A survey of the lowland vegetation of the upper clutha district of otago, new zealand

Abstract

The low-altitude parts of the Upper Clutha have the nearest to a continental climate in New Zealand, with little-described vegetation comprising a mixture of native and exotic species. The vegetation ranges from remnants of Kunzea ericoides woodland to a “semi-desert” with bare soil between mats of scabweed (Raoulia australis). A vegetation survey was made, and the vegetation summarised for convenience by Cluster Analysis into eight major communities. The “Salix” community occurs in the wettest sites. Other wet sites had a variety of vegetation, and are categorised as “Wet Miscellaneous”. “Dactylis/Cirsium pasture” includes agricultural pasture plants and weeds. Three drier communities can best be characterised overall by the presence of Rumex acetosella and Vulpia megalura. The “Verbascum/Thymus/Rumex” community tends to have present one or more of V. thapsus, T. vulgaris and R. acetosella. It tends to occur at lower altitude than the following two communities, and on east-facing aspects. The “Rosa/Leucopogon” community occurs on steeper slopes where agricultural disturbance has been less intensive. The “Echium/Verbascum” community is characterised by E. vulgare, V. virgatum and Bromus diandrus. The “Dry Bromus” community occurs on dry but relatively deep soils, quite flat sites, always with Bromus tectorum, often with Trifolium arvense and Bromus mollis, and with very few other species. The “Dry Trifolium/Echium” community, characterised by T. arvense and E. vulgare, occurs more towards the east, on moderately deep soils, with little slope. The “Scabweed” community is probably the most water-deficient, with Raoulia australis the most constant species. Ordination confirms the importance of moisture in controlling the distribution of communities. The communities identified, although considered the best summary available of variation in the vegetation, are nevertheless hard to characterise by particular species, are only loosely related to the environment, and are widespread geographically. Together with poor concentration of presences in the classification two-way table, poor performance by a monothetic classification, and poor summarisation by the first ordination axis, this suggests that the vegetation is weakly structured. This could be because of complicated environmental control, or because of a stochastic element in species occurrence, but it more probably reflects lack of equilibrium in the vegetation. © 1988 Taylor & Francis Group, LLC.