Dylan Fischer - The Evergreen State College

Dylan Fischer - The Evergreen State College
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Dylan Fischer
The Evergreen State College
Ecology
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Papers by Dylan Fischer
Community development by forest understory plants after prolonged burial by tephra
Plant Ecology
, Jan 16, 2022
Testing conceptual models of early plant succession across a disturbance gradient
Journal of Ecology
, 2019
Studies of succession have a long history in ecology, but rigorous tests of general, unifying pri...
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Studies of succession have a long history in ecology, but rigorous tests of general, unifying principles are rare. One barrier to these tests of theory is the paucity of longitudinal studies that span the broad gradients of disturbance severity that characterize large, infrequent disturbances. The cataclysmic eruption of Mount St. Helens (Washington, USA) in 1980 produced a heterogeneous landscape of disturbance conditions, including primary to secondary successional habitats, affording a unique opportunity to explore how rates and patterns of community change relate to disturbance severity, post‐eruption site conditions and time. In this novel synthesis, we combined data from three long‐term (c. 30‐year) studies to compare rates and patterns of community change across three ‘zones’ representing a gradient of disturbance severity: primary successional blast zone, secondary successional tree blowdown/standing snag zone and secondary successional intact forest canopy/tephra deposit zo...
Do genetically-specific tree canopy environments feed back to affect genetically specific leaf decomposition rates?
Plant and Soil
, Feb 1, 2019
Aims In forest ecosystems, trees may have genetically distinct patterns in leaf decomposition. Tr...
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Aims In forest ecosystems, trees may have genetically distinct patterns in leaf decomposition. Trees also can have genetically distinct canopy environments which modify temperature, moisture, and microbial communities on the forest floor. The interaction between these factors may result in underexplored interactions between microenvironment and leaf decomposition at the genotype level. Methods We compare litter decomposition rates for distinct genotypes of Fremont cottonwood (Populus fremontii) grown in a common garden environment under three different riparian conditions: 1) under a 16-tree stand of the same genotype, 2) under a 16-tree stand of another genotype, and 3) under a 16-tree stand of 16 different genotypes. Genotypes differed in canopy size and phenology. Results While genotype exerted a strong effect on decomposition, this effect was most pronounced when litter was decomposed under a self-similar (Bhome^) canopy. The strongest driver of decomposition rates across all factors (including litter quality and environmental factors) was spring (leaf-out) and fall (leaf-drop) phenology, but responses were variable by genotype. Conclusions The influence of genetics on litter decomposition, canopy environment, and tree phenology provides justification for the inclusion of stand-level traits like canopy cover into models of decomposition and complicates the results of studies that rely on litter quality traits alone.
Secondary disturbance following a deposit of volcanic tephra: a 30-year record from old-growth forest understory
Canadian Journal of Forest Research
, 2021
Forest disturbance is usually described by effects on trees, and small disturbances to forest und...
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Forest disturbance is usually described by effects on trees, and small disturbances to forest understory are seldom studied. Nevertheless, effective analyses of succession need to consider both stand-replacing and subsequent “secondary” disturbances in both the canopy and understory. We estimated the characteristics of 13 types of secondary disturbances in old-growth forest understory, as well as change in the canopy cover, after the deposition of tephra (aerially transported volcanic ejecta) in 1980 from Mount St. Helens, Washington. We sampled 100 plots (1 m2) at each of four sites for vegetation change and types of disturbance at 10 different times from 1980 to 2010; we sampled the tree canopy above each plot in 1980 and 2016. The number of canopy gaps increased by 23% and mean gap dimension increased by 68% over 36 years, mostly from the loss of Abies amabilis (Douglas ex Loudon) Douglas ex Forbes. Secondary disturbance in understory affected 1.4% of stand area per year. The are...
Distinct Rainfall Interception Profiles among Four Common Pacific Northwest Tree Species
Forests
Forest tree canopies have a critical influence on water cycles through the interception of precip...
