Changes in species and phylogenetic diversity in tropical seasonal rainforests on steep karst hillslopes in southwestern China: implications for conservation

1. Methods that assess patterns of phylogenetic relatedness, as well as character distribution and evolution, allow one to infer the ecological processes involved in community assembly. Assuming niche conservatism, assemblages should shift from phylogenetic clustering to evenness with decreasing geographic scale because the relative importance of mechanisms that shape assemblages is hypothesized to be scale-dependent. Whereas habitat filtering is more likely to act at regional scales because of increased habitat heterogeneity that allows sorting of ecologically similar species in contrasting environments, competition is more likely to act at local scales because low habitat heterogeneity provides few opportunities for niche partitioning. 2. We used species lists to assess assemblage composition, data on ecologically-relevant traits, and a molecular phylogeny, to examine the phylogenetic structure of antbird (Thamnophilidae) assemblages at three different geographical scales: regional (ecoregions), intermediate (100-ha plots) and local (mixed-flocks). In addition, we used patterns of phylogenetic beta diversity and beta diversity to separate the factors that structure antbird assemblages at regional scales. 3. Contrary to previous findings, we found a shift from phylogenetic evenness to clustering with decreasing geographical scale. We argue that this does not reject the hypothesis that habitat filtering is the predominant force in regional community assembly, because analyses of trait evolution and structure indicated a lack of niche conservatism in antbirds. 4. In some cases, phylogenetic evenness at regional scales can be an effect of historical biogeographic processes instead of niche-based processes. However, regional patterns of beta diversity and phylogenetic beta diversity suggested that phylogenetic structure in our study cannot be explained by the history of speciation and dispersal of antbirds, further supporting the habitat-filtering hypothesis. 5. Our analyses suggested that competitive interactions might not play an important role locally, which would provide a plausible explanation for the high alpha diversity of antbirds in Amazonia. 6. Finally, we emphasize the importance of including trait information in studies of phylogenetic community structure to adequately assess the mechanisms that determine species co-existence.

Xishuangbanna, located in south Yunnan, southwest China, is the northern border of the tropical zone. It maintains large areas of tropical rainforest called tropical seasonal rainforest. Like most tropical rainforests all over the world, these tropical seasonal rainforests are under high pressure of long_term disturbance caused by forest utilization. Amomum villosum, a shade_tolerant perennial herb, prefers to grow in forest gaps. It is one of the main cash crops of local people as its fruit is widely used in Chinese traditional medicine. It has been widely planted in tropical seasonal rainforest understorey in Xishuangbanna. To promote its growth and fruit yield by raising the light level of habitat, the forest shrub and herb layers are cleaned and about 60% 70% of trees are thinned. As a result, A. villosum planting has become the most serious disturbance to the tropical seasonal rainforest. Net primary productivity ( NPP ) is the primary element of nutrient cycling and energy flow within an ecosystem. It reflects the ability of a plant community to use natural resources. Most of the studies on forest NPP change after disturbance have focused on secondary forest, and few studies report the impact on NPP of forest canopy damage. This paper aims to determine the effect of A. villosum planting on forest NPP , and to study if that disturbance is the current most important limiting factor on NPP of the rainforest in Xishuangbanna. The study was carried out at Menglun, Xishuangbanna. Three primary seasonal rainforest sites and three disturbed rainforest sites with A. villosum plantation were chosen for the study and one 0.25 hm 2 plot was established at each site. All six study sites were distributed along ravines, within 21°55′ 21°59′N,101°08′ 101°13′E and at altitude of 650 800 m. Pometia tomentosa is the dominant tree species of the top tree layers at all research sites. At each plot, all trees and lianas with diameter at breast height ( DBH ) ≥5 cm were numbered and marked at breast height, and their DBH were measured annually. The biomass ( B ) and its annual increment ( ΔB ) of the research plots was estimated using the allometric regression equation relating tree mass to DBH of Xishuangbanna tropical rainforest. The amount of dead wood on all plots was recorded annually. At the same time, 20 litter fall traps were placed at each plot and litter was collected every half month. Leaf herbivory was measured by leaf samples and the total leaf herbivory ( G ) was estimated through annual leaf litterfall. The primary net productivity was calculated using the NPP equation NPP = ΔB+L+G, in which L is annual litterfall together with dead wood. The shrub and herb biomass were determined by the harvest method and their biomass increment was estimated by biomass divided by age. The biomass increment for shrub and herb was approximate to NPP . The results show that the annual mean NPP (mean±SE) of the primary rainforest is 23.47±2.12 t·hm -2 ·a -1 , with 22.04±2.09 t·hm -2 ·a -1 in the tree layer, 0.75±0.08 t·hm -2 ·a -1 in the shrub layer, 0.43±0.05 t·hm -2 ·a -1 in woody liana and 0.25±0.03 t·hm -2 ·a -1 in the herb layer. The allocation of NPP of the tree layer was: for litterfall, 11.75±0.54 t·hm -2 ·a -1 ; for tree fall, 0.62±0.21 t·hm -2 ·a -1 ; for leaf herbivory, 0.66±0.05 t·hm -2 ·a -1 ; and for biomass accumulation, 9.01±2.70 t·hm -2 ·a -1 . Compared to the primary rainforest, the NPP of the tree layer, shrub layer, woody liana and total community of the disturbed rainforest decreased 26.1%, 65.7%, 86.1% and 22.5% respectively, but the herb NPP increased 536% because of the dominance of A. villosum. Similarly, litterfall and biomass accumulation of the tree layer decreased 25.5% and 53.4% respectively. The tree fall increased 356% relative to the primary forest due to the change of microenvironment after disturb

