RESUMO
Shrub is an important part of forest ecosystem. Exploring the species composition, structure and spatial distribution of shrub layer can lay an important foundation for further clarifying the mechanisms underlying species coexistence, biodiversity maintenance and community succession. In this study, species composition, spatial distribution, and species diversity of shrub layer were analyzed in 25 hm2 of Huangguan forest plot. A total of 20716 individual shrubs (with 10463 branches) were recorded in the plot, belonging to 54 species, 45 genera, 28 families. The status of dominant species in the shrub layer was not obvious, with all the importance values being less than 10. The diameter structure of shrub layer vegetation was inverted 'J' type. Shrubs showed aggregated distribution in the plot, with obvious altitude differences in spatial distribution. The diameter structure and spatial distribution of the nine shrub species with the largest abundance in the plot were consistent with the overall situation of shrub layer. With increasing altitude, the Shannon diversity index (H) and Simpson dominance index (D) did not change significantly, while the Pielou evenness index (E) decreased. Those indices decreased with the increases of the abundance of dominant species in tree layer, and E increased with the increase of the number of dominant species in sub-tree layer. The indices of H, D, E were significantly negatively correlated with soil total phosphorus (TP). The H index was significantly positively correlated with soil pH, and the E index was significantly positively correlated with soil total potassium. The shrub layer was rich in species, stable in community structure and well regenerated. The species diversity of shrub layer was mainly affected by the number of dominant species in the tree layer, soil pH, and TP.
Assuntos
Ecossistema , Florestas , Biodiversidade , China , Humanos , Fósforo , Solo , ÁrvoresRESUMO
The objective of this study was to analyze the dynamic characteristics of seed rain on abandoned slopes in the hilly-gullied Loess Plateau region and identify the relationship between seed rain and standing vegetation. Three abandoned slopes were chosen as sampling sites in Zhifanggou watershed. Thirty traps were installed at each site to collect seed rain from October 2010 to April 2013. Standing vegetation was surveyed to identify dominant species in August 2011 and 2012, respectively. Thirty-seven species belonging to seventeen families were identified in the seed rain, and the dominant species, i.e., Lespedeza davurica, Astragalus scaberrimus, Setaria viridis, Cleistogenes squarrosa, Stipa bungeana, Bothriochloa ischcemum, Artemisia scoparia, A. gmelinii, and Heteropappus altaicus, took up to 95.8% of the total seed rain. Three species in seed rain were not found in the standing vegetation. The Sorensen similarity index between seed rain and standing vegetation was 0.77. Seed rain densities were 3737 and 6449 seeds · m(-2) in May 2011-April 2012 and May 2012-April 2013, respectively, and alternate bearing existed. During the study period, seed rain from different positions varied from 3853 to 37923 seeds · m(-2) and belonged to 7-15 species. The results indicated the space limitation of seed dispersal. Seed rain densities were in the middle of the pack compared with similar ecosystems in other studies. High temporal and spatial heterogeneity of seed rain was observed because of rainfall, microtopography and so on.