Land Resources and Environmental Sciences Department, Montana State University, Bozeman, Montana, 59717, USA.
Earth Sciences Department, Montana State University, Bozeman, Montana, 59717, USA.
Ecology. 2017 Mar;98(3):678-687. doi: 10.1002/ecy.1673. Epub 2017 Feb 1.
Invasive plant species that have the potential to alter fire regimes have significant impacts on native ecosystems. Concern that pine invasions in the Southern Hemisphere will increase fire activity and severity and subsequently promote further pine invasion prompted us to examine the potential for feedbacks between Pinus contorta invasions and fire in Patagonia and New Zealand. We determined how fuel loads and fire effects were altered by P. contorta invasion. We also examined post-fire plant communities across invasion gradients at a subset of sites to assess how invasion alters the post-fire vegetation trajectory. We found that fuel loads and soil heating during simulated fire increase with increasing P. contorta invasion age or density at all sites. However, P. contorta density did not always increase post-fire. In the largest fire, P. contorta density only increased significantly post-fire where the pre-fire P. contorta density was above an invasion threshold. Below this threshold, P. contorta did not dominate after fire and plant communities responded to fire in a similar manner as uninvaded communities. The positive feedback observed at high densities is caused by the accumulation of fuel that in turn results in greater soil heating during fires and high P. contorta density post-fire. Therefore, a positive feedback may form between P. contorta invasions and fire, but only above an invasion density threshold. These results suggest that management of pine invasions before they reach the invasion density threshold is important for reducing fire risk and preventing a transition to an alternate ecosystem state dominated by pines and novel understory plant communities.
具有改变火行为潜力的入侵植物物种对本地生态系统有重大影响。人们担心南半球的松树入侵会增加火灾活动和严重程度，从而促进进一步的松树入侵，这促使我们研究火在巴塔哥尼亚和新西兰的松树入侵之间的潜在反馈。我们确定了燃料负荷和火效如何被入侵的 P. contorta 改变。我们还在一些地点的入侵梯度上检查了火灾后的植物群落，以评估入侵如何改变火灾后的植被轨迹。我们发现，在所有地点，模拟火灾期间的燃料负荷和土壤加热随着 P. contorta 入侵年龄或密度的增加而增加。然而，P. contorta 密度并不总是在火灾后增加。在最大的火灾中，只有在火灾前 P. contorta 密度高于入侵阈值的情况下，P. contorta 密度才会显著增加。低于这个阈值，P. contorta 不会在火灾后占据主导地位，植物群落对火灾的反应与未入侵的群落相似。在高密度下观察到的正反馈是由燃料的积累引起的，这反过来又导致火灾期间土壤加热增加和火灾后 P. contorta 密度增加。因此，P. contorta 入侵和火之间可能形成正反馈，但仅在入侵密度阈值之上。这些结果表明，在松树入侵达到入侵密度阈值之前进行管理对于降低火灾风险和防止过渡到以松树和新的林下植物群落为主的替代生态系统状态非常重要。
