The breakdown and decomposition of sweet chestnut (Castanea sativa Mill.) and beech (Fagus sylvatica L.) leaf litter in two deciduous woodland soils : I. Breakdown, leaching and decomposition.

Weight losses from sweet chestnut and beech leaves, attributable to biotic and abiotic breakdown processes, leaching and microbial decomposition have been studied using tethered leaves and litter bags. The experimental sites were two adjacent areas of deciduous woodland. In one area (the Castanea site) a mor-like moder humus form has developed under a stand dominated by coppiced chestnut, in the other a mull-like moder underlies a stand of coppiced beech (the Fagus site).Chestnut leaves in the Castanea site are primarily comminuted by abiotic processes (wind, rain, hygroscopic movements, etc.) and soil animals make a relatively small contribution to leaf litter breakdown. After 31 months in the field 36.03% of the initial weight of chestnut leaves remained in the fine mesh bags against 22.82% in the coarse mesh bags. Weight losses from the coarse and fine mesh bags containing beech litter were not significantly different after 31 months when a mean weight of 57.10% of the litter remained.In the Fagus site, leaf litter breakdown was mainly due to the feeding activities of earthworms. However, chestnut leaves were more readily selected than beech leaves. After 8 months in the field nearly 45% more chestnut leaf material had been lost from the coarse mesh bags than from the fine mesh bags. Weight losses from the coarse and fine mesh bags containing beech litter were not significantly different after 31 months, when a mean weight of 43.30% of the litter remained.The leaching and decomposition rates of either type of leaves were not significantly different in the two sites. Chestnut leaves in fine mesh bags lost weight at twice the rate of beech leaves under similar conditions during the first 20 months of the study; however, most of the weight losses from beech and up to 75% of the losses from chestnut were attributable to leaching rather than to microbial decomposition. The rates of weight losses from the chestnut litter in fine mesh bags declined over the last year of the study, but beech maintained approximately constant weight loss rates for 31 months in the field. This difference may be due to different rates at which similar proportions of water soluble materials were leached from the leaves.A major defect in the litterbag technique is demonstrated. The litter bags maintain the micro-environmental characteristics of the surface litter layers and do not follow the breakdown and decomposition pattern of the leaf litter year class from which the experimental material was drawn.