Long-term effects of single prescribed fires on hardwood regeneration in oak shelterwood stands

One of the arguments against using prescribed fire to regenerate oak (Quercus spp.) forests is that the improvement in species composition of the hardwood regeneration pool is temporary and multiple burns are necessary to achieve and maintain oak dominance. To explore this concern, I re-inventoried a prescribed fire study conducted in the mid-1990s to determine the longevity of the effects of a single prescribed fire on hardwood regeneration. The initial study was conducted in three oak shelterwood stands in central Virginia, USA. In 1994, each stand was divided into four treatments (spring, summer, and winter burns and a control) and the hardwood regeneration was inventoried before the fires. During the burns, fire intensity was measured and categorized in each regeneration sampling plot. Second-year postfire data showed marked differences in species mortality rates, depending on season-of-burn and fire intensity: oak and hickory (Carya spp.) regeneration dominated areas burned by medium- to high-intensity fire during the spring and summer while yellow-poplar (Liriodendron tulipifera) and red maple (Acer rubrum) seedlings dominated unburned areas and all areas treated with low-intensity fire regardless of season-of-burn. The treatments were re-inventoried in 2006 and 2007 to determine whether these fire effects were still present. The new data show that the species distributions by season-of-burn and fire intensity found in 1996 still existed 11 years after the treatments. The fact that fire effects in oak shelterwood stands can last at least a decade has important management implications for resource professionals interested in sustaining oak forests in the eastern United States.     

Landscape hierarchies influence riparian ground-flora communities in Wisconsin, USA

We examined the distribution of ground-flora species (herbaceous and woody species <1 m tall) across riparian areas of northeastern Wisconsin in an effort to understand how hierarchical landscape properties, such as the physiographic system (ground moraine and outwash plain), valley system (constrained and unconstrained), and valley floor landforms influence distribution patterns of ground-flora species and functional plant guilds across riparian areas of small streams and rivers in a glacial landscape. A total of 162 species were recorded on 417 (1 m²) plots stratified by four different valley types that reflect the dominant physiographic system and valley system (constrained ground moraine, constrained outwash plain, unconstrained ground moraine, unconstrained outwash plain) and transverse geomorphic structure (valley floor landforms including floodplains, terraces, slopes, and adjacent uplands). Although distribution patterns of individual ground-flora species are highly variable among the four valley types, canonical correspondence analyses (CCA) of individual valley types indicate that ground-flora vegetation is related strongly to hierarchical landscape properties, including valley type and the transverse geomorphic structure of the stream valley. Vegetation ultimately reflects the influence of hydrogeomorphic processes that shape valley floor landforms. Constrained valley types tend to be characterized by diverse floodplain ground-flora communities dominated by graminoids and pteridophytes, while the terraces and slope plant communities are comprised of facultative upland and obligate upland perennial forb and woody species whose distribution appears to be a function of topographic features, such as aspect. However, ground-flora communities of unconstrained valley types appear to be responding not only to changes associated with the transverse geomorphic structure of the riparian ecotone, but also to more localized changes in environmental conditions associated with flooding and hydrologic regime. As a result, floodplain, terrace, and slope ground-flora communities tend to be diverse, dominated by a mixture of obligate wetland, facultative wetland, and facultative species. Thus, variation in riparian plant community characteristics can be explained using a nested, hierarchical landscape framework to organize and group different riparian settings based on the underlying geomorphic processes shaping stream valleys. Based on these results, we suggest that riparian management zones (RMZs) designed to maintain riparian function should be variable in width rather than fixed, encompassing variation in valley floor landforms and valley walls, regardless of the physiographic system.     

