The Experts below are selected from a list of 1596 Experts worldwide ranked by ideXlab platform
David R. Foster - One of the best experts on this subject based on the ideXlab platform.
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Multivariate climate change, the climate niche, and the Holocene history of eastern hemlock (Tsuga canadensis)
2019Co-Authors: Bryan N. Shuman, W. Wyatt Oswald, David R. FosterAbstract:Forests in the eastern North America have changed progressively over the 11,700 years of the Holocene Epoch. To understand the dynamics involved, we focus on eastern hemlock ( Tsuga canadensis ), which shifted its distribution through time and, notably, exhibited a rapid range-wide decline at 5280±180 YBP. We consider how climate could have shaped this history by comparing fossil pollen records from eight New England sites with quantitative temperature and effective precipitation reconstructions and evaluating the realization of Tsuga ′s climate niche through time. The comparisons indicate that multivariate climate change significantly influenced Tsuga abundance, including its abrupt decline and recovery. The comparisons show that the realized climate niche of Tsuga expressed today includes two important features that persisted through time. First, Tsuga pollen percentages reach their maxima (>30%) where July temperatures equal 18-20°C, but do so at two modes where annual precipitation equals either ~1100 or ~775 mm. The bimodality reflects Tsuga ′s two geographic modes in the Great Lakes and Appalachian regions today, and explains past dynamics, such as short-lived peaks in Tsuga abundance associated with effective precipitation of ~775 mm at ca. 10,000 years before CE 1950 (YBP). Second, the two peaks in Tsuga abundance follow negative correlations between temperature and precipitation such that the two modes shift toward high precipitation if temperatures are low (e.g., ~1400 and ~1000 mm at Tsuga declines because cooling did not coincide with increased precipitation. Abundance declined as local climates departed from optimal temperature and precipitation combinations. Recovery only followed as effective precipitation increased by >150 mm over the past 4000 years. A regionally calibrated model of the relationship of Tsuga pollen percentages to temperature and precipitation explains 70-75% of the variance in the percentages at eight study sites. Iteratively excluding each site from the model shows that accurately representing the major features of the climate niche enables the model to predict the mid-Holocene decline and other past changes at the excluded site (site-level RMSE = 2.1-5.6%). Similar multivariate climate dynamics closely modulated the species′ abundance throughout the Holocene with no evidence of additional large-scale disturbances.
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Lasting legacies of historical clearcutting, wind, and salvage logging on old-growth Tsuga canadensis-Pinus strobus forests
Forest Ecology and Management, 2018Co-Authors: Emma M. Sass, Anthony W. D'amato, David R. FosterAbstract:Abstract Disturbance events affect forest composition and structure across a range of spatial and temporal scales, and subsequent forest development may differ after natural, anthropogenic, or compound disturbances. Following large, natural disturbances, salvage logging is a common and often controversial management practice in many regions of the globe. Yet, while the short-term impacts of salvage logging have been studied in many systems, the long-term effects remain unclear. We capitalized on over eighty years of data following an old-growth Tsuga canadensis-Pinus strobus forest in southwestern New Hampshire, USA after the 1938 hurricane, which severely damaged forests across much of New England. To our knowledge, this study provides the longest evaluation of salvage logging impacts, and it highlights developmental trajectories for Tsuga canadensis-Pinus strobus forests under a variety of disturbance histories. Specifically, we examined development from an old-growth condition in 1930 through 2016 across three different disturbance histories: (1) clearcut logging prior to the 1938 hurricane with some subsequent damage by the hurricane (“logged”), (2) severe damage from the 1938 hurricane (“hurricane”), and (3) severe damage from the hurricane followed by salvage logging (“salvaged”). There were no differences in current overstory composition between the different disturbance histories, as most areas shifted strongly away from pre-hurricane composition through nearly complete elimination of P. strobus and corresponding increases in hardwoods (Betula and Acer spp.), while T. canadensis remained dominant. In contrast, eight decades later, structural characteristics remain distinct between logged, hurricane, and salvaged sites. Specifically, trees were larger in the logged and salvaged sites, and pit and mound structures were largest and most abundant in the hurricane site. Tree densities and coarse woody debris biomass was greater in the hurricane site than the logged sites, but not significantly different from salvaged sites. These findings underscore the long-term influence of salvage logging on forest development, indicating convergence in overstory composition over time between logged, salvaged, and non-salvaged areas, but persistent structural differences, especially in microtopographic structures and live tree development. Future salvage logging efforts should consider these impacts and provide a greater range of unsalvaged areas across the landscape to maintain important structural legacies over the long term.
