Environmental and Conservation Sciences, Murdoch University, Murdoch, Perth, 6150, Western Australia, Australia.
Biodiversity and Conservation Science, Department of Biodiversity, Conservation and Attractions, 1 Kattidj Close, Kings Park, Perth, 6005, Western Australia, Australia.
Ecol Appl. 2021 Oct;31(7):e02411. doi: 10.1002/eap.2411. Epub 2021 Aug 11.
Unseasonal fire occurrence is increasing globally, driven by climate change and other human activity. Changed timing of fire can inhibit postfire seedling recruitment through interactions with plant phenology (the timing of key processes, e.g., flower initiation, seed production, dispersal, germination), and therefore threaten the persistence of many plant species. Although empirical evidence from winter-rainfall ecosystems shows that optimal seedling recruitment is expected following summer and autumn (dry season) fires, we sought experimental evidence isolating the mechanisms of poor recruitment following unseasonal (wet season) fire. We implemented a seed-sowing experiment using nine species native to fire-prone, Mediterranean-climate woodlands in southwestern Australia to emulate the timing of postfire recruitment and test key mechanisms of fire seasonality effects. For seeds sown during months when fire is unseasonal (i.e., August-September: end of the wet winter season), seedling recruitment was reduced by up to 99% relative to seeds sown during seasonal fire months (i.e., May-June: end of the dry summer season) because of varying seed persistence, seedling emergence, and seedling survival. We found that up to 70 times more seedlings emerged when seeds were sown during seasonal fire months compared to when seeds were sown during unseasonal fire months. The few seedlings that emerged from unseasonal sowings all died with the onset of the dry season. Of the seeds that failed to germinate from unseasonal sowings, only 2% survived exposure on the soil surface over the ensuing hot and dry summer. Our experimental results demonstrate the potential for unseasonal fire to inhibit seedling recruitment via impacts on pregermination seed persistence and seedling establishment. As ongoing climate change lengthens fire seasons (i.e., unseasonal wildfires become more common) and managed fires are implemented further outside historically typical fire seasons, postfire seedling recruitment may become more vulnerable to failure, causing shifts in plant community composition towards those with fewer species solely dependent on seeds for regeneration.
非季节性火灾在全球范围内不断增多，这是气候变化和其他人类活动的结果。火灾发生时间的改变会通过与植物物候（关键过程的时间，如花芽形成、种子生产、散布、发芽）的相互作用，抑制火灾后的幼苗补充，从而威胁到许多植物物种的生存。尽管来自冬雨生态系统的实证证据表明，在夏季和秋季（旱季）火灾后，最佳的幼苗补充预期会出现，但我们还是试图寻找在非季节性（雨季）火灾后幼苗补充不佳的实验证据，以隔离火灾季节性影响的机制。我们在澳大利亚西南部易发生火灾的地中海气候林地的九种本土物种中实施了播种实验，以模拟火灾后的幼苗补充时间，并测试火灾季节性影响的关键机制。对于在非季节性（即 8 月至 9 月：雨季结束）月份播种的种子，由于种子的持久性、幼苗的出现和幼苗的存活率不同，与在季节性火灾月份（即 5 月至 6 月：旱季结束）播种的种子相比，幼苗的补充减少了 99%。我们发现，在季节性火灾月份播种的种子比在非季节性火灾月份播种的种子，幼苗的出现率高出多达 70 倍。从非季节性播种中出现的少数幼苗都随着旱季的到来而死亡。在非季节性播种中未能发芽的种子中，只有 2%在接下来的炎热干燥的夏季中在土壤表面暴露后幸存下来。我们的实验结果表明，非季节性火灾通过对预发芽种子持久性和幼苗建立的影响，可能抑制幼苗的补充。随着持续的气候变化延长了火灾季节（即，非季节性野火变得更加普遍），以及进一步在历史上典型的火灾季节之外实施受控火灾，火灾后的幼苗补充可能变得更加脆弱，导致植物群落组成发生变化，向那些仅依赖种子进行再生的物种更少的群落转移。
