Woodward F I, Lomas M R, Kelly C K
NERC Centre for Terrestrial Carbon Dynamics and Department of Animal and Plant Sciences, University of Sheffield, Sheffield S10 2TN, UK.
Philos Trans R Soc Lond B Biol Sci. 2004 Oct 29;359(1450):1465-76. doi: 10.1098/rstb.2004.1525.
Biomes are areas of vegetation that are characterized by the same life-form. Traditional definitions of biomes have also included either geographical or climatic descriptors. This approach describes a wide range of biomes that can be correlated with characteristic climatic conditions, or climatic envelopes. The application of remote sensing technology to the frequent observation of biomes has led to a move away from the often subjective definition of biomes to one that is objective. Carefully characterized observations of life-form, by satellite, have been used to reconsider biome classification and their climatic envelopes. Five major tree biomes can be recognized by satellites based on leaf longevity and morphology: needleleaf evergreen, broadleaf evergreen, needleleaf deciduous, broadleaf cold deciduous and broadleaf drought deciduous. Observations indicate that broadleaf drought deciduous vegetation grades substantially into broadleaf evergreen vegetation. The needleleaf deciduous biome occurs in the world's coldest climates, where summer drought and therefore a drought deciduous biome are absent. Traditional biome definitions are quite static, implying no change in their life-form composition with time, within their particular climatic envelopes. However, this is not the case where there has been global ingress of grasslands and croplands into forested vegetation. The global spread of grasses, a new super-biome, was probably initiated 30-45 Myr ago by an increase in global aridity, and was driven by the natural spread of the disturbances of fire and animal grazing. These disturbances have been further extended over the Holocene era by human activities that have increased the land areas available for domestic animal grazing and for growing crops. The current situation is that grasses now occur in most, if not all biomes, and in many areas they dominate and define the biome. Croplands are also increasing, defining a new and relatively recent component to the grassland super-biome. In the case of both grassland and croplands, various forms of disturbance, particularly frequent disturbance, lead to continued range extensions of the biomes.
生物群落是指以相同生命形式为特征的植被区域。传统的生物群落定义还包括地理或气候描述。这种方法描述了一系列与特征气候条件或气候包络相关的生物群落。遥感技术在生物群落频繁观测中的应用，使得生物群落的定义从通常主观的定义转向了客观的定义。通过卫星对生命形式进行仔细特征化的观测，已被用于重新考虑生物群落分类及其气候包络。基于叶片寿命和形态，卫星可识别出五种主要的树木生物群落：针叶常绿林、阔叶常绿林、针叶落叶林、阔叶寒落叶林和阔叶旱落叶林。观测表明，阔叶旱落叶植被在很大程度上逐渐演变为阔叶常绿植被。针叶落叶生物群落出现在世界上最寒冷的气候区，那里不存在夏季干旱，因此也不存在旱落叶生物群落。传统的生物群落定义相当静态，意味着在其特定的气候包络内，其生命形式组成不会随时间变化。然而，当草原和农田在全球范围内侵入森林植被时，情况并非如此。一种新的超级生物群落——草的全球扩张，可能始于3000万至4500万年前全球干旱加剧之时，并由火灾和动物放牧等干扰的自然传播所推动。在全新世时期，这些干扰因人类活动而进一步扩大，人类活动增加了可供家畜放牧和种植作物的土地面积。目前的情况是，草现在出现在大多数（如果不是所有）生物群落中，并且在许多地区它们主导并定义了生物群落。农田也在增加，成为草原超级生物群落中一个新的且相对较新的组成部分。就草原和农田而言，各种形式的干扰，尤其是频繁的干扰，导致了生物群落持续的范围扩展。
