Dipterocarpoidae genomics reveal their demography and adaptations to Asian rainforests.

Dipterocarpoideae species form the emergent layer of Asian rainforests. They are the indicator species for Asian rainforest distribution, but they are severely threatened. Here, to understand their adaptation and population decline, we assemble high-quality genomes of seven Dipterocarpoideae species including two autotetraploid species. We estimate the divergence time between Dipterocarpoideae and Malvaceae and within Dipterocarpoideae to be 108.2 (97.8‒118.2) and 88.4 (77.7‒102.9) million years ago, and we identify a whole genome duplication event preceding dipterocarp lineage diversification. We find several genes that showed a signature of selection, likely associated with the adaptation to Asian rainforests. By resequencing of two endangered species, we detect an expansion of effective population size after the last glacial period and a recent sharp decline coinciding with the history of local human activities. Our findings contribute to understanding the diversification and adaptation of dipterocarps and highlight anthropogenic disturbances as a major factor in their endangered status.

[Species composition and community structure of coniferous-broadleaved mixed forest in Xiaolong Mountain, Gansu Province, Northwest China]. / 甘肃小陇山暖温带针阔混交林物种组成和群落结构.

Xiaolong Mountain, located in warm temperate subtropical transition zone, is one of the important biodiversity conservation areas in China. We analyzed species composition, community structure, and habitat preferences of all woody plant species with DBH (diameter at breast height)≥1 cm in a 6 hm2 plot in Xiaolong Mountain, Gansu Province, Northwest China. A total of 29251 individuals (41735 stems) belonging to 33 families, 65 genera, and 124 species were recorded. The 28 species with importance value ≥1 contributed 82.9% to the total abundance. The top four species with the highest importance value were Quercus aliena var. acuteserrata, Betula platyphylla, Lindera aggregata var. playfairii and Corylus heterophylla. The structure of DBH size class of all stems showed an inverse 'J' type, indicating a successful regeneration tendency in the understory. Results from the indicator species analysis showed that 11 species had significant habitat prefe-rences, an two species (Ostrya japonica and Acer stachyophyllum subsp. betulifolium) had the most obvious preferences. Results from the redundancy analysis and partial methods showed that topographic factors played a dominant role in determining species distribution.

[Community structure and species composition in a subtropical evergreen broad-leaved forest in Wuchaoshan, Hangzhou, Zhejiang Province, China].

The numerical classification and ordination of plant communities can reveal the relationship between plant distribution and environment, with implications on vegetation restoration and forest management. Community types were classified using a clustering method based on 45 forest dynamic plots with each area of 0.04 hm2 in Wuchaoshan, Hangzhou, Zhejiang Province, China. The ordination of plant community and the relationship between communities and edaphic variables (soil nutrient availability and topography) were explored using redundancy analysis. Results showed there were three community types in the study area, including Schima superba community type, Quercus fabri-Symplocos anomala community type, and Cyclobalanopsis glauca community type. Stem density and basal area of trees were not significantly different among those community types. Species richness in the C. glauca community was higher than that in S. superba community, but not significantly different from the Q. fabri-S. anomala community. Results from the redundancy analysis showed that community distribution was significantly related to edaphic factors. Topographic and soil factors accounted for 46.4% of the total variation in community distribution while total soil phosphorus, available phosphorus, available potassium, elevation, slope, aspect, and canopy openness had significant effects on community composition. Total soil phosphorus, available potassium, and altitude were the main factors influencing community distribution in Wuchaoshan. 53.6% of the total variation in community distribution were not explained, perhaps due to anthropogenic disturbance.

Variation in three community features across habitat types and scales within a 15-ha subtropical evergreen-deciduous broadleaved mixed forest dynamics plot in China.

The evergreen and deciduous broadleaved mixed forests (EDBMFs) belong to one of the ecosystems most sensitive to environmental change, however, little is known about the environmental determinants for their plant diversity and forest structure at different habitat types and spatial scales. Here, we used data from a 15-ha (300 × 500 m) forest dynamic plot (FDP) of an old-growth EDBMF to examine the patterns and determinants of the three community features (stem abundance, rarefied species richness and basal area [BA]) in three habitat types (ridge, hillside and foothill) and at three spatial scales (20 × 20 m, 50 × 50 m, and 100 × 100 m). We found that the three community features significantly changed with habitat type, but only one of them (rarefied richness) changed with scale. Among spatial scales, the principle environmental factors that widely affected community features were pH, soil organic matter, and total phosphorus, while these effects only taken place at certain habitat. Variations in the three community features explained by soil conditions were generally greater than those explained by topographical conditions. With changes in habitat type, the proportion of variations explained by environmental conditions was 31%-53%, 8%-25%, and 18%-26% for abundance, rarefied richness, and BA, respectively. With increasing spatial scale, the variations explained by environmental conditions were 44%-75% for abundance, 28%-95% for rarefied richness, and 18%-86% for BA. Our study demonstrated that environmental factors had great impacts on the plant diversity and forest structure in the EDBMFs, especially the soil factors such as pH. In addition, the importance of the environmental determinants on these community features was highly related to the spatial scale.

[Geographic variation of seed morphological traits of Picea schrenkiana var. tianschanica in Tianshan Mountains, Xinjiang of Northwest China].

