干旱区生态环境知识资源中心

We tested the hypothesis that diversity and productivity of herbaceous plane communities in disturbed soil are related to the physical and biological heterogeneity of the landscape. Our study was carried out on vegetation responses in porcupine diggings on a rocky slope in the central Negev desert in Israel. We measured aboveground biomass and plant density per species in 150 porcupine diggings (15 cm deep and 15 to 20 cm wide) and in equally sized adjacent control samples in the undisturbed soil matrix. We calculated mean annual biomass production, plant density and species richness for 10 sample areas along the slope. In addition, we divided the plants into groups according to propagule size and dispersal mode. We denoted two types of landscape heterogeneity, which we called physical and biological patchiness. Physical patchiness was measured as the ratio of bare rock to soil surface. Biological patchiness was the area of the soil covered by shrubs with associated soil mound and understory relative to the total soil surface. We also measured disturbance density, as the long term (17 yr) average density of newly made porcupine diggings. We found that 1) the physical patchiness explained 30% of the variation of biological patchiness along the slope, while 2) the patterns of disturbance intensity and biological patchiness were similar (R(2)=0.386). 3) Biomass, density and species richness were significantly higher in diggings than in the soil matrix. 4) Plant density in the matrix, but not in the diggings, was significantly correlated with physical patchiness, 5) species richness in diggings was significantly correlated with biological patchiness, but 6) biomass production in diggings and matrix was not affected by either physical or biological patchiness of the landscape. 7) Disturbance density did not affect vegetation responses in diggings and matrix. 8) A shift in the plant communities in the matrix towards plants with smaller seeds was associated with increasing physical patchiness, while in diggings there was an opposite shift. 9) The proportion of wind dispersers was higher in diggings than outside, while the proportion of runoff dispersers was lower, 10) the densities of runoff dispersers in diggings and matrix were positively correlated with physical and biological patchiness. 11) Physical and biological patchiness formed the two major gradients of species composition, explaining 30 and 25% respectively. We conclude that the network of physical and biological patchiness and soil disturbance are important in the redistribution of resources and seeds, which control plant biomass, density, species richness and diversity. The bare rock surface is the main source for runoff flow with associated soil, organic matter and nutrients. The understory vegetation of shrubs provides seeds for creating and maintaining diversity. The soil matrix absorbs runoff flow, and disturbances absorb runoff and trap seeds. Thus, differences in landscape heterogeneity and their effects on resource and seed movement interact in controlling plant community productivity and diversity in the landscape.