Recovery of aboveground biomass, species richness and species composition in tropical secondary forests in SW Costa Rica

Tropische Sekundärwälder umfassen mehr als die Hälfte der tropischen Wälder der Welt, weshalb ihr Schutzwert lebhaft diskutiert wird. Studien belegen die große Biomasse-Resilienz und die schnelle Akkumulation von Arten. Viele Studien konzentrierten sich auf die Regeneration von Biomasse wobei die Ergebnisse bezüglich der Regenerationsraten widersprüchlich sind. Wir untersuchten 12 tropische Sekundärwälder in Süd-West Costa Rica In einer 55 Jahre umfassenden Chronosequenz und evaluierten die Regeneration von Biomasse, Anzahl von Baumarten und Zusammensetzung von Baumarten im Verhältnis zu nahegelegenen Primärwäldern. In den ersten Jahren der Sukzession fanden wir eine schnelle Anhäufung von Biomasse vor. Die Wälder zeigten eine asymptotische Zunahme von Biomasse und akkumulierten bereits nach 20 Jahren 187 t/ha. Dies entspricht einer Akkumulationsrate von 9.35 t/ha/a in den ersten 20 Jahren. Im Gegensatz dazu fanden wir eine lineare Akkumulation von Baumarten. Die Artzusammensetzung der Sekundärwälder näherte sich jener der Primärwälder nur sehr langsam an. In 55 Jahren konnten sich jedoch keine der untersuchten Eigenschaften vollständig regenerieren. Darüber hinaus fanden wir eine hohe Variabilität von Regenerationsraten zwischen den untersuchten Sekundärwäldern. Daraus schließen wir, dass die Resilienz von Sekundärwäldern sehr variabel ist und Sekundärwälder daher - besonders in Bezug auf Artenvielfalt - einen eingeschränkten Schutzwert haben.The conservational value of tropical secondary forests is much debated, as they comprise more than half of the world’s tropical forests. They were found to have high biomass resilience and accumulate species at fast rates. However, many studies focussed on aboveground biomass recovery and findings for recovery rates are contradictory. We studied 12 secondary forests in the wet tropics of SW Costa Rica along a chronosequence of 55 years and evaluated the recovery of aboveground biomass, tree species richness and tree species composition in relation to nearby old-growth forests. We found fast rates of aboveground biomass accumulation, especially in the first years of succession. The studied forests showed an asymptotic aboveground biomass accumulation and recovered an average of 187 Mg/ha after 20 years with an accumulation rate of 9.35 Mg/ha/yr in the first 20 years. Species richness showed a rather linear accumulation. We could find species composition of secondary forests to approach old-growth species composition, yet, at a very slow rate only. Over 55 years, however, the studied secondary forests did neither fully recover aboveground biomass or species richness nor species composition. Moreover, we found a high variability of recovery rates among different secondary forests. Considering this variability and contradictory findings for the recovery of secondary forests among other studies, we conclude that the resilience of secondary forests is highly variable and, particularly regarding biodiversity, secondary forests have a limited conservation value

Artificial Top Soil Drought Hardly Affects Water Use of Picea abies and Larix decidua Saplings at the Treeline in the Austrian Alps

This study quantified the effect of shallow soil water availability on sap flow density (Qs) of 4.9 ± 1.5 m tall Picea abies and Larix decidua saplings at treeline in the Central Tyrolean Alps, Austria. We installed a transparent roof construction around three P. abies and three L. decidua saplings to prevent precipitation from reaching the soil surface without notably influencing the above ground microclimate. Three additional saplings from each species served as controls in the absence of any manipulation. Roofing significantly reduced soil water availability at a 5–10 cm soil depth, while soil temperature was not affected. Sap flow density (using Granier-type thermal dissipation probes) and environmental parameters were monitored throughout three growing seasons. In both species investigated, three years of rain exclusion did not considerably reduce Qs. The lack of a significant Qs-soil water content correlation in P. abies and L. decidua saplings indicates sufficient water supply, suggesting that whole plant water loss of saplings at treeline primarily depends on evaporative demand. Future work should test whether the observed drought resistance of saplings at the treeline also holds for adult trees

First chemo-enzymatic synthesis of the ( R )-Taniguchi lactone and substrate profiles of CAMO and OTEMO, two new Baeyer– Villiger monooxygenases

This study investigates the substrate profile of cycloalkanone monooxygenase and 2-oxo-Δ3-4,5,5-trimethylcyclopentenylacetyl-coenzyme A monooxygenase, two recently discovered enzymes of the Baeyer–Villiger monooxygenase family, used as whole-cell biocatalysts. Biooxidations of a diverse set of ketones were performed on analytical scale: desymmetrization of substituted prochiral cyclobutanones and cyclohexanones, regiodivergent oxidation of terpenones and bicyclic ketones, as well as kinetic resolution of racemic cycloketones. We demonstrated the applicability of the title enzymes in the enantioselective synthesis of (R)-(−)-Taniguchi lactone, a building block for the preparation of various natural product analogs such as ent-quinine.Austrian Scientific Foundation (FWF)EU-FP7 Oxygree

Multidimensional tropical forest recovery

International audienceTropical forests disappear rapidly because of deforestation, yet they have the potential to regrow naturally on abandoned lands. We analyze how 12 forest attributes recover during secondary succession and how their recovery is interrelated using 77 sites across the tropics. Tropical forests are highly resilient to low-intensity land use; after 20 years, forest attributes attain 78% (33 to 100%) of their old-growth values. Recovery to 90% of old-growth values is fastest for soil (12 decades). Network analysis shows three independent clusters of attribute recovery, related to structure, species diversity, and species composition. Secondary forests should be embraced as a low-cost, natural solution for ecosystem restoration, climate change mitigation, and biodiversity conservation

Strong floristic distinctiveness across Neotropical successional forests

International audienceForests that regrow naturally on abandoned fields are important for restoring biodiversity and ecosystem services, but can they also preserve the distinct regional tree floras? Using the floristic composition of 1215 early successional forests (≤20 years) in 75 human-modified landscapes across the Neotropic realm, we identified 14 distinct floristic groups, with a between-group dissimilarity of 0.97. Floristic groups were associated with location, bioregions, soil pH, temperature seasonality, and water availability. Hence, there is large continental-scale variation in the species composition of early successional forests, which is mainly associated with biogeographic and environmental factors but not with human disturbance indicators. This floristic distinctiveness is partially driven by regionally restricted species belonging to widespread genera. Early secondary forests contribute therefore to restoring and conserving the distinctiveness of bioregions across the Neotropical realm, and forest restoration initiatives should use local species to assure that these distinct floras are maintained