Effect of a prescribed burn on density of the weed <scp> <i>Chrysanthemoides monilifera</i> </scp> ssp. <scp> <i>monilifera</i> </scp> (boneseed) and native orchid taxa in a South Australian Conservation Park

Abstract Prescribed burns are widely used in South Australia to mitigate bushfire risk. Their impact on the weed Chrysanthemoides monilifera ssp. monilifera (boneseed) and native orchids has received little attention there. We examined the effect of a 2023 prescribed burn at Morialta Conservation Park on boneseed and native orchid occurrence. Surveys of the burnt site and adjacent unburnt site showed significantly more boneseed plants at the burnt site, indicating that fire triggered mass germination, with some plants maturing in ≤ 16 months. The estimated cost of weeding was 17 times higher for burnt areas. The orchid Pyrorchis nigricans was significantly more abundant at the unburnt site. Burning could enhance boneseed spread extensively and may reduce the occurrence of “fire orchids.” We suggest a pause in burning, research including modeling the fire response of these taxa and control effort of boneseed over time, and formal surveys before and after burns.