Forest management affects ecosystem functioning (predation and herbivory) but not ecosystem constancy: A comparative study across four forest ecosystems around the world

Forest management can affect both the functioning and stability of ecosystems. Constancy, along with persistence are key factors that contribute to the overall stability of an ecosystem. These effects can be highly variable and change across forest ecosystems. We studied the effects of forest management on the strength of resource–consumer interactions (bird predation and insect herbivory) as important measures of ecosystem functioning, as well as on their constancy in time in four different forested regions globally. Within each region, we selected (i) three heavily managed or plantation forests, and (ii) three urban/peri-urban forests or urban plantings, and paired each of them with pristine/semi-natural forests. Bird predation was estimated using plasticine caterpillars with different colors. Chewer, galler, and miner herbivory on leaves were estimated for 15 plants (shrubs and trees) per study site. Constancy was quantified as the invariability of both predation and herbivory during a period of three years. We found no consistent responses in terms of either predation or herbivory to forest management practices across forest ecosystems. Bird predation was higher in urban/peri-urban forests than pristine/semi-natural forests in Patagonian and boreal forest, with intermediate levels of predation in managed or plantation forests. These differences might be explained by the increase of resource winter availability and by the higher abundances of generalist predators due to increase of temperatures (i.e., urban heat effect), for those regions where winter temperatures could be a limiting factor. Chewing insect herbivory was lower in urban/peri-urban forests, probably explained by the exclusion of certain herbivores in response to warming and the higher predation pressure. No differences were found in other types of herbivory, which support that effects of urbanization are guild-specific. In addition, we consistently found no effects of forest management practices on predation invariability and herbivory, thereby demonstrating the high constancy of ecosystem functioning to different forest management practices across regions. This can be a consequence of ecosystem stability. These findings improve our knowledge of the generalized effects of forest management on ecosystem functions and stability by establishing a connection between the ecology and management and conservation of plantations and natural forests.