Shrubs reduced light availability by ~30% in both open sites and the forest interior. However, shrubs appear to have no effect on N availability in the forest interior while lowering N availability by 50% in open sites. Shrubs could either suppress or facilitate seedling survival and growth depending on tree species identity and ecological context (e.g., growing in open or forest interior). In general, shrubs strongly influenced seedling survival and growth in the open, but had little effect in the forest interior. There were two distinct patterns of response to manipulations in open sites. First, for white pine (Pinus strobus), red maple (Acer rubrum) and paper birch (Betula papyrifera) shade increased survival and roots decreased survival. The facilitative effects above ground and competitive effects below ground were of similar magnitude and counterbalanced each other such that survival of these species was similar whether shrubs were present or removed completely. The second pattern, found in jack pine (Pinus banksiana), red oak (Quercus rubra) and red pine (Pinus resinosa), showed a strong negative effect of roots and no effect of shade. In general, biomass growth responses mirrored those of survival. The results highlight the complexity of species interactions in forested ecosystems and the critical importance of belowground competition in structuring species interactions.

Publications

  • Montgomery, R.A., and T.J. Givnish. 2008. Adaptive radiation of photosynthetic physiology in the Hawaiian lobeliads: dynamic photosynthetic responses. Oecologia 155:455-467. http://dx.doi.org/10.1007/s00442-007-0936-3.
  • Montgomery, R.A., G. Goldstein, and T.J. Givnish. 2008. Photoprotection of PSII in Hawaiian lobeliads from diverse light environments. Functional Plant Biology 35:595-605.
  • Lopez, O.R., K. Farris-Lopez, R.A. Montgomery, and T.J. Givnish. 2008. Leaf phenology in relation to canopy closure as a determinant of shade tolerance in southern Appalachian trees. American Journal of Botany 95:1395-1407.
  • Lusk, C.H., P.B. Reich, R.A. Montgomery, D.A. Ackerly, and J.C. Cavender-Bares. 2008. Why are evergreen leaves so contrary about shade Trends in Ecology and Evolution 23:299-303.
  • Pelc, B.D. 2008. American hazel (Corylus cornuta) reprout dynamics and influence on understory community in Midwestern Oak savanna. M.S. Thesis. University of Minnesota.


Progress 01/01/07 to 12/31/07

Outputs
OUTPUTS: Activities - continued work on the effects of dense shrub understories in red pine and oak savanna ecosystems in MN and the mechanisms that underlie these effects. We continued field studies of the affects of above and below ground competition from shrubs for seedling in red pine and herbaceous biodiversity in oak savannas. We continued to process biomass of more than 1500 individuals harvested in Fall 2006. We continued to explore the resprout capability of Corylus cornuta (hazel) following various frequencies of disturbance (clipping) that simulates mechanical removal of competing vegetation. I mentored one undergraduate (Emily Mierendorf) and one graduate student (Brian Pelc) in work related to this project. Events - annual meeting of the Ecological Society of America, Schoolyard Ecology Explorations summer education workshop with K-12 teachers, field day with Chippewa National Forest & USDA Forest Service employees. Products - We gained new knowledge on effects of hazel on oak savanna biodiversity. Dissemination - Brian Pelc gave a presentation on work related to the project at the annual meeting of the Ecological Society of America. I participated in a workshop with K-12 teachers on bringing ecology into the classroom. We organized a field day for staff of USDA Forest Service Northern Research Station and Chippewa National Forest. PARTICIPANTS: Individuals - Rebecca Montgomery, PI. I provided leadership in data collection and processing related to the project. Partner organizations - USDA Forest Service Northern Research Station, Cedar Creek Ecosystem Science Center, Chippewa National Forest. Collaborators: Training and professional development: Emily Mierendorf - undergraduate student; Brian Pelc - graduate student; K-12 teachers through the Schoolyard Ecology Explorations program of the Cedar Creek Ecosystem Science Center. TARGET AUDIENCES: Target audiences - K-12 teachers through the Schoolyard Ecology Explorations program of the Cedar Creek Ecosystem Science Center. Efforts - I participated in one-day education workshop with teachers from the greater Minneapolis-St Paul region related to oak savanna ecology including the role of fires and dense shrub understories in biodiversity and function of this "endangered" ecosystem. Students conducted field research projects at both my study sites (Cedar Creek Ecosystem Science Center & Chippewa National Forest).

Impacts
Change in knowledge - We found that high clipping frequencies led to less total biomass produced over the course of the season and progressive declines in the ability to resprout. Monthly clipping is necessary to control shrubs and cutting once in a season is not effective. We learned that hazel density is negatively correlated with herbaceous species richness in oak savanna. We found that shrubs reduce light availability by 27-28% in both gaps and forest. Shrubs reduce survival by 12% across species and overstory conditions (gaps and closed canopy). For P. banksiana, trees alone reduced survival by 24%, while shrubs reduced survival by 25% in forest and 28% in gaps. We found that aboveground interactions reduce survival in forested sites whereas belowground interactions reduce survival in open sites.

Publications

  • No publications reported this period


Progress 01/01/06 to 12/31/06

Outputs
(1) Research continued on the effects of dense shrub understories in red pine ecosystems in MN and the mechanisms that underlie these effects. Shrubs reduce light availability by 27-28% in both gaps and forest. Shrubs reduce survival by 12% across species and overstory conditions (gaps and closed canopy). For P. banksiana, trees alone reduced survival by 24%, while shrubs reduced survival by 25% in forest and 28% in gaps. Aboveground interactions were found to reduce survival in forested sites whereas belowground interactions reduce survival in open sites. (2) We harvested this experiment and are processing the biomass of >1500 individuals. (3) This study has been expanded into oak savanna ecosystems and to explore impacts of shrubs on herbaceous biodiversity and mechanisms for those impacts. In open savanna sites, light availability below shrubs varies from 3-10% and less than 1% of the light reaching the shrub layer penetrates to the forest floor. (4) We explored the resprout capability of hazel following various frequencies of disturbance (clipping), simulating mechanical removal of competing vegetation. We found that high clipping frequencies led to less total biomass produced over the course of the season and progressive declines in the ability to resprout. These data suggest that frequent control in a single year may be more effective for vegetation control than annual control over multiple years.