Taking the Picea schrenkiana var. tianschanica forests at three sites with different longitudes (Zhaosu, Tianchi, and Qitai) in Tianshan Mountains as the objects, the cones were collected along an altitudinal gradient to analyze the variation of their seed morphological traits (seed scale length and width, seed scale length/width ratio, seed wing length and width, seed wing length/ width ratio, seed length and width, and seed length/width ratio). All the seed traits except seed width tended to decrease with increasing altitude. The seed traits except seed wing width, seed width, and seed length/width ratio all had significant negative correlations with altitude. Seed scale length and width and seed scale length/width ratio had significant positive correlations with longitude. Seed scale length, seed scale length/width ratio, and seed wing length/width ratio had significant negative correlations with slope degree. No significant correlations were observed between the seed traits except seed wing width and the slope aspect. Altitude was the main factor affecting the seed scale length, seed scale length/width ratio, and seed wing length/width ratio.

[Distribution patterns of Picea schrenkiana var. tianschanica population in Tianshan Mountains].

A vertical transect investigation on Picea schrenkiana var. tianschanica forests was conducted at five different longitudinal sites (Zhaosu, Gongliu, Wusu, Urumqi, and Hami) in Tianshan Mountains, and the distribution pattern of P. schrenkiana var. tianschanica population at each site was analyzed based on theoretical distribution model and aggregation intensity index. On the whole, the P. schrenkiana var. tianschanica population in Tianshan Mountains presented a clumped distribution, and the distribution pattern and clustering intensity were affected by the developmental stages of stem and the ranges of altitude to some degree. The clustering intensity increased with the increasing size (DBH) or developmental stage of stem, and had the highest values at high altitudes.

[Species richness patterns of Picea schrenkiana var. tianschanica communities along an altitudinal gradient at different longitudes in Xinjiang of Northwest China].

The Picea schrenkiana var. tianschanica forest in Zhaosu, Gongliu, Wusu, Urumqi and Hami that covered about 12 longitudes (81 degrees 05'-93 degrees 41.5'E) along the Tianshan Mountains was investigated by using vertical transects to analyze the species richness of the forest along an altitudinal gradient at different longitudes. The results showed that at most longitudinal positions, P. schrenkiana var. tianschanica forest was basically of pure forest, with P. schrenkiana var. tianschanica as the dominant species, very few of other arbor and shrub species, and the species richness of herbs being controlled by the growth of P. schrenkiana var. tianschanica. This forest had the widest distribution, highest canopy density, best growth, and highest stand volume at middle altitudes, resulting in the lowest species richness of herbs. The herb species richness in P. schrenkiana var. tianschanica forest in Tianshan Mountains showed an inverse hump-shaped variation along the altitude, which could be described by the quadratic equation y = ax2 - bx + c (a, b, c > 0).

Seed dynamics in relation to gaps in a tropical montane rainforest of Hainan Island, South China: (II) seed bank.

Spatial and temporal patterns of seed bank dynamics in relation to gaps in an old growth tropical montane rainforest of Hainan Island, South China, were studied over two consecutive years. From June 2001 to June 2003, soil seed bank sampling blocks were taken near each of the four sides of each seed trap and immediately put into a nursery for observation of seedling emergence dynamics in four seasons (each experiment in each season). The abundances of seedlings that emerged from seed banks showed the trend of vine functional group (VFG) > shrub functional group (SFG) > tree functional group (TFG) > herb functional group (HFG), but the trend in species richness of seedlings that emerged from the soil seed banks was TFG > VFG > SFG > HFG. The abundances of seedlings that emerged from seed banks in the three gap zones showed no significant differences, but significant differences did exist for the species richness. The time of sampling or seasons of experiments had significant influences on both the species richness and seedling abundances. The seedling emergence processes of each experiment all revealed the unimodal patterns. Few emergences occurred 1 year after each experiment. Compared with those under closed canopies, the recruitment rates from seed to seedlings and from seedlings to saplings in gaps were higher, but the mortality rates from saplings to big trees were also higher in the gaps.

Spatiotemporal patterns and dynamics of species richness and abundance of woody plant functional groups in a tropical forest landscape of Hainan Island, South China.

Tropical forests are among the most species-diverse ecosystems on Earth. Their structures and ecological functions are complex to understand. Functional group is defined as a group of species that play similar roles in an ecosystem. The functional group approach has been regarded as an effective way of linking the compositions of complex ecosystems with their ecological functions. To understand the variation of functional groups in species-rich ecosystems after disturbance, the present study investigated the spatial pattern and temporal dynamics of woody plants in a typically fragmented natural forest landscape of Hainan Island in South China. The study area was classified into eight landscape types based on vegetation type, disturbance manner and the time of recovery. The woody plant species were aggregated into seven functional groups based on the growth form, successional status and plant size. The results gained from the present study showed that all functional groups, except for the emergent and canopy tree species, were present in all eight landscape types. Each landscape type had different numbers of dominant functional groups. There are similar species richness and stem abundance structure among functional groups between mid-successional clear cut lowland rainforest and old growth tropical coniferous forest. This similarity exists in selective logged lowland rainforest and old-growth lowland rainforest, as well as among landscape types of montane rainforest. The functional groups with the same successional status had similar patterns of species richness and stem abundance ratios among different landscape types. The variation patterns of functional groups along the successional stages in terms of species richness and stem abundance among the tropical lowland rainforest landscape types were more similar to each other than those in the tropical montane rainforest landscape types. This study provides further support for the competition-colonization tradeoff and successional niche theory as opposed to models of neutrality and ecological equivalence.