Popescu V.D.,University of Maine, United States |
Patrick D.A.,Paul Smiths College |
Hunter Jr. M.L.,University of Maine, United States |
Calhoun A.J.K.,University of Maine, United States
Forest Ecology and Management | Year: 2012
Conservation of forest-dependent amphibians is dependent on finding a balance between timber management and species' habitat requirements. To examine the effect of short-term vegetative regrowth post-harvesting on amphibian habitat use, we studied the response of eight species (four forest specialists and four habitat generalists) to four forestry treatments (partial harvest, clearcut with coarse woody debris [CWD] removed, clearcut with CWD retained, and uncut control) over a 6-year period, using replicated experimental treatments in Maine, USA. Forest amphibians showed a strong negative response to clearcutting through the duration of the study, regardless of the presence of CWD, but only during the post-breeding season (i.e., summer). The spring breeding migrations of wood frogs and spotted salamanders to experimental pools were not affected by the forestry treatments. The use of partial cut treatments by forest amphibians differed between animals emerging from experimental pools (i.e., juvenile wood frogs and spotted salamanders), and animals originating from outside the experimental arrays (i.e., adults of all forest species, juvenile wood frogs and spotted salamanders). Animals emerging from our experimental pools showed no difference in the use of control and partial cut treatments, while all the other animals preferred control plots. In addition, we found a modest increase in the use of clearcuts over the 6. years following harvesting by juvenile wood frogs from experimental pools (from an 8-fold difference between forest and clearcut treatments in the first year post-clearcutting to a 3-fold difference during years 3-5). However, this increase was not significantly associated with vegetation regrowth. Forest specialists declined in abundance in all treatments beginning 2-3. years post-disturbance. Despite high yearly fluctuations in abundance, there was a shift in relative abundance towards habitat generalist species, most notably green frog juveniles. Most habitat generalist species were not affected by clearcutting or vegetative regrowth; however, we observed a lower use of clearcut treatments by green frogs starting 3. years post-harvesting, perhaps due to an increase in habitat resistance to movements associated with vegetative regrowth. These general patterns of habitat use were overridden at the local scale by site-specific variation in the use of forestry treatments, most evident in emigrating juvenile wood frogs. From a management standpoint, implementing broad silvicultural prescriptions could be a viable strategy in extensively forested landscapes, but local variation in habitat use has to be acknowledged when managers focus on a limited area. © 2012 Elsevier B.V.
Garnas J.R.,Dartmouth College |
Ayres M.P.,Dartmouth College |
Liebhold A.M.,Us Forest Service Northern Research Station |
Evans C.,Paul Smiths College
Journal of Ecology | Year: 2011
Introduced pests and pathogens are a major source of disturbance to ecosystems world-wide. The famous examples have produced dramatic reductions in host abundance, including virtual extirpation, but most introductions have more subtle impacts that are hard to quantify but are potentially at least as important due to the pathogens' effects on host reproduction, competitive ability and stress tolerance. A general outcome could be reduced host abundance with concomitant increases in the abundance of competitors. Beech bark disease (BBD) is a widespread, fatal affliction of American beech (Fagus grandifolia), currently present in c.50% of beech's distribution in eastern North America. Despite high adult mortality, beech remains a dominant component of the forest community. Employing spatially extensive data from the national Forest Inventory and Analysis program of the United States Forest Service, we show that forests have changed dramatically in the presence of BBD. Within the 2.3million km2 range of beech, size-specific mortality was 65% higher in the longest-infected regions, and large beech (>90cm diameter at breast height) have declined from c.79individualskm-2 to being virtually absent. Small stem beech density was dramatically higher (>350%) such that infested forests contain a roughly equivalent cross-sectional (basal) area of beech as before BBD. There was no evidence for compensation by sugar maple or other co-occurring tree species via increased recruitment or adult survivorship at the landscape scale. Overall, community composition remained roughly unchanged as a result of BBD. Surprisingly, trajectory of stand dynamics (shifts in stem density and mean tree size reflecting normal stand maturation (self-thinning) or retrogression (more abundant, smaller trees over time)) did not differ between affected and unaffected regions. Variance in stand dynamics was greater in afflicted forests, however, indicating that predictability of forest structure has been diminished by BBD. Synthesis. Forests of eastern North America have shifted to increased density and dramatically smaller stature - without notable change in tree species composition - following the invasion of a novel forest disease. Our results reinforce the conclusion that introduced diseases alter fundamental properties of ecosystems, but indicate that the spectrum of potential effects is broader than generally appreciated. © 2011 The Authors. Journal of Ecology © 2011 British Ecological Society.