Disentangling the distribution patterns of biodiversity along altitudinal gradients and their drivers has been a hot topic in ecological research. Different forest strata show multiple distribution patterns influenced by different community assembly mechanisms. Here, we measure the dominant ecological processes affecting three forest strata (tree, shrub, and herb layers) along altitudinal gradients. We sampled plants with different forest strata in 21 plots located from 2500 to 3700 m in Lasha Mountain, northwestern Yunnan. The taxonomic alpha diversity of the herb layer showed a monotonic decreasing trend with increasing altitude, while the shrub layer was characterized by a single peak, and the tree layer showed no significant change with increasing altitude. We observed a decreasing pattern of phylogenetic diversity with increasing altitude in the herb layer, whereas phylogenetic diversity did not change in the tree and shrub layers. The phylogenetic structure of these three layers showed the same pattern: phylogenetic clustering at low altitudes and overdispersion at middle and high altitudes. The diversity and phylogenetic structure of the herb layer were driven by climate (average dry season precipitation) and topographic (slope and aspect) factors, while shrub layer diversity was mainly influenced by tree layer richness. Overall, the phylogenetic structure pattern of the three forest strata changed from clustered to overdispersed with increasing altitude, indicating that environmental filtering was the main driver at low altitudes, while interspecific competition dominated at middle and high altitudes.

Changbai pine (Pinus sylvestris var.Sylvestriformis) is an endemic and important tree species in Changbai Mountain. There were only 63 plant species in Changbai pine plantation, where hemicryptophyte was dominant(39.68%). Simpson diversity index was 0.87, Shannon-Wiener diversity index was 2.96, and evenness index was 0.82. Community structure were divided into three layers: tree layer, shrub layer and herb layer. The total biomass and net production were 111.982 t/hm2 and 8942.80 kg/(hm2 a) respectively. The total biomass for tree, shrub and herb layers were 106.150, 2.230, 2.264 t/hm2, accounting for 94.79%, 1.99%, and 2.02%, respectively, and net production for those were 7465, 223, and 1182 kg/(hm2 a), accounting for 83.47%, 2.49%, and 13.22% of the total respectively. The nutrient content in various organs is in the order of needle> branch> root> bark> trunk, For the assimilated organ, the nutrient content is in the order of N> K> Ca> P> Mg, and that in absorption organ is in the order of Ca> N> K> P> Mg. For the whole plantation ecosystem, nutrient content is in the order of soil> litter> herb layer> shrub layer> tree layer. Nutrient storage and its accumulation rate in tree layer take up 88.79% and 76.43% of the total, respectively.

