Production Ecology I. Standing Crops of Natural Vegetation

Abstract

apparently point to some features of general interest. Our data refer entirely to attempts to estimate the average weight of a complete vegetation cover. The estimate is based on the dry weight of the standing crop towards the end of the growing season and is limited to species in which this can be made directly by cutting the aerial shoots. We used for this purpose material such as the leaves and shoots of grasses, sedges and rushes as well as leaves of bracken (Pteridium aquilinum). It is probable that in order to make such estimates accurately we should require detailed knowledge of the seasonal physiology of some of the species under field conditions. In addition, no account is taken in these estimates of the proportion of the plant underground or of the proportion of the dry weight gain that is translocated from the shoots to these subterranean storage organs. In the present survey, however, we were more concerned with the attempt to define the problems of estimation than with the accurate analysis of any one of them. For this purpose it is necessary only to remark that the species examined were all perennial and therefore, in some respects at least, the standing crop will represent an integration of the present season's dry weight accumulation, the organic matter stored in the previous growing season and the manner in which the general habitat conditions controlling growth have affected the growth process and dry weight accumulation. The basis of the method used was to estimate the dry weight of the standing crop in a quadrat of known area. In the first season (1952), for work mainly on fen vegetation and reedswamps (with four or six collectors), we used one sq. m. quadrats, but the weight of material collected and the difficulties met with in transporting and drying it, soon made it apparent that we could only conveni