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Forest tree canopies have a critical influence on water cycles through the interception of precipitation. Nevertheless, radial patterns of canopy interception may vary interspecifically. We analyzed canopy interception using catchments along radial transects underneath four common forest tree species (Acer macrophyllum, Alnus rubra, Pseudotsuga menziesii, and Thuja plicata) in the Pacific Northwest over two years. Near the center of the canopy in the leaf-off season, interception was 51.6%–67.2% in conifer species and only 20.1%–40.1% in broadleaf species, and interception declined to 19.9–29.9 for all species near the edge of the canopy. One deciduous species (A. rubra) showed spatially uniform interception during the leaf-off period (19.9%–20.96%), while another varied from 23.1%–40.1%. Patterns were more pronounced in the leaf-on period (under high vapor pressure deficit conditions), where conifers intercepted 36.5%–95.9% of precipitation, depending on the species and position un...
Residual Large Trees Influence Short-term Succession Following a Volcanic Eruption in a Valdivian Temperate Rainforest
Airborne volcanic ejecta (tephra) can strongly in uence forest ecosystems through initial disturb...
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Airborne volcanic ejecta (tephra) can strongly in uence forest ecosystems through initial disturbance processes and subsequent ecological response. Within a tephra-disturbed forest, large trees may promote plant growth and create favorable sites for colonization. Three primary ways trees can in uence post-eruption vegetation response include: 1) amelioration of volcanic substrates, 2) as source propagules from the tree or from associated epiphytes, and 3) by sheltering understory vegetation, thereby increasing rate of recovery near tree bases. Here, we evaluate Valdivian temperate rainforest understory vegetation response and soil characteristics in close proximity to large trees that survived the 2015 eruption of Calbuco Volcano. Understory vegetative cover was higher near the base of trees for mosses, many epiphytes, and some herbaceous, shrub, and trees species. However, signi cant interactions with year of measurement, and individualistic responses by many species made generalizations more di cult. Small shrubs and trees in particular demonstrated patterns of recovery that were frequently independent of distance. In some cases, percent cover of colonizing vegetation actually increased far from trees by 2019. The soil surface was similarly variable where bare soil cover was associated with locations proximal to tree bases, but material shed from living and dead standing vegetation increased wood and litter abundances on the soil surface away from the base of trees. Soils near trees had lower pH, elevated organic matter, and higher nitrogen and carbon. Our results support the assertion that in this temperate rainforest ecosystem, large trees can modify edaphic conditions and provide important early refugia for vegetative regrowth following a tephra fall event. Nevertheless, complex interactions through time with species and growth form, suggest the in uence of large trees on plant establishment and growth with close proximity tree boles is more complex than a simple facilitative model might suggest.
Vegetation dynamics under residual large trees following a volcanic eruption in a Valdivian temperate rainforest
Plant Ecology
, 2021
Airborne volcanic ejecta (tephra) can strongly influence forest ecosystems through initial distur...
more
Airborne volcanic ejecta (tephra) can strongly influence forest ecosystems through initial disturbance processes and subsequent ecological response. Within a tephra-disturbed forest, large trees may promote plant growth and create favorable sites for colonization. Three primary ways trees can influence posteruption vegetation response include: (1) amelioration of volcanic substrates, (2) providing source propagules from the tree or from associated epiphytes, and (3) sheltering understory vegetation, thereby increasing the rate of recovery near tree bases. Here, we evaluate Valdivian temperate rainforest understory vegetation responses in close proximity to large trees that survived the 2015 eruption of Calbuco Volcano. Understory vegetative cover was higher near the base of trees for mosses, many epiphytes, and some herbaceous, shrub, and trees species. However, significant interactions with year of measurement, and individualistic responses by many species made generalizations more difficult. Shrubs and trees in particular demonstrated patterns of recovery that were frequently independent of distance. In some cases, percent cover of colonizing vegetation actually increased away from trees by 2019. The soil surface was similarly variable where bare soil cover was associated with locations proximal to tree bases, but material shed from living and dead standing vegetation increased wood and litter abundances on the soil surface away from the base of trees. Soils near trees had lower pH, elevated organic matter, and higher nitrogen and carbon. Our results support the assertion that in this temperate rainforest ecosystem large trees may provide important early refugia for vegetative regrowth following a tephra-fall event with altered edaphic conditions. Nevertheless, individualistic dynamics of different species and growth forms suggest the influence of large trees on nearby understory plants is more complex than a simple facilitative model might suggest.