村落文化林与非文化林多尺度物种多样性加性分配

In order to examine the nutrient content, and the distribution and accumulation patterns of individual nutrients in the natural secondary forests (NSFs), sample NSF plots were selected in the Caijiachuan watershed on the Loess Plateau. On the basis of a comprehensive field inventory to the NSFs in Caijiachuan watershed, a 40 m × 40 m sample plot was selected as the representative plot. Each tree plant was then measured to select the standard tree in accordance with a diameter-scale. For measurement of the biomass in the above-ground part of the tree, it was divided into parts and measured. The study measured the concentration of the 5 major macronutrients (namely N, P, K, Ca and Mg) and the 8 major micronutrients (namely Cd, Fe, Mn, Cu, Zn, Pb, Ni and B) in plant organs. An appropriate amount of the samples were weighed and exposed to H2SO4-H2O2 using the Kjeldahl heating digestion method. While N content was measured with the semi-micro determination method, P content was measured using vanadium molybdate yellow colorimetric method HNO3-HClO4 ICP heating digestion method was applied to determine the contents of Ca, Mg, K, Na, Fe, Cu, Zn, Mn, B, Cd, Pb, Ni. As for soil samples, corresponding approaches were employed to work out the contents of each of the above-mentioned nutrient elements. Among the tree, shrub and herbaceous layers, the content of macro-nutrients follows the sequence of Ca > N > K > Mg > P, compared with their counterpart of K > N > Ca > P > Mg in the litter layer. For the micronutrient contents, similar sequences (i.e., Fe > Mn > Zn > B > Cu > Pb > Ni > Cd) were observed in the tree, shrub and litter layers; whereas the herbaceous layer demonstrated a different sequence of Fe > Mn > B > Zn > Cu > Pb > Ni > Cd. Within the NSF ecosystem, total accumulation of the 5 major macronutrients (excluding that in the soil) reached 1089.82 kg/ha, of which the tree layer took up the largest share, 40.82%, followed in turn by the shrub layer (31.28%), the herbaceous layer (12.55%) and the litter layer (15.36%). In terms of nutrient-concentration in the plant organs within the tree layer, the overall sequence can be expressed as branches > roots > wood > bark > leaves. The total accumulation of the 5 major macro-nutrient in the soil reached 634.97 t/ha. In terms of the accumulation coefficients in each of the layers, the general pattern can be summed up as: shrub layer > tree layer > herbaceous layer, and N > P > Ca > K > Mg. In terms of the plant organ accumulation coefficients at the tree layer, the sequence was leaves > branches > roots > bark > wood. As for the accumulation coefficients of the micronutrients, the overall sequences for the tree layer, the shrub layer and the herbaceous layer can be listed as Cd > B > Zn > Cu > Mn > Ni > Pb > Fe; Cd > B > Zn > Mn > Cu > Ni >Pb > Fe and Cd > B > Mn > Zn > Cu > Ni > Pb > Fe, respectively. The study also revealed that the macronutrients that are absorbed, assimilated and returned by the NSF stand annually reached 99.054kg/(ha·year), 49.155 kg/(ha·year) and 49.899 kg/(ha·year), respectively, demonstrating a well-balanced state of nutrient cycling. With an average of 0.0013, the absorbance index of the macro-nutrients was ranked in the following sequence, N > P > K > Ca > Mg; whereas their utilization and cycling indexes were respectively sequenced as K > P > N > Mg > Ca and K > P > N > Mg > Ca. For the micronutrients the corresponding annual figures were 117.35 g/(ha·year), 50.96 g/(ha·year) and 66.39 g/(ha·year), respectively. The micronutrients, as a whole, showed a relatively small absorbance index (e.g.,Cd was the largest =0.0036). The average utilization index of all the microelements was 0.12.

