Why biodiversity increases after variable retention harvesting: A meta-analysis for southern Patagonian forests.

Abstract

Effects of forest harvesting on biodiversity can be varied and complex to understand. We provide a metaanalysisof 553 studies plants, insects and birds to identify the general responses to Variable Retentionharvesting (VR) 1?8 years post-harvest in Nothofagus pumilio forests of southern Patagonia. The analysisis focused on: (i) richness and abundance, (ii) origin and habitat (native forest specialist species, nativespecies of other habitats, alien species), and (iii) temporal trends after harvesting. Our objective was toevaluate why biodiversity increases after variable retention harvesting, by assessing the effects on (i) speciesrichness and abundance in general, (ii) native forest specialists, native generalist species and alienspecies, and (iii) the recovery of biodiversity toward original conditions. Forests managed with VR supportedhigher overall richness and abundance of plants, insects and birds in aggregate and dispersedretention than unmanaged stands, but with similar values each other. However, origin and habitat of speciesaffected responses to VR. Aggregates support higher native forest specialist plant and lower plants ofhabitats other than dispersed retention. However, both retention treatments increased alien plants,although its richness and abundance was higher in dispersed retention. Native forest specialist insectswere reduced in comparison to unmanaged forest, while insects of other habitats showed a positiveresponse to both aggregate and dispersed retention as well as did for bird species richness and abundancecompared to unmanaged forests. We found evidence for recovery of original conditions for native forestspecialist plants and insects, and plants of other habitats. In contrast, alien plants and native insects ofother habitats increased continuously in the studies included through those representing 8 years postharvest.Major differences among both retention patterns included significantly higher richness andabundance of alien plants and native insects of other habitats in dispersed retention. Our synthesis showsrecovery toward original conditions for some taxa, but demonstrates long-term establishment of alienplants as well as insect species not associated with native N. pumilio forests. These have emerged as amain potential threat to conservation of forests under VR prescription, at least at the stand level.Retention forestry could play a fundamental role for conservation in productive temperate forests, butthe influence of retention pattern and aggregate size are still unclear.