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

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 gradientdirected transects were accurate for both richness and abundance, even for uncommon species, and with much greater efficiency than random sampling.