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Facultative and Obligate Trees in a Mesic Savanna: Fire Effects on Savanna Structure Imply Contrasting Strategies of Eco-Taxonomic Groups

机译:杂乱的稀树草原上的兼性和专性树:稀树草原结构的火势暗示了生态分类学群体的对策

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摘要

Fire is a major determinant of savanna tree communities and, as such, manipulation of fire frequency is an important management tool. Resolving the effects of fire management on tree size class distributions can help managers predict and plan for short-term ecological and economic outcomes, reveal different strategies by which woody plants cope with frequent fire, and help us predict vegetation changes under future fire scenarios. Savanna structure and size class distribution are strongly influenced by the ability of suppressed tree resprouts to escape stem death by frequent fire. A widespread assumption is that resprouts have an imperative to escape fire to reach sexual maturity in the canopy and thereby ensure long-term species viability. We use a census of Australian mesic savanna tree communities subjected to annual, triennial, and fire exclusion (unburnt) fire treatments to ask how fire frequency affects size class distributions within and between eco-taxonomic groups of species. Total tree densities did not significantly differ, but were highest in the triennial (7,610 ± se 1,162 trees ha−1) and unburnt fire treatments (7,051 ± se 578 trees ha−1) and lowest in the annual fire treatment (6,168 ± se 523 trees ha−1). This was caused by increased sapling densities in the triennial and unburnt fire treatments, predominantly of Acacia and pantropical genera. Eucalypts (Eucalyptus and Corymbia spp.) dominated the canopy across all fire treatments indicating relatively greater success in recruiting to larger sizes than other species groups. However, in the sub-canopy size classes eucalypts co-dominated with, and in some size classes were outnumbered by, pantropicals and Acacia, regardless of fire treatment. We hypothesize that such results are caused by fundamental differences in woody plant strategies, in particular sexual reproduction, that have not been widely recognized in Australian savannas.
机译:火灾是大草原树木群落的主要决定因素,因此,控制火灾频率是重要的管理工具。解决火灾管理对树木大小类别分布的影响,可以帮助管理人员预测和计划短期生态和经济结果,揭示木本植物应对频繁火灾的不同策略,并帮助我们预测未来火灾情况下的植被变化。大草原的结构和大小等级分布在很大程度上受到抑制的树苗在频繁火灾下逃脱茎杆死亡的能力的影响。一个普遍的假设是,芽菜必须逃生,以使其在树冠层中达到性成熟,从而确保物种长期生存。我们使用了接受年度,三年期和防火(未燃烧)防火处理的澳大利亚大麦大草原树木群落普查,以询问火灾频率如何影响物种的生态分类组内和之间的大小等级分布。总树木密度没有显着差异,但在三年期最高(7,610±se 1,162公顷ha -1 )和未燃烧处理(7,051±se 578公顷ha -1 )最高>),并且在年度火灾处理中最低(6,168±se 523公顷ha -1 )。这是由于三年生和未燃火处理中的树苗密度增加所致,主要是相思树和泛热带属。桉树(桉树和Corymbia物种)在所有防火处理中都占据着树冠的主导地位,这表明与其他物种相比,在招募更大规模的树上取得更大的成功。但是,在子冠层大小的类别中,无论采用何种火种处理,桉树都与泛热带和相思树种并存,在某些大小类别中,桉树的数量最多。我们假设这种结果是由木本植物策略的根本差异引起的,特别是有性生殖,这在澳大利亚稀树草原中尚未得到广泛认可。

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