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a foundation tree at the precipice Tsuga canadensis health after the arrival of adelges Tsugae in central new england
Ecosphere, 2012Co-Authors: David A. Orwig, Jonathan R Thompson, Nicholas A Povak, Megan Manner, Donald Niebyl, David R. FosterAbstract:Hemlock (Tsuga canadensis) plays a unique role in Eastern forests, producing distinctive biogeochemical, habitat, and microclimatic conditions and yet has begun a potentially irreversible decline due to the invasive hemlock woolly adelgid (Adelges Tsugae; HWA) that causes foliar damage, crown loss, and mortality of host trees. Understanding the regional, landscape, site, and stand factors influencing HWA spread and impact is critical for predicting future landscape dynamics and directing effective management. Using aerial photographs, we documented hemlock distribution throughout central Massachusetts and subsampled 123 stands to examine the spatial pattern of HWA and its impact on tree vigor and mortality since its arrival in 1989. In the study region, over 86,000 ha of hemlock forest were mapped in 5,127 stands. White pine (Pinus strobus), red oak (Quercus rubra), red maple (Acer rubrum), and black birch (Betula lenta) were common overstory associates. Hemlock abundance increased from south to north, commonly on western and northwestern slopes. Average stand size was 55 ha, overstory basal area ranged from 23 to 55 m2 ha−1 and overstory stem densities averaged 993 ha−1. By 2004, 40% of sampled stands were infested, but most stands remained in good health overall; only 8 stands contained high HWA densities and only two had lost >50% overstory hemlock. Out of fifteen stand and landscape predictor variables examined, only latitude and winter climate variables were related to HWA density. Cold temperatures appear to be slowing the spread and impact of HWA at its northern extent as HWA infestation intensity and hemlock mortality and vigor were significantly correlated with average minimum winter temperature. Contrary to predictions, there was no regional increase in hemlock harvesting. The results suggest that regional HWA-hemlock dynamics are currently being shaped more by climate than by a combination of landscape and social factors. The persistence and migration of HWA continues to pose a significant threat regionally, especially in the northern portion of the study area, where hemlock dominates many forests.
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Middle-Holocene dynamics of Tsuga canadensis (eastern hemlock) in northern New England, USA
The Holocene, 2011Co-Authors: W. Wyatt Oswald, David R. FosterAbstract:The abrupt, range-wide decline of Tsuga canadensis ~5500 calibrated years before present (cal. yr BP) is one of the most-studied events in North American paleoecology. Little attention, however, has been given to an earlier Tsuga decline, dated to ~6000 cal. yr BP in southern Ontario, Canada. To investigate whether this event occurred elsewhere in eastern North America, we analyzed the middle-Holocene interval of a lake-sediment record from Knob Hill Pond, located in northern Vermont, USA, an area of historically high Tsuga abundance. A dramatic, short-lived drop in Tsuga pollen abundance does occur at ~6000 cal. yr BP in the Knob Hill Pond record, indicating that Tsuga populations declined in various parts of its range. We hypothesize that both middle-Holocene declines of Tsuga were caused by the deleterious effects of pronounced droughts on this moisture-sensitive tree. Close examination of pollen data from a transect of sites across New England reveals that the earlier decline of Tsuga is present in ot...
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understory vegetation in old growth and second growth Tsuga canadensis forests in western massachusetts
Forest Ecology and Management, 2009Co-Authors: David A. Orwig, Anthony W Damato, David R. FosterAbstract:We compared the understory communities (herbs, shrubs, and tree seedlings and saplings) of oldgrowth and second-growth eastern hemlock forests (Tsuga canadensis) in western Massachusetts, USA. Second-growth hemlock forests originated following clear-cut logging in the late 1800s and were 108– 136 years old at the time of sampling. Old-growth hemlock forests contained total ground cover of herbaceous and shrub species that was approximately 4 times greater than in second-growth forests (4.02 � 0.41%/m 2 versus 1.06 � 0.47%/m 2 ) and supported greater overall species richness and diversity. In addition, seedling and sapling densities were greater in old-growth stands compared to second-growth stands and the composition of these layers was positively correlated with overstory species composition (Mantel tests, r > 0.26, P < 0.05) highlighting the strong positive neighborhood effects in these systems. Ordination of study site understory species composition identified a strong gradient in community composition from second-growth to old-growth stands. Vector overlays of environmental and forest structural variables indicated that these gradients were related to differences in overstory tree density, nitrogen availability, and coarse woody debris characteristics among hemlock stands. These relationships suggest that differences in resource availability (e.g., light, moisture, and nutrients) and microhabitat heterogeneity between old-growth and second-growth stands were likely driving these compositional patterns. Interestingly, several common forest understory plants, including Aralia nudicaulis, Dryopteris intermedia, and Viburnum alnifolium, were significant indicator species for old-growth hemlock stands, highlighting the lasting legacy of past land use on the reestablishment and growth of these common species within second-growth areas. The return of old-growth understory conditions to these second-growth areas will largely be dependent on disturbance and self-thinning mediated changes in overstory structure, resource availability, and microhabitat heterogeneity.
Julian L Hadley - One of the best experts on this subject based on the ideXlab platform.