Impacts
This project furthers our understanding of the mechanisms by which shrubs interact with tree seedling regeneration in two Minnesota -- ecosystems red pine forests and oak savannas. Better understanding of mechanisms of competition and facilitation provides information that will inform management decision making from both ecological and economic perspectives. In addition, our work on resprout capability highlights the importance of timing, duration and efficacy of mechanical vegetation control methods.

Publications

  • Dickie, I. A., R. A. Montgomery, P. B. Reich and S. A. Schnitzer. 2006. Physiological and phenological responses of oak seedlings to oak forest soil in the absence of trees. Tree Physiology 27: 133-140.


Progress 01/01/05 to 12/31/05

Outputs
(1) During this reporting period, I completely revised this project during this period shifting from the prior PIs focus on NPP to understanding mechanisms of competition. (2) In many Minnesota forests, shrub densities are rising. Suppression of fire has been implicated in current high shrub densities and in S. Minnesota invasive shrubs (e.g., buckthorn) also contribute. Thick shrub understories deter regeneration through increased mortality and slow growth of tree seedlings and saplings. Here I report on the first two years of a field experiment manipulating competition for light and soil resources between shrubs and trees in red pine forest in N. Central Minnesota. (3) Shrubs had significant effects on survival. We found evidence of both competition and facilitation and differences among species that depend on whether seedlings are growing in open (e.g., post-logging clearings) or forest interior. White pine (Pinus strobus) had significantly higher survival in forest compared to the open; removing shrubs increased survival in both treatments. In contrast, jack pine (Pinus banksiana) and red oak (Quercus rubra) had higher survival in large gaps but this effect was significant only in the absence of shrubs. Red maple (Acer rubrum) showed evidence of facilitation as it had higher survival in gaps when grown under shrub cover. White pine also showed higher survival in gaps under shrub cover but only when roots were not present (e.g., under simulated shade only). Addition of shade in the forest understory (due to shrubs or shadecloth) decreased survival in shade intolerant jack and red pine (Pinus resinosa). Finally, it appears that roots always have a negative or competitive effect. Jack pine showed decreased survival in open plots where shrub roots were present and white pine had lower survival in all plots with roots even if they were in open of forest conditions.

Impacts
This project furthers our understanding of the mechanisms by which shrubs interact with tree seedling regeneration in two Minnesota ecosystems red pine forests and oak savannas. Better understanding of mechanisms of competition and faciliation provides information that will inform management decision making from both ecological and economic perspectives.

Publications

  • No publications reported this period


Progress 01/01/04 to 12/31/04

Outputs
This period involved a turnover of the PI from E.V. Carey to R.A. Montgomery. Research examined seedling growth and survival of red, jack and white pine, red oak, red maple and paper birch under an aggregate retention silvicultural system with and without shrub control. Resource preemption by shrubs and the relative importance of above versus below ground competition was also examined. Data is currently being analyzed. These data will address questions involving balancing productivity and structural/compositional diversity and how shrubs influence tree regeneration in silvicultural systems. The graduate student supported during this period is scheduled to defend her thesis in Jan 2005.

Impacts
Understanding the mechanisms of change in productivity through time is essential to accurately predict forest response to global climate change and the potential of forests to store carbon in the future. The results of this project will provide data to refine models of NPP and baseline data for landowners, industry and government regarding the impacts of shrubs and other nontarget species on tree regeneration and productivity.

Publications

  • Montgomery, R.A. 2004. Effects of understory vegetation on patterns of light attenuation near the forest floor. Biotropica 36:33-39.
  • Harms, K.E., J.S. Powers, and R.A. Montgomery. 2004. Variation in small sapling density, understory cover and resource availability in four Neotropical forests. Biotropica 36:40-51.
  • Givnish T.J., R.A. Montgomery, and G. Goldstein. 2004. Adaptive radiation of photosynthetic physiology in the Hawaiian lobeliads: light regimes, static light responses, and whole-plant compensation points. American Journal of Botany 91:228-246.
  • Montgomery, R.A. 2004. Relative importance of photosynthetic physiology and biomass allocation for tree seedling growth across a broad light gradient. Tree Physiology 24:155?167.


Progress 01/01/03 to 12/31/03

Outputs
Project objectives are: (1) to determine how rates of net primary productivity (NPP) and carbon sequestration change over the course of stand development and (2) to explain declining NPP as forest stands age. Research efforts focused on objective one on an old growth forest site suggest that forests continue to be net sinks for atmospheric carbon at ages up to 400 years old. Initial carbon budget comparisons between Sylvania and a second-growth forest in the region indicate that both soil and stem respiration were similar between sites for 2002 and 2003; suggesting that other elements of the ecosystem carbon budget are responsible for the declines in carbon sequestration that occur as forest stands age. With respect to declining NPP as forest stands age, there were no significant differences within species as a function of tree size. Stem respiration rates decreased with increasing tree age. Rates scaled to the stand level showed wood respiration accounted for approximately 13 percent of total nighttime respiration. In contrast, soil respiration account for approximately 76 percent of total nighttime respiration. Graduate student=1.

Impacts
Understanding how and why net primary productivity (NPP) and carbon storage change in a forest over time is essential to accurately predict global NPP and the potential of forests to store carbon in the future. The results of this project will provide data to refine models of global NPP, provide baseline data to landowers, industry, and government intereseted in carbon sequestration as an added value to old forests.

