tend to have higher tree lines than more isolated mountains due to heat retention and wind shadowing. This effect predicts that zonation of rain forests on lower mountains may mirror the zonation expected on high mountains, but the belts occur at lower elevations. A similar effect is exhibited in the Santa Catalina Mountains of Arizona, where the basal elevation and the total elevation influence the elevation of vertical zones of vegetation. Other factors In addition to the factors described above, there are a host of other properties that can confound predictions of altitudinal zonations. These include: frequency of disturbance (such as fire or monsoons), wind velocity, type of rock, topography, nearness to streams or rivers, history of tectonic activity, and latitude. Elevation levels Elevation models of zonation are complicated by factors discussed above and thus the relative elevations each zone begins and ends is not tied to a specific elevation. However it is possible to split the altitudinal gradient into five main zones used by ecologists under varying names. In some cases these level follow each other with the decrease in elevation, which is called vegetation inversion. Nival level (glaciers): Covered in snow throughout most of the year. Vegetation is extremely limited to only a few species that thrive on silica soils. Alpine level: The zone that stretches between the tree line and snowline. This zone is further broken down into Sub-Nival and Treeless Alpine (in the tropics-Tierra fria; low-alpine) Sub-nival: The highest zone that vegetation typically exists. This area is shaped by the frequent frosts that restrict extensive plant colonization. Vegetation is patchy and is restricted to only the most favorable locations that are protected from the heavy winds that often characterize this area. Much of this region is patchy grassland, sedges and rush heaths typical of arctic zones . Snow is found in this region for part of the year. Treeless alpine (low-alpine): Characterized by a closed carpet of vegetation that includes alpine meadows, shrubs and sporadic dwarfed trees. Because of the complete cover of vegetation, frost has less of an effect on this region, but due to the consistent freezing temperatures tree growth is severely limited. Montane level: Extends from the mid-elevation forests to the tree line. The exact level of the tree line varies with local climate, but typically the tree line is found where mean monthly soil temperatures never exceed 10.0 degrees C and the