Effects of harvest management practices on forest biomass and soil carbon in eucalypt forests in New South Wales,Australia: Simulations with the forest succession model LINKAGES

Understanding long-term changes in forest ecosystem carbon stocks under forest management practices such as timber harvesting is important for assessing the contribution of forests to the global carbon cycle. Harvesting effects are complicated by the amount, type, and condition of residue left on-site, the decomposition rate of this residue, the incorporation of residue into soil organic matter and the rate of new detritus input to the forest floor from regrowing vegetation. In an attempt to address these complexities, the forest succession model LINKAGES was used to assess the production of aboveground biomass, detritus, and soil carbon stocks in native Eucalyptus forests as influenced by five harvest management practices in New South Wales, Australia. The original decomposition sub-routines of LINKAGES were modified by adding components of the Rothamsted (RothC) soil organic matter turnover model. Simulation results using the new model were compared to data from long-term forest inventory plots. Good agreement was observed between simulated and measured above-ground biomass, but mixed results were obtained for basal area. Harvesting operations examined included removing trees for quota sawlogs (QSL, DBH >80 cm), integrated sawlogs (ISL, DBH >20 cm) and whole-tree harvesting in integrated sawlogs (WTH). We also examined the impact of different cutting cycles (20, 50 or 80 years) and intensities (removing 20, 50 or 80 m³). Generally medium and high intensities of shorter cutting cycles in sawlog harvesting systems produced considerably higher soil carbon values compared to no harvesting. On average, soil carbon was 2–9% lower in whole-tree harvest simulations whereas in sawlog harvest simulations soil carbon was 5–17% higher than in no harvesting.     

Woody plant regeneration after blowdown, salvage logging, and prescribed fire in a northern Minnesota forest

Salvage logging after natural disturbance has received increased scrutiny in recent years because of concerns over detrimental effects on tree regeneration and increased fine fuel levels. Most research on tree regeneration after salvage logging comes from fire-prone systems and is short-term in scope. Limited information is available on longer term responses to salvage logging after windstorms or from forests outside of fire-prone regions. We examined tree and shrub regeneration after a stand-replacing windstorm, with and without salvage logging and prescribed fire. Our study takes place in northern Minnesota, USA, a region where salvage logging impacts have received little attention. We asked the following questions: (i) does composition and abundance of woody species differ among post-disturbance treatments, including no salvage, salvage alone, and salvage with prescribed burning, 12 years after the windstorm?; (ii) is regeneration of Populus, the dominant pre-blowdown species, inhibited in unsalvaged treatments?; and (iii) how do early successional trajectories differ among post-blowdown treatments? Twelve years after the wind disturbance, the unsalvaged forest had distinctly different composition and abundance of trees and woody shrubs compared to the two salvage treatments, despite experiencing similar wind disturbance severities and having similar composition immediately after the blowdown. Unsalvaged forest had greater abundance of shade tolerant hardwoods and lower abundance of Populus, woody shrubs, and Betulapapyrifera, compared to salvage treatments. There was some evidence that adding prescribed fire after the blowdown and salvage logging further increased disturbance severity, since the highest abundances of shrubs and early successional tree species occurred in the burning treatment. These results suggest that salvage treatments (or a lack thereof) can be used to direct compositional development of a post-blowdown forest along different trajectories, specifically, towards initial dominance by early successional Populus and B.papyrifera with salvage logging or towards early dominance by shade tolerant hardwoods, with some Populus, if left unsalvaged.     

江苏龙潭森林公园森林群落类型及植物组成分析

利用典型样地取样法,对江苏龙潭森林公园植被进行了调查,发现共有种子植物1 063种(变种),隶属于146科515属,其中,木本植物65科163属348种(变种),草本植物77科345属708种(变种)。依据优势种组成,可将森林植被分为7种次生林群落:松阔混交林、糙叶树-朴树-榉树林、青冈栎林、紫楠林、落叶栎林、枫香林和毛竹林群落;5种人工林群落:杉木林、国外松林、板栗林、茶林及毛竹林群落。与邻近宜兴地区森林资源相比,植被组成具有一定相似性和重叠性,但比位于北亚热带的南京紫金山、常熟虞山森林植物资源总量明显增加,丰富性增强。基于植被现状,对不同森林群落类型提出了相应合理林分改造措施,以提高森林群落的稳定性。     