Publications

  • No publications reported this period


Progress 01/01/02 to 12/31/02

Outputs
The objectives of the project are to: (1) determine how rates of net primary productivity (NPP) and carbon sequestration change over the course of stand development and (2) test hypotheses to explain declining NPP as forest stands age. Research efforts focused on objective one have yielded exciting results. Preliminary data from an old growth forest site indicate that during the period from October 2001-October 2002 the site was a net carbon sink of 161 gC/m2 yr. Spring and summer of 2002 had abundant precipitation, average temperatures, and no insect outbreaks resulting in favorable growing season conditions. Although net ecosystem exchange (NEE) at the old growth site is lower than at a paired earlier successional site (400 gC/m2 yr1), these data suggest that forests continue to be net sinks for atmospheric carbon at ages up to 400 years old. With respect to testing hypotheses to explain declining NPP as forest stands age, objective two, photosynthesis, water use, and respiration were measured on sugar maple and yellow birch ranging in age from 50-300 years old. Light and CO2 response curves were made at upper and lower canopy positions. Light saturated photosynthetic rates were greater from upper canopy foliage in sugar maple but were similar across canopy positions in yellow birch. Leaf-area-based maximum Rubisco activity (Vcmax) and rates of electron transport (Jmax) were greater for upper canopy leaves in both species and greater on average in yellow birch than sugar maple. There were no significant differences within species as a function of tree size. Maximum sapflow velocity was higher in sugar maple than in yellow birch. Velocity data will be scaled to whole tree water use when sample trees are examined after the 2002 growing season. Stem CO2 efflux rates were also greater in sugar maple. Stem respiration rates decreased with increasing tree age. Rates were scaled to the stand level by expressing CO2 efflux rates per unit stem volume and scaling to the respective whole tree wood volume per area of each species in the stand. Wood respiration accounted for approximately 13% of total nighttime respiration. In contrast soil respiration accounted for approximately 76% of total nighttime respiration. Future efforts will focus on how trees and forests of different ages respond to interrannual variability. Graduate students = 1

Impacts
Understanding how and why net primary productivity (NPP) and carbon storage change in a forest over time is essential to accurately predict global NPP and the potential of forests to store carbon in the future. By quantifying how forest function changes over the course of stand development, the results of this project will provide data to refine models of global NPP, provide baseline data to landowners and industry interested in carbon sequestration as an added value to old forests, and test hypotheses of why NPP declines as stand age increases.

Publications

  • No publications reported this period


Progress 01/01/01 to 12/31/01

Outputs
The objectives of the project are to: (1) determine how rates of net primary productivity (NPP) and carbon sequestration change over the course of stand development and (2) test hypotheses to explain declining NPP as forest stands age. The past growing season's research efforts were focused in two areas. Changes in conductive properties of xylem with increasing sapwood depth were characterized in red pine growing at the Cloquet Forestry Center in Cloquet, MN. These observations will help to refine estimates of the contribution of water limitations to NPP decline in this species. In addition, extensive stem and soil CO2 efflux measurements were made to characterize the respiratory component of forest carbon budgets in stands of varying ages. Preliminary results from this work are pending data analysis that will be completed prior to the 2002 field season. Graduate students = 0. Undergraduate directed research = 1.

Impacts
Understanding how and why net primary productivity (NPP) and carbon storage change in a forest over time is essential to accurately predict global NPP and the potential of forests to store carbon in the future. By quantifying how forest function changes over the course of stand development the results of this project will provide data to refine models of global NPP, provide baseline data to landowners and industry interested in carbon sequestration as an added value to older forests, and test hypotheses of why NPP declines as stand age increases.

Publications

  • No publications reported this period


Progress 01/01/00 to 12/31/00

Outputs
The objectives of the project are to: (1) determine how rates of net primary productivity (NPP) and carbon sequestration change over the course of stand development and (2) test hypotheses to explain declining NPP as forest stands age. The past year's research has focused on Objective 2. Research plots were established at Cloquet Forestry Center in Cloquet, MN and data were collected to compare water use and leaf-level photosynthesis of trees along an age gradient. These data from Minnesota were compared with data collected from sites in wetter and drier climates. The results demonstrated that potential leaf-level carbon gain of large trees is limited by available moisture in areas where potential evapotranspiration exceeds precipitation. Potential carbon gain of smaller trees was compromised to a lesser degree in these potentially water stressed areas. In contrast, large, old-growth stands growing in areas where precipitation exceeds evapotranspiration showed no signs of decreased leaf-level carbon gain relative to small trees. Overall, these data suggest that the mechanisms to explain age-related growth decline likely differ with environment. Graduate students = 0.

Impacts
Understanding how and why net primary productivity (NPP) and carbon storage change in a forest over time is essential to accurately predict global NPP and the potential of forests to store carbon in the future. By quantifying how forest function changes over the course of stand development, the results of this project will provide data to refine models of global NPP, provide baseline data to landowners and industry interested in carbon sequestration as an added value to old growth forests, and test hypotheses of why NPP declines as stand age increases. The current year's work has revealed that at least one mechanism to explain growth decline (hydraulic limitations to photosynthesis) varies with environment.

Publications

  • Carey, E.V., A. Sala, R. Keane and R. M. Callaway. 2000. (in press) Are old forests underestimated as global carbon sinks? Global Change Biology.


Progress 01/01/99 to 12/31/99

Outputs
In a multi-year study into the CA requirements of aspen (Populus tremuloides) seedlings were grown in hydroponic solutions. Response curves were developed between seedling growth and Ca level in solutiosn that had various levels of Ca, pH, trivalent Al, Mg, K, and NH4. Response curves were also developed showing how the uptake of Ca and other nutrients varied with the different mineral compositions in the solution. On these same seedlings, response curves were developed between growth and tissue concentrations of Ca and other elements. The results quantified levels of solution and tissue Ca that were associated with low growth under these various conditions. The probability that Ca is currently deficient in Lake States soils was evaluated. Also concluded was a multi-year study that determined how herbicides affected the abundance of vegetative and reproductive components of the major nectaring host plants of Karner blue butterfly (Lycaedies melissa samuelis), an endangered species. Graduate students = 1

Impacts
The aspen study was a step in developing guidelines to assess when CA deficiency is occurring in Minnesota's most important timber species. Some have raised the possibility that intensive harvesting and acid precipitation could lower current levels of Ca to the point where tree growth would be diminished. Although levels of solution Ca associated with our study have been reported in Lake States soils, there are many reasons to be cautious before stating that these soils are deficient in Ca.

Publications

  • Lu, E.-Y. 1999. Calcium requirements of Quaking aspen (Populus tremuloides) seedlings. PhD thesis. St. Paul, MN: University of Minnesota, Department of Forest Resources.
  • Sucoff, E. 1999. Herbicide effects on host plants of Karner Blue Butterfly and on butterfly development from egg to adult. Final Report to National Council of Air and Stream Improvement. St. Paul, MN: University of Minnesota, Department of Forest Resources.


