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Semesterfrage 2018 “Wie retten wir unser Klima?”

Leben und Sterben der Regenwälder, Klimawandel, Vielfalt tropischer Pflanzen und Tierarten. Themen, denen in der wohl südlichsten Außenstelle der Uni Wien auf den Grund gegangen wird. Zum 25. Jubiläum der costa-ricanischen Tropenstation La Gamba spricht uni:view mit dem Biologen Florian Hofhansl.

Von Wien nach La Gamba und zurück: Mit Zahlen, Proben und neuen Erkenntnissen im Gepäck ist Florian Hofhansl gerade von einer Forschungsexkursion aus Costa Rica zurückgekehrt. “Costa Rica zählt zu den artenreichsten Ländern der Erde”, schwärmt der Uni Wien-Biologe: “Allein der Esquinas-Wald rund um La Gamba beheimatet bis zu 2.700 Pflanzenspezies und 850 Vogelarten – perfekte Bedingungen zum Forschen.”

Link: http://medienportal.univie.ac.at/uniview/forschung/


 

Sensitivity of tropical aboveground carbon stocks to climate anomalies in south-western Costa Rica

Albeit the fact that tropical forests store large amounts of carbon (C) in aboveground tree biomass, the sensitivity of forest C stocks to projected increases in climate fluctuations remains elusive to date. Here, we opt to upscale local findings to the regional level by extrapolating corresponding C stock estimates from these habitat types using the terrain position index (TPI) based on remote sensing products from ASTER digital elevation data to estimate potential landscape-scale C gain/loss under projected climate scenarios.

We conclude that the impact of climate anomalies on tropical forest productivity is strongly related to local site characteristics. Whereas tropical tree communitiesat the more exposed ridge forest site (Rid) were adversely affected by anomalous climate extremes of the ENSO event, highdensity trees at the moist ravine forest site (Rav) showed less sensitivity to climatic fluctuations. Albeit the fact that ridge forests sites only represent approx. 10% of forest cover at the landscape scale, they harbor a distinct tree species composition, which due to functional adaptation could potentially compensate for short-term C loss in response to projected climate anomalies. Resolving spatial habitat heterogeneity and functional response spectra of tropical forest ecosystems to projected climatic changes should reduce current uncertainty in model projections of tropical C sink strength and improve biodiversity conservation and management strategies.

Link: https://meetingorganizer.copernicus.org/EGU2018/EGU2018-16094.pdf


 

Medienportal Universität Wien

Die durch den Klimawandel zunehmenden Wetterextreme bringen mikrobielle Gemeinschaften aus dem Gleichgewicht. Das zeigen MikrobiologInnen rund um Maria Mooshammer, Wolfgang Wanek und Andreas Richter von der Universität Wien in einer aktuellen Publikation.

Durch Temperaturstress werden Nährstoffkreisläufe bei Mikroben, die normalerweise koordiniert ablaufen, voneinander entkoppelt. Im Bild ein Buchenwald in Klausen-Leopoldsdorf. (Foto: Universität Wien/Maria Mooshammer)

“Durch den Klimawandel nehmen extreme Wetterereignisse wie Hitze- und Frostwellen zu. Diese schädigen die Bakterien und Pilze im Boden und bringen ihre Nährstoffkreisläufe aus dem Gleichgewicht”, berichten Maria Mooshammer, Wolfgang Wanek und Andreas Richter vom Department für Mikrobiologie und Ökosystemforschung der Universität Wien. Die Mikroben können sich nach solchen Widrigkeiten zwar ganz gut erholen, doch ihr Phosphat-Stoffwechsel kommt nicht mehr ins Rollen, erklären sie im Fachblatt “Science Advances”.

Link: https://medienportal.univie.ac.at/uniview/forschung/detailansicht/artikel/mikroben-kommen-mit-klimawandel-nicht-klar/

 

 

Landscape-scale controls on aboveground forest carbon stocks along environmental gradients on the Osa peninsula, Costa Rica

Albeit the fact that tropical forests store large amounts of carbon (C) in aboveground tree biomass, the mechanistic controls on forest C stocks remain poorly resolved at the landscape-scale. Here, we aim at unraveling the mechanistic links between environmental controls such as edaphic factors (i.e. geology, soil type, topographic position) and climatic drivers (i.e. temperature, precipitation), and demographic parameters (species composition and vegetation structure).

