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

Jamie B. Kirkpatrick; Ian Jenkinson; Kerry L. Bridle

doi:10.1071/BT24042

RESEARCH ARTICLE (Open Access)

Previous Contents Vol 73(1)

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

Jamie B. Kirkpatrick

^A , Ian Jenkinson ^A and Kerry L. Bridle

^A ^*

+ Author Affiliations

- Author Affiliations

^A School of Geography, Planning and Spatial Sciences, University of Tasmania, Private Bag 78, Hobart, Tas 7001, Australia.

^* Correspondence to: Kerry.Bridle@utas.edu.au

Handling Editor: Steve Sinclair

Australian Journal of Botany 73, BT24042 https://doi.org/10.1071/BT24042

Submitted: 21 July 2024 Accepted: 3 December 2024 Published: 9 January 2025

© 2025 The Author(s) (or their employer(s)). Published by CSIRO Publishing. This is an open access article distributed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License (CC BY-NC-ND)

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 2022/23 in a period of climate change and changes in vegetation management, with the aim of discerning appropriate conservation management regimes.

Methods

Sixty-nine 1 × 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-squared.

Key results

The native tree Allocasuarina verticillata was the only significantly varying consistent increaser 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 among 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, whereas 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 influenced 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.

Keywords: fire regimes, grassland, grassy woodland, mowing, nature conservation values, rare and threatened plants, synthetic vegetation, temporal change, vascular plants.

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