Progress 01/01/98 to 12/31/98

Outputs
(1) Ca requirements of Trembling aspen. Growth of young seedlings at low solution concentrations of Ca was inhibited by increasing levels of Mg and NH4. (2) Potassium concentrations had no effect on growth. When grown at various levels of Ca and Al, young seedling growth was positively correlated with the Ca:Al ratio in the nutrient solution. (3) Herbicides and Karner blue butterflies: Documentation was obtained for the effects of herbicide on both vegetative growth and flowering of many nectaring plants of Karner blue butterflies. However, some species including lupine survived and were stimulated by the herbicides. (4) Long-term effects of herbicides. Changes in plant populations that occurred the sixth year after spraying were documented.

Impacts
(N/A)

Publications

  • Bates, P., E. Sucoff, and C. Blinn. 1998. Flooding effects on root suckering of trembling aspen. Northern Journal of Applied Forestry (in press).
  • Sucoff.E. 1998. The effect of herbicides on the development of Karner blue butterfly from egg to adult. FVMC Report 98-1
  • Sucoff, E. 1998. Effects of three herbicides on the vegetative growth and flowering of wild lupine. FVMC Report 98-2
  • Sucoff, E. 1998. Effects of three herbicides on the vegetative growth and flowering of 14 nectaring plants for Karner blue butterfly. FVMC Report 98-3


Progress 01/01/97 to 12/31/97

Outputs
(1) Calcium requirements of trembling aspen: Young seedlings in natural low Ca soils did not respond to Ca fertilization. When a complete nutrient solution, with and without Ca was applied to these soils, the aspen in the -Ca treatment grew less. (2) Fertilization with biosolids: Municipal sludge (39 or 78 metric tons/ha) and/or pulp and paper mill ash (13 metric tons/ha) had no significant effect on the growth of seedlings of six tree species. (3) Herbicides and Karner blue butterflies: Lupine, the obligate host of the endangered Karner blue butterfly was not adversely affected by the application of operational levels of herbicides. Some nectaring plants were adversely affected and others were not. Modeling combined with experiments suggests that herbicides sprayed directly on butterfly eggs will not affect the development of these eggs.

Impacts
(N/A)

Publications

  • Bates, P., E. Sucoff, and C. Blinn. 1997. Flooding effects on root suckering of trembling aspen. Northern Journal of Applied Forestry. (In press)
  • Sucoff, E. 1997. Comparative effects of woody and herbaceous competition on first 8-years of growth of white spruce. FVMC Report 97#1
  • Sucoff.E. 1997. The effect of herbicides on the development of Karner blue butterfly from egg to adult. FVMC Report # 2
  • Sucoff, E. 1997. Effects of three herbicides on the vegetative growth and flowering of wild lupine. FVMC Report #97-3


Progress 01/01/96 to 12/30/96

Outputs
(1) Nutrient (Ca) requirements of trembling aspen: In nutrient solution, growth of aspen was reduced by 20% when the Ca/Mg ratio in the root media fell below 0.1; a ratio rare in nature. Growth of aspen was reduced when the Ca/Al ratio in the root media fell below 1.8, a very low value for MN soils. (2) Ca and N fertilization: Nitrogen (135kg/ha) and Ca (195 kg/ha) applied singly and in combination did not change growth of mid-aged trembling aspen on Omega sands. The N alone treatment significantly increased the growth of young aspen. (3) Compost as a fertilizer: When municipal solid waste compost was applied at 70 tons or 140 tons per acre to 35 year old red pine, basal area growth did not change the first 3 years. The compost improved the moisture holding capacity and fertility of the sandy soil. (4) Pine growth reduced by competition: On one site, red pine kept free of all vegetative competition for 8 years, produced 3 to 10 times more volume than red pine sharing the site with sedge and/or woody competitors. On two other sites vegetative competition had much less effect on growth.

Impacts
(N/A)

Publications

  • Greene, T, T Nichols. 1996. Effects of long-term military training traffic on forest vegetation in central Minnesota. North J Appl For 13:157-63.
  • Greene, T, T Nichols, E Sucoff. 1996. Development of tactical vehicle guidelines for Camp Ripley - Phase II: Field testing of management prescriptions and vegetation model enhancement. Final Report to MN Dept. of Military Affairs.
  • Nichols, TJ. 1996. Activities of the University of Minnesota Forest Vegetation Management Cooperative. 1984-1995. FVMC Report #96-1.
  • Nichols, TJ. 1996. Effects of pulp mill sludge and ash on competing vegetation and tree growth. FVMC Report #96-3.
  • Nichols, T, EY Lu, E Sucoff. 1996. Effects of municipal solid waste compost application on early growth of forest plantations. Final Report to MN Office of Waste Management.


Progress 01/01/95 to 12/30/95

Outputs
(1) Ecological classification: successional pathways for 4 mapping units of the system used by the Chippewa National Forest. On sandy soils, aspen and pine forests are diverging to various mixtures of red maple, birch, fir, and other hardwoods. On heavier soils, most forests are converging to sugar maple stands differentiated by the associated hardwoods. (2) Nutrient calcium (and pH) effects on trembling aspen: in dilute nutrient solutions, Ca levels of 50 to 100 micromoles resulted in more growth than higher or lower concentrations. As Ca solution levels increased from 5 to 50 micromoles, tissue levels of Ca and many other essential nutrients increased. (3) Vegetation management: September release of red pine with glyphosate, trichlopyr or 2-4-D, damaged lamas shoots. Four surfactants added to commercial mixture of Accord did not damage red pine, but height growth of white spruce was reduced at least 40%. Addition of kerosene did not increase silvicidal activity of trichlopyr-bee. Preliminary results suggest that treating stumps with a pathogenic fungus may cause sprout mortality and reduce sprout growth during the second year. Fifteen to 30 tons/acre of pulpmill sludge produced excellent control of herbs on cutover site. Municipal solid waste compost increased weed growth while decreasing seedling growth of both red pine and white spruce.