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hydraulic responses to environmental perturbations in Tsuga canadensis and betula lenta
Tree Physiology, 2008Co-Authors: Michael J Daley, Nathan Phillips, Justin C Pettijohn, Julian L HadleyAbstract:Eastern hemlock (Tsuga canadensis (L). Carr.) is a late-successional species found across the northeastern United States of America that is currently threatened by the exotic pest, hemlock woolly adelgid (Adelges Tsugae Annand). Because whole-tree physiological characteristics may scale to influence ecosystem processes, we considered whole-tree hydraulic controls in eastern hemlock and the replacement species black birch (Betula lenta L.). Through a series of misting perturbations, whole-tree resistances (R), capacitances (C) and time constants (tau) were determined from time series sap flux data in eastern hemlock and black birch. Black birch trees responded more rapidly to environmental perturbations than eastern hemlock. Utilizing the step function after applied treatments, whole-tree tau ranged between 9.4 and 24.8 min in eastern hemlock trees compared with 5.9 to 10.5 min in black birch. Species was not a significant predictor of R or C when controlling for tree size. In both species, R decreased with sapwood area and C increased. Our tau results indicate that the loss and replacement of eastern hemlock by black birch will decrease the lag between transpiration and absorption of water from the soil and potentially alter the diurnal pattern of carbon and water uptake.
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water use by eastern hemlock Tsuga canadensis and black birch betula lenta implications of effects of the hemlock woolly adelgid
Canadian Journal of Forest Research, 2007Co-Authors: Michael Daleym J J Daley, Nathan Phillipsn G G Phillips, Cory Pettijohnc Pettijohn, Julian L HadleyAbstract:Eastern hemlock (Tsuga canadensis (L.) Carr.) is a coniferous evergreen species found across the northeastern United States that is currently threatened by the exotic pest hemlock woolly adelgid (HWA; Adelges Tsugae Annand). As HWA kills eastern hemlock trees, black birch (Betula lenta L.) has been found to be a dominant replacement species in the region. Seasonal changes in water use by eastern hemlock and black birch were investigated utilizing whole-tree tran- spiration measurement techniques. Annual evapotranspiration in an eastern hemlock and deciduous stand was also esti- mated. During the peak growing season, daily rates of transpiration were 1.6 times greater in black birch. Cumulative transpiration in black birch exceeded hemlock transpiration by 77 mm from June until October. During the dormant sea- son, evapotranspiration rates were higher in the hemlock stand; however, estimated annual evapotranspiration was 327 mm in eastern hemlock compared with 417 mm in the deciduous stand. Our results suggest that a transition from a hemlock- dominated to a black birch-dominated stand will alter the annual water balance with the greatest impact occurring during the peak growing season. Late in the growing season, flow may be unsustainable in streams that normally have light or moderate flow because ofincreased water use by black birch. Resume´ : La pruche du Canada (Tsuga canadensis (L.) Carr.) qui est une espece de conifere a feuilles persistantes pre´-
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water use by eastern hemlock Tsuga canadensis and black birch betula lenta implications of effects of the hemlock woolly adelgid
Canadian Journal of Forest Research, 2007Co-Authors: Michael Daleym J J Daley, Nathan Phillipsn G G Phillips, Cory Pettijohnc Pettijohn, Julian L HadleyAbstract:Eastern hemlock (Tsuga canadensis (L.) Carr.) is a coniferous evergreen species found across the northeastern United States that is currently threatened by the exotic pest hemlock woolly adelgid (H...
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carbon exchange of an old growth eastern hemlock Tsuga canadensis forest in central new england
Tree Physiology, 2002Co-Authors: Julian L Hadley, Jessica L SchedlbauerAbstract:Carbon (C) exchange of an approximately 200-year-old eastern hemlock (Tsuga canadensis L.) forest in central Massachusetts, USA, was estimated from mid-October 2000 through October 2001 based on eddy covariance measurements and statistical modeling from microclimatic data. Measurements were made in 68% of the hours during the year of study, with > 50% coverage in all months except December and August. Data were filtered by wind direction and atmospheric turbulence to remove invalid measurements. Analysis of filtered data showed that photosynthetically active radiation (PAR) was significant in predicting C exchange, except during the winter. Daily minimum air temperature affected C exchange in autumn and winter, whereas time of day, water vapor pressure deficit and air temperature had significant effects on C storage in spring, summer and fall. Most C storage in the stand occurred in April through July and in October 2001, with maximum rates in April and May. Persistent cold weather prevented C storage in December through March. In early spring 2001, C uptake was sensitive to nocturnal frost: daily minimum air temperatures below 0 degrees C reduced C fixation, and minima below -5 degrees C caused its virtual cessation. Soil temperature was a poor predictor of C balance during this period. In August, high soil and air temperatures (averaging 16.7 and 21.1 degrees C, respectively) drove high ecosystem respiration, which approximately balanced C uptake. These patterns show potential for stimulated C storage in hemlock forests in a warmer climate with fewer spring and autumn frosts, but reduced C storage during warmer summers. Estimated annual C storage was 3.0 Mg ha(-1), which is higher than for younger coniferous and deciduous forests during earlier years in the northeastern USA. Long-term data are needed to determine if the estimated high C storage in this hemlock forest is a result of interannual climate variation or an effect of forest composition.
