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Unsustainable exploitation of tropical forest resources is raising worldwide concern. In Papua New Guinea (PNG) timber harvesting has been identified as a major contributor to deforestation and forest degradation but its impact on biodiversity is still poorly understood. In this study we investigated the effect of selective logging on tree taxonomic composition, structure and diversity of PNG forests. We used data from 101 one-hectare permanent sample plots (PSPs) belonging to two vegetation types: low altitude forests on plains and fans (type P) and low altitude forests on uplands (type H). We used multivariate techniques to test for significant differences in species composition between plots of different vegetation types and disturbance regimes, identifying the tree taxa to which these differences could be ascribed. ANOVA was used to test for differences between logged-over and unlogged forest PSPs with respect to biodiversity (richness, Shannon’s diversity, Pielou’s evenness) and stand structure (stem density, basal area - BA). Temporal trends of forest features were analyzed using linear regression. Significant differences in taxonomic composition were found between logged-over and unlogged plots of the H type (p = 0.04). No differences were found in richness, diversity and evenness between logged-over and unlogged forest plots, while stem density was higher in the latter (421 ± 153 stems ha-1). Greater BA was found in unlogged forests (30.28 ± 4.45 m2 ha-1) of the H type when compared to the logged-over stands (15.52 ± 4.04 m2 ha-1). We detected positive trends in richness (0.55 ± 0.19 taxa ha-1 yr-1) and diversity after logging. Furthermore, H type forest exhibited positive trends in stem density (9 ± 1 stems ha-1 yr-1) and BA (0.42 ± 0.06 m2 ha-1 yr-1) with elapsed time since harvesting. Our analysis highlights some significant effects of logging activities on biodiversity and structure of PNG forests. Additionally, forests exhibited a significant recovery with respect to richness, diversity and stand structure. These preliminary results will be compared with data collected by the forthcoming National Forest Inventory in order to assess and monitor the effects of human activities and ecological factors on PNG forest biodiversity and develop appropriate conservation measures and sustainable management strategies.

Litter decomposition is an important process occurring in forest ecosystems, where it affects the carbon balance as a whole. In Mediterranean area, seasonal changes and climate variations associated to latitude and structural characteristics of forest stands have a real effect on decomposition rates. Current leaf litter decomposition models are frequently too general to represent local climate variations in Mediterranean forests. We developed a new dynamic semi-empirical-based model, which simulated the early stage of decomposition of leaf litter based on local climate conditions and few operational parameters. Leaf litter was divided in two components, settled on different carbon compound concentrations. The effects of temperature and moisture were characterized by specific equations and the decomposition rates were time-depending functions. Equations were calibrated by the best fitting procedure performed on field data obtained by the litterbag method followed in mixed deciduous forests in central Apennines (Italy). Model validation showed an excellent correlation between observed and predicted values (R2 between 0.89 and 0.95), predicting thus differences in decomposition rates among different local climates. The simple structure of the model and the satisfactory reliability of outputs are important features for a practical alternative to other CO2 release evaluation methods applied to forest ecosystems.

A semi-empirical model has been used to estimate total net primary productivity, canopy transpiration and the water use efficiency under actual and future climate projections (B1 and A2 IPCC Scenarios) of two deciduous (Fagus sylvatica, Quercus cerris) and one evergreen tree species (Quercus ilex) growing in Italy. In response to changes in the air temperature, the two deciduous species showed a strong reduction of NPP values, whereas the evergreen one showed very limited reductions. Under future warmer conditions, Q. ilex proved to be the best adapted species, probably for its drought-tolerant water-saving strategy, while Q. cerris suffered a reduction of transpiration, due to stomatal closure which was sensitive to the change of evaporative demand. Water Use Efficiency (WUE) values did not increase in the B1 and A2 scenarios, indicating a non-conservative water-saving strategy, which likely affected the distribution pattern of Q. cerris under these conditions. Similar functional behaviour have been noted for F. sylvatica, although this species adopted a water spending strategy, typical of species growing in mesic environments, that could represent a risk for survival of beech population under extreme air temperature change. In this respect, the reduced suitable area for this species under the A2 scenario could reduce the possibilities of an upward shift toward higher altitudes.

The elaboration of conservation strategies at regional scale, dealing with the potential effects of climate change on the abundance and distribution of tree species, should be supported by models produced at the appropriate scale. We used a bioclimatic model aimed at analysing the large-scale effects of climate change on the abundance and distribution of tree species with respect to their chorological and ecological characteristics. Abundance data for 16 species, sampled in 912 plots, distributed on a 3x3 km grid were used. A climatic model provided high resolution current climatic surfaces and a climatic scenario for 2080 was obtained using the A1FI emission scenario of HadCM3 GCM. A deterministic Regression Tree Analysis (RTA) and Multiple Linear Regression (MLR) were applied in order to define the realised niche of the species in relation to the chosen environmental variables. The comparison between RMSE values showed that RTA always outperforms MLR, in terms of predicting species distribution. Zonal species were better predicted than rare species (extrazonal or with specific habitat requirements). Climate change is expected to determine a general increase of the average potential altitude. Only the Mediterranean species are likely to be favoured by the predicted climate change, while for the two other chorological types (Sub-Mediterranean and Eurosiberian) the response seems to be species-specific, depending on the ecological characteristic of each species: the more thermophilous and xerophilous species should benefit from the predicted drought in terms of area and mean abundance, while mesophilous species should suffer a strong reduction.