Impacts
(N/A)

Publications


    Progress 01/01/94 to 12/30/94

    Outputs
    Biodiversity: Hexazinone, imazapyr, and glyphosate were applied on cutover sites. Species diversity (measured by Hills indexes) was little affected by the herbicides over a two-year period. Species composition, as measured by DCA was altered. Logging had a greater effect on species composition than did herbicides. Ca and pH effects on trembling aspen: We further identified the levels Ca, Al, and pH that influence the performance of trembling aspen. Succession: Preliminary measurements indicate differences in successional pattern among some upland ecological classification units on the Chippewa Plains in MN. Vegetation Management: (1) Herbaceous vegetation was still inhibiting the growth of red pine and white spruce 6 to 8 years after planting. (2) Release of 9-year-old white spruce plantations from herbaceous and bramble competition increased basal area growth by 41 percent. (3) Although imazapyr caused needle and shoot damage to red pine the year of spraying, at rates of 0.28 kg/ha, the treatment still resulted in improved growth after several years. (4) Among 8 treatments, a combination of 0.07 kg/ha imazapyr and 0.175 kg/ha sulfometuron-methyl proved most effective in grass control in seed orchards. (5) A survey indicated that herbicide use in MN decreased by over two-thirds in the last decade as a result of altered practices on USDA-FS and MN DNR lands.

    Impacts
    (N/A)

    Publications


      Progress 01/01/93 to 12/30/93

      Outputs
      Vegetative Management: (1) Effects of imazapyr on stem volume growth continue toincrease during 4th year after treatment. (2) Imazapyr had reduced effect on noncrop vegetation, 3 yrs after treatment. (3) Early and late summer treatments of clorpyralid controlled Canada thistle on CRP lands; white spruce and red pine not damaged. (4) Soils collected 2 yrs after application of sulfometuron still toxic to red pine in greenhouse trial. (5) Garlon 4 sprayed on one side of stem controlled maple, spraying entire circumference required to completely control white birch and red oak. (6) Simazine was more toxic to balsam fir and blue spruce when applied on soils treated with municipal solid waste. Biodiversity: Rate of recovery of preapplication vegetation following treatment with herbicides varied with herbicide (imazapyr, glyphosate, hexazinone) and with soil texture (loamy sand, loam). Ca, N and pH requirements of trembling aspen: (1) Aspen seedlings in water culture grew well at pH 3.8 and 5.5 but no roots grew at pH 3.0. Ca levels between 1.5 and 12.0 reduced root and shoot growth. Growth was vigorous at 100-200 micromolar Ca. (2) Visual Ca deficiency symptoms were described for leaves and roots. (3) One year after application to 10 to 40-year old aspen stands on three soils, Ca fertilizer showed no effect while N increased growth on one soil. In young stands growth increased linearly as the N concentration in the leaves continued up to at least 2.2% ODW. GSY=1.0.

      Impacts
      (N/A)

      Publications


        Progress 01/01/92 to 12/30/92

        Outputs
        Water Relations: A quantitative model was developed relating regulators of watersupply (root length, root hydraulic conductivity) to regulators of water demand (leaf area, leaf specific conductivity, and water potential gradient from root to leaf). The relationship was valid for red oak seedlings in moist soil. Forest Vegetation Management: (1) Sulfometuron applied prior to planting kept out most competing herbaceous vegetation for 3 years, but phytotoxicity to the red oak and black walnut seedlings crop trees was unacceptable. (2) Imazapyr used in site preparation effectively reduced herbaceous and woody competition; imazapyr damaged the red pine, but not the jack pine or white spruce. (3) An imazapyr release spray over white spruce caused extensive top kill, but lower branch growth was not affected and stem volume growth increased. (4) A tank mix of dicamba with imazapyr was more effective against black locust than imazapyr alone, possibly because the chemical was retained longer. (5) Glyphosate, hexazinone and imazapyr were sprayed for site preparation. The sensitivity to at least one of these chemicals was determined for 128 grasses, sedges, herbs, half shrubs or vines as well for 38 species of trees and shrubs. Results will be developed as part of vegetation management guidelines.

        Impacts
        (N/A)

        Publications


          Progress 01/01/91 to 12/30/91

          Outputs
          (1) Trees and Carbon Storage. The amount and cost of fixing carbon which would result from alternative strategies of tree planting in Minnesota was modeled using published yield data and estimated economic values. (2) Root-shoot Communications. The sites of resistance to water transport in red oak was characterized for the first time. (3) Vegetation Management. Site preparation and release. Stem-applied imazapr killed aspen but retarded growth of adjacent unsprayed red pine. Imazapyr + glyphosate did not control weeds,possibly because of the hot dry weather. Sulfometuron-methyl + glyphosate controlled competitors but may have inhibited red oak and black walnut growth. Tree response to competition. After 2-4 years of treatments, red pine and white spruce growth was stimulated equally by removal of all woody vegetation or removal of all herbaceous vegetation; growth was fastest when both were removed. (4) Community Classification. Vegetation on the Anoka sand plain was ordinated into species associations. Dept to water table and soil pH were closely related to the floristics. GSY=3.0.

          Impacts
          (N/A)

          Publications


            Progress 01/01/90 to 12/30/90

            Outputs
            ASPEN SUCKERING ?root sprouting?: Spring-collected aspen roots never initiated sprouts if flooded for 10 days beginning at replanting. In another experiment, roots sprouts which initiated in favorable conditions were killed by 1 to 2 weeks of flooding. CARBON STORAGE. The amount of carbon stored in the vegetation, mineral and organic soils, and lakes of Minnesota were calculated from survey data. TREES AND ENERGY USE, Minnesota. The effects over 40 years of landscape trees on residential heating and cooling were modeled in dollars, BTUs and carbon. ROOT-SHOOT COMMUNICATIONS. Patterns of root and shoot growth and patterns of leaf turgor suggest rejection of the Borchert hypothesis that water stress is the cause of repeated flushing in oaks. VEGETATION MANAGEMENT. Site preparation and release. The most effective way to use hexazinone, imazapyr, glyphosate, picloram, triclopyr, oxyfluorfan, sulfometuron methyl, 2,4-dichlorophenoxyacetic acid and several other chemicals were examined, as were several mechanical methods. Tree response to competition. In early results of this long-term study, red pine and white spruce are growing larger in the absence of any competition than when only woody or only herbaceous competition are removed.

