Person:
Foster, David

Profile Picture

Email Address

AA Acceptance Date

Birth Date

Research Projects

Organizational Units

Job Title

Last Name

Foster

First Name

David

Name

Foster, David
Author's Publications: search.filters.isAuthorOfPublication.aa42482b-7b1d-48d8-b4d0-a75af529e23e

Search Results

Now showing 1 - 10 of 45
  • Thumbnail Image
    Publication
    Ungulate browsers promote herbaceous layer diversity in logged temperate forests
    (John Wiley and Sons Inc., 2016) Faison, Edward K.; DeStefano, Stephen; Foster, David; Motzkin, Glenn; Rapp, Joshua
    Abstract Ungulates are leading drivers of plant communities worldwide, with impacts linked to animal density, disturbance and vegetation structure, and site productivity. Many ecosystems have more than one ungulate species; however, few studies have specifically examined the combined effects of two or more species on plant communities. We examined the extent to which two ungulate browsers (moose [Alces americanus]) and white‐tailed deer [Odocoileus virginianus]) have additive (compounding) or compensatory (opposing) effects on herbaceous layer composition and diversity, 5–6 years after timber harvest in Massachusetts, USA. We established three combinations of ungulates using two types of fenced exclosures – none (full exclosure), deer (partial exclosure), and deer + moose (control) in six replicated blocks. Species composition diverged among browser treatments, and changes were generally additive. Plant assemblages characteristic of closed canopy forests were less abundant and assemblages characteristic of open/disturbed habitats were more abundant in deer + moose plots compared with ungulate excluded areas. Browsing by deer + moose resulted in greater herbaceous species richness at the plot scale (169 m2) and greater woody species richness at the subplot scale (1 m2) than ungulate exclusion and deer alone. Browsing by deer + moose resulted in strong changes to the composition, structure, and diversity of forest herbaceous layers, relative to areas free of ungulates and areas browed by white‐tailed deer alone. Our results provide evidence that moderate browsing in forest openings can promote both herbaceous and woody plant diversity. These results are consistent with the classic grazing‐species richness curve, but have rarely been documented in forests.
  • Thumbnail Image
    Publication
    Widespread sampling biases in herbaria revealed from large-scale digitization
    (Wiley-Blackwell, 2017) Daru, Barnabas; Park, Daniel; Willis, Richard; Barrington, David; Whitfield, Timothy; Seidler, Tristram; Sweeney, Patrick; Foster, David; Ellison, Aaron; Davis, Charles
    SUMMARY 1. Non-random collecting practices may bias conclusions drawn from analyses of herbarium records. Recent efforts to fully digitize and mobilize regional floras online offer a timely opportunity to assess commonalities and differences in herbarium sampling biases. 2. We determined spatial, temporal, trait, phylogenetic, and collector biases in ~5 million herbarium records, representing three of the most complete digitized floras of the world: Australia (AU), South Africa (SA), and New England, USA (NE). 3. We identified numerous shared and unique biases among these regions. Shared biases included specimens i) collected close to roads and herbaria; ii) collected more frequently during biological spring and summer; iii) of threatened species collected less frequently; and iv) of close relatives collected in similar numbers. Regional differences included i) over-representation of graminoids in SA and AU and of annuals in AU; and ii) peak collection during the 1910s in NE, 1980s in SA, and 1990s in AU. Finally, in all regions, a disproportionately large percentage of specimens were collected by very few individuals. We hypothesize that these mega-collectors, and along with their associated preferences and idiosyncrasies, shaped patterns of collection bias via ‘founder effects’. 4. Studies using herbarium collections should account for sampling biases, and future collecting efforts should avoid compounding these biases to the extent possible.
  • Thumbnail Image
    Publication
    Four Centuries of Change in Northeastern United States Forests
    (Public Library of Science, 2013) Thompson, Jonathan R.; Carpenter, Dunbar N.; Cogbill, Charles; Foster, David
