Life zones

Leemans, R. World Map of Holdridge Life Zones International Institute of Applied Systems Analysis Laxenburg, Austria, 1989. 

Fig. 11.6 Schematic representation of the Milky Way with the galactic life zone , in which life should be possible. The centre of the galaxy is kept practically sterile by extreme radiation, while areas in which stars are formed are localized in the spiral arms...

II. Where animals live in caves—the life zones... 

Post W. M., Emanuel W. R., Zinke P. J., and Stangenberger A. G. (1982) Soil carbon pools and world life zones. Nature 298, 156-159. 

As a result of water availability, variety of soils and microhabitats, physical gradients, rough terrain and relative isolation, mountains create altitudinally segregated life zones at short distances and physical barriers to gene flow, which are conditions favoring the development of high species diversity. 

The roughness of the moimtain topography, ravines, slopes, open rocky surfaces, exposed meadows, bogs, crevices and other features, create a mosaic of niches of varying resource availability, climate and soil characteristics that exert a pressure of positive selection on only those plants capable of colonizing them while many other species are excluded. The reduced surface of these habitats on the one hand, and the variety of climates -temperature and water availability- on the other bring about an unparallel diversity of life zones per unit area, each one at a short distance... 

This question has been examined for many years e.g. see review of Komer, 1998). At a global scale, the montane life zone occupies a well defined strip. Within the intertropical band this zone lies between 1500 and 3200 m altitude, regardless of continent and tree species. At higher latitudes this band descends progressively until at, about 60 N and around 55 S, its upper limits are found on ground nearly at sea level, as is the... 

Robberecht, R., Caldwell, M. M., Billings, W. D. 1980. Leaf ultraviolet optical properties along a latitudinal gradient in the arctic-alpine life zone. Ecology 61 612-619. 

FIGURE 1 SOC distribution in kg/m among Holdridge life-zones (Post et al, 1982). 

Holdridge (1947) provided a simple climatic classification of vegetation in terms of rainfall and precipitation, dividing the world into 30 life zones. While this classification has been superceded by more recent work, it can serve as a guide to the number of sample regions that might be needed to cover the globe, that is, 120 locations (fine- and coarse-textured sites duplicated in each life zone). 

When an external force is applied to an equilibrium system, the system adjusts to minimize the effect of the force, life zone... 

A climatically-defined class that can be associated with regions of soil and biota with a high uniformity in species composition and environmental adaptation. See Holdridge life zone, lithosphere... 

Seasonally dry tropical forests generally occur on fertile soils with a moderate to high pH and nutrient status and low levels of aluminium. Such soils are very suitable for agriculture (Ratter et al., 1978), which has resulted in enormous forest deshuction in many areas (e.g. less than 2% of seasonally dry forests on the Padlic coast of Mesoamerica are still intact Janzen, 1988), a problem exacerbated by the large human populations in many neotropical dry forest life zones (Murphy and Lugo, 1995). 

Holdridge, L.R. et al., Forest Environments in Tropical Life Zones, A Pilot Study, Pergamon, Oxford, 1971. 

Brown and Lugo (1980) estimated that dry forests comprised 50%, 23%, 14% and 10% of the area of Bahamas, Dominican Republic, Puerto Rico and Trinidad, respectively. More recently, Helmer (2004) analyzed the areas of the various geoclimatic zones of Puerto Rico in relation to the level of development, forest cover and conservation as public lands (Table 15.5). Her analysis shows that 15% of Puerto Rico is in the dry forest life zone. A total of 24% of the island s development has occurred in this life zone, which means that the development burden is disproportionately high... 

In general, Helmer s analysis for Puerto Rico reflects the situation elsewhere of Antillean dry forests. These forests suffer a disproportionate effect of human activity because human populations tend to be high in this life zone (Murphy and Lugo, 1986a). In addition, humans convert Antillean dry forests to alternative uses particularly where soils are nutrient rich, as is the case of forests on alluvial soils. Moreover, local people use these dry forests as a source of fuel-wood and grazing for goats and cattle, which results in altered forest structure and species composition (McDonald and McLaren, 2(X)3). 

Holdridge, L.R., Life Zone Ecology, Tropieal Seience Center, San Jose, Costa Rica, 1967. 

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