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Heather D Alexander - One of the best experts on this subject based on the ideXlab platform.
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changes in Stand Structure and tree vigor with repeated prescribed fire in an appalachian hardwood forest
Forest Ecology and Management, 2015Co-Authors: Mary A Arthur, Heather D Alexander, Beth A Blankenship, Angela Schorgendorfer, David L LoftisAbstract:Abstract Without large scale disturbances to alter forest Structure and open the canopy, historically oak-dominated forests of the central and Appalachian hardwood regions of eastern North America are shifting to dominance by shade-tolerant, ‘mesophytic’ species. In response, prescribed fire is applied with increasing frequency and spatial extent to decrease non-oak species and promote dominance of oak species. However, relatively few studies have examined impacts of repeated fire to forest Structure and tree vigor across multiple years and varied terrain. In this study, we examined tree vigor, tree mortality, and Stand Structure in response to different burn treatments: Frequent (burned 4 times in eight years), Less Frequent (burned 2 times in eight years), and Fire-Excluded. We hypothesized that fire-driven decreases in stem density and basal area would be greatest for small size classes, especially of shade-tolerant species on drier landscape positions, and would increase with burn frequency and fire temperature. We expected trees surviving fire to exhibit increased crown vigor over time since fire. Prescribed fire effects depended on tree size-class and landscape position. About 60% of surviving midstory trees (10–20 cm diameter at breast height (DBH)) and 25% of overstory trees (⩾20 cm DBH) on sub-xeric and intermediate landscape positions experienced crown dieback. Fire-Excluded sites had fewer trees with crown dieback (11–28% across size classes) compared to burned sites (21–87%). Throughout the duration of the study, midstory and overstory maples had significantly greater likelihood of increased crown dieback compared to oaks. Paradoxically, midstory maples had a higher survival probability than similarly-sized oaks, while overstory maples had lower survival than overstory oaks. The greatest reductions in density and basal area occurred in saplings (trees 2–10 cm DBH) and midstory trees on sub-xeric and intermediate (but not sub-mesic) landscape positions. Both Less Frequent and Frequent burning reduced density and basal area of sapling and mid-story shade-tolerant species, but also of mid-story chestnut oaks. Individual tree mortality was positively correlated with char height after the first burn regardless of burn frequency. A large and significant initial sprouting response to fire dissipated over time and with repeated burning. Future assessments of mortality and vigor of residual trees following fire are essential for evaluating the long-term effectiveness of prescribed fire management in shifting species composition away from ‘mesophytic’ species and toward oaks, and could help guide management choices regarding repeated prescribed burning.
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implications of increased deciduous cover on Stand Structure and aboveground carbon pools of alaskan boreal forests
Ecosphere, 2012Co-Authors: Heather D Alexander, Michelle C Mack, Scott J Goetz, Pieter S A Beck, Fay E BelsheAbstract:Fire activity in boreal forests has increased recently with climate warming, altering Stand Structure and composition in many areas. Changes in Stand dynamics have the potential to alter C cycling and biophysical processes, with feedbacks to global and regional climate. Here, we assess the interactions between fire, Stand Structure, and aboveground C accumulation and storage within boreal forests of interior Alaska, where increased fire severity is predicted to shift forest composition from predominantly black spruce (Picea mariana) to greater deciduous cover. We measured aboveground biomass and net primary productivity (ANPP) of trees and large shrubs, snags, and downed woody debris across 44 mid-successional (20–59 years since fire) Stands of varying deciduous importance value (IV), determined by relative density, basal area, and frequency of deciduous trees and large shrubs within each Stand. Aboveground biomass, ANPP, and deciduous snag biomass increased significantly with increased deciduous IV and years since fire. Deciduous IV had little influence on evergreen snag biomass and downed woody debris, but both C pools decreased with years since fire. Forest type also affected Stand Structure and C pools. Black spruce Stands had shorter trees with less basal area and aboveground biomass and slower rates of biomass accumulation and ANPP compared to those dominated by trembling aspen (Populus tremuloides) or Alaska birch (Betula neoalaskana). These parameters in black spruce Stands were similar to mixed Stands of black spruce and aspen but were often lower than mixed Stands of black spruce and Alaska birch. Much of the biomass accumulation in deciduous Stands was attributed to higher tree-level ANPP, allowing individual stems of deciduous species to accumulate more stemwood/bark faster than black spruce trees. If increased fire activity shifts Stand composition from black spruce to increased deciduous cover, ANPP, aboveground tree/large shrub biomass, and deciduous snag biomass will increase, leading to increased aboveground C pools in mid-successional forest Stands of interior Alaska. While species dominance shifts like these will impact aboveground patterns of landscape-level C cycling in boreal forests, variations in soil C pools and forest properties like albedo must also be assessed to accurately determine implications for global and regional climate.
