The woody vegetation of Central Otago, New Zealand

Abstract

The present native and exotic woody vegetation of the rainshadow region of Central Otago, in eastern South Island, New Zealand, is described. Fourteen present-day associations of woody species are related to a gradient in elevation and climate, and to the degree of disturbance by fire and mammalian grazing since human settlement. A few closed-canopy forest remnants remain only in the montane zone, while more modified forest relicts are scattered across a wider range of environments. Remaining woody plant associations have originated as secondary successions following fire, and range from exotic-species-invaded lowland associations on semi-arid basin floors to prostrate, native-species-dominated associations on mountain tops. Indigenous short-tussock grasslands and seral shrublands are being invaded by exotic trees and shrubs, especially in lowland environments. Dwarf and prostrate low shrub associations on the range tops may have replaced tussock grasslands since the commencement of pastoralism, where taller tussockshrubland communities were destroyed by fires soon after human settlement. The region's vegetation is not at equilibrium, and taller, woody communities tend to develop following removal of fire and B03034;

Macrofossil evidence for pre‐settlement vegetation of Central Otago's basin floors and gorges

“…In particular, some have argued that grasslands or shrub-grassland mosaics were extensive in the interior basins of Central Otago, either because an extreme climate (combining late summer water deficits and severe winter frosts) excluded tall woody vegetation (e.g., Wardle 1991 ) or because fire m aintained m ixtures of grasses and shrubs and prevented woody dominance (e.g., Mark & Dickinson 2003;Bond et al 2004). These propositions have been challenged by evidence that water deficits and winter temperature minima are not sufficiently severe to have excluded tall woody vegetation from these intermontane basins and valley floors (Walker et al 2004a), and that pre-settlement fires were rare and/or local (Rogers et al 2007a). …”

“…Rainfall and temperature gradients are steep, and range tops receive several metres of rainfall each year (mark 1965). The present vegetation patterns of the region reflect these environmental gradients but are strongly influenced by past disturbances of fire and herbivory (Walker et al 2004a). Plants introduced by european settlers are widespread and prominent, especially sweet briar (Rosa rubiginosa), thyme (Thymus vulgaris), pasture grasses, and herbs.…”

“…although representation of Poaceae in pre-settlement Central Otago pollen diagrams is higher than in those from other eastern South island regions (Rogers et al 2007a), overall percentages are relatively minor compared with post-settlement levels (Clark et al 1996;mcGlone & moar 1998;Rogers et al 2007a). Walker et al (2004a) showed that many native woody plant species tolerate the most extreme climatic conditions of Central Otago, and therefore the natural vegetation of the lowlands was not necessarily restricted to grassland.…”

“…Discaria toumatou is also currently widespread in Central Otago woody plant associations (Walker et al 2004a). This study found just a single spine from this species, in earnscleugh Cave (Table 2), which could have been derived from modern plants.…”

Palynology and the Ecology of the New Zealand Conifers

“…Therefore, in New Zealand, palaeoecological and neoecological researchers frequently collaborate as our exploration of conifer history shows. Not only that, neoecologists have often taken the lead in study of the past, as exemplified by Peter Wardle with his Quaternary investigations of soil charcoal (Wardle, 2001a), Colin Burrows and the palaeoecology of the South Island mountains (Burrows et al, 1993), Susan Walker, Bill Lee and Geoff Rogers on the history of the drylands of the southern South Island (Walker et al, 2004b), and the ground-breaking neo-palaeoresearch by ecologist John Ogden and colleagues on many aspects of northern plant successions and Quaternary history (for example: Ogden et al, 1992Ogden et al, , 1997.…”