The legacy of pasture improvement causes recruitment failure in grassy eucalypt woodland conservation reserves in the Midlands of Tasmania

Abstract

Australia’s most fragmented and least reserved landscapes are the grassy eucalypt woodlands of the south-east. Two hundred years of agricultural disruption have transformed these landscapes, and agricultural enterprises continue to expand and develop, meaning the threats to these landscapes have not abated. The Tasmanian Midlands is primarily privately owned, with very little area devoted to conservation of biodiversity. In this landscape, conservation covenants have been enacted on many private properties with the intention of encouraging tree recruitment and conservation of threatened plant communities and rare species. Evidence of the effectiveness of these covenants in protecting overstorey tree population health is lacking. This study compared the demographic structures of overstorey Eucalyptus species and midstorey tree genera on public and private properties with contrasting land use histories. Reserves on private lands had little tree recruitment, probably because exotic pasture species were common, whereas tree recruitment was abundant in public reserves, where pasture improvement has not occurred. Active measures are needed to restore ecological structure and function in grassy woodland conservation reserves on private land by encouraging regeneration of Eucalyptus and Acacia species as well as returning the ground layer to a functionally native state. This will entail reinstating fire disturbance, reducing exotic pasture species cover and managing domesticated, feral and native herbivores.

Fire, herbivores and the management of temperate Eucalyptus savanna in Tasmania: Introducing the Beaufront fire – mammalian herbivore field experiment

“…Summers are warm and winters are cold, with a mean monthly maximum temperature of 24.8°C in January and a mean monthly minimum temperature of 1.4°C in June at Ross (Bureau of Meteorology 2020). Frost occurs on an average of 100 days annually and is possible in any month (Romanin et al 2019). The region exists in a topographic rain shadow, with the Central Plateau blocking the prevailing, rain-bearing westerly winds and the Eastern Tiers intercepting periodic moist easterly flows.…”

“…The region exists in a topographic rain shadow, with the Central Plateau blocking the prevailing, rain-bearing westerly winds and the Eastern Tiers intercepting periodic moist easterly flows. There is approximately 500 mm mean annual precipitation, distributed evenly throughout the year (Romanin et al 2019). During the late Pleistocene, when Tasmania was a peninsula of mainland Australia, the Midlands experienced lower temperatures and much greater aridity, resulting in the development of aeolian landforms such as dunes (McIntosh et al 2012).…”

“…A number of schemes have been developed to provide financial incentives to landowners to conserve these fragments (Iftekhar et al 2014). Nonetheless, there is evidence that tree populations are declining because of death of veteran trees and recruitment failure, both attributed to the combined effects of grazing, chemical fertilisers and absence of fire (Davidson et al 2007;Romanin et al 2019). Furthermore, excluding fire from fragments can result in occasional unplanned fires which are more intense and cause substantial tree mortality (Prior et al 2016).…”

“…For example, ash beds are of prime importance in the establishment of Eucalyptus seedlings (Bailey et al 2012). It has been suggested that patch burning is one approach that could restore the health of remnant fragments by providing localised ash beds for Eucalyptus regeneration while reducing the fuel loads and mortality of the remaining large trees in subsequent fires (Davidson et al 2007;Close et al 2009;Prior et al 2016;Romanin et al 2019), although this concept has received limited investigation. Of particular importance is determining the effect of different scales and intensities of burning within remnant patches to achieve a balance between tree recruitment and mortality.…”

“…Specifically, these authors suggest that frequent and extensive fires in landscapes with grazing lawns could lead to the dominance of flammable tussock grasslands, whereas targeted patchy fires may increase the occurrence of lawns. The combination of fire and herbivory is likely to affect woody tree recruitment given the importance of ash beds for seedling establishment (Bailey et al 2012) and grazing exclusion alone does not enhance recruitment of Eucalyptus in temperate savanna fragments (Romanin et al 2019).…”