Influence of grazing on the decomposition of Pinus pinea L. needles in a silvopastoral system in Doñana, Spain
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The aim of this study was to determine whether goat grazing in the understory of a pine forest at Doñana Natural Park could accelerate the decomposition of the pine needles accumulated on the soil surface and, if so, through which mechanisms. Specifically, the roles of trampling (mechanical fragmentation) and nutrient enrichment through defecation (fertilization) were evaluated in terms of their effect on pine needle decomposition rates.
An experiment was conducted featuring the following 4 treatments: 1) intact needles (control), 2) trampled needles, 3) intact needles fertilized with liquid manure, and 4) trampled needles fertilized with liquid manure. Litter decomposition was determined as a function of mass loss over time, using the litter-bag method. Bags were recovered 4, 8, 16, 24 and 36 months after burial in soil, dried and weighed. Needle length, leaf mass per area and C and N concentration were also measured in the buried litter-bags.
Four months after burial, mass loss was greater in the trampled (23–27 %) than non-trampled (14–16 %) treatments. However, from 8 months onwards, decomposition rates in the fertilized treatments were significantly higher than those in the non-fertilized treatments (between 5 % and 15 % less mass loss). Meanwhile, fertilized treatments presented higher N content (2.1 %) than the non-fertilized ones (1.2 %), with a significantly lower C:N ratio also found in the in the fertilized treatment.
Trampling and fertilization during grazing accelerates litter decomposition and thus promotes the incorporation of N into the system. Acceleration of decomposition reduces the accumulation of pine needles on the soil surface, reducing the risk of fire.
KeywordsDecomposition rate Leaf litter Carbon Nitrogen Goat grazing Pine needles
The authors wish to thank Doñana Natural Park and Dehesa de Gatos S.L. for the logistic support and field facilities. We also thank Dr. R. Fernández-Ales and Dr. J.A. Merino for their useful comments on an earlier version of this manuscript. Dr. R. F. Lo Faso and Keith MacMillan revised the English version of the manuscript. This study was funded by the Consejería de Medio Ambiente (Junta de Andalucía) (OG-052/07). J.M. Mancilla-Leytón gratefully acknowledges a F.P.D.I. grant (Junta de Andalucía).
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