    The northeastern United States is a predominately-forested region that, like most of the eastern U.S., has undergone a 400-year history of intense logging, land clearance for agriculture, and natural reforestation. This setting affords the opportunity to address a major ecological question: How similar are today's forests to those existing prior to European colonization? Working throughout a nine-state region spanning Maine to Pennsylvania, we assembled a comprehensive database of archival land-survey records describing the forests at the time of European colonization. We compared these records to modern forest inventory data and described: (1) the magnitude and attributes of forest compositional change, (2) the geography of change, and (3) the relationships between change and environmental factors and historical land use. We found that with few exceptions, notably the American chestnut, the same taxa that made up the pre-colonial forest still comprise the forest today, despite ample opportunities for species invasion and loss. Nonetheless, there have been dramatic shifts in the relative abundance of forest taxa. The magnitude of change is spatially clustered at local scales (<125 km) but exhibits little evidence of regional-scale gradients. Compositional change is most strongly associated with the historical extent of agricultural clearing. Throughout the region, there has been a broad ecological shift away from late successional taxa, such as beech and hemlock, in favor of early- and mid-successional taxa, such as red maple and poplar. Additionally, the modern forest composition is more homogeneous and less coupled to local climatic controls.
  • Thumbnail Image
    Publication
    Soil Respiration in a Northeastern US Temperate Forest: A 22-Year Synthesis
    (Ecological Society of America, 2013) Giasson, M.-A.; Ellison, Aaron; Bowden, R. D.; Crill, P. M.; Davidson, E. A.; Drake, J. E.; Frey, S. D.; Hadley, Julian; Lavine, M.; Melillo, J. M.; Munger, J. W.; Nadelhoffer, K. J.; Nicoll, L.; Ollinger, S. V.; Savage, K. E.; Steudler, P. A.; Tang, J.; Varner, R. K.; Wofsy, Steven; Foster, David; Finzi, A. C.
    To better understand how forest management, phenology, vegetation type, and actual and simulated climatic change affect seasonal and inter-annual variations in soil respiration (R\(_{s}\)), we analyzed more than 100,000 individual measurements of soil respiration from 23 studies conducted over 22 years at the Harvard Forest in Petersham, Massachusetts, USA. We also used 24 site-years of eddy-covariance measurements from two Harvard Forest sites to examine the relationship between soil and ecosystem respiration (R\(_{e}\)). R\(_{s}\) was highly variable at all spatial (respiration collar to forest stand) and temporal (minutes to years) scales of measurement. The response of R\(_{s}\) to experimental manipulations mimicking aspects of global change or aimed at partitioning R\(_{s}\) into component fluxes ranged from −70% to +52%. The response appears to arise from variations in substrate availability induced by changes in the size of soil C pools and of belowground C fluxes or in environmental conditions. In some cases (e.g., logging, warming), the effect of experimental manipulations on R\(_{s}\) was transient, but in other cases the time series were not long enough to rule out long-term changes in respiration rates. Inter-annual variations in weather and phenology induced variation among annual R\(_{s}\) estimates of a magnitude similar to that of other drivers of global change (i.e., invasive insects, forest management practices, N deposition). At both eddy-covariance sites, aboveground respiration dominated R\(_{e}\) early in the growing season, whereas belowground respiration dominated later. Unusual aboveground respiration patterns—high apparent rates of respiration during winter and very low rates in mid-to-late summer—at the Environmental Measurement Site suggest either bias in R\(_{s}\) and R\(_{e}\) estimates caused by differences in the spatial scale of processes influencing fluxes, or that additional research on the hard-to-measure fluxes (e.g., wintertime R\(_{s}\), unaccounted losses of CO\(_{2}\) from eddy covariance sites), daytime and nighttime canopy respiration and its impacts on estimates of R\(_{e}\), and independent measurements of flux partitioning (e.g., aboveground plant respiration, isotopic partitioning) may yield insight into the unusually high and low fluxes. Overall, however, this data-rich analysis identifies important seasonal and experimental variations in R\(_{s}\) and R\(_{e}\) and in the partitioning of R\(_{e}\) above- vs. belowground.
