An Assembly Rule in the Ground and Herbaceous Strata of a New Zealand Rain Forest

Lowland temperate rain forest was sampled in Fiordland, New Zealand. An assembly rule was sought in terms of relative constancy in the proportion of species from seven synusial (stratum) guilds, compared to a null model in which species associate at random. Two forest types were examined (coastal broadleaved and Nothofagus broadleaved), separately and together. 2. The results show more significances than expected on a random basis. 3. In two forest-type/synusia analyses, guild proportions were more variable than expected under the null model. For lianes this is suggested to be the result of old canopy gaps and for shrubs because of topographic variation. 4. There was significant constancy in the proportion of species from the herb synusia. This effect was seen separately in both forest types. A similar effect was seen for the ground synusia, significant when the two forest types were combined. These effects suggest that there is a limitation on the assembly of these forest communities, a constraint on species coexistence that ensures relatively constant representation from the ground and herb guilds. This represents one of the first demonstrations of an assembly rule in plant communities