Decreasing negative impacts of harvesting over insect communities using variable retention in southern Patagonian forests.

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

JOURNAL OF INSECT CONSERVATION

SPRINGER

Lugar: Berlin; Año: 2014 vol. 18 p. 479 - 495

1366-638X

Insects could act as indicators of temperate forest sustainability, health and conservation status due to their role in the importance in ecosystem function. Insect conservation in managed forests depends on the retention degree after harvesting impacts on forest insect diversity usually depends on their intensity. Variable retention has been proposed to mitigate the harmful effects of harvesting, but its effectiveness remains unknown in southern 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-cuts, aggregated and dispersed retention, and compare these to old-growth unmanaged forests; and (iii) assess temporal changes during the first four years after harvesting (YAH). A 61 ha N. pumilio forest was selected, where mobile epigean insect richness and relative abundance were characterized duringin summer ofor five consecutive years. One year before harvesting, baseline was characterized along a site quality gradient. After harvesting, two different harvesting practices were studiedimplemented: combined dispersed (DR) and aggregated (AR) retention (AR+DR), with one aggregate per hectare (30 m radius) and 10-15 m² ha-1 of trees among the aggregatesdispersed retention (40-50% total retention); and AR with clear-cuts pure aggregated retention (AR+CC), with one aggregate per hectare (30 m radius) and removal of all trees clear-cuts among them (28% retention). Each treatmentforest condition (AR, DR and CC) was analyzed aloneas separate treatment and compared with old-growth forests (OGF) as control treatment. Data analyses included parametric and permutational ANOVAs, multivariate classification and ordinations. Before harvesting, 79 insect species were found, whereose richness and abundance were slightlyfew related to site quality of the stands. After harvesting, 84 new species were added to those found in baseline, but species richness and abundance directly diminished directly with retention degreeharvesting intensity (OGF > AR > DR > CC). These differences were , significantly for at least some orders (e.g., mainly Diptera and Lepidoptera) and response type groupss (old-growth forest species sensitive to any harvesting, and speciesthose conserved in the aggregatesd retention). Beside this,Meanwhile, only harvesting-favored species presented significantly higher richness and abundance in DR and CC treatments. Changes in insect biodiversity were found along the yearscommunity composition were highlighted with time after harvesting, but with high abundance fluctuations among years. Harvesting reduce insect richness in N. pumilio forests independently of the treatmentsilvicultural regeneration systems applied, but the original insect species community assemblage changes significantly changed due to the loss of sensitive and the introduction , by income of species from other surrounding environments and loss of sensitive ones. Despite this, aggregated retention conserves richness and abundance at high and similar levels than old-growth forests have. The original insect species assemblageOld-growth forest insect diversity is favored when some of the structural complexity is preserved; therefore, aggregated retention greatly diminished the harvesting impacts over insect community conservation, although introductionincome of species afterfollowing harvesting can?t be avoidedtotally stopped. Aggregated retention must be included in N. pumilio silvicultural practices to better achieve long-term insect diversity conservation, but more studies are necessary to evaluate effects of different size, shape and distribution of aggregates into harvested timber forests, over forest insect assemblages, as well as their fragmentation and connectivity at landscape level.