The use of point quadrats for the analysis of heathland

Abstract

A brief theoretical examination of the relationships between the orientation of leaves on a plant and the area of their projections is made and it is then shown how, for heathland species, inclined point quadrats give appreciably different and usually higher estimates of percentage cover than do vertical point quadrats. The use of inclined point quadrats for estimation of percentage contribution to the vegetation is examined and found to have no real advantage since no increase in precision is obtained with their use. Errors caused by the thickness of point quadrat pins are found to be large for the estimation of percentage cover in the microphyllous heathland vegetation. These can be minimized by the use of a cross-wire sighting tube, but an experiment shows that caution must be exercised in using this device because of the intertangling of the foliage of the various species. Estimates of percentage contribution were hardly affected by pin size. When pins were randomised independently over the test area, considerably lower variance for both percentage cover and contribution estimates were obtained compared with pins held in frames of 10.