Forest ecosystem carbon (C) storage primarily includes vegetation layers C storage, litter C storage, and soil C storage. The precise assessment of forest ecosystem C storage is a major concern that has drawn widespread attention in global climate change worldwide. This study explored the C storage of different layers of the forest ecosystem and the nutrient enrichment capacity of the vegetation layer to the soil in the Castanopsis eyeri natural forest ecosystem (CEF) present in the northeastern Hunan province, central China. The direct field measurements were used for the estimations. Results illustrate that trunk biomass distribution was 48.42% and 62.32% in younger and over-mature trees, respectively. The combined biomass of the understory shrub, herb, and litter layers was 10.46 t·hm-2, accounting for only 2.72% of the total forest biomass. On average, C content increased with the tree age increment. The C content of tree, shrub, and herb layers was 45.68%, 43.08%, and 35.76%, respectively. Litter C content was higher in the undecomposed litter (44.07 %). Soil C content continually decreased as the soil depth increased, and almost half of soil C was stored in the upper soil layer. Total C stored in CEF was 329.70 t·hm-2 and it follows the order: tree layer > soil layer > litter layer > shrub layer > herb layer, with C storage distribution of 51.07%, 47.80%, 0.78%, 0.25%, and 0.10%, respectively. Macronutrient enrichment capacity from vegetation layers to soil was highest in the herb layer and lowest in the tree layer, whereas no consistent patterns were observed for trace elements. This study will help understand the production mechanism and ecological process of the C. eyeri natural forest ecosystem and provide the basics for future research on climate mitigation, nutrient cycling, and energy exchange in developing and utilizing sub-tropical vegetation.

Trait and evolutionary differences among coexisting species are increasingly used to comprehend the processes shaping communities. However, they do not consistently yield congruent insights due to methodological limitations and scale dependence. Utilizing two plastid DNA genes (rbcL and matK) and one nuclear DNA gene (internal transcribed spacer, ITS), we first constructed the phylogenies of 147 woody species from 98 line transects in the forest areas of the Loess Plateau and subsequently measured three functional traits. Five plots (2500 m2) were constructed within Quercus forests to analyze the functional and phylogenetic structures at three spatial scales (100, 400, 2500 m2) and two vertical structural layers (tree colonization and shrub layer). In contrast to the phylogenetic convergence observed at the genus level, using plant DNA barcodes, we found that the entire forest communities and the tree layer exhibited phylogenetic randomness across all three spatial scales; even the shrub layer showed phylogenetic overdispersion with increasing scale. Specific leaf area (SLA) exhibited functional convergence in both the shrub and tree layers. In contrast, seed mass (SM) and plant height (PH) displayed distinct functional structures. In the tree layer, these traits showed phylogenetic overdispersion, while in the shrub layer, they demonstrated functional convergence. This contrast highlights the different ecological roles and processes at play in the two layers. Specifically, the scale dependency of assembly patterns in the shrub layer was more pronounced than in the tree layer for both functional and phylogenetic structures. Our findings underscore the significance of employing DNA barcodes to assess the phylogenetic structure of communities with closely related coexisting species and emphasize niche-based functional assembly and multi-process phylogenetic assembly among vertical structural layers in the Quercus community. Decoupling functional and phylogenetic disparities between species could facilitate the understanding of complex species differences influencing community assembly.

Еловые леса Ижорской возвышенности (Ленинградская область): типология и современное состояние

