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- Derroire, Geraldine
(författare)
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Isolated trees as nuclei of regeneration in tropical pastures: testing the importance of niche-based and landscape factors
- 2016
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Ingår i: Journal of Vegetation Science. - : Wiley. - 1100-9233 .- 1654-1103. ; 27, s. 679-691
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Tidskriftsartikel (refereegranskat)abstract
- QuestionsOur study tests the relative importance of different attributes of isolated trees in explaining the properties of the regeneration assemblage beneath their crowns to evaluate their effect on the composition of early successional stages and understand the processes underlying this effect. We asked: (1) does the regeneration assemblage contain a high proportion of individuals conspecific with the isolated tree; (2) how does the landscape surrounding an isolated tree influence the properties of the regeneration assemblage; and (3) what is the respective importance of structural variables and functional traits of isolated trees for their influence on the properties of the regeneration assemblage?LocationThree pasture sites in Guanacaste Province, a tropical seasonally dry area, Costa Rica.MethodsNinety isolated trees were characterized by their position in the landscape relative to patches of trees, individual structural variables related to tree and crown size, and species functional traits. The assemblage of woody plants regenerating under their crowns was characterized by number of individuals and species, and taxonomic and functional composition. To understand the mechanisms underlying the facilitative effect of isolated trees on regeneration, correlations between their attributes and properties of the regeneration assemblage were assessed.ResultsWe found that a low proportion of regenerating individuals were conspecific with the isolated trees beneath which they have established. Landscape factors influenced the regeneration but their effects were site-dependent. The attributes of isolated trees correlated well with the functional composition of the regeneration assemblage: their structure and phenological habits with traits associated with drought tolerance, and their dispersal syndrome with the dispersal syndrome of the regeneration assemblage. However, isolated tree attributes correlated poorly with the regeneration assemblage's taxonomic composition.ConclusionsOur study shows that an approach based on functional composition can provide a better understanding of community assembly mechanisms than does a taxonomic approach. Two main mechanisms are suggested to explain the influence of isolated trees on the regeneration assemblage: modification of micro-scale environmental conditions (shade and moisture) and influence on dispersal agents. The effect of attributes of isolated trees on the properties of the regeneration assemblage predicts a long-term legacy of the early stages of succession.
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| 2. |
- Derroire, Geraldine, et al.
(författare)
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Resilience of tropical dry forests – a meta-analysis of changes in species diversity and composition during secondary succession
- 2016
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Ingår i: Oikos. - : Wiley. - 0030-1299 .- 1600-0706. ; 125, s. 1386-1397
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Tidskriftsartikel (refereegranskat)abstract
- Assessing the recovery of species diversity and composition after major disturbance is key to understanding the resilience of tropical forests through successional processes, and its importance for biodiversity conservation. Despite the specific abiotic environment and ecological processes of tropical dry forests, secondary succession has received less attention in this biome than others and changes in species diversity and composition have never been synthesised in a systematic and quantitative review. This study aims to assess in tropical dry forests 1) the directionality of change in species richness and evenness during secondary succession, 2) the convergence of species composition towards that of old-growth forest and 3) the importance of the previous land use, precipitation regime and water availability in influencing the direction and rate of change. We conducted meta-analyses of the rate of change in species richness, evenness and composition indices with succession in 13 tropical dry forest chronosequences. Species richness increased with succession, showing a gradual accumulation of species, as did Shannon evenness index. The similarity in species composition of successional forests with old-growth forests increased with succession, yet at a low rate. Tropical dry forests therefore do show resilience of species composition but it may never reach that of old-growth forests. We found no significant differences in rates of change between different previous land uses, precipitation regimes or water availability. Our results show high resilience of tropical dry forests in term of species richness but a slow recovery of species composition. They highlight the need for further research on secondary succession in this biome and better understanding of impacts of previous land-use and landscape-scale patterns.Synthesis Secondary forests account for an increasing proportion of remaining tropical forest. Assessing their resilience is key to conservation of their biodiversity. Our study is the first meta-analysis of species changes during succession focussing on tropical dry forests, a highly threatened yet understudied biome. We show a gradual species accumulation and convergence of composition towards that of old-growth forests. While secondary tropical dry forests offer good potential for biodiversity conservation, their capacity for recovery at a sufficient rate to match threats is uncertain. Further research on this biome is needed to understand the effect of land use history and landscape processes.
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| 3. |
- Derroire, Geraldine
(författare)
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Secondary succession in tropical dry forests : drivers and mechanisms of forest regeneration
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Secondary succession is a complex process involving numerous factors acting across scales. Understanding secondary succession in tropical dry forests is important for the conservation and restoration of this highly threatened biome. My research aims to improve knowledge of the trajectories and drivers of secondary succession in this biome, and the underlying mechanisms. I used a combination of literature synthesis, observational and experimental approaches to study plant-plant interactions and community changes during succession. Through review of published studies, I showed that established trees have a mainly positive effect on the seed dispersal, survival and germination of the subsequent generation of woody plants. However, the balance between positive and negative effects is more complex at the seedling establishment stage and can be influenced by the precipitation regime. Meta-analyses of chronosequence studies showed an increase in tree and shrub species richness with succession and a slow convergence of successional forest species composition with that of old-growth forests. Using survey of young woody plants establishing under isolated trees in pastures, I showed that the attributes of the trees influence the functional composition of the regeneration assemblages but are only weakly related to their taxonomic composition. The position of isolated trees in the landscape is also influential, but this is complex and site-specific. Through extensive sampling of leaf functional traits of sapling communities in secondary forests of different successional age, I found that community functional composition shifts from conservative towards acquisitive strategies of resource economics, through both species turnover and intraspecific variation of trait values. Five of the measured traits also showed directional changes with tree ontogeny. Lastly, an experimental test of seed fate showed that leaf litter reduced seed removal in successional forests. Seed germination rate was higher in successional forests compared with open sites and generally benefited from the presence of litter. Overall, this research suggests a higher predictability of successional trajectories when studied through functional rather than taxonomic composition. It also shows heterogeneity in successional trajectories among tropical dry forests that require further study.
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| 4. |
- Derroire, Geraldine, et al.
(författare)
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The Effects of Established Trees on Woody Regeneration during Secondary Succession in Tropical Dry Forests
- 2016
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Ingår i: Biotropica. - : Wiley. - 0006-3606. ; 48, s. 290-300
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Forskningsöversikt (refereegranskat)abstract
- Understanding the mechanisms controlling secondary succession in tropical dry forests is important for the conservation and restoration of this highly threatened biome. Canopy-forming trees in tropical forests strongly influence later stages of succession through their effect on woody plant regeneration. In dry forests, this may be complex given the seasonal interplay of water and light limitations. We reviewed observational and experimental studies to assess (1) the relative importance of positive and negative effects of established trees on regeneration; (2) the mechanisms underlying these effects; and (3) to test the 'stress gradient hypothesis' in successional tropical dry forests. The effects of established trees on seed dispersal, seed survival, and seed germination-either through direct changes to moisture and temperature regimes or mediated by seed dispersers and predators-are mainly positive. The balance between positive and negative effects on seedling establishment is more complex and depends on the season and leaf phenology of both trees and seedlings. Seedling survival is generally enhanced by established trees mitigating dry conditions. Established trees have counteracting effects on water and light availability that influence seedling growth. The probability of a positive effect of established trees on seedling survival decreases with increased rainfall, which supports the stress gradient hypothesis. Priorities for future research are experiments to test for facilitation and competition and their underlying mechanisms, long-term studies evaluating how these effects change with ontogeny, and studies focusing on the species-specificity of interactions.
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