Keppel Gunnar, Sarnow Udo, Biffin Ed, Peters Stefan, Fitzgerald Donna, Boutsalis Evan, Waycott Michelle, Guerin Greg R
UniSA STEM and Future Industries Institute, University of South Australia, GPO Box 2471, SA 5001 Adelaide, Australia; AMAP, Université de Montpellier, CIRAD, CNRS, INRAE, IRD, Montpellier, France.
UniSA STEM and Future Industries Institute, University of South Australia, GPO Box 2471, SA 5001 Adelaide, Australia.
Sci Total Environ. 2023 Jun 10;876:162697. doi: 10.1016/j.scitotenv.2023.162697. Epub 2023 Mar 9.
Refugia can facilitate the persistence of species under long-term environmental change, but it is not clear if Pleistocene refugia will remain functional as anthropogenic climate change progresses. Dieback in populations restricted to refugia therefore raises concerns about their long-term persistence. Using repeat field surveys, we investigate dieback in an isolated population of Eucalyptus macrorhyncha during two droughts and discuss prospects for its continued persistence in a Pleistocene refugium. We first confirm that the Clare Valley in South Australia has constituted a long-term refugium for the species, with the population being genetically highly distinct from other conspecific populations. However, the population lost >40 % of individuals and biomass through the droughts, with mortality being just below 20 % after the Millennium Drought (2000-2009) and almost 25 % after the Big Dry (2017-2019). The best predictors of mortality differed after each drought. While north-facing aspect of a sampling location was significant positive predictor after both droughts, biomass density and slope were significant negative predictors only after the Millennium Drought, and distance to the north-west corner of the population, which intercepts hot, dry winds, was a significant positive predictor after the Big Dry only. This suggests that more marginal sites with low biomass and sites located on flat plateaus were more vulnerable initially, but that heat-stress was an important driver of dieback during the Big Dry. Therefore, the causative drivers of dieback may change during population decline. Regeneration occurred predominantly on southern and eastern aspects, which would receive the least solar radiation. While this refugial population is experiencing severe decline, some gullies with lower solar radiation appear to support relatively healthy, regenerating stands of red stringybark, providing hope for persistence in small pockets. Monitoring and managing these pockets during future droughts will be essential to ensure the persistence of this isolated and genetically unique population.
避难所能够促进物种在长期环境变化下的存续，但随着人为气候变化的加剧，更新世避难所是否仍能发挥作用尚不明朗。因此，局限于避难所的种群数量减少引发了人们对其长期存续的担忧。通过重复进行实地调查，我们研究了大桉（Eucalyptus macrorhyncha）一个孤立种群在两次干旱期间的数量减少情况，并探讨了其在更新世避难所中持续存续的前景。我们首先确认，南澳大利亚的克莱尔谷一直是该物种的长期避难所，该种群在基因上与其他同种种群高度不同。然而，在干旱期间，该种群损失了超过40%的个体和生物量，在千年干旱（2000 - 2009年）后死亡率略低于20%，在大旱（2017 - 2019年）后接近25%。每次干旱后，死亡率的最佳预测指标有所不同。虽然采样地点朝北在两次干旱后都是显著的正向预测指标，但生物量密度和坡度仅在千年干旱后是显著的负向预测指标，而距离种群西北角（拦截炎热干燥风）的距离仅在大旱后是显著的正向预测指标。这表明，最初生物量低的边缘地带和平原上的地点更易受灾，但在大旱期间，热应激是数量减少的重要驱动因素。因此，在种群数量下降过程中，数量减少的致病驱动因素可能会发生变化。更新主要发生在朝南和朝东的方向，这些方向接收的太阳辐射最少。虽然这个避难所种群正在急剧减少，但一些太阳辐射较低的沟壑似乎支撑着相对健康、正在更新的红桉林分，为小范围内的存续提供了希望。在未来干旱期间对这些区域进行监测和管理对于确保这个孤立且基因独特的种群的存续至关重要。
