Changes In Tree Species Diversity Research Articles

Diversity-biomass relationships are shaped by tree mycorrhizal associations and stand structural diversity at different spatial scales

Diversity-biomass relationships (DBRs) in terrestrial ecosystems tend to vary across spatial scales, but, particularly in hyperdiverse forests, the mechanisms driving these trends remain uncertain. Until now, few have simultaneously investigated the connections between tree species diversity, stand structural diversity, mycorrhizal associations, and ecosystem functioning. In addition, DBRs have only been studied at limited spatial scales, with limited focus on the direct and indirect effects of environmental factors. We addressed these research gaps using a 30-ha forest dynamics plot located in Pu’er City, Southwest China. Through piecewise structural equation models, we quantified the direct effects of tree species diversity (α, β, γ), stand structural diversity, mycorrhizal associations (AM, EcM), and the environmental factors (soil fertility and topography), as well as the indirect effects of the environmental factors on aboveground tree biomass across spatial scales ranging from 400 to 230,400 m2. We hypothesized that complex interactions among these factors underpin the variation in DBRs in natural ecosystems across spatial scales. Our results showed that environmental conditions indirectly affected the tree biomass via changes in tree species diversity, and these effects became stronger as the spatial scale increased. At small to moderate spatial scales, environmental factors were more predictive of tree biomass than tree species diversity (or its components); the effects of stand structural diversity on biomass also gradually increased with spatial scale. Conversely, from the intermediate to the largest spatial scales, mycorrhizal associations gradually became the best predictors of DBR dynamics. Our research offers novel empirical evidence demonstrating the importance of environmental conditions, structural diversity, and mycorrhizal associations in shaping cross-scale DBRs. Future comprehensive studies should consider these factors to assess the mechanisms shaping scale-dependent DBRs in complex natural ecosystems.

Recent tree diversity increase in NE Iberian forests following intense management release: A task for animal‐dispersed and drought‐tolerant species

Abstract Under increasing human‐related threats to forests, many studies suggest that increasing tree species diversity may boost forest resilience by enhancing the range of species' responses to disturbances. However, it remains unclear whether passive or active forest management strategies should be applied to increase tree diversity. This issue would benefit from investigating which management and environmental factors, together with species' functional traits, influence temporal changes in tree species diversity. We explored the influence of the bioclimatic region, land‐use history, forest cover, protection, management, forest structure and changes in temperature and precipitation, to explain tree species diversity changes in NE Iberian forests, by comparing 3141 plots from the Spanish National Forest Inventory sampled between 1989 and 2016. Moreover, we assessed which species' functional traits (dispersal habit, drought and shade tolerance) were most relevant for diversity changes. After 27 years, tree species richness and diversity moderately increased in the tree and regeneration layers. This trend occurred mostly in long‐established, non‐recently managed forests and in those with a lower initial basal area. Increasing temperature had negative effects for diversity increase in the tree layer but positive for the regeneration compartment, while decreasing precipitation showed the opposite effects. Tree species with higher drought tolerance, and especially those animal‐dispersed ones arriving from the regional pool, mostly contributed to the local diversity increase. This pattern occurred in all forest types, although the taxonomic array of species varied. Synthesis and applications. The main drivers influencing the passive increase in tree species diversity suggest a primary role of diminishing forest exploitation in this recovery process, fine‐tuned by climatic changes. This ecological scenario has particularly favoured animal‐dispersed tree species with higher drought tolerance, which mostly led the diversity increase. A higher presence of such highly mobile and drought‐tolerant species can be crucial to increase functional diversity and, ultimately, increase forest resilience under future scenarios of greater aridity. In light of these results, management strategies should continue fostering the restoration of diversity in once intensively exploited forests while ensuring the maintenance of the already gained tree species diversity.

