BIOL 4120: Principles of EcologyBIOL 4120: Principles of Ecology

Lecture 22: Biogeographical Lecture 22: Biogeographical EcologyEcology

Dafeng HuiDafeng Hui

Room: Harned Hall 320Room: Harned Hall 320

Phone: 963-5777Phone: 963-5777

Email: dhui@tnstate.eduEmail: dhui@tnstate.edu

23 Terrestrial Ecosystems23 Terrestrial Ecosystems

23.1 Biomes and climate 23.2 Tropical forests (Equatorial zone)23.3 Tropical savannas (semiarid regions with

seasonal rainfall)23.4 Desert23.5 Temperate zone (Mediterranean climate)23.6 Forest ecosystems (Temperate wetter

regions)23.7 Grassland ecosystems (Temperate zone

vary with climate and geography23.8 Conifer forests (cool temperature and boreal

zones)23.9 Arctic tundra (cold temperatures and low

precipitation)

Biomes are classified according to the

predominat plant types

Concept of Biomes:

F.E. Clements and V.E. Shelford, 1939

Combining broad-scale distribution of both plants and associated animals into a single classification

Biomes: classified according to the predominant plant types

Campbell 1996: the world's major communities, classified according to the predominant vegetation and characterized by adaptations of organisms to that particular environment.

Major terrestrial biome types:

Tropic forest, temperate forest, conifer forest (taiga and boreal forest), tropical savanna, temperate grasslands, chaparral (shrublands), tundra, and desert.

three general plant forms: trees, shrubs, and grasses.

Robert Whittaker, Cornell Uni.

Biomes and climate

Boundaries between biomes are broad and often indistinct

Other factors: topography, soils, and exposure to disturbances such as fire

23.1 Terrestrial ecosystems reflect adaptations of dominant plant life forms

Why are there consistent patterns in the distribution and abundance of three dominant plant life forms that relate to climate and physical environment?

Terrestrial ecosystems reflect adaptations of dominant plant life forms

These three forms represent different patterns of carbon allocation and morphology

Grass: less C to production of supporting tissue (stem) than do wood plants (shrubs and trees), more to photosynthetic tissues (leaves)

Woody plants: shrubs allocate lower percentage to stem than trees.

Trees: more to stem, advantage of height and access to light, cost more for maintenance and respiration.

As environmental conditions become adverse for photosynthesis (dry, low nutrient, cold T), trees will decline in both stature and density until they are no longer able to persist as a component of the plant community.

Forests

Within broad classes of forest and woodland ecosystem (trees are dominant or co-dominant), leaf form is another plant characteristic.

Based on longevityDeciduous (live for only one year or growing season)• Winter-deciduous (temperate regions, low winter T)• Drought-deciduous (subtropical and tropical, leaf shed on

dry periods)Evergreen (live beyond a year)• Broadleaf-evergreen (tropic rainforest, no distinct growing

season, year-round photosynthesis)• Needle-leaf evergreen (growing season is short or nutrient

availability constrains photosynthesis and plant growth)

Economic model to explain adaptation of leaf form: cost to produce leaf and gain from photosynthesis.

Ecosystems characteristic of warm, wet climates with no distinct seasonality are dominated by broadleaf evergreen trees (tropic or subtropical rain forest).

As conditions become drier, with a distinct dry season, broadleaf evergreen habit gives way to drought-deciduous trees (seasonal tropical forest)

As PPT declines further, trees decline and giving rise to woodland and savannas (shrub and grasses).

PPT further declines, no trees can be supported, giving rise to arid shrubland and desert.

Similar for T control.

Winter-deciduous

Drought-deciduous

Broadleaf evergreen in tropic rain forest in Australia

Needle-leaf evergreen in Sierra Nevada, US

23.2 Tropic rain forest

Location: Equatorial zone between latitudes 10oN and 10oS

T: warm all year, annual mean T>18oCPPT: rainfall occurs daily, min.

monthly>60mmTypical example: Amazon basin of

South America

Tropic rain forests in Amazon (a), Malaysia (b), and Northeast Australia (c)

High net primary productivity (NPP)

High diversity of plant and animal life

7% land surface, >50% plant and animal species

10-km2 contain 1500 species of flowing plants and 750 tree species.

Richest area in Malaysia, 7900 species

90% of all primate species live in the tropical rain forest

orangutan (an arboreal ape)

Gibbons, langurs, macaques

(Malaysian)

Gorillas, and chimpanzees

(Africa)

Lemurs

Beetles, butterflies

Vertical stratification of a tropic rain forest

Plank-like buttresses

Tropical dry forest

drought-deciduous trees

Africa, South America, Central America, Australia, India, Southeast Asia

Undergo a dry season, influenced by the seasonal migration of Intertropical Convergence Zone (ITCZ)

23.3 Tropic Savannas

Location: Equatorial zone between latitudes 30oN and 30oS, Dry tropic and subtropical.

T: warm all year, annual mean T>18oCPPT: distinct seasonality in rainfall,

large interannual variationTypical example: South America

Tropic SavannasSavanna: means the treeless areas of South America

An array of vegetation types representing a continuum of increasing cover of woody vegetation, from open grassland to widely spaced shrubs or trees to woodland

CharacteristicsOccur on land surfaces of little relief, often on old plateaus,

interrupted by escarpments and dissected by riversPoor in nutrients, especially PDominant species are fire-adapted, subjected to recurrent

fires.Grass cover with or without wood vegetation is always presentWoody component is short-lived (less than a few decades).Two-lay vertical structure (ground level grass + shrubs or

trees)Support a large and varies assemblage of herbvores,

invertebrate and vertebrate, grazing and browsing.

