The climate then helps to determine the biome the plant communities that is present in the region So what are the major terrestrial biomes and what are their characteristics 2500 2000 1500 1000 500 0 Tundra We ll start in the north with the Tundra biome Although most of this biome type is found around the Arctic there also are significant sections above the treeline in mountain ranges alpine tundra The Tundra occupies about 5 million acres 7812 mi2 mostly in the northern hemisphere The tundra biome is characterized by permafrost only the top few centimeters of soil ever thaw the soil below remains frozen year round This has two effects 1 plant roots are limited in how deep they can go 2 water is not lost from the system as evaporation is low and the water cannot percolate through the permafrost So even though precipitation amounts are low water is not a limiting factor Temperature and sunlight generally are Tundra temperatures are below freezing during much of the year and are not really hot at anytime Arctic tundra receives light only in the summer 24hrs but none in the winter The vegetation of tundra is characterized by dwarf shrubs and grasses and lichens Plants must remain below the snow surface in winter to avoid being killed by blowing ice Soils are acidic and wet permafrost The 24 hrs of sunlight allow for surprisingly high levels of productivity during the short 1 2 mo growing season Tundra is productive enough that many animals migrate to it especially birds during the growing season Most migrate away or hibernate during the winter 2500 2000 1500 1000 500 0 Boreal Forest Also referred to as Taiga evergreen forest between 50 and 60 N latitude Coverage of 2 9 billion acres 4 6 million mi2 Still cold biome and precipitation relatively low but longer growing season than tundra with deeper to no permafrost The majority of precipitation falls as snow snow pack critical for ecosystem Although still cold the mean temperatures during the relatively short growing season are considerably higher than tundra Day length in summer compensates for the short growing season not 24 hours but long days 18 22 hours Evaporation rates low so even with low precipitation water not limiting Vegetation is dominated by gymnosperms evergreens adapted for snow cover and cold temperatures Can photosynthesize at a moments notice Needles very nutrient poor decomposition rates very low and soil acidic Productive summers also make this biome attractive migratory stop Carbon sink Residents often hibernate or subnivean below snow during winter 2500 2000 1500 1000 500 0 Deciduous forest Biome characterized by temperate seasonal climate with high levels of precipitation 650 3000 mm precipitation Interspersed in the mid latitudes usually costal Growing season considerably longer than boreal forest Precipitation fairly evenly distributed throughout the year may be biased to growing season Generally productivity limited by seasonality of biome and somewhat by light Near total absence of photosynthesis in winter no leaves Soils not deep A horizon but very productive high nutrient levels Leaves have much higher nutrient content than needles so decomposition nutrient cycling much higher Plant communities dominated by deciduous trees lose leafs in winter Partly adaptation to prevent winter damage growing season sufficient for the plant Has distinct levels within forest Canopy the very top of the largest tree Understory smaller trees Shrub herb layer grasses and other low laying plants Greatly increases productivity 2500 2000 1500 1000 500 0 Temperate grassland Climatically similar to temperate forest but precipitation greatly reduced 100 1000 mm Often associated with rain shadows Climate is variable cold winters and hot summers Precipitation highly seasonal mostly falling in spring to summer Evaporation can be significant in summer drought prone Soils deep A horizon and very fertile most converted to agriculture Grass leaves high in nutrient levels so nutrient cycling fairly rapid Plant communities dominated by herbaceous vegetation grasses Trees found only in areas with high water availability e g river banks Limiting factor generally water but can be light at fine scale Wetter grasslands e g tallgrass prairie can be as productive as temperate forest Low faunal diversity but some impressive e g bison herds Fire adapted to fire dependent system 2500 2000 1500 1000 500 0 Savanna Very similar to grasslands but with a few more trees Similar to grasslands in that they are climatically similar to forest in the same latitude but water limited Savannas are found in tropical climates so the growing season is year round Temperature is fairly constant and warm Precipitation is highly seasonal so evaporative water loss is high during the dry season functionally this eliminates photosynthesis Soils tend to fine grained clay which exacerbates the evaporation in savannas with high precipitation but allows their existence in areas with low precipitation Dominated by both grasses and drought tolerant trees shrubs Drought tolerance big key plants must take advantage of the short period where water is available Productivity is high but concentrated in the periods of water availability Soil not deep and very nutrient poor dry season prevents rapid cycling of nutrients Feedback loop plants need to keep nutrients so they sequester what they have in the roots so it is not available to decomposers so there is less available 2500 Consumer populations often nomadic System fire adapted 2000 1500 1000 500 0 Fire the chicken or the egg Both grasslands and savannas are maintained in part by fire Growth tissue of grass apical meristem below soil level heat from fire only penetrates top cm of soil Apical meristem of trees above ground so fire kills trees but not grass Fires are started by lightning or cigarette butts and generally only during the spring grassland or dry season savanna This is due to favorable conditions dry grass to provide fuel warm temps low moisture So the presence of grassland or savanna promotes fire and the presence of fire promotes grassland or savanna which promotes fire Grasslands and savannas are fire adapted but are they fire dependent Forests and fire are a different story the effect of a fire on a forest is dependent on the severity of the fire a low intensity fire is often beneficial but high intensity crown fire is devastating at least in the short term Desert Characterized by low precipitation high evaporation