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effect of daily minimum temperature on photosynthesis in eastern hemlock Tsuga canadensis l in autumn and winter
Arctic Antarctic and Alpine Research, 2000Co-Authors: Julian L HadleyAbstract:Most coniferous trees are capable of photosynthesis throughout the year, but low temperatures and frozen soil limit winter photosynthesis in many regions. In eastern hemlock (Tsuga canadensis L.) in central Massachusetts, U.S.A., midday light saturated photosynthesis (Pmax) in autumn was limited by subfreezing temperatures during the previous one to two nights. In autumn, minimum air temperature (Tm,n) during the previous 24 h had a strong effect on midday Pmax only if Tmn, was below -2?C. Pmax averaged about 5 ,umol m-2 s-~ after Tmin near -2?C, but fell to about 1 ,umol m-2 s-l after a Tni of -8?C. Maximum measured Pmax in winter was about 2.5 uxmol m-2 s-1 after a Tmin of 7?C in mid-March, and Pmax in winter was more strongly related to average Tmin during the previous week than to the Tmin just prior to measurement. However, no major mid-winter thaws, with several successive above-freezing minimum temperatures, occurred during this study. A model of annual carbon exchange for the hemlock forest showed that daily ecosystem carbon exchange in December through March was very sensitive to variation between -5 and 2?C in average daily Tmn during the past 2 d. Fewer autumn frosts and prolonged winter thaws could increase annual photosynthesis and carbon storage in eastern hemlock forests in the northeastern United States.
Christopher R Webster - One of the best experts on this subject based on the ideXlab platform.
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press pulse odocoileus virginianus herbivory in relict Tsuga canadensis stands in the western upper peninsula of michigan usa
Forests, 2019Co-Authors: Grace L Parikh, Christopher R WebsterAbstract:Ungulate herbivory occurring within a forest plant community’s natural range of variation may help maintain species diversity. However, acute or chronically elevated levels of herbivory can produce dramatic changes in forest communities. For example, chronically high levels of herbivory by white-tailed deer (Odocoileus virginianus Zimmerman) in regions of historically low abundance at northern latitudes have dramatically altered forest community composition. In eastern hemlock (Tsuga canadensis L. Carriere) stands where deer aggregate during winter, high deer use has been associated with a shift towards deciduous species (i.e., maples [Acer spp.]) dominating the regeneration layer. Especially harsh winters can lead to deer population declines, which could facilitate regeneration of species that have been suppressed by browsing, such as hemlock. To enhance our understanding of how fluctuations in herbivory influence regeneration dynamics, we surveyed regeneration and deer use in 15 relict hemlock stands in the western Upper Peninsula of Michigan in 2007 and again in 2015. With the exception of small seedlings (0.04–0.24 m height), primarily maples whose abundance increased significantly (p 1.4 m tall ≤ 4 cm diameter at breast height) over the study period. Midway through our study period, the region experienced a high severity winter (i.e., “polar vortex”) which resulted in a substantial decline in the white-tailed deer population. Given the dominance of maples and dearth of hemlock in the seedling layer, the decline in the deer population may fail to forestall or possibly hasten the trend towards maple dominance of the regeneration layer as these stands recover from pulses of acute herbivory associated with high-severity winters and the press of chronically high herbivory that precedes them.
