Nutrient cycling in deciduous forest ecosystems of the Sierra de Gata mountains: aboveground litter production and potential nutrient return

The potential nutrient return in a chestnut coppice (Castanea sativa Miller ) over a period of 3 years (1991-1994) has been established and compared wi th the returns found in four deciduous oak (Quercus pyrenaica Wild.) forest s (1990-1993) located in the Sierra de Gata mountains (central Spanish syst em). A convergence of abscission phenology patterns was observed among the different ecosystems studied,together with a delay in leaf fall at the warm est plot. This similarity is logical since the plots harbour the same decid uous species which are, however, subjected to climatological variations. Th e chestnut coppice was found to be more productive than the oak forests, th e amounts of leaves, branches, flowers and total litterfall being significa ntly greater. Statistical analysis showed a highly significant correlation between the chestnut coppice and the oak forest aboveground production, ran ging between 0.82 and 0.96 for the leaves and between 0.72 and 0.89 for the total litter. In general, the leaf organs of the chestnut trees showed a h igher concentration of bioelements than the oaks, with N and Ca predominant in the buds, Ca and Zn in the branches, K in the fruits, and above all Fe and Cu in the other plant remains. In all the forests studied, the potentia l nutrient supply fluctuated over the years and depended strongly on phenol ogical factors; above all it was found to be governed by the leaves, which contributed most to the return of mineral nutrients to the soil. The most m arked potential nutrient return through the oak aerial organs occurred on t he plot with the lowest rainfall, particularly with respect to P and Ca. Co nsidering all the forest plots, the general sequence of the amount of bioel ements returning with the litterfall to the soil was as follows: C > N > Ca > K > Mg > P > Mn > Na > Fe > Zn > Cu with the exception of one oak plot (with an acid soil reaction and poor soi l drainage), when the Mn return was higher than that of P owing to the high concentration of Mn in all the litter components. (C) Inra/Elsevier, Paris .