Land Use Modulates Herbivory on Juvenile Stages of Woody Species in a Chaco Dry Forest

Abstract

Land use and herbivory are two environmental filters influencing plant communities´ structure in the Chaco dry forest, and their combined effects are particularly relevant for juveniles of woody species, a key stage for plant regeneration. Land use modifies natural disturbance regimes by changing the assembly of herbivores, due to cattle introduction and the consequent alteration of structural complexity that impact on invertebrate diversity. In this study, we analyzed how herbivory on the regenerative stages of woody plants is affected by land use. We assessed the invertebrate and vertebrate herbivory on seedlings and saplings of woody species, during summer and winter seasons, at four different land use types of a Chaco dry forest. Land use types were classified according to the increasing intensity of disturbance (logging and grazing) they are subjected to: Conserved Forest (CF; no disturbance), Secondary Forest (SF; low disturbance), Closed Species-rich Shrubland (CS; intermediate disturbance), and Open Shrubland (OS; high disturbance). We found that total herbivory was consistently higher in SF and CS in both seasons. Vertebrate herbivory was higher than invertebrate herbivory in winter (except in CF), with the inverse pattern in summer. Differences between seedling and sapling stages were scarce, with not consistent patterns of herbivory between seasons.This study shows a pronounced effect of land use on seasonal herbivory patterns and dynamics. The vegetation structure of communities under low and intermediate disturbance intensities would promote diversity of invertebrate herbivores which, combined with cattle introduction, could result in herbivory complementation and additivity. Understanding how environmental filters, like anthropic activities and herbivory interplay and affect early growth stages is crucial to achieve land use practices that do not compromise forest resilience and regeneration.