Changes In Forest Communities Research Articles

Warming enhanced the interaction effects of fungi and fungivores and soil potassium mineralization in tropical forest

Potassium (K) cycling in forest systems has received less attention than nitrogen (N) and phosphorus (P) cycles, despite its critical role in maintaining primary production and regulating water economy and use under climate warming. This study conducted a 10-year study in which we translocated dominant tropical forest tree seedlings and underlying soil (i.e., in situ soil) from high-altitude sites (600 m a.s.l.) to lower altitude sites at 300 m a.s.l. (+1.0 °C) and 30 m a.s.l. (+2.1 °C) to simulate climate warming in southern China. We investigated soil microbial and nematode communities, soil and foliar K concentrations at the aggregate level, and tree growth under different altitude sites. Microbial community was characterized by high-throughput sequencing, nematodes were identified to the genus level using microscope. The findings revealed that warming treatments significantly (p < 0.01) increased soil fungal gene abundance (+78 % at 300 m and +62 % at 30 m), fungal/bacterial abundance ratio (+121 % at 300 m and +101 % at 30 m), and soil fungivore abundance (+274 % at 300 m and +233 % at 30 m). These results indicate a shift in the soil decomposition pathway from bacterial to fungal-based channels. In addition, warming amplifies the interactions between fungi and fungivores. Aggregates had few effects on microbial biomass, but had significant effect on nematode abundance. Soil microcosm experiments consistently demonstrated that addition of the dominant fungivore Aphelenchoides significantly (p < 0.05) enhanced soil-exchangeable K by stimulating fungal gene abundance and activity. Furthermore, warming-induced changes in forest communities were observed. At the species-specific tree level, Syzygium rehderianum demonstrated the ability to take advantage of this scenario, exhibiting increased K uptake (−4% at 300 m and +32 % at 30 m). This may be attributed to the species being ectomycorrhizal-forming, where colonizing root surfaces can mobilize interlayer and structural K from the minerals. In contrast, Machilus breviflora exhibited lower foliar K concentrations (−42 % at 300 m and −41 % at 30 m) and reduced growth. However, warming had little effect on Schima superba, Myrsine seguinii, Itea chinensis, and Ardisia lindleyana growth. Warming-induced changes in the plant–soil system K cycle highlight the emergence of a new ecosystem structure with different soil web structures and distinct plant community species composition. Our results prompt further research to understand the microbiome-mediated complexities of understudied nutrient cycles, which are likely to be further altered in the future owing to climate change.

Anthropogenic disturbance produces divergent effects in the community structure and composition of tropical semi-evergreen forests in the Eastern Himalaya

Studies documenting anthropogenic disturbance-driven changes in forest communities of the Eastern Himalaya, a global biodiversity hot spot, are largely lacking. We studied six forest sites of tropical semi-evergreen forests in Arunachal Pradesh in the Eastern Himalaya to understand the effects of varying disturbance intensities on the forest community structure and composition. Based on the magnitude of disturbance, forest sites were classified as experiencing low, moderate and high disturbance. Mean species richness (SR) of trees and shrubs decreased from low disturbance to high disturbance. Mean SR of herbs was maximum in moderately disturbed forest sites. Maximum values of the Shannon-Wiener Diversity Index (SD) were recorded for trees at sites with low disturbance, for shrubs at sites with high disturbance and for herbs in moderately disturbed forests. Pilelou Evenness Index (EI) values were maximum for trees at sites with high disturbance, while maximum EI values for shrubs and herbs were recorded in the forest sites with low disturbance. The number of tree families decreased from 18 to 13 in the forests with low and high disturbance, respectively. Moderate disturbance led to increased herb species richness and diversity, while increasing disturbance produced contrasting effects on trees. High anthropogenic disturbance led to low species richness, but high diversity amongst shrubs. Our investigations suggest that the magnitude of disturbance elicits differential responses in different physiognomic classes in the forest ecosystems and further our understanding of the effects of disturbance in tropical forest ecosystems of a global biodiversity hotspot.

