Abstract
Lianas (woody vines) are particularly abundant in tropical forests, and their abundance is increasing in the neotropics. Lianas can compete intensely with trees for above- and belowground resources, including water. As tropical forests experience longer and more intense dry seasons, competition for water is likely to intensify. However, we lack an understanding of how liana abundance affects soil moisture and hence competition with trees for water in tropical forests. To address this critical knowledge gap, we conducted a large-scale liana removal experiment in a seasonal tropical moist forest in central Panama. We monitored shallow and deep soil moisture over the course of three years to assess the effects of lianas in eight 0.64 ha removal plots and eight control plots. Liana removal caused short-term effects in surface soils. Surface soils (10 cm depth) in removal plots dried more slowly during dry periods and accumulated water more slowly after rainfall events. These effects disappeared within four months of the removal treatment. In deeper soils (40 cm depth), liana removal resulted in a multi-year trend towards 5–25% higher soil moisture during the dry seasons with the largest significant effects occurring in the dry season of the third year following treatment. Liana removal did not affect surface soil temperature. Multiple and mutually occurring mechanisms may be responsible for the effects of liana removal on soil moisture, including competition with trees, and altered microclimate, and soil structure. These results indicate that lianas influence hydrologic processes, which may affect tree community dynamics and forest carbon cycling.
Highlights
Intact tropical forests were once thought to be relatively resistant to anthropogenic changes in climate and atmospheric chemistry; these ecosystems appear to be experiencing significant changes [1, 2]
For parameters estimated in our models we report the mean of the posterior distribution and 95% credible intervals
Soil moisture at the 10 cm depth dropped in an exponential-like fashion, but never fell below 20%
Summary
We conducted our study in a semi-deciduous, secondary, tropical moist forest on Gigante Peninsula (9.11 N, 79.85 W), Barro Colorado Nature Monument (BCNM), Republic of Panama. The Smithsonian Tropical Research Institute (STRI) has acted as the steward of BCNM for more than 50 years, and research conducted on the BCNM does not need a governmental (ANAM) permit. Our studies did not involve any protected or endangered species. The nearest meteorological station, on Barro Colorado Island, located 5.8 km to the northeast, receives 2700 mm of rainfall in an average year and temperatures average 27°C. Rainfall occurs throughout the year, but less than 5% typically falls in the dry season between mid-December and April. Most of the soils on the Gigante Peninsula are clay-rich, highly weathered Oxisols developed from andesite that overlies sedimentary material [37]
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