Semi-natural habitats are key components of rural landscapes because they shelter a significant number of overwintering arthropods that are beneficial to agriculture. However, woodlots are semi-natural habitats with high patch-level heterogeneity and this aspect has been poorly studied. The purpose of this study was to determine the influence of woodlot heterogeneity on overwintering ground beetles. Woodlot heterogeneity was characterized in terms of distance from the woodlot boundary and date of the most recent logging operation. We used emergence traps to quantify the population density of ground beetles that overwintered in the different parts of the woodlot. In woodlot edges the densities and species richness of ground beetles were significantly higher than in the rest of the woodlot. Ground beetles that are active in crop fields overwintered in the edges but not in the inner zone of the woodlot. Species assemblages of ground beetles overwintering in the edges were highly diverse. The date of the most recent logging operation did not explain the distribution of ground beetles that overwintered in the woodlot. Our results show that woodlots, and in particular their edges, are used as a winter shelter by ground beetles that spend part of their life in crops, which potentially favours biological control in adjacent crop fields. and Anthony Roume, Annie Ouin, Laurent Raison, Marc Deconchat.
Foliar gas exchange characteristics, understorey microclimate, and crown irradiation were assessed for saplings of eight canopy tree species in two plots of neotropical rain forest with different degrees of canopy opening. Species studied belonged to different putative guilds: shade intolerants (both short-lived--pioneers--and long-lived), intermediates, and shade-tolerants. A considerable overlap was recorded between species in values of the photosynthetic rate per unit leaf area (PN). The highest median PN (1.26 µmol m-2 s-1) was recorded in the pioneer Croton killipianus, while slightly lower median values were recorded in Simarouba amara and Pentaclethra macroloba, and markedly lower values in two species of Vochysiaceae (Qualea paraense and Vochysia ferruginea), both putative intolerants. Highest median stomatal conductance (gs) was also shown by C. killipianus, while S. amara, P. macroloba, and L. procera exhibited intermediate values, and the lowest gs was shown by V. ferruginea and Q. paraense. Overall irradiance and crown irradiation, PN, and gs of saplings were higher in the plot which had previously received a silvicultural treatment. Most values of photosynthetic photon flux density (PPFD) were <100 µmol m-2 s-1 in both plots, with shortlived peaks of up to 2000 µmol m-2 s-1 in the treated plot. When the relationship between PN and irradiance (I) was examined by fitting PN/I curves, the degree of fit varied markedly between species, values of the regression coefficient r2 were between 0.09 and 0.51. No significant differences between species were recorded in Pmax and species also demonstrated little variation in the predicted values of dark respiration (RD), values varying between -0.51 and -1.46 µmol m-2 s-1 in Q. paraense and Minquartia guianensis, respectively. Fitted values of apparent quantum efficiency were also fairly uniform, generally falling within the range 0.02-0.03 mol(CO2) mol-1(photon). and N. E. Vera, B. Finegan, A. C. Newton.