A desert is a landscape or region that receives an extremely low amount of precipitation, less than enough to support growth of most plants. Deserts are defined as areas with an average annual precipitation of less than 250 millimetres (10 in) per year, or as areas where more water is lost by evapotranspiration than falls as precipitation.

source: Wikipedia

Forest Ecology is the study of the relationships, in an environment dominated by trees, between the populations of plants, animals and microorganisms that are occupying this area, and the environment itself. Forested Ecosystems are communities of plants, animals and microorganisms, and the physical environment they occupy, in which trees are the dominant life form. This dominance by trees is important because it produces vertical stratification, in terms of livable space and micro-climate of that space. This vertical stratification distinguishes forested ecosystems from other ecosystem classifications. On a time scale, forested ecosystems are an ever-changing assemblage of species, dominated by trees, shaped by climate and other physical processes. On a spatial scale, forested ecosystems can be comparable to the "stand" or group of trees that are reasonably similar in age, structure and species composition, which occupy a contiguous space.

Grasslands are areas where the vegetation is dominated by grasses (Poaceae) and other herbaceous (non-woody) plants (forbs). However, sedge (Cyperaceae) and rush (Juncaceae) families can also be found. Grasslands occur naturally on all continents except Antarctica.

A savanna, or savannah, is a grassland ecosystem characterized by the trees being sufficiently small or widely spaced so that the canopy does not close. The open canopy allows sufficient light to reach the ground to support an unbroken herbaceous layer consisting primarily of grasses.

Shrubland, scrubland, scrub or brush is a plant community characterized by vegetation dominated by shrubs, often also including grasses, herbs, and geophytes.

Source: Wikipeida

In physical geography, tundra is a biome where the tree growth is hindered by low temperatures and short growing seasons. There are three types of tundra: Arctic tundra, alpine tundra, and Antarctic tundra. The vegetation is composed of dwarf shrubs, sedges and grasses, mosses, and lichens. Scattered trees grow in some tundra. The ecotone (or ecological boundary region) between the tundra and the forest is known as the tree line or timberline.

Source: Wikpedia<-i>