Investigating the effect of selective logging on tree biodiversity and structure of the tropical forests of Papua New Guinea

Abstract: 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

Investigating the effect of selective logging on tree biodiversity and structure of the tropical forests of Papua New Guinea

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

Xylem hydraulic and photosynthetic function of Gnetum (Gnetales) species from Papua New Guinea

• Gnetum (Gnetales) species are suggested to be unique extant gymnosperms that have acquired high photosynthetic and transpiration capacities as well as greater xylem hydraulic capacity and efficiency compared with all other extant gymnosperms. This is because Gnetum is the only extant gymnosperm lineage that combines vessels, broad pinnate-veined leaves and an ecological distribution in wet, productive lowland tropical rainforest habitats. Yet, field-based observations on the group's ecophysiological performance are lacking.\ud \ud • To test a hypothesis that Gnetum species are ecophysiologically analogous to light-demanding woody tropical angiosperms, stem xylem hydraulic performance, photosynthesis and stomatal conductance were investigated in Gnetum as compared with a diverse group of co-occurring woody plants in a lowland tropical rainforest.\ud \ud • It was found that Gnetum species combined low photosynthetic capacity and low stomatal conductances with a low stem water transport ability. The physiological observations are consistent with the general occurrence of Gnetum species in shady, primary forest habitats.\ud \ud • These results on Gnetum ecophysiology indicate that the coupling of vessels, broad pinnate-veined leaves and the liana habit do not signal the evolution of a highly opportunistic, light-demanding life history in gymnosperms

Long-term effects of forest regrowth and selective logging on the seed bank of tropical forests in NE Costa Rica

To investigate long-term effects of land use on the soil seed bank, we compared the abundance/density, species richness, life form distribution, and species composition of seeds sotred in the soil of four 15-20 yr-old second-growth stands, two old-growth stands, and two previously selectively-logged stands in the Caribbean lowlands of Costa Rica. Surface soil (10 cm deep, 4.7 cm diameter) was collected at 10 m intervals along three 120-160 m long transects in each stand (44-48 soil cores, 22-24 combined seed bank samples per site). Seed density was highest but variable in second-growth stands (8331-1435 seeds/m2), low and homogeneous in old-growth stands (2258-2659 seeds/m2), and intermeidate and highly variable in selectively-logged stands (1165-6954 seeds/m2), which also had contrasting logging intensities. Species richness was strongly dependent on seed density, but showed less variation. Life form distribution did not differ statistically among or within land-use categories. In each stand, herbs-forbs, shrubs, and vines dominated the seed bank (>75% of the species richness and abundance), whereas trees were a minor component (<20% of the species richness and <5% of the abundance) and were predominantly early successional. Shrubs and vines were most abundant in second-growth stands where regrowth vegetation was repeatedly cut before abandonment, whereas grasses and sedges were most abundant in the only forest stand that was completely surrounded by pastures. In terms of species composition, old-growth stands were more similar to selectively-logged stands than to second-growth stands, but across stands, selectively-logged forests were most distinct from the other two forest types. An inventory of the standing woody vegetation in each site showed little representation of the woody taxa found in the seed bank. We discuss these results in the context of the main factors that have been postulated to influence the abundance, life form, and species composition of tropical forest seed banks, and explore the role of the latter during intermediate phases of tropical forest succession and regeneration