biome

Desert Biome: Hot Deserts

  • Key idea: Deserts are the driest biomes on Earth; water loss usually exceeds precipitation; vegetation is sparse to absent; biodiversity is driven by extreme conditions and strong behavioral adaptations.
  • Color coding on climate/biome graphs: deserts are represented with yellow/light yellow at the bottom of the precipitation axis (low precipitation).
  • Global location: deserts are typically just north or south of the Equator, not exactly on it; major bands occur around 30^\ ext{\circ}N and 30^\ ext{\circ}S.
  • Deserts expand with climate change (extreme heat, extreme dryness, desertification) and can push deserts further into savannahs or new arid zones.
  • Desert climate and heat transfer:
    • Very dry conditions; humidity is low, which reduces heat retention; water normally helps retain heat, so deserts can experience large diurnal temperature swings (hot days, cool nights).
    • Some deserts are warm/hot year-round; others are cold deserts with significant seasonal temperature variation.
  • Land area and water balance:
    • Deserts cover about 20\% of Earth’s land surface: ext{Desert area} \approx 0.20 \times \text{Earth land area}.
    • Water loss exceeds precipitation in many desert regions.
  • Soils and productivity:
    • Soil tends to be extremely low in organic matter; soil fertility is poor.
    • Plant cover ranges from sparse to absent; limited primary production.
  • Examples of adaptations (plants and animals):
    • Thorny Devil (Australia): ant specialist lizard; has spines and thick body; remarkable water collection from skin (water is wicked toward the mouth when hits the skin).
    • Horny Toad (North America) and other ant-eating lizards; convergent evolution with desert lizards elsewhere.
    • Rabbit adaptations: large ears to dissipate heat; also behaviorally minimize heat stress and predation.
    • Cacti and succulents (e.g., Euphorbia in Africa; cacti in Americas) with thick stems, reduced or absent leaves, and spines to limit water loss and herbivory.
    • Lithops (living stones): a succulent that looks like a rock to camouflage and reduce water loss; little or no leaves.
    • Hognose snake (Western North America): burrowing adaptation with a hardened nose used to dig in dry substrates; burrowing is common among desert fauna.
  • Human interactions:
    • Humans tend to cluster around oases and river valleys within deserts; oases can be keystone habitats that support surrounding ecosystems.
    • Deserts can be labelled cartoons-like in popular culture, but oases are real ecological features with significant ecological importance.
  • Desert climate examples and variability:
    • One desert area (Chad) shows precipitation near P \approx 0 for much of the year, highlighting extreme aridity.
    • In Mongolia, deserts can show a seasonal pattern where temperatures peak and moisture increases seasonally, creating a narrow growing season when temperatures exceed freezing.
  • Desert flora: convergent adaptations across deserts (e.g., succulents with thick stems, spines to deter herbivores) that reduce water loss and protect against heat.
  • Desert fauna and behavior: many animals rely on behavioral strategies to avoid heat and conserve water; some species have specialized physiology to cope with aridity.
  • Oasis imagery and perception: oases function as moisture pockets that support diverse life and human activities within the desert matrix.
  • Quick terminology:
    • Absent or sparse vegetation leads to low soil organic matter and limited habitat complexity.
    • Burrowing adaptations (e.g., hardened snouts, claws) help organisms exploit dry soils.

Mediterranean Woodland and Shrubland (Chaparral)

  • Key idea: Mediterranean biomes occur on all continents except Antarctica; they feature cooler, wet falls/winters and hot, dry summers with fragile soils and relatively high plant-to-soil turnover.
  • Climate and soils:
    • Fall, spring, and winter are cooler and wetter; summers are hot and dry.
    • Soils are often fragile with only moderate fertility due to dry summers.
    • Vegetation is evergreen: trees and shrubs retain leaves year-round.
    • Fire is a common and important ecological driver due to hot, dry summers; ecosystems often exhibit fire-adapted traits.
  • Plant adaptations and economy of defense:
    • Evergreen shrubs and trees with leaves adapted to reduce water loss (thick cuticles, reduced leaf area).
    • Fire resistance and fast post-fire regeneration are common.
    • South Africa’s fynbos shrubs (fynbos) showcase specialized leaves to limit water loss and maintain drought tolerance.
    • Plants like grapes, olives, citrus, figs, rosemary, and lavender thrive in dry, sun-drenched Mediterranean zones; many of these have essential oils that deter herbivores and contribute to plant defense.
  • Humans and land use:
    • Long histories of human intrusion and agricultural clearance; Mediterranean climates have been heavily modified for crops.
    • Vineyards and crops are common in sun-davored, drier slopes (e.g., south-facing slopes with ample sun and moderate dryness).
  • Global distribution:
    • Chaparral-like systems (Mediterranean woodlands/shrublands) occur around the Mediterranean basin, Western Europe, North Africa, Western Asia, Southern Australia, parts of South Africa, and coastal Chile.
  • Plant and oil chemistry:
    • Essential oils (e.g., rosemary, lavender) are common in these drier, sun-drenched biomes and contribute to pest resistance.
  • Climate-vegetation relationships:
    • Temperature peaks align with precipitation troughs; hot summers coincide with drier soils, shaping plant communities and fire regimes.
  • Notable examples and crops:
    • Viticulture (grapes) in Mediterranean-like climates, leveraging dry summers and mild winters.
  • Global context:
    • Mediterranean woodlands and shrublands form a recognizable biome across multiple continents with similar climate and vegetation strategies.