Our results indicate that by accounting for species diversity and vegetation structure, both associated to environmental gradients and thus shaped by geographic region and forest type, current uncertainty in estimates of tropical aboveground C stocks across the landscape-scale could be greatly reduced. We conclude that resolving spatial patterns of tree species composition and vegetation structure associated with landscape-scale gradients of environmental controls will be crucial to create a mechanistic understanding of how these factors shape the distribution of aboveground C stocks and will be key to more accurately predict the C sequestration potential of tropical forests under scenarios of projected environmental changes.

Link: https://www.atbc2017.org


 

Amazon forest responses to elevated atmospheric CO2 

The impacts of elevated atmospheric CO2 (eCO2) and alterations in nutrient availability on the carbon storage capacity and resilience of the Amazon forest remain highly uncertain. Carbon dynamics are controlled by multiple eco-physiological processes responding to environmental change, but we lack solid experimental evidence, hampering theory development and thus representation in ecosystem models.

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Here, we present two ecosystem-scale manipulation experiments, to be carried out in the Amazon, that examine tropical ecosystem responses to eCO2 and alterations in nutrient availability and thus will elucidate the representation of crucial ecological processes by ecosystem models.

We highlight current gaps in our understanding of tropical ecosystem responses to projected global changes in light of the eco-physiological assumptions considered by current ecosystem models.

We conclude that a more detailed process- based representation of the spatial (e.g., soil type; plant functional type) and temporal (seasonal and inter-annual) variability of tropical forests is needed to enhance model predictions of ecosystem responses to projected global environmental change.

Link: http://journal.frontiersin.org/article/10.3389/feart.2016.00019/full


 

A high resolution monitoring network investigating tropical stem growth

The proportion of carbon (C) allocated to tree stems is an important determinant of the C sink-strength of global forest ecosystems. Understanding the mechanisms controlling stem growth is essential for parameterization of global vegetation models and to accurately predict future responses of global forest ecosystems in terms of C sequestration. However, due to their underrepresentation in global synthesis we still lack a thorough understanding of intra-annual variations in stem growth of tropical forest ecosystems, which could be especially prone to projected climatic changes.

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We here present high-resolution data (≤ 6 µm; ≥ 1 min) from a novel monitoring network of wireless devices for automated measurement of expansion and contraction in tree diameter using a membrane potentiometer, point dendrometers on phloem and xylem and sap flow modules to analyze diurnal changes in stem growth. Our results indicate that diurnal changes in stem diameter were associated with sap flow and related to seasonal variations in daytime temperature and water availability, such that daily maximum stem growth was positively related to temperature during the wet season but showed the opposite trend during the onset of the dry season. We show that high-resolution monitoring of wood hydraulics and carbon storage of tropical trees is crucial to determine the response of tropical C storage to intra-annual climate variation and therefore will be key to accurately predict future responses of tropical aboveground carbon storage, and should be of special interest for tropical ecosystem research and earth system science.

Link: http://abstractsearch.agu.org/


 

 

Medienportal Universität Wien

Sie bedecken weniger als zwölf Prozent der gesamten Landfläche der Welt und spielen doch eine der Hauptrollen im globalen Kohlenstoff- und Wasserkreislauf: tropische Waldökosysteme. Ein Team der Universität Wien publiziert ein neues Prognosemodell zur Entwicklung unserer Regenwälder im Klimawandel.

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Tropische Wälder speichern über ein Viertel des global in pflanzlicher Biomasse gespeicherten Kohlenstoffs. Im Bild wird gerade der Stammumfang eines Urwaldriesen vermessen. (Foto: Florian Hofhansl).

