An examination of the potential efficacy of high-intensity fires for reversing woody encroachment in savannas
An examination of the potential efficacy of high-intensity fires for reversing woody encroachment in savannas
复制标题
检查高强度火灾扭转稀树草原木质侵占的潜在功效
DOI：
10.1111/1365-2664.12738
复制
发表时间：
2016
影响因子：
5.7
通讯作者：
B. W. Wilgen
中科院分区：
文献类型：
--
作者：
I. Smit;G. Asner;N. Govender;N. Vaughn;B. W. Wilgen
总结
频繁的火灾通常被认为是防止稀树草原木质侵占的一种方法，但很少有研究探讨高强度火灾是否可以有效扭转木质侵占。
我们采用连续火处理来检查火强度对木本植被结构的影响。处理措施包括早期旱季、低强度火灾；旱季后期，火灾强度更高；和一个未烧毁的控件。我们使用火灾前和火灾后机载激光雷达来比较不同强度火灾带来的植被结构变化。
旱季早期火灾的强度 (1400–2100 kW m−1) 低于旱季晚期火灾 (2500–4300 kW m−1)。两种处理在燃料消耗、焦烧高度和炭化高度方面也存在差异，表明火灾强度和严重程度存在明显差异。
经过 4 年和两次火灾处理后，在低强度和控制处理后，不同高度类别的相对木本覆盖率增加了 20% 至 110%，而在高强度火灾处理后则下降了 3% 至 70%。两次重复发生高强度火灾后的下降幅度明显高于先发生高强度火灾后发生中等强度火灾的下降幅度。由于较低高度级别的木本灌木可以迅速恢复，因此需要反复高强度火灾来维持较低的覆盖范围。
人们通常认为高大的树木不会受到火灾的影响。然而，我们发现树木损失率与火灾强度直接相关，反复发生高强度火灾后，树木损失率为 36%，而高强度火灾和中等强度火灾后损失率为 22%，两次低强度火灾后损失率为 6%（没有火灾时损失率为 3%）。
合成与应用。利用激光雷达数据，我们表明，高强度火灾至少在短期内会显着减少南非稀树草原的木质覆盖。反复使用高强度火灾会同时产生积极的结果（减少矮灌木的覆盖）和消极的结果（失去高大的树木），管理者在考虑使用火灾强度来实现特定目标时需要进行权衡。一种可能的解决方案可能是对某些区域重复进行高强度治疗，而对其他区域则不进行。这可能会产生异质景观，在某些地方，草类占主导地位，高大的树木变得稀少，但在另一些地方，高大的树木持续存在（或至少以较慢的速度下降），而矮小的木本灌木则占据主导地位。这是否可以接受，或者是否实用，还有待检验。
Summary
Frequent fires are often proposed as a way of preventing woody encroachment in savannas, yet few studies have examined whether high-intensity fires can effectively reverse woody encroachment.
We applied successive fire treatments to examine the effect of fire intensity on woody vegetation structure. The treatments included early dry season, low-intensity fires; late dry season, higher-intensity fires; and an unburnt control. We used pre- and post-fire airborne LiDAR to compare vegetation structural changes brought about by fires of different intensity.
Early dry season fires were of lower intensity (1400–2100 kW m−1) than late dry season fires (2500–4300 kW m−1). The two treatments also differed in terms of fuel consumed, scorch heights and char heights, indicating that clear differences in fire intensity and severity were achieved.
After 4 years and two fire applications, relative woody cover increased by between 20 and 110% in different height categories following low-intensity and control treatments and declined by between 3 and 70% following high-intensity fire treatments. Declines were markedly higher following two repeated high-intensity fires than following a high and then a moderate-intensity fire. Because woody shrubs in lower height classes can recover rapidly, repeated high-intensity fires would be needed to maintain lower cover.
Tall trees are often assumed to be unaffected by fires. However, we found that the rate of tree loss was directly related to fire intensity, where 36% of trees were lost following repeated high-intensity fires, compared to 22% after a high- and then a moderate-intensity fire and 6% after two low-intensity fires (3% without fire).
Synthesis and applications. Using LiDAR data we show that high-intensity fires can, at least in the short term, significantly reduce woody cover in South African savannas. The use of repeated high-intensity fires simultaneously causes both a positive (reduction in cover of short shrubs) and a negative (loss of tall trees) outcome, and managers need to make trade-offs when contemplating the use of fire intensity to achieve specific goals. One potential solution may be to repeatedly apply high-intensity treatments to some areas, and not to others. This could generate a heterogeneous landscape where grasses become dominant and tall trees become scarce in some places, but in others, tall trees persist (or at least decline at slower rates), and shorter woody shrubs increase in dominance. Whether this would be acceptable, or practical, remains to be tested.