An understanding of the physical environment is key to understanding all ecological phenomena
Biomes
Large-scale biological communities sharing similar plant growth forms; often owing to convergent adaptations to similar physical environments; determined largely by temperature and rainfall (climate)
Primary productivity on Land
Primary productivity in Oceans
Almost half of all primary productivity on Earth
Ecoregions (867 distinct ones)
Olson et al 2001 Bioscience
Other factors such as soil types and elevation can also have strong influences
Major Determinants of Global Climate
1. Spherical shape of the earth: uneven heating
Major Determinants of Global Climate
2. Revolution of the Earth around the Sun on a tilted axis (seasons)
Seasons
Wind is caused by differential heating of the Earth’s surface
Major Determinants of Global Climate
3. Rotation of Earth around Earth’s axis. Creates Coriolis effects (conservartion of momentum)
Air circulation patterns (surface)
Ocean currents are driven by winds and redistribute heat, and modified by Coriolis effects
Rising warm airs --> Rain
Why does it rain on the windward side of mountains, and why is it dry on the leeward side?
Kauai 22° N
Rain shadow effect
Tropical rain forests
Dominant canopy plants: broad-leaved evergreen trees
Also epiphytes, lianas, palms, and generally sparse understory
More-or-less continuous growing season
Contain ~50% of Earth’s species & ~37% of terrestrial carbon in ~11% of terrestrial veg. cover
Tropical seasonal forests and savannas
Tropical dry forests
Thorn woodlands
Tropical savannas
Generally smaller-stature trees and more deciduousness than in rain forests
Resource availability, fire & large herbivores help determine the balance between grasses vs. woody species
Pronounced wet / dry seasons
Deserts
Populations of plants & animals are often sparse (owing to resource limitation)
Succulence (fleshy water-storage tissue in leaves, stems, etc.) is common among the plants
Sustained periods of high temp. & low water avail.
Temperate Grasslands
Dominant plants = grasses
Greater temp. variation than tropics
Relatively warm, moist summers & cold, dry winters
Some have sufficient rainfall to support woody veg., but fire & grazers maintain grasslands
Soils rich in organic matter (especially from proliferation of grass roots)
Temperate Shrubland and Woodlands
Winter rainy season (e.g., Mediterranean-type climates – water and temperature conditions for growth are somewhat asynchronous)
Fire is a common feature
Evergreen, sclerophyllous (tough, leathery) leaves are common
Temperate Deciduous Forests
Tree-dominated
Deciduous leaves owing to freezing temperatures
Sufficient rainfall & soil fertility to support tree growth (trees largely outcompete grasses)
Temperate Evergreen Forests
From warm coastal zones to cool maritime or continental climates
Generally on nutrient-poor soils
Northern Hemisphere – needle-leaved conifers
Southern Hemisphere – needle-leaved & broad-leaved trees
Boreal Forests / Taiga
Generally above 50º N latitude
Coniferous tree species in continental climate zones and deciduous birch forests in some maritime zones
Extreme weather
Permafrost common
Largest terrestrial biome, with ~33% of forested land
Tundra
Beyond latitudinal tree line, e.g., above ~65º N latitude
Dominated by sedges, grasses, forbs, lichens, mosses & prostrate shrubs
Primarily in the Arctic
Extreme weather and adaptations for prolonged dormancy
Permafrost very common