Egan A.F.,Paul Smiths College |
Morin L.J.,University of Maine, United States
Journal of Forestry | Year: 2010
Forests and large population centers dominate the landscape of New England (NE) and New York. We investigated factors that may impact the ability of sawmill procurement organizations in the region to obtain wood raw material by surveying mill procurement managers in the region. We found that, although symptoms of population pressures, such as decreasing size of forest parcels and terminal harvesting due to land-use change, were important constraints for many mills and appeared to be increasingly problematic, other factors, such as energy costs, appeared to present far greater challenges to most mills. Results have implications for both near- and long-term procurement strategies and may be relevant to forest products businesses nationwide. Copyright © 2010 by the Society of American Foresters.
Garnas J.R.,Dartmouth College |
Garnas J.R.,University of Pretoria |
Houston D.R.,U.S. Forest Service retired |
Ayres M.P.,Dartmouth College |
Evans C.,Paul Smiths College
Ecography | Year: 2012
Biotic threats to trees often arise from interactions among two or more species, frequently insects and fungi, that function together to defeat host defenses, secure resources and colonize new hosts. Feedbacks among plant enemies can have large effects on host population and disease dynamics, either by promoting stabilizing negative feedbacks or contributing to positive feedbacks that can destabilize populations and permit outbreaks. Feedbacks can be rapid and direct (e.g. within trees or among years) or can arise from slowly developing changes in host resource quantity or quality at the scale of forest stands or landscapes. Climate may also influence system dynamics by altering feedbacks within or among species or through density independent effects. We evaluated major drivers of population dynamics of beech bark disease (BBD), an important forest disease in eastern deciduous forests of North America, using data from 28 study sites in the eastern United States monitored for up to 14 yr between 1979 and 1992. Both primary causal agents of BBD - the introduced felted beech scale Cryptococcus fagisuga and native fungi Neonectria spp. - showed strong simple density dependence in all study populations. Surprisingly, densities of scale insects and fungi had little or no effects on population growth rates of the other, despite their habit of living in close physical relationships. For both insects and fungi, ecologically important features of the density dependent functions (slope, carrying capacity and density independent variance) were variable across sites. Climatic effects on density-dependent functions (and scatter around them) were evident but generally weak and variable. The most striking predictor of patterns in density dependence was duration since establishment of BBD in the region. Apparently BBD alters forests over decades in ways that strengthen self-regulation among causal agents without eliminating or even dramatically reducing host populations. © 2011 The Authors. Journal compilation © 2011 Ecography.
Kudish M.,Paul Smiths College
Annals of the New York Academy of Sciences | Year: 2013
Red spruce (Picea rubens Sarg.) and balsam fir (Abies balsamea (L.) Mill.) were present by 13,700 years B.C.E. in the Catskills Mountains of southeastern New York State. These conifers were, and still are, largely confined to the eastern and far western portions of the region. A gap in the distribution exists between these populations. Both species are absent from the intervening East Branch Delaware River watershed. No red spruce macrofossils were found in this watershed, suggesting that this conifer never colonized the gap postglacially. Rare macrofossils of balsam fir were found in only three of the 24 peatlands in this watershed, the conifer having disappeared between 11,300 and 8,200 years B.C.E. © 2013 New York Academy of Sciences.