Mapping tree species diversity in a typical natural secondary forest by combining multispectral and LiDAR data

Accurate monitoring of tree species diversity is crucial for understanding the dynamic changes in tree species diversity and its relationships with other services and functions in forest ecosystems. Traditional optical remote sensing data have been widely used for monitoring tree species diversity based on the spectral variation hypothesis (SVH). However, this method cannot capture the three-dimensional structural variations in complex species compositions under different stand conditions. In this study, we modeled tree species diversity in terms of spectral variation and stand structural complexity in a typical natural secondary forest in Northeast China by combining Sentinel-2 data and UAV-borne light detection and ranging (LiDAR) point cloud data. First, species diversity indices (including the Shannon index H' and Simpson index D1) were derived from 60 field-measured plots. Second, recursive feature elimination (RFE) was utilized for feature filtering of ten spectral bands and four vegetation indices extracted from Sentinel-2 data and Rao's Q index, as well as eleven features extracted from LiDAR point clouds reflecting the complexity of the stand structure. Subsequently, the random forest method was utilized to fit and predict the relationship between the remote sensing feature set and tree species diversity. The results showed that the use of multisource remote sensing feature set to estimate tree species diversity had the highest accuracy (R2 = 0.44, RMSE = 0.28 for H') compared to the use of only one data source. Moreover, when using a single remote sensing feature set, the estimation accuracy of the optical remote sensing feature set is higher than that of the LiDAR feature set for H' and D1, and the NIRv is the most influential spectral feature. This study clarified the value of spectral variation and productivity heterogeneity embodied in optical remote sensing features for monitoring tree species diversity, as well as evaluating the shortcomings and possibilities of using LiDAR point cloud features independently, and fully confirmed the positive significance of complementary effects between multisource remote sensing feature sets.

Structural and species diversity explain aboveground carbon storage in forests across the United States: Evidence from GEDI and forest inventory data

Since biodiversity often increases ecosystem functioning, changes in tree species diversity could substantially influence terrestrial carbon cycling. Yet much less is known about the relationships between forest structural diversity (i.e., the number and physical arrangement of vegetation elements in a forest) and carbon cycling, and the factors that mediate these relationships. We capitalize on spaceborne lidar data from NASA's Global Ecosystem Dynamics Investigation (GEDI) and on-the-ground forest inventory and analysis (FIA) data from 1796 plots across the contiguous United States to assess relationships among the structural and species diversity of live trees and aboveground carbon storage. We found that carbon storage was more strongly correlated with structural diversity than with species diversity, for both forest inventory-based metrics of structural diversity (e.g., height and DBH diversity) and GEDI-based canopy metrics (i.e., foliage height diversity (FHD)). However, the strength of diversity‑carbon storage relationships was mediated by forest origin and forest types. For both plot-based and GEDI-based metrics, the relationship between structural diversity (i.e., height diversity, DBH diversity, and FHD) and carbon storage was positive in natural forests for all forest types (broadleaf, mixed, conifer). For planted forests, structural diversity showed positive relationships in planted conifer forests but not in planted mixed forests. Species diversity did not show strong associations with carbon storage in natural forests but showed a positive relationship in mixed coniferous-broadleaf planted forests. Although plot-based structural diversity metrics refine our understanding of drivers of forest carbon balances at the plot scale, remotely sensed metrics such as those from GEDI can help extend that understanding to regional/national scales in a spatially continuous manner. Carbon storage showed stronger associations with plot-based structural diversity than with stand age, soil variables, or climate variables. Incorporating structural diversity into management and restoration strategies could help guide efforts to increase carbon storage and mitigate climate change as nature-based solutions.

Monitoring recovery of tree diversity during tropical forest restoration: lessons from long-term trajectories of natural regeneration.

