ELSEVIER 0006-3207(94)00122-7 Biological Conservation 74 (1995) 1-8 Elsevier Science Limited Printed in Great Britain 0006-3207/95/$09.50+.00 MAINTAINING INTEGRITY COMPARED WITH MAINTAINING RARE AND THREATENED TAXA IN REMNANT BUSHLAND IN SUBHUMID TASMANIA J. B. Kirkpatrick & L. Gilfedder Department of Geography and Environmental Studies, University of Tasmania, Box 252C, GPO, Hobart 7001, Australia (Received 19 May 1994; revised version received 14 October 1994; accepted 19 October 1994) Abstract The native vegetation remnants in the agricultural coun- try of subhumid Tasmania are important strongholds for regionally and globally rare and threatened species. A detailed survey of the best 100 of these remnants indi- cated that there was no relationship between the size, age and juxtaposition of the remnants and an index of rare and threatened species, either in the data set as a whole or in phytosociologically defined subsets. Rare and threatened species were found in remnants of widely varying integrity, as indicated by native and exotic species richness and cover. Some species were only found in remnants that were of poor integrity. Efforts to preserve vegetation remnants need to be directed towards both those that are representative and of high.integrity, and those that contain rare and threatened species. No great coincidence can be expected, because the causes of maintenance of good condition are not necessarily the causes of survival of many rare and threatened taxa. Keywords: rare and threatened, plants, vegetation, integrity, Tasmania. INTRODUCTION During the two centuries of European settlement of Australia the vegetation of the temperate subhumid cli- matic zone of Australia has been largely transformed from a native species composition to cultural vegeta- tion composed of exotic species. Remnants of native vegetation have survived on shallow soils, steep slopes, roadsides, rail reserves, other small special-purpose reserves and home and back paddocks. Elements of the native biota also survive in the seminatural vegetation that forms part of variegated (McIntyre & Barrett, 1992) grazing country landscapes. Remnants that largely consist of native species form a very small pro- portion of the original areas of particular vegetation types. For example, only 0.5% of the original area of southeastern Australian lowland temperate grassland remains intact (McDougall & Kirkpatrick, 1994). In Tasmania, 88% of the grassy woodland has been con- verted into agricultural land (Kirkpatrick et al., 1988). In Western Australia more than half the kwongan veg- etation has been cleared (Beard, !984) and in some parts of the wheat belt less than 6% of the original veg- etation survives (Hobbs & Saunders, 1991). The loss of this native vegetation continues apace (e.g. Kirkpatrick, 1991; McDougall & Kirkpatrick, 1994), as do processes of remnant degradation. The high proportional losses to clearance and degra- dation experienced by the temperate subhumid ecosys- tems have resulted in a high concentration of rare and threatened species and communities in the surviving remnants (e.g. Hopper & Muir, 1984; Kirkpatrick et al., 1988). The lack of extensive areas suitable for eco- logical reserves sensu Specht et al. (1974), and the vari- able incidence of rare and threatened species and communities between remnants, makes it imperative that we conserve biological diversity by the mainte- nance or improvement of the condition of some very small areas (Saunders et al., 1987). Remnant size has been traditionally regarded as a critical variable in influencing the survival of native species and the invasion of exotics (Saunders et al., 1991). Small remnants have a greater proportion of their area subject to edge effects and a higher prob- ability of low population sizes, and therefore extinction, than larger remnants, all else being equal. Remnant shape also influences viability through its effect on the proportion of the total area subject to edge effects. Remnant connectivity through corridors may be important for maintaining the populations of some taxa (Saunders & Hobbs, 1991), although for most this is an unproven hypothesis (Simberloff et al., 1992). Increased proximity of remnants is likely to increase the rate of immigration of some native species that may become locally extinct. As edge effects and exotic species immigration are time-dependent phenom- ena, the age of remnants may have a critical bearing on their condition. Natural systems of high ecological integrity are taken by some authors to be those that maintain their pro- ductivity, stability and resilience (Pearce et al., 1989). We use the term in the narrower sense of systems that are relatively unaltered from their natural state. In the Australian context the term 'natural' refers to the con- dition of the system prior to European settlement. It has often been implicitly assumed that a reserva- tion/protection strategy that looks after rare and threatened elements of biological diversity will also protect the areas of highest ecological integrity or vice- versa. In this paper we use native and exotic species richness and cover as indicators of integrity of the bush