Tasmania is home to a treasure trove of ancient vegetation that emerged when Australia was part of the Gondwanda super continent. Most of the relict vegetation is not fire adapted (fire being a relatively recent arrival to Australia compared to Gondwanaland). Widespread wildfires in early 2016 caused devastating damage across large areas of the Tasmanian World Heritage Area, including significant sections of vegetation which is not fire adapted, such as Pencil Pine forests.
At the time, and in follow up investigations, it became clear that increased fire risk due to climate change posed an existential threat to these vegetation types. Now additional research has confirmed the trend towards more extreme fire seasons. It suggests that we reached a ‘tipping point’ sometime around the year 2000and that, since then, there has been an increase in the number of lightning-caused fires and an increase in the average size of the fires, “resulting in a marked increase in the area burnt”.
Research just released through the journal Global Change Biology, titled ‘Population collapse and retreat to fire refugia of the Tasmanian endemic conifer Athrotaxis selaginoides following the transition from Aboriginal to European fire management’ underscores the threat posed to these forest types.
Known as King Billy Pine, A. selaginoides is a Tasmanian tree mostly found in higher altitude rainforest, although it sometimes occurs as an alpine shrub or a lowland rainforest tree. It is endemic to Tasmania. It is quite fire sensitive and is found in the rainforests of many parts of western and southern Tasmania.
The authors, Andres Holz, Sam W Wood, Carly Ward, Thomas T Veblen, and David MJS Bowman, say that ‘untangling the nuanced relationships between landscape, fire disturbance, human agency, and climate is key to understanding rapid population declines of fire‐sensitive plant species’.
Their work documented ‘landscape‐scale population collapse of the long‐lived, endemic Tasmanian conifer Athrotaxis selaginoides in remote montane catchments in southern Tasmania’.
They note that ‘Population declines followed European colonization commencing in 1802 ad that disrupted Aboriginal landscape burning. Prior to European colonization, fire events were infrequent but frequency sharply increased afterwards’.
‘The multiple fires that followed European colonization caused near total mortality of A. selaginoides and resulted in pronounced floristic, structural vegetation, and fuel load changes. Burned stands have very few regenerating A. selaginoides juveniles yet tree‐establishment reconstruction of fire‐killed adults exhibited persistent recruitment in the period prior to European colonization.’
Bad ‘fire years were associated with abnormally warm/dry conditions, with below‐average streamflow, and were strongly teleconnected to the Southern Annular Mode’ (which is a climate driver that can influence rainfall and temperature in Australia).
‘Our findings indicate that this fire‐sensitive Gondwanan conifer was able to persist with burning by Aboriginal Tasmanians, despite episodic widespread forest fires. By contrast, European burning led to the restriction of A. selaginoides to prime topographic fire refugia’. So, we have driven this tree into the wettest areas most suitable for the species, reducing its range for the pre European distribution.
However, climate change poses another threat to remaining populations: ‘Increasingly, frequent fires caused by regional dry and warming trends and increased ignitions by humans and lightning are breaching fire refugia; hence, the survival Tasmanian Gondwanan species demands sustained and targeted fire management’.