Methods for monitoring herbivory and growth of New Zealand mistletoes (Loranthaceae)

This study provides the first quantitative comparison of methods for monitoring herbivory and growth of New Zealand beech mistletoes (Alepis flavida, Peraxilla colensoi and Peraxilla tetrapetala). Four monitoring methods-leaf maps, volume estimates visual estimates of browse and foliage density, and rePeat fixed-point photographs-were used to assess the health of 60 permanently tagged mistletoe plants in four South Island beech forests between February 1997 and February 1998. Leaf maps provided the most detailed information but were extremely labour-intensive so could only be used to monitor a small number of plants. Photographs were much faster to use, and the results corresponded well to leaf map data, but A. flavida could not be photographed because it was frequently hidden by host foliage. Visual scoring methods and volume measurements did not correlate well with leaf maps, probably because leaf loss and growth were not obvious without images of plants from previous seasons. Thus, photographs can provide valuable reference points for future evaluation of plant condition. However, because photos require more time and money than visual scoring and can only be used on a subset of the population, their most practical use is as a supplement to visual scoring.