Red Spruce Stand Dynamics, Simulations, and Restoration Opportunities in the Central Appalachians

Red spruce (Picea rubens)–dominated forests occupied as much as 600,000 ha in West Virginia prior to exploitive logging era of the late nineteenth and early twentieth centuries. Subsequently, much of this forest type was converted to northern hardwoods. As an important habitat type for a number of rare or sensitive species, only about 12,000 ha of red spruce forests presently remain in the state. In order to assess the prospects for restoration, we examined six northern hardwood stands containing understory red spruce to (1) characterize stand dynamics and regeneration patterns and (2) simulate the effectiveness of restoration silviculture to enhance red spruce overstory recruitment. Stands originated in the late 1800s to early 1900s and are currently in the (late) stem exclusion or understory reinitiation stages. Five of the six stands had even‐aged overstories that originated after clear‐cutting. Tree‐ring chronologies show high initial growth rates consistent with stand initiation. One stand, partially harvested in 1915, was uneven aged with older, legacy residuals in the canopy. Most stands had two cohorts of understory red spruce, with more than 40% of these individuals showing prior release. Our 100‐year growth simulation suggested that a 50% basal area thinning from above could double red spruce basal area to support a mixed spruce–hardwood stand in approximately 20–40 years. These results indicate that restoration silviculture could be an effective tool for increasing the amount and quality of this reduced forest type in the central Appalachians.     

Conservation value of timber quality versus associated non-timber quality stands for understory diversity in Nothofagus forests

Conservation strategies of forested landscapes must consider biodiversity of the included site types, i.e. timber-quality forests and associated non-timber-quality stands. The objectives were to characterize forest overstory structure in timber-quality versus associated non-timber-quality stands; and to compare their understory communities. Six forest types were sampled in Nothofagus forests of Tierra del Fuego (Argentina): two timber-quality N. pumilio forests, and four associated non-timber-quality stands (edge, N. antarctica, wetlands and streamside forests). Overstory structure and understory vegetation (species richness, frequencies, cover and biomass) were characterized during spring and summer seasons. Analysis of variance and multivariates were carried out. Overstory structure differed across the site types, with higher tree size, canopy closure and tree volume in timber-quality stands. Fifty-one understory plant species were observed, but understory variables varied with site types, especially wetlands (highest native and exotic richness, cover and biomass, and 25% of exclusive species). Site types were grouped in three: N. antarctica stands, streamside stands and the other N. pumilio forests according to multivariate analysis. Forty three percent of plants were distributed in all site types, and all timber-quality forest understory species were present in some associated non-timber-quality stands. Timber-quality N. pumilio forests have a marginal value for understory conservation compared to associated non-timber-quality stands, because these last include all the plants observed in timber-quality forests and also possess many exclusive species. Therefore, protection of associated non-timber-quality stands during forest management planning could increase understory conservation at landscape level, and these could be better reserves of understory diversity than retentions of timber-quality stands.     

Woodland restoration and forest structure affect nightjar abundance in the Ozark Highlands

Chuck-will's-widow (Antrostomus carolinensis) and eastern whip-poor-will (Antrostomus vociferus) are nightjars in eastern North America that have declined 69% and 67%, respectively, in abundance since 1966, resulting in conservation concerns for these species. We investigated relationships between nightjar abundance and landscape composition, forest structure, and application of tree thinning and prescribed fire because of regional interest in woodland restoration and nightjar conservation. We conducted nocturnal nightjar surveys at 385 points in southern Missouri, USA, in 2014 and 2015 and related counts to pine (Pinus spp.) and hardwood basal area, canopy closure, percent forest cover, and percent of area thinned or burned within 500 m of survey points. We modeled abundance of chuck-will's-widow and eastern whip-poor-will using time-removal models that included a detection process and an abundance process within a hierarchical Bayesian framework. We detected 534 eastern whip-poor-will and 186 chuck-will's-widow during surveys. Our data supported global models that included all 6 vegetation and management variables for both species. Chuck-will's-widow abundance was negatively related to hardwood basal area and peaked at intermediate values of percent area burned and percent forest cover. Eastern whip-poor-will abundance was negatively related to hardwood basal area and canopy cover, positively related to percent forest cover and percent of area burned, and peaked at low to moderate levels of percent of area thinned. Relationships to forest structure and management activities generally supported the conclusion that woodland restoration benefits nightjars and that chuck-will's-widow select landscapes with less forest cover than eastern whip-poor-will.     