Threshold effects of variable retention harvesting on understory plant communities in the boreal mixedwood forest

We studied the effects of six levels of dispersed green-tree retention (GTR) harvesting (clearcut (0%), 10%, 20%, 50%, and 75%, and unharvested reference (100%)) on understory plant communities in the 8th growing season post-harvest in the mixedwood boreal forest in northwestern Alberta. For the partial harvest treatments (10%, 20%, 50%, 75%) sample plots were located in the partially harvested (retention) strips as well as in the intervening machine corridors used by the harvesting equipment. The understory plant community was significantly influenced by the gradient of retention level. The cover of understory vegetation, especially graminoids, increased with increasing harvesting intensity for the retention strips and overall considering both plots types. Species richness was unaffected by retention level but did decrease as tree density increased. Lower levels of retention lead to increased abundance of early successional, shade-intolerant species. The results suggest a threshold in understory response to GTR harvesting between the 10% and 20% retention treatments. In terms of understory cover and composition, machine corridors within partially harvested forests resembled clearcuts. The results suggest that retaining more than 10% during GTR harvesting could have significant benefits in terms of maintaining understory plant communities more similar to unharvested reference forest.     

From clearfell coupe to old-growth forest: Succession of bird assemblages in Tasmanian lowland wet eucalypt forests

As forests undergo succession after major disturbance events their assemblages of birds also change. Thus the frequency and extent of wildfire or clearfelling in the landscape can potentially affect the species-richness and abundance of forest birds. We used a chronosequence approach to investigate succession of bird communities in Tasmanian lowland wet eucalypt forest, from shortly after disturbance through to old-growth forest aged approximately 200–250 years. The number of native bird species recorded per survey per site increased as a linear function of stand-age. However, succession did not involve a unidirectional transition in assemblage-composition because of differences in successional responses among individual species and also among guilds of birds that mostly inhabited different strata of the forest. This was exemplified by the crescent honeyeater, which was observed most frequently in the youngest (6–8 years) and oldest (200–250 years) forests that we surveyed, and by the superb lyrebird (introduced to Tasmania from mainland south-eastern Australia) which favoured mid-aged regrowth (42–43 years) after clearfelling. Forests aged 200–250 years had the greatest richness-per-survey of those native species that were observed mostly in the lower layer or mid-layer. However, the greatest richness-per-survey of canopy-dwelling species and the highest native species-richness across the survey period were found in forests aged around 150 years. Younger regrowth was generally less rich in birds, although regrowth in the first decade after clearfelling was the only seral stage inhabited by superb fairy-wrens. These results suggest that, in the Tasmanian lowland wet eucalypt forest landscape, species-richness of birds may be greatest when old-growth forest is interspersed with young regrowth forests. Hence for bird conservation, a challenge is to ensure that old-growth forest continues to prevail in the production forest landscape.     

Short-term responses of soil decomposer and plant communities to stump harvesting in boreal forests

Recently, in addition to logging residues, stumps have become an important component in energy production since there is growing global interest in the use of renewable energy sources in order to decrease anthropogenic carbon emissions. Harvesting of stumps influences the forest floor by changing vegetation and soil organic layers and exposing mineral soil across large areas. We studied whether stump harvesting after clear felling poses further short-term changes in boreal forest soil decomposer community (microbes and mesofauna) and vegetation when compared to the traditional site preparation practice (mounding). In general, stump harvesting caused decline in enchytraeid abundance but did not induce further major changes in decomposer community otherwise nor in vegetation of each soil micro-habitat (intact soil and exposed mineral soil). However, the abundances of almost all decomposer animals were lower in the exposed mineral soil than in the intact soil. Stump removal increased the area of exposed mineral soil in the clear felled areas, leading to lower amount of high quality habitat for most decomposer organisms. Hence, it is obvious that there are (or will be) differences in the decomposer community dynamics between the treatments at the forest stand level. Both species richness and coverage of plants benefitted from large-scale exposure of mineral soil. Because the stump removal procedure disturbs soil organic layers and negatively affects the decomposer community, it has the potential to alter nutrient dynamics in forests.     

