Chapter 20 Part 2 – Terrestrial Ecosystems & Biomes

Terrestrial ecosystem = all land-based portions of Earth; complements freshwater & marine ecosystems discussed in Part 1.
Entire continents (except Antarctica on the instructor’s slide) are included; Arctic shown because it is floating ice over ocean, whereas Antarctica is a true landmass.
Antarctica was once connected to Australia & South America (plate-tectonic aside).

Biome: large terrestrial habitat type defined chiefly by
- dominant vegetation (plants are rooted, slow-moving climate indicators)
- long-term climate patterns (≈ 10–20 yr datasets or more)
Vegetation ↔ climate are inseparable; you can infer one from the other.
Weather ≠ climate
- Weather = short-term, day-to-day conditions (e.g., “hot & sunny today”).
- Climate = long-term statistical pattern (e.g., “Mediterranean climates are generally dry”).
- Example: Early European colonists mis-classified California as wetter than it truly is because they arrived during an unusually rainy period; our frequent droughts merely reflect the region’s actual climate.

Tropical forests cluster around the Equator between the Tropic of Cancer & Tropic of Capricorn.
Deserts form belts near $\approx30^{\circ}$ N & $\approx30^{\circ}$ S because of descending, dry Hadley-cell air.
Boreal forests sit in upper mid-latitudes, tundra even closer to the poles.
Chaparral rings the Mediterranean Sea & occurs in Southern California.

Quick ID: any biome dominated by trees.
Presently ≈ $\frac13$ of Earth’s land area, yet stores ≈ 70 % of the planet’s total biomass.
- Footprint explanation: trees occupy small ground area but build massive vertical biomass.
- Historically ≈ 75 % of original global forest cover has been removed or heavily altered by humans.
Three sub-types:

Location: Equatorial belt (between the tropics).
Climate: high rainfall, constant warmth, nearly 12 h sunlight daily (sunrise ≈ 05:30, sunset ≈ 17:30 year-round).
Frequent cloud/fog → cloud forests (perpetual dripping moisture).
Consequence: extremely high NPP (net primary productivity) → highest terrestrial biodiversity.
- Ecuador (~Nevada-to-California size) hosts ≈ 1,800–2,000 bird species vs. ≈ 700 in the entire USA (≈ 3× richer).
Instructor photo: standing beside a large tree-fern (ancient lineage, “looks 100 M yr old”).

Latitude: mid-latitudes.
Dominant vegetation: deciduous broadleaf trees; some evergreens mixed.
Moderate growing season; pronounced seasons (spring–summer–fall–winter).
Example regions: U.S. East Coast, much of Europe, China, Japan, parts of California foothills.

Latitude: >50^{\circ} N or <−50^{\circ} S, and also at high mountain elevations.
Dominant vegetation: conifers/evergreens (needle leaves = adaptation for year-round photosynthesis & water conservation).
Short, cool summers; very cold, long winters; low precipitation (snow or moisture frozen part of year).

Key trait: dominated by non-woody grasses; few scattered trees/shrubs.
Fire plays a critical ecological role – burns suppress woody plants, grasses resprout quickly, maintaining the biome.

Climate: tropical temperatures + extreme wet/dry seasonal swings (monsoon flood vs. drought).
Example: African savannahs; seasonal flooding of the Okavango Delta.
Vegetation: grasses with occasional drought-resistant trees.

Latitude: mid-latitudes; subject to annual (seasonal) fluctuations in temperature & precipitation.
Example: North American Great Plains, European steppes.
Trees typically limited to riparian corridors where moisture is steadier.

Defined by low precipitation: <50\text{ cm yr}^{-1} (≈ 1 ft).
Global pattern: belts near $30^{\circ}$ N/S where descending air loses moisture aloft and returns to ground hot & dry.
Temperature: often very hot days, very cold nights (large diurnal range).
Adaptations: water-harvesting structures (cactus spines & “hairy” surfaces condense dew and funnel it to roots).
Biodiversity: lower than forests/grasslands but far from zero; many species are nocturnal to exploit cool nights.
Cold deserts: Antarctica & Greenland qualify—minimal liquid precipitation, mostly snow; proof a desert need not be sandy.

Location: poleward of boreal forests (high latitudes) or high alpine zones.
Climate: very short growing season; extreme photoperiod shifts (long summer days, long winter nights).
Soil: permafrost—permanently frozen ground a few cm below surface; restricts root depth and drainage.
Vegetation: low-stature plants (mosses, grasses, dwarf shrubs); “low profile” strategy minimizes energy/water demands.
Visual: landscape of tiny grasses & scattered dwarf bushes; ponds form where surface thaw sits atop ice-sealed subsoil.

Mountains: elevation-driven climatic shifts; can replicate boreal & tundra conditions over short vertical distances.
Polar ice: Greenland & Antarctica—thick ice sheets, minimal terrestrial vegetation; overlap with cold-desert concept.

Forests’ 70 % biomass = giant carbon sink; deforestation releases that carbon, accelerates climate change.
Desertification & biome shifts are linked to atmospheric circulation changes & human land-use.
Quote (Jonas Salk, polio vaccine pioneer): “Eventually we’ll realize that if we destroy our ecosystem, we destroy ourselves.”
- Serves as warning about the ongoing “sixth extinction event” driven by habitat loss & climate change.