Monica E Queijeirobolanos - One of the best experts on this subject based on the ideXlab platform.
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effects of dwarf mistletoe on Stand Structure of lodgepole pine forests 21 28 years post mountain pine beetle epidemic in central oregon
PLOS ONE, 2014Co-Authors: Michelle C Agne, David C Shaw, Travis Woolley, Monica E QueijeirobolanosAbstract:Lodgepole pine (Pinus contorta) forests are widely distributed throughout North America and are subject to mountain pine beetle (Dendroctonus ponderosae) epidemics, which have caused mortality over millions of hectares of mature trees in recent decades. Mountain pine beetle is known to influence Stand Structure, and has the ability to impact many forest processes. Dwarf mistletoe (Arceuthobium americanum) also influences Stand Structure and occurs frequently in post-mountain pine beetle epidemic lodgepole pine forests. Few studies have incorporated both disturbances simultaneously although they co-occur frequently on the landscape. The aim of this study is to investigate the Stand Structure of lodgepole pine forests 21–28 years after a mountain pine beetle epidemic with varying levels of dwarf mistletoe infection in the Deschutes National Forest in central Oregon. We compared Stand density, Stand basal area, canopy volume, proportion of the Stand in dominant/codominant, intermediate, and suppressed cohorts, average height and average diameter of each cohort, across the range of dwarf mistletoe ratings to address differences in Stand Structure. We found strong evidence of a decrease in canopy volume, suppressed cohort height, and dominant/codominant cohort diameter with increasing Stand-level dwarf mistletoe rating. There was strong evidence that as dwarf mistletoe rating increases, proportion of the Stand in the dominant/codominant cohort decreases while proportion of the Stand in the suppressed cohort increases. Structural differences associated with variable dwarf mistletoe severity create heterogeneity in this forest type and may have a significant influence on Stand productivity and the resistance and resilience of these Stands to future biotic and abiotic disturbances. Our findings show that it is imperative to incorporate dwarf mistletoe when studying Stand productivity and ecosystem recovery processes in lodgepole pine forests because of its potential to influence Stand Structure.
Miguel A Zavala - One of the best experts on this subject based on the ideXlab platform.
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Stand Structure and recent climate change constrain Stand basal area change in european forests a comparison across boreal temperate and mediterranean biomes
Ecosystems, 2014Co-Authors: Paloma Ruizbenito, Jaime Madrigalgonzalez, Sophia Ratcliffe, David A Coomes, Gerald Kandler, Aleksi Lehtonen, Christian Wirth, Miguel A ZavalaAbstract:European forests have a prominent role in the global carbon cycle and an increase in carbon storage has been consistently reported during the twentieth century. Any further increase in forest carbon storage, however, could be hampered by increases in aridity and extreme climatic events. Here, we use forest inventory data to identify the relative importance of Stand Structure (Stand basal area and mean d.b.h.), mean climate (water availability), and recent climate change (temperature and precipitation anomalies) on forest basal area change during the late twentieth century in three major European biomes. Using linear mixed-effects models we observed that Stand Structure, mean climate, and recent climatic change strongly interact to modulate basal area change. Although we observed a net increment in Stand basal area during the late twentieth century, we found the highest basal area increments in forests with medium Stand basal areas and small to medium-sized trees. Stand basal area increases correlated positively with water availability and were enhanced in warmer areas. Recent climatic warming caused an increase in Stand basal area, but this increase was offset by water availability. Based on recent trends in basal area change, we conclude that the potential rate of aboveground carbon accumulation in European forests strongly depends on both Stand Structure and concomitant climate warming, adding weight to suggestions that European carbon stocks may saturate in the near future.
