Seeing the forest for the heterogeneous trees: stand-scale resource distributions emerge from tree-scale structure

Abstract. Forest ecosystem processes depend on local interactions that are modified by the spatial pattern of trees and resources. Effects of resource supplies on processes such as regeneration are increasingly well understood, yet we have few tools to compare resource heterogeneity among forests that differ in structural complexity. We used a neighborhood approach to examine understory light and nutrient availability in a well-replicated and largescale variable-retention harvesting experiment in a red pine forest in Minnesota, USA. The experiment included an unharvested control and three harvesting treatments with similar tree abundance but different patterns of retention (evenly dispersed as well as aggregated retention achieved by cutting 0.1-or 0.3-ha gaps). We measured light and soil nutrients across all treatments and mapped trees around each sample point to develop an index of neighborhood effects (NI). Field data and simulation modeling were used to test hypotheses that the mean and heterogeneity of resource availability would increase with patchiness because of greater variation in competitive environments. Our treatments dramatically altered the types and abundances of competitive neighborhoods (NI) in each stand and resulted in significantly nonlinear relationships of light, nitrogen and phosphorus availability to NI. Hence, the distribution of neighborhoods in each treatment had a significant impact on resource availability and heterogeneity. In dense control stands, neighborhood variation had little impact on resource availability, whereas in more open stands (retention treatments), it had large effects on light and modest effects on soil nutrients. Our results demonstrate that tree spatial pattern can affect resource availability and heterogeneity in explainable and predictable ways, and that neighborhood models provide a useful tool for scaling heterogeneity from the individual tree to the stand. These insights are needed to anticipate the outcomes of silvicultural manipulations and should become more holistically integrated into both basic ecological and management science

Biomass growth response to spatial pattern of variable-retention harvesting in a northern Minnesota pine ecosystem

Variable-retention harvesting (VRH) is an approach for sustaining complex structure in managed forests. A criticism of VRH is that ecological benefits may come at a cost of reduced growth of regeneration, due to competition with residual trees. However, the spatial pattern of retention, i.e., dispersed or aggregated, in VRH systems can be manipulated to minimize suppression of regeneration, and resource limitation to regeneration might be mitigated by reduction of woody shrubs. Continued growth of the residual cohort will compensate for growth reduction of regeneration, although this may differ with retention pattern. We examined aboveground whole-stand biomass growth of trees in a VRH experiment in Pinus resinosa forest in Minnesota, USA. Treatments included dispersed retention, aggregated retention, and an uncut control, as well as a shrub treatment (reduced density or ambient). We addressed the following hypotheses: (1) biomass growth of a cohort of planted pine seedlings will be highest with aggregated rather than dispersed retention, (2) biomass growth of the planted seedlings will increase with shrub reduction, and (3) biomass growth of the residual overstory will be higher with dispersed rather than aggregated retention. Aboveground biomass growth of the planted pines ranged from 0.4 kg·ha−1·yr−1 in the overstory-control–ambient-shrub treatment to 23 kg·ha−1·yr−1 in the aggregated-retention–shrub-reduction treatment. The difference between the control and the retention treatments was significant (P 100% increase) with shrub reduction (P = 0.001), supporting our second hypothesis. Biomass growth of residual trees ranged from 2404 kg·ha−1·yr−1 in the uncut-control–ambient-shrub treatment to 1043 kg·ha−1·yr−1 in the aggregated-retention–shrub-reduction treatment. Differences were significant between the control and retention treatments (P = 0.003), and marginally higher with dispersed vs. aggregated retention (P = 0.09), lending support to our third hypothesis. Our results suggest that managers have flexibility in application of VRH and can expect similar stand-level biomass growth of planted regeneration regardless of retention pattern, but somewhat higher stand-level biomass growth of retained trees with dispersed retention