Convergence in Arthropod Assemblages with Various Restoration Approaches for Canadian Deciduous Forests

Silvicultural practices are traditionally aimed at increasing forest profits; however, recent approaches to forest conservation have broadened to include nature-based silviculture for regenerating forests. In southern Ontario (Canada), originally dominated by deciduous forests, conifer plantations were established on abandoned agricultural sites. Currently, there is an increasing interest to convert these conifer stands to a state that mimics the original deciduous forest. We investigated arthropod abundance, species richness of carabid beetles, and abundance of arthropod assemblages (trophic and prey groups) under five silvicultural treatments conducted to regenerate deciduous forests (the natural forest type) from the old conifer plantations. The treatments included: (1) uniform canopy removal; (2) uniform canopy removal and understory removal; (3) group canopy removal; (4) group canopy removal and understory removal; and (5) untreated control plots (relatively pure red pine). Insects were sampled annually using sweepnets and pitfall traps. Results revealed treatment effects on the abundance of Coleoptera, Heteroptera, herbivores, and small arthropods (<3 mm) caught in sweepnet samples, where plots subjected to group shelterwood removal and understory removal supported higher abundances than the control plots. There was no treatment effect on the abundance of other arthropod groups or on the species richness and abundance of carabid beetles. The silvicultural treatments used to encourage natural regeneration did not seem to affect arthropod food availability for insectivorous vertebrates. Thus, the type of silvicultural strategy used to convert pine plantations to a stage that mimics the natural deciduous forests had little overall impact on arthropods.     

Cultivation of Non‐timber Forest Products Alters Understory Light Availability in a Humid Tropical Forest in Mexico1

The planting of non‐timber forest products (NTFPs) in the understory of tropical forests is promoted in many regions as a strategy to conserve forested lands and meet the economic needs of rural communities. While the forest canopy is left intact in most understory plantations, much of the midstory and understory vegetation is removed in order to increase light availability for cultivated species. We assessed the extent to which the removal of vegetation in understory plantations of Chamaedorea hooperiana Hodel (Arecaceae) alters understory light conditions. We also examined how any changes in light availability may be reflected by changes in the composition of canopy tree seedlings regenerating in understory plantations. We employed a blocked design consisting of four C. hooperiana plantation sites; each site was paired with an adjacent, unmanaged forest site. Hemispherical canopy photographs were taken and canopy tree seedlings were identified and measured within 12 3 × 2 m randomly placed plots in each site for a total of 96 plots (4 blocks × 2 sites × 12 plots). Plantation management did not affect canopy openness or direct light availability but understory plantations had a higher frequency of plots with greater total and diffuse light availability than unmanaged forest. Comparisons of canopy tree seedling composition between understory plantations and unmanaged forest sites were less conclusive but suggest that management practices have the potential to increase the proportion of shade‐intolerant species of tree seedlings establishing in plantations. Given the importance of advanced regeneration in gap‐phase forest dynamics, these changes may have implications for future patterns of succession in the areas of forest where NTFPs are cultivated.     

Overstory Community Composition and Elevated Atmospheric CO2 and O3 Modify Understory Biomass Production and Nitrogen Acquisition

