Grass Communities Differ Floristically Under Different Dominant Trees in Savannas in Thailand and Cambodia

Abstract

Southeast Asian savannas are some of the least studied ecosystems, with understanding of their function and resilience limited by a lack of understanding of grass species richness and composition. Since savannas are characterized by their grassy ground layer, we conducted field surveys in Thailand and Cambodia to assess grass community composition under different dominant tree genera. We conducted field surveys in four savanna ecosystems characterized by (i) Dipterocarpus, (ii) Pinus, (iii) Pterocarpus, and (iv) Shorea tree genera. In each, we recorded grass species composition and richness. We assessed differences in composition using PERMANOVA, patterns of grass species discovery using species accumulation curves, and common species with relative frequency distributions. In total, we recorded 160 unique grass species. These savannas support distinct grassy assemblages, with diverse patterns of species accumulation, richness, and overlap. Common grasses were frequently shared between ecosystems. Grass assemblages were functionally similar, comprising mostly C4 perennial species. Across the ecosystems, grass communities were mostly composed of tribe Andropogoneae, although we recorded common fire-adapted C3 grasses including Vietnamosasa ciliata (A. Camus) T.Q. Nguyen and Vietnamosasa pusilla (A. Chev. & A. Camus) T.Q. Nguyen. The savanna ecosystems of Thailand and Cambodia are characterized by Dipterocarpus, Pinus, Pterocarpus, and Shorea tree species, which support distinct grass assemblages. Diversity varies across savanna landscapes, with the highest grass species diversity found in the Dipterocarpus and Shorea savannas. Increased sampling is necessary to fully characterize the grass flora of Southeast Asian savannas and their responses to environment.