Plant Ecology – Chapter 18 Biomes

Plant Ecology - Chapter 18 Biomes

Terrestrial biomes Defined by the physiognomy of the predominant vegetation

Boundaries? No sharp boundaries between biomes Intergrades

Importance of climate Prevailing climate is most important factor in determining what kind of biome will develop Precipitation, temperature are most important

Desert biomes 10 inches ( 25.4 cm) of rain per year Cool Temperate Tropical

Grassland biomes 10-30 inches (25.4-76.2 cm) of rain per year Tundra Temperate grassland Tropical savanna

Forest biomes 30 inches ( 76.2 cm) of rain per year Taiga or coniferous forest Temperate deciduous forest Tropical rain forest

Climatograph

Climatograph Temperature, precipitation not sole determiners Overlap among different biomes on plot suggests that other factors also are important Seasonality of precipitation Temperature fluctuations around mean Soil composition (based on geology)

Deserts Lands where evaporation exceeds rainfall High evaporation rate 7-50X precipitation

Deserts Occur in 2 distinct belts between 15-35 N & S latitude Result primarily from worldwide circulation of air masses (dry over deserts) 25% of world’s land mass

True deserts 10 inches of rain per year Semi-deserts may have 2-3X that, but have high evaporation rates Low humidity results in very hot days, but cool or cold nights Life is keyed to rainfall events Infrequent, but usually heavy when they occur

Desert life Plants are either drought evaders or drought resistors

Evaders Plants survive dry periods as seeds, but germinate, grow, and reproduce after rainfall

Resistors Plants develop deep roots to become independent of rainfall events (woody shrubs) or are succulents to store water in stems (cactus)

Grasslands Tropical savannas - grasslands with scattered individuals trees Central S. Amer., Central & S. Africa

Savannas 3 distinct seasons Cool-dry, hot-dry, warm-wet Frequent fires suppress trees, maintain grasses and forbs Herbaceous, low-growing annuals & perennials (dicots) Regrow from roots or seeds every year

Temperate grasslands Similar to tropical savanna, but occur in cooler regions N. Amer. prairie (French for plains) Russian steppe Hungarian pusztas S. Amer. pampas African veldt

Temperate grasslands At one time covered 42% of world land surface Much under cultivation today Excellent soils Rich topsoil layer

Temperate grassland climate High rates of evaporation Periodic severe drought Rainfall 25-75 cm/year Too light to support forest, but too heavy to encourage desert

Temperate grassland grasses Sod-forming Kentucky bluegrass Bunch grasses Big, little bluestem

Temperate grasslands Most require periodic fires for maintenance, renewal, elimination of incoming/invading woody growth

Tundra Northernmost limits for plant growth, and at high altitudes Plants generally low-growing Mat or shrubby

Arctic tundra Encircles north pole Brief warm summers with nearly 24 hrs of sun/day Presence of permafrost Water-logged soils - low evaporation Shrubs, sedges grasses, mosses, lichens

Alpine tundra At high elevations at all latitudes Variable daylength, many of the same restrictions, plant species

Tropical forests Equatorial, mean temp. 25 C, 12 hrs sunlight per day Rainfall highly variabledetermines type of tropical forest present

Types of tropical forests Thorn forests - furthest from equator, prolonged dry season

Types of tropical forests Tropical deciduous forest More rainfall nearer equator, distinct wet, dry seasons Lose leaves during dry seasons

Types of tropical forests Tropical rain forest 250 cm of rain per year Perpetual midsummer conditions Uninterrupted plant growth

Tropical rain forests Contain as many species of plants and animals as all other types of ecosystems combined 4 mi2 area - 750 species of trees, 1500 species of flowering plants

Tropical rain forests Typically stratified into 5 layers Each layer has characteristic plants, animals May reach height of 80 m

Tropical rain forest soil Very poor - little or no topsoil Easily weathered Subsoil with iron-based clay laterite Major problems with slash-andburn agriculture

Tropical rain forests today Deforestation

Deforestation Loss of forests at present rate will mean disappearance within next 15-25 years Major problems will result from climate change, loss of species of medicinal, economic importance

Temperate deciduous forest Eastern N. Amer, N. Europe and east Moderate temps., moderate moisture levels 5-6-month growing season

Temperate deciduous forest Dominated by broad-leaved deciduous trees Relatively nutrient-rich soil provides for good growth Typically have 4 layers present Ground, shrub, sapling, canopy Rich diversity of plant, animal life

Taiga Boreal forest, coniferous forest Harsh winters with lots of snow

Taiga Dominated by conifers - spruce, pine, fir, hemlock Best suited for short growing season because they are not deciduous Can carry out photosynthesis whenever temps. rise above freezing Needle shape, waxy cuticle conserve moisture

Taiga soils Thin, acidic, develