Dynamics,productivity and species richness of tropical rainforests along elevational and edaphic gradients on Mount Kinabalu,Borneo

We studied the dynamics of nine tropical rainforests on Mount Kinabalu, Borneo, at four elevations (700, 1,700, 2,700 and 3,100 m) on various edaphic conditions for four 2-year periods over 8 years (1995–2003), and examined the relationships with above-ground productivity. Mean growth rate of stem diameter, basal area turnover rate and estimated recruitment rate (using growth rate and size distribution) correlated with productivity among the nine forests in all periods. These rates based on growth rates of surviving stems appeared to be good measures of stand turnover. However, observed recruitment rate and mortality (and turnover rate as mean of these rates) based on direct observation of recruits and deaths did not correlate with productivity in some periods. These rates may not be useful as measures of stand turnover given small sample size and short census interval because they were highly influenced by stochastic fluctuation. A severe drought associated with the 1997–1998 El Niño event inflated mortality and depressed mean growth rate, recruitment rate and basal area turnover rate, but had little effect on the correlations between these rates (except mortality) and productivity. Across broad elevational and edaphic gradients on Mount Kinabalu, forest turnover, productivity and species richness correlated with each other, but the causal interpretation is difficult given the different histories and species pools among forests at different elevations.     

Plant biodiversity and conservation of tropical semi-evergreen forest in the Shervarayan hills of Eastern Ghats, India

Species diversity, density, population structure and dispersion patterns of all trees and lianas (30cm gbh) were inventoried in a tropical semi-evergreen forest in the Shervarayan hills of Eastern Ghats, south India. Such data are necessary for ecosystem conservation of the under-studied Eastern Ghats, as extensive forests here have already been converted to coffee and orange plantations and the landscape changed due to aluminium ore mining and quarrying. Four 1-ha plots were established in Sanyasimalai (SM) reserve forest of the Shervarayan hills, one plot (SM1) located close to mining and quarrying area, two other contiguous plots (SM2 and SM3) located in selective felling area and the fourth (SM4) in a relatively undisturbed forest. These are 1 to 4km apart in the same semi-evergreen forest tract. In the four study plots a total of 3260 stems (mean density 815ha–1) covering 80 species in 71 genera and 44 plant families were recorded. Species richness was greatest in the undisturbed plot SM4 (50), while lowest (33) in the selectively felled site SM2. The forest stand (SM4) was also denser (986 stemsha–1) and more voluminous (basal area 44.3m2ha–1 as compared with the site mean of 35m2ha–1) than the other plots. Four trees, Chionanthus paniculata, Syzygium cumini, Canthium dicoccum and Ligustrum perrottetii dominated the stand, collectively contributing to >50% of the total density. Species richness and stand density decreased with increasing tree girths. The forest stand contained a growing population, but there was considerable variation in basal area distribution between the plots. Trends in species population structure varied, particularly for selective-felled species. Most species exhibited clumped dispersion of individuals both at 0.25ha and 1-ha scales. Variation in plant diversity and abundance are related to site attributes and human impacts.     

Forest aboveground biomass along an elevational transect in Sulawesi,Indonesia, and the role of Fagaceae in tropical montane rain forests

Aim This study investigates how estimated tree aboveground biomass (AGB) of tropical montane rain forests varies with elevation, and how this variation is related to elevational change in floristic composition, phylogenetic community structure and the biogeography of the dominant tree taxa. Location Lore Lindu National Park, Sulawesi, Indonesia. Methods Floristic inventories and stand structural analyses were conducted on 13 plots (each 0.24 ha) in four old‐growth forest stands at 1050, 1400, 1800 and 2400 m a.s.l. (submontane to upper montane elevations). Tree AGB estimates were based on d.b.h., height and wood specific gravity. Phylogenetic diversity and biogeographical patterns were analysed based on tree family composition weighted by AGB. Elevational trends in AGB were compared with other Southeast Asian and Neotropical transect studies (n = 7). Results AGB was invariant from sub‐ to mid‐montane elevation (309–301 Mg ha^?1) and increased slightly to 323 Mg ha^?1 at upper montane elevation. While tree and canopy height decreased, wood specific gravity increased. Magnoliids accounted for most of the AGB at submontane elevations, while eurosids I (including Fagaceae) contributed substantially to AGB at all elevations. Phylogenetic diversity was highest at upper montane elevations, with co‐dominance of tree ferns, Podocarpaceae, Trimeniaceae and asterids/euasterids II, and was lowest at lower/mid‐montane elevations, where Fagaceae contributed > 50% of AGB. Biogeographical patterns showed a progression from dominant tropical families at submontane to tropical Fagaceae (Castanopsis, Lithocarpus) at lower/mid‐montane, and to conifers and Australasian endemics at upper montane elevations. Cross‐continental comparisons revealed an elevational AGB decrease in transects with low/no presence of Fagaceae, but relatively high AGB in montane forests with moderate to high abundance of this family. Main conclusions AGB is determined by both changes in forest structure and shifts in species composition. In our study, these two factors traded off so that there was no net change in AGB, even though there were large changes in forest structure and composition along the elevational gradient. Southeast Asian montane rain forests dominated by Fagaceae constitute important carbon stocks. The importance of biogeography and species traits for biomass estimation should be considered by initiatives to reduce emissions from deforestation and forest degradation (REDD) and in taxon choice in reforestation for carbon offsetting.     

Interactions between Canopy Structure and Herbaceous Biomass along Environmental Gradients in Moist Forest and Dry Miombo Woodland of Tanzania

We have limited understanding of how tropical canopy foliage varies along environmental gradients, and how this may in turn affect forest processes and functions. Here, we analyse the relationships between canopy leaf area index (LAI) and above ground herbaceous biomass (AGB_H) along environmental gradients in a moist forest and miombo woodland in Tanzania. We recorded canopy structure and herbaceous biomass in 100 permanent vegetation plots (20 m × 40 m), stratified by elevation. We quantified tree species richness, evenness, Shannon diversity and predominant height as measures of structural variability, and disturbance (tree stumps), soil nutrients and elevation as indicators of environmental variability. Moist forest and miombo woodland differed substantially with respect to nearly all variables tested. Both structural and environmental variables were found to affect LAI and AGB_H, the latter being additionally dependent on LAI in moist forest but not in miombo, where other factors are limiting. Combining structural and environmental predictors yielded the most powerful models. In moist forest, they explained 76% and 25% of deviance in LAI and AGB_H, respectively. In miombo woodland, they explained 82% and 45% of deviance in LAI and AGB_H. In moist forest, LAI increased non-linearly with predominant height and linearly with tree richness, and decreased with soil nitrogen except under high disturbance. Miombo woodland LAI increased linearly with stem density, soil phosphorous and nitrogen, and decreased linearly with tree species evenness. AGB_H in moist forest decreased with LAI at lower elevations whilst increasing slightly at higher elevations. AGB_H in miombo woodland increased linearly with soil nitrogen and soil pH. Overall, moist forest plots had denser canopies and lower AGB_H compared with miombo plots. Further field studies are encouraged, to disentangle the direct influence of LAI on AGB_H from complex interrelationships between stand structure, environmental gradients and disturbance in African forests and woodlands.     

The influence of historical dispersal on the phylogenetic structure of tree communities in the tropical Andes

We test for evidence of the Tropical Niche Conservatism or the Out of The Tropics hypotheses in structuring patterns of tree community composition along a 2000 + meter elevational gradient in the northern tropical Andes. By collecting and integrating data on the presence–absence of tree species within plots with phylogenetic information, we analyzed the following: (a) patterns of phylogenetic dispersion and species diversity along the elevational gradient based on indexes of net relatedness, nearest taxon relatedness, and species richness (α‐diversity); and (b) the replacement of lineages along the gradient using the PhyloSorensen metric (β‐diversity). More specifically, we established 20 0.25‐ha permanent tree inventory plots between 750 and 2,802 m asl where all individuals with diameter at breast height (DBH) ≥ 10 cm were measured and identified. We then used a series of linear models to test for changes in α and β diversity between plots in relation to elevation. Neither the net relatedness index nor the nearest taxon index showed a significant relationship with elevation. However, there was greater phylogenetic overdispersion at intermediate elevations; this likely reflects the mixing of species with contrasting origins from tropical and temperate lineages. β‐diversity between plots was negatively related to the corresponding difference in elevation, indicating that closely related lineages occupy similar ranges of elevation and temperature. We conclude that the immigration of lineages from extra‐tropical regions has significant effects in determining the phylogenetic structure of tree communities in tropical Andean forests. Abstract in Spanish is available with online material.     

Evaluation of Forest Recovery over Time and Space Using Permanent Plots Monitored over 30 Years in a Jamaican Montane Rain Forest

Conservation of tropical forest biodiversity increasingly depends on its recovery following severe human disturbance. Our ability to measure recovery using current similarity indices suffers from two limitations: different sized individuals are treated as equal, and the indices are proportionate (a community with twice the individuals of every species as compared with the reference community would be assessed as identical). We define an alternative recovery index for trees – the Tanner index, as the mean of the quantitative Bray-Curtis similarity indices of species composition for stem density and for basal area. We used the new index to compare the original (pre-gap) and post-gap composition of five experimental gap plots (each 90–100 m²) and four control plots over 24–35 years in the Blue Mountains of Jamaica. After 24–35 years, these small gaps surrounded by undisturbed forest had recovered 68% of the sum of per species stem density and 29% of the sum of per species basal area, a recovery index of 47%. Four endemic species were especially reduced in density and basal area. With the incorporation of basal area and stem density, our index reduces over-estimations of forest recovery obtained using existing similarity indices (by 24%–41%), and thus yields more accurate estimates of forest conservation status. Finally, our study indicates that the two kinds of comparisons: 1) over time between pre-gap and post-gap composition and 2) over space between gap plots and spatial controls (space-for-time substitution) yield broadly similar results, which supports the value of using space-for-time substitutions in studying forest recovery, at least in this tropical montane forest.     

The determinants of land snail diversity along a tropical elevational gradient: insularity,geometry and niches

Aim We investigated the patterns of species richness in land snails and slugs along a tropical elevational gradient and whether these patterns correlate with area, elevation, geographic constraints, and productivity. We did so both at the scale at which land snail population processes take place and at the coarser scale of elevational zones. Location Mount Kinabalu (4096 m) and the adjacent Mount Tambuyukon (2588 m) in Kinabalu Park, Sabah, Malaysian Borneo. Methods We used an effort‐controlled sampling protocol to determine land snail and slug species richness in 142 plots of 0.04 ha at elevations ranging from 570 to 4096 m. Extents of elevational ranges were determined by interpolation, extended where appropriate at the lower end with data from lowlands outside the study area. We used regression analysis to study the relationships between species density and richness on the one hand and elevation and area on the other. This was done for point data as well as for data combined into 300‐m elevational intervals. Results Species density (based on the individual samples) showed a decline with elevation. Elevational range length profiles revealed that range lengths are reduced at greater elevations and that a Rapoport effect is absent. Diversity showed a mild mid‐domain effect on Kinabalu, but not on Tambuyukon. When the data were combined into 300‐m elevational intervals, richness correlated more strongly with elevation than with area. Ecomorphospace was seen to shrink with increasing elevation. Main conclusions The elevational species richness patterns show the combined effects of (1) reduced niche diversity at elevations with lower productivity and (2) historical events in which the upward migration of lowland species as well as the speciation of highland endemics took place.     

Local and regional dominance of woody plants along an elevational gradient in a tropical montane forest of northwestern Bolivia

The aim of this study was to investigate the dominance patterns of woody plants in a tropical montane forest of northwestern Bolivia and to understand underlying processes at the local and regional scales. We inventoried three elevation ranges: lower (1,200–1,500 m), intermediate (2,000–2,300 m), and upper montane forests (2,800–3,100 m). At each elevation, we inventoried two sites that were ~100 km apart. Specifically, we asked the following questions: (1) are dominant taxa distributed locally, or are they also dominant at larger scales? And (2) is the local importance of shared taxa congruent among sites at the same elevation range? We inventoried 18,876 woody plant individuals with a diameter at breast height ≥2.5 cm belonging to 877 species, 286 genera, and 100 families in 54 0.1-ha plots. A strong floristic congruence was found at the family and genus levels within and across elevations, but not at the species level. The pattern of species dominance for the whole study regions was similar to that reported for similar scales in the Amazonia (10–15 % of species accounted for 50–75 % of individuals), although dominant species were not oligarchic across the whole elevational gradient due to the high environmental heterogeneity. Dominant taxa were shared to a larger degree between sites at the same elevational range than non-dominant taxa, indicating that oligarchy does not mean uniformity. Finally, the shared taxa exhibited similar importance between sites at the lower elevation range but dissimilar importance at the higher elevation range, reflecting an increase in the relative importance of local processes versus regional processes with increasing elevation.     

Ant Diversity and Abundance along an Elevational Gradient in the Philippines1

Ant communities were surveyed along an elevational gradient in the Philippines extending from lowland dipterocarp forest (250 m elevation) to mossy forest (1750 m). Standardized pitfall trapping in arboreal and terrestrial microhabitats at seven sites yielded 51 species. Collecting by hand at five of the sites yielded 48 species. The two methods produced substantially different assemblages, with only 22 species (29%) taken in common. Only a fraction of the total ant community appeared to be sampled at most of the sites. Measures of species richness and relative abundance peaked at mid-elevations and declined sharply with increasing elevation. Ants were extremely rare above 1500 m elevation. Arboreal ants were trapped much less frequently than terrestrial ants at all sites. Ant species that were abundant had broader elevational distributions than those that were less common, but most species were rare and occurred at only one or two sites. The elevational patterns for ants are largely the inverse of those documented for Philippine small mammals which reach their greatest diversity and abundance at high elevations where ants are rare. This suggests that the two groups may interact competitively. Some of the patterns observed or inferred from this study may apply to tropical ant communities in general, and are presented as series of testable hypotheses as a guide and stimulus for future research.     

Changes in tropical forest vegetation along an altitudinal gradient in the Udzungwa Mountains National Park, Tanzania

This study describes changes in woody vegetation in the Mwanihana forest, Udzungwa Mountains National Park, Tanzania, over an altitude range of 470–1700 m. Two methods, fixed‐ and variable‐area plots, are compared to elucidate altitudinal variation in tropical forest structure, diversity and community composition. Six 25 m × 100 m fixed area plots recorded a total of 2143 woody stems of ≥3 cm d.b.h. from 204 species. The 78 variable‐area plots recorded the nearest twenty trees of ≥20 cm d.b.h. to an objectively chosen point, giving a total of 1560 stems in 9.1 ha from 156 species. A linear trend of increasing stem density with altitude was seen for variable‐area plots. Species diversity is highest at high elevations. There was no clear zonation of elevational vegetation types. Restricted range taxa occur at all altitudes sampled. The study also revealed some methodological considerations. Bias in sample size and plot area can be tested by employing two sampling methods. Of the two methods used, fixed area plots are preferred as variable area plots are impractical in tangled understorey. Plot size must be controlled for in order to make reliable observations of diversity. Sampling along a continuous or near‐continuous altitudinal gradient with sufficient replication is also important.     

Phylogenetic community patterns suggest Central Indian tropical dry forests are structured by montane climate refuges

Aim

We used an eco-phylogenetic approach to investigate the diversity and assembly patterns of tropical dry forests (TDFs) in Central India. We aimed at informing conservation and restoration practices in these anthropogenically disturbed forests by identifying potential habitats of conservation significance and elements of regional biodiversity most vulnerable to human impact and climate change.

Location

Tropical dry forests of Madhya Pradesh, Central India.

Methods

We analysed the species richness, stem density, basal area and phylogenetic structure (standardized effect size of MNTD, MPD, PD and community evolutionary distinctiveness cED) of 117 tree species assemblages distributed across a ~230 to ~940 m elevational gradient. We examined how these community measures and taxonomic (Sørensen) and phylogenetic (UniFrac) beta diversity varied with elevation, precipitation, temperature and climatic stress.

Results

Species richness, phylogenetic diversity, stem density and basal area were positively correlated with elevation, with high-elevation plots exhibiting cooler temperatures, higher precipitation and lower stress. High-elevation assemblages also trended towards greater phylogenetic dispersion, which diminished at lower elevations and in drier, more stressful plots. Phylogenetic turnover was observed across the elevation gradient, and species evolutionary distinctiveness increased at lower elevations and under harsher abiotic conditions.

Main Conclusions

Harsher abiotic conditions at low elevations may act as a selective filter on plant lineages, leading to phylogenetically clustered low-diversity assemblages. These assemblages contained more evolutionarily distinct species that may contribute disproportionately to biodiversity. Conversely, milder abiotic conditions at high elevations may serve as refuges for drought-sensitive species, resulting in more diverse assemblages. Conservation practices that prioritize both high- and low-elevation habitats could promote the persistence of evolutionarily distinct species and areas of high biodiversity within the Central Indian landscape. Establishing connectivity between these habitats may provide a range of climatic conditions for species to retreat to or persist within as climates change.     

Tropical montane forest ecotones: climate gradients, natural disturbance, and vegetation zonation in the Cordillera Central, Dominican Republic

Aim We examined relationships between climate–disturbance gradients and patterns of vegetation zonation and ecotones on a subtropical mountain range. Location The study was conducted on the windward slopes of the Cordillera Central, Dominican Republic, where cloud forest appears to shift in a narrow ecotone to monodominant forest of Pinus occidentalis. Methods Climate, disturbance and vegetation data were collected over the elevation range 1100–3100 m and in 50 paired plots along the ecotone. Aerial photographs were georeferenced to a high‐resolution digital elevation model in order to enable the analysis of landscape‐scale patterns of the ecotone. Results A Shipley–Keddy test detected discrete compositional ecotones at 2200 and 2500 m; the distributions of tree species at lower elevations were continuous. The elevation of the ecotone determined with aerial photographs was fairly consistent, namely ± 164 m (SD) over its 124‐km length, but it exhibited significant landscape variation, occurring at a lower elevation in a partially leeward, western zone. The ecotone also occurred significantly lower on ridges than it did in drainage gullies. Ecotone forest structure and composition differed markedly between paired plots. In pine paired plots, the canopy height was 1.7 times higher and the basal area of non‐pine species was 6 times lower than in the cloud forest directly below. Fire evidence was ubiquitous in the pine forest but rare in the abutting cloud forest. Mesoclimate changed discontinuously around the elevation of the ecotone: humidity and cloud formation decreased markedly, and frost frequency increased exponentially. Main conclusions The discreteness of the ecotone was produced primarily by fire. The elevational consistency of the ecotone, however, resulted from the overarching influence of mesoclimate on the elevational patterns of fire occurrence. Declining temperature and precipitation combine with the trade‐wind inversion to create a narrow zone where high‐elevation fires extinguish, enabling fire‐sensitive and fire‐tolerant taxa to abut. Once established, mesotopography and contrasting vegetation physiognomy probably reinforce this boundary through feedbacks on microenvironment and fire likelihood. The prominence of the pine in this study – and of temperate and fire‐tolerant taxa in subtropical montane forests in general – highlights the importance of climate‐disturbance–biogeography interactions in ecotone formation, particularly where fire mediates a dynamic between climate and vegetation.     

Impact of human foraging on tree diversity,composition, and abundance in a tropical rainforest

Tropical forest tree communities are structured by a range of large-scale drivers including elevation, certain high-impact anthropogenic activities (e.g., deforestation), and fires. However, low-impact human activities such as foraging may also be subtly but notably altering the composition of tropical forest tree communities. The study assessed the (i) differences in species diversity, patterns of relative abundance, and pairwise beta diversity between trees with edible and inedible fruits and seeds along an elevation gradient, and (ii) impact of human foraging on the forest tree communities in Oban Division of Cross River National Park, Nigeria. Fifteen permanent 40 by 40 m plots were established along an elevational gradient (120–460 m above mean sea level). All trees of 0.1 m diameter at breast height (dbh) and above were measured, identified, and, with the aid of structured questionnaires, classified into those with edible and inedible fruits/seeds. A total of 35 edible species with density of 128 stems/hectare and basal area of 11.99 m²/hectare, and 109 inedible species with density of 364 stems/hectare and basal area of 22.42 m²/hectare were sampled. However, the evenness of edible and inedible species was similar at pooled and plot levels. For inedible species, there was a positive relationship between pairwise beta diversity and elevation, and this was driven mainly by turnover. In contrast, edible species exhibited a non-significant trend between elevation and beta diversity. Thus, the study showed that human foraging of edible fruits may have subtly influenced patterns of species diversity and community structure in this tropical forest.     

Plant biodiversity inventory and conservation of two tropical dry evergreen forests on the Coromandel coast, south India

Species diversity, population structure, abundance and dispersion patterns of all woody plants 10cm gbh were inventoried in two 1-ha plots of tropical dry evergreen (sacred grove or temple) forests at Kuzhanthaikuppam (KK) and Thirumanikkuzhi (TM) on the Coromandel coast of south India. Site KK is a stunted forest (average tree height ca 6 m) and TM a tall forest (average tree height ca 10 m). A total of 54 species (in 47 genera and 31 families) were recorded. Species richness and stand density were 42 and 38 species and 1367 and 974 individuals ha–1 respectively for the sites KK and TM. About 50% of the total species were common to both the sites. Site TM is twofold more voluminous (basal area 29.48 m2 ha–1) than KK (basal area 15.44 m2 ha–1). Nearly one third of the individuals are multi-stemmed in the low-statured site KK whereas one fourth of the tree density is multi-stemmed in TM. Species abundance pattern varied between the two sites. The abundance of three species in KK and two species in TM is pronounced. Memecylon umbellatum, the most abundant species contributing to one third of total stand density in KK, is least represented in TM. Species richness, density and diversity indices decreased with increasing girth threshold. Most species exhibited clumped dispersion of individuals both at 0.25 and 1-ha scales. Population structure for girth frequency is an expanding one for both the sites, except for basal area distribution in KK. Variations in plant diversity and abundance are related to site attributes and human impacts. In the light of habitat uniqueness, species richness and sacred grove status, the need for conservation is emphasized.     

Altitudinal Change in LAI and Stand Leaf Biomass in Tropical Montane Forests: a Transect Study in Ecuador and a Pan-Tropical Meta-Analysis

Abstract Leaf area index (LAI) is a key parameter controlling plant productivity and biogeochemical fluxes between vegetation and the atmosphere. Tropical forests are thought to have comparably high LAIs; however, precise data are scarce and environmental controls of leaf area in tropical forests are not understood. We studied LAI and stand leaf biomass by optical and leaf mass-related approaches in five tropical montane forests along an elevational transect (1,050–3,060 m a.s.l.) in South Ecuador, and conducted a meta-analysis of LAI and leaf biomass data from tropical montane forests around the globe. Study aims were (1) to assess the applicability of indirect and direct approaches of LAI determination in tropical montane forests, (2) to analyze elevation effects on leaf area, leaf mass, SLA, and leaf lifespan, and (3) to assess the possible consequences of leaf area change with elevation for montane forest productivity. Indirect optical methods of LAI determination appeared to be less reliable in the complex canopies than direct leaf mass-related approaches based on litter trapping and a thorough analysis of leaf lifespan. LAI decreased by 40–60% between 1,000 and 3,000 m in the Ecuador transect and also in the pan-tropical data set. This decrease indicates that canopy carbon gain, that is, carbon source strength, decreases with elevation in tropical montane forests. Average SLA decreased from 88 to 61 cm² g⁻¹ whereas leaf lifespan increased from 16 to 25 mo between 1,050 and 3,060 m in the Ecuador transect. In contrast, stand leaf biomass was much less influenced by elevation. We conclude that elevation has a large influence not only on the leaf traits of trees but also on the LAI of tropical montane forests with soil N (nitrogen) supply presumably being the main controlling factor.     

Tree population dynamics in Kibale National Park, Uganda 1975–1998

Changes in species composition, stem abundance, and basal area of trees taller than or equal to 10 m in a medium altitude tropical rain forest at the Ngogo study area, Kibale National Park, Uganda are described for the period between 1975 and 1998 ( n  = 23 years). Two enumeration episodes were conducted in 263 plots of 5 m by 50 m during 1975–80 and 1997–98. During this period, species richness decreased by 3% (from 92 to 89). Species diversity (H') also declined slightly from 2.97 to 2.86. The number of trees recorded in the sample plots decreased by 8% (from 2545 to 2329), while basal area decreased from 49.48 m² ha⁻¹ to 48.68 m² ha^−1. However, stem abundance and basal area increased for some species.     

三峡水库长期水淹条件下耐淹植物甜根子草的资源分配特征

为研究历经三峡水库长期水淹的驯化后,不同海拔高程之间相同种源的甜根子草的生物量分配特征是否发生改变,进而探讨该物种对水淹胁迫表现出的适应性进化特征,试验于2008年初选育相同种源的甜根子草同龄幼苗栽植于三峡水库消落区甜根子草种植试验示范区,并考察了2012年、2013年不同海拔高程甜根子草植株的形态和生物量特征。试验共设置3个海拔高程,即水淹高程168、172m和不受水淹对照高程176m。试验结果表明:(1)较低高程的甜根子草植株较矮小细弱,168m高程的甜根子草植株主茎长和主茎基径显著低于对照176m高程(P0.05);平均节间长度随高程的降低而缩短;与之相反,主茎长/主茎基径随高程的降低而增大。(2)甜根子草的叶片厚度、叶片长/叶片宽、叶片长/叶鞘长均随海拔高程的降低而减小;与之相反,比叶面积随高程的降低而增大。(3)水淹前,甜根子草近端成熟节间的质量密度随高程的降低而增大;水淹后,其地上存活茎段基部成熟节间的质量密度在各高程之间无显著差异(P0.05)。以上研究结果表明,甜根子草历经三峡水库长期水淹的驯化后,生物量分配特征在不同海拔高程之间发生了改变,表现出了相应的驯化特征。相较于高高程的甜根子草植株而言,低高程的植株生长缓慢,采取低株高下的高向生物量投资策略;对叶的物质投资大部分分配到叶面积的增加、叶鞘的伸长生长和叶片的直立生长上,以加强植株的光合生产。     

Factors that shape the elevational patterns of plant diversity in the Yatsugatake Mountains,Japan