Given the importance of species diversity as a tool for assessing recovery during forest regeneration and active restoration, robust approaches for assessing changes in tree species diversity over time are urgently needed. We assessed changes in tree species diversity during natural regeneration over 12-20 years in eight 1-ha monitoring plots in NE Costa Rica, six second-growth forests and two old-growth reference forests. We used diversity profiles to show successional trajectories in measures of observed, asymptotic and standardized tree diversity and evenness as well as sample completeness. We randomly subsampled 1-ha plot data to evaluate how well smaller spatial subsamples would have captured temporal trajectories. Annual surveys in eight 1-ha plots were missing substantial numbers of rare or infrequent species. Older second-growth sites showed consistent declines in tree diversity, whereas younger sites showed fluctuating patterns or increases. Subsample areas of 0.5 ha or greater were sufficient to infer the diversity of abundant species, but smaller subsamples failed to capture temporal trajectories of species richness and yielded positively biased estimates of evenness. In tropical forest regions with high levels of diversity, species diversity from small sample plots should be assessed using methods that incorporate abundance information and that standardize for sample coverage. This article is part of the theme issue 'Understanding forest landscape restoration: reinforcing scientific foundations for the UN Decade on Ecosystem Restoration'.

Soil Fungal Communities and Enzyme Activities along Local Tree Species Diversity Gradient in Subtropical Evergreen Forest

The majority of studies have found that an increase in tree species diversity can increase the productivity of forest stands thanks to complimentary effects with enhanced resource use efficiency or selection effects; however, it is unclear how tree species diversity affects the soil fungal community and enzyme activities in subtropical evergreen forests. In this study, we used soil high-throughput sequencing to investigate the soil fungal community structure and diversity in the central area of tree clusters in the gradient of tree species richness formed by four possible dominant tree species (Pinus massoniana Lamb., Choerospondias axillaris Roxb., Cyclobalanopsis glauca Thunb. and Lithocarpus glaber Thunb.) in subtropical evergreen broad-leaved forest. The results showed that soil organic carbon content and total nitrogen content were significantly higher in mixed tree clusters, and that soil fungal richness and diversity increased with the increase in tree species diversity (1–3 species). Soil acid phosphatase and urease activity were also enhanced with tree species diversity (p < 0.05). The relative abundance of soil symbiotic fungi (ectomycorrhizal fungi) decreased, while the relative abundance of saprotrophic fungi increased. Redundancy analysis (RDA) revealed that soil acid phosphatase activity was the main factor affecting soil fungal communities and functional guilds, and that soil water content was the main driving force behind fungal trophic modes. In subtropical forests, changes in tree species diversity have altered the soil fungal community structure and trophic modes and functions, accelerating the decomposition of organic matter, increasing nutrient cycling, and perhaps also changing the nutrient absorption of trees.

Changes of tree species diversity in peatland impacted by moderate fire severity at Teluk Meranti, Pelalawan, Riau Province, Indonesia

Abstract. Syaufina L, Hamzah AA. 2021. Changes of tree species diversity in peatland impacted by moderate fire severity at Teluk Meranti, Pelalawan, Riau Province, Indonesia. Biodiversitas 22: 2899-2908. Riau is one of the fire-prone provinces in Indonesia, which contributes to environmental problems not only in the country but also in neighboring countries. Peatland fire occurs annually in the province that causes transboundary haze pollution. Despite being an important threat to biodiversity, study on peatland fire impacts seems limited. The aims of this study are to analyze changes in tree species diversity due to fire and to assess fire severity. The study was conducted at Teluk Meranti Sub-district, Pelalawan District, Riau Province, Indonesia by establishing 18 sample plots in six transect lines for both burned and unburned areas. Fire severity classification was assessed by aggregate scoring of vegetation condition (individual tree damages, burned vegetation severity, and biodiversity) and soil condition (physical properties, chemical properties, and burned peat depth) indicators. The research revealed a significant change in tree species diversity from 24 species (unburned area) to 2 species (burned area) from high diversity index (2.86) to low diversity index (0.57); only 29% of burned trees can survive; average burned peat depth was about 33 cm; a significant difference of soil condition for both areas was observed. The severity of forest fires in Teluk Meranti, Pelalawan, Riau was classified as the moderate category, with a total score of 58.80%.

Spatial heterogeneity of tree diversity response to climate warming in montane forests.

