Estimation of plant species richness from systematically placed plots in a managed forest ecosystem

Abstract

A Danish managed forest of 325 hectares was sampled for plant species richness in a regular 100 × 100 m grid using four nested quadrates of 2, 4, 25, and 200 m2, respectively, at each sample point. The survey resulted in total counts of 161, 171, 224, and 289 species depending on size of quadrates. A list of more than 370 species, however, was accumulated for the forest based on the present study, the literature, and additional personal observations. It was shown that species richness estimators and especially the log-log estimator resulted in improved estimates of species richness. It was also shown that a search strategy in which plots with high habitat diversity in the immediate neighbourhood or plots close to forest roads were chosen first was more effective than a random search strategy. The random strategy, on the other hand, was more efficient than emphasising core areas of major habitat types in the beginning of the search. The study has clearly demonstrated that a managed forest ecosystem with its mixture of open areas and different stands can harbour a very high plant species diversity (in this case ca. 25% of the total Danish flora in only 325 hectare). It is also shown, however, how difficult and time consuming it is to count all species in a heterogeneous ecosystem.