Ecological Research On Population And Community Stability In Karst Forest Vegetation

Karst forest in Maolan of southeastern Guizhou is a specific forest ecosystem. The mixed evergreen and deciduous broadleaf forest is an azonal climax community in the karst area, which has the important research value in the field of azonal vegetation at the same latitude in China or even in the world. This forest has the specific habitat, complex community structure and rich biodiversity, providing an ideal place for ecological study under the karst geological background. The two 1 hm2 (100m×100m) plots were set up using the DQL-1 forest compass in Maolan National Nature Reserve. Each plot was divided into 100 contiguous 10m×1Om quadrats. All free-standing woody plants, including lianas and vines, with≥1 cm diameter at breast height (DBH) were investigated. The species names, relative location of each individual, DBH, height, crown width (the greatest diameter of the vertical projection of the crown in two directions, i.e. north-south or east-west), survival status (living or dead) and microhabitat (e.g. soil surface, rocky surface, rocky gully, rocky-soil surface, and rocky crevice) were recorded The paper analyzed the population ecology and community stability of karst forest using statistics method such as dominance index, diversity index, Godron method, O-ring statistics, the Pielou's coefficient of segregation, Geostatistic, TWINSPAN and DCCA. These would provide important theoretical guide to quick vegetation recovery and ecological restoration in karst forest of southwestern China. The main results are as follows:1. The general characteristics of old-growth karst forests communities in MaolanThe species composition and population structure were investigated in karst old-growth forest in Maolan National Nature Reserve. The topography of P1 plot is complicated and heterogeneous. It is located in Dongge site on a steep southeast-facing slope, rock outcrops occur on almost the entire plot (ca.85%of the ground surface). The soils are slightly alkaline and shallow. There are 4281 genotype individuals, belonging to 199 species,140 genera and 65 families in P1 plot. There are mainly Platycarya longipes, Celtis biondii, Acer wangchii, Clausena dunniana, Cyclobalanopsis glauca, Carpinus pubescens, Viburnum brachybotryum and Pittosporum crispulum. In the P2 plot, two slopes facing the southeast and the northeast, respectively, are included. The topography is only gently sloping in the lower and higher altitudes, and rather moderate or steep at middle altitude. The mean slope is ca.30°. Relatively fewer outcrops occur in this plot, and the rocks occupy mainly in mid-lower part of the plot. The soils are slightly acidic to neutral and relatively thick. There are 3857 genotype individuals, belonging to 191 species,121 genera and 58 families in P2 plot. It is dominated by Castanopsis carlesii var. spinulosa, Cyclobalanopsis myrsinaefolia, Platycarya longipes, Distylium myricoides, Rhododendron latoucheae, Osmanthus fragrans, P.longipes, Engelhardtia roxburghiana and C. pubescens. Its floristic composition is mainly tropical floristic elements dominated in the community, reflecting the tropical and subtropical nature. The evergreen element in the two communities is dominant, but deciduous leaf element is also in a certain proportion, which indicates that the mixed evergreen-deciduous broad-leaved forests are the main climax community in Maolan karst region. Community physiognomy was characterized mainly by mixed evergreen and deciduous broadleaf mesophaenerophytes and microphanerophytes with small-sized, single, leathery leaves. The vertical structure of the forest is clear; there are three layers from the top of the canopy to the ground floor, two tree layers, one shrub layer and one herb layer. The structure of DBH size class of all species in the two plots generally appears reverse "J" shape, which indicates successful community regeneration. The spatial distribution patterns of six dominant species in the two plots are generally aggregated in different spatial scales and varied with the DBH size classes.2. Identification of the woody plant key-stone species and the structure and spatial pattern of the key species in karst forest of MaolanBased on investigation of two plots in a karst forest, we classified woody plant functional groups based on leaf trait and life form. Keystone species within each functional group were identified using a dominance index (DI). The result showed that identification of keystone species within evergreen shrub, evergreen liana, deciduous shrub and deciduous liana functional groups were clearer than within evergreen tree and deciduous tree functional groups.The O-ring statistics were used to characterize the spatial patterns and interspecific associations of main dominant tree species in two 1-ha old-growth karst forest plots in Maolan National Natural Reserve, southwestern China. We found that most of twelve key tree species in two forests were continuously regenerating populations. Nine species (Platycarya longipes, Acer wangchii, Clausena dunniana, Viburnum brachybotryum, Cyclobalanopsis glauca, Castanopsis carlesii var. spinulosa, Distylium myricoides, Rhododendron latoucheae and Platycarya longipes) exhibited significantly aggregations at the majority of scales while others (Celtis biondii, Cyclobalanopsis myrsinaefolia and Carpinus pubescens) showed a random distribution pattern at most scales. Negative association was a dominant pattern for most species pairs in the two plots, while positive associations were found at most scales for only five species pairs. Results also indicated that the two main factors of habitat complexity and heterogeneity-the elevation and rock-bareness rate-play important roles in determining spatial distribution patterns and interspecific associations of tree species in karst forests of Maolan. Thus, the observed spatial