Many studies reported biotic change along a continental warming gradient. However, the temporal and spatial change of tree diversity and their sensitivity to climate warming might differ from region to region. Understanding of the variation among studies with regard to the magnitude of such biotic changes is minimal, especially in montane ecosystems. Our aim is to better understand changes in spatial heterogeneity and temporal dynamics of mountain tree communities under climate warming over the past four decades. In 2017, we resurveyed and recorded all tree species from 107 long‐term monitoring plots that were first studied between 1974 and 1976. These plots were located in montane forests in the Giant Panda National Park (GPNP), China. Our results showed that spatial differences were found in tree species diversity changes response to mean annual temperature change over the past four decades. Tree species richness increased significantly under climate warming in Minshan (MS) and Xiaoxiangling (XXL) with higher warming rate than Qionglai (QLS) and Liangshan (LS). The trees species diversity in MS and XXL were more sensitive to climatic warming. MS and XXL should receive priority protection in the next conservation plan of the GPNP. The GPNP should avoid taking a “one‐size‐fits‐all” approach for diversity conservation due to spatial heterogeneity in plant community dynamics.

Scenario Analysis of Renewable Energy–Biodiversity Nexuses Using a Forest Landscape Model

The introduction of renewable energy (RE) in harmony with nature is essential for building a sustainable society. However, the poorly designed introduction of RE can cause conflicts between energy production and biodiversity conservation. This study conducted a scenario analysis to evaluate potential conflicts in the nexuses between energy and biodiversity for a case study area, the Bekambeushi River watershed located in northeastern Japan. The increasing rate of pastureland abandonment resulting from a decreasing farmer population is a source of great uncertainty in this area. Two alternative sources of RE were selected to utilize these abandoned pasturelands, each taking a contrasting approach to meet targets stipulated by regional energy plans, thereby implying different ecological consequences at the landscape level. Thirty-one RE introduction cases were simulated, comprising a range of pastureland abandonment expansion speeds and ratios of solar photovoltaic (PV) plant installation to biomass energy use. These were superimposed using two IPCC representative concentration pathway (RCP) scenarios, 2.6 and 8.5, resulting in 62 cases that were summarized as three scenarios based on the RE supply–demand balance and the ecological impacts. The LANDIS-II model was used to simulate these scenarios from 2016 to 2100. The results indicate that both the rate of pastureland abandonment and the ratio of the two RE sources had a large impact on changes in tree species diversity and the habitat suitability of raptorial birds. Abandoned pastureland converted to tree biomass energy production shifted to pioneer species-dominated forest. The plant species composition of transitional forests varied between the climate scenarios. The higher temperature of the RCP 8.5 scenario toward 2100 prevented the establishment of Betula platyphylla and altered tree species diversity and the habitat suitability of Ketupa blakistoni blakistoni. Biomass energy utilization produced less energy than the demand but increased the three ecological indicators. Solar PV systems provided more energy than the regional demand, but the three ecological indicators decreased. However, an appropriate mixture of the two RE sources satisfied the regional energy demand and maintained ecological conditions. Our results suggest that land–energy planning should consider energy–biodiversity nexuses to a strike balance between decarbonization and biodiversity conservation.

Changes in tree species diversity, composition and aboveground biomass in areas of fuelwood harvesting in miombo woodland ecosystems of southern Malawi

ABSTRACTFuelwood is an essential forest product for small-holder farmers in the tropics, but fuelwood harvesting may cause forest degradation and impact ecosystem services. Understanding tree species composition, diversity and biomass changes in forests with active fuelwood collection is important for informing sustainable forest harvesting. In the miombo woodlands of southern Malawi, using forest plots, we investigated: 1) if forests with fuelwood harvesting (n = 50) have different tree, sapling and seedling stem density, species diversity, species composition, and aboveground biomass (AGB) than forests with minimal use (n = 36); and 2) if forest product harvesting pressure and access are predictors of tree stem density, diversity and AGB. We found a significant reduction in tree diversity and AGB but not stem density, and different species composition in areas with fuelwood harvesting compared to reference sites. For saplings, stem density was higher and species composition was different in fuelwood harvesting sites. Seedling Shannon index and Simpson’s diversity were lower in fuelwood harvesting sites. Harvesting pressure and access were predictors of AGB and tree stem density. The reduced AGB and tree species diversity may hinder collection of fuelwood and other forest products, and may reduce ecosystem functioning. Exploring the possibility of forest landscape restoration in the area could be beneficial.