Temperate Grasslands (Prairies) and Steppe

  • Visual cues on climate graphs:
    • Described color cues for temperate grasslands range around the left side of the graph; common responses include purple/purple-green bands.
  • Global distribution:
    • The Great Plains of the United States; parts of Southern Europe; the Asian Steppe; large grassland regions in the Southern Hemisphere (South America, Africa, Australia).
  • Notable fauna and historical range:
    • Pronghorn (Antilocapra americana): fastest land mammal in the Western Hemisphere; range extends from Mexico to Canada across the American prairies.
    • Western North American prairies historically overlapped with the range of the American cheetah; evolutionary pressure from predators and prey interactions contributed to extreme speed in prey like the pronghorn; cheetahs in North America went extinct around the late Pleistocene.
    • The pronghorn range also aligns broadly with the range of the Western US grasslands; pronghorn are sometimes cited as among the fastest animals outside of birds.
  • Paleoclimatology and megafauna:
    • About ten thousand years ago, climatic shifts contributed to the extinction of many large herbivores; the cheetah-like predator in North America vanished with other megafauna.
  • Climate and growing season:
    • Temperate grasslands lie roughly between 30^\ ext{\circ} and 55^\ ext{\circ} latitude; annual precipitation typically 300\text{ to }1000\ \text{mm yr}^{-1}.
    • Winters are usually dry; growing seasons are shorter in colder regions.
  • Soils and vegetation:
    • Extremely deep and fertile soils, dominated by herbaceous vegetation (grasses) with limited tree cover; prairie relics are regions that have not been tilled or heavily altered by agriculture.
    • Some grasses can reach great heights (e.g., up to 8\ ft in some prairie relics).
  • Human impact and agriculture:
    • Temperate grasslands have been largely converted to agriculture (croplands: corn, soybeans, etc.); this has reduced organic matter and biodiversity in soils.
    • Croplands overlap with grassland regions across Eurasia and the Americas; agriculture often expands into these biomes due to fertile soils.
  • Paleoecology and soil fertility:
    • Deep, fertile soils support extensive agriculture; soil microbes and organic matter are impacted by tilling and disturbance.
  • Notable historical ecosystems:
    • Large herds of herbivores (e.g., bison) once grazed temperate grasslands; their decline dramatically changed ecosystem dynamics.
  • Biodiversity and biomass patterns:
    • Biomass in temperate grasslands is dominated by grasses and their herbivores; predator biomass varies with time and region.