Fire-driven oak regeneration in French Mediterranean ecosystems

Regeneration by seeds for cork oak (Quercus suber) and companion oaks (holm oak Quercus ilex and downy oak Quercus pubescens) is likely to be poor in the fire-prone Maures massif (southern France) but the causes are poorly known. Our objective was to assess the effective recruitment for these three oak species and their temporal pattern of recruitment, in order to determine the main limitation factors and the regeneration window of each species. We studied oak recruits (height <3 m) in naturally regenerated populations according to a gradient of fire recurrence and in five main vegetation types including shrublands and mixed mature woodlands. Fire recurrence was the main explanatory factor of oak recruitment, either directly or through vegetation type and microsite characteristics. The results indicate nil to low recruitment for holm oak and downy oak in shrublands, especially those recurrently burned and dominated by Cistus species. Cork oak recruited better than the other oaks in medium and high shrublands dominated by Erica arborea. In contrast, recruitment was high for holm and downy oak in mixed oak stands and mixed pine-oak stands that have not burned for decades. Microsite conditions such as coverage by litter and shrubs influenced oak recruitment, whereas landscape configuration and stand basal area had no influence. Our results suggest that strategic shrub-clearing, oak planting and protection of mixed oak woodlands as seed sources would help maintaining oak populations in the woodland–shrubland mosaic.     

An individual-tree diameter growth model for managed uneven-aged oak-shortleaf pine stands in the Ozark Highlands of Missouri, USA

The Pioneer Forest encompasses more than 60,000 ha in the Ozark Highlands of Missouri, USA and has been managed using single-tree selection since the early 1950s. This paper quantifies the influence of tree size and competitive position, stand density, species composition, and site quality on ten-year (1992-2002) diameter increment within oak (Quercus spp.) and shortleaf pine (Pinus echinata Mill.) stands on the Pioneer Forest. An individual-tree model was developed for each species using mixed-effects regression and 290 inventory plots. Model efficiency (R²) ranged from 0.26 to 0.57 and fit was generally better for oak species. Basal area in larger trees (BAL) and tree diameter were significant predictors for all species and crown competition factor improved prediction for shortleaf pine and hickory (Carya spp.). Effect of species composition and site quality on diameter growth was not consistent across species. Models were evaluated using a subset of data not included in model fitting and the effect of single tree and standwise (1, 3, or 5 sample trees) calibration on model predictions were evaluated. Inclusion of random effects through calibration improved model prediction for all species and fit was best following single tree and 3 tree calibration.     

Tree Regeneration and Sapling Damage of Pedunculate Oak Quercus robur in a Grazed Forest in Galicia, NW Spain: A Comparison of Continuous and Rotational Grazing Systems

Forest grazing has been recognised as being a useful tool in fire-risk reduction, in addition to having the potential to preserve or enhance forest biodiversity if managed correctly. Concern for natural regeneration of forest trees in Europe has also prompted interest in the effects of large herbivores on seedling and sapling growth and mortality. An investigation was carried out into sapling damage and density of natural regeneration of oak (Quercus robur) in a mature, pony-grazed, Pinus radiata forest in Galicia, NW Spain under two different grazing regimes (continuous and rotational). In all treatments significantly more oak seedlings and saplings were recorded in areas of grass sward than areas dominated by taller ground flora species. Damage to oak saplings was assessed from the form (height and canopy) relative to stem diameter. The height and average canopy diameter of similar-aged saplings were found to be significantly greater in ungrazed (control) than both continuous and rotationally grazed treatments. Height and canopy diameters of similar-aged oak were not significantly different between the two grazing treatments. Significant differences were observed in tree form, with unbrowsed saplings having the greatest height to canopy width ratio and those in the continuously browsed plots having the smallest. An obvious decrease in the goodness of fit (R²) of regression analyses were found in continuously grazed areas compared to rotational and control plots for both height and canopy data. The differences in damage observed were not significantly different enough to suggest one method of grazing over the other as being better for minimising sapling damage. Management requirements are more likely to dictate grazing regime. Overall, stock density is likely to have a more significant effect on damage than stocking system.     