  • Thumbnail Image
    Publication
    Survivors, Not Invaders, Control Forest Development Following Simulated Hurricane
    (Ecological Society of America, 2013) Plotkin, Audrey Barker; Foster, David; Carlson, Joel; Magill, Alison
    Wind disturbance profoundly shapes temperate forests but few studies have evaluated patterns and mechanisms of long-term forest dynamics following major windthrows. In 1990, we initiated a large hurricane simulation experiment in a 0.8-ha manipulation (pulldown) and 0.6-ha control area of a maturing Quercus rubra–Acer rubrum forest in New England. We toppled 276 trees in the pulldown, using a winch and cable, in the northwesterly direction of natural treefall from major hurricanes. Eighty percent of canopy trees and two-thirds of all trees ≥5 cm dbh (diameter at breast height) suffered direct and indirect damage. We used 20 years of measurements to evaluate the trajectory and mechanisms of forest response after intense disturbance. Based on the patch size and disturbance magnitude, we expected pioneer tree and understory species to drive succession. The first decade of analyses emphasized tree seedling establishment and sprouting by damaged trees as the dominant mechanisms of forest recovery in this extensive damaged area. However, despite 80% canopy damage and 8000-m2 patch size, surviving overstory and advance regeneration controlled longer-term forest development. Residual oaks make up 42% of stand basal area after 20 years. The new cohort of trees, dominated by black birch advance regeneration, contributes 30% of stand basal area. There were shifts in understory vegetation composition and cover, but few species were gained or lost after 20 years. Stand productivity rebounded quickly (litterfall recovered to pre-disturbance levels in six years), but we predict that basal area in the pulldown will lag behind the control (which gained 6 m2/ha over 20 years) for decades to come. This controlled experiment showed that although the scale and intensity of damage were great, abundant advance regeneration, understory vegetation, and damaged trees remained, allowing the forest to resist changes in ecosystem processes and invasion by new species.
  • Thumbnail Image
    Publication
    Quantifying the impact of an extreme climate event on species diversity in fragmented temperate forests: the effect of the October 1987 storm on British broadleaved woodlands
    (Wiley-Blackwell, 2014) Smart, S. M.; Ellison, Aaron; Bunce, R. G. H.; Marrs, R. H.; Kirby, K. J.; Kimberley, A.; Scott, W. A.; Foster, David
    We report the impact of an extreme weather event, the October 1987 severe storm, on fragmented woodlands in southern Britain. We analysed ecological changes between 1971 and 2002 in 143 200-m2 plots in 10 woodland sites exposed to the storm with an ecologically equivalent sample of 150 plots in 16 non-exposed sites. Comparing both years, understorey plant species-richness, species composition, soil pH and woody basal area of the tree and shrub canopy were measured. We tested the hypothesis that the storm had deflected sites from the wider national trajectory of an increase in woody basal area and reduced understorey species-richness associated with ageing canopies and declining woodland management. We also expected storm disturbance to amplify the background trend of increasing soil pH, a UK-wide response to reduced atmospheric sulphur deposition. Path analysis was used to quantify indirect effects of storm exposure on understorey species richness via changes in woody basal area and soil pH. By 2002, storm exposure was estimated to have increased mean species richness per 200 m2 by 32%. Woody basal area changes were highly variable and did not significantly differ with storm exposure. Increasing soil pH was associated with a 7% increase in richness. There was no evidence that soil pH increased more as a function of storm exposure. Changes in species richness and basal area were negatively correlated: a 3.4% decrease in richness occurred for every 0.1-m2 increase in woody basal area per plot. Despite all sites substantially exceeding the empirical critical load for nitrogen deposition, there was no evidence that in the 15 years since the storm, disturbance had triggered a eutrophication effect associated with dominance of gaps by nitrophilous species. Synthesis. Although the impacts of the 1987 storm were spatially variable in terms of impacts on woody basal area, the storm had a positive effect on understorey species richness. There was no evidence that disturbance had increased dominance of gaps by invasive species. This could change if recovery from acidification results in a soil pH regime associated with greater macronutrient availability."