Elevated atmospheric CO₂ and O₃ have the potential to affect the primary productivity of the forest overstory, but little attention has been given to potential responses of understory vegetation. Our objective was to document the effects of elevated atmospheric CO₂ and O₃ on understory species composition and biomass and to quantify nitrogen (N) acquisition by the understory vegetation. The research took place at the aspen free-air CO₂ and O₃ enrichment (FACE) experiment, which has four treatments (control, elevated CO₂, elevated O₃, and elevated CO₂+O₃) and three tree communities: aspen, aspen/birch, and aspen/maple. In June 2003, each FACE ring was uniformly labeled with 15N applied as NH₄Cl. Understory biomass was harvested in June of 2004 for productivity, N, and 15N measurements, and photosynthetically active radiation (PAR) was measured below the canopy. The understory was divided into five species groups, which dominate in this young aggrading forest: Taraxacum officinale (dandelion), Solidago sp. (goldenrod), Trifolium repens and T. pretense (clover), various species from the Poaceae family (grass), and composited minor components (CMC). Understory species composition, total and individual species biomass, N content, and 15N recovery showed overstory community effects, but the direct effects of treatments was masked by the high variability of these data. Total understory biomass increased with increasing light, and thus was greatest under the open canopy of the aspen/maple community, as well as the more open canopy of the elevated O₃ treatments. Species were different from one another in terms of 15N recovery, with virtually no 15N recovered in clover and the greatest amount recovered in dandelion. Thus, understory species composition and biomass appear to be driven by the structure of the overstory community, which is determined by the tree species present and their response to the treatments. However, N acquisition by the understory does not appear to be affected by either the overstory community or the treatments at this point.     

How Does Restoration of Native Canopy Affect Understory Vegetation Composition? Evidence from Riparian Communities of the Hunter Valley Australia

Restoration of native vegetation often focuses on the canopy layer species, with the assumption that regeneration of the understory elements will occur as a consequence. The goal of this study was to assess the influence of canopy restoration on the composition and abundance of understory plant species assemblages along riparian margins in the Hunter Valley, NSW, Australia. We compared the floristic composition (richness, abundance, and diversity) of understory species between nonrevegetated (open) and canopy revegetated plots across five sites. A number of other factors that may also influence understory vegetation, including soil nutrients, proximity to main channel, and light availability, were also measured. We found that sites where the canopy had been restored had lower exotic species richness and abundance, as well as higher native species cover, but not native species richness, compared with open sites. Multivariate analysis of plots based on plant community composition showed that revegetated sites were associated with lower total species diversity, light availability, and exotic cover. This study has found that the restoration of the canopy layer does result in lower exotic species richness and cover, and higher native species cover and diversity in the understory, a desirable restoration outcome. Our results provide evidence that restoration of native canopy species may facilitate restoration of native understory species; however, other interventions to increase native species richness of the understory should also be considered as part of management practice.     

An Analysis of Vegetation Restoration on Opencast Oil Shale Mines in Estonia

We compared four types of 30‐year‐old forest stands growing on spoil of opencast oil shale mines in Estonia. The stand types were: (1) natural stands formed by spontaneous succession, and plantations of (2) Pinus sylvestris (Scots pine), (3) Betula pendula (silver birch), and (4) Alnus glutinosa (European black alder). In all stands we measured properties of the tree layer (species richness, stand density, and volume of growing stock), understory (density and species richness of shrubs and tree saplings), and ground vegetation (aboveground biomass, species richness, and species diversity). The tree layer was most diverse though sparse in the natural stands. Understory species richness per 100‐m² plot was highest in the natural stand, but total stand richness was equal in the natural and alder stands, which were higher than the birch and pine stands. The understory sapling density was lower than 50 saplings/100 m² in the plantations, while it varied between 50 and 180 saplings/100 m² in the natural stands. Growing stock volume was the least in natural stands and greatest in birch stands. The aboveground biomass of ground vegetation was highest in alder stands and lowest in the pine stands. We can conclude that spontaneous succession promotes establishment of diverse vegetation. In plantations the establishment of diverse ground vegetation depends on planted tree species.     

Gap-scale disturbance processes in secondary hardwood stands on the Cumberland Plateau,Tennessee, USA