Response of woodpeckers to changes in forest health and harvest: Implications for conservation of avian biodiversity

Woodpeckers (family Picidae) merit specific monitoring and management efforts, both as keystone/facilitator species and as indicators of forest condition. Recent studies indicated that species richness of woodpeckers was correlated with richness of all forest birds, thus suggesting potential exists for management practices that can address needs of woodpeckers in particular and other forest birds in general. We used data from a long-term study (1995–2008) from forest sites in the interior of British Columbia to evaluate how abundances of seven woodpecker species varied with habitat variables previously identified as associated with forest bird richness. We found that tree species richness had either a neutral or positive effect on the abundance of all woodpecker species, whereas abundances of most woodpecker species tended to be lower in stands with high densities of lodgepole pine. Abundances of most woodpecker species were positively correlated with density of beetle-killed pines. Relative to control sites, higher densities of most woodpecker species were found at harvested sites where most trembling aspen and large Douglas-fir trees had been retained. Therefore, management strategies that favour a mixture of tree species, with particular attention to retention of aspen, should safeguard populations of most woodpecker species. Abundances of individual woodpecker species were weakly but positively inter-correlated before the beetle outbreak, and less so during and post-outbreak. It thus appears that no strong trade-offs exist among woodpecker species. These results, combined with previously identified positive correlations between woodpecker and forest bird richness, indicate woodpeckers can be managed as a suite for the purpose of managing avian biodiversity as a whole.     

Detecting forest stress and decline in response to increasing river flow in southwest Florida, USA

Forest stress and decline resulting from increased river levels were investigated in Myakka River State Park (MRSP), FL, USA. Since 1977, land-use changes around the upper Myakka River watershed have resulted in significant increases in water entering the river, which have caused extensive mortality in the upper watershed. The present study assessed whether similar forest stress and mortality was occurring downstream within the park. Our objectives were to (1) determine if tree die-off and/or stress resulting from increased river levels were present in MRSP and (2) determine the relationship between historical and present river levels regimes and growth of actively managed forested stands undergoing restoration located both above and below a dam. We used two methodological approaches. The first was recording indications of tree stress and decline (crown dieback, crown thinning, trunk rot, foliage discoloration, and parasitism) in Fraxinus caroliniana Miller dominated forested wetlands, Pinus elliottii Englem. var. densa Little & Dorman dominated mesic pine flatwoods, and Quercus laurifolia Michaux dominated oak palm hammocks. Our second approach was tree-ring analyses, which allows for more detailed analyses of growth in response to precipitation and river flow (a surrogate variable for water table depth) in the pine flatwoods stands.

Our results indicate significant stress and decline in some forested wetlands upstream of the dam, significant mortality in wet-mesic pine flatwoods sites close to the river, and significant amounts of stress in wet-mesic pine flatwoods sites upstream of the dam. F. caroliniana sites located upstream of the dam had more individuals with symptoms of stress than those downstream of the dam (67% versus 43%, P=0.031). In Q. laurifolia sites, 70–85% of the trees had evidence of flooding stress and mortality, which is comparable to distributions found in severely disturbed forest in the upper watershed. P. elliottii var. densa sites located <1000 m from the river had higher mortality than sites located >1050 m from the river (P<0.01), and the stressed trees in sites upstream of the dam had significantly lower growth rates in the 1990s versus the 1960s than those downstream. Although, the onset of stress and decline coincided with increasing river levels, we found that river levels were positively correlated with tree growth, both before and after flow increases in the system. Increasing river levels may play an indirect role through increased competition in the stress and decline in wet-mesic pine flatwoods, however, increased river levels seems to be the direct cause for stress and decline found in forested wetland stands.     

Use of LiDAR and supplemental data to estimate forest maturity in Charles County,MD, USA

This study evaluated the utility of remotely sensed data to estimate forest maturity within Charles County, MD. We calculated tree canopy height using airborne scanning LiDAR (light detection and ranging) data over the entire county, and compared this to crown top height, stand age, and other data collected from randomly selected plots on the ground. Canopy height was a strong predictor of forest age, and we improved predictive power by including other variables such as land cover, slope, stream proximity, wetlands, and floodplains. These comparisons allowed us to construct a spatial model classifying forest in the study area into three age categories: ≤30 years old, 30–70 years old, and >70 years old, corresponding to young, intermediate, and mature. This spatial model was used to help characterize ecosystem condition and wildlife habitat, and help prioritize conservation decisions in the study area.     

