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TERRESTRIAL BIOMES
FE Clements & VE Shelford
• Introduced in 1939 an approach for combining the broad scale distribution of both plants and associated animals into a single classification system called biomes.
8 Major Terrestrial Biomes
• Tropical forest• Temperate forest• Conifer forest (Taiga)• Tropical savanna• Temperate grasslands• Chaparral (Shrublands)• Tundra• Desert
The pattern of terrestrial biomes in relation to temperature and moisture
Classification of terrestrial ecosystems are based from
• Plant distribution• Climate• Annual precipitation
Tropical Forest• Key feature is constant temperature
– Average temperature from one month to the other is usually within ± 2C
– However, daytime temp may be 34 C during the day and 20 C at night.
• Much rain: annual rainfall ranges from 2,000 mm to 15,000 mm (79 – 591 inches; 1.6 inches per day).
• Found in the equatorial zone between 10°N and 10°S where the temperatures are warm
Tropical Forest• Long Dry Season
– Dry season = 6-8 months– Many trees drop their leaves during the dry
season not to escape cold, but to prevent overheating
• Short Dry Season– Dry season < 3 months– Tropical rain forest: 2,300 – 5,000 mm of rain
per year (extreme years some places may get 15,000 mm = 50 feet).
LAYERS OF TROPICAL RAINFORESTS
1. Emergent Trees/Layer2. Canopy Layer
a.Highb.Low Tree Stratum
3. Shrub Understory4. Ground Layer of Herbs
and Ferns /Forest Floor
• Climbing vines grow upward into the canopy
• Epiphytes grow on trunks and branches• Stranglers grow downward from the
canopy to the ground• Buttresses-plant-like outgrowths; prop
roots, provides support to trees• Floor of laced with roots both large and
small forming a dense mat on the ground
Tropical Forest (Rain)• Huge diversity
– Perhaps 50 - 75% of all organisms on Earth inhabit theses forests.
– Temperate forest may have 20 - 30 tree species per hectare (2.47 acres); rain forests can support more than 350 – 450 tree species per hectare• To fit that many tress each species may only be
represented once or twice • Most productive terrestrial biome
– High temp, moisture, uninterrupted growing season
– Decomposers / nutrient cycling
Tropical Rain Forest
Tropical Savannas• Originally used to describe the treeless areas of
South America• Characterized by a ground cover of grasses with
scattered shrubs or trees• Has warm continental climate with seasonality
in rainfall• Mean monthly temperature do not fall typically
below 18°C• Continuous weathering produces phosphorus-
deficient Oxisols, Alfisols in drie savannas and Entisols on driest savannas
• Consists of two-layer vertical structure (as a result of ground cover and shrubs and trees)
• PLANT ACTIVITY– Controlled by seasonal precipitation and changes
in available moisture; leaf litter decomposed during wet season; woody debris consumed by termites during the dry season
• Home to at least 60 animal species• Wildebeest and zebra are migratory during dry
season• Insects: flies, grasshoppers, locusts, crickets,
carabid beetle, ants and detrital feeding dung beetles and termites
• Carnivores-lion, leopard, cheetah, hyena and wild dog
• Scavengers- vultures and jackals
Desert• Lies between 15° and 30° where the air is
caused aloft the Intertropical Convergence Zone
• Difference in moisture, temperature, soil drainage, topography, alkalinity, and salinity create variations in vegetation covering, dominant plants, and groups of associated species
Types of Deserts• Cool Desert- Great Basin of North America,
Gobi, Takla Makan, and Turkestan deserts of Asia and high elevations of hot deserts are dominated by chenopod shrubs(shrub steppes/desert scrub)
• Hot desert-range from these lacking vegetation to ones with some combination of chenopods, dwarf shrubs and succulents.– Southwestern North America-the Mojave, the
Sonoran and the Chihuahuan dominated by creosote bush and bursage
Plants
• Desert plants may be deep-rooted woody shrubs like mesquite and Tamarix, whose taproots reach the water table