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an analytical model of Stand dynamics as a function of tree growth mortality and recruitment the shade tolerance Stand Structure hypothesis revisited
Journal of Theoretical Biology, 2007Co-Authors: Miguel A Zavala, Oscar Angulo, Rafael Bravo De La Parra, J C LopezmarcosAbstract:Abstract Light competition and interspecific differences in shade tolerance are considered key determinants of forest Stand Structure and dynamics. Specifically two main Stand diameter distribution types as a function of shade tolerance have been proposed based on empirical observations. All-aged Stands of shade tolerant species tend to have steeply descending, monotonic diameter distributions (inverse J-shaped curves). Shade intolerant species in contrast typically exhibit normal (unimodal) tree diameter distributions due to high mortality rates of smaller suppressed trees. In this study we explore the generality of this hypothesis which implies a causal relationship between light competition or shade tolerance and Stand Structure. For this purpose we formulate a partial differential equation system of Stand dynamics as a function of individual tree growth, recruitment and mortality which allows us to explore possible individual-based mechanisms—e.g. light competition—underlying observed patterns of Stand Structure—e.g. unimodal or inverse J-shaped equilibrium diameter curves. We find that contrary to expectations interspecific differences in growth patterns can result alone in any of the two diameter distributions types observed in the field. In particular, slow growing species can present unimodal equilibrium curves even in the absence of light competition. Moreover, light competition and shade intolerance evaluated both at the tree growth and mortality stages did not have a significant impact on Stand Structure that tended to converge systematically towards an inverse J-shaped curves for most tree growth scenarios. Realistic transient Stand dynamics for even aged Stands of shade intolerant species (unimodal curves) were only obtained when recruitment was completely suppressed, providing further evidence on the critical role played by juvenile stages of tree development (e.g. the sapling stage) on final forest Structure and composition. The results also point out the relevance of partial differential equations systems as a tool for exploring the individual-level mechanisms underpinning forest Structure, particularly in relation to more complex forest simulation models that are more difficult to analyze and to interpret from a biological point of view.
James Fownes - One of the best experts on this subject based on the ideXlab platform.
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age related decline in forest ecosystem growth an individual tree Stand Structure hypothesis
Ecosystems, 2002Co-Authors: Dan Binkley, Jose Luiz Stape, Michael G Ryan, H R Barnard, James FownesAbstract:Forest growth is important both economically (yielding billions of dollars of annual revenues) and ecologically (with respect to ecosystem health and global carbon budgets). The growth of all forests follows a predictable general trend with age. In young forests, it accelerates as canopies develop; it then declines substantially soon after full canopy leaf area is reached. The classic explanation for the decline in growth invoked the increasing respiration costs required to sustain the larger masses of wood characteristic of older forests. Direct measurements of respiration have largely refuted this hypothesis, and recent work has focused on Stand-level rates of resource supply, resource use, and growth. We developed and tested a hypothesis at the scale of individual trees (in relation to Stand Structure) to explain this declining Stand-level rate of stem growth. According to our hypothesis, changes in Stand Structure allow dominant trees to sustain high rates of growth by increasing their acquisition of resources and using these resources efficiently (defined as stem growth per unit of resource used); smaller, nondominant trees grow more slowly as a result of their more limited acquisition of resources and a reduced rate of growth per unit of resource acquired. In combination, these two trends reduce overall Stand growth. We tested this hypothesis by comparing growth, growth per unit of leaf area, and variation among trees within plots in two series of plantations of Eucalyptus in Brazil and by estimating individual-tree rates of growth and use of light, water, and nutrients in a plantation of Eucalyptus saligna in Hawaii. Our results supported the individual-tree hypothesis. We conclude that part of the universal age-related decline in forest growth derives from competition-related changes in Stand Structure and the resource-use efficiencies of individual trees.