Bird communities following high-severity fire: Response to single and repeat fires in a mixed-evergreen forest,Oregon, USA

Fire is a widespread natural disturbance agent in most conifer-dominated forests. In light of climate change and the effects of fire exclusion, single and repeated high-severity (stand-replacement) fires have become prominent land management issues. We studied bird communities using point counting in the Klamath-Siskiyou ecoregion of Oregon, USA at various points in time after one or two high-severity fires. Time points included 2 and 3 years after a single fire, 17 and 18 years after a single fire, 2 and 3 years after a repeat fire (15 year interval between fires), and >100 years since stand-replacement fire (mature/old-growth forest). Avian species richness did not differ significantly among habitats. Bird density was highest 17 and 18 years after fire, lowest 2 years after fire, and intermediate in repeat burns and unburned forest. Bird community composition varied significantly with habitat type (A = 0.24, P < 0.0001) with two distinct gradients in species composition relating to tree structure (live to dead) and shrub stature. Using indicator species analysis, repeat burns were characterized by shrub-nesting and ground-foraging bird species while unburned mature forests were characterized by conifer-nesting and foliage-gleaning species. Bird density was not related to snag basal area but was positively related to shrub height. Contrary to expectations, repeated high-severity fire did not reduce species richness, and bird densities were greater in repeat burns than in once-burned habitats. Broad-leaved hardwoods and shrubs appear to play a major role in structuring avian communities in the Klamath-Siskiyou region. In light of these results, extended periods of early seral broadleaf dominance and short-interval high-severity fires may be important to the conservation of avian biodiversity.     

Influence of forest planning alternatives on landscape pattern and ecosystem processes in northern Wisconsin,USA

Incorporating an ecosystem management perspective into forest planning requires consideration of the impacts of timber management on a suite of landscape characteristics at broad spatial and long temporal scales. We used the LANDIS forest landscape simulation model to predict forest composition and landscape pattern under seven alternative forest management plans drafted for the Chequamegon-Nicolet National Forest in Wisconsin. We analyzed 20 response variables representing changes in landscape characteristics that relate to eight timber and wildlife management objectives. A MANOVA showed significant variation in the response variables among the alternative management plans. For most (16 out of 20) response variables, plans ranked either directly or inversely to the extent of even-aged management. The amount of hemlock on the landscape had a surprising positive relationship with even-aged management because hemlock is never cut, even in a clear cut. Our results also show that multiple management objectives can create conflicts related to the amount and arrangement of management activities. For example, American marten and ruffed grouse habitat are maintained by mutually exclusive activities. Our approach demonstrates a way to evaluate alternative management plans and assess if they are likely to meet their stated, multiple objectives.     

黑龙江省东部山区森林植物多样性与环境梯度的相关性研究

为了探讨森林植物多样性与环境梯度的相关关系,本研究在黑龙江省帽儿山国家森林公园调查了23块不同结构的森林群落,每个群落布设的样方面积为400m2。森林植物多样性的计算采用Shannon-Wiener多样性指数,环境梯度的量化采用Whittaker的集合环境梯度计算方法,同时,采用相似性测度方法计算了Beta多样性指数。结果表明:Shannon-Wiener多样性指数随环境梯度的增大而增大,并且β多样性指数与环境梯度呈线性增加的趋势。图2表3参12。     

Post-1935 changes in forest vegetation of Grand Canyon National Park, Arizona, USA: Part 2—Mixed conifer, spruce-fir, and quaking aspen forests