Long-term responses of forest-floor bryophytes buried by tephra in the 1980 eruption of Mount St. Helens
Botany
, 2021
Responses in bryophyte communities following volcanic disturbance are not well understood. The er...
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Responses in bryophyte communities following volcanic disturbance are not well understood. The eruption of Mount St. Helens on 18 May 1980 deposited large amounts of tephra (aerially transported volcanic ejecta) on nearby forests in southwestern Washington and presented an opportunity to examine bryophyte succession, with a focus on mosses. We examined changes in moss community over 36 years following this disturbance, using permanent plots located in old-growth conifer forests. We used an experimental design where we removed the tephra from some of the plots shortly after the eruption. Initial dramatic decreases in total bryophyte cover, moss species richness, and diversity in plots with intact tephra were followed by increases by 2016. Community profiles also shifted through time but were somewhat site-specific. Moss community change was related to changes in vascular plant species and was driven by changes in a few key moss species with distinct growth strategies. Bryophyte chang...
Belowground morphology and population dynamics of two forest understory herbs of contrasting growth forms
Botany
, 2021
Forest understory herbs exhibit a large range of variation in morphology and life history. Here, ...
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Forest understory herbs exhibit a large range of variation in morphology and life history. Here, we expand the reported range of variation by describing the belowground structures of two very different species, Xerophyllum tenax (Pursh) Nutt. and Chimaphila umbellata (L.) Nutt. We excavated individuals in forests of the Cascade Mountains in the Pacific Northwest of the United States. Xerophyllum tenax has short rhizomes but an extensive root system that is exceptionally large among forest understory species. The roots reach 4 m in length and may occupy an area 50 times that of the aboveground canopy. In contrast, C. umbellata has very small roots but an extensive rhizome system. The largest plant we excavated had 57 m of connected rhizomes and still had a seedling source. Both species have long-lived individuals but differ in response to disturbance. On the basis of monitoring 151 permanent 1 m2 plots in an old-growth forest, X. tenax increased only minimally in density over 40 year...
Self-Similarity, Leaf Litter Traits, and Neighborhood Predicting Fine Root Dynamics in a Common-Garden Forest
Frontiers in Environmental Science
, 2019
While individual tree genotypes are known to differ in their impacts on local soil development, t...
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While individual tree genotypes are known to differ in their impacts on local soil development, the spatial genetic influence of surrounding neighboring trees is largely unknown. We examine the hypothesis that fine root dynamics of a focal tree is based on the genetics of the focal tree as well as the genetics of neighbor trees that together define litter inputs to soils of the focal tree. We used a common garden environment with clonal replicates of individual tree genotypes to analyze fine root production, turnover and allocation with respect to modeled neighborhood: (1) foliar mass, (2) foliar condensed tannins (CT), (3) genetic identity of trees, and (4) genetic dissimilarity of neighbors. In support of our central hypothesis, we found that the presence of genetically dissimilar trees and high leaf CT contributions to the soil predicted increased fine root production. In fact, the modeled effects of neighbors accounted for ∼90% of the explanatory weight of all models predicting root production. Nevertheless, the ultimate fate of those roots in soil (turnover) and the balance of fine roots relative to aboveground tree mass were still more predictable based on the leaf traits and genetics of the individual focal trees (explaining 99% of the variation accounted for by models). Our data provide support for a method allowing a comparison of the relative effects of individuals vs. spatial neighborhood effects on soils in a genetic context. Such comparisons are important for placing plant-soil feedbacks in a genetic and evolutionary framework because neighbors can decouple feedbacks between an individual and the surrounding environment.