Range size and growth temperature influence Eucalyptus species responses to an experimental heatwave.

Understanding forest tree responses to climate warming and heatwaves is important for predicting changes in tree species diversity, forest C uptake, and vegetation-climate interactions. Yet, tree species differences in heatwave tolerance and their plasticity to growth temperature remain poorly understood. In this study, populations of four Eucalyptus species, two with large range sizes and two with comparatively small range sizes, were grown under two temperature treatments (cool and warm) before being exposed to an equivalent experimental heatwave. We tested whether the species with large and small range sizes differed in heatwave tolerance, and whether trees grown under warmer temperatures were more tolerant of heatwave conditions than trees grown under cooler temperatures. Visible heatwave damage was more common and severe in the species with small rather than large range sizes. In general, species that showed less tissue damage maintained higher stomatal conductance, lower leaf temperatures, larger increases in isoprene emissions, and less photosynthetic inhibition than species that showed more damage. Species exhibiting more severe visible damage had larger increases in heat shock proteins (HSPs) and respiratory thermotolerance (Tmax ). Thus, across species, increases in HSPs and Tmax were positively correlated, but inversely related to increases in isoprene emissions. Integration of leaf gas-exchange, isoprene emissions, proteomics, and respiratory thermotolerance measurements provided new insight into mechanisms underlying variability in tree species heatwave tolerance. Importantly, warm-grown seedlings were, surprisingly, more susceptible to heatwave damage than cool-grown seedlings, which could be associated with reduced enzyme concentrations in leaves. We conclude that species with restricted range sizes, along with trees growing under climate warming, may be more vulnerable to heatwaves of the future.

Woody species diversity as an indicator of the forest recovery after shifting cultivation disturbance in the northern Amazon

The Amazon region harbors the most important tropical forest in the world. However, its biodiversity is seriously threatened due to land-use change. Here, we evaluated changes in tree species diversity and composition after shifting cultivation in the northern Amazon forest, Amazon state, Venezuela, through a chronosequence approach. We selected three sites over a 12 km2 extension of an old-growth forest matrix with secondary forest patches of different stand ages. A total 45 plots (each having 20 × 50 m = 1000 m2) were established. At each site, woody plant diversity and the composition of trees having diameter ≥ 5 cm were assessed in four secondary forests (5, 10, 15, and 20 years old stands after shifting cultivation) and in one old-growth forest (>100 years old), and three plots were established in each forest type. Species richness and dissimilarity pairwise beta-diversity metric were calculated for paired plots among different forest types. We analyzed differences in diversity among the four successional stages and the old-growth forest using individual-based approach. Additionally, multivariate analyses were performed to examine differences among the sampled forest areas in terms of species composition along soil gradient. Species richness showed consistently increasing pattern along the succession to old-growth forest. Species richness in the old-growth forest was up to three times higher than in forests at early successional stages. Richness recovery rate in the 20-years old secondary forest two decades after the abandonment of shifting cultivation was on average equal to 70% of the species richness in the old-growth forest. In contrast, the recovery of species composition reached an average 25% in relation to the old-growth forest during the same period. Our results show that the effect of stand age and environmental drivers (i.e., soil properties) determine species diversity along succession. The environmental heterogeneity between successional stages can be analyzed by the differences in floristic composition and beta diversity observed among the analyzed plots. For that reason, we presume that beta diversity is the major determinant of species richness in secondary forests. The proposed approach contributes to the sustainable management of forest communities because it allows estimating the woody species diversity recovering after shifting cultivation disturbance across successional stages.

