Browsing by Autor "Christian Seiler"

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Modeling forest dynamics along climate gradients in Bolivia
(Wiley, 2014) Christian Seiler; Ronald Hutjes; Bart Kruijt; Jhazel Quispe; S. Añez; Vivek K. Arora; Joe R. Melton; Thomas Hickler; P. Kabat
Abstract Dynamic vegetation models have been used to assess the resilience of tropical forests to climate change, but the global application of these modeling experiments often misrepresents carbon dynamics at a regional level, limiting the validity of future projections. Here a dynamic vegetation model (Lund Potsdam Jena General Ecosystem Simulator) was adapted to simulate present‐day potential vegetation as a baseline for climate change impact assessments in the evergreen and deciduous forests of Bolivia. Results were compared to biomass measurements (819 plots) and remote sensing data. Using regional parameter values for allometric relations, specific leaf area, wood density, and disturbance interval, a realistic transition from the evergreen Amazon to the deciduous dry forest was simulated. This transition coincided with threshold values for precipitation (1400 mm yr −1 ) and water deficit (i.e., potential evapotranspiration minus precipitation) (−830 mm yr −1 ), beyond which leaf abscission became a competitive advantage. Significant correlations were found between modeled and observed values of seasonal leaf abscission ( R 2 = 0.6, p <0.001) and vegetation carbon ( R 2 = 0.31, p <0.01). Modeled Gross Primary Productivity (GPP) and remotely sensed normalized difference vegetation index showed that dry forests were more sensitive to rainfall anomalies than wet forests. GPP was positively correlated to the El Niño–Southern Oscillation index in the Amazon and negatively correlated to consecutive dry days. Decreasing rainfall trends were simulated to reduce GPP in the Amazon. The current model setup provides a baseline for assessing the potential impacts of climate change in the transition zone from wet to dry tropical forests in Bolivia.
The sensitivity of wet and dry tropical forests to climate change in Bolivia
(Wiley, 2015) Christian Seiler; Ronald Hutjes; Bart Kruijt; Thomas Hickler
Abstract Bolivia's forests contribute to the global carbon and water cycle, as well as to global biodiversity. The survival of these forests may be at risk due to climate change. To explore the associated mechanisms and uncertainties, a regionally adapted dynamic vegetation model was implemented for the Bolivian case, and forced with two contrasting climate change projections. Changes in carbon stocks and fluxes were evaluated, factoring out the individual contributions of atmospheric carbon dioxide ([CO 2 ]), temperature, and precipitation. Impacts ranged from a strong increase to a severe loss of vegetation carbon ( c v ), depending on differences in climate projections, as well as the physiological response to rising [CO 2 ]. The loss of c v simulated for an extremely dry projection was primarily driven by a reduction in gross primary productivity, and secondarily by enhanced emissions from fires and autotrophic respiration. In the wet forest, less precipitation and higher temperatures equally reduced c v , while in the dry forest, the impact of precipitation was dominating. The temperature‐related reduction of c v was mainly due to a decrease in photosynthesis and only to lesser extent because of more autotrophic respiration and less stomatal conductance as a response to an increasing atmospheric evaporative demand. Under an extremely dry projection, tropical dry forests were simulated to virtually disappear, regardless of the potential fertilizing effect of rising [CO 2 ]. This suggests a higher risk for forest loss along the drier southern fringe of the Amazon if annual precipitation will decrease substantially.