Interaction between annual PPT and soil texture in defining biomes

Access by plants to soil moisture is more limited on the heavy textured soils (clay) than sandy oil.

23.4 Desert

Area: 25 to 35%Location: latitudes between 15 and 30oCause: Global air mass circulation T: High in summer, could be cold in winterPPT: low, <150 mmTypical examples: majority in Northern

Hemisphere, Sahara in Africa, Gobi in Asia, western North America

Deserts are not the same everywhere

Cold desert: Great Basin of North America, the Gobi, Takla Makan, and Turkestan deserts of Asia

Species: sagebrush, shadscale, chenopods, etc

Hot desert: Mojave, the Sonoran, and Chihuahuan

Vegetation: none to some combination of chenopods, dwarf-shrubs, and succulents

Hot desert: a. Chihuahuan Desert, b. Great Victorian Desert in Australia, c. Dunes in Saudi Arabian desert.

DesertSurvive of desert plants:

Adapted to scarcity of water, low primary productivityFlowering only when moisture is presentFast grow, flower, produce seeds and dieDeep-rooted (mesquite, taproots reach water table)CAM pathway, species leaf structure

Survive of animalsSupport a diversity of animal life (bettles, ants, locusts, lizards, snakes, birds and mammals)Grazing herbivores: generalists, consume a wide range of species. Desert carnivores,such as fox and coyotes, have mixed diet include leaves and fruits.

23.5 Temperate shrublands

Shrublands: shrub is dominant or co-dominant, but difficult to categorize

Shrub: no good definition, a plant with multiple woody, persistent stems but no central trunk and a height from 4.5 to 8 m.

(Tree can grow less than 8m under severe environmental conditions)

Temperate shrublands

Location: between latitudes 30o and 40o, five regions

T: hot dry summers, cool, moist wintersPPT: 65% annual PPT falls during winter

months.Five regions: semiarid region of western

North America, regions bordering Mediterranean Sea, central Chile, cape region of south Africa, south-western and southern Australia

Chaparral is the dominant mediterranean shrub vegetation of southern California

Mediterranean vegetation (fynbos) of the western cape region of South Africa

23.6 Forest Ecosystems

Forest ecosystems dominate the wetter regions of the temperate zone

Deciduous forest covered large area of Europe and China, but mostly converted to croplands, only exist in eastern China

Southern Hemisphere, temperate evergreen forest become predominant

North America, deciduous forests consist of a number of associations (show later)

Asiatic broadleaf forest found in eastern China, Japan, Korea is similar to the North American deciduous forest

Large scale distribution of temperature forest in eastern US (showed before?)

Temperate forest in fall and spring

23.7 Grassland ecosystems

Rainfall is very important: 250 to 800 mmOther factors: fire, and human activity

(convert from forest to grassland)Area: dropped from 42% to <12% of original

sizeLocation: mid-latitudes in mid-continental

regionsTypical: prairies of North America, steppes of

central Eurasia

Grassland in North America

a. Tallgrass prairie in Iowa, b. mixed-grass prairie; c. shortgrass steppe

Tallgrass prairie

Big bluestem, >1m

Mixed-grass prairie

Needlegrass-grama grass

Shortgrass prairie

Blue grama and buffalo grass

Aboveground primary productivity is related to MAP (52 grassland)

Grasslands are most productive when MAP>800 mm and MAT > 15oC

23.8 Conifer forests

Conifer forests: needle-leaf evergreenLocation: Northern Hemisphere and mountain

rangesVarious composition: wide range of climate they can

growEurope: Norway spruceNorth America: Rocky: Engelmann spruce, subalpine

fir; Douglas-fir, ponderosa pine, lodgepool pine; giant sequoia (in California Sierra)

Boreal forest (11% of Earth’s land surface) Alaska and Canada in N. America, Euroasia (from

Scotland to northern Japan)

Black spruce in North America taiga (boreal forest)

Some coniferous forest. A. Norway spruce, b. Rocky Mountaine subalpine forest, c. montane coniferous forest in Rocky Mountains

23.9 Arctic TundraTundra is treeless plainArctic tundra is a frozen plain, clothed in sedges, heaths, and

willows, dotted with lakes, and crossed by streamsCold Temperature and low precipitation

Two types:tundra: up to 100% plant coverage, wet to moist soilpolar desert: dry soil, less than 5% plant cover

Unique conditions:permafrost: isolate and protect soil OMvegetation: simple form, slow growth, allocate more to rootstransfer of heat

Principles of EcologyWhat we covered in this course:

Ecology is study of interaction of Organisms and environmental conditions

Organisms: adaptation and evolution, life history

Environmental conditions: Climate, terrestrial and aquatic environments

Subdisplinary of ecology

Population ecology: growth, competition, predation, parasitism

Community ecology: structure and dynamics, influence factors

Ecosystem ecology: Ecosystem energetic, decomposition, biogeochemical cycle

Global change ecology: climate change and ecosystem researches

Others: biogeography, human ecology

Thank you!