Regional effects and local climate jointly shape the global distribution of sexual systems in woody flowering plants

Abstract. Understanding the evolution and maintenance of plant sexual diversity needs to incorporate both regional processes and local climate factors across large geographic scales. Using data of woody flowering plants from a global set of large-scale forest plots and multinomial logistic regression, we quantified regional effects on the proportions of dioecious, monoecious, and hermaphroditic species and their abundance while incorporating evolutionary history and local climate factors. Our results showed that plants were more likely to be dioecious than hermaphroditic in Oceania and tropical Asia but were more likely to be monoecious than dioecious in Europe and North America compared with tropical Africa. We further found that plants were more likely to be monoecious than dioecious in island communities. Plants were more likely to be monoecious than dioecious in areas with high precipitation but were more likely to be dioecious than monoecious in areas with high precipitation of coldest quarter. Our results suggest that both regional processes and local climate factors play important roles in shaping the geographic distribution of plant sexual systems, providing a baseline for predicting future changes in forest communities in the context of global change.

Three Censuses of a Mapped Plot in Coastal California Mixed-Evergreen and Redwood Forest

Large, mapped forest research plots are important sources of data to understand spatial and temporal changes in forest communities in the context of global change. Here, we describe the data from the first three censuses of the 16-ha UC Santa Cruz Forest Ecology Research Plot, located in the Mediterranean-climate forest on the central coast of California, USA. The forest includes both mixed-evergreen forest and redwood-dominated forest and is recovering from significant logging disturbances in the early 20th century. Each woody stem with a diameter ≥ 1 cm at 1.3 m was mapped, tagged, identified, and measured, with censuses performed at ~5-year intervals. The first census included just 6 ha (previously described), and the area was then expanded to 16 ha in the second census. We describe the temporal dynamics of the forest in the original 6 ha, as well as the structure and temporal dynamics of the full 16 ha. The community includes 34 woody species, including 4 gymnosperm and 9 angiosperm tree species, 18 species of shrubs, and 3 species of lianas. The community includes eight non-native species, representing less than 0.5% of the stems. More than half the species show greater rates of mortality than recruitments, reflective of a dynamic forest community. Over a decade, the number of living woody stems has declined, but the basal area has increased, reflecting a self-thinning process.

Actor-driven institutional change in forest communities: insights from the Bakossi Landscape of Cameroon

The institutions-cum-forest use dynamics literature is growing, albeit marred by scanty evidence on actor roles in shaping the process in sub-Saharan Africa. Cameroon represents a useful “laboratory” to explore such actor-driven change processes. Recent studies have reported the change process linked to a colonial hangover in parts of Cameroon that came under French influence, suggesting the need for fresh evidence to uncover such change processes in parts of the country which came under British influence. Using the Bakossi Landscape as a case, this article (i) traces the pathways of forest-linked institutional change, (ii) estimates the role of actor groups in shaping forest-linked institutional change, and (iii) explores the determinants of forest-linked institutional change in the Bakossi Landscape. A representative sample of 116 households in 3 selected communities was performed. This was complemented by focus group discussions (n = 6) and key informant interviews (n = 10). Descriptive statistics were used to establish forest-linked institutional change, while the ordinary least square was employed to estimate the effect of actor groups and other determinants on forest-linked institutional change. The results lead us to the following conclusions: First, both forest-linked institutional structures and processes witnessed changes over the years. Second, raising the intensity of actor group processes (in-migrants, local elites, traditional leadership, timber dealership and NTFP traders) significantly decreases changes in forest-linked traditional rules, while migration, state officials and the church significantly increase changes in forest-linked institutional structure. Finally, an increase in the composite index of process-mix traditional leadership and NTFP traders decreases changes in forest-linked institutional structures. Future studies should uncover gender dimensions of changes in forest-based institutions, as well as the role of conflict actors in engendering institutional change.

