The impacts of inter- and intra-seasonal burns on the terrestrial orchid Pterostylis curta

Abstract

Abstract Prescribed burning is a management tool used for both management of fuel loads and for ecological purposes across fire prone areas. While in temperate areas wildfires usually occur during the hottest summer months, prescribed burns are generally conducted in autumn and spring to reduce risk. Plant species such as orchids are adapted to summer fires and maintain avoidance mechanisms, such as persisting as dormant tubers during the predominant fire season, and therefore may be at risk from prescribed burns occurring during their active life cycle period. Using a glasshouse experiment, we investigated the impacts of fire season on the Australian orchid species Pterostylis curta. This approach allowed us to i) implement seasonal burns and relate impacts to quantifiable life cycle stages of the study species, ii) isolate and assess the role of smoke, and iii) control for life stage of the study species at each of the treatment levels to enable robust comparison. We found that late autumn burns caused complete failure of a cohort in our glasshouse study. Another key finding is that heat alone is not the driver of tuber mortality, because soil heating was similar across all burn seasons, and plants burnt in the three other seasons were able to resprout strongly in the first growing season after fire. Generally, burning orchids like P. curta at the latter stages of their growing season seems to have low risk, while burning at the start of the growing season is of greater risk but potentially with minimal negative impacts.