Gignoux Jacques, Clobert Jean, Menaut Jean-Claude
Ecole normale supérieure, laboratoire d'écologie, 46 rue d'Ulm, 75230 Paris Cedex 05, France fax: (33 1) 44 32 38 85; e-mail:
Oecologia. 1997 May;110(4):576-583. doi: 10.1007/s004420050198.
Bark properties (mainly thickness) are usually presented as the main explanation for tree survival in intense fires. Savanna fires are mild, frequent, and supposed to affect tree recruitment rather than adult survival: trunk profile and growth rate of young trees between two successive fires can also affect survival. These factors and fire severity were measured on a sample of 20 trees near the recruitment stage of two savanna species chosen for their contrasted fire resistance strategies (Crossopteryx febrifuga and Piliostigma thonningii). Crossopteryx has a higher intrinsic resistance to fire (bark properties) than Piliostigma: a 20-mm-diameter stem of Crossopteryx survives exposure to 650°C, while Piliostigma needs a diameter of at least 40 mm to survive. Crossopteryx has a thicker trunk than Piliostigma: for two trees of the same height, the basal diameter of Crossopteryx will be 1.6 times greater. Piliostigma grows 2.26 times faster than Crossopteryx between two successive fires. The two species have different fire resistance strategies: one relies on resistance of aboveground structures to fire, while the other relies on its ability to quickly re-build aboveground structures. Crossopteryx is able to recruit in almost any fire conditions while Piliostigma needs locally or temporarily milder fire conditions. In savannas, fire resistance is a complex property which cannot be assessed simply by measuring only one of its components, such as bark thickness. Bark properties, trunk profile and growth rate define strategies of fire resistance. Fire resistance may interact with competition: we suggest that differences in fire resistance strategies have important effects on the structure and dynamics of savanna ecosystems.
树皮特性（主要是厚度）通常被视为树木在高强度火灾中存活的主要解释。稀树草原火灾较为温和且频繁，被认为会影响树木的更新而非成年树木的存活：连续两次火灾之间幼树的树干形态和生长速率也会影响其存活。在两种因其截然不同的耐火策略而被选中的稀树草原物种（Crossopteryx febrifuga和Piliostigma thonningii）处于更新阶段附近的20棵树的样本上，对这些因素和火灾严重程度进行了测量。Crossopteryx比Piliostigma具有更高的固有耐火性（树皮特性）：直径20毫米的Crossopteryx茎干在暴露于650°C时仍能存活，而Piliostigma至少需要直径40毫米才能存活。Crossopteryx的树干比Piliostigma更粗：对于两棵相同高度的树，Crossopteryx的基部直径将是Piliostigma的1.6倍。在连续两次火灾之间，Piliostigma的生长速度比Crossopteryx快2.26倍。这两个物种具有不同的耐火策略：一个依赖于地上结构对火灾的抗性，而另一个则依赖于其快速重建地上结构的能力。Crossopteryx几乎能够在任何火灾条件下更新，而Piliostigma则需要局部或暂时较为温和的火灾条件。在稀树草原中，耐火性是一种复杂的特性，不能仅通过测量其一个组成部分（如树皮厚度）来简单评估。树皮特性、树干形态和生长速率决定了耐火策略。耐火性可能与竞争相互作用：我们认为耐火策略的差异对稀树草原生态系统的结构和动态具有重要影响。