• Larrea and Atriplex are deep-rooted perennials with superficial laterals that extend, as far as 15 to 30 m from the stems. Others have shallow roots often extending no more than a few centimeter below the surface
Animals• Drought-evading animals adopt an annual
cycle of activity or go into estivation or some other stage of dormancy during the dry season (spadefoot toad)
• Includes wide assortment of beetles, ants, locusts, lizards, snakes, birds, and mammals
• Mammals are mostly herbivorous; grazing herbivores tend to be generalists or opportunists
• Desert rodents (Heteromyidae) and ants feed largely on seeds and are important in the dynamics of desert ecosystem
• Desert carnivores, foxes and coyotes, have mixed diets
• Omnivory rather than carnivory and complex food web seems to be the rule in desert ecosystem
Desert
Productivity• Infrequent rainfall coupled with high rates of
evaporation limit the availability of water to plants and so primary productivity is low
• Desert soils are poorly developed Ardisols and Entisols and land limits the ability of vegetation to modify soil environment
SHRUBLANDS• Plant communities where the shrub growth is
dominant or codominant• Five widely disjunct region between 30° and 40°
latitude dominated by evergreen shrubs and sclerophyllus trees– Semi-arid regions of Western North America– Regions bordering the Mediterranean Sea– Central Chile– Cape Region of South Africa– Southwestern and Southern Australia
CLIMATE• Has hot, dry summer with at least one month
of protracted drought, and cool, moist winters• 65% of annual precipitation falls during the
winter months with temperature average of 10-12°C with a risk of frost
• Persistent flow of dry air during summer brings several months of hot, dry weather
• Fire is a frequent hazard during the periods.
PLANTS AND VEGETATION• Support similar looking communities of xeric
broadleaf evergreen shrubs and dwarf trees as “sclerophyllous”(scleros-hard, phyll-leaf) vegetation with an herbaceous understory
1. Mediterranean Sea in Southern Europe and North Africa dominated by mixed evergreen woodland such as holm oak and cork oak2. Southern Africa – vegetation is known as fymbos composed of broadleaf protenoid shrubs that grow to a height of 1.5-2.5 m
3. Southwestern Australia- mediterranean shrub community known as mallee dominated by low-growing Eucalyptus, 5-8 m in height with broad sclerophyllous leaves4. North America – sclerophyllus shrub community is known as chaparral (a word Spanish origin meaning a thicket of shrubby evergreen oaks)5. Central Chile –mattoral shrub communities occur in coastal lowlands and on the west –facing slopes of Andes; mattoral species are evergreen shrubs 1-3 m in height with small sclerophyllous leaves
ANIMALS• Mediterranean-parallel and convergent
evolution among bird species and some lizard species
• NA-mule deer, coyotes, a variety of rodents, jackrabbits and sage grouse
• Australian mallee-birds including endemic mallee-fowl which incubates its egg in a large mound; gray kangaroo and species of wallaby
PRODUCTIVITY• Diverse soil conditions but soils are typically
classified as Alfisols• Generally deficient in nutrients, litter
decomposition is limited by low temperature during winter and low soil moisture during the summer months
• Vary in productivity depending on the annual precipitation and the severity of summer droughts
TEMPERATE FOREST
• Forests dominated by broadleaf deciduous trees• North America – mixed mesophytic forested of
the unglaciated Appalachian plateau; the beech-maple and Northen hardwood forests (with pine and hemlock) in northern regions , the maple-basswood forests of the Great Lake states; the oak-chestnut of central hardwood forests; the magnolia-oak forests of the Gulf Coast staes; and the oak-hickory forests of the Ozarks
• The Asiatic broadleaf forest (Eastern China, Japan, Taiwan, Korea) contains a number of plant species of the same genera found in NA;broadleaf evergreen species become increasingly present and in the west foothills of the Himalayas.