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Post-Disturbance Plant Community Dynamics following a Rare Natural-Origin Fire in a Tsuga canadensis Forest
2016Co-Authors: Bryan D. Murray, Christopher R Webster, Stacie A. Holmes, Jill C WittAbstract:Opportunities to directly study infrequent forest disturbance events often lead to valuable information about vegetation dynamics. In mesic temperate forests of North America, stand-replacing crown fire occurs infrequently, with a return interval of 2000–3000 years. Rare chance events, however, may have profound impacts on the developmental trajectories of forest ecosystems. For example, it has been postulated that stand-replacing fire may have been an important factor in the establishment of eastern hemlock (Tsuga canadensis) stands in the northern Great Lakes region. Nevertheless, experimental evidence linking hemlock regeneration to non-anthropogenic fire is limited. To clarify this potential relationship, we monitored vegetation dynamics following a rare lightning-origin crown fire in a Wisconsin hemlock-hardwood forest. We also studied vegetation in bulldozer-created fire breaks and adjacent undisturbed forest. Our results indicate that hemlock establishment was rare in the burned area but moderately common in the scarified bulldozer lines compared to the reference area. Early-successional, non-arboreal species including Rubus spp., Vaccinium angustifolium, sedges (Carex spp.), grasses, Epilobium ciliatum, and Pteridium aquilinium were the most abundant post-fire species. Collectively, our results suggest that competing vegetation and moisture stress resulting from drought may reduce the efficacy of scarification treatments as well as the usefulness of fire for preparing a suitable seedbed for hemlock. The increasing prevalence of growing-season drought suggests that silvicultural strategies based on historic disturbance regimes may need to b
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post disturbance plant community dynamics following a rare natural origin fire in a Tsuga canadensis forest
PLOS ONE, 2012Co-Authors: Bryan D. Murray, Christopher R Webster, Stacie A. Holmes, Jill C WittAbstract:Opportunities to directly study infrequent forest disturbance events often lead to valuable information about vegetation dynamics. In mesic temperate forests of North America, stand-replacing crown fire occurs infrequently, with a return interval of 2000–3000 years. Rare chance events, however, may have profound impacts on the developmental trajectories of forest ecosystems. For example, it has been postulated that stand-replacing fire may have been an important factor in the establishment of eastern hemlock (Tsuga canadensis) stands in the northern Great Lakes region. Nevertheless, experimental evidence linking hemlock regeneration to non-anthropogenic fire is limited. To clarify this potential relationship, we monitored vegetation dynamics following a rare lightning-origin crown fire in a Wisconsin hemlock-hardwood forest. We also studied vegetation in bulldozer-created fire breaks and adjacent undisturbed forest. Our results indicate that hemlock establishment was rare in the burned area but moderately common in the scarified bulldozer lines compared to the reference area. Early-successional, non-arboreal species including Rubus spp., Vaccinium angustifolium, sedges (Carex spp.), grasses, Epilobium ciliatum, and Pteridium aquilinium were the most abundant post-fire species. Collectively, our results suggest that competing vegetation and moisture stress resulting from drought may reduce the efficacy of scarification treatments as well as the usefulness of fire for preparing a suitable seedbed for hemlock. The increasing prevalence of growing-season drought suggests that silvicultural strategies based on historic disturbance regimes may need to be reevaluated for mesic species.
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regeneration dynamics in remnant Tsuga canadensis stands in the northern lake states potential direct and indirect effects of herbivory
Forest Ecology and Management, 2010Co-Authors: Jill C Witt, Christopher R WebsterAbstract:Abstract We examined the effects of white-tailed deer (Odocoileus virginianus) herbivory and microsite limitation on Tsuga canadensis regeneration in 39 randomly selected remnant T. canadensis stands in Michigan's Upper Peninsula. Deer of the region migrate to and congregate in T. canadensis stands in winter resulting in strong seasonal habitat use patterns. In each study stand, we quantified vegetation, microsite availability, and deer use (via pellet counts). While some stands contained high densities of T. canadensis regeneration (stems
Aaron M. Ellison - One of the best experts on this subject based on the ideXlab platform.
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when a foundation crumbles forecasting forest dynamics following the decline of the foundation species Tsuga canadensis
Ecosphere, 2017Co-Authors: David A. Orwig, Audrey Barker Plotkin, Bradley S Case, Hannah L Buckley, Aaron M. EllisonAbstract:In the forests of northeastern North America, invasive insects and pathogens are causing major declines in some tree species and a subsequent reorganization of associated forest communities. Using observations and experiments to investigate the consequences of such declines are hampered because trees are long-lived. Simulation models can provide a means to forecast possible futures based on different scenarios of tree species decline, death, and removal. Such modeling is particularly urgent for species such as eastern hemlock (Tsuga canadensis), a foundation species in many northeastern forest regions that is declining due to the hemlock woolly adelgid (Adelges Tsugae). Here, we used an individual-based forest simulator, SORTIE-ND, to forecast changes in forest communities in Central Massachusetts over the next 200 yr under a range of scenarios: a no-adelgid, status quo scenario; partial resistance of hemlock to the adelgid; adelgid irruption and total hemlock decline over 25 yr, adelgid irruption and salvage logging of hemlock trees; and two scenarios of preemptive logging of hemlock and hemlock/white pine. We applied the model to six study plots comprising a range of initial species mixtures, abundances, and levels of hemlock dominance. Simulations indicated that eastern white pine, and to a lesser extent black birch and American beech, would gain most in relative abundance and basal area following hemlock decline. The relative dominance of these species depended on initial conditions and the amount of hemlock mortality, and their combined effect on neighborhood-scale community dynamics. Simulated outcomes were little different whether hemlock died out gradually due to the adelgid or disappeared rapidly following logging. However, if eastern hemlock were to become partially resistant to the adelgid, hemlock would be able to retain its dominance despite substantial losses of basal area. Our modeling highlights the complexities associated with secondary forest succession due to ongoing hemlock decline and loss. We emphasize the need both for a precautionary approach in deciding between management intervention or simply doing nothing in these declining hemlock forests, and for clear aims and understanding regarding desired community- and ecosystem-level outcomes.