Biodiversity and climate change: consequences for upper tree line in Slovakia

Abstract Study of the effects of climate change on upper tree limit has mainly focused on the diversity of tree species as a result of the ability of species to tolerate temperature and moisture changes as well as some effects of disturbance regime changes. The tree species diversity changes due to climate change has been analysed via gap model and biodiversity indices. Gap models are individually based on simulations of establishment, growth, and mortality of each tree on the forest plot. Input ecological data for model calculations have been taken from the permanent research plots located in primeval forests in mountainous regions in Slovakia. The results of regional scenarios of the climatic change for the territory of Slovakia have been used, from which the values according to the CGCM3.1 (global) model, KNMI and MPI (regional) models. Model results for conditions of the climate change scenarios suggest a shift of the upper forest limit to the region of the present subalpine zone, in supramontane zone. The most significant tree species diversity changes have been identified for the upper tree line and current belt of dwarf pine (Pinus mugo) occurrence. Hill’s index of biodiversity in the upper forest line increased by 30 – 35% for horizon of 2050, resp. by 45 – 50% modeled for the horizon of 2075. Calculated values of Shannon’s index show an even higher increase due to climate change. For horizon 2050 is a roughly of three fold increase and horizon for 2075 by almost fivefold increase in the value of the index. Results from the gap model indicate the increase of tree species diversity 2 – 2,5 times.

Fundamental shifts of central hardwood forests under climate change

The Central Hardwood Region (CHR) of the United States constitutes one of the most diverse ecoregions in North America and the most extensive temperate deciduous forest in the world. Despite the economic and ecological significance of the CHR, the long-term effects of changes in climate and fire regime on forest structure remain largely unknown. In this study, we developed an integrated Climate-Sensitive Matrix framework to synchronously couple (1) forest dynamics, (2) mean fire interval, (3) population density, and (4) future climate scenarios to study the community and population structure of CHR forests under climate change and associated changes of fire regimes. Using Monte Carlo simulations and coupled forest dynamics-disturbance models, we projected that the CHR would undergo a major shift in forest community structure from the present to year 2100. The fundamental changes would consist of a transition of dominant species from oak and hickory to maple species, reduced species diversity (9.6–11.5%), and substantial declines in stand basal area (55.1–62.0%) and stand volume (56.3–62.4%). These projected changes will have profound ecological and economic implications. Ecologically, changes in tree species diversity favoring maples would alter ecosystem processing of nutrients and subsequent nutrient flows to drainage waters within the region. Habitat change would alter the broad spectrum of organisms relying on the forest, leading to a redistribution of wildlife species, further heightening the risks for endangered species. Economically, the total stumpage value throughout the CHR would be reduced by 54.5–59.8% from approximately $1317 billion to $529–599 billion. On the brink of these fundamental shifts, our study calls for ecologically- and economically-informed conservation and mitigation strategies to better prepare society for the associated changes in ecosystem services and economic benefits derived from CHR forests.

An estimate of climate-related changes in tree species diversity based on the results of forest fund inventory

Changes in the areas of wood and bush species in Russia are characterized based on the data of forest fund inventories for 1988–2009. Criteria are suggested for revealing the extent of climatic influence on the discovered trends. Comparisons with the results of independent field and model investigations are carried out. Climate is ascertained as the evident cause of changes in areas occupied by spruce and oak and as the probable cause of changes in the areas of black alder, poplar, and tree willows.

Changes in tree species diversity and dominance across a disturbance gradient in Nepalese Sal (Shorea robusta Gaertn. f.) forests

Disturbance is often touted as a management tool, as moderate disturbance is believed to enhance diversity; thus an understanding of frequent and fluctuating disturbance regimes in forests and their effects on stand structure, dominance and diversity is very crucial. Here, the effects of different disturbance regimes, along a gradient, on diversity and dominance of five Shorea robusta Gaertn. f.-dominated forests were investigated in 25 one-ha plots in Nepal. A total of 67 tree species were recorded; of which 41 species were encountered in least disturbed and 10 species in heavily disturbed forest. Significant variations among forests were observed for all measures of alpha diversity. Alpha diversity measures declined linearly along a disturbance gradient while dominance increased linearly. Relative basal area of S. robusta increased as the level of disturbance increased, which in turn produced more than two-fold higher important value index in heavily disturbed forest than the least disturbed forest. All alpha diversity measures declined in an order of three with increasing relative basal area of S. robusta. The similarity in species composition between each pair of disturbed forests was generally low (Jaccard’s similarity index < 57%), suggesting a higher Beta diversity. It can be concluded that diversity of Sal forests declines with increasing magnitude of disturbance, which in turn favors a higher dominance of S. robusta. Controlling the population of the dominant species, mainly S. robusta, is recommended to enhance diversity and to achieve multiple-use forest management objectives.