            Impacts
            (N/A)

            Publications


              Progress 01/01/89 to 12/30/89

              Outputs
              ALUMINUM TOXICITY STUDY: Al reduces the fluidity of the lipid bilayer of northern red oak cell membranes. This may be a primary site of Al toxicity. ROOT-SHOOT COMMUNICATIONS. Growth was related to daily changes in shoot water relations during the first two flushes of northern red oak seedlings. Variables include, stomatal resistance transpiration and water, osmotic, and turgor potential. ASPEN SUCKERING. The hypothesis that low oxygen (O(2)) is the cause of poor suckering in aspen is being investigated. Sprouting from spring collected roots was delayed by 6-12% O(2) (v/v). Lower concentrations killed roots. Sprouting from summer collected roots was greatly reduced by 3 to 7 days of flooding. VEGETATION MANAGEMENT. A. Site preparation and release methods. The effectiveness of herbicides on major forest weeds was determined from a survey of user experience. Currently 16 field trials are evaluating the efficacy, treatment cost and crop tree tolerance for various forest herbicides at different rates, mixes, timing and method of application. B. Crop tree response to competition. Growth response of white spruce, red pine and hybrid aspen to competing vegetation is being quantified in 5 field studies. The results of these long-term studies will continue to improve forest weed control practices in Minnesota and the Lake States.

              Impacts
              (N/A)

              Publications


                Progress 01/01/88 to 12/30/88

                Outputs
                ALUMINUM TOXICITY STUDIES: Membrane effects: Al increases the activation energy for transport of water and other nonelectrolytes across oak root membranes. Al decreased by 1 to 3C the ability of membranes to remain fluid at low temperatures. Water stress x Al toxicity: Both water and stress and Al toxicity reduced vernal root initiation on white spruce. Synergistic amplification by having both stresses was not apparent. Al did not decrease transpiration of honeylocust. Studies to date do not show an ecologically signnificant intensification of Al toxicity as a result of mild water stress. VEGETATION MANAGEMENT STUDIES: Site preparation and conifer release methodology: Studies were continued and initiated into ways to improve the efficacy and lower costs of: site preparation prior to planting and release of crop trees from competition after planting. Numerous treatments were evaluated including different herbicides, herbicide mixtures, timing of application, methods of application and mechanical alternatives to chemicals. Response to competition: The response of white spruce to woody and herbaceous vegetation singly and in competition is being quantified. The results from these studies are already improving weed control practices in Minnesota.

                Impacts
                (N/A)

                Publications


                  Progress 01/01/87 to 12/30/87

                  Outputs
                  Six studies of the response of honeylocust to hydroponic and soil solution Al were synthesized. Growth was related to many soil solution variables, most closely to -exp Al solution activity and -(inorganic MAL)/Ca. Root branchiness was reduced at lower levels of A1 than were other growth measures. Tissue (Ca) (Al) and Al/Mg gave good predictions of growth. Response curves were also developed for Quercus rubra between soil solution Al and growth of nutrient accumulation. Al changes to activation energy for water transport across root membranes in red oak. Al had no effect on transpiration of red spruce, but Al increased transpiration of honeylocust at pH 4.0. Green ash seedling weight increased as soil temperatures rose from 8 to 20C. At lower temperatures stems weight was relatively high and root weight relatively low. P deficiency did not limit growth at low temperature nor did the response of seedlings to VA mycorrhizae vary with temperature.

                  Impacts
                  (N/A)

                  Publications


                    Progress 01/01/86 to 12/30/86

                    Outputs
                    The project shifted focus in 1986 to examine how soil conditions influence root growth and function of coniferous and deciduous species. I. Seedlings of red oak, honey locust and red spruce were grown in soils with a range of pH's (H(2)O) of 4.0 to 5.0 and A1 (saturated paste extracts) of 0.05 to 0.8 mM. Growth was correlated with solution chemistry and with elemental composition of tissues. High A1, low Mg, low Ca and low Ca/A1 ratios in the tissues were often the best indicators of reduced growth. Red oak seedlings were grown in solution cultures of varying A1/Ca ratios. In general low solution and tissue Ca exacerbated the effects of high A1. II. High A1 concentrations in solution culture lowered the hydraulic conductivity of the root systems of red oak. The effect may not be a direct result of A1 on the transport system. Phosphorous deficiency decreased root hydraulic conductivity in green ash but the effect seems to be indirect.

                    Impacts
                    (N/A)

                    Publications


                      Progress 01/01/85 to 12/30/85

                      Outputs
                      Physiologic studies on transplant technology: Coldstored bareroot red pine (RP)and white spruce (WS) seedlings were exposed to air and then dipped in water for 3 h or returned to moist cold storage (3C to 8C) for 1 to 5 days. Root and shoot growth after planting were less when exposure had reduced shoot psi of WS below -1.8 MPa and RP below -1.7 MPa. Our previous results with RP were confirmed: storage after exposure reduces growth; dipping was neutral or harmful. Bareroot RP was planted in soil at 8, 12, 16 and 20C. Total root length increased progressively with temperature and was very suppressed at 12 and 8C. Root tips were most numerous at 16C. Temperature had no effect on food reserves measured as soluble sugars. Red spruce and loblolly pine containerized stock grew into natural soil but not into acidified soil. Honey locust grew slower when soils had 800-6000 mu M A1. Root system hydraulic conductivity (Lp) and root cell permeability (Kw): Short term exposure to 3700 mu M A1 had no effect on Lp. A1 lowered the Kw of oak root cells; Ca had the opposite effect. A1 may have altered the packing density of polar head groups on membrane lipids. GSY = 1.0.

                      Impacts
                      (N/A)

                      Publications


                        Progress 01/01/84 to 12/30/84

                        Outputs
                        Red pine and white spruce seedlings were exposed in a range of environments, andtheir root and shoot water potentials were measured. For each situation root and shoot WP's were linearly related. Because the differences between root and shoot WP can be large and roots are more sensitive to WP, we suggest that root WP of seedling stock may be the preferred indicator of subsequent growth and mortality. Following root exposure RP seedlings were rehydrated for various durations at various temperatures. None of the rehydration techniques improved survival or growth of once-desiccated seedlings.

