The effect of the local environmental conditions on associated organisms of Lombardy poplar (Populus nigra cv Italica)

Lombardy poplar (Populus nigra cv ‘Italica’) has been planted all over Europe, mostly as single trees or in rows along roads or around squares. This clone represents a unique opportunity to study local effects (e.g. associated community diversity) on a single genotype. We investigated the effect of local environmental conditions (biogeographical species pools, site conditions, surrounding vegetation) and clines in environmental conditions (climate, latitude) on the diversity of associated organisms, notably insect species. Pairs of trees were selected at least on five urban and five rural sampling sites in each of the following countries: France, Germany, Hungary, Italy and Poland. Fifty leaves per tree were selected randomly once a month from May until September and evaluated for damage by six functional groups of insect: chewers, skeletonizers, leaf miners, sucking and sap feedings, gall makers and leaf rollers. Insect species were also determined for leaf miners and gall makers. There was no significant difference in damage levels between pairs of trees at each site, but significant differences were found among sites and among countries for the means of leaves damaged by each functional group. The same leaf miner species were found in the five counties but at different frequencies. The dominant gall-maker species was the aphid, Pemphigus spyrothecae, in all countries; however both species composition and dominance varied strongly among sites. Remarkably, species diversity (Shannon-Wiener Index) of gall makers and leaf miners was higher on urban sites than on rural sites.