CHAPTER 2.1 Terrestrial Ecosystem.pptx

Terrestrial Ecosystems – General Concepts

• Ecosystems differ widely in size, structure, composition, yet all share:

  • Basic structural components (producers, consumers, decomposers).

  • Fundamental functions (energy flow, nutrient cycling, regulation of climate & water, etc.).

• Classification by origin

  • Natural ecosystems – self-sustaining, nature-controlled.

  • Terrestrial: forests, grasslands, deserts, tundra, mountain systems, etc.

  • Aquatic: freshwater & marine.

  • Artificial ecosystems – human-made & maintained (e.g.0aquarium, cropland).

Forest Ecosystem – Definition & Scope

• A forest = more than a stand of trees; it is an integrated biological & physical system composed of:

  • Trees plus the substrate supplying nutrition & moisture.

  • Associated plants (mutual shelter, competition, facilitation).

  • Animals that feed on or shelter in vegetation.

  • Micro-organisms (beneficial or antagonistic).

  • Atmosphere & micro-climate (wind, fire, humidity, light).

• Formal definitions:

  • Ford-Robertson (1983): “forest stand” = sub-community of trees with sufficient uniformity in composition, age, spatial arrangement.

  • FRA 2015: land > $0.5\,\text{ha}$, trees > $5\,\text{m}$ tall, canopy cover > $10\%$ (excludes agricultural/urban land).

• Broad ecosystem functions:

  • Watershed protection.

  • Atmospheric regulation (tropical forests supply a large share of global $\mathrm{O_2}$).

  • Temperature & weather moderation.

  • Soil & wind erosion control.

  • Maintenance of global fresh-water supplies.

Major Forest Types

• Tropical evergreen (rain) forest

• Temperate deciduous (monsoon) forest

• Taiga (boreal coniferous) forest

• Mangrove forest
  (Each discussed in detail below.)

Tropical Evergreen (Rain) Forest

Key Characteristics

• Year-round leaf retention (no defined leaf-shedding season).

• Annual rainfall > $200\,\text{cm}$; dense, multilayered vegetation.

• Common tree genera: ebony, mahogany, rosewood, rubber, etc.

Structural Concepts

• Synusia (plural synusiae) – group of species with similar life form / habitat demand acting as a functional class within the community.

  • Well defined in temperate forests; more numerous & less obvious spatially in tropical forests.

• Rain-forest stands form an irregular mosaic of young, mature, senescent patches—reflecting gap-phase dynamics.

Density & Dispersion

• Tree density highly variable; diameter-class distributions likewise.

• Seed dispersal mode influences pattern: heavy-seeded species often clump.

Stratification / Layers

• Emergent layer – tops exceed $45!{-}70\,\text{m}$; windy, hot, hostile; few species (harpy eagle, macaw, bats, occasional monkeys).

• Canopy layer – $30!{-}45\,\text{m}$; ~$99\%$ of sunlight captured; highest biodiversity (lianas, epiphytes, red-eyed tree frog, sloth, toucan, iguana, etc.).

• Understory – < $4\,\text{m}$ vegetation; enlarged leaves, constant shade & high humidity; supports insects, frogs, leopards.

• Forest floor – 2 % sunlight; rapid decay (leaf decomposes in $\approx6$ weeks vs $\approx52$ weeks in temperate zones); site for giant anteaters.

Regeneration Guilds

• Light-demanding (pioneers) – need full light entire life (e.g. Cecropia).

• Shade-intolerant – establish in shade but mature only in canopy gaps.

• Semi-shade tolerant – germinate under varying light, later require higher irradiance.

Temperate Deciduous (Monsoon) Forest

Attributes

• Trees shed leaves $6{-}8$ months in dry season; hence lower canopy density.

• Rainfall $70{-}200\,\text{cm/yr}$.

• Species: teak, sal, sandalwood.

Global Distribution / Biome Notes

• Eastern USA & Canada, most of Europe, parts of China/Japan.

• Soils nutrient-poor, acidic, rapidly decomposed & heavily leached.

• Annual mean temperature ~$20{-}25\,^{\circ}\text{C}$ with low seasonal range.

Seasonal Dynamics

• Four distinct seasons.

  • Winters cold, summers warm.

  • Broad leaves lose water quickly → abscission during frozen-soil months ➔ winter dormancy, spring renewal.

Taiga (Boreal Forest)

Overview

• Largest terrestrial biome; lies between tundra (N) & temperate forest (S).

• Sub-arctic position just south of Arctic Circle.

• Short growing season with long daylight; long, cold, snowy winters.

