Terrestrial Biomes

Characterization, Stressors, and Changes

Biomes of the World

Temperature & Precipitation

Raunkiaer's life forms. Plants with specific distribution of dormant buds are better suited to different biomes. (a) phanerophytes(b) nanophanerophytes - chamaephytes, (c) hemicryptophytes(d) Geophytes(e) Therophytes(f) epiphytes

Life form Ph (a) Ch (b) H (c) G/HH (d) Th (e)

World standard 46 9 26 6 13

Tropical 61 6 12 5 16

Desert 10 17 20 6 46

Mediterranean 12 6 50 18 19

Warm Temperate 8 6 50 18 19

Arctic 1 22 66 15 2

Alpine - 25 68 4 4

Raunkiaer's life form spectrum in the worldTropical: Ph Warm temperate: H Arid (desert and Mediterranean): ThAlpine and arctic: H/G (woody) and Perennials + long-day plant

Climate vs. ContinentLife-form Spectra: Traits that vary with

climate such as perennating organ or tissues that give rise to new growth the following season

Life forms are more alike in similar climates on different continents than they are in different climates on the same continent

Tropical Forests• Centered on the Equator• Little seasonal variation

• High yearly rainfall• Constant Warm Temperature

• Layered vegetative cover• > half of all terrestrial species• Highest Biodiversity & Primary Productivity

2-3 kg/m2-yr• Leached Soils dominated by fungi• Multiple sub-biomes dependent on seasonal patterns of precipitation, elevation, soils

The global distribution of land and ocean net primary production (NPP) estimated from spectral data gathered by NASA's MODIS satellite

Savannah• Transitional biome between

tropical rainforests and deserts– Seasonal precipitation– Consistently warm

temperatures

• Mixed grasses and small trees– Drought deciduous– Fire balances grasses & trees

• Dominant Herbivores– Consume 60% of biomass/yr

• Net Primary Productivity– 0.4 – 0.6 kg/m2-yr– Dependent on soil depth

Desert• Most occur between 15-30° N & S

– Regional high pressure– Less than 250 mm/yr precipitation

• Rain Shadows a result of Topography• 26-35% of Earth’s land surface• Highly variable in biodiversity,

productivity, and types of organisms– Perennial shrubs

• extensive roots• Small gray, white or light green leaves

– Annual herbs• Long-term seed storage in soil• Rapid growth/life cycle

– NPP• 0-0.12 kg/m2-yr• Dependent on precipitation, drainage systems,

soils

Distribution of arid landDry air descends at 30° latitude, drawing moisture from the soil and contributing to the creation of arid climates.

Chaparral/ Mediterranean

• 30-40° N & S– Hot dry summers– Cool moist winters

• Convergent Evolution– Evergreens and Sclerophytes– Therophytes

• Net Primary Productivity– 0.3-0.6 kg/m2-yr– Dependent on water

availability, soil, age of system

• Fires aid in nutrient cycling– flowering– seed germination

• California

Temperate Grassland• Interior of continents

– Large seasonal temperature and precipitation variations

– Grade into temperate forests and deserts with shifting borders• Precipitation (i.e. drought)• Disturbance (i.e. fire)

• Grasses spread underground– rhizomes, leaves grow from the

bottom up, decay-resistant– Favored by fire, drought, grazing– Tall-grass = high precipitation– Short-grass = low precipitation

• Net Primary Productivity– 0.4-1 kg/m2-yr

• Support large herds of herbivores (bison, horses, etc.)

Temperate Deciduous Forest• Mid-Latitudes – cool winters, warm

summers, high year-round precipitation

• Net Primary Productivity– 0.6-1.5 kg/m2-yr– Leaf litter = nutrient recycling– Trees – 20-30 m tall– Shrubs – up to 5 m tall– Herbaceous plants as ground cover

• Niche Partitioning is prevalent– Increased complexity and biodiversity

with forest height

1. Daily/Seasonal NPP variationsa) Solar radiationb) Precipitationc) Length of growing

season2. Annual NPP variations

due to longer-term trends in climate

3. Decadal patterns of NPP track changes in ecological succession

(Gough et al. 2007, 2008).

Patterns of terrestrial NPP at different timescales in a temperate forest

Coniferous Forest• High latitude

– Long cold winters– Short cool summers

• Low Biodiversity– Overstory of Evergreen Trees:

needle-leaved and drought tolerant (1-4 sp.)

– Ground cover: herbs and mosses

– Shallow roots rely on mycorrhizae for nutrients

• Low Net Primary Productivity– 0.2-0.6 kg/m2-yr– Dependent on precipitation,

frost-free days, soil drainage– Flooded areas – acidic, anoxic

peat

• Slow decomposition, leached soils, permafrost

Tundra: Arctic & Alpine

• Poleward of the Coniferous forests– Very short growing season– Most of the year is below 0°C– High Winds

• Very low Net Primary Productivity– 0.1-0.2 kg/m2-yr– Dependent on snowfall depth and

drainage

• Low Biodiversity– Mosses, lichens, and low-growing

shrubs with rounded canopies and closely spaced leaves and branches • Reduces wind speeds• Increases solar radiation absorption

– 3% of world’s flora Hemicryptophytes– Low nutrient soils

• Lichen fix N

– Animals hibernate or migrate

Consequences of Change on the Biomes and Us

Putting Ecology Studies Together to Understand the Impacts of Global Changes

Sustaining Ecosystems

Examining the relative importance of various types of stabilizing species interactions and the effect of these interactions on biodiversity and ecosystem functioning and stability

Impacts of Potential Stressors on Species Interactions