Dendroecology and species co-existence in an old-growth Quercus–Acer–Tilia talus slope forest in the central Appalachians,USA

Dendroecological techniques were used to examine the disturbance history and patterns of species recruitment in an old-growth Quercus rubra L. (northern red oak)–Acer saccharum Marsh. (sugar maple)–Tilia americana L. (basswood) forest on a steep, talus slope in eastern West Virginia. The forest was uneven-aged as were the populations of red oak. Sugar maple dominated the sapling layer, which comprised little or no basswood and red oak. A compilation of major and moderate releases (indicative of disturbance) in 25 cores revealed single or multiple release events in every decade from 1870–1990. The high elevation of the forest coupled with a fertile sub-soil beneath the talus ameliorated the outwardly harsh conditions of the site, allowing for the domination of typically mesophytic, nutrient demanding tree species. We observed several fire scarred trees as well as extensive small-scale blow-down throughout the forest. Frequent disturbance events were probably crucial to the co-existence and continuous canopy recruitment of the relatively light demanding red oak with highly shade tolerant sugar maple and basswood. The strong successional replacement tendencies of red oak by northern hardwoods noted elsewhere in the eastern US may be less apparent on high elevation, rocky sites in the central Appalachians. Thus, this is a unique case study of long-term red oak domination with later successional species in an old-growth forest.     

Does tree species composition control soil organic carbon pools in Mediterranean mountain forests?

We compared soil organic carbon (SOC) stocks and stability under two widely distributed tree species in the Mediterranean region: Scots pine (Pinus sylvestris L.) and Pyrenean oak (Quercus pyrenaica Willd.) at their ecotone. We hypothesised that soils under Scots pine store more SOC and that tree species composition controls the amount and biochemical composition of organic matter inputs, but does not influence physico-chemical stabilization of SOC. At three locations in Central Spain, we assessed SOC stocks in the forest floor and down to 50 cm in the mineral in pure and mixed stands of Pyrenean oak and Scots pine, as well as litterfall inputs over approximately 3 years at two sites. The relative SOC stability in the topsoil (0-10 cm) was determined through size-fractionation (53 μm) into mineral-associated and particulate organic matter and through KMnO₄-reactive C and soil C:N ratio.Scots pine soils stored 95-140 Mg ha⁻¹ of C (forest floor plus 50 cm mineral soil), roughly the double than Pyrenean oak soils (40-80 Mg ha⁻¹ of C), with stocks closely correlated to litterfall rates. Differences were most pronounced in the forest floor and uppermost 10 cm of the mineral soil, but remained evident in the deeper layers. Biochemical indicators of soil organic matter suggested that biochemical recalcitrance of soil organic matter was higher under pine than under oak, contributing as well to a greater SOC storage under pine. Differences in SOC stocks between tree species were mainly due to the particulate organic matter (not associated to mineral particles). Forest conversion from Pyrenean oak to Scots pine may contribute to enhance soil C sequestration, but only in form of mineral-unprotected soil organic matter.     

Effects of white-tailed deer on vegetation structure and woody seedling composition in three forest types on the Piedmont Plateau

White-tailed deer (Ododcoileus virginiana) can substantially affect the structure and species composition of a forest. The tolerance of a forest community to browsing may vary by type as a result of varying biotic and abiotic factors of the environment. To date, no studies have compared the effects of browsing among forest communities within a physiographic region. We investigated the effects of browsing on vegetation structure and woody seedling composition in three forest types (oak–hickory, Virginia pine–eastern red cedar, bottomland hardwood) in Manassas National Battlefield Park (MNBP), Virginia, USA. We compared forb cover, vertical plant cover (0–1.5 m tall), and survival of tagged seedlings in 10 exclosed (2 m × 6 m) and 10 unexclosed plots in each forest type during a 5-year period. No differential effects of browsing were found among forest types. In all forest types, deer (67 deer/km²) suppressed forb and vertical plant cover to levels less than would be expected in the absence of deer. Seedling survival rates of most species were significantly reduced by browsing. By the 4th year of the study, box elder (Acer negundo), hickory (Carya spp.), and red maple (Acer rubrum) had been eliminated from unexclosed plots, and red and white oaks (Quercus spp.) dramatically reduced. Ash (Fraxinus spp.), black cherry (Prunus serotina), and hackberry (Celtis occidentalis), although significantly impacted, remained the most abundant species throughout the study. These findings suggest that white-tailed deer may be modifying the structure of the forest interior to the extent that it adversely affects wildlife species dependent on a dense understory to thrive. We predict that the future composition of forests in MNBP will shift towards stands with fewer species and a greater dominance of ash, black cherry, and hackberry, particularly in the oak–hickory and bottomland hardwood forests, where the majority of current dominants are most affected.     