Spatiotemporal Modeling of Coniferous Forests Dynamics along the Southern Edge of Their Range in the Central Russian Plain

Forests with predominance of Norway spruce (Picea abies (L.) H. Karst.) and Scots pine (Pinus sylvestris L.) within the hemiboreal zone are considered as secondary communities formed under long-term human activity (logging, plowing, fires and silviculture). This study raises the question—how stable is current state of coniferous forests on the southern border of their natural distribution in the center of Eastern Europe using the example of the Moscow region (MR)? The object of the study are spruce and pine forests in different periods of Soviet and post-Soviet history within the Moscow Region (MR). The current proportion of spruce forests is 21.7%, and the proportion of pine forests is 18.5% from total forest area according to our estimates. The direction and rate of forest succession were analyzed based on current composition of populations of the main forest-forming species (spruce, pine, birch, aspen, oak, linden, and ash) based on ground-based research materials collected in 2006–2019. This allowed to develop the dynamic model (DM) of forest communities with the participation of Norway spruce and Scots pine for several decades. Assessment of the spatial distribution of coniferous communities is based on field data and spatial modeling using remote sensing data—Landsat 8 mosaic for 2020. In parallel, a retrospective model (RM) of the spatial-temporal organization of spruce and pine forests for a 30-year period was developed using two Landsat 5 mosaics. For this, nine different algorithms were tested and the best one for this task was found—random forest. Geobotanical relevés were used as a training sample combined with the 2006–2012 mosaic; the obtained spectral signatures were used for modeling based on the 1984–1990 mosaic. Thus, two multi-temporal spatial models of coniferous formations have been developed. Detailed analysis of the structure of spruce and pine forests based on field data made it possible to track trends of successional dynamics for the first time, considering the origin of communities and the ecological conditions of habitats. As a result, ideas about the viability of spruce and pine cenopopulations in different types of communities were formulated, which made possible to develop a dynamic model (DM) of changes in forest communities for future. Comparison of the areas and nature of changes in the spatial structure of coniferous formations made possible to develop the RM. Comparison of two different-time models of succession dynamics (DM and RM) makes possible to correct the main trends in the transformation of coniferous forests of natural and artificial origin under the existing regime of forestry. A set of features was identified that indicates risk factors for coniferous forests in the region. A further decrease of the spruce and pine plantations and increase of the spruce-small-leaved and deciduous formations are expected in the study area. The proportion of pine-spruce forests does not exceed 3% of the area and can be considered as the most vulnerable type of forest.

Developing Species-Age Cohorts from Forest Inventory and Analysis Data to Parameterize a Forest Landscape Model

Simulating long-term, landscape level changes in forest composition requires estimates of stand age to initialize succession models. Detailed stand ages are rarely available, and even general information on stand history often is lacking. We used data from USDA Forest Service Forest Inventory and Analysis (FIA) database to estimate broad age classes for a forested landscape to simulate changes in landscape composition and structure relative to climate change at Fort Drum, a 43,000 ha U.S. Army installation in northwestern New York. Using simple linear regression, we developed relationships between tree diameter and age for FIA site trees from the host and adjacent ecoregions and applied those relationships to forest stands at Fort Drum. We observed that approximately half of the variation in age was explained by diameter breast height (DBH) across all species studied (r2 = 0.42 for sugar maple Acer saccharum to 0.63 for white ash Fraxinus americana). We then used age-diameter relationships from published research on northern hardwood species to calibrate results from the FIA-based analysis. With predicted stand age, we used tree species life histories and environmental conditions represented by ecological site types to parameterize a stochastic forest landscape model (LANDIS-II) to spatially and temporally model successional changes in forest communities at Fort Drum. Forest stands modeled over 100 years without significant disturbance appeared to reflect expected patterns of increasing dominance by shade-tolerant mesophytic tree species such as sugar maple, red maple (Acer rubrum), and eastern hemlock (Tsuga canadensis) where soil moisture was sufficient. On drier sandy soils, eastern white pine (Pinus strobus), red pine (P. resinosa), northern red oak (Quercus rubra), and white oak (Q. alba) continued to be important components throughout the modeling period with no net loss at the landscape scale. Our results suggest that despite abundant precipitation and relatively low evapotranspiration rates for the region, low soil water holding capacity and fertility may be limiting factors for the spread of mesophytic species on excessively drained soils in the region. Increasing atmospheric temperatures projected for the region could alter moisture regimes for many coarse-textured soils providing a possible mechanism for expansion of xerophytic tree species.