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when a foundation crumbles forecasting forest community dynamics following the decline of the foundation species Tsuga canadensis
bioRxiv, 2017Co-Authors: Bradley S Case, David A. Orwig, Audrey Barker Plotkin, Hannah L Buckley, Aaron M. EllisonAbstract:In the forests of northeastern North America, invasive insects and pathogens are causing major declines in some tree species and a subsequent reorganization of associated forest communities. Using observations and experiments to investigate the consequences of such declines are hampered because trees are long-lived. Simulation models can provide a means to forecast possible futures based on different scenarios of tree species decline, death, and removal. Such modeling is particularly urgent for species such as eastern hemlock ( Tsuga canadensis ), a foundation species in many northeast forest regions that is declining due to the hemlock woolly adelgid ( Adelges Tsugae ). Here, we used an individual-based forest simulator, SORTIE-ND, to forecast changes in forest communities in central Massachusetts over the next 200 years under a range of scenarios: a no-adelgid, status-quo scenario; partial resistance of hemlock to the adelgid; adelgid irruption and total hemlock decline over 25 years, adelgid irruption and salvage logging of hemlock trees; and two scenarios of preemptive logging of hemlock and hemlock/white pine. We applied the model to six study plots comprising a range of initial species mixtures, abundances, and levels of hemlock dominance. Simulations indicated that eastern white pine, and to a lesser extent black birch and American beech, would gain most in relative abundance and basal area following hemlock decline. The relative dominance of these species depended on initial conditions and the amount of hemlock mortality, and their combined effect on neighborhood-scale community dynamics. Simulated outcomes were little different whether hemlock died out gradually due to the adelgid or disappeared rapidly following logging. However, if eastern hemlock were to become partially resistant to the adelgid, hemlock would be able to retain its dominance despite substantial losses of basal area. Our modeling highlights the complexities associated with secondary forest succession due to ongoing hemlock decline and loss. We emphasize the need both for a precautionary approach in deciding between management intervention or simply doing nothing in these declining hemlock forests, and for clear aims and understanding regarding desired community- and ecosystem-level outcomes.
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assessing the impacts of the decline of Tsuga canadensis stands on two amphibian species in a new england forest
Ecosphere, 2016Co-Authors: Aaron M. Ellison, Ahmed A H Siddig, Brooks G MathewsonAbstract:Disturbances such as outbreaks of herbivorous insects and pathogens can devastate unique habitats and directly reduce biodiversity. The foundation tree species Tsuga canadensis (eastern hemlock) is declining due to infestation by the nonnative insect Adelges Tsugae (hemlock woolly adelgid). The decline and expected elimination of hemlock from northeastern U.S. forests is changing forest structure, function, and assemblages of associated species. We assessed 10 years of changes in occupancy, detection probability, and relative abundance of two species of terrestrial salamanders, Plethodon cinereus (eastern red-back salamander) and Notopthalmus viridescens viridescens (eastern red-spotted newt), to the experimental removal in 2005 of T. canadensis at Harvard Forest. Salamanders were sampled under cover boards and using visual encounter surveys before (2004) and after (2005, 2013, 2014) canopy manipulations in replicate 0.81-ha plots. In 2004, occupancy of P. cinereus was 35% lower in stands dominated by T. canadensis than that in associated mixed-hardwood control stands, whereas detection probability and estimated abundance of P. cinereus were, respectively, 60% and 100% greater in T. canadensis stands. Estimated abundance of N. v. viridescens in 2004 was 50% higher in T. canadensis stands. Removal of the T. canadensis canopy increased occupancy of P. cinereus but significantly reduced its estimated detection probability and abundance. Estimated abundance of N. v. viridescens also declined dramatically after canopy manipulations. Our results suggest that ten years after T. canadensis loss due to either the adelgid or pre-emptive salvage logging, and 50–70 years later when these forests have become mid-successional mixed deciduous stands, the abundance of these salamanders likely will be <50% of their abundance in current, intact T. canadensis stands. This study adds to our understanding of how forest disturbance, directly and indirectly caused by invasive species, can contribute to declines in the relative abundance of amphibians.
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building a foundation land use history and dendrochronology reveal temporal dynamics of a Tsuga canadensis pinaceae forest
Rhodora, 2014Co-Authors: Aaron M. Ellison, Michael Lavine, Peter Kerson, Audrey Barker Plotkin, David A. OrwigAbstract:Abstract We used historical documents, stand mapping, and new methods of dendrochronological analysis to reconstruct 250 y of land-use history of the Simes Tract in Petersham, MA. These data were then used to interpret the origin of the current forest's stand structure within the experimental plots of the Harvard Forest Hemlock Removal Experiment within the Simes Tract, an experiment that examines the effects of the ongoing decline of Tsuga canadensis on forest ecology. Data from tree cores revealed that the trees in the experimental plots were < 150 y old. These trees have established continually since the 1870s, with recruitment pulses following successive episodes of land division and re-aggregation, logging, irruptions of nonnative insects and pathogens, two moderate droughts, and the 1938 “Great Hurricane”. Our new method of dendrochronological analysis used generalized additive models and focused on year-to-year dynamics to highlight associations between fine-scale changes in tree growth, and both e...
