Mechanisms driving understory evergreen herb distributions across slope aspects: as derived from landscape position
Mechanisms driving understory evergreen herb distributions across slope aspects: as derived from landscape position
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DOI：
10.1007/s11258-008-9406-1
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发表时间：
2008-02
期刊：
影响因子：
1.7
通讯作者：
R. Warren
中科院分区：
文献类型：
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作者：
R. Warren
在北半球，朝南的斜坡表面朝向太阳，因此接受更长时间和更强的太阳辐射，导致相对温暖、干燥的小气候和季节性环境极端。这为必须忍受所有条件的常绿植物创造了潜在的有害条件。我假设(1)南向增加将与常绿林下植物分布负相关；(2)导出的环境变量(夏季和冬季光和热负荷)将预测常绿植物分布的变化，以及地形位置(坡向、坡度和海拔)；(3)冬季光照将最好地预测常绿林下植物分布。为了验证这些假设，收集了北卡罗来纳州山脉和佐治亚州皮埃蒙特的10种常绿林下草本植物的分布(存在、丰度和繁殖)以及相应的地形信息的调查数据。使用AIC选择最好的预测模型，并使用贝叶斯分层广义线性模型来估计保留系数的强度。正如预测的那样，常绿林下草本植物在朝南的坡面上出现和繁殖的次数比朝北的坡面少，尽管坡度和海拔高度也有很强的预测能力，而且两者都很好地区分了常绿树种。虽然景观变量解释了植物出现在哪里，但冬季的光和热负荷对植物出现在那里提供了最好的解释。由于夏季土壤水分低，气温高，冬季光照强，气温低，常绿植物很可能在南向的山坡上受到限制。林下常绿草本植物对冬季光照增加的强烈负响应也表明，冬季环境而不是夏季(或生长季)环境为林下常绿分布提供了最好的预测能力，这对预测对全球气候变化的反应具有实质性意义。
In the Northern Hemisphere, the surface of south-facing slopes orients toward the sun and thus receives a greater duration and intensity of solar irradiation, resulting in a relatively warmer, drier microclimate and seasonal environmental extremes. This creates potentially detrimental conditions for evergreen plants which must endure the full gamut of conditions. I hypothesize that (1) increased southerly aspect will correlate negatively with evergreen understory plant distributions; (2) derived environmental variables (summer and winter light and heat load) will predict variance in evergreen distributions as well as topographic position (aspect, slope, and elevation) and (3) winter light will best predict evergreen understory plant distributions. In order to test these hypotheses, survey data were collected characterizing 10 evergreen understory herb distributions (presence, abundance, and reproduction) as well as the corresponding topographical information across north- and south-facing slopes in the North Carolina mountains and Georgia piedmont. The best predictive models were selected using AIC, and Bayesian hierarchical generalized linear models were used to estimate the strength of the retained coefficients. As predicted, evergreen understory herbs occurred and reproduced less on south-facing than north-facing slopes, though slope and elevation also had robust predictive power, and both discriminated well between evergreen species. While the landscape variables explainedwherethe plants occurred, winter light and heat load provided the best explanationwhythey were there. Evergreen plants likely are limited on south-facing slopes by low soil moisture combined with high temperatures in summer and high irradiance combined with lower temperatures in winter. The robust negative response of the understory evergreen herbs to increased winter light also suggested that the winter rather than the summer (or growing season) environment provided the best predictive power for understory evergreen distributions, which has substantive implications for predicting responses to global climate change.