7 research outputs found
Damage to tropical forests caused by cyclones is driven by wind speed but mediated by topographical exposure and tree characteristics
Get PDFEach year, an average of 45 tropical cyclones affect coastal areas and potentially impact forests. The proportion of the most intense cyclones has increased over the past four decades and is predicted to continue to do so. Yet, it remains uncertain how topographical exposure and tree characteristics can mediate the damage caused by increasing wind speed. Here, we compiled empirical data on the damage caused by 11 cyclones occurring over the past 40 years, from 74 forest plots representing tropical regions worldwide, encompassing field data for 22,176 trees and 815 species. We reconstructed the wind structure of those tropical cyclones to estimate the maximum sustained wind speed (MSW) and wind direction at the studied plots. Then, we used a causal inference framework combined with Bayesian generalised linear mixed models to understand and quantify the causal effects of MSW, topographical exposure to wind (EXP), tree size (DBH) and species wood density (ρ) on the proportion of damaged trees at the community level, and on the probability of snapping or uprooting at the tree level. The probability of snapping or uprooting at the tree level and, hence, the proportion of damaged trees at the community level, increased with increasing MSW, and with increasing EXP accentuating the damaging effects of cyclones, in particular at higher wind speeds. Higher ρ decreased the probability of snapping and to a lesser extent of uprooting. Larger trees tended to have lower probabilities of snapping but increased probabilities of uprooting. Importantly, the effect of ρ decreasing the probabilities of snapping was more marked for smaller than larger trees and was further accentuated at higher MSW. Our work emphasises how local topography, tree size and species wood density together mediate cyclone damage to tropical forests, facilitating better predictions of the impacts of such disturbances in an increasingly windier world
Microhabitat specialization of tropical rain-forest canopy trees in the Sovi Basin, Viti Levu, Fiji Islands
Get PDFIsland biotas often have lower species diversity and less intense competition has been hypothesized as a result. This should result in lower habitat specificity compared with mainland habitats due to larger realized niches. We investigate microhabitat associations of canopy trees with regard to differences in topography on an oceanic island (Viti Levu, Fiji) using twenty 10 × 60-m plots. We find high tree-species diversity (112 species with dbh ≥ 10 cm in a total of 1.08 ha) and high endemism (c. 60%), compared with other islands in Western Polynesia. Our sample plots aggregate into three distinct groups that are mostly defined by micro-topography: (1) ridges and steep slopes (well-drained sites), (2) moderate slopes and ridge flats (moderate drainage), and (3) flats (poor drainage). Associations with microhabitat are found for more than 50% of the 41 most common species but only one species is apparently restricted to a single habitat. These findings are similar to other rain forests and demonstrate considerable niche differentiation among island rain-forest tree species
Priority forests for conservation in Fiji: landscapes, hotspots and ecological processes
No full textFiji's National Biodiversity Strategy and Action Plan encourages refinements to conservation priorities based on analyses of new information. Here we propose a network of Priority Forests for Conservation based on a synthesis of new studies and data that have become available since legislation of the Action Plan in 2001. For selection of Priority Forests we considered minimum-area requirements for some native species, representation goals for Fiji's habitats and species assemblages, key ecological processes and the practical realities of conservation areas in Fiji. Forty Priority Forests that cover 23% of Fiji's total land area and 58% of Fiji's remaining native forest were identified. The analysis confirms the majority of conservation priority areas previously identified, recommends several new areas, and supports the Government of Fiji's policy goal of protecting 40% of remaining natural forests to achieve the goals of the National Biodiversity Strategy and Action Plan and sustain ecosystem services for Fijian communities and economies
Canopy specialist Hylaeus bees highlight sampling biases and resolve Michener’s mystery
Get PDFLarge parts of the Pacific were thought to host low bee diversity. In Fiji alone, our recent estimates of native bee diversity have rapidly increased by a factor of five (from 4 to >22). Here, we show how including sampling of the forest canopy has quickly uncovered a new radiation of Hylaeus (Hymenoptera: Colletidae) bees in Fiji. We also show that Hylaeus are more common across the Pacific than previously thought and solve one of Charles Michener’s mysteries by linking the previously enigmatic French Polynesian Hylaeus tuamotuensis to relatives in Fiji. We use systematic techniques to describe eight new Hylaeus species in Fiji (n = 6), French Polynesia (n = 1), and Micronesia (n = 1), and discuss impressive dispersal events by this genus. These clades also double the number of Hylaeus dispersals out of Australia from two to four. Our discovery highlights the severe impact of bee sampling methods on ecological interpretations and species discovery, specifically that canopy sampling is needed to correctly assess forest bee diversity even where there is a very long record of sampling. It further highlights the potential for forests to host higher-than-anticipated diversity and conservation value. This has broad methodological and regulatory impacts for land managers seeking to make choices about pollination services and diversity. The new species are Hylaeus (Euprosopoides) chuukensis Dorey, Davies, and Parslow; H. (Prosopisteron) albaeus Dorey, Davies, and Parslow; H. (P.) apertus Dorey, Davies, and Parslow; H. (P.) aureaviridis Dorey, Magnacca, and Parslow; H. (P.) breviflavus Magnacca; H. (P.) derectus Dorey, Davies, and Parslow; H. (P.) navai Dorey, Davies, and Parslow; and H. (P.) veli Dorey, Davies, and Parslow
