Life in Land.docx

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30 Jan 2013

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- activity of soil organisms
-influences the rates of carbon and nutrient cycling, soil respiration, transfer nutrients to
vascular plants
- provide food and habitat for larger organisms
- key to the development of soil structure
Soil: Foundation of Terrestrial Biomes
- soil structure results from the long term interaction of climate, organisms, topography, and parent
- diagram illustrated
- Plants secrete root exudates, along with the living roots and plant litter, serve as substrates for
bacterial, fungal, and animal species.
- Growth and activity of organisms provides stability to mineral components
allowing development and maintenance of complex canals of air spaces and
cavities within the soil
- Climate affects rates of weathering of parent materials, leaching of organic and
inorganic substances, erosion, and decomposition of organic matter through direct
weathering effects
- also alter decomposition by directly impacting the activity of soil organisms
and indirectly altering soil activity by influencing the type and amount of plant
species that can grow in a given area
Natural History and Geography of Biomes
- geography distribution of terrestrial biomes corresponds closely to variation in climate, especially
prevailing temp. and precipitation
Tundra: (starting at the most northerly areas of vegetation)
- open landscape of mosses, lichens, dwarf willows, small ponds, clear streams , quite warm summer
- covers most of the lands north of the Arctic circle
- extends from northern-most Scandinavia, across Northern European Russia,
through northern Siberia, across northern Alaska and Canada
- reaches far south of Arctic circle into the Hudson Bay region of Canada
- also found on the coast of Greenland and in northern Iceland
- typically cold and dry
- not as cold in winter or as warm in summer as boreal boreal forest to the south
- defining characteristic of northern tundra: short summers
- precipitation: less than 200mm to a little over 600mm
- low avg annual temp. > precipitation exceeds evaporation
- soil building slow in old: rate of decomposition low > organic matter accumulates in
deposits of peat and humus
- surface soils thaw in summer but often underlain by layer of permafrost (many meters thick) :
perm frozen later of soil that remains frozen even during summer
freezing and thawing of surface soil combines with actions of water and gravity
- solifluction: slowly moves soils down slopes
- brings stones to the surface of the soil, forming a netlike, or polygonal, pattern on the
surface of tundra soils
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Biology :
- herbaceous plants : especially grasses, sedges, mosses, lichens
- lichens, associations of fungi and algae often eaten by reindeer and caribou
- woody vegetation: dwarf willows and birches, variety of low-growing shrubs
- short growth due to short summer:
-slow growing plants, nearly all of the living biomass below ground
- plants with very short and strong stems to withstand fierce winds of the north
- one of the last biomes on earth that supports substantial no.s of large native mammals: caribou,
reindeer, musk ox, bear, wolves
- small mammals: fox, weasel, lemming, ground squirrel
- birds: ptarmigan, snowy owl
- insects: not as diverse as in biomes farther south but abundant (swarms of mosquitoes and insects
in summer)
Human Influences
- intense exploration and extraction of oil, natural gas, and a variety of minerals
- rapidly rising temperatures on the permafrost and rates of decomposition
- patterns of global air and ocean circulation causing areas of arctic tundra rapidly warming
- deep expanses of permafrost in the arctic: as permafrost melts, the rich organic material it contains
becomes available to soil microbes and insects for decomposition = releasing amounts of CO2 into
atmosphere > greenhouse effect and global warming
Boreal Forest/Taiga: world of wood and water covering over 11% of earth's land area
- confined to northern hemisphere
- extends from Scandinavia, through European Russia, across Siberia, to central
Alaska, and across all of central Canada in a band b/t 50 and 65 degree latitude
- bounded in the south either by temperate forests or temperate grasslands and in north by
- winters usually longer than six months
- summers too short to support temperate forest
- fairly moderate climates (Sweden) moderated by the nearby Baltic Sea
- some are variable: ranges from -70 in winter to over 30 in summer (annual temp. range of
100degree celsius)
- precipitation moderate, ranging from 200-600mm
- low temp and long winters > evaporation rates low > drought infrequent/brief (burn vast areas
of boreal forest)
- low fertility, thin, and acidic
- low temp and low ph slow down decomposition of plant litter and the rate of soil
building > nutrients largely tied up in a thick layer of plant litter that carpets forest floor
- most trees in boreal forests have a dense network of shallow roots that, along with
associated mycorrhizal fungi, tap directly into the nutrients bound up in this litter layer
- topsoil (underlies litter layer) is thin
- dominated by evergreen conifers (spruce, fir, pines)
- larch, a deciduous conifer, dominates in the most extreme siberian climates
- deciduous aspen and birch trees : Canada (dominant during early stages of
recovery following fire)
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- willows: along shores of rivers and lakes
- mosses and other non-vascular plants along base of most trees and on
forest floor
- traps rainfall, home to insects and other organisms
- steep vertical gradient in light from canopy to soil surface (leaves on
outside of canopy absorbs much of the visible light, light levels attenuate as u
move down in both intensity and color)
- large expanses of bogs and fens dominated by moss species, these areas have
waterlogged 'soils', with islands of vascular plants centered around a few trees and
shrubs, home to plants that feed on insects
- winter: migratory caribou and reindeer
- year-round: mousse and woodland bison
- wolf --- major predator
- N. America: black bears, grizzly bears
- Eurasia: brown bear
- smaller mammals: lynx, wolverine, snowshoe hare, porcupines, red
- nesting habitat for many birds that migrate from tropics each spring and year-
round home of other birds (crossbills and spruce grouse)
Human influences:
- hunting and trapping impact populations of wildlife species
- forest rapidly cut for lumber and pulp and oil and gas exploration (potential econ gain)
Temperate Forest
- largest living organisms on earth
- found b/t 30 and 55 degree latitude
- Asia: Japan, eastern China, Korea, eastern Siberia
- Western Europe: southern Scandinavia to northwestern Iberia, from British Isles through Eastern
- northern Cali through southeastern Alaska
- Southern Hemisphere: Chile, New Zealand, southern Aussie
- temp forests may be either coniferous or deciduous at where temperatures not extreme and annual
precipitation avg's anywhere from 650mm to over 3000mm
- receive more winter precipitation than temp. grasslands
- deciduous trees dominate (growing season moist and at least 4 months long
- deciduous forests: winters 3 to 4 mths, usually mild (snowfall heavy)
- coniferous forests: winters more severe or summers drier (conifers more abundant than deciduous
- pacific coast of North America receive most precipitation during fall, winter, spring,and
subject to summer drought
- usually fertile
- most fertile under deciduous forests (neutral or slightly acidic in pH, rich in organic matter and
inorganic nutrients)
- coniferous forests: less fertile due to acidity of the needles leading to reduced decomposition
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