AN ECOLOGICAL STUDY OF THE MID-APPALACHIAN SHALE BARRENS AND OF THE PLANTS ENDEMIC TO THEM
AN ECOLOGICAL STUDY OF THE MID-APPALACHIAN SHALE BARRENS AND OF THE PLANTS ENDEMIC TO THEM
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DOI：
10.2307/1948652
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发表时间：
1951-01-01
影响因子：
6.1
通讯作者：
PLATT, RB
中科院分区：
文献类型：
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作者：
PLATT, RB
“页岩贫瘠地”是阿巴拉契亚山脉中部的某些页岩斜坡，支持橡树、松树、杜松和其他木本植物的稀疏灌木状生长，并且在它们之间存在主要由几种特有物种主导的开放草本覆盖物。Brallier页岩（主要是贫瘠的页岩）的裂变、硅质、更耐风化的特性，加上20度以上的坡度和向南的暴露，是形成sha 'le贫瘠地层的主要原因。在无明显旱季的暖温带气候下，黑化土壤深4-12英寸，无分化淋溶带。它们与植被斜坡土壤的不同之处在于，A-Ao层由1-3”深的扁平岩石碎片表层替代。pH为4.5-5.5。土壤养分和次表层水分基本相似。在127种特征植物中，有19种为指示植物。其中8种为严格特有种：紫菀（Aster lowrieanus）、南芥（Arabis coronina）。铁线莲Clematis albicoma、铁线莲C.蔓荆子、阿氏羊耳草、泥生月见草。哈氏一枝黄花，弗吉尼亚三叶草。97种开花植物的生活型谱为：高位芽植物21种，地面芽植物40种，地下芽植物33种，一年生植物6种。所有成熟的植物都能很好地适应越冬。在不利的夏季条件下，后两种类型很好地适应了生存，因为在C层中建立了相当大的根系（根冠比）;高位芽植物随着年龄的增长而严重发育不良;一年生植物仅限于潮湿的地区。虽然早春的水分条件允许有限的发芽，但极端不利的水分和温度。碎石表层生长季节剩余的条件几乎完全消除了幼苗的建立，这是植物生命稀少的主要原因。地方性植物已经成为专性的高光照强度，土壤足以为他们广泛的根系，和低水平的竞争。它们被限制在页岩贫瘠之地，因为该地区没有其他栖息地拥有这种独特的土壤和光照条件，允许它们生长，但不允许令人窒息的竞争对手生长。地方病具有共同的隔离机制和明显的年轻性。相当大的多样性已被证明与参考可能的起源中心，distr。模式、种群密度和生物型变异性。页岩荒地的存在时间至少与地方性植物的进化时间一样长，最有可能是数千年，因为这种地方性植物群不可能受到最后一个冰河时代气候的支持。
"Shale barrens" are certain shale slopes of the Mid-Appalachian Mountains which support a sparse shrubby growth of oak, pine, juniper and other woody plants and between which exists an open herbaceous cover dominated chiefly by several endemic spp. The fissile, siliceous, more weather-resistant character of Brallier shale (on which barrens mostly occur), when combined with a slope of over 20[degree] and a southerly exposure are primary causes of sha''le barren formation. Under the warm temperate climate with no distinct dry season, the melanized soils are 4-12 inches deep without a differentiated eluviation zone. They differ from soils of vegetated slopes by substitution of a surface layer of flattened rock fragments 1-3" deep for the A-Ao horizon. pH is 4.5-5.5. Soil nutrients and sub-surface moisture are essentially similar. Gully and sheet erosion is negligible as is effect of fire and man. Of 127 characteristic plants given, 19 are indicator spp. and of these, 8 are strict endemics: Aster lowrieanus, Arabis serotina. Clematis albicoma, C. viticaulis, Eriogonum alleni, Oenothera argillicola. Solidago harrissii, Trifolium virginicum. Life-form spectrum of the 97 flowering plants is: phanerophytes 21, hemicryptophytes 40, geophytes 33, and therophytes 6. All mature plants are well adapted to over-winter survival. Under adverse summer conditions the two latter types are well adapted to survival because of proportionately larger root systems (root-shoot ratios) well established in the C horizon;[long dash]phanerophytes become severely stunted with age; and therophytes are restricted to moister areas. Although moisture conditions in early spring permit limited germination, extremely adverse moisture and temp. conditions for remainder of growing season in surface layer of rock fragments almost completely eliminate seedling establishment and this is primary cause of sparsity of plant life. The endemics have become obligate upon a high light intensity, a soil adequate for their extensive root systems, and a low level of competition. They are restricted to the shale barrens because no other habitat in the region possesses this unique combination of soil and light conditions which permits them[long dash]but does not permit stifling competitors[long dash]to grow. The endemics hold in common isolating mechanisms and evident youthfulness. Considerable diversity has been demonstrated with reference to probable centers of origin, distr. patterns, population densities and biotype variability. Shale barrens have been in existence for at least as long as the time required for evolution of the endemics, most likely thousands of years, since it is improbable that this endemic flora could have been supported by the climate of the last ice age.