NATURAL REGENERATION DURING SECONDARY SUCCESSION IN TROPICAL SEASONALLY DRY FORESTS

Transcription

1 NATURAL REGENERATION DURING SECONDARY SUCCESSION IN TROPICAL SEASONALLY DRY FORESTS Géraldine Derroire - Bangor University

2 Landscape patterns Landscape scale Past and present land uses Remnant vegetation Trees in early succession Long term trajectories Community scale Seed input Environmental factors Microenvironmental conditions Regeneration Individual scale Time since the beginning of succession

3 1. Changes in species diversity and composition during secondary succession 2. Isolated trees as nuclei of regeneration in tropical pastures 3. Influence of canopy trees on the fate of seeds underneath 4. Seedling establishment under different above- and below-ground influences of canopy trees 5. Sapling leaf trait variation within and across species in secondary succession

4 1. Changes in species diversity and composition during secondary succession 2. Isolated trees as nuclei of regeneration in tropical pastures 3. Influence of canopy trees on the fate of seeds underneath 4. Seedling establishment under different above- and below-ground influences of canopy trees 5. Sapling leaf trait variation within and across species in secondary succession

5 1. Changes in species diversity and composition during secondary succession A meta-analysis of about 15 studies (chronosequences in TDF) Study the changes of indices of species diversity with secondary succession Work in progress: analyses to be done using meta-analysis statistical tools Simpson diversity index

6 1. Changes in species diversity and composition during secondary succession 2. Isolated trees as nuclei of regeneration in tropical pastures 3. Influence of canopy trees on the fate of seeds underneath 4. Seedling establishment under different above- and below-ground influences of canopy trees 5. Sapling leaf trait variation within and across species in secondary succession

7 2. Isolated trees as nuclei of regeneration in tropical pastures Structural traits Size Crown shape Functional traits Nitrogen fixation Leaf phenology Dispersal syndrome Landscape factors Distance to seed source Area of seed source in a buffer Number of individuals Life form Leaf compoundness Species richness Species composition Dispersal syndrome Leaf phenology

8 2. Isolated trees as nuclei of regeneration in tropical pastures Main findings 6802 regenerating individuals under 90 trees, 126 species, 46 families => Importance of isolated trees in pasture for the regeneration Effect of attributes of isolated trees on the functional composition of the regeneration => Isolated trees differ in their capacity to attract seed dispersers => Isolated trees modify the environmental conditions Isolated trees differ in their role as nuclei of regeneration. Derroire, G., Coe, R. & Healey, J.R. under review

9 1. Changes in species diversity and composition during secondary succession 2. Isolated trees as nuclei of regeneration in tropical pastures 3. Influence of canopy trees on the fate of seeds underneath 4. Seedling establishment under different above- and below-ground influences of canopy trees 5. Sapling leaf trait variation within and across species in secondary succession

10 3. Influence of canopy trees on the fate of seeds underneath Litter treatment 3 sites: open site, intermediate secondary forest (15y), older secondary forest (30y), 4 plots per site 2 litter treatments 2 predation treatments 7 species Predation treatment (protection) without with left Germination plot (4 per sites x 3 sites) removed Wooden frame with wire net (135 cm x 90 cm x 10 cm) Depot (15cm diameter)

11 3. Influence of canopy trees on the fate of seeds underneath 7 abundant species with contrasting seed traits and dispersal mode Astronium graveolens Cochlospermum vitifolium Dalbergia retusa Hymena courbaril Simarouba glauca Stemmadenia obovata Thouinidium decandrum

12 1. Changes in species diversity and composition during secondary succession 2. Isolated trees as nuclei of regeneration in tropical pastures 3. Influence of canopy trees on the fate of seeds underneath 4. Seedling establishment under different above- and below-ground influences of canopy trees 5. Sapling leaf trait variation within and across species in secondary succession

13 4. Seedling establishment under different above- and below-ground influences of canopy trees 2 sites: intermediate secondary forest (15y), older secondary forest (30y), 4 plots per site 2 litter treatments 2 root interaction treatments 6 species Monitoring of growth and survival during 2 years Next step: measurement of some functional traits associated with resource acquisition strategies => understand the effect of biotic and abiotic environment on seedling establishment, as mediated by strategies of resource acquisition

14 4. Seedling establishment under different above- and below-ground influences of canopy trees 6 abundant species with contrasting leaf and seed traits, dispersal mode and phenology Astronium graveolens Cochlospermum vitifolium Dalbergia retusa Hymena courbaril Simarouba glauca Thouinidium decandrum

15 1. Changes in species diversity and composition during secondary succession 2. Isolated trees as nuclei of regeneration in tropical pastures 3. Influence of canopy trees on the fate of seeds underneath 4. Seedling establishment under different above- and below-ground influences of canopy trees 5. Sapling leaf trait variation within and across species in secondary succession

16 5. Sapling leaf trait variation within and across species in secondary succession

17 thickness petiole length leaf area specific leaf area dry matter content density P content C content N content C/N ratio N/P ratio 0 Main findings at the individual scale 5 0 Tree strategies consistent with the leaf economic spectrum but Legumes appear as a distinct functional group IDtree Intra-specific variations of trait values are important and correlated with => ontogeny => environmental factors % 75 % 75 percent_var 50 % % 25 0 % 0 thick petiol LA SLA LDMC dens P C N CN NP trait scale leaf_error IDtree_error IDtree heigth sp plot site scale scale scale leaf_error leaf_error scale scale leaf_error leaf_error IDtree_error IDtree_error leaf_error leaf_error IDtree_error scale IDtree_error IDtree_error heigth IDtree between leaves leaf_error heigth IDtree between trees sp heigth between height IDtree_error class sp heigth between species plot sp IDtree IDtree between plots plot sp site between plot site heigth site plot site sp site 5. Sapling leaf trait variation within and across species in secondary succession

18 5. Sapling leaf trait variation within and across species in secondary succession Main findings at the community scale => Change from conservative to acquisitive with succession => An interplay of water and light limitation, changing with: season succession Leaf trait variations within and across species provide information on community assembly processes.

19 Thank you for your attention