Tropische Wälder sind nicht nur wichtig, weil sie mehr als die Hälfte der weltweit vorkommenden Pflanzen- und Tierarten beherbergen. Sie beinhalten auch über ein Viertel des global in pflanzlicher Biomasse gespeicherten Kohlenstoffs und gelten daher als sogenannte “Kohlenstoff-Senken”.

Dabei spielen die Regenwaldbäume eine besondere Rolle: Sie können Kohlenstoff langfristig in ihrer Biomasse speichern – manche Arten mehr, manche weniger – und damit den Anteil des klimaaktiven Treibhausgases Kohlendioxid in der Atmosphäre verringern. “Der Verlust tropischer Regenwälder hat daher einen immensen Einfluss auf die globale Biodiversität und das Weltklima”, so der Ökosystemforscher Florian Hofhansl, Doktorand in der Forschungsgruppe von Wolfgang Wanek am Department für Mikrobiologie und Ökosystemforschung der Universität Wien.

Link: http://medienportal.univie.ac.at/uniview/forschung/detailansicht/artikel/klimawandel-szenarien-fuer-den-regenwald/

 

 

Mechanisms driving carbon allocation in tropical forests

Tropical forest ecosystems play a major role in global water and carbon cycles. However, mechanisms of C allocation in tropical forests and their response to environmental variation are largely unresolved as, due to the scarcity of data, they are underrepresented in global syntheses of forest C allocation. Allocation of gross primary production to wood production exerts a key control on forest C residence time and biomass C turnover, and therefore is of special interest for terrestrial ecosystem research and earth system science. Here, we synthesize pantropical data from 105 old-growth rainforests to investigate relationships between climate (mean annual precipitation, mean annual temperature, dry season length and cloud cover), soil nutrient relations (soil N:P) and the partitioning of aboveground net primary production (ANPP) to wood production (WPart) using structural equation modelling.

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Our results show a strong increase of WPart with ANPP, pointing towards allometric scaling controls on WPart, with increasing light competition in more productive forests triggering greater ANPP allocation to wood production. ANPP itself was positively affected by mean annual temperature and soil N:P. Beyond these allometric controls on WPart we found direct environmental controls. WPart increased with dry season length in tropical montane rainforests and with mean annual precipitation in lowland tropical rainforests. We discuss different trade-offs between plant traits, such as community-wide changes along the wood economics spectrum, the leaf economics spectrum and the plant resource economics spectrum, as underlying mechanisms for direct climatic controls on WPart. We thereby provide new insights into mechanisms driving carbon allocation to WPart in tropical rainforests and show that low and high productive tropical rainforests may respond differently to projected global changes.

Link: http://meetingorganizer.copernicus.org/EGU2014/EGU2014-10223.pdf


 

Sensitivity of tropical lowland net primary production to climate anomalies

While drivers of tropical forest productivity such as edaphic properties (geology, topography) and climate (precipitation, temperature, light) are well established, knowledge on the sensitivity of tropical lowland net primary production to climate anomalies remains scarce. We here investigate tropical lowland forest sites differing in topography and disturbance history to study the response of aboveground net primary production (ANPP) in relation to (1) climate extremes as triggered by El-Niño Southern Oscillation (ENSO), as well as (2) topographic position and (3) land-use history.

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In general, climate anomalies resulted in decreased precipitation and increased temperature. The production of wood decreased while the production of canopy material increased in years with prolonged periods of drought and elevated temperature. However, the impact strongly depended on local characteristics of the forest sites, such that ANPP was only negatively affected at ridges but not at ravine forest sites. We moreover show that the productivity of primary forests was significantly affected by precipitation and drought, while in secondary forests temperature was the major predictor of ANPP. Our results suggest that site-specific parameters such as topographic position and disturbance history determine the response of tropical lowland forests to climate extremes. Hence we conclude that the impact of climate anomalies on tropical forest productivity is strongly related to local conditions and thus will likely prevent uniform responses of tropical lowland forests to projected global changes.