  • Thumbnail Image
    Publication
    A continuous measure of gross primary production for the conterminous United States derived from MODIS and AmeriFlux data
    (Elsevier BV, 2010) Xiao, Jingfeng; Zhuang, Qianlai; Law, Beverly E.; Chen, Jiquan; Baldocchi, Dennis D.; Cook, David R.; Oren, Ram; Richardson, Andrew; Wharton, Sonia; Ma, Siyan; Martini, Timothy A.; Verma, Shashi B.; Suyker, Andrew E.; Scott, Russell L.; Monson, Russell K.; Litvak, Marcy; Hollinger, David Y.; Sun, Ge; Davis, Kenneth J.; Bolstad, Paul V.; Burns, Sean P.; Curtis, Peter S.; Drake, Bert G.; Falk, Matthias; Fischer, Marc L.; Foster, David; Gu, Lianhong; Hadley, Julian L.; Katul, Gabriel G.; Matamala, Roser; McNulty, Steve; Meyers, Tilden P.; Munger, J.; Noormets, Asko; Oechel, Walter C.; Paw U, Kyaw Tha; Schmid, Hans Peter; Starr, Gregory; Torn, Margaret S.; Wofsy, Steven
    The quantification of carbon fluxes between the terrestrial biosphere and the atmosphere is of scientific importance and also relevant to climate-policy making. Eddy covariance flux towers provide continuous measurements of ecosystem-level exchange of carbon dioxide spanning diurnal, synoptic, seasonal, and interannual time scales. However, these measurements only represent the fluxes at the scale of the tower footprint. Here we used remotely sensed data from the Moderate Resolution Imaging Spectroradiometer (MODIS) to upscale gross primary productivity (GPP) data from eddy covariance flux towers to the continental scale. We first combined GPP and MODIS data for 42 AmeriFlux towers encompassing a wide range of ecosystem and climate types to develop a predictive GPP model using a regression tree approach. The predictive model was trained using observed GPP over the period 2000–2004, and was validated using observed GPP over the period 2005–2006 and leave-one-out cross-validation. Our model predicted GPP fairly well at the site level. We then used the model to estimate GPP for each 1 km × 1 km cell across the U.S. for each 8-day interval over the period from February 2000 to December 2006 using MODIS data. Our GPP estimates provide a spatially and temporally continuous measure of gross primary production for the U.S. that is a highly constrained by eddy covariance flux data. Our study demonstrated that our empirical approach is effective for upscaling eddy flux GPP data to the continental scale and producing continuous GPP estimates across multiple biomes. With these estimates, we then examined the patterns, magnitude, and interannual variability of GPP. We estimated a gross carbon uptake between 6.91 and 7.33 Pg C yr− 1 for the conterminous U.S. Drought, fires, and hurricanes reduced annual GPP at regional scales and could have a significant impact on the U.S. net ecosystem carbon exchange. The sources of the interannual variability of U.S. GPP were dominated by these extreme climate events and disturbances.
  • Thumbnail Image
    Publication
    Toward an Integrated Model for Raised-Bog Development: Theory and Field Evidence
    (Wiley-Blackwell, 1995) Almquist-Jacobson, H.; Foster, David
    The development and distribution of Northern mires, including minerotrophic fens and ombrotrophic raised bogs, frequently are presumed to be strongly controlled by the interplay of regional climate and site geomorphology and history. Investigations of these relationships provide insights into long-term trends in ecosystem development by linking geological and landscape-scale processes. In this study, a theoretical model for raised-bog development integrates internal bog hydrodynamics with external factors, including local substrate characteristics, and regional temperature and moisture conditions. The model is used to interpret the development of raised bogs in the Bergslagen region, which coincides with the modern northern distributional limit of those mires in central Sweden. The development of minerotrophic fens that precede bog formation is also considered. Basal radiocarbon dates along surveyed transects are used to assess the pattern and timing of peatland