                        Impacts
                        (N/A)

                        Publications


                          Progress 01/01/83 to 12/30/83

                          Outputs
                          Studies on water uptake in red pine seedlings continued in the context that rootbehavior is the key to subsequent survival. 1. A method for distinguishing and quantifying the contribution to water flow of symplastic and apoplastic pathways was developed. Anaerobic conditions reversibly simulated apoplastic flux. 2. The hypothesis was disproved that rapid increase in specific water flux is caused by the initiation of new roots. The reasons that root conductivity increases with time from planting are being explored. 3. The relation of water flux to root length was quantified for bareroot planting stock. A physiologic rationalization was developed to explain the empirical observation that top:root ratio influences survival. ABA content in leaves of eastern cottonwood increased exponentially with decreases in turgor and water potentials. ABA content was not related to osmotic potential. Experiments were initiated to relate needle water potential of bareroot seedlings to subsequent survival. Early results suggest that the published relationships do not apply to red pine and white spruce.

                          Impacts
                          (N/A)

                          Publications


                            Progress 01/01/82 to 12/30/82

                            Outputs
                            A series of studies related to the root permeability of red pine transplants gave these results: the major site of resistance to water uptake is in the roots. It is experimentally difficult and perhaps theoretically impossible to achieve constant flow at meaningful rates using the pressure pot method of measuring root permeability. Published results appear to underestimate true conductivity. Image analysis can be used to measure root length short cutting the standard method of Newman. The extract of the Yucca plant greatly stimulated root initiation of highly stressed red pine transplants, but had no effect on root initiation or growth in less stressed seedlings. No practical application is currently envisaged. Work was initiated on the relation of turgor in poplar leaves to the synthesis and metabolism of ABA. GS = 2.

                            Impacts
                            (N/A)

                            Publications


                              Progress 01/01/81 to 12/30/81

                              Outputs
                              THIRSTY, a model which predicts soil moisture depletion beneath aspen over-stories was developed. The model compared favorably with three previously published water depletion models. Using historic weather data, 40 years of soil moisture deficits were recreated and then compared with plot growth data over the same period. Inclusion of the moisture variable did not reduce variation predicted by the Chapman-Richards equation. Variation in the height growth of red pine nursery seedlings generally could not be explained in terms of nutrient deficiency. A study was initiated to evaluate if Fiscus-Dalton techniques for determining root permeability apply to transplanted seedlings.

                              Impacts
                              (N/A)

                              Publications


                                Progress 01/01/80 to 12/30/80

                                Outputs
                                Several models for predicting soil moisture depletion have been developed and tested on data collected during 1979 on four aspen stands. Data was similarly collected from five stands during 1980. The initial models have proved unsatisfactory and work to adjust them and find additional models is continuing. Ratios of potential to actual ET were determined for other sites in Northern Minnesota. The literature on the water relations of the true aspens was reviewed and synthesized into a report.

                                Impacts
                                (N/A)

                                Publications


                                  Progress 01/01/79 to 12/30/79

                                  Outputs
                                  Deep supercooled water in woody xylem freezes in many independent events over a span of as much as 20 C; e.g. -20 to -40 C. The unit which freezes in an event is a single cell or a small group of cells. The percent of water frozen can correlate well with viability as judged by staining. Ray cells can be plasmolyzed as alternative test of viability. Sixty to 80% of the day-to-day variation in height growth of hybrid poplars can be explained by temperature. Dawn leaf water potential and soil matric potential were effective in predicting drought-induced reduction in height growth. The 2-year-old trees are on siltloams. The 7-year remeasurement was made on the long-term plot system which monitors growth appearance and salt damage along Minnesota roadways.

                                  Impacts
                                  (N/A)

                                  Publications


                                    Progress 01/01/78 to 12/30/78

                                    Outputs
                                    Field measurements relating poplar growth to plant and soil water continued. Results to date suggest that plant water potential can sometimes but not always be used to indicate when stem elongation is being inhibited by water stress. To date the correlation has not proved reliable on coppice stands in deep loamy sands. Patterns of soil moisture depletion as determined for several stands of poplar are consistent with existing knowledge for other species. The various hypotheses of stomatal control in trembling aspen were tested. Preliminary results favor the pattern of sudden closing at minus 17 bars. The effect of various experimental and natural factors on deep supercooling of xylem is being studied.

                                    Impacts
                                    (N/A)

                                    Publications


                                      Progress 01/01/77 to 12/30/77

                                      Outputs
                                      Collected field data relating leaf water potential and leaf diffuse resistance of hybrid poplar to stem elongation and leaf growth as well as to soil moisture and potential evapotranspiration. Summarized first year of data. The sensitivity of most major forest weed and crop species to the herbicide tebuthiuron was determined. The toxicity to all species persists at least two growing seasons. Nitrogen-fixing capacity of organisms free-living on plant surfaces were determined for a second summer.

                                      Impacts
                                      (N/A)

                                      Publications


                                        Progress 01/01/76 to 12/30/76

                                        Outputs
                                        Collected field data relating leaf water potential and leaf resistance of hybridpoplar to soil moisture and potential evapotranspiration. Rangewide variation in jackpine was described for 3 isosymes; amylase, leucine amino peptidase and esterase. Seed sources varied only in esterase for which system heterozygosity is suggested. It was determined that activity of the herbicide, tebuthiuron persists in the soil for at least one year. Tebuthiuron applied in 1 foot wide bands 9 feet apart, totally kills aspen overstory. Relative sensitivity of major overstory and understory plants was measured. Propagules of some native symbiotic nitrogen fixing plants were collected and grown in the greenhouse. Nitrogen fixing capacity of organisms free-living on plant surfaces were collected from selected forest stands in Minnesota and Oregon.

                                        Impacts
                                        (N/A)

                                        Publications


                                          Progress 01/01/75 to 12/30/75

                                          Outputs
                                          Determined that kinetin applied to excised roots decreases their permeability towater. Determined that tebuthiuron, 1-(5-tert-butyl-1,3,4-thiadiozol-2-yl)-1,3-dimethylurea, acts as a broad spectrum herbicide and that Populus tremuloides is particularly sensitive. Determined that NaCl decreases the ability of Malus sp. to harden in response tobrief exposure to low temperature. Determined that NaCl sprayed on garden treesdecreases their hardiness. Ranked major species which grow in Minnesota according to their tolerance to salt damage.