Link: http://meetingorganizer.copernicus.org/EGU2014/EGU2014-10585.pdf


 

Controls on aboveground net primary production of tropical rainforests

Aboveground net primary production (ANPP) of tropical forests is driven by soil fertility and climate, the latter receiving special attention as recent projections of global circulation models predict large tracts of tropics to become drier and warmer. Given the scarcity of manipulative experiments, global climate-ecosystem relations and interannual climate variations caused by El Niño Southern Oscillation have been used to assess potential responses of tropical ANPP to projected climate change.

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The focus of this study was to investigate how seasonal and interannual climate variations affect ANPP and the partitioning between canopy and wood production at three forest sites differing in topography and disturbance history in SW Costa Rica. In each of the three forests, wood production and fine litterfall were monitored at monthly time resolution since 2005. We moreover identify major drivers of tropical forest ANPP by integrating our results into a dataset of >100 tropical old growth forests where canopy and wood production have been reported respectively. Across all forest sites MAT was the strongest predictor of ANPP (0.31 Mg C ha-1 yr-1 per °C) but the response differed between lowland and montane forests. Our results suggest a shift in the allocation of biomass towards greater nutrient conservation (i.e. production of wood biomass) in more productive lowland forests, whereas nutrient recycling processes (i.e. production of canopy biomass) predominate in less productive, montane forests. We demonstrate that both ANPP components are sensitive to climate variation, both in a local and a global context, but that the controls differ for canopy and wood production. Climate change may therefore shift the balance between nutrient recycling (canopy production) and carbon sequestration (wood production) and thus adversely affect ecosystem functions of the tropical forest biome.

Link: ATBC/OTS 2013, San José, Costa Rica


 

The importance of small gallery forest strips as biological corridors for forest species in a human-dominated landscape in southern Costa Rica

Small riparian tropical forest strips represent biological corridors besides protecting human-dominated landscapes against soil erosion. Using butterflies, dragonflies and birds, we studied the importance of such common structures for forest species in the Pacific lowlands of southern Costa Rica. All taxonomic groups were surveyed at primary forest sites as well as in gallery forests connected to remaining forest and isolated from closed old-growth forest.

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Butterflies and dragonflies were recorded along transects. Point counts and mist-netting were used to inventory bird assemblages. Our results indicate that, although primary forest sites represent the most diverse habitat type, substantial numbers of forest species can be found in gallery forests, particularly when connected to remnant forest fragments. Although these riparian forest strips may act as a filter for a major proportion of forest birds, dragonflies and butterflies, our studies emphasize their potential for contributing to an increase of the permeability of human-dominated landscapes for forest species.

Link: https://atbc.confex.com/atbc/2013/webprogram/Paper2589.html


 

Controls on aboveground net primary production of tropical rainforests

Aboveground net primary production (ANPP) of tropical forests is driven by soil fertility and climate, the latter receiving special attention as recent projections of global circulation models predict large tracts of tropics to become drier and warmer. Given the scarcity of manipulative experiments, global climate-ecosystem relations and interannual climate variations caused by El Niño Southern Oscillation have been used to assess potential responses of tropical ANPP to projected climate change. The focus of this study was to investigate how seasonal and interannual climate variations affect ANPP and the partitioning between canopy and wood production at three forest sites differing in topography and disturbance history in SW Costa Rica. In each of the three forests, wood production and fine litterfall were monitored at monthly time resolution since 2005. We moreover identify major drivers of tropical forest ANPP by integrating our results into a dataset of >100 tropical old growth forests where canopy and wood production have been reported respectively.

Across all forest sites MAT was the strongest predictor of ANPP (0.31 Mg C ha-1 yr-1 per °C) but the response differed between lowland and montane forests. Our results suggest a shift in the allocation of biomass towards greater nutrient conservation (i.e. production of wood biomass) in more productive lowland forests, whereas nutrient recycling processes (i.e. production of canopy biomass) predominate in less productive, montane forests. We demonstrate that both ANPP components are sensitive to climate variation, both in a local and a global context, but that the controls differ for canopy and wood production. Climate change may therefore shift the balance between nutrient recycling (canopy production) and carbon sequestration (wood production) and thus adversely affect ecosystem functions of the tropical forest biome.

Link: http://abstractsearch.agu.org/