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experiments are revealing a foundation species a case study of eastern hemlock Tsuga canadensis
Advances in Ecology, 2014Co-Authors: Aaron M. EllisonAbstract:Foundation species are species that create and define particular ecosystems; control in large measure the distribution and abundance of associated flora and fauna; and modulate core ecosystem processes, such as energy flux and biogeochemical cycles. However, whether a particular species plays a foundational role in a system is not simply asserted. Rather, it is a hypothesis to be tested, and such tests are best done with large-scale, long-term manipulative experiments. The utility of such experiments is illustrated through a review of the Harvard Forest Hemlock Removal Experiment (HF-HeRE), a multidecadal, multihectare experiment designed to test the foundational role of eastern hemlock, Tsuga canadensis, in eastern North American forests. Experimental removal of T. canadensis has revealed that after 10 years, this species has pronounced, long-term effects on associated flora and fauna, but shorter-term effects on energy flux and nutrient cycles. We hypothesize that on century-long scales, slower changes in soil microbial associates will further alter ecosystem processes in T. canadensis stands. HF-HeRE may indeed continue for >100 years, but at such time scales, episodic disturbances and changes in regional climate and land cover can be expected to interact in novel ways with these forests and their foundation species.
David A. Orwig - One of the best experts on this subject based on the ideXlab platform.
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when a foundation crumbles forecasting forest dynamics following the decline of the foundation species Tsuga canadensis
Ecosphere, 2017Co-Authors: David A. Orwig, Audrey Barker Plotkin, Bradley S Case, Hannah L Buckley, Aaron M. EllisonAbstract:In the forests of northeastern North America, invasive insects and pathogens are causing major declines in some tree species and a subsequent reorganization of associated forest communities. Using observations and experiments to investigate the consequences of such declines are hampered because trees are long-lived. Simulation models can provide a means to forecast possible futures based on different scenarios of tree species decline, death, and removal. Such modeling is particularly urgent for species such as eastern hemlock (Tsuga canadensis), a foundation species in many northeastern forest regions that is declining due to the hemlock woolly adelgid (Adelges Tsugae). Here, we used an individual-based forest simulator, SORTIE-ND, to forecast changes in forest communities in Central Massachusetts over the next 200 yr under a range of scenarios: a no-adelgid, status quo scenario; partial resistance of hemlock to the adelgid; adelgid irruption and total hemlock decline over 25 yr, adelgid irruption and salvage logging of hemlock trees; and two scenarios of preemptive logging of hemlock and hemlock/white pine. We applied the model to six study plots comprising a range of initial species mixtures, abundances, and levels of hemlock dominance. Simulations indicated that eastern white pine, and to a lesser extent black birch and American beech, would gain most in relative abundance and basal area following hemlock decline. The relative dominance of these species depended on initial conditions and the amount of hemlock mortality, and their combined effect on neighborhood-scale community dynamics. Simulated outcomes were little different whether hemlock died out gradually due to the adelgid or disappeared rapidly following logging. However, if eastern hemlock were to become partially resistant to the adelgid, hemlock would be able to retain its dominance despite substantial losses of basal area. Our modeling highlights the complexities associated with secondary forest succession due to ongoing hemlock decline and loss. We emphasize the need both for a precautionary approach in deciding between management intervention or simply doing nothing in these declining hemlock forests, and for clear aims and understanding regarding desired community- and ecosystem-level outcomes.
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layering and rejuvenation in Tsuga canadensis pinaceae on wachusett mountain massachusetts
Rhodora, 2017Co-Authors: Peter Del Tredici, David A. OrwigAbstract:Abstract The phenomenon of layering in trees involves the production of adventitious roots by low-growing lateral branches and their subsequent reorientation from horizontal to vertical. This study provides the first documentation of layering in any natural populations of eastern hemlock, Tsuga canadensis. Twelve layered hemlock clumps, consisting of 5 to 20 layered branch stems originating from a parent tree, were observed on the upper slopes of Wachusett Mountain in central Massachusetts. Layered hemlocks ranged from 7 to 17 m tall, and several layered branches produced second-generation layers. Harsh growing conditions, slow hemlock growth, and the open habitat associated with small-statured hardwood species and exposed bedrock allowed the hemlocks to retain their lower branches for extended periods of time. Fallen limbs and debris associated with past disturbances pinned these branches to the ground and likely set the stage for layering. The production of physiologically rejuvenated hemlock ramets thr...