formation and rates of lateral expansion. Previous palynological and lake-level studies from the same region provide independent evidence for changes in Holocene climate. Fen initiation in the region occurred throughout the Holocene under a broad range of environmental conditions. Once established, fens appear to expand faster during moister periods. Locally, substrate slope is an important mediator of fen development, with slopes >0.5% inhibiting lateral expansion. Accumulation of Sphagnum peat, an indicator of raisedbog initiation, occurred from -4000 to 5000 yr BP during relatively dry phases. Rates of lateral expansion were not significantly affected by increasing moisture or by decreasing temperatures until at least 2000 yr BP However, modern geographic trends in cross sectional shape of mires suggest that, at the northern limit of their range today, raised bogs are limited by low temperatures.
  • Thumbnail Image
    Publication
    Analytic Webs Support the Synthesis of Ecological Data Sets
    (Ecological Society of America, 2006) Ellison, Aaron; Osterweil, Leon; Hadley, Julian; Wise, Alexander; Boose, Emery; Clarke, Lori; Foster, David; Hanson, Allen; Jensen, David Michael; Kuzeja, Paul; Riseman, Edward; Schultz, Howard
    A wide variety of data sets produced by individual investigators are now synthesized to address ecological questions that span a range of spatial and temporal scales. It is important to facilitate such syntheses so that ‘‘consumers’’ of data sets can be confident that both input data sets and synthetic products are reliable. Necessary documentation to ensure the reliability and validation of data sets includes both familiar descriptive metadata and formal documentation of the scientific processes used (i.e., process metadata) to produce usable data sets from collections of raw data. Such documentation is complex and difficult to construct, so it is important to help ‘‘producers’’ create reliable data sets and to facilitate their creation of required metadata. We describe a formal representation, an ‘‘analytic web,’’ that aids both producers and consumers of data sets by providing complete and precise definitions of scientific processes used to process raw and derived data sets. The formalisms used to define analytic webs are adaptations of those used in software engineering, and they provide a novel and effective support system for both the synthesis and the validation of ecological data sets. We illustrate the utility of an analytic web as an aid to producing synthetic data sets through a worked example: the synthesis of long-term measurements of whole-ecosystem carbon exchange. Analytic webs are also useful validation aids for consumers because they support the concurrent construction of a complete, Internet-accessible audit trail of the analytic processes used in the synthesis of the data sets. Finally we describe our early efforts to evaluate these ideas through the use of a prototype software tool, SciWalker. We indicate how this tool has been used to create analytic webs tailored to specific data-set synthesis and validation activities, and suggest extensions to it that will support additional forms of validation. The process metadata created by SciWalker is readily adapted for inclusion in Ecological Metadata Language (EML) files.
  • Thumbnail Image
    Publication
    Moose Foraging in the Temperate Forests of Southern New England
    (Humboldt Field Research Institute, 2010) Faison, Edward; Motzkin, Glenn; Foster, David; McDonald, John E.
    Moose have recently re-colonized the temperate forests of southern New England, raising questions about this herbivore’s effect on forest dynamics in the region. We quantifi ed Moose foraging selectivity and intensity on tree species in relation to habitat features in central Massachusetts. Acer rubrum (Red Maple) and Tsuga canadensis (Eastern Hemlock) were disproportionately browsed; Pinus strobus (White Pine) was avoided. Foraging intensity correlated positively with elevation, distance to development, and watershed type and negatively with time since forest harvest, explaining 26% of the variation. Moose may interact with forest harvesting to contribute to a decline in Red Maple and Eastern Hemlock and an increase in White Pine in intensively browsed patches. Nonetheless, foraging impacts may diminish over time, as increasing temperatures and sprawling development increasingly restrict suitable Moose habitat.