How we improved a landscape study of species richness of beetles in woodland key habitats, and how model output can be improved

In an earlier study (Franc et al., 2007), local species richness of saproxylic oak beetles (including red-listed beetles) in forests was predicted mainly by the landscape (area of woodland key habitat within 1 km of plots). Such results are important for conservation work, but need to be backed up well, for reliable advice. We tested a two-stage method that improved our earlier models and our advice for conservation planning. We studied temperate mixed forest, rich in oaks Quercus robur/Quercus petraea, in a large landscape in Sweden. Franc et al. (2007) analysed 21 forests. Here we selected the significant explanatory variables (predictors) and other biologically relevant predictors, used the earlier 21 forests and sampled 11 new forests such that we expanded the range on the axes of the predictors. We collected in total 320 species of saproxylic oak beetles (23,137 individuals) of which 65 and 38 were red-listed (IUCN criteria, Swedish list 2000 and 2005, respectively). We partly confirmed our original results, but the results also changed in important ways: local species richness is now predicted by a combination of local, landscape and regional factors. Moreover, a local variable (dead wood) was the main predictor of saproxylic oak beetles (all species included), while for red-listed saproxylic oak beetles the landscape (woodland key habitat within 1 km of plots) was the main predictor, of local species richness. Thus, species richness of red-listed saproxylic oak beetles seems to depend mainly on landscapes factors, while total species richness of saproxylic oak beetles seems to depend more on local stand factors. We conclude that a two-stage research design can be useful in landscape and conservation studies, especially for species-rich taxa that require large samples per site.     

Species substitution for carbon storage: Sessile oak versus Corsican pine in France as a case study

Species choice is potentially an important management decision for increasing carbon stocks in forest ecosystems. The substitution of a slow-growing hardwood species (Quercus petraea) by a fast-growing conifer plantation (Pinus nigra subsp. laricio) was studied in central France. Simulations of carbon stocks in tree biomass were conducted using stand growth models Fagacées for sessile oak and PNL for Corsican pine. The changes in soil carbon were assessed using the Century model and data from two European soil monitoring networks: 16 km × 16 km grid and RENECOFOR. Carbon in wood products was assessed with life cycle analysis and lifespan of final products. However, only carbon stocks and their variation were accounted for: effects of energy-consuming materials or fossil fuel substitution are excluded from the analysis. To compare the growth of these two types of forest stands, an important part of the study was to assess the productivity of both species at the same site, using National Forest Inventory data.     

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.     

Forest management conditioning ground ant community structure and composition in temperate conifer forests in the Pyrenees Mountains

The search for indicators to monitor management impact on biodiversity is a crucial question because management practices promote changes in community structure and composition of different animal groups. This study explores the effect of widely conducted management practices (forest logging and livestock) in Pinus uncinata forests in the Pyrenees range (NE Spain) on the structure and composition of ground ant communities compared to those of old-growth stands. Forest structure clearly differed in stands with different forest managements. These stands managed for different uses also showed marked differences in structure and composition of ground ant communities. There was a great dominance of a single species, Formica lugubris, which accounted for 99% of ants collected in pitfall traps. Rarefaction curves indicated that species richness was highest in old-growth stands and lowest in even-aged ones, with woodland pasture stands showing an intermediate value. Classification methods allowed us to identify two groups of species: six species related to old-growth plots and three species (including F. lugubris) associated to managed stands. Habitat structure played an important role in determining the structure of ant communities: forests with high tree density but low basal area were the most favourable forest type for F. lugubris, while the abundance of the remaining ant species was negatively affected by the abundance of F. lugubris and by tree cover.     

