Oak decline reduces soil respiration and nitrogen and phosphorus availability in Mediterranean mixed forests

Poster presentado en el 99th Annual Meeting will be held August 10-15, 2014, in Sacramento, CA. This meeting's theme is “From Oceans to Mountains: It’s All Ecology.”.

Background/Question/Methods In the last decades an increasing number of tree decline events have been detected worldwide. Extensive work has been conducted to analyze the main causes underlying these processes (climate change, pollution, exotic pathogens). However, few works have focused on the potential consequences of forest decline for ecosystem functioning. Oak forests of the Iberian Peninsula are affected by severe tree mortality of one of their dominant species, cork oak (Quercus suber). A soil-borne exotic oomycete pathogen, Phytophthora cinnamomi, has been identified as the main cause of this decline. In this work, we assessed the consequences of cork oak decline on C, N and P cycles in six mixed oak forests of Southern Spain. Specifically, we measured soil respiration and N and P availability in spring and summer of three consecutive years (2010-2012), and developed spatially-explicit neighborhood models that predicted the effects of the distribution and abundance of cork oak trees of different health status (healthy, defoliated and dead) on these ecosystem properties. Results/Conclusions Soil respiration rates were lower in tree neighborhoods dominated by dead cork oaks than in neighborhoods dominated by alive oaks (either healthy or defoliated). Furthermore, we detected a negative effect of the abundance of defoliated and dead cork oak neighbors on nutrient availability. These negative effects on C, N and P cycles could be due to a decrease in root activity and in primary production in trees affected by decline. Neighborhood effects were detected mainly in summer, and their magnitude varied between sites. In summary, our results suggest that the decline and mortality of cork oak trees imply important ecosystem alterations by decreasing cycling rates and pools of carbon and nutrients in soils of Mediterranean forests.

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