                                          Impacts
                                          (N/A)

                                          Publications


                                            Progress 01/01/74 to 12/30/74

                                            Outputs
                                            The following results were obtained in studying the effects of deicing salts on woody vegetation: Salt spray is the major cause of twig-dieback and needle browning of red, white and Austrian pine. The soil-salt concentration is increased with an exchange sodium percentage of more than 13 percent usually present. The higher soil salt concentration (NaC1) lowers cold-hardiness which enhances midwinter dieback in some species. This damage is enhanced during periods of drought. Soil-salt damage is high along city streets, intersections,and depressed medians of major highways. Methods for reducing salt damage of vegetation by deicing salts are recommended.

                                            Impacts
                                            (N/A)

                                            Publications


                                              Progress 01/01/73 to 12/30/73

                                              Outputs
                                              The following progress was made in studying effects of deicing salts on woody vegetation. A permanent plot system was established to monitor over time the effects of deicing salts on plant growth. It was determined that most highway-associated twig dieback occurs in midwinter in association with increases in NaC1. Extent of salt damage along city streets was evaluated. Classification of highway sites into damage risk classes continued. Studies were initiated into interaction between salt damage and cold hardiness. The research with cytokinins showed that benzyl adenine inhibits potassium transfer from soil to root exudate.

                                              Impacts
                                              (N/A)

                                              Publications


                                                Progress 01/01/72 to 12/30/72

                                                Outputs
                                                In the study on the effects of deicing salts, progress was as follows: Amounts of salt moving aerially from highways were monitored at 11 locations with slope,distance from road, and road orientation as variables. The role of salt in causing damage to pines was assessed by controlled sprays, by relating external salt, and by internal NaCl to damage. Relative salt sensitivity for Minnesota species was listed from literature and observation. A preliminary classification of highway sites into damage risk classes was made. In the studyof the effects of cytokinins on growth, progress was as follows: Hypothesis to explain effect of cytokinin on cation transfer was developed. The effect of cytokinin and root decapitation on root exudation was examined. Initiated literature review of aging in woody plants.

                                                Impacts
                                                (N/A)

                                                Publications


                                                  Progress 01/01/71 to 12/30/71

                                                  Outputs
                                                  The diurnal pattern of water potential in redpine was measured part of a second year, and manuscript concluding study prepared. Growth was probably limited by water stress every day of summer. Water potential varied inversely with potential evapotranspiration and directly with soil moisture, (dawn readings.) Little variation was observed with needle age or branch position. Water potential was compared second year on thinned and unthinned stands and manuscript was prepared. Needle elongation stopped sooner than cataphyll deposition in red and Scots pine. The reason current needles needed for bud development was explored. A literature compilation was made giving the relativesensitivity of 99 species of woody plants grown in Minnesota to five air pollutants.

                                                  Impacts
                                                  (N/A)

                                                  Publications


                                                    Progress 01/01/70 to 12/30/70

                                                    Outputs
                                                    Eight years of measurement following fertilization of pole-sized aspen on Milacasoils gave these results. Net gross basal area growth of all species was reduced 31 and 17% respectively by lime, increased 17% and 20% by NPK and increased by 37% and 21% by NPK-Lime. Height growth of dominant aspen trees wasdecreased 21% by lime and increased 28% by NPK and 18% by NPK-lime. Absolute increases are too small to justify commercial application. Field work was done on study relating needle growth to apical meristem activity in red pine and Scots pine. Time of bud formation in red pine was studied for second year. Apical activity began about same time as bud elongated and continued into late August. Activity was correlated with temperature. The thermocouple psychrometer was found less accurate than the pressure bomb for determining water potential in pine needles. The currently recommended use of the psychrometer as a standard was not confirmed.

                                                    Impacts
                                                    (N/A)

                                                    Publications


                                                      Progress 01/01/69 to 12/30/69

                                                      Outputs
                                                      Studies with the properties of aspen wetwood were concluded with an examination of their mineral and nitrogen content. Compared to normal wood, aspen wetwood was 300 percent richer in ash, with calcium, and potassium salts accounting for most of the increase. Nitrogen contents were consistently, lower, contradictingearlier evidence that the bacteria may accumulate nitrogen in wet wood. N-N'-dinitroethylenediamine about doubled height and dry weight growth of Gymnocladus dioicus but had no stimulatory effect on legumes from four other genera. The internal water deficits of thinned and unthinned red pine were compared throughout a growing season. The rate of development of the buds of Pinus resinosa was described. Plastochron time was correlated with the size of the apical dome and needle growth.

                                                      Impacts
                                                      (N/A)

                                                      Publications


                                                        Progress 01/01/68 to 12/30/68

                                                        Outputs
                                                        N-N'-Dinitroethylenediamine sprayed in a commercial nursery retarted the growth of Juniperus spp. and Thuja. Good form and color were maintained only in arborvitae. Numbers and genera of microorganism found in fresh green wood of aspen were determined. Average numbers of the bacteria Erwinia per ml of expressed sap were were 290 in sapwood, 501,000 in wetwood and 145,000 in heartwood. Among a wide range of forest types and within a single jackpine stand, actual light measurements correlated closely with values determined by averaging synecological light coordinates of all species present. A 47-year oldred pine stand tolerated up to 90% defoliation by an early spring fire with only14% mortality.

                                                        Impacts
                                                        (N/A)

                                                        Publications


                                                          Progress 01/01/67 to 12/30/67

                                                          Outputs
                                                          Experimental freezing and thawing intact xylem of arborvitae, spruce and pine did not produce air blockage. The result is reconciled to the cohesion-tension theory (CTT) by model postulating tension release through expansion of single largest bubble in a number of interconnected tracheids. The model based on experiment and physical calculations hopefully removes a serious objection to accepting CTT. Fertilizing aspen with NPK and lime on a Milaca-like soil increased 5-year volume growth 20 percent. Unless fertilized trees live longer,the increase in insufficient to justify commercial application. In greenhouse screening, N-N',-dinitroethylenediamine (EDNA) more than halved height growth ofred cedar and arbovitae without adversely affecting form or color. The role of bacteria in the etiology of aspen wetwood is being examined. Several hundred times more bacterial cells are at times found in wetwood than in adjacent sapwood. Few bacterial species occur in either wetwood or normal sapwood.

                                                          Impacts
                                                          (N/A)

                                                          Publications