Effects of mechanized pine straw raking on population densities of longleaf pine seedlings

Longleaf pine communities occupy a small fraction of their original extent in the southeastern United States and are in great need of restoration and conservation management. Recent anthropogenic disturbances, such as pine straw raking, may interfere with seedling survival and, hence, restoration efforts. We examined the effects of mechanized straw raking on longleaf pine (Pinus palustris Mill.) seedlings (pre-grass stage, or <3-yr-old) in natural, fire-maintained plant communities in Croatan National Forest, North Carolina, by testing the effects of number of rakings (0–4 times during a 2-yr period (1992–1994)) and community type (pine-turkey oak, dry savanna, and mesic savanna) on seedling densities in 1-m² quadrats. Despite initial differences in densities of seedlings among communities, analyses of variance did not detect significant differences among communities as averaged over time and raking treatment. Both raked and unraked quadrats exhibited declines in seedling density during the study, but the declines were greater for raked quadrats. After 2 yr, initial densities were, on average, reduced by 34% in unraked quadrats and by 47%, 63%, 78%, and 77% in quadrats raked one, two, three, and four times, respectively. In quadrats raked four times, censuses performed after each raking indicated significant declines in densities in response to all but the first raking. Raking either injures pine seedlings directly and/or modifies microsite conditions in ways unfavorable for seedling survival. Having established a link between raking and mortality, we now recommend additional work to reveal the causal mechanisms. Land management decisions should accommodate the potential adverse effects of mechanized raking on pine regeneration.     

中山市生态景观林带建设技术探讨

文章根据广东省中山市不同的生态景观林带类型,分析了中山市生态景观林带建设过程中在造林、景观节点建设及取土场、采石场生态植被修复等方面采取的一些关键技术措施,对构建以森林植被为主体的、森林和园林和谐统一的森林生态网络和城市森林绿化网络,建设宜业宜居的“幸福中山”具有重要意义。     

Effect of habitat and grazing on the regeneration of wild Agave cupreata in Guerrero, Mexico

Agave cupreata is harvested from tropical dry forests, oak forests, and other habitats by rural communities in the Chilapa region of Guerrero, Mexico to make mescal, a traditional and culturally important liquor. Local management systems use various techniques to regulate Agave harvest and encourage regeneration, including the exclusion of cattle. This study examines the impacts of cattle exclusion and of the different habitat types on the population structure and density of A. cupreata. Sampling was conducted in pastures, oak forest, tropical dry forest, and mixed oak-tropical dry forest using 54 transects of 1000 m², where Agave was counted by size-class and measurements were taken of the vegetation and physical environment. Transects were divided between areas with cattle present and cattle excluded in all four habitats except for oak forest, where all areas were open to cattle. Agave density per 1000 m² was highest in pasture (148 ± 5, mean ± SE), followed by oak forest (100 ± 4), tropical dry forest (88 ± 5) and mixed oak-dry forest (81 ± 2). The size-class structures of Agave populations were also significantly different between vegetation types, with oak forest supporting higher seedling densities but lower numbers of juveniles. A regression subset selection algorithm showed that one of the most important factors influencing Agave populations was the presence of cattle, which can reduce densities by trampling and grazing on seedlings and floral stalks. Cattle presence significantly lowered Agave densities in the smaller size classes in all vegetation types but did not significantly alter size-class structure. Total Agave density per 1000 m² was significantly higher in transects where cattle were absent (148 ± 4) than where cattle were present (81 ± 1). In all areas sampled, the high number of juveniles relative to other size-classes suggests that Agave populations are successfully regenerating in the Chilapa region, and the higher Agave densities in fenced areas suggest that local management techniques are effectively increasing Agave yields. These results highlight the potential for sustainable management of Agave to conserve forest habitats while also providing important income from mescal to local communities in the region.     

