Analysis of the “shelter tree-effect” of natural and exotic forest canopies on the growth of young Podocarpus falcatus trees in southern Ethiopia
Analysis of the “shelter tree-effect” of natural and exotic forest canopies on the growth of young Podocarpus falcatus trees in southern Ethiopia
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埃塞俄比亚南部天然和外来森林冠层对罗汉松幼树生长的“防护树效应”分析
DOI：
10.1007/s00468-011-0554-x
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发表时间：
2011
期刊：
影响因子：
--
通讯作者：
E. Beck
中科院分区：
文献类型：
--
作者：
Simone Strobl;M. Fetene;E. Beck
据报道，在热带森林已被砍伐一空的地区种植外来树种有助于本地树种的再生。这种所谓的护林树效应在埃塞俄比亚南部的一个山地半湿润地区进行了调查，在那里，松林和盐柳桉树的种植园生长在天然falcatus Podocarpus混交林附近。研究了在外来林和天然林中生长的镰形小叶树苗的生理性能。与天然林相比，松林显著提高了幼树的光合碳增益和生长，而盐柳桉则显著减缓了幼树的生长。不同密度林冠对幼树的发散效应可以追溯到林冠下小气候的差异，特别是光合有效辐射（PAR）的强度和时间分布的差异。水分对光合碳增益也有重要影响：上午CO2吸收模式与太阳斑的模式显著相关，而下午气孔导度是决定性因素。对太阳斑光合效率的分析表明，太阳斑的量子产率低于基本漫射PAR强度。与理论上均匀分布的日PAR相比，在真实光照气候下，松林和天然林的CO2吸收量为70%，桉树为59%。小气候条件下，松林下小气候对小气候光合作用的影响是天然林的2.5倍，是桉树小气候的5倍。
Plantations of exotic trees on areas where tropical forest has been clear-felled have been reported to facilitate regrowth of indigenous tree species. This so-called nurse- or shelter tree effect was investigated in a montane semihumid site in southern Ethiopia where plantations of Pinus patula and Eucalyptus saligna grow in close vicinity to the natural Podocarpus falcatus mixed forest. Physiological performance of P. falcatus saplings growing in the exotic and the natural forests was investigated over the year. Compared with the natural forest, photosynthetic carbon gain and growth of the saplings were significantly enhanced under Pinus patula while likewise retarded under Eucalyptus saligna. Diverging effects of the differently dense shelter canopies on the saplings could be traced to differences in the sub-canopy microclimates and particularly to the intensities and temporal distribution of photosynthetic active radiation (PAR). Moisture also played an important role for photosynthetic carbon gain: while the morning patterns of CO2 uptake were significantly correlated with the patterns of sunflecks, stomatal conductance was the determinant factor in the afternoon. Analysis of the photosynthetic efficiency of sunflecks revealed a lower quantum yield than the basic diffuse PAR intensity. Compared with a theoretically even distribution of the daily PAR, CO2 uptake under the real light climate was 70% under Pinus and in the natural forest, and 59% under Eucalyptus. Relating growth rates of Podocarpus saplings to photosynthesis the microclimate under Pinus was 2.5 times as effective as that in the natural forest and five times more effective than under Eucalyptus.