Understorey succession after burial by tephra from Mount St. Helens
Journal of Ecology
, 2018
This is the author manuscript accepted for publication and has undergone full peer review but has...
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This is the author manuscript accepted for publication and has undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. Please cite this article as
A little disturbance goes a long way: 33-year understory successional responses to a thin tephra deposit
Forest Ecology and Management
, 2016
Large volcanic eruptions can alter forest plant communities through a variety of mechanisms, incl...
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Large volcanic eruptions can alter forest plant communities through a variety of mechanisms, including direct destruction of forests and changes to forest soils through tephra (aerially transported volcanic ejecta) deposits. While many studies have examined succession following direct destruction of forests, impacts to plant communities through tephra effects are less obvious, especially where the tephra depth is less than plant height. We used a 33-year experiment in an old growth forest that received shallow tephra deposition in the 1980 eruption of Mount St. Helens (WA, USA), to examine plant communities. We determined if community differences between plots with and without tephra: 1) were detectable, and 2) changed over time. We found that plant communities differed significantly between plots with and without tephra after 33 years. Further, differences were stronger after 33 years than at two years following the eruption. Species richness increased over time in both plots with and without tephra, but live cover was largely stable after two years. Nevertheless, communities shifted in different directions over time, where the changes in species composition and abundance immediately following tephra deposition were inconsistent with net changes that occurred over 30 years afterwards. These results suggest that widespread and apparently minor deposits of tephra, usually interpreted to be of transient importance if any, may induce long-term modifications of understory plant communities.
Tree genetics strongly affect forest productivity, but intraspecific diversity–productivity relationships do not
Functional Ecology
, 2016
This is the author manuscript accepted for publication and has undergone full peer review but has...
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This is the author manuscript accepted for publication and has undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. Please cite this article as
Mercury Accumulation in Old-Growth and Recently Clear-Cut Forests in the Tephra Fall Zone of the 1980 Mount St. Helens Eruption
Salmon carcasses influence genetic linkages between forests and streams
Canadian Journal of Fisheries and Aquatic Sciences
, 2016
Biodiversity at many scales (functional group, species, genetic) can result in emergent ecologica...
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Biodiversity at many scales (functional group, species, genetic) can result in emergent ecological patterns. Here we explore the influence of tree genotypic variation and diversity on in-stream ecosystem processes and aquatic communities. We test whether genetically diverse inputs of leaf litter interact with a keystone organism, anadromous salmon, to influence in-stream ecosystem function. We used reach-level manipulation of salmon carcasses and leaf litter bags to examine how nutrient inputs interact with genetic variation in leaf litter decomposition. Genotypic variation in black cottonwood (Populus balsamifera ssp. trichocarpa) significantly influenced leaf litter chemistry, litter mass loss, and fungal biomass, but these variables were only weakly influenced by salmon carcass presence or a genotype × salmon (G × E) interaction. Mixtures of genotypes tended to demonstrate antagonistic effects (slower than expected decomposition) in the absence of salmon, but synergistic effects ...
Effects of fire and invasive species legacy on plant communities in a Northwest prairie
Background/Question/Methods In this study we used a matrix of restoration management practices in...
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Background/Question/Methods In this study we used a matrix of restoration management practices in a glacial outwash prairie south of the Puget Sound in Washington to evaluate treatments of fire and herbicide as well as the legacy effects of the N-fixing non-native species Cytisus scoparius on prairie plant communities. We measured plant community diversity and abundance across five data sets spanning three years for both spring and fall seasons. We compared native and non-native plant communities, community structure, composition, and diversity among 1) different aged burn treatments (2002, 2006, no burn) and pre/post burn treatments, 2) graminoid specific herbicide treatments over 1 and 4 years, and 3) we evaluated legacy effects of C. scoparious using historic aerial photos showing distribution and subsequent removal across all fire and herbicide treatments. Results/Conclusions There are three major findings of this work: 1) Species richness was highest in the most recently burned...