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when a foundation crumbles forecasting forest community dynamics following the decline of the foundation species Tsuga canadensis
bioRxiv, 2017Co-Authors: Bradley S Case, David A. Orwig, Audrey Barker Plotkin, Hannah L Buckley, Aaron M. EllisonAbstract:In the forests of northeastern North America, invasive insects and pathogens are causing major declines in some tree species and a subsequent reorganization of associated forest communities. Using observations and experiments to investigate the consequences of such declines are hampered because trees are long-lived. Simulation models can provide a means to forecast possible futures based on different scenarios of tree species decline, death, and removal. Such modeling is particularly urgent for species such as eastern hemlock ( Tsuga canadensis ), a foundation species in many northeast forest regions that is declining due to the hemlock woolly adelgid ( Adelges Tsugae ). Here, we used an individual-based forest simulator, SORTIE-ND, to forecast changes in forest communities in central Massachusetts over the next 200 years under a range of scenarios: a no-adelgid, status-quo scenario; partial resistance of hemlock to the adelgid; adelgid irruption and total hemlock decline over 25 years, adelgid irruption and salvage logging of hemlock trees; and two scenarios of preemptive logging of hemlock and hemlock/white pine. We applied the model to six study plots comprising a range of initial species mixtures, abundances, and levels of hemlock dominance. Simulations indicated that eastern white pine, and to a lesser extent black birch and American beech, would gain most in relative abundance and basal area following hemlock decline. The relative dominance of these species depended on initial conditions and the amount of hemlock mortality, and their combined effect on neighborhood-scale community dynamics. Simulated outcomes were little different whether hemlock died out gradually due to the adelgid or disappeared rapidly following logging. However, if eastern hemlock were to become partially resistant to the adelgid, hemlock would be able to retain its dominance despite substantial losses of basal area. Our modeling highlights the complexities associated with secondary forest succession due to ongoing hemlock decline and loss. We emphasize the need both for a precautionary approach in deciding between management intervention or simply doing nothing in these declining hemlock forests, and for clear aims and understanding regarding desired community- and ecosystem-level outcomes.
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building a foundation land use history and dendrochronology reveal temporal dynamics of a Tsuga canadensis pinaceae forest
Rhodora, 2014Co-Authors: Aaron M. Ellison, Michael Lavine, Peter Kerson, Audrey Barker Plotkin, David A. OrwigAbstract:Abstract We used historical documents, stand mapping, and new methods of dendrochronological analysis to reconstruct 250 y of land-use history of the Simes Tract in Petersham, MA. These data were then used to interpret the origin of the current forest's stand structure within the experimental plots of the Harvard Forest Hemlock Removal Experiment within the Simes Tract, an experiment that examines the effects of the ongoing decline of Tsuga canadensis on forest ecology. Data from tree cores revealed that the trees in the experimental plots were < 150 y old. These trees have established continually since the 1870s, with recruitment pulses following successive episodes of land division and re-aggregation, logging, irruptions of nonnative insects and pathogens, two moderate droughts, and the 1938 “Great Hurricane”. Our new method of dendrochronological analysis used generalized additive models and focused on year-to-year dynamics to highlight associations between fine-scale changes in tree growth, and both e...
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a foundation tree at the precipice Tsuga canadensis health after the arrival of adelges Tsugae in central new england
Ecosphere, 2012Co-Authors: David A. Orwig, Jonathan R Thompson, Nicholas A Povak, Megan Manner, Donald Niebyl, David R. FosterAbstract:Hemlock (Tsuga canadensis) plays a unique role in Eastern forests, producing distinctive biogeochemical, habitat, and microclimatic conditions and yet has begun a potentially irreversible decline due to the invasive hemlock woolly adelgid (Adelges Tsugae; HWA) that causes foliar damage, crown loss, and mortality of host trees. Understanding the regional, landscape, site, and stand factors influencing HWA spread and impact is critical for predicting future landscape dynamics and directing effective management. Using aerial photographs, we documented hemlock distribution throughout central Massachusetts and subsampled 123 stands to examine the spatial pattern of HWA and its impact on tree vigor and mortality since its arrival in 1989. In the study region, over 86,000 ha of hemlock forest were mapped in 5,127 stands. White pine (Pinus strobus), red oak (Quercus rubra), red maple (Acer rubrum), and black birch (Betula lenta) were common overstory associates. Hemlock abundance increased from south to north, commonly on western and northwestern slopes. Average stand size was 55 ha, overstory basal area ranged from 23 to 55 m2 ha−1 and overstory stem densities averaged 993 ha−1. By 2004, 40% of sampled stands were infested, but most stands remained in good health overall; only 8 stands contained high HWA densities and only two had lost >50% overstory hemlock. Out of fifteen stand and landscape predictor variables examined, only latitude and winter climate variables were related to HWA density. Cold temperatures appear to be slowing the spread and impact of HWA at its northern extent as HWA infestation intensity and hemlock mortality and vigor were significantly correlated with average minimum winter temperature. Contrary to predictions, there was no regional increase in hemlock harvesting. The results suggest that regional HWA-hemlock dynamics are currently being shaped more by climate than by a combination of landscape and social factors. The persistence and migration of HWA continues to pose a significant threat regionally, especially in the northern portion of the study area, where hemlock dominates many forests.
