Variable retention improves insect diversity conservation in South Patagonian Nothofagus pumilio forests.

MV LENCINAS; G MARTÍNEZ PASTUR; E GALLO; JM CELLINI

San Jose

Congreso; III Congreso Latinoamericano de IUFRO; 2013

CATIE

Insects could act as indicators of temperate forest sustainability, health and conservation status due to their importance in ecosystem functioning. Harvesting impacts on forest insect diversity mainly depends on their intensity. Variable retention has been proposed to mitigate the harmful effects of timber harvesting, but its effectiveness remains unknown in South Patagonian Nothofagus pumilio forests. The objectives of this study were to: (i) define a baseline of insect diversity in old-growth forests along a site quality gradient; (ii) evaluate stands with different harvesting treatments including clear-cut (CC), aggregated (AR) and dispersed (DR) retention, and compare with old-growth forests (OGF); and (iii) assess temporal changes during four years after harvesting (YAH). Mobile epigean insect assemblages were characterized using a wide spectrum trap system during summer. Richness and relative abundance of insects were analyzed by rarefaction, univariate parametric ANOVAs and multivariate permutational ANOVAs and ordinations. There were observed 163 species and morphospecies (26% of doubletons and singletons), which 78 were found in the base-line and 85 were added after harvesting. Diptera, Hymenoptera, Coleoptera and Lepidoptera were the most represented. Site quality did not show a significant impact on the measured variables in the base-line characterization. Contrary, insect richness and abundance generally diminished after harvesting with cut intensity (AR>OGF>DR>CC) and with time, but particularities for some orders were observed (eg., diminishing in Lepidoptera richness with time after harvesting). Different species response types were observed for all orders and in all treatments, from those that only occurred in old-growth forests to those than preferred harvested stands. But, richness in all response types diminished proportionally to harvesting intensity compared to OGF, both in sensitive-to-harvesting species and in favoured-by-harvesting species. Complementary, species added after harvesting followed the same pattern (AR>DR>CC). Therefore, old-growth forest characteristic species had better conservation in AR than in DR or CC, but fewer introductions of species from other surrounding environments was observed in DR than in the other harvested treatments. As a conclusion, stands with some kind of retention improves insect conservation, but variable retention combining different patterns and levels of retention also limits the introduction of alien species, which enhance conservation of original insect biodiversity in South Patagonian N. pumilio forests.