Variable retention effects on vascular plants and beetles along a regional gradient in Nothofagus pumilio forests

LENCINAS, MARÍA VANESSA; SOLA, FRANCISCO JAVIER; MARTÍNEZ PASTUR, GUILLERMO JOSÉ

FOREST ECOLOGY AND MANAGEMENT

ELSEVIER SCIENCE BV

Año: 2017 vol. 406 p. 251 - 265

0378-1127

Variable retention mitigates harmful effects of traditionalpractices on biodiversity of forest ecosystems, preserving habitats for speciesaffiliated with closed forests and providing habitats for early-seral species. InNothofagus pumilio forests variable retention effects on several taxa havebeen actively monitored in short- and medium-terms. However, these have rarely beeninvestigated further than six years since harvesting, seldom consideringmultiple taxonomic groups in the same research. Furthermore, there is a lack ofinformation about responses along the regional gradient of a forest natural distribution.We evaluated the effect of variable retention on plant and beetle assemblages,seven to eleven years after harvesting, in three locations along a regionalgradient of the natural distribution of N.pumilio forest in Tierra del Fuego, Argentina.We surveyed three silvicultural treatments(aggregated retention-AR, dispersed retention-DR, old growth forests-OGF) atthree localities, where we characterized understory vascular plant and beetle communities during mid-summer by species richness,abundance, Shannon-Wiener diversity and Pielou evenness indices, as well ascommunity structure. We found 58 plantsand 45 species of beetles. Assemblages of old growth forests showeddifferences among the three locations along the studied regional gradient, withonly 25% of plants and one beetle shared among them. Plant distribution may bedriven by microclimatic and geographical conditions, while availability of foodresources or habitat structural complexity could influence beetles. Likewise,variable retention modified original assemblages with greater effects in DRthan in AR. However, this trend was not uniform for each taxa or locality, andseems to be related to the composition of original assemblages and the influxof species from surrounding environments. The specialist vs. generalist quantitiesin the original assemblage could influence the resistance/resilience of thecommunity, since old growth assemblages with a greater proportion of generalistand/or non-sensitive species could maintain more similarity between aggregatesand old growth forest. The influx of species (mainly generalists or exploiters)occurred mainly in DR, generating higher dissimilarities between DR and OGF. Thecorrelation between taxa was not so clear for all locations; therefore,retention effects cannot be generalized among taxa and localities. Finally, theutility of potential bioindicators in the whole region could differ for aparticular locality, and vice versa. Particularities in the biotic assemblagesof different taxa in a regional gradient are important for management andconservation planning, and support variable retention as a useful strategy tocombine conservation and production objectives in a managed landscape.