Onward but not always upward: individualistic elevational shifts of tree species in subtropical montane forests

Ongoing global climate change is driving widespread shifts in species distributions. Trends show frequent upwards shifts of treelines, but information on changes in montane forest below the treeline and in the tropics and subtropics is limited, despite the importance of these areas for biodiversity and ecosystem function. Patterns of species shifts in tropical and subtropical regions are likely to be more complex and individualistic than global averages suggest due to high species diversity and strong influence of competition, alongside direct climatic limitations on distributions. To address the question of how subtropical montane tree species are likely to move as climate changes, we used an extensive national forest inventory to estimate distribution shifts of 75 tree species in Taiwan by comparing the optimum elevation and range edges of adults and juveniles within species. Overall there was a significant difference in optimum elevation of adults and juveniles. Life stage mismatches suggested upward shifts in 35% of species but downward shifts of over half (56%), while 8% appeared stable. Upward elevation shifts were disproportionately common in high elevation species, whilst mid to low elevation species suggested greater variation in shift direction. Whilst previous research on mountain forest range shifts has been dominated by work addressing changes in treeline position, we show that although high elevation species shift up, below the treeline species may shift individualistically, heralding widespread changes in forest communities over coming decades. The wide variation of responses indicated is likely driven by individual species responses to interacting environmental factors such as competition, topography and anthropogenic influences across the broad range of forest types investigated. As global environmental changes continue, more detailed understanding of tree range shifts across a wide spectrum of forests will allow us to prepare for the implications of such changes for biodiversity, ecosystem function and dependent human populations.

Fourteen years of swamp forest change from the onset, during, and after invasion of emerald ash borer

Since beginning its invasion of eastern North America by 2002, the Asian-origin beetle emerald ash borer (EAB; Agrilus planipennis) has decimated ash trees (Fraxinus spp.). In the Great Black Swamp in northwestern Ohio, USA, 90 km south of the epicenter of EAB invasion, we examined changes in forest communities during a 14-year period spanning EAB’s arrival in 2005 through 2018. No green ash (Fraxinus pennsylvanica) trees larger than 4 cm in diameter were alive on study sites in 2018, but ash saplings 1–4 cm in diameter (764 stems/ha) and seedlings (1.5% cover) were plentiful. Basal area growth of other tree species did not compensate for ash loss; total basal area averaged 8% lower in 2018 than in 2005. In the understory, non-native plants were negligible (< 2% cover, < 3 species/0.05 ha) among years and did not change significantly after EAB’s arrival. Native plant cover was twice as high in 2018 than when EAB arrived in 2005. Changes in understory cover primarily entailed reorganization of species already established when EAB arrived, rather than colonization by new species. New colonizers proportionally comprised only 0.05–0.07 of total cover among years. The shrub spicebush (Lindera benzoin) and forb Virginia creeper (Parthenocissus quinquefolia) dominated understories throughout the study. From a perspective of maintenance of native understories in EAB-aftermath forests, observed changes were probably as favorable as could be expected. Native species already present increased the most, neither floristic quality nor wetland indicator species declined, and non-native plants did not increase.

Spatio-temporal dynamics of seedling communities are determined by seed input and habitat filtering in a subtropical montane forest

Spatial and temporal variation in species abundances and distributions of the seedling community, which plays a pivotal role in maintaining species diversity, can help predict future changes in forest communities. We monitored the dynamics of 12,830 seedlings within 405 1-m2 seedling plots in the Badagongshan (BDGS) 25-ha forest dynamic plot over a 6-year period (2012–2017). We presented changes in the relative abundance for 15 dominant seedling species during the last six years, assessed temporal changes in species richness, species turnover, seedling density, species reordering (mean rank shift of the relative abundance; MRS) and community similarity within three topographically defined habitats (ridge, slope and valley), and explored the mechanisms underlying dynamics of seedling communities. Furthermore, we explored differences in species’ ecological indicator values (EIVs) and functional groups for species gained and lost during the study period. Across three habitat types, there were enormous reordering of the 15 dominant seedling species; a few mast-seedling events were clearly identified. Both species richness and seedling density continually declined over the entire census year, except for an increase of species richness during 2012–2013. Species turnover fluctuated temporally in three habitat types; overall, species emigration rate was higher than species immigration rate in three habitats. Valleys with lower soil C:N ratio, light availability and VDCN (vertical distance above the channel network), but higher soil pH and TWI (topographic wetness index), had lower species richness and stem density, and higher species turnover and species reordering than slopes and ridges. At the community-wide scale, significant directional changes in species composition occurred on ridges and slopes. Newly colonizing species were typically more shade- tolerant, water- and temperature- demanding shrub species and grown on soil with low pH but high fertility. In the BDGS plot, species richness and seedling density fluctuated in the first two years and then decreased over time, which reflects that both habitat filtering and seed input regulated temporal dynamics of species composition, but the relative importance varied among studied years. In this subtropical forest, species composition showed obvious directional changes. Shrub species increased more than species of other strata in ridge and slope areas. It is worth noting that an increased dominance of species that are more water-demanding could increase the risk of mortality under global climate change (e.g. drought).