Temperate Forests: Subtypes and Key Traits

  • Overview:
    • Temperate forests occur in mid-latitudes and include deciduous forests, conifer-dominated forests, and temperate rainforests; they sit between the warmer subtropics and the boreal zones.
  • Temperate rainforests (a distinct subtype):
    • Location examples: West Coast of the US (Olympic National Park and the Olympic Peninsula); Chile (west coast of South America).
    • Characteristics: high rainfall, mist, and persistent clouds; nutrient-rich soils and lush undergrowth; often mountain-influenced with rain shadows shaping microclimates.
    • Hyperion: the legendary tall tree in the temperate rainforest was measured at 381\ \text{ft} tall (approx. 116\ \text{m}); considered among the tallest trees on Earth; its exact location is kept secret to prevent vandalism.
    • Smoky Mountains temperate rainforest: not always labeled as a separate rainforest on some maps, but it exhibits rainforest-like moisture and evergreen-adapted biology; contributes to regional biodiversity.
    • Important species and examples in US East: eastern North American temperate forests feature a mix of deciduous trees (broadleaf) and some conifers; diversity tends to be higher in the US than in many other regions because of historical biogeography and geography.
    • Largest trees on Earth: temperate rainforests host some of the tallest and oldest tree species; the tallest trees are among the giants of the planet in these habitats.
  • Temperate deciduous forests (broadleaf):
    • Geography: Eastern North America, Northern Europe, East Asia (China), and parts of temperate regions in these zones.
    • Structure: dominated by deciduous broadleaf trees that lose leaves in autumn; conifers may be present, especially on harsher, drier sites or in transitional zones.
    • Seasonal dynamics: warm summers and cold winters; leaves shed in autumn to conserve water during winter; seasonal cycles strongly influence food webs and nutrient cycling.
  • Biogeography and climate patterns:
    • The majority of temperate forests lie between 40^\ ext{\circ} and 50^\ ext{\circ} latitude.
    • Annual precipitation ranges from 650\text{ to }3000\ \text{mm yr}^{-1} (roughly 25\text{ to }118\ \text{inches yr}^{-1}).
    • Biomass production tends to be high because leaf drop in autumn recycles nutrients and supports detritivores and decomposers; leaf litter fuels a dynamic food web.
  • Important ecological processes:
    • Abscission (leaf drop): seasonal shedding of leaves; a key process controlling energy balance and nutrient cycling.
    • Mast (mast seeding): periodic, synchronized, large seed production events (e.g., acorns) that overwhelm seed predators and promote seedling establishment.
  • Biomass and trophic structure in temperate forests:
    • The most biomass in some Appalachian forests is in salamanders, especially during rainy, damp seasons; in other contexts, deer or bears can have high biomass, depending on region and time of year.
    • In some Appalachian forests, salamanders can outweigh deer in overall biomass within a given area due to microhabitat suitability and consumption patterns.
  • Typical forest structure and tree life-history traits:
    • Deciduous trees (broadleaf) dominate many temperate forests; conifers are more common on steeper slopes or in drier microhabitats.
    • Conifer-dominated zones (e.g., on higher elevations or drier soils) exhibit a seasonal drought pattern: high summer temperatures with reduced precipitation; such habitats favor evergreen conifers.
    • Mixed forests often occur along ecotones with interplay between coniferous and deciduous species.
  • Notable local features and examples:
    • Lynnville Gorge (regional example): pine trees tend to grow on ridges where conditions are hotter and drier; deciduous trees are more common in valleys with more shade and moisture.
    • Eastern white pine as a common canopy species; Fraser fir on high elevations (e.g., Grandfather Mountain region) as evergreen trees tolerant of cold, windy sites.
    • The potential for very tall trees in temperate rainforests and high-biomass forests; debates about the exact maximum tree heights and historical height estimates (e.g., a tree possibly exceeding 465 ft in Washington state, though verification is debated).
  • Global comparison:
    • Temperate forests in North America, Europe, and East Asia share similar climate regimes and broadleaf/conifer mixtures; East Asia contributes many tree species (e.g., weeping willows from China) that thrive in temperate climates outside their native ranges.
  • Summary of key ecosystem attributes:
    • Latitude range: roughly 40^\ ext{\circ}–50^\ ext{\circ}.
    • Precipitation: 650\text{ to }3000\ \text{mm yr}^{-1}.
    • Biomass production: high due to leaf litter and productive understory.
    • Dominant vegetation: deciduous broadleaf trees with possible conifers; mix in some regions.
    • Seasonal dynamics: strong leaf cycling, mast events, and rich detrital food webs.

Miscellaneous notes on biomes and themes mentioned

  • Mountain biomes and microclimates:
    • The lecture notes acknowledge that fine-scale climatic variation exists between biomes, and mountains can host multiple microclimates and biomes within a small area.
  • Historical context and ecological change:
    • Temperate grasslands and their soils have been heavily impacted by agriculture, leading to loss of original biodiversity and soil organic matter.
    • Large herbivores (e.g., bison) historically shaped temperate grassland ecosystems; their near-extinction led to cascading ecological changes (predator populations, vegetation structure, nutrient cycling).
  • Conservation highlights:
    • Black-footed ferrets and kit foxes (if referenced) have experienced severe population declines but some programs (captivity breeding and reintroduction) have helped recover small populations.
    • Elk and other large mammals have faced range contractions to a fraction of their historic extents; some regions maintain local populations with monitoring (e.g., NC Smoky Mountains shows ongoing management of elk with collars).
  • Key terms to remember:
    • Abscission: seasonal leaf drop in deciduous trees.
    • Mast: synchronous, large seed production events.
    • Biodiversity and biomass concepts: biomass distribution can be surprising (e.g., salamanders vs. deer in Appalachia) due to habitat complexity and life-history strategies.
    • Fire-adapted traits in chaparral and other Mediterranean systems.
    • Oasis concept in deserts: ecologically important moisture pockets that sustain life in an otherwise arid matrix.

Note: The lecture occasionally shifts between specific regional examples and general biome patterns. When studying, focus on the core diagnostic features of each biome (precipitation regime, temperature regime, soil/fertility, typical flora, typical fauna, key adaptations, and human impacts), and use the examples (thorny devil, lithops, Hyperion, bison, mast seeding, etc.) as illustrative cases that demonstrate those principles.