This study examined changes in never-harvested mixed conifer (MCF), spruce-fir (SFF), and quaking aspen forests (QAF) in Grand Canyon National Park (GCNP), Arizona, USA based on repeat sampling of two sets of vegetation study plots, one originally sampled in 1935 and the other in 1984. The 1935 plots are the earliest-known, sample-intensive, quantitative documentation of forest vegetation over a Southwest USA landscape. Findings documented that previously described increases in densities and basal areas attributed to fire exclusion were followed by decreases in 1935-2004 and 1984-2005. Decreases in MCF were attributable primarily to quaking aspen (Populus tremuloides) and white fir (Abies concolor), but there were differences between dry-mesic and moist-mesic MCF subtypes. Decreases in SFF were attributable to quaking aspen, spruce (Picea engelmannii + Picea pungens), and subalpine fir (Abies lasiocarpa). Decreases in QAF resulted from the loss of quaking aspen during succession. Changes in ponderosa pine forest (PPF) are described in a parallel paper (Vankat, J.L., 2011. Post-1935 changes in forest vegetation of Grand Canyon National Park, Arizona, USA: part 1 - ponderosa pine forest. Forest Ecology and Management 261, 309-325). Graphical synthesis of historical and modern MCF data sets for GCNP indicated tree densities and basal areas increased from the late 19th to the mid 20th century and then decreased to the 21st century. Changes began earlier, occurred more rapidly, and/or were larger at higher elevation. Plot data showed that basal area decreased earlier and/or more rapidly than density and that decreases from 1935 to 2004 resulted in convergence among MCF, SFF, and PPF. If GCNP coniferous forests are trending toward conditions present before fire exclusion, this implies density and basal area were more similar among these forests in the late 19th century than in 1935. Changes in MCF and SFF can be placed in a general framework of forest accretion, inflection, and recession in which increases in tree density and basal area are followed by an inflection point and decreases. Accretion was triggered by the exogenous factor of fire exclusion, and inflection and recession apparently were driven by the endogenous factor of density-dependent mortality combined with exogenous factors such as climate. Although the decreases in density and basal area could be unique to GCNP, it is likely that the historical study plots provided a unique opportunity to quantitatively determine forest trends since 1935. This documentation of post-1935 decreases in MCF and SFF densities and basal areas indicates a shift in perspective on Southwestern forests is needed.     

The role of disturbance severity and canopy closure on standing crop of understory plant species in ponderosa pine stands in northern Arizona,USA

Concerns about the long-term sustainability of overstocked dry conifer forests in western North America have provided impetus for treatments designed to enhance their productivity and native biodiversity. Dense forests are increasingly prone to large stand-replacing fires; yet, thinning and burning treatments, especially combined with other disturbances such as drought and grazing, may enhance populations of colonizing species, including a number of non-native species. Our study quantifies plant standing crop of major herbaceous species across contrasting stand structural types representing a range in disturbance severity in northern Arizona. The least disturbed unmanaged ponderosa pine stands had no non-native species, while non-native grasses constituted 7–11% of the understory plant standing crop in thinned and burned stands. Severely disturbed wildfire stands had a higher proportion of colonizing native species as well as non-native species than other structural types, and areas protected from grazing produced greater standing crop of native forbs compared to grazed unmanaged stands. Standing crop of understory plants in low basal area thinned and burned plots was similar to levels on wildfire plots, but was comprised of fewer non-native graminoids and native colonizing plants. Our results also indicate that size of canopy openings had a stronger influence on standing crop in low basal area plots, whereas tree density more strongly constrained understory plant standing crop in dense stands. These results imply that treatments resulting in clumped tree distribution and basal areas <10 m² ha⁻¹ will be more successful in restoring native understory plant biomass in dense stands. Multiple types and severity of disturbances, such as thinning, burning, grazing, and drought over short periods of time can create greater abundance of colonizing species. Spreading thinning and burning treatments over time may reduce the potential for non-native species colonization compared to immediately burning thinned stands.     

Importance of forest structure versus floristics to composition of avian assemblages in tropical deciduous forests of Central Highlands,India

We investigated how much forest structure and floristics independently contributed to the composition of avian assemblages at multiple scales and for individual foraging guilds in tropical deciduous forests of Central Highlands, India. We derived dissimilarity matrices between all pairs of the 36 sampling sites with respect to forest structure, floristics, and bird species composition and ran Mantel's randomization tests to detect significant associations among the matrices after partialling out the effect of geographic distance between sites. Bird species composition was found to be significantly related to forest structure across habitats, and floristics within the moist-deciduous forests. This finding is consistent with earlier observations that birds respond, in their species composition, to vegetation structure across habitats and to vegetation composition within a habitat. As predicted, the composition of insectivorous birds was influenced by forest structure, but the phytophagous guild did not show any relation to vegetation composition in contrast to patterns observed elsewhere. We explain this anomaly as a result of availability of a wide choice of food plants for phytophagous birds in central Indian tropical forests and weak species–environment relationships on account of their nomadism. Extraction of non-timber forest products remains a key economic activity in central India and our results imply that it can potentially influence the composition of forest bird communities through alteration of forest structure and floristics.     