Climate & Hydrology

• Winters up to $6$ months below ${0}^{\circ}\text{C}$.

• Summer frost-free days: $50{-}100$.

• Mean annual precipitation: $15{-}20\,\text{in}$ ($\approx38{-}50\,\text{cm}$); low evaporation ⇒ humid.

Biota

• Early successional broadleaf shrubs/trees; conifers dominate mature stages.

• >$200$ bird species breed; mammals include lynx, black bear, moose, coyote, hares, timber wolf.

Mangrove Forest

Definition & Taxonomy

• Community of $\approx110$ plants tolerant of tidal, saline, anoxic coastal mud; “true mangroves” = $54$ species in $20$ genera (families e.g.0Rhizophoraceae, Avicenniaceae, Palmae).

Global Distribution

• Strictly tropical/sub-tropical; intolerant of freeze events.

• Require sheltered, low-wave-energy coasts for seedling establishment & sediment accumulation.

• Regional area statistics:

  • South & SE Asia $41.4\%$ (≈$75{,}170\,\text{km}^2$).

  • The Americas $27.1\%$; West Africa $15.4\%$; Australasia $10.4\%$; East Africa/Middle East $5.7\%$.

• Country leaders (area in $10^3$ ha): Indonesia $4250$ (≈$30\%$ global), Brazil $1376$, Australia $1150$, etc.

Habitat Conditions

• Tidal inundation, salinity gradient increasing seaward.

• Sandy-clay, nutrient-poor soils; $\mathrm{N}$ & $\mathrm{P}$ limiting → growth constrained unless enriched by freshwater siltation.

• Overall harsh environment.

Adaptations

• Specialized roots: prop roots, buttresses, & pneumatophores for stability & gas exchange in anoxic mud.

• Salt management: salt excretion through leaf & root pores; some store/exclude.

• Vivipary: propagules germinate on parent tree, then float until rooting substrate encountered.

Ecological & Human Importance

• Detrital food-web base ➔ supports plankton → higher trophic levels.

• Nursery & breeding habitat for fish, crustaceans, mollusks, birds, reptiles (incl. endangered West Indian manatee, brown pelican, hawksbill turtle, eastern indigo snake).

• Shoreline stabilization, storm & hurricane buffering, sediment trapping, water-clarity maintenance.

• Carbon sequestration (“blue carbon”) in flooded soils.

• High economic value to fisheries & ecotourism.

Desert Ecosystem

General Traits

• Very low rainfall, sparse clouds; extremes of temperature.

• Global belt near $30^{\circ}$ latitude plus rain-shadow deserts.

• Example: Mojave Desert in California.

Desert Types

1. Hot deserts

   • Hot, dry air; minimal annual precipitation; rough, harsh soils.

   • Regions: Central America, North Africa (Sahara), South Asia, Australia, SW USA.

2. Cold deserts

   • Moist winters with snowfall; short, mild summers; snow dunes possible.

   • Locations: Greenland, Antarctica, Nearctic high latitudes.

Plant Adaptations

• Grow low to ground; thick succulent stems, spines instead of leaves; shallow wide roots; thick waxy cuticle conserve water.

• Common taxa: cacti, saguaro, creosote bush.

Animal Adaptations

• Water from food or succulents; nocturnal or crepuscular activity; burrowing; reflective/hard body surfaces; estivation or torpor.

• Fauna: camel, lizard, rattlesnake, kangaroo rat, beetles, etc.

Grassland Ecosystem

Definition & Distribution

• Regions with sufficient mean precipitation for grasses but too erratic (plus fire) for tree dominance.

• Present on every continent except Antarctica.

Categories

1. Tropical grasslands (Savannas)

2. Temperate grasslands (Prairies, Pampas, Veldt, Steppes)

3. Polar grasslands (Tundra – often grouped separately but shares open herbaceous physiognomy).

Tropical Savanna

• Warm year-round; two prolonged dry seasons and rainy remainder.

• Locations: central & southern Africa (largest), South America, Australia, SE Asia.

• Fauna: wildebeest, gazelle, giraffe, cheetah, lion, hyena, raptors.

• Flora: Bermuda grass, elephant grass, eucalyptus, whistling thorn.

Temperate Prairie

• Interiors of North/South America, Europe, Asia.

• Cold winters, hot dry summers; uneven $\text{ppt}$ distribution.

• Tall-grass vs short-grass variants.

• Iconic species: prairie dog, bison (historically), coyote, bald eagle; plants – big bluestem, buffalo grass.

• Example prairie food web:

  • Producers – grasses.

  • Primary consumers – prairie dog, grasshopper, jackrabbit, pronghorn.