Interactions between salmon carcasses and genetically distinct leaf litters in streams
Background/Question/Methods Two major forms of allochthonous inputs are important for Pacific Nor...
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Background/Question/Methods Two major forms of allochthonous inputs are important for Pacific Northwest streams: leaf litter and salmon carcasses. Although much is known about these two input types in isolation, few studies have examined their interaction, and no studies have examined interactions between salmon carcasses and genetically distinct litter types within tree species. In this study, we created leaf litter bags of seven genotypes of black cottonwood (Populus balsamifera L. ssp. trichocarpa [Torr. & A. Gray ex Hook.] Brayshaw) made from litter collected in a 25-year old common garden, four mixtures of two genotypes each, and one mixture with six genotypes. All leaf litter treatments were placed in blocks in McKenna Creek (Yelm, WA) directly downstream of chum salmon (Oncorhynchus keta) carcasses or no-salmon controls. Our major research questions included: 1) Does leaf litter from genotypes of P. trichocarpa collected from across a latitudinal gradient from OR, USA to BC, ...
Integrating carbon flux measurements with above and belowground curriculum and undergraduate research
Background/Question/Methods We report on efforts to integrate curricular activities with research...
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Background/Question/Methods We report on efforts to integrate curricular activities with research on diversity and forest above-ground net primary productivity (ANPP), carbon (C) stocks, net soil CO2 efflux rate (NCER), and fine root production (FRP) in a temperate rainforest permanent plot network near the Puget Sound, Washington, USA. Measurements were conducted with four 16-credit courses, involving more than 200 students, at the Evergreen State College. We used several models to examine efficacy of integrating ecosystem measurements with high numbers of students. Models we used included using student measurements as analytical replicates, detailed one-on-one instruction with a small number of students, having student groups error check and re-collect data, peer review of student work, and community-based ownership of data and research outcomes. Results/Conclusions Using student work on a 30-year-old permanent plot network, and another 3-year-old 44-plot permanent plot network (h...
Genotype by genotype interactions and genetic diversity influence leaf litter decomposition in a large-scale riparian common garden
Background/Question/Methods In riparian environments, leaf litter inputs provide crucial sources ...
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Background/Question/Methods In riparian environments, leaf litter inputs provide crucial sources of organic matter to riparian soils and subsidies of carbon and nutrients to in-stream communities. The physical nature of these environments means leaf litter may decompose in place (under donor canopies) or be transported downstream to decompose under the canopies of other riparian tree populations. Using a large-scale common garden of Fremont cottonwood (Populus fremontii) that includes 16 genotypes collected from across the range of P. fremontii (from southern AZ to northern UT), we selected five genotypes from across this range and collected naturally abscising leaf litter. We compared leaf litter decomposition rates of these genotypes under three different riparian conditions: 1) at home (under a donor canopy of 16 individual clones of the same genotype), 2) away (under the canopy of another genotype, again a stand of 16 individual clones), and 3) under a diverse canopy of all 16 d...
Comparison of clear-cut and old-growth forest understory community structure 33 years after a volcanic eruption
Background/Question/Methods Ecosystem response to large disturbances, such as volcanic eruptions,...
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Background/Question/Methods Ecosystem response to large disturbances, such as volcanic eruptions, is likely to depend on pre-disturbance conditions and pre-existing vegetation. Here, we compare the response of clear-cut and old-growth forest understory plant communities to disturbance produced by tephra deposits from the eruption of Mount St. Helens in 1980. Previous research focused on the understory plant community response over 30 years in old-growth forests; ours is the first study to compare communities in paired old-growth and clear-cut forests. We use two sites, one with high and one with low diversity of herbaceous understory plants prior to the eruption, in order to clarify the potential range of responses. At each site we paired a clear-cut that predated the eruption with an adjacent old-growth forest, of either high or low diversity. All other topo-edaphic factors were controlled for, so as to allow comparison of responses to tephra in the different forest types. Accordin...
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