Walters Michele, Midgley Jeremy J, Somers Michael J
Conservation Ecology Department, University of Stellenbosch, Matieland, 7602, South Africa.
BMC Ecol. 2004 Apr 7;4:3. doi: 10.1186/1472-6785-4-3.
While fire has been used in some instances to control the increase of woody plants, it has also been reported that fire may cause an increase in certain fire-tolerant Acacia tree species. This study investigated germination of Acacia karroo, A. luederitzii and Dichrostachys cinerea, thought to be increasing in density, as well as the historically successful encroaching woody species, A. nilotica, in savanna grassland, Hluhluwe-iMfolozi Park, South Africa. A. karroo is thought to be replacing A. nilotica as the dominant microphyllous species in the park. We tested the hypothesis that observed increases in certain woody plants in a savanna were related to seed germination and seedling establishment. Germination is compared among species for burnt and unburnt seeds on burnt and unburnt plots at three different locations for both hot and cool fires.
Acacia karroo showed higher germination (A. karroo 5.1%, A. nilotica 1.5% and A. luederitzii 5.0%) levels and better establishment (A. karroo 4.9%, A. nilotica 0.4% and A. luederitzii 0.4%). Seeds of the shrub Dichrostachys cinerea did not germinate in the field after fire and it is thought that some other germination cue is needed. On average, burning of A. karroo, A. nilotica and A. luederitzii seeds did not affect germination. There was a significant difference in the germination of burnt seeds on burnt sites (4.5%) and burnt seeds on unburnt plots (2.5%). Similarly, unburnt seeds on unburnt sites germinated better (4.9%) than unburnt seeds on burnt sites (2.8%).
We conclude that a combination of factors may be responsible for the success of A. karroo and that fires may not be hot enough or may occur at the wrong time of year to control A. karroo establishment in HiP. Although germination and establishment of A. karroo was higher than for A. nilotica a competitive advantage after fire could not be shown.
虽然在某些情况下会用火来控制木本植物的增加，但也有报道称火可能会导致某些耐火金合欢树种数量增加。本研究调查了南非伊洛沃卢韦 - 伊莫洛齐公园热带稀树草原中，被认为密度正在增加的卡鲁金合欢、吕德里茨金合欢和银合欢的种子萌发情况，以及历史上成功入侵的木本物种尼罗金合欢的种子萌发情况。卡鲁金合欢被认为正在取代尼罗金合欢成为该公园中占主导地位的小叶树种。我们检验了这样一个假设，即热带稀树草原中某些木本植物数量的增加与种子萌发和幼苗建立有关。在三个不同地点，针对热火和凉火，比较了在已燃烧和未燃烧地块上已燃烧和未燃烧种子的不同物种间的萌发情况。
卡鲁金合欢表现出更高的萌发率（卡鲁金合欢5.1%，尼罗金合欢1.5%，吕德里茨金合欢5.0%）和更好的定植率（卡鲁金合欢4.9%，尼罗金合欢0.4%，吕德里茨金合欢0.4%）。灌木银合欢的种子在火灾后未在田间萌发，人们认为需要一些其他的萌发线索。平均而言，卡鲁金合欢、尼罗金合欢和吕德里茨金合欢种子的燃烧对萌发没有影响。已燃烧地块上的已燃烧种子的萌发率（4.5%）与未燃烧地块上的已燃烧种子的萌发率（2.5%）存在显著差异。同样，未燃烧地块上的未燃烧种子比已燃烧地块上的未燃烧种子萌发得更好（4.9% 比 2.8%）。
我们得出结论，多种因素的综合作用可能是卡鲁金合欢成功的原因，而且火灾可能不够热，或者可能发生在一年中的错误时间，从而无法控制卡鲁金合欢在该公园的定植。虽然卡鲁金合欢的萌发和定植高于尼罗金合欢，但火灾后其竞争优势并未显现出来。