  • Secondary consumers – owl, rattlesnake, coyote.

  • Scavengers – coyotes, beetles.

  • Decomposers – fungi, bacteria, insects.

Abiotic Factors & Soil

• Sunlight, water, air, rocks; deep fertile mollisols formed from annual grass die-back.

• Plowing damages root mat → soil erosion risk.

Polar Grassland (Tundra) – see dedicated section below.

Tundra (Polar Grassland)

General Facts

• Covers $\approx20\%$ of Earth; coldest biome (“ice desert”, “frozen prairie”).

• Word origin: Finnish tunturia (= treeless plain).

Key Characteristics

• Extremely cold climate, low biotic diversity, simple structure, poor drainage, short growing season, large population oscillations.

Types

1. Arctic Tundra – encircles North Pole south to taiga.

   • Winter mean $-34^{\circ}\text{C}$; summer $3{-}12^{\circ}\text{C}$.

   • Annual $\text{ppt}$ $15{-}25\,\text{cm}$.

   • Permafrost – permanently frozen sub-soil.

2. Alpine Tundra – high-altitude mountains worldwide above treeline.

   • Growing season $\approx180$ days; shrubs & small leafy plants dominate.

Soil & Hydrology

• Thin thaw layer (active layer) in summer; below lies permafrost.

• Nutrient-poor; relies on animal droppings; poor drainage ⇒ wetlands.

Flora

• ~$1{,}700$ species: shrubs, sedges, mosses, lichens, grasses, cushion plants, saxifrages, water lilies.

• Plant adaptations: low stature, shallow roots, antifreeze chemistry, rapid life cycles.

Fauna

• Mammals: caribou (reindeer), musk ox, polar bear, arctic hare, arctic fox, ground squirrel.

• Adaptations: heavy insulation, migration, hibernation, burrowing.

Climate Summary

• Two main seasons: long winter, short cool summer; spring & fall are brief transitions.

Mountain Ecosystem

Physical Definition & Zonation

• Mountain: landform elevated > $900\,\text{m}$ above sea level.

• Climate becomes colder with altitude; vertical stratification results:

  • Lower slopes – montane forests (tropical or temperate), savanna, scrub, desert, tundra depending on latitude.

  • Middle – dense temperate/tropical forests.

  • High alpine – treeless alpine meadows; harsh conditions.

Global Coverage & Ranges

• Mountains cover $24\%$ of land.

• Major ranges: Himalaya, Andes, Rockies, Alps, Urals, Appalachians, Zagros, Great Dividing Range, Atlas, Ellsworth, etc.

• Highest continental peaks:

  • Asia – Mount Everest $8850\,\text{m}$.

  • South America – Aconcagua $6962\,\text{m}$.

  • North America – Denali (McKinley) $6194\,\text{m}$.

  • Africa – Kilimanjaro $5892\,\text{m}$.

  • Europe – Elbrus $5642\,\text{m}$.

  • Antarctica – Vinson Massif $4892\,\text{m}$.

  • Australia – Kosciuszko $2228\,\text{m}$ (or Puncak Jaya $4884\,\text{m}$ in wider Oceania context).

Ecological Importance

• Habitats for diverse & often endemic biota; biodiversity hotspots.

• Provide fresh water to $\frac{1}{2}$ the human population via snow-melt & orographic rainfall.

• Sources of clean air, renewable energy (hydro, wind), recreation & tourism.

• Traditional zoogeographic barriers/centers of speciation.

Biodiversity Examples

• Temperate mountains: conifer → alpine meadows; fauna deer, bear, wolf, cougar.

• Tropical mountains: evergreen forests, grasslands, heather belts; fauna from gorillas to jaguars.

• Desert mountains: xeric plants (cacti, ferns); fauna big-horn sheep, bobcat, coyote.

Management Challenge

• Need sustainable practices to prevent degradation that would propagate poverty & hunger in dependent populations.

Ethical, Practical & Conservation Implications (Cross-Cutting)

• Forest loss threatens climate regulation, oxygen production, biodiversity & indigenous cultures.

• Mangrove clearance (for shrimp farms, development) heightens coastal vulnerability & reduces fishery yield.

• Desertification from mis-managed grasslands intensifies drought & socio-economic hardship.

• Mountain deforestation or mining triggers erosion, landslides, downstream flooding.

• Global climate change may shift biome boundaries (e.g.0taiga advancing north, tundra shrinking), altering ecosystem services & livelihoods.

These bullet-point notes distill every major and minor concept, definitions, examples, statistics, structural details, and implications discussed across the transcript’s coverage of terrestrial ecosystems.