Efficiency in assessment and monitoring methods: scaling down gradient-directed transects

Abstract

Rapid survey methods are needed that accurately detect both species richness and relative abundance for surveying new sites and/or for long-term monitoring.We investigate whether the large-scale gradsect survey method of Gillison can be adapted for a smaller scale more suitable for monitoring or research. Three different designs that are compared are typical random small plot sampling and two transect designs that are modifications of gradient-directed transects (gradsects).We did intensive work at one site, and surveyed another eight sites. In contrast to most methods comparison work, we develop a baseline reference dataset for ‘true species richness and relative abundance’ by using more than 400 randomly-located small plots. Monte Carlo randomizations determined the minimum sample number for each type of sampling method for thresholds of species richness and abundance. The modified gradient- directed transects were accurate for both richness and abundance, even for uncommon species, and with much greater efficiency than random sampling.