Intensive tree planting facilitates tropical forest biodiversity and biomass accumulation in Kibale National Park, Uganda

The extensive area of degraded tropical land and the calls to conserve forest biodiversity and sequester carbon to offset climate change demonstrate the need to restore forest in the tropics. Deforested land is sometimes replanted with fast-growing trees; however, the consequences of intensive replanting on biomass accumulation or plant and animal diversity are poorly understood. The purpose of this study was to determine how intensive replanting affected tropical forest regeneration and biomass accumulation over ten years. We studied reforested sites in Kibale National Park, Uganda, that were degraded in the 1970s and replanted with five native tree species in 1995. We identified and measured the size of planted versus naturally regenerating trees, and felled and weighed matched trees outside the park to calculate region-specific allometric equations for above-ground tree biomass. The role of shrubs and grasses in facilitating or hindering the establishment of trees was evaluated by correlating observed estimates of percent cover to tree biomass. We found 39 tree species naturally regenerating in the restored area in addition to the five originally planted species. Biomass was much higher for planted (15,675 kg/ha) than naturally regenerated trees (4560 kg/ha), but naturally regenerating tree regrowth was an important element of the landscape. The establishment of tree seedlings initially appeared to be facilitated by shrubs, primarily Acanthus pubescens and the invasive Lantana camara; however, both are expected to hinder tree recruitment in the long-term. Large and small-seeded tree species were found in the replanted area, indicating that bird and mammal dispersers contributed to natural forest restoration. These results demonstrate that intensive replanting can accelerate the natural accumulation of biomass and biodiversity and facilitate the restoration of tropical forest communities. However, the long-term financial costs and ecological benefits of planting and maintaining reforested areas need to be weighed against other potential restoration strategies.     

Soil-solution chemistry in black locust, pine/mixed-hardwoods and oak/hickory forest stands in the southern Appalachians, U.S.A.

Soil-solution chemistry was measured over a 15-month period in three forest stands of contrasting nitrogen mineralization and nitrification rates in the southern Appalachians of North Carolina, U.S.A., using porous-cup lysimeters. In a black-locust-dominated stand, soil solution NO₃---N was 3.73 and 5.04 mg l⁻¹ at 30- and 60-cm depth respectively, and dissolved organic N ( ) was 0.718 and 0.582 mg l⁻¹ respectively. Values at 30 and 60 cm for a pine/mixed-hardwood stand were 0.032 and 0.058 mg l⁻¹ NO₃---N, and 0.201 and 0.168 mg l⁻¹ (values are means over the whole duration of the study). At both depths, soil solution conductivity, pH, Ca, Mg, K and PO₄---P were higher in black locust than in pine/mixed-hardwoods, and there were no differences in soil solution Na. In an oak/hickory stand, soil solution NO₃---N at 30-cm depth was 0.008 mg l⁻¹, and was 0.357 mg l⁻¹. At 30-cm depth, soil-solution conductivity, Ca, Mg and PO₄---P were higher in black locust than in oak-hickory, with no differences in pH, K and Na; , pH and K were higher in oak/hickory than in pine/mixed-hardwoods. In the oak/hickory and pine/mixed-hardwoods forest stands, with relatively lower soil N turnover rates, was a major portion of soil solution N.     

