Fire-adapted traits of threatened shrub species in riparian refugia: implications for fire regime management

Abstract

Fire management at the landscape scale may be detrimental to threatened species restricted to fire refugia, such as riparian zones, if their fire response is assumed based on the broader vegetation community type. Conserving threatened plant species in fire-prone habitats requires understanding how life-history traits allow persistence under prevailing fire regimes. Using three threatened Pomaderris species associated with riparian zones in south-east Australia, we tested for evidence of fire-adapted traits to identify if key life-history traits are coupled to specific fire cues and determine how their current distribution relates to prevailing fire regimes. We did this by (i) exposing seeds to heat-shock treatments with fire-related temperatures (60–100 °C) in germination trials; (ii) testing for the presence of a soil-stored seed bank and its response to fire by using ex-situ experimental burns on soil samples and (iii) conducting field surveys of post-fire demographic responses for P. adnata. All species showed maximum germination following heat-shock treatment at 100 °C, strongly suggesting adaptation to high severity fire. Seedling emergence from soil samples was positively affected by fire for P. bodalla and P. walshii, while there was an in situ post-fire germination pulse in P. adnata seedling recruitment and moderate increases in resprouting and survivorship of mature plants. The study demonstrates that these riparian-occurring species have life-history traits that may enable persistence under high severity fire and highlights how the possession of bet-hedging strategies may allow species to use riparian zones as fire refugia in a landscape dominated by an anthropogenically altered fire regime.