No abstract

The dry-weight losses of samples of oak and ash litter, enclosed in nylon hairnets and placed on two sites with contrasting humus forms, a mull and a moder, have been followed for a period of 14 months. Sub-samples of the same oak litter disappear at similar rates on the two sites. Sub-samples of the same ash litter disappear at different rates on the two sites, but always more quickly than oak litter. On the mull site the loss of whole ash leaflets as well as fragments of leaflets is considerable whereas oak leaves on both sites and ash leaflets on the moder site disappear mainly as small fragments. For both oak and ash litter the results from the mull site are more variable than those from the moder site, suggesting that there are differences in the heterotrophic activity on the two sites.

Different trends have been demonstrated in the changes in composition taking place in sub-samples of the same ash litter placed in nylon hair-nets on neighbouring sites with mull and moder-type humus forms. Similar trends have been shown to occur for oak litter and ash Iitter pIaced on the same moder site. T h e percentage nitrogen content of ash litter on the mull site remains virtually constant during the first 7 months of decomposition whereas on the moder site the content increases steadily for both ash litter and oak litter. T h e nitrogen content of oak litter is increased by considerable addition from outside. Possible sources of this additional nitrogen are considered. Extraction with hot water of litter at different stages of decomposition shows that the initially large water-soluble fraction, which is poor in nitrogen, is leached out more quickly from ash than from oak litter.