Study of landscape change under forest harvesting and climate warming-induced fire disturbance

We examined tree species responses under forest harvesting and an increased fire disturbance scenario due to climate warming in northern Wisconsin where northern hardwood and boreal forests are currently predominant. Individual species response at the ecosystem scale was simulated with a gap model, which integrates soil, climate and species data, stratified by ecoregions. Such responses were quantified as species establishment coefficients. These coefficients were used to parameterize a spatially explicit landscape model, LANDIS. Species response to climate warming at the landscape scale was simulated with LANDIS, which integrates ecosystem dynamics with spatial processes including seed dispersal, fire disturbance, and forest harvesting. Under a 5 °C annual temperature increase predicted by global climate models (GCM), our simulation results suggest that significant change in species composition and abundance could occur in the two ecoregions in the study area. In the glacial lake plain (lakeshore) ecoregion under warming conditions, boreal and northern hardwood species such as red oak, sugar maple, white pine, balsam fir, paper birch, yellow birch, and aspen decline gradually during and after climate warming. Southern species such as white ash, hickory, bur oak, black oak, and white oak, which are present in minor amounts before the warming, increase in abundance on the landscape. The transition of the northern hardwood and boreal forest to one dominated by southern species occurs around year 200. In the sand barrens ecoregion under warming conditions, red pine initially benefits from the decline of other northern hardwood species, and its abundance quickly increases. However, red pine and jack pine as well as new southern species are unable to reproduce, and the ecoregion could transform into a region with only grass and shrub species around 250 years under warming climate. Increased fire frequency can accelerate the decline of shade-tolerant species such as balsam fir and sugar maple and accelerate the northward migration of southern species. Forest harvesting accelerated the decline of northern hardwood and boreal tree species. This is especially obvious on the barrens ecoregion, where the intensive cutting regime contributed to the decline of red pine and jack pine already under stressed environments. Forest managers may instead consider a conservative cutting plan or protective management scenarios with limited forest harvesting. This could prolong the transformation of the barrens into prairie from one-half to one tree life cycle.     

Forest composition,leaf litter,and songbird communities in oak- vs. maple-dominated forests in the eastern United States

Within the eastern deciduous forest region, forest composition varies, with some areas dominated by a mix of oaks (Quercus spp.) and other areas dominated by a mix of sugar maple (Acer saccharum) and other tree species. Prescribed fire is being used on an experimental basis to assess its effectiveness in restoring and maintaining oak-dominated forests. Maple-dominated forests are susceptible to invasion by non-native earthworms, such as Lumbricus terrestris, given the palatability of leaf litter and suitable soil conditions, especially in northern parts of the region. What are the implications of this variation on leaf litter availability and habitat for ground-nesting songbirds? We investigated this question by comparing forest composition, leaf litter, and songbird communities in maple-dominated forests in west-central Indiana and oak-dominated forests, recently burned and unburned, in southeastern Ohio. We also assessed abundance of earthworms and decomposition rates of different types of leaves in the maple-dominated forests in Indiana. Leaf litter and ground-nesting bird species were abundant in unburned oak-dominated forests, but were absent or nearly absent in recently burned oak-dominated forests and in maple-dominated forests. The lack of leaf litter and absence of ground-nesting bird species in maple-dominated forests may be due to the combination of abundant non-native earthworms, alkaline and calcium-rich soils, palatable leaves, and rapid leaf litter decomposition rates. Effects of burning on leaf litter and ground-nesting bird species in oak-dominated forests are probably temporary, as long as prescribed fires are not applied on a frequent or widespread basis. Our study is the first one to show a correlation between forest composition, leaf litter availability, earthworm abundance, and songbird populations. Many researchers are investigating effects of non-native earthworm invasions on ecosystem properties in eastern deciduous forests. We recommend that researchers should also monitor songbird populations to assess whether declines in ground-nesting bird populations are occurring in response to these changes.     

我国栓皮栎分布及其生态学研究

栓皮栎作为广泛分布的树种之一,在全球气候变化的大环境下,成为研究树木生长应对气候变化的重要树种。文中分析了我国栓皮栎水平分布和垂直分布的特点及其与气候的关系,栓皮栎在不同地区的森林类型,主要包括栓皮栎纯林、松栎混交林、栎类混交林等类型;综述了我国对栓皮栎生态学、群落结构、更新等研究的最新进展和主要结论;提出今后开展栓皮栎研究的重点和方向,以期为栓皮栎生理生态学及其对气候变化响应研究提供参考。