Aims Determination of species abundance distribution is important in research on species diversity. Our major objective was to determine species abundance distribution models to advance understanding of distribution mechanisms and to assist preservation of biological diversity. Methods Based on data collected from field surveys, we examined the species abundance patterns of tree, shrub and herb layers in Pinus tabulaeformis forest in Huoshan Mountain, Shanxi Province. We used niche preemption (NPM), broken stick (BSM) and overlapping niche (ONM) models and two species abundance statistical models (log-series distribution model (LSD) and log-normal distribution model (LN)) and neutral theory model (NT). The simulation effects were verified by Chi-square tests, Likelihood-ratios (L-R) tests, Kolmogorov-Smirnov (K-S) tests and Akaike Information Criterion (AIC). Important findings The best niche model for the tree layer is NPM, because it had the smallest AIC value and no significant difference (p > 0.05) between the theory predictions and observed species abundance distributions. The next best is ONM; BSM does not fit the tree layer. All three niche models are suitable for the shrub layer. ONM is the best for the herb layer, followed by BSM and NPM. LSD is good for understanding distribution mechanisms in Pinus tabulaeformis forest. LN can fit both the herb and shrub layers, but not the tree layer. NT cannot explain any layer. These findings indicate that the community has relatively few dense species and more sparse species, the species richness and diversity indices of the tree and shrub layers are much smaller than those of the herb layer, and the community evenness is relatively smaller. We conclude that one model cannot fit differ- ent data but that more than one model can fit the same data even for the same layer. Therefore, we should choose different models to study the species abundances of forest communities. We suggest that these methods might be useful for the protection of the biodiversity of forest dominated by Pinus tabulaeformis.

Novel evidence from Taxus fuana forests for niche-neutral process assembling community

Phylogenetic α- and β-diversity elevational gradients reveal consistent patterns of temperate forest community structure

Ostrya multinervis is an endangered species to China. To understand the O. multinervis plant community's structural characteristics and species diversity so as to protect this rare and endangered plant. A survey of the community structure and species diversity of O. multinervis was conducted through quadrat sampling at Shiyang Forest Farm, Wencheng County, Zhejiang Province. Using permanent plots and the technique of examining every individual, all trees in quadrats established in the community to quantify the community structural characteristics were identified and measured. Analysis included the Shannon-Wiener, Simpson, and Pielou indexes. Results showed 40 families, 52 genera, and 60 species of vascular plants with eight species of pteridophyte belonging to seven genera in six families, one species of gymnosperms belonging to one genus in one family, and 51 species of angiosperms belonging to 44 genera in 33 families. The vertical structure was composed of three layers:tree layer, shrub layer, and herb layer, in which O. multinervis was the dominant species in the tree layer, Illicium lanceolatum was the dominant species in the shrub layer, and Diplopterygium glaucum was the dominant species in the herb layer. Overall, phanerophytes accounted for the greatest number (41.7%). Species richness for the shrub layer was the largest of the three communities with the Shannon-Wiener, Simpson, and Pielou indexes larger than herb and tree layers(P < 0.05). Tree height distribution in the tree layer for whole trees was relatively uniform, the diameter order was an inverse J type species distribution, and tree height and diameter structure showed near normal distributions for O. multinervis. In summary, O. multinervis communities had a high species diversity and community stability, but were endangered by a lack of young individuals which could be overcome with closure of hillsides to facilitate afforestation, strengthening of research on highly efficient breeding technologies for O. multinervis, and implementation of artificial rearing measures to ensure a normal development of the population.

Soil factors rather than stand age drive tree phylogenetic diversity along Amazon Forest succession

Species diversity is a key indicator of community composition with its spatial pattern and basic causes being important components of species diversity research. To study changing trends in species diversity on various scales, for characteristics of species diversity at all forest layers based on different scales, and for relationships between tree structure and species diversity of undergrowth vegetation, a 1 hm2 plot of Pinus tabulaiformis mixed forest on Huanglong Mountain was utilized. Analysis was conducted with Richness, Pielou, Simpson, and Shannon-Wiener Diversity Indexes. Also, the relationship between density and mingling degree of tree layers as well as species diversity indexes of shrub and herb layers were analyzed with a grey relational analysis. Results showed that （1） as the scale increased, the Richness had no clear trend, whereas Simpson, Shannon-Wiener and Pielou Diversity Indexes all stabilized after a certain scale, with their spatial variation decreased. （2） At scales of 5 000 m2 and larger, diversity index relationships between varying layers remained unchanged with the shrub layer having the greatest species diversity. The herb layer had the lowest species richness with higher uniformity for species distribution than tree layers. （3） The grey relational analysis showed that the structure of the tree layer was related to species diversity of the shrub and herb layers. The results showed that sampling scale should be taken into account when studying species diversity in a Pinus tabulaeformis mixed forest.［Ch, 2 fig. 3 tab. 30 ref.］