Half a century of change in floristics and structure in an urban grassy woodland – implications for conservation management

James Kirkpatrick; Ian Jenkinson; Kerry Bridle

Just Accepted

This article has been peer reviewed and accepted for publication. It is in production and has not been edited, so may differ from the final published form.

Half a century of change in floristics and structure in an urban grassy woodland – implications for conservation management

James Kirkpatrick , Ian Jenkinson, Kerry Bridle

Abstract

Context. Vegetation remnants enveloped by built up areas tend to drift away in their character from vegetation on similar sites in more extensive patches of native vegetation, but may stabilise in synthetic (novel) form with time in harmony with disturbance regimes and environmental change. Managers may be able to induce a synthetic state that maintains the nature conservation values of such remnants. Aims. We examine the degree to which the nature conservation values of the the vegetation of a 19th century urban reserve in nipaluna (Hobart), lutruwita (Tasmania) changed between 1974 and 2022/3 in a period of climate change and changes in vegetation management, with the aim of discerning appropriate conservation management regimes. Methods. Sixty-nine 1 x 15 m quadrats were randomly located in the non-cultivated part of the Domain in 1974 and roughly relocated for sampling in 1984, 1994, 2001 and 2022. Tree diameters were recorded using the point-centred quarter method in 1974, 1984, 1994, 2001 and 2023. The responses of native and exotic species richness, and the frequency of the more common species, to time and other predictor variables related to time since last fire, evidence of mowing at the time of the survey, and topography were determined using linear modelling, correlation, analysis of variance and Chi-square. Key results. The native tree, Allocasuarina verticillata was the only significantly varying consistent increaser out of 67 taxa. The native perennial herbs Acaena echinata and Leptorhynchos squamatus and the non-native shrubby weed Chrysanthemoides monilifera were the only significantly varying consistent decreasers. However, several rare and threatened species too infrequent for statistical analysis also declined between 2022/23 and 2000. Twenty-four of the 67 taxa with sufficient data for analysis did not significantly vary between years. The percentage of native species in quadrats did not change through time. It was negatively related to mowing and the time since fire. Native tree stems 10-30 cm in diameter and those over 30 cm increased through time, while those less than 10 cm in diameter increased dramatically until 2000 then strongly decreased by 2023. Total stem density increased through time. Conclusions. Mowing and fire regimes strongly influence the distributions of a large proportion of native taxa independent of time and underlying environment, largely by controlling the density of the small tree layer which can potentially form closed-forest without eucalypts. Implications. It is possible to use fire, mowing and slashing to maintain nature conservation values in synthetic urban grassy woodland, although the maintenance of the rarest native species requires more specific and varied interventions.

BT24042 Accepted 03 December 2024