Press-Pulse Odocoileus Virginianus Herbivory in Relict Tsuga Canadensis Stands in the Western Upper Peninsula of Michigan, USA

Ungulate herbivory occurring within a forest plant community’s natural range of variation may help maintain species diversity. However, acute or chronically elevated levels of herbivory can produce dramatic changes in forest communities. For example, chronically high levels of herbivory by white-tailed deer (Odocoileus virginianus Zimmerman) in regions of historically low abundance at northern latitudes have dramatically altered forest community composition. In eastern hemlock (Tsuga canadensis L. Carrière) stands where deer aggregate during winter, high deer use has been associated with a shift towards deciduous species (i.e., maples [Acer spp.]) dominating the regeneration layer. Especially harsh winters can lead to deer population declines, which could facilitate regeneration of species that have been suppressed by browsing, such as hemlock. To enhance our understanding of how fluctuations in herbivory influence regeneration dynamics, we surveyed regeneration and deer use in 15 relict hemlock stands in the western Upper Peninsula of Michigan in 2007 and again in 2015. With the exception of small seedlings (0.04–0.24 m height), primarily maples whose abundance increased significantly (p &lt; 0.05), we observed widespread significant declines (p &lt; 0.05) in the abundance of medium (0.25 ≤ 1.4 m height) and large regeneration (&gt;1.4 m tall ≤ 4 cm diameter at breast height) over the study period. Midway through our study period, the region experienced a high severity winter (i.e., “polar vortex”) which resulted in a substantial decline in the white-tailed deer population. Given the dominance of maples and dearth of hemlock in the seedling layer, the decline in the deer population may fail to forestall or possibly hasten the trend towards maple dominance of the regeneration layer as these stands recover from pulses of acute herbivory associated with high-severity winters and the press of chronically high herbivory that precedes them.

Pine vs. oaks revisited: Conversion of Madrean pine-oak forest to oak shrubland after high-severity wildfire in the Sky Islands of Arizona

Abstract Fire regimes have changed dramatically in most dry woodlands and forests of the American Southwest from frequent surface fires prior to Euro-American settlement, to fire suppression in the 20th century, to a current era characterized by large, higher-severity wildfires. The recent increase in fire activity and consequent changes in forest communities are key management concerns across the region. We use sampling from before and after the 1994 Rattlesnake and 2011 Horseshoe Two Wildfires in the Chiricahua Mountains to address the extent to which higher-severity fire is converting Madrean pine-oak forest to oak shrubland in the Sky Islands of Arizona. Plant communities changed from mixed pine-oak forest before the wildfires to oak shrublands and grasslands by 2016 where fires burned at high-severity. In those sites, nearly all stems were killed above ground, oaks regenerated vigorously, mainly by resprouting, and pines recruited at very low levels. These patterns were consistent after each fire and for up to 14 years after the Rattlesnake Fire. Across the Horseshoe Two Fire, seedling recruitment of pines and oaks declined with increasing fire-severity, but oak resprouting increased. Differential recruitment success of oaks over pines was amplified by their far greater juvenile height and more ramets per resprouting genet. Resprouting in Pinus leiophylla (Chihuahua pine) after top-kill was low, but sufficient to suggest that this behavior may maintain this species at low density after high-severity fire. The impact of fire depended on topography, as less exposed plots (e.g. in drainages) experienced lower-severity fire and less conversion to oak shrublands, suggesting that these sites provided refugia for species, such as pines, sensitive to high-severity fire. Low pine recruitment occurred in all plots, not only in sites subject to high-severity fire, suggesting that vegetation conversion may have been exacerbated by the extreme drought of the past two decades. Given the episodic nature of their regeneration, pine recovery is possible in the future, but projections call for intensification of aridity and fire activity in the Southwest, which could lead to continued transition of Madrean pine-oak forests to more fire- and drought-resilient communities dominated by oaks. The results of this study point to the need for protective vegetation management and restoration experiments targeting pines.

