Community Structure (Niche Limitation and Guild Proportionality) in Relation to the Effect of Spatial Scale, in a Nothofagus Forest Sampled with a Circular Transect

A Nothofagus-dominated rainforest in eastern Fiordland, New Zealand, was sampled by shoot frequency in contiguous 1 x 1 m quadrats, along a topologically-circular transect. The data were analysed at five scales up to 5 x 1 m, to search for assembly rules, i.e., generalised restrictions on species co- occurrences. There was no evidence of niche limitation in terms of the whole community, at any scale examined. Rather, variance in species richness was greater than expected from a null model, suggesting environmental heterogeneity. This conclusion was confirmed by using a patch-model. Guild structure was examined in terms of synusiae, based on vertical stratification. The proportion of species in a quadrat that were from the Herb guild was significantly more constant than expected under the null model. However, using a patch-model this effect was reduced, and no longer significant. This suggests pools of species adapted to different micro- environments, but with parallel guild composition. Liane guild proportions were more variable than predicted by the null model; although this effect was not significant, it parallels reports from other South Island forests. The work confirms conclusions from previous work, that plant assembly rules are to be found only at small spatial scales. Processes leading to high and low variance in species richness and in guild proportions are discussed. Selection of a uniform site in the present work, and use of a patch-model, make it less likely that effects are due to environmental or historical effects. The use of guild proportionality as the criterion eliminates the effect of limitation on the number of individuals that can co-occur locally.