patterns among the twelve tree species are influenced by habitat heterogeneity in the context of karst topographical variations. The partitioning of habitat niches contributes to the promoting species coexistence and stability of communities in species-rich karst forests.3. Species diversity and community stabillity in Maolan ksrst forestKarst forest in Maolan has rich biodiversity and the two plots have higher diversity index. This study analyzes the effect of spatial scale on species abundance and richness in two 1-ha karst forest plot in the Maolan, southwest China. The result showed that species abundance and richness depend not only on spatial scales, but also on study area, and such a regional pattern was scale-dependent. Variance of the species abundance increased with increasing scale, while variance of the species richness was unimodal with increasing scale; the coefficient of variation of species abundance and richness decreased with increasing scale. Habitat heterogeneity played an important role in construction of forest community structure. Community stability of two karst forest was studied by using the Godron method. The cross points between the species proposition lines (x) and accumulation relative frequency lines (y) were located close to the stabilizing point (20/80), indicating a typical stability state of the two forest communities. Two plots with rich species diversity, to a certain extent, reflect also the stability of communities.4. Interspecific segregation of old-growth karst forests in MaolanThe distribution map of 43 trees with abundance≥20 individuals from two karst forest communities were drawn using the GIS software (ArcGIS). The nearest neighbors of each individual and the distances between every individual-neighbor pair were obtained by using ArcGIS's extension module. The interspecific segregation in the multi-species community was then studied with a sub-table method of an N×N nearest-neighbor contingency table. The Pielou's coefficient of segregation (S) was adopted to measure the segregated degree between two species. The results show that segregation relations between most of the species are random in two karst forests communities (60.91%and 63.34%, respectively). Some species pairs are positively segregated (38.76%and 35.66%, respectively) and a few pairs are negatively segregated (0.33%and 1.0%, respectively). Our results support the Pielou's opinion that negative segregation is rare in old-growth plant communities. This showed that interspecific competitive exclusion is weakened between the species, and the two forests were at a stable climax stage. According to their adaptability to the environment and relationships between plants and environment, the 43 species from two forest plots were divided into three ecological species groups. The ecological characteristics and habitat preference of the species in each group showed significant differences. The results also indicated that interspecific segregation is closely related to habitat heterogeneity of karst terrain. Species pairs in different habitats mostly tend to be more positively segregated, but species with similar habitat preference or widely distributed are more likely to be random neighbor or negatively segregated. Therefore, interspecific relationship based on differentiation of habitat may be one of the important mechanisms of species coexistence in species-rich karst forest.5. Spatial heterogeneity of soil nutrients and nutrient element contents in plants in Maolan karst forestClassic statistics and geostatistic was used to study the spatial variability of soil nutrients in two karst forest in Maolan. The results showed that the quantity of soil nutrient are high both the plots, and the highest nutrient content was P1 plot. The most of soil nutrients showed moderate variation in both the plots. Analysis of semi-variograms revealed that soil nutrient content had good spatial autocorrelation in both the plots, clear patches with well continuum, but its spatial heterogeneity differed. Topography, high heterogeneity of micro-habitat and Vegetation were the main fators caused the differences of the spatial distribution patterns of soil nutrients in the Reserve, and topography was the important influencing factors on the spatial and temporal variability and distribution patterns of soil nutrients of the two karst forest plots. The element contents of plant of two plots are characterized as being of "Ca>K>Mg" type, indicating that the plants of karst area have the characteristic of high concentration of Ca. The obvious relationship was found between the plant elements and soil nutrient contents in two forests, indicating the nutrient contents in the plant was affected by the siol conditions, and meanwhile, is the result of long-term adaptive evolution in the special karst habitat.6. Gradient analysis and environmental interpretation of woody plant communities in Maolan karst forestThe two forest communities were classified into 4 eco-types, respectively, by TWINSPAN. In plot P1, along the first DCCA axis, the pattern of communities is from primary sub-climax forest with shade-tolerant plants towards primary climax forests with shade-intolerant and drought resistance plants, an increase of topography factors and a steady decline in major soil nutrients. In plot P2, along the first DCCA axis, the pattern of communities is from primary forest with shade-intolerant and drought resistance plants towards primary forests with shade-tolerant plants, accompanying a shift from sunny to shady or semi-shady slopes, an increase of elevation, a steady decline in the ratio of bare rocks in the ground cover and major soil nutrients. Through the study of relationships between vegetation and its environmental variables, niche differentiation mechanism may play a key role in maintenance of species diversity in Maolan karst forest, thus ensuring the stability of karst forest communities.