The use of plant functional types as a method of determining plant biodiversity and keystoneness in a northern New Zealand isocline : a thesis presented in partial fulfilment of the requirements for the degree of Master of Applied Science in Plant Science at Massey University, New Zealand

Abstract

New Zealand vegetation, like the rest of the world, is undergoing increased perturbations due to global climate change. Whether anthropocentric in origin or part of a natural climatic cycle, increased CO₂, increased temperature plus changing regimes of precipitation have been recorded. Environmental change, especially at local levels, does affect community structure. New Zealand's ancient endemic trees and shrubs face the greatest threat of extinction, mainly due to habitat destruction by man for development and by introduced pests. The consequence could be that these trees and shrubs would not be able to migrate naturally in the time frame that climatic change will allow. The use of Plant Functional Types in climate change research is extensive and these groupings are being used more frequently in the study of diversity response to environmental change. The objectives of the Maunganui Bluff study were to develop a methodology to construct PFTs and to utilise these functional groupings in an analysis of the isocline. These analyses were; a diversity study based on richness and abundance, a site ordination and a group analysis. A total of forty-eight PFTs were constructed, then reduced to seventeen. The final seventeen functional groups were used in the following analyses. 1. A diversity analysis. While not appearing useful in comparing species evenness to PFT evenness over the isocline, the analysis did confirm that at that point in space and time when sampling was undertaken, PFTs did conform to the assembly rule for groups. This rule states that there should be equal representation of functional groups at each site from the total available pool 2. Ordination. The second analysis was to determine the effect of the local environment on the spatial position of the PFTs on the isocline. Detrended Correlation Analysis (DCA), an ordination technique, was used to map the groups and the sites against environmental gradients. The results signified that a small number of groups were strongly influenced by potassium (K) but the majority of groups occupied specific sites, on an altitude – phosphorus and nitrogen gradient, due to competition for resources. This summation is supported by altitude being linked to precipitation and leaching, since most of the other environmental data, measured and analysed, were correlated to altitude. 3. Group analysis using Indicator Species Analysis in the computer programme PCORD. The statistical analysis highlighted three PFTs with high keystone rankings p*>.800), one of which was missed by a subjective analysis of the site map of PFTs distribution. When these three groups were deconstructed back to species, the membership of each group was only one species. Of these three species, only Haloragis erecta appeared to be out of place within the gradient. Four hundred metres in altitude is well beyond the plants recognised limit of approximately 120 metres. Since sea level to one hundred and fifty metres is the shrubland zone and site K is also, by species sampled, designated a shrubland, there is evidence that some environmental factor may be associated with these sites. Obviously, this cannot be tested, as there were no Haloragis erecta in the sampled sites from sea level to one hundred and fifty metres. The analysis suffered from a lack of replication for the site under study, as well as comparative sites, to determine the validity of the methodologies. The results while encouraging only reflect a point in both space and time. The work would have needed a much larger range of environmental data, over a longer time frame to ensure that the results were not chance, and would be sustained under more detailed statistical rigor. Many of the premises that the work was based on are subjective. However, despite the lack of statistical rigor, the study confirms the work being carried out using PFTs in other countries. New Zealand's endemic plants do have assembly rules and PFTs constructed with New Zealand natives are valid assemblages that can be used in statistical analysis, and may well turn out to be important in monitoring environmental change.