When a foundation crumbles: forecasting forest dynamics following the decline of the foundation species Tsuga canadensis

AbstractIn the forests of northeastern North America, invasive insects and pathogens are causing major declines in some tree species and a subsequent reorganization of associated forest communities. Using observations and experiments to investigate the consequences of such declines are hampered because trees are long‐lived. Simulation models can provide a means to forecast possible futures based on different scenarios of tree species decline, death, and removal. Such modeling is particularly urgent for species such as eastern hemlock (Tsuga canadensis), a foundation species in many northeastern forest regions that is declining due to the hemlock woolly adelgid (Adelges tsugae). Here, we used an individual‐based forest simulator, SORTIE‐ND, to forecast changes in forest communities in Central Massachusetts over the next 200 yr under a range of scenarios: a no‐adelgid, status quo scenario; partial resistance of hemlock to the adelgid; adelgid irruption and total hemlock decline over 25 yr, adelgid irruption and salvage logging of hemlock trees; and two scenarios of preemptive logging of hemlock and hemlock/white pine. We applied the model to six study plots comprising a range of initial species mixtures, abundances, and levels of hemlock dominance. Simulations indicated that eastern white pine, and to a lesser extent black birch and American beech, would gain most in relative abundance and basal area following hemlock decline. The relative dominance of these species depended on initial conditions and the amount of hemlock mortality, and their combined effect on neighborhood‐scale community dynamics. Simulated outcomes were little different whether hemlock died out gradually due to the adelgid or disappeared rapidly following logging. However, if eastern hemlock were to become partially resistant to the adelgid, hemlock would be able to retain its dominance despite substantial losses of basal area. Our modeling highlights the complexities associated with secondary forest succession due to ongoing hemlock decline and loss. We emphasize the need both for a precautionary approach in deciding between management intervention or simply doing nothing in these declining hemlock forests, and for clear aims and understanding regarding desired community‐ and ecosystem‐level outcomes.

The implications of American chestnut reintroduction on landscape dynamics and carbon storage

AbstractIn the eastern United States, American chestnut (Castanea dentata) was historically a major component of forest communities, but was functionally extirpated in the early 20th century by an introduced pathogen, chestnut blight (Cryphonectria parasitica). Because chestnut is fast‐growing, long‐lived, and resistant to decay, restoration of American chestnut using blight‐resistant stock could have the potential to increase carbon sequestration or storage in forested landscapes. However, carbon dynamics are also affected by interspecific competition, succession, natural disturbance, and forest management activities, and it is unknown how chestnut restoration might interact with these other processes. We used the PnET‐Succession extension of the LANDIS‐II forest landscape model to study the implications of chestnut restoration on forest composition and carbon storage in the context of other disturbances, including timber harvest and insect pest outbreaks. Our results imply that it could take a millennium or more for chestnut to fully occupy landscapes without aggressive restoration efforts. When successful, chestnut restoration activities displaced other species approximately in proportion to their abundance on the landscape, rather than replacing a single species or genus (e.g., Quercus). Insect pests increased the rate of chestnut colonization by reducing the abundance of competitors, and also had a dominant effect on carbon dynamics. Although chestnut is fast‐growing, moderately shade‐tolerant, and decomposes very slowly, our results suggest that it can only modestly increase the carbon storage potential of eastern forests. However, our results also demonstrate that compositional changes in forest communities can have noticeable effects on biomass accumulation, even with the large uncertainties introduced by invasive pests.