Damage to tropical forests caused by cyclones is driven by wind speed but mediated by topographical exposure and tree characteristics
No full textInternational audienceEach year, an average of 45 tropical cyclones affect coastal areas and potentially impact forests. The proportion of the most intense cyclones has increased over the past four decades and is predicted to continue to do so. Yet, it remains uncertain how topographical exposure and tree characteristics can mediate the damage caused by increasing wind speed. Here, we compiled empirical data on the damage caused by 11 cyclones occurring over the past 40 years, from 74 forest plots representing tropical regions worldwide, encompassing field data for 22,176 trees and 815 species. We reconstructed the wind structure of those tropical cyclones to estimate the maximum sustained wind speed (MSW) and wind direction at the studied plots. Then, we used a causal inference framework combined with Bayesian generalised linear mixed models to understand and quantify the causal effects of MSW, topographical exposure to wind (EXP), tree size (DBH) and species wood density (ρ) on the proportion of damaged trees at the community level, and on the probability of snapping or uprooting at the tree level. The probability of snapping or uprooting at the tree level and, hence, the proportion of damaged trees at the community level, increased with increasing MSW, and with increasing EXP accentuating the damaging effects of cyclones, in particular at higher wind speeds. Higher ρ decreased the probability of snapping and to a lesser extent of uprooting. Larger trees tended to have lower probabilities of snapping but increased probabilities of uprooting. Importantly, the effect of ρ decreasing the probabilities of snapping was more marked for smaller than larger trees and was further accentuated at higher MSW. Our work emphasises how local topography, tree size and species wood density together mediate cyclone damage to tropical forests, facilitating better predictions of the impacts of such disturbances in an increasingly windier world
Recommended from our members
Damage to tropical forests caused by cyclones is driven by wind speed but mediated by topographical exposure and tree characteristics.
No full textPublication status: PublishedFunder: National Geographical SocietyFunder: Clemson Caribbean InitiativeFunder: Department of Marine and Wildlife Resources American SamoaFunder: French Pacific FundsFunder: San Diego State University Research FoundationFunder: Strategic Science Investment Fund of the New Zealand Ministry of BusinessFunder: Montpellier Advanced Knowledge Institute on TransitionsFunder: National Park of American SamoaEach year, an average of 45 tropical cyclones affect coastal areas and potentially impact forests. The proportion of the most intense cyclones has increased over the past four decades and is predicted to continue to do so. Yet, it remains uncertain how topographical exposure and tree characteristics can mediate the damage caused by increasing wind speed. Here, we compiled empirical data on the damage caused by 11 cyclones occurring over the past 40 years, from 74 forest plots representing tropical regions worldwide, encompassing field data for 22,176 trees and 815 species. We reconstructed the wind structure of those tropical cyclones to estimate the maximum sustained wind speed (MSW) and wind direction at the studied plots. Then, we used a causal inference framework combined with Bayesian generalised linear mixed models to understand and quantify the causal effects of MSW, topographical exposure to wind (EXP), tree size (DBH) and species wood density (ρ) on the proportion of damaged trees at the community level, and on the probability of snapping or uprooting at the tree level. The probability of snapping or uprooting at the tree level and, hence, the proportion of damaged trees at the community level, increased with increasing MSW, and with increasing EXP accentuating the damaging effects of cyclones, in particular at higher wind speeds. Higher ρ decreased the probability of snapping and to a lesser extent of uprooting. Larger trees tended to have lower probabilities of snapping but increased probabilities of uprooting. Importantly, the effect of ρ decreasing the probabilities of snapping was more marked for smaller than larger trees and was further accentuated at higher MSW. Our work emphasises how local topography, tree size and species wood density together mediate cyclone damage to tropical forests, facilitating better predictions of the impacts of such disturbances in an increasingly windier world
Diversification history and hybridisation of Dacrydium (Podocarpaceae) in remote Oceania
Get PDFWe examined evolutionary relationships, hybridisation and genetic diversity in species of Dacrydium (Podocarpaceae) in Remote Oceania, where it is restricted to New Caledonia and Fiji. We used cpDNA sequence (trnL–trnF) data to construct a phylogeny and estimate taxon divergence by using a relaxed molecular clock approach. The phylogeny was verified using allozymes, which were also used to investigate genetic diversity of all species and the hybridisation dynamics of two endangered species, D. guillauminii and D. nidulum. Our results suggested that Dacrydium species in Remote Oceania form a monophyletic group that arose and diversified within the last 20 million years through long-distance dispersal and a range of speciation mechanisms. Whereas we detected no hybridisation between the Fijian species D. nausoriense and D. nidulum, we confirmed hybridisation between D. guillauminii and D. araucarioides in New Caledonia and determined introgression to be assymetric from the widespread D. araucarioides into the rare, restricted-range species D. guillauminii. In addition, D. guillauminii had lower genetic diversity than did the other species of Dacrydium studied, which had genetic diversity similar to that of other gymnosperms. Our results provided evidence for the recent and complex diversification of Dacrydium in Remote Oceania. In addition, low genetic diversity of and introgression from D. araucarioides, are of grave concern for the conservation of D. guillauminii