Family folklore: illustrating family characteristics

honors thesisCollege of HumanitiesEnglishMagaret K. BradyJohn R. NelsonThrough analysis of my own family folklore, I have found this statement to be true, and quite accurate in describing my "clannish" and independent family. The motivation for this study stems from a desire to understand why I am the way I am, and why I have much in common with other members of my family. I have attempted to pinpoint and discuss a few of the many complex characteristics I see prominently throughout several generations of my family, tracing these characteristics to four specific; family lines, those of my four grandparents. The process through which personality traits and traditions are passed on can certainly be studied through several disciplines, but I have chosen folklore as one of the best, least self-conscious, and most revealing media through which to gain an understanding of my family

Maintenance and monitoring system for diabetics : utilizing interface, product, and interactive design

M.S.Joseph A. Konceli

COMPETITION AMONG EUCALYPTUS TREES DEPENDS ON GENETIC VARIATION AND RESOURCE SUPPLY

Genetic variation and environmental heterogeneity fundamentally shape the interactions between plants of the same species. According to the resource partitioning hypothesis, competition between neighbors intensifies as their similarity increases. Such competition may change in response to increasing supplies of limiting resources. We tested the resource partitioning hypothesis in stands of genetically identical (clone-origin) and genetically diverse (seed-origin) Eucalyptus trees with different water and nutrient supplies, using individual-based tree growth models. We found that genetic variation greatly reduced competitive interactions between neighboring trees, supporting the resource partitioning hypothesis. The importance of genetic variation for Eucalyptus growth patterns depended strongly on local stand structure and focal tree size. This suggests that spatial and temporal variation in the strength of species interactions leads to reversals in the growth rank of seed-origin and clone-origin trees. This study is one of the first to experimentally test the resource partitioning hypothesis for intergenotypic vs. intragenotypic interactions in trees. We provide evidence that variation at the level of genes, and not just species, is functionally important for driving individual and community-level processes in forested ecosystems.International Paper of BrazilBrazil Eucalyptus Productivity Potential projectUniversity of Sao Paulo in Piracicaba (USP/ESALQ)Colorado State University[DGE-0221595003

New cohort growth and survival in variable retention harvests of a pine ecosystem in Minnesota, USA

There is significant interest in silvicultural systems such as variable retention harvesting (VRH) that emulate natural disturbance and increase structural complexity, spatial heterogeneity, and biological diversity in managed forests. However, the consequences of variable retention harvesting for new cohort growth and survival are not well characterized in many forest ecosystems. Moreover, the relative importance of resource preemption by existing ground layer vegetation after variable retention harvests is unclear. We addressed both in a VRH experiment implemented as a randomized block design replicated four times in red pine forest in Minnesota, USA. Treatments included a thinning with residual trees dispersed evenly throughout the stand (dispersed) and two patch cuts that left 0.1 ha gaps (small gap) or 0.3 ha gaps (large gap) in a forest matrix. Residual basal area was held near constant in the three harvest treatments. We planted seedlings of three common pines (Pinus banksiana, P. strobus and P. resinosa) and measured light, soil nutrients and growth over seven growing seasons. We hypothesized that forests with equivalent average structures (e.g., basal area) would have higher stand-level seedling growth and survival in aggregated retention versus dispersed retention stands. However, variable retention harvest resulted in relatively small differences in growth and survival across the three retention treatments (although all differed as expected from uncut controls). Species specific responses to overstory treatments were partially related to shade tolerance. Tolerant white pine had high survival across all overstory treatments whereas intolerant red and jack pine had lower survival in uncut controls. In general, jack pine had the strongest growth response to reduction of overstory density. However, both white and jack pine achieved highest growth in the dispersed treatment despite differences in shade tolerance. Regardless of species, shrubs had a strong impact on seedling growth. Indeed, differences in growth were often larger across shrub treatments than among retention treatments. Our results support the hypothesis that shrubs preempt resources and dampen the impacts of different overstory retention patterns on new cohort growth and survival. Our results imply that managers have considerable flexibility to employ various types of retention patterns coupled with planting in red pine ecosystems at least at the levels of retention studied here