Climate change impacts on forest landscapes along the Canadian southern boreal forest transition zone

Forest landscapes at the southern boreal forest transition zone are likely to undergo great alterations due to projected changes in regional climate. We projected changes in forest landscapes resulting from four climate scenarios (baseline, RCP 2.6, RCP 4.5 and RCP 8.5), by simulating changes in tree growth and disturbances at the southern edge of Canada’s boreal zone. Projections were performed for four regions located on an east–west gradient using a forest landscape model (LANDIS-II) parameterized using a forest patch model (PICUS). Climate-induced changes in the competitiveness of dominant tree species due to changes in potential growth, and substantial intensification of the fire regime, appear likely to combine in driving major changes in boreal forest landscapes. Resulting cumulative impacts on forest ecosystems would be manifold but key changes would include (i) a strong decrease in the biomass of the dominant boreal species, especially mid- to late-successional conifers; (ii) increases in abundance of some temperate species able to colonize disturbed areas in a warmer climate; (iii) increases in the proportions of pioneer and fire-adapted species in these landscapes and (iv) an overall decrease in productivity and total biomass. The greatest changes would occur under the RCP 8.5 radiative forcing scenario, but some impacts can be expected even with RCP 2.6. Western boreal forests, i.e., those bordering the prairies, are the most vulnerable because of a lack of species adapted to warmer climates and major increases in areas burned. Conservation and forest management planning within the southern boreal transition zone should consider both disturbance- and climate-induced changes in forest communities.

Forest plant community changes in the Spačva lowland area (E Croatia)

The forests in the Spačva Basin are a complex of lowland forests in the region of Slavonia (eastern Croatia). The present state of the forests is strongly influenced by intensive exploitation and hydro-ameliorative activities carried out in the past. The aim of this study was to consider the extent of changes in species composition, and the extent of environmental changes in forest communities of the Spačva Basin in relation to research conducted between 1969 and 1971. The species composition of four communities (Carpino betuli-Quercetum roboris, Genisto elatae-Quercetum roboris aceretosum tatarici, and caricetosum remotae, and Leucojo-Fraxinetum angustifoliae) is studied by comparing 41 old and 57 new relevés. Changes were estimated using ordinations (RDA, CCA, DCA) and changes in species frequency and cover. A general trend of moisture reduction was noticeable among all communities. All vegetation types are becoming floristically more similar. An increase in frequency and cover of flood intolerant woody species (such as Carpinus betulus, Cornus sanguinea, Tilia tomentosa, and Acer tataricum) as well as a decrease of vernal species related to wet habitats are particularly evident. The succession of all studied communities is resulting in loss of the mosaic community pattern characteristic of lowland alluvial forests.

Biotic homogenisation and differentiation along a habitat gradient resulting from the ageing of managed beech stands

Understanding the processes driving biodiversity changes in forest communities helps to better evaluate sustainable forest management methods and their effects on forest ecosystems. This, in turn, is crucial for the appropriate management of protected areas, in particular those covered under the European protection program Natura 2000. Two datasets from the Polish Eastern Carpathians collected in the 1970s and 2000s were compared to analyse the temporal and spatial changes in the species composition of beech forests in a habitat gradient of soil moisture, acidity and fertility. We found that species favouring fertile and alkaline soils, with low ability for vegetative propagation and without a persistent seed bank became less frequent, whilst frequency of good competitors tolerant to lower soil pH and fertility with a persistent seed bank and a capacity for dispersing seeds over long distances increased. Herb layer vegetation on poor and rich soils became less similar in the past 30years, though two opposite processes occurred. In poor habitats, the biotic differentiation of herb layer vegetation prevailed, whilst biotic homogenisation was more important in fertile habitats. It is suggested that the ageing of the managed beech stands might have contributed to these changes through the accumulation of litter, top soil acidification and the lowering of the concentration of nutrients as well as due to altered disturbance regimes in older stands. The observed relationships between biotic homogenisation/differentiation and the habitat gradient indicate that differences in soil conditions not only shape the spatial pattern of the forest vegetation, but also the spatial and temporal patterns of changes in vegetation composition resulting from the ageing of tree stands. Our results also suggest that in spite of continuous management the studied beech forests have only slightly changed in their specific species composition. Moreover, the ageing of tree stands did not necessarily generate better conditions for the conservation of the species richness of herbaceous plants, at least those species that are considered a measure of naturalness in beech forests.

Quantifying deer and turkey leaf litter disturbances in the eastern deciduous forest: have nontrophic effects of consumers been overlooked?