Dan Binkley - One of the best experts on this subject based on the ideXlab platform.
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factors controlling eucalyptus productivity how water availability and Stand Structure alter production and carbon allocation
Forest Ecology and Management, 2010Co-Authors: Dan Binkley, Jose Luiz Stape, Michael G Ryan, Sebastiao Fonseca, Rodolfo Araujo Loos, Ernesto N Takahashi, Claudio R Silva, Sergio Ricardo Silva, Rodrigo HakamadaAbstract:Wood production varies substantially with resource availability, and the variation in wood production can result from several mechanisms: increased photosynthesis, and changes in partitioning of photosynthesis to wood production, belowground flux, foliage production or respiration. An underStanding of the mechanistic basis for patterns in wood production within a Stand and across landscapes requires a complete annual carbon budget. We measured annual carbon flows to wood production, foliage production and total belowground carbon flux (the sum of root production, root respiration, and mycorrhizal production and respiration) from ages three to five years in clonal Eucalyptus plantations at four sites in Brazil to test if fertility, water availability and Stand Structure changed wood production and by what mechanism. We also quantified the patterns in light interception and the efficiency of light use to provide additional mechanistic insights into growth responses and to determine if light-use efficiency was related to changes in flux and partitioning. The routine level of forest fertilization at these four sites was high enough that further increases in nutrient supply did not increase wood growth. Irrigation increased wood net primary productivity (age three to five) from 1.45 to 1.84 kg m � 2 year � 1 of C (27%), because of increases in light interception (5%), photosynthetic efficiency (from 0.028 to 0.031 mol C/mol photons absorbed, 11%), gross primary productivity (from 3.62 to 4.28 m � 2 year � 1 of C, 18%), and partitioning to wood (from 0.397 to 0.430 of photosynthesis, 8%). These changes increased light-use efficiency by 20%. Annual flux belowground varied among sites from 0.43 to 1.0 m � 2 year � 1 of C but did not vary with water availability. Across the four sites
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age related decline in forest ecosystem growth an individual tree Stand Structure hypothesis
Ecosystems, 2002Co-Authors: Dan Binkley, Jose Luiz Stape, Michael G Ryan, H R Barnard, James FownesAbstract:Forest growth is important both economically (yielding billions of dollars of annual revenues) and ecologically (with respect to ecosystem health and global carbon budgets). The growth of all forests follows a predictable general trend with age. In young forests, it accelerates as canopies develop; it then declines substantially soon after full canopy leaf area is reached. The classic explanation for the decline in growth invoked the increasing respiration costs required to sustain the larger masses of wood characteristic of older forests. Direct measurements of respiration have largely refuted this hypothesis, and recent work has focused on Stand-level rates of resource supply, resource use, and growth. We developed and tested a hypothesis at the scale of individual trees (in relation to Stand Structure) to explain this declining Stand-level rate of stem growth. According to our hypothesis, changes in Stand Structure allow dominant trees to sustain high rates of growth by increasing their acquisition of resources and using these resources efficiently (defined as stem growth per unit of resource used); smaller, nondominant trees grow more slowly as a result of their more limited acquisition of resources and a reduced rate of growth per unit of resource acquired. In combination, these two trends reduce overall Stand growth. We tested this hypothesis by comparing growth, growth per unit of leaf area, and variation among trees within plots in two series of plantations of Eucalyptus in Brazil and by estimating individual-tree rates of growth and use of light, water, and nutrients in a plantation of Eucalyptus saligna in Hawaii. Our results supported the individual-tree hypothesis. We conclude that part of the universal age-related decline in forest growth derives from competition-related changes in Stand Structure and the resource-use efficiencies of individual trees.