• Southern Europe, their presence reflects the transition into the mediterranean region. Evergreen oaks and pines are also widely distributed I the Southeastern US (associated with poorly developed sandy soils
• In Southern Hemisphere they are found only in the drier parts of the Southern Andes
• In Southern Chile, broadleaf evergreen rain forests have developed in an oceanic climate that is virtually frost-free
• Also found in New Zealand, Tasmania and parts of Southeastern Australia
• In broadleaf deciduous forests of the temperate region, the growing season is marked by the autumn colors of foliage shortly before the trees enter into their leafless winter period;trees resume growth in the spring in response to increasing temperature and longer daylengths; many herbaceous species flower at this time before the developing canopy casts a heavy shade on the forest floor.
4 VERTICAL STRATA/LAYERS
1. Upper canopy – dominant tree species2. Lower tree canopy3. Shrub layer4. Ground layer
ANIMALS
• Associated vertical stratification and the growth form of plants– Arthropods– Mice, shrews, ground squirrels, and forest
salamanders burrow into soil/litter for shelter and food
– Larger mammals live on ground layer and feed on herbs, shrubs and low trees
– Birds move freely among several strata
PRODUCTIVITY• Differences in climate, bedrock, and drainage are
reflected in the variety of soil conditions that are present
• Soil types: Alfisols, Inceptisols, Uttisols associated glacial materials in more Northen region
• Influenced largely by temperatures and the length of the growing season
• Leaf fall in deciduous forests occur over a short period in autumn, and the availability of nutrients is related to rates of decomposition and mineralization
GRASSLANDS• Occupy regions where rainfall is between 250 mm and
800 mm a year; many exist through the intervention of fire and human activity
• Occur in the midlatitudes in midcontinental regions where annual precipitation dclines as air masses move inward from the coastal environments
• Northern Hemisphere – include the prairree of North America and steppes of Central Eurasia
• Sothern Hemisphere – include pampas of Argentina and the grassveld of high plateaus of Southern Africa;smaller areas occur in Southeast Australia and the drier parts of New Zealand
• Northern Hemisphere– Climate is recurring drought; tallest and most
productive where mean annual precipitation is greater than 800 mm and mean annual temperature is above 15°
– 3 Main Types• Tallgrass prairie- big blue stem growing 1m tall with
flowering stalk• Mixed-grass prairie- Great Plains;needle grass, grama
grass• Shortgrass prairie- rod-forming blue grama and blue
grass
• Desert grassland (Southeast Texas to Southern Arizona into Mexico) similar to shortgrass plains except that three-awn grass replaces buffalo grass
• Annual grassland (Central valley of California) associated with mediterranean type climate characerized by rainy winters and hot, dry summers. Growth occurs during early spring, and most plants are dormant in summer, turning the hills a dry tan color accented by the deep green foliage of scattered California oaks
• Steppes – treeless except for ribbons and patches of forest divided into four belts of latitude
• Southern Hemisphere (Southern Africa, Southern America)– pampas, the South American grasslands extend
westward in a large semicircle from Buenos Aires to cover about 15% of Argentina
– With European forage grasses and alfalfa and the eastern tallgrass pampas have been converted to wheat and corn
– Velds of Southern Africa occupy eastern part of a high plateau 1500 m to 2000 m above sea level
ANIMALS
• Dominated by herbivorous species• Vertebrates like large burrowing mammals and
ungulates• NA-once dominated by herds of bisons and
pronghorned-antelope;prairie dog with gophers and the mound
• Eurasian steppes and pampas lack herds of ungulates; 2 major herbivores are pampas deer, guanaco, small relative of the camel
• African grassveld once supported migratory herds of wildebeest and zebras along with lion, hyena and leopard; They have been greatly destroyed and was replaced by sheep, cattle, and horses
• Australia-marsupial mammals evolved many forms; dominant grazing animals are kangaroos (the red and the gray)