Within community patch dynamics in a tropical montane rain forest of Hainan Island, South China

Abstract According to the forest-growth-cycle theory, forest communities are dynamic, mosaic systems composed of patches in different developmental phases. Based on an investigation in a sample of tropical montane rain forest of Hainan Island in South China, four distinct growth phases or patch types were recognized and patterns of patch mosaics and changes in tree species diversity were studied. Diurnal changes in light and temperature regimes in different patch types of the forest growth cycle were measured and analysed. Our results were as follows: (1) The percentages of different patch types within the sampled forest community were for the gap phase 38.5%, building phase 28.5%, mature phase 27.0% and degenerate phase 6.0%; (2) The change of densities (number of individuals/ha) of trees in the forest growth cycle was mainly caused by the larger sized trees; (3) The changes of species diversity with the forest growth cycle showed a humpback pattern; (4) The average DBH, average height, average basal area at DBH, and average volume of each individual and stand volume all increased with the forest cycle process; (5) Tree species richness and tree density at each phase of the forest cycle were positively correlated; (6) The environmental factors changed significantly, both diurnally and with progress of the forest cycle. Light intensity and soil surface temperature changed more in the gap phase than the other three phases. A framework to explain the mechanism for maintaining biological diversity within the tropical montane forest of Hainan Island is described.

Changes in tree species diversity after successive clearcuts in the Southern Appalachians

A 16 ha watershed in the Coweeta Basin was clearcut in 1939 and 1962. Vegetation was inventoried in 1934 and at about 7-year intervals to 1991. After the first clearcut, tree diversity remained high until after the second cut. Diversity based on density and basal area decreased significantly 14 years after the second clearcut and remained low through 1991. Diversity was highest in the early establishment stage of stand development, then declined at the intermediate stage with canopy closure. Evenness based on basal area declined more than evenness based on density because basal area of Liriodendron tulipifera increased substantially from 1977 to 1991. Trends in diversity were due to changes in evenness rather than changes in species richness.

Two Decades of Change in a Great Smoky Mountains Spruce-Fir Forest

BUSING, R. T., E. E. C. CLEBSCH (Grad. Program in Ecol., Univ. Tennessee, Knoxville, TN 37996-1610), C. C. EAGAR (Uplands Field Research Lab, Great Smoky Mtns. Natl. Park, Gatlinburg, TN 37738) AND E. F. PAULEY (Grad. Program in Ecol., Univ. Tennessee, Knoxville, TN 37996-1610). Two decades of change in a Great Smoky Mountains spruce-fir forest. Bull. Torrey Bot. Club 115: 25-31. 1988.-Two 0.405-ha old-growth spruce-fir forest plots established in the 1960's were resampled in 1986 to quantify changes in stand composition, structure and growth. The plots represented typical middle to upper (1750-1800 m elev.) spruce-fir zone vegetation of the Great Smoky Mountains. Recent balsam woolly adelgid (Adelges piceae Ratz.) infestation had killed almost all Fraser fir (Abiesfraseri (Pursh.) Poir.) canopy trees causing fir basal area reductions of 54 and 97%. Stand basal area decreased by an average of 28%, while red spruce (Picea rubens Sarg.) density and total sapling density increased by 132% and 93%, respectively. Fir density and sapling basal area increased in one plot, but decreased in the other. Spruce basal area values were similar over time. Enhanced radial growth of spruce canopy trees following fir mortality was not indicated by radial growth measurements. Tree species diversity changes were minor and showed no common trend between plots.