Schoettle A W, Rochelle S G
USDA Forest Service, Rocky Mountain Research Station, 240 West Prospect Road, Fort Collins, Colorado 80526 USA.
Am J Bot. 2000 Dec;87(12):1797-806.
Limber pine (Pinus flexilis James) grows across a wider range of elevations than any other tree species in the central Rockies, from ∼1600 m at Pawnee Buttes to >3300 m at Rollins Pass. In this study we investigated two possible explanations for limber pine's success across a broad range of elevations: (1) the sites on which it is found, although separated by >1000 m elevation, may not be very different with respect to environmental factors that affect tree growth, and (2) limber pine growth is insensitive to environmental factors that change with elevation. We compared site characteristics of 12 limber pine stands at elevations ranging from 1630 to 3328 m as well as the growth and morphology of trees in each of these stands. Mean daily air temperature in July decreased linearly with the elevation of the site from 22.8° to 12.6°C. The growth and morphology of limber pine leaves, shoots, and trees were, in general, not related to the elevation or July mean air temperature of the sites. There was, however, a significant decrease in stomatal density with increasing elevation, which may be an acclimational response to restrict water loss at high elevations. Our data suggest that the fundamental and realized niche of limber pine is broad with respect to air temperature. In light of the high gene flow and only slight genetic differentiation among populations of species with bird-dispersed seeds, such as limber pine, it is especially unusual to see similar growth throughout an environmental gradient. Physiological and anatomical plasticity or wide physiological tolerance ranges may enable limber pine to uncouple its growth from its environment.
扭叶松（Pinus flexilis James）生长的海拔范围比落基山脉中部的任何其他树种都要广，从波尼丘的约1600米到罗林斯山口的超过3300米。在本研究中，我们调查了扭叶松在广泛海拔范围内成功生长的两种可能解释：（1）它生长的地点，尽管海拔相差超过1000米，但在影响树木生长的环境因素方面可能差异不大；（2）扭叶松的生长对随海拔变化的环境因素不敏感。我们比较了海拔在1630米至3328米之间的12个扭叶松林地的立地特征，以及每个林地中树木的生长和形态。7月的日平均气温随立地海拔从22.8°C线性下降至12.6°C。扭叶松的叶子、嫩枝和树木的生长及形态总体上与立地海拔或7月平均气温无关。然而，气孔密度随海拔升高显著降低，这可能是一种适应性反应，以限制在高海拔地区的水分流失。我们的数据表明，扭叶松在气温方面的基础生态位和实际生态位都很宽泛。鉴于像扭叶松这样种子由鸟类传播的物种，其种群间基因流高且遗传分化很小，在整个环境梯度中出现相似的生长情况尤其不同寻常。生理和解剖可塑性或宽泛的生理耐受范围可能使扭叶松能够使其生长与环境脱钩。