• Grasslands evolve under the selective pressure of grazing which stimulates primary production
• Strata1. Tall, green ephemeral herbaceous growth2. Ground layer3. Below-ground root layerGrasslands accumulate a layer of mulch that retains moisture and with continuous turnover of fine roots, add organic matter to the mineral soilThe soil type is Mollisols where there is a relatively thick, dark-brown to black surface horizon that is rich in organic materials
CONIFER FOREST• Dominated by needle-leaf evergreen trees• Found primarily in broad circumpolar belt
across the Northern Hemisphere and on mountain ranges where low temperature limits the growing season– Central Europe-dominated by Norway spruce– North America-Engelmann spruce, subalpine fir,
Douglas fir, and panderosa pine and stands of lodgepole pine
4 MAJOR VEGETATION TYPES
1. Forest tundra ecotone with open stands of stunted spruce, lichens, moss
2. Open boreal woodland with stands of lichens and black spruce
3. Main boreal forest with continuous stands of spruce and pine broken by poplar and birch
4. Boreal-mixed forest where it grades into the temperate forest of Southern Canada and the Northern US
CLIMATE• Cold continental climate with seasonal
variation• Summers are short, cool and moist• Winters are prolonged, harsh and dry with
prolonged period of snowfall• Driest winters are most extreme in Interior
Alaskaand Central Siberia which experience as much as 100°Cseasonal temperature extreme
• Under the controlling influence of permafrost
PERMAFROST
• The perennially frozen subsurface that may be hundreds of meters deep. It develops where the ground temperature remain below 0°C for extended periods of time. Its upper layer may thaw in summer and refuge in winter. Because it is impervious to water, it forces all water to remain and move about it. Thus, the ground stays soggy even though precipitation is low,enabling plants to exist in the driest parts of the Arctic.
ANIMAL COMMUNITY• Caribou, moose (elk in Eurasia), cyclic
snowshoe hare, aboreal red squirrel, quill-bearing porcupine
• Predators include wolf lynx, pine martins and owls, migratory neotropical birds (for nesting ground)
• Habitat for seed-eating birds like crossbills, grosbeaks, and siskins
• Herbivorous insects line spruce budworm
PRODUCTIVITY• Generally low in comparison to more temperate
forests, limited by low nutrients, cooler temperatures, and the short-growing season
• Inputs of plant litter are low under the cold, wet conditions
• Rates of decomposition are low• Soils are Spodosols characterized by a thick organic
layer; mineral soil beneath mature coniferous forests are comparatively infertile, and growth is often limited by the rate at which mineral nutrients are reccycled through the ecosystem
TUNDRA• Top of Northern Hemisphere; frozen plain
clothed in sedges, heaths and willows dotted with lakes and crossed by streams
• Came form the Finnish ‘tunturi’ meaning a treeless plainTwo Broad Types:1. Tundra with up to 100% plant cover and wet to
moist soil2. Polar desert with less than 5% plant cover and
dry soil
CONDITIONS UNIQUE TO TUNDRA
1. Permafrost2. Vegetation3. Transfer of heat
VEGETATION• Simple and few and growth is slow; only species
able to withstand constant disturbance of the soil; buffeting by the wind and debrasion from wind-carried particles of soil and ice can survive
• Sphagnum on low ground with cotton grasses and sedges
• Heath shrubs, dwarf willows and birches, herbs, mosses and lichens
• Cructose, foliose, lichens on rocks
• Plants propagate through vegetative means • Photosynthetically active on the Arctic tundra about 3
months out of the year as snow cover disappears, plants commence photosynthetic activity. They maximize use of the growing season and light even at midnight.
• Goes into production of new growth but about one month before the growing season ends
• Most tundra vegetation is underground • Most shoot ratios of vascular plants range from 3:1 to 10:1• Roots are concentrated in the upper soil;above ground
parts seldomgrow taller than 30 cm• Below grouns activity is typically 3x that of the aboveground
productivity
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