Seeing the forest for the heterogeneous trees : stand-scale resource distributions emerge from tree-scale structure

Forest ecosystem processes depend on local interactions that are modified by the spatial pattern of trees and resources. Effects of resource supplies on processes such as regeneration are increasingly well understood, yet we have few tools to compare resource heterogeneity among forests that differ in structural complexity. We used a neighborhood approach to examine understory light and nutrient availability in a well-replicated and largescale variable-retention harvesting experiment in a red pine forest in Minnesota, USA. The experiment included an unharvested control and three harvesting treatments with similar tree abundance but different patterns of retention (evenly dispersed as well as aggregated retention achieved by cutting 0.1- or 0.3-ha gaps). We measured light and soil nutrients across all treatments and mapped trees around each sample point to develop an index of neighborhood effects (NI). Field data and simulation modeling were used to test hypotheses that the mean and heterogeneity of resource availability would increase with patchiness because of greater variation in competitive environments. Our treatments dramatically altered the types and abundances of competitive neighborhoods (NI) in each stand and resulted in significantly nonlinear relationships of light, nitrogen and phosphorus availability to NI. Hence, the distribution of neighborhoods in each treatment had a significant impact on resource availability and heterogeneity. In dense control stands, neighborhood variation had little impact on resource availability, whereas in more open stands (retention treatments), it had large effects on light and modest effects on soil nutrients. Our results demonstrate that tree spatial pattern can affect resource availability and heterogeneity in explainable and predictable ways, and that neighborhood models provide a useful tool for scaling heterogeneity from the individual tree to the stand. These insights are needed to anticipate the outcomes of silvicultural manipulations and should become more holistically integrated into both basic ecological and management science

Effects of density and ontogeny on size and growth ranks of three competing tree species

Summary: 1.Rank reversals in species performance are theoretically important for structuring communities, maintaining diversity and determining the course of forest succession. Species growth ranks can change with ontogeny or in different microenvironments, but interactions between ontogeny and the environment are not well-understood because of the lack of long-term forest competition studies. While early differences in growth among species may reflect intrinsic differences in shade-tolerance and physiology, ontogenetic trends in growth and variation in neighbourhood density and composition may change or even reverse early patterns of growth rankings. 2.We experimentally studied spatial and temporal patterns of species interactions and growth for three northern tree species: Larix laricina, Picea mariana and Pinus strobus. We compared species size and growth rankings over an 11-year period, for different species mixtures planted at four density levels in north-eastern Minnesota, USA. 3.The benefits of different growth strategies changed with ontogeny and density leading to reversals in the size rank of competing species over time and space. High-density stands promoted dominance and resource pre-emption by L. laricina, whereas lower-density stands favoured gradual accumulation of biomass and eventual dominance by P. strobus. In the absence of strong neighbour competition, ontogenetic trends in growth had greater influence on growth patterns. 4.Species interactions affected the productivity of mixed stands vs. monocultures. Species generally grew more in monoculture than when planted with P. strobus at low density, or with L. laricina at high density. Only L. laricina and P. mariana showed potential for greater overall productivity, or over-yielding, when planted together than alone, probably because of improved resource uptake by the highly stratified canopy. 5.Synthesis. Density predictably determined whether size-asymmetric growth or ontogenetic growth trends would drive early establishment and growth patterns. Variation in vertical and horizontal structure that results from early competitive dynamics can influence the successional trajectory or character of the mature forest. This study extends previous efforts to identify the causes of rank reversals in communities and understand the importance of temporal changes beyond the early years of seedling establishment

Appendix A. Treatment averages and standard deviations for residual basal areas remaining following tree removal.

Treatment averages and standard deviations for residual basal areas remaining following tree removal

Appendix B. A comparison of neighborhood and light distributions for three simulated forest stands with different overstory patterns.

A comparison of neighborhood and light distributions for three simulated forest stands with different overstory patterns