Role of Tree Vegetation and Associated Environmental Factors on the Understory Herb-Layer Composition in a Reforested Area: A Study from “Kulon Progo Community Forestry”

We assessed the understory herb-layer species composition in response to tree vegetation and its associated environmental factors in the reforested area of the Kulon Progo Community Forestry, Yogyakarta, Indonesia. The understory herb-layer composition among different stand types, including Pinus (PN), Aleurites-Swietenia (AS), Swietenia-Acacia (SA), Melaleuca-Acacia (MA) and Tectona-Dalbergia (TD), was compared using some comparison analyses. The influence of tree vegetation characteristics and associated environmental factors on the understory herb-layer species was analyzed by employing canonical correspondence analysis (CCA). Our result showed variation in understory herb-layer species composition despite equality in richness and diversity indices. Among all stand types, the MA stand showed fewer shade-tolerant species, and the TD stand exhibited the smallest number of shade-intolerant species. Seedling availability also varied between AS and MA, which contained fewer seedling species. One of the main species in the two stands did not even regenerate. Moreover, all indicator species in MA were shade-intolerant species with invasive characteristics, while those in TD were shade-tolerant and semi-shade-tolerant species. CCA showed that stand types held an important role in the herb-layer species composition, where the number of shade-tolerant and seedling species commonly native to forest were directly proportional to tree canopy coverage, silt proportion in soil texture and concentration of soil organic carbon yet inversely proportional to below-stand utilization. In contrast, the number of shade-intolerant species had positive correlation to below-stand utilization and inversely to other correlated factors. Our study also indicated the possibility of tree vegetation controlling several environmental factors, where the increase in canopy coverage was followed by an increasing proportion of silt in soil texture and concentration of soil organic carbon, as well as a decreasing percentage of below-stand utilization. Accordingly, we recommend tree species enrichment with dense-canopy trees and adaptive management of below-stand utilization for better forest development and tree regeneration. This finding provides important knowledge for evaluation and improvement in the ecological restoration of degraded forests.