Elevation is involved in determining plant diversity in montane ecosystems. This study examined whether the distribution of plants in the Yatsugatake Mountains, central Japan, substantiated hypotheses associated with an elevational diversity gradient. Species richness of trees, shrubs, herbs, ferns, and bryophytes was investigated in study plots established at 200‐m elevational intervals from 1,800 to 2,800 m. The changes in plant diversity (alpha and beta diversities, plant functional types, and elevational ranges) with elevation were analyzed in relation to climatic factors and elevational diversity gradient hypotheses, that is, mass effect, mid‐domain effect, and Rapoport''s elevational rule. In addition, the elevational patterns of dominance of plant functional types were also analyzed. A comparison of alpha and beta diversities revealed that different plant groups responded variably to elevation; the alpha diversity of trees and ferns decreased, that of herbs increased, whereas the alpha diversity of shrubs and bryophytes showed a U‐shaped relationship and a hump‐shaped pattern. The beta diversity of shrubs, herbs, and bryophytes increased above the subalpine–alpine ecotone. In accordance with these changes, the dominance of evergreen shrubs and graminoids increased above this ecotone, whereas that of evergreen trees and liverworts decreased. None of the plant groups showed a wide elevational range at higher elevations. These elevational patterns of plant groups were explained by climatic factors, and not by elevational diversity gradient hypotheses. Of note, the changes in the dominance of plant groups with elevation can be attributed to plant–plant interactions via competition for light and the changes in physical habitat. These interactions could alter the elevational diversity gradient shaped by climatic factors.     

Tropical moist <Emphasis Type="Italic">Polylepis</Emphasis> stands at the treeline in East Bolivia: the effect of elevation on stand microclimate,above- and below-ground structure,and regeneration

We studied Polylepis forests along an elevational transect between 3,650 and 4,050 m a.s.l. at the treeline of the moist eastern cordillera in Bolivia to examine changes in above- and below-ground stand structure, leaf and root morphology, and regeneration in relation to stand microclimate. Field measurements and model predictions indicated relatively cold growth conditions of the Polylepis forests. Tree height, stem diameter, and basal area of the stands decreased markedly while stem density increased with elevation. Leaf morphology differed between the two occurring Polylepis species, and trees at the treeline had smaller leaves with higher specific leaf area. In contrast, fine root biomass increased from 37 g m⁻² at the lowermost stand to 234 g m⁻² at the treeline. Trees of the uppermost stand had higher specific root surface area and a much higher number of root tips per unit dry mass. Thus, root surface area and total number of root tips per unit ground area increased conspicuously from the lowermost stand to the treeline. Density of young growth inside the forest increased towards the treeline, while density in the open grassland decreased with elevation. Young growth originated from sexual reproduction at the lower forest but was comprised exclusively of root suckers at the treeline stand. We conclude that both the marked change in carbon allocation towards the root system, as well as the changes in root morphology with elevation indicate an adaptation to reduced nutrient supply under cold conditions of these Polylepis stands at the treeline in E Bolivia.

Tree population changes in a tropical dry evergreen forest of south India over a decade (1992–2002)

Changes in species composition and density of trees >10 cm gbh in a tropical dry evergreen forest in Puthupet, south India are interpreted for the period between 1992 and 2002. A 1-ha plot was inventoried in 1992 and was recensused in 2002. During the 10-year interval tree taxa diversity as well as stand density increased, but the basal area value decreased. Tree species richness increased by 21% (from 24 to 29 species) by an addition of eight species and local extinction of three species. The tree density increased just by eight individuals (from 1330 stems ha⁻¹ in 1992 to 1338 ha⁻¹ in 2002), but the basal area decreased by 8% (from 37.5 to 34.5 m² ha⁻¹). Many species (11 numbers) have increased in abundance rather than decreased. Many surviving species seem to have considerable stability in abundance at the local scale. The density of smaller stems (10 29 cm gbh) increased by 15.3%, while that of the larger trees decreased drastically (81.6%). Ninety percent of the missing stems were from the middlestorey of the forest. Tree density changes among the three ecological guilds revealed a decrease in stem density and an increase in basal area in the lowerstorey; while the middlestorey exhibited a reverse trend. Family-wise, tree density changes revealed that the majority of families (67%) showed an increase in stem density. Long-term studies on tree population changes are essential to estimate tree mortality and recruitment rates, which will provide a greater insight in tropical forest dynamics.