Selective removal of non-woody species released water limitation on vegetation community stagnated at early successional stages in a humid karst region

Abstract

The use of plantations and natural restoration enhance vegetation coverage and contribute significantly to the hydrologic functions of degraded terrestrial ecosystems. Researchers have investigated the development and use of plantations, however, few studies looked at naturally-restored vegetation, especially for early successional areas. We applied a series of treatments and their impacts on water status and the dominant woody species were monitored. Our goal is to enhance the hydrologic functions of naturally-restored karst vegetation that stagnated as early successional shrubby-grassland. Our results show that vegetation on both the upper and lower slopes intercepted approximately 50 % of the rainfall because of the dense community structure. With more than 60 % of the community-level root biomass concentrated in the upper 20 cm soil depth, shallow soil water content (SSWC) decreased continuously even when there was scattered light rain events. On the lower slopes, competition-reducing oriented removal of non-woody species significantly reduced canopy interception of water, which contributed to the increase of SSWC and water availability for the remaining dominant woody species. Moreover, dominant woody species in the treated plot exhibited more negative leaf carbon isotope values than the same species in the control plot, indicating released water limitation on plant growth because of the treatment. On the contrary, this treatment exhibited negligible effects on SSWC on the upper slope, environmental water status could only be improved by improving soil water storage capacity. Our results highlight strong competition on SSWC for naturally-restored vegetation on karst hillslopes that stagnated during the early successional stages. In lower slope position where soil is relatively deep, competition-reducing oriented treatment alone can release water limitations on plant growth and provide opportunities for the settlement of species with different hydrologic niches, thus providing a path for enhancing hydrologic functions of naturally-restored karst vegetation.