Vertebrate herbivores and omnivores modify forest regeneration not only via direct and indirect trophic pathways, but also via nontrophic pathways such as litter and soil disturbances that may favor the regeneration of some species but not others. Deer are overabundant throughout vast portions of the eastern deciduous forest, and turkeys, once nearly extirpated, are now far more common; their foraging habits disturb litter over large areas, though this has rarely been evaluated. We quantified the size and frequency of litter disturbances created by both deer and turkeys. In addition, we tested the hypothesis that excluding vertebrates via fences would cause a reduction in the abundance and size of litter disturbances. We tested this hypothesis inside and outside six exclosures and adjacent control plots in an old-growth deciduous forest in Pennsylvania. Bare soil patches were ∼60% smaller and between 50% and 90% less abundant inside exclosures. The mean size of turkey litter disturbances was large (mean &gt; 30 m2) and significantly greater than deer disturbances (p = 0.002), though turkey disturbances were less frequent. Our findings should apply broadly and are some of the first to demonstrate the extent of turkey disturbances. In addition, we demonstrate that exclosure studies reduce physical disturbances as well as browsing, both of which may synergistically act to cause changes in forest communities. We also caution that many deer fences exclude other vertebrates such as turkeys, which are important herbivores, seed predators, and major agents of disturbance. Consequently, we argue that studies that use fences to exclude deer should explicitly consider nontrophic indirect effects, particularly leaf disturbances and the potential impact of other large consumers as well (e.g., turkeys).

Impacts of Changing Hydrology and Hurricanes on Forest Structure and Growth Along a Flooding/Elevation Gradient in a South Louisiana Forested Wetland from 1986 to 2009

Alterations to Louisiana’s coastal landscape during the last 200 years have resulted in major changes to the natural hydrologic regime. Hurricane and tornado winds further impact coastal forests by exacerbating conditions that affect community structure, growth, and regeneration. Twenty-three years of study of forested wetlands in the Lake Verret watershed provide an opportunity to relate changes in forest communities to precipitation, drought, storms, and rising water levels. The area had two communities in 1986, but four communities were present by 2009. A major change in community composition occurred in drier sites after Hurricane Andrew (1992), when Chinese tallow (Triadica sebifera) became established. Swamp plots were generally not affected by hurricanes, but composition continued to change as a result of flooding. After Hurricane Andrew, net primary productivity (NPP) declined dramatically until 2001. Subsequent hurricanes in 2004 and 2005 also caused reductions in NPP, but recovery was rapid. Low-lying and transition areas are trending from bottomland communities toward more of a deepwater swamp as baldcypress (Taxodium distichum) and water tupelo (Nyssa aquatica) increase their stature, likely due to the system-wide flooding. Natural ridges are flooded less often and have remained primarily bottomland, though Chinese tallow (Triadica sebiferum) numbers increased following Hurricane Andrew.

Learning from the past: Trends and dynamics in livelihoods of Bolivian forest communities

• Social ecological systems (SES) characterize dynamics of Bolivian forest communities. • Communities experience SES thresholds as multiple social and economic challenges. • Communities confront negative SES feed-backs with new forestry innovations. • Competition, population growth and economic opportunities threaten benign forest extraction. We use social ecological systems theory (SES) to analyse change in forest communities in the northern Bolivian Amazon. SES characterizes interdependent dynamics of social and ecological systems and we hypothesized it to be a useful frame to grasp dynamics of forest communities affected by changes in forest policies, regulations and institutions, as well as economic demands and conservation objectives. We analysed the long-term historical changes since the region became incorporated in the global tropical forest product value chain since the late 19th century and quantitatively analysed changes in 85 forest communities between 1997 and 2009. We collected information on 16 variables related to demographic, productive, and socio-economic characteristics. Results show that forest communities have experienced major changes and have adapted to these changes. Social thresholds, a key concept in SES, are consistent with multiple social economic forces experienced by forest communities. Detrimental feed-back effects of SES can be confronted when innovative exploration mechanisms, such as new productive chains are developed, or the agro-extractive cycles of current productive system are expanded. Competition among households, population growth and more profitable economic opportunities may threaten benign forms of forest products extraction that have persisted through various cycles of internal and external changes.