Historical fire and vegetation dynamics in dry forests of the interior Pacific Northwest,USA, and relationships to Northern Spotted Owl (Strix occidentalis caurina) habitat conservation

Regional conservation planning frequently relies on general assumptions about historical disturbance regimes to inform decisions about landscape restoration, reserve allocations, and landscape management. Spatially explicit simulations of landscape dynamics provide quantitative estimates of landscape structure and allow for the testing of alternative scenarios. We used a landscape fire succession model to estimate the historical range of variability of vegetation and fire in a dry forest landscape (size ca. 7900 km²) where the present-day risk of high severity fire threatens the persistence of older closed canopy forest which may serve as Northern Spotted Owl (Strix occidentalis caurina) habitat. Our results indicated that historically, older forest may have comprised the largest percentage of the landscape (∼35%), followed by early successional forest (∼25%), with about 9% of the landscape in a closed canopy older forest condition. The amount and condition of older forest varied by potential vegetation type and land use allocation type. Vegetation successional stages had fine-grained spatial heterogeneity in patch characteristics, with older forest tending to have the largest patch sizes among the successional stages. Increasing fire severities posed a greater risk to Northern Spotted Owl habitat than increasing fire sizes or frequencies under historical fire regimes. Improved understanding of historical landscape-specific fire and vegetation conditions and their variability can assist forest managers to promote landscape resilience and increases of older forest, in dry forests with restricted amounts of habitat for sensitive species.     

The relation of harvesting intensity to changes in soil, soil water, and stream chemistry in a northern hardwood forest, Catskill Mountains, USA

Previous studies have shown that clearcutting of northern hardwood forests mobilizes base cations, inorganic monomeric aluminum (Al_im), and nitrate (NO₃⁻-N) from soils to surface waters, but the effects of partial harvests on NO₃⁻-N have been less frequently studied. In this study we describe the effects of a series of partial harvests of varying proportions of basal area removal (22%, 28% and 68%) on Al_im, calcium (Ca²⁺), and NO₃⁻-N concentrations in soil extracts, soil water, and surface water in the Catskill Mountains of New York, USA. Increases in NO₃⁻-N concentrations relative to pre-harvest values were observed within a few months after harvest in soils, soil water, and stream water for all three harvests. Increases in Al_im and Ca²⁺ concentrations were also evident in soil water and stream water over the same time period for all three harvests. The increases in Al_im, Ca²⁺, and NO₃⁻-N concentrations in the 68% harvest were statistically significant as measured by comparing the 18-month pre-harvest period with the 18-month post-harvest period, with fewer significant responses in the two harvests of lowest intensity. All three solutes returned to pre-harvest concentrations in soil water and stream water in the two lowest intensity harvests in 2-3 years compared to a full 3 years in the 68% harvest. When the results of this study were combined with those of a previous nearby clearcut and 40% harvest, the post-harvest increases in NO₃⁻-N concentrations in stream water and soil water suggest a harvesting level above which the relation between concentration and harvest intensity changes; there was a greater change in concentration per unit change in harvest intensity when basal area removal was greater than 40%. These results indicate that the deleterious effects on aquatic ecosystems previously demonstrated for intensive harvests in northern hardwood forests of northeastern North America that receive high levels of atmospheric N deposition can be greatly diminished as harvesting intensity decreases below 40-68%. These results await confirmation through additional incremental forest harvest studies at other locations throughout the world that receive high levels of atmospheric N deposition.     

Numerical response of birds to an irruption of elm spanworm (Ennomos subsignarius [Hbn.]; Geometridae: Lepidoptera) in old-growth forest of the Appalachian Plateau, USA

Populations of forest birds were studied during two years of an outbreak of the elm spanworm Ennomus subsignarius (Hbn.) in a silviculturally unmanaged, old-growth conifer–northern hardwood forest on the Appalachian Plateau, PA. Canopy defoliation of hardwoods (mostly American beech Fagus grandifolia and red maple Acer rubrum) increased by at least 50% during the local peak of the outbreak (1993); territorial densities of birds were the highest (15% greater) during the regional peak of the outbreak (1994). Compared to a nearby but uninfested forest of similar age and composition, total bird abundance was as much as 22–33% higher at sites with extensive spanworm defoliation. In addition to canopy gleaners, several other foraging guilds exhibited one or more significant numerical responses to outbreak location or intensity, including bark foraging, understory gleaning, ground foraging, and pursuing species. Like other irruptions of forest Lepidoptera, populations of arboreal canopy-gleaning Parulinae (the warblers D. magnolia, D. fusca) were especially prone to fluctuate during this geometrid irruption.