Case study for the integration of faunistic data series in selected Italian LTER forest sites

Abstract

The Italian Long Term Ecological Research Network (LTER Italy) was founded, and included in the International Network (ILTER), in 2006. The National Network includes today twenty sites in different environments, five of them are in forest ecosystems. Most of monitoring and research activities at Italian forest sites are carried on according to the protocols of the ICP Forests Programme, based on a permanent monitoring plot of fixed shape and size (a square fenced area, 50x50 m wide) and focused on vegetation. The present project was aimed at investigating the suitability of these monitoring plots to conduct ecological research on a selected animal group, thus introducing a new research line on fauna at LTER Italy forest sites. Saproxylic beetles were selected as target animal group. Saproxylic organisms are species living in or depending on deadwood in one or more stages of their life cycle; for this reason, saproxylic beetles are very significant for forest ecosystems. Two field tests were performed: the first field test was developed in 2010 at four Italian forest plots in Lazio (Monte Rufeno, Acquapendente-VT; Monte Circeo, San Felice Circeo-LT) and Abruzzo (Selva Piana, Collelongo-AQ; Rosello, Rosello-CH) Regions; the second field test was conducted in 2011 in two forest plots in Oregon (U.S.A.), at the HJ Andrews Experimental Forest. All the study areas are LTER sites. Emergence traps and flight interception traps were used to collect insects. One thousand three hundred and seventy-two beetles were collected at the Italian study plots; three thousand six hundred and ninety-four beetles were collected at U.S. plots. With the present research, significant differences concerning assemblages of saproxylic beetles were detected among plots. Among Italian forest sites, Rosello showed the highest species richness and diversity, while Monte Rufeno exhibited the highest abundance. Results returned by the Andrews forest were consistent with the main findings, in spite of the coarser taxonomic level of beetle data (family level): abundance was higher in the old-growth forest, richness and diversity resulted slightly higher in the young stand. We found that, at the considered study areas, saproxylic beetles are poliphagous species, they are not linked to species composition of tree communities, but they exhibit preferences for structural traits of forests. We also found that, among habitat factors, deadwood amount, decay class of deadwood, slope and stand age have the strongest effects on the composition of assemblages of beetles.We can therefore say that the plot scale was able to reveal ecological patterns. Saproxylic beetles represented a suitable target animal group to be investigated at small (plot) scale. These outcomes are relevant with regards to LTER Italy forest sites, firstly because we demonstrate that forest plots are useful to shift from vegetation monitoring to ecological investigations; secondly, because we can suggest the integration of a research line regarding forest dwelling beetles inside existing long term data sets. A few suggestions to improve the consistency of researches on saproxylic beetles at LTER forest plots are the following: 1) field sampling based on random points: in fact, locations of ICP Forests plots were not originally selected on a systematic grid, but subjectively chosen. Traps located randomly may overcome statistical constraints deriving from non-random locations of study sites; 2) a higher number of space and time replicates of plot sampling: multiple 50 x 50m sampling plots within the huge homogeneous area and multiple sampling seasons may facilitate the ongoing process of plot upscaling. Ultimately, results of the present project demonstrate that studies on lists of species or on indices derived from lists of species may indeed be suitable to long term ecological research, unlike what other authors stated in the past.