Disturbance regimes in many temperate, old growth forests are characterized by gap-scale events. However, prior to a complex stage of development, canopy gaps may still serve as mechanisms for canopy tree replacement and stand structural changes associated with older forests. We investigated 40 canopy gaps in secondary hardwood stands on the Cumberland Plateau in Tennessee to analyze gap-scale disturbance processes in developing forests. Gap origin, age, land fraction, size, shape, orientation, and gap maker characteristics were documented to investigate gap formation mechanisms and physical gap attributes. We also quantified density and diversity within gaps, gap closure, and gap-phase replacement to examine the influence of localized disturbances on forest development. The majority of canopy gaps were single-treefall events caused by uprooted or snapped stems. The fraction of the forest in canopy gaps was within the range reported from old growth remnants throughout the region. However, gap size was smaller in the developing stands, indicating that secondary forests contain a higher density of smaller gaps. The majority of canopy gaps were projected to close by lateral crown expansion rather than height growth of subcanopy individuals. However, canopy gaps still provided a means for understory trees to recruit to larger size classes. This process may allow overtopped trees to reach intermediate positions, and eventually the canopy, after future disturbance events. Over half of the trees located in true gaps with intermediate crown classifications were Acer saccharum, A. rubrum, or Liriodendron tulipifera. Because the gaps were relatively small and close by lateral branch growth of perimeter trees, the most shade-tolerant A. saccharum has the greatest probability of becoming dominant in the canopy under the current disturbance regime. Half of the gap maker trees removed from the canopy were Quercus; however, Acer species are the most probable replacement trees. These data indicate that canopy gaps are important drivers of forest change prior to a complex stage of development. Even in relatively young forests, gaps provide the mechanisms for stands to develop a complex structure, and may be used to explain patterns of shifting species composition in secondary forests of eastern North America.     

Effects of selective logging on the arboreal ants of a Bornean rainforest

We examined the effect of selective logging and corresponding forest canopy loss on arboreal ant diversity in a tropical rainforest. Arboreal ants were collected from an unlogged forest plot and from forest plots selectively logged 14 years and 24 years earlier in Danum Valley, Sabah, Malaysia, using a canopy fogging method. Selective logging was associated with a significant decrease in canopy cover and an increase in understory vegetation density relative to unlogged forest. Our study showed that selective logging in primary forest might not dramatically decrease total species number and overall abundance of arboreal ants; however, it may influence the species composition and dominance structure of the ant community, accompanied by an increase in abundance of shrub‐layer species and trophobiotic species. In view of the results of this study, management techniques that minimize logging impact on understory vegetation structure are likely to help maintain the conservation value of logged forests for arboreal ants. Our results also suggest that accurate assessment of the impacts on biodiversity should not be based only on measurement of species number and overall abundance, but also on analysis of species composition and community structure.     

伏牛山自然保护区森林冠层结构对林下植被特征的影响

在伏牛山自然保护区典型地段设立样方,测定了森林生态系统内几种典型群落类型的冠层结构、光环境特征,调查了林下植被的特征,分析了它们之间的相互关系.结果显示:各群落的冠层结构和光环境有一定的差异,单因素方差分析表明,部分群落间的差异性达到显著水平;各群落灌木层物种丰富度、多样性和均匀度均高于草本层,而优势度正相反;线性拟合的结果表明,草本层的物种丰富度、多样性与冠下光合量子通量密度间呈极显著负相关,优势度与冠下光合量子通量密度间呈显著正相关,灌木层各参数与冠层结构特征间相关性不显著.研究表明,冠层结构的变化对草本层(包括更新幼苗)的影响显著高于灌木层.林隙/林窗或林中空地的出现可能对草本物种或其他阳性及先锋物种具有促进作用,而对优势种幼苗的萌发和定植产生负效应.推测在典型的落叶阔叶林生态系统演替进程中,林下光照强度可能不是最主要的限制因素,优势种种子的扩散、萌发和定植限制可能更重要.     

Linking vegetation structure and bird organization: response of mixed-species bird flocks to forest succession in subtropical China

As forests undergo natural succession following artificial afforestation, their bird assemblages also change. However, interspecific avian social organization associated with forest succession has not been fully understood, particularly for mixed-species bird flocks. To disentangle how mixed-species flocks change as a function of local forest structure, we analyzed flock characteristics (particularly species richness, flocking frequency and propensity) and vegetation physiognomies along a presumed successional series (early, middle, and advanced) simultaneously in subtropical forests in southern China. As hypothesized, monthly point counts demonstrated that complexity of flocks increases with the progression of natural forest succession at a local scale. Advanced forests differed significantly from pioneering plantations with respect to vegetation structure, flock characteristics and constituents (especially for understory specialists). Importantly, forest succession affected flock patterns particularly in relation to the flocking propensity of regular species, and the frequency of nuclear species (Huet’s fulvetta Alcippe hueti), which in turn determined flocking occurrence at different successional stands. Canonical correspondence analysis indicated that understory flocking species (mainly Timaliidae babblers) were significantly associated with intact native canopy cover, complex DBH diversity, as well as high densities of dead trees and large trees, representing a maturity level of successional stands. Our study reveals that the effect of natural forest succession on mixed-species bird flocks is species-specific and guild-dependent. From a conservation perspective, despite a high proliferation of pine plantation in southern China, priority should be placed on protecting the advanced forest with a rich collection of understory flocking specialists.     

Understory vegetation indicates historic fire regimes in ponderosa pine‐dominated ecosystems in the Colorado Front Range

Question: Can current understory vegetation composition across an elevation gradient of Pinus ponderosa‐dominated forests be used to identify areas that, prior to 20th century fire suppression, were characterized by different fire frequencies and severities (i.e., historic fire regimes)? Location: P. ponderosa‐dominated forests in the montane zone of the northern Colorado Front Range, Boulder and Larimer Counties, Colorado, USA. Methods: Understory species composition and stand characteristics were sampled at 43 sites with previously determined fire histories. Indicator species analyses and indirect ordination were used to determine: (1) if stands within a particular historic fire regime had similar understory compositions, and (2) if understory vegetation was associated with the same environmental gradients that influence fire regime. Classification and regression tree analysis was used to ascertain which species could predict fire regimes. Results: Indicator species analysis identified 34 understory species as significant indicators of three distinct historic fire regimes along an elevation gradient from low‐ to high‐elevation P. ponderosa forests. A predictive model derived from a classification tree identified five species as reliable predictors of fire regime. Conclusions: P. ponderosa‐dominated forests shaped by three distinct historic fire regimes have significantly different floristic composition, and current understory compositions can be used as reliable indicators of historical differences in past fire frequency and severity. The feasibility demonstrated in the current study using current understory vegetation properties to detect different historic fire regimes, should be examined in other fire‐prone forest ecosystems.     

Forest plant community as a driver of soil biodiversity: experimental evidence from collembolan assemblages through large‐scale and long‐term removal of oak canopy trees Quercus petraea

Plant–soil interactions are increasingly recognized to play a major role in terrestrial ecosystems functioning. However, few studies to date have focused on slow dynamic ecosystems such as forests. As they are vertically stratified by multiple vegetation strata, canopy tree removal by thinning operations could alter forest plant community through tree canopy opening. Very little is known about cascading effects on soil biodiversity. We conducted a large‐scale, multi‐site assessment of collembolan assemblage response to long‐term canopy tree removal in sessile oak Quercus petraea temperate forests. A total of 33 experimental plots were studied covering a large gradient of canopy tree basal area, stand age and local abiotic contexts. Collembolan abundance strongly declined with canopy tree removal in early forest successional stage and this was mediated by negative effect of understory plant community composition changes, i.e. shift from moss and forb to tree seedling, fern, shrub and grass species. Negative effect of this composition shift on collembolan species richness was largely offset by positive effect of the increase in understory plant species richness. This gives support to both the plant mass‐ratio and functional diversity hypotheses. Collembolan functional groups had contrasting response patterns, which were mediated by different ecological factors. Epedaphic (r‐strategist) abundance and species richness increased with canopy tree removal in relation with the increase in understory plant species richness. In contrast, euedaphic (K‐strategist) abundance and species richness declined with canopy tree removal in early forest successional stage in relation with changes in understory plant community composition and species richness, as well as microclimatic conditions. Overall, our study provides experimental evidence that forest plant community can be a strong driver of collembolan assemblages. It also emphasizes the role of trees as foundation species of forest ecosystems that can shape soil biodiversity through their regulation of understory plant community and ecosystem abiotic conditions.     

Disparate distribution patterns between canopy and subcanopy life-forms in two temperate North American forests

Quantitative vegetational data of canopy and woody subcanopy species (two life-forms adapted to occupy different strata at maturity) were compared with data collected in two temperate forest ecosystems to determine whether they exhibit a similar pattern of distribution. Tidal freshwater swamps (21 stands) and southern Appalachian forests (19 stands) were examined from data obtained using identical sampling methods. Separate structural analyses of the canopy, sapling, and subcanopy species were compared using the indirect ordination algorithm Detrended Correspondence Analysis. Environmental measurements collected in each stand were assessed for their relationship to the distribution of stands depicted by the ordination diagrams.Canopy trees and saplings showed a similar pattern of distribution, suggesting that the resource requirements of saplings and canopy-statured adults are similar. In contrast, the subcanopy species (species genetically adapted to an understory existence, i.e., shrubs and small understory trees) of neither ecosystem showed any discernable distributional relationship to the canopy or sapling layers (in tidal swamps, there was no clear way to even segregate subcanopy stands into communities). Environmental gradients associated with the subcanopy ordinations differed from those of the canopy and sapling strata in both forest systems, suggesting that subcanopy species partition different resources than do canopy species.If a lack of similarity in distribution patterns between canopy and subcanopy species is universal in temperate forests, then the common practice of combining sapling and subcanopy species in structural analyses may hinder our understanding of subcanopy structural patterns in forests.     

Influence of forest structure on density and nest success of mature forest birds in managed landscapes

Managing for forest wildlife requires attention not only to quantity but quality of forests within the landscape. We examined the extent to which local structural attributes and landscape context of forest stands explained variation in density and reproductive success of mature forest birds across 12 sites in southeast Ohio, USA, 2004–2006. Results suggest that several structural characteristics influenced bird–habitat relationships in our study. Densities of 3 songbird species (i.e., ovenbird [Seiurus aurocapilla], cerulean warbler [Setophaga cerulea], and scarlet tanager [Piranga olivacea]) were positively related to canopy openness, which is usually a function of canopy gaps. Habitat attributes described by ground litter, understory density, and canopy height were positively associated with densities of ground (i.e., worm-eating warbler [Helmitheros vermivorum]), or shrub nesting species (i.e., Kentucky and hooded warblers [Geothlypis formosa and Setophaga citrina], respectively). Furthermore, the number of small trees likely drove the positive relationship between density of wood thrush (Hylocichla mustelina), a subcanopy nester. After accounting for temporal variability in daily nest survival rates, the odds of nest survival for all species increased 10.5% for every 1% increase in canopy openness and decreased 1.4% for each 5% increase in understory vegetation density. Habitat–nest survival relationships were not apparent at the level of the individual species. Our results suggest that structural attributes produced by increasing habitat heterogeneity may be necessary for conservation of forest bird communities. © 2012 The Wildlife Society.     

Vegetation effects on microclimate in lowland tropical forest in Costa Rica

The temperature and atmospheric humidity in a tropical lowland rain forest in Costa Rica were measured in order to assess the microclimate in different forest environments. Two disturbed sites, a single tree fall gap (400 m²) and an 0.5 hectare clearing, were compared for periods up to two years after disturbance. Two locations in primary forest, the canopy and understory, were also monitored. Temperatures were highest in the clearing, intermediate in the canopy and gap which were similar, and lowest in the understory. Vapor pressure deficits (VPD) were highest in the clearing, followed by the canopy, the gap and the understory. With regrowth of the vegetation in the gap and clearing sites, the temperatures and vapor pressure deficits significantly decreased. After 1 year, the microclimate at seedling height in the clearing resembled that of the gap, and after two years the microclimate of the gap was very similar to that of the understory. Seasonal differences in temperature and VPD were small compared to differences caused by changes in the stature of the vegetation.     

Succession of bird communities in young temperate rainforests following thinning

We repeated bird and vegetation surveys in 1991–1992 and 2005–2006 among young managed stands and old-growth forests in southeast Alaska to evaluate whether pre-commercial thinning of managed stands influenced the bird community. We compared decadal changes in bird densities and forest vegetation among 3 stand types: managed stands originating from clearcuts 35 years ago that were left untreated (unthinned), managed stands thinned at uniform spacing (thinned), and old growth with no prior timber harvest. We did not detect differences in decadal trends in avian densities between thinned and unthinned stands for 15 of 16 common bird species using a repeated-measures design. Thinning did not result in greater recruitment of overstory-nesting species as predicted. This was likely because of 1) similar increases in tree heights ( = 9–10 m) and canopy cover ( = 29–43%) between unthinned and thinned stands across decades and 2) the relatively young successional stage of these stands, which had only begun to recruit medium and large size conifers (dbh ≥ 36 cm). Decadal trends in densities of most (88%) understory-nesting bird species did not differ between thinned and unthinned stands. Shrub cover decreased by 22% and 31% across decades in thinned and unthinned stands, respectively. Bird community composition in managed stands reflected the general decadal changes in forest vegetation with a shift in dominance from understory species in the early 1990s (80–85% of total bird density) to an equal abundance of understory (45–54%) and overstory species in the mid-2000s. The latter was more similar to old-growth stands, which were dominated by overstory species (67–71%). Overstory-nesting birds in old growth increased in density by 49% across decades. Densities of cavity-nesting species remained unchanged in managed stands and less than densities in old growth across decades, possibly because of a lack of large trees and snags for nest sites. Overall, thinning of clearcut stands, the primary silvicultural system in the region, had few measurable benefits to birds nearly 20 years after treatment. Monitoring over the 70–100-year harvest rotation may be necessary to fully test whether thinning accelerates succession of bird communities in clearcut stands. However, partial harvests that retain large trees and snags should also be explored as alternatives to better maintain late-succession avifauna throughout the harvest rotation in southeast Alaska. © 2012 The Wildlife Society.     

Understorey vegetation in boreal Picea mariana and Populus tremuloides stands in British Columbia

Abstract. We compared the species composition and species density of vascular plants in the understorey vegetation of boreal forest between Picea mariana (Black spruce) and Populus tremuloides (Trembling aspen) stands in British Columbia, Canada, and related differences in species composition and species density between the two forest types to dominant canopy tree species as well as a wide variety of environmental factors. We analysed 231 stands, distributed in three different climatic regions representing drier, wetter, and milder variations of montane boreal climate. Of these stands 118 were dominated by P. mariana and 113 by P. tremuloides. P. tremuloides stands had higher species density than P. mariana stands in all climatic regions, but species density of each dominance type varied among climatic regions. The floristic composition of the understorey vegetation was markedly different for P. mariana and P. tremuloides dominated stands. A detailed study on the effect of canopy dominance and local environmental factors on the understorey vegetation of the boreal forest was conducted using 88 stands from one of the three climatic regions. Using a combination of ordination and variation partitioning by constrained ordination we demonstrated a small but unique effect of canopy dominance type on the understorey vegetation, while a larger amount of compositional variation was shared with other factors. Our results accord with a scenario in which differences in primary environmental factors and humus form properties, the latter accentuated by the canopy dominants themselves, are the most important causes of higher species density in P. tremuloides stands than in P. mariana stands, as well as differences in species composition among the two canopy dominance types. Processes and time scales involved in the small but significant direct and indirect effects of the canopy dominant on understo‐ rey species composition are discussed.     

Understory vegetation in reclaimed and unreclaimed post-mining forest stands

In the Sokolov coal mining district of the Czech Republic, spoil heaps are reclaimed by forest plantations, which are planted directly into the rough substrate (alkaline tertiary clay). We compared the understory that spontaneously developed in seven types of forest stands: one type was unreclaimed stands (spontaneously overgrown by Betula pendula and Salix caprea) and six were plantations, each dominated by one tree genus (Alnus, Larix, Picea, Pinus, Quercus, and Tilia). The age of the stands ranged from 22 to 33 years. The cover of understory plant species in each stand was estimated, and 16 other environmental and community variables were quantified. The number of plant species was highest in Quercus, Larix, and unreclaimed stands, and was negatively correlated with forest canopy cover and with the cover of the understory dominant, the grass Calamagrostis epigejos. Understory composition differed considerably among the types of forest stands and was significantly explained by the measured environmental variables. Forward selection in redundancy analysis indicated that the most important variable driving understory composition was thickness of the fermentation layer, which is clearly connected with soil development. Environmental variables, including fermentation layer, were also affected by the type of forest stand. Therefore, all of the explained variability in understory composition could be attributed to the type of forest stand, which apparently affected the understory by its impact on soil formation. However, the most favorable soil conditions were not favorable for understory development, as they supported mainly C. epigejos, which suppressed other species. Our study also showed that even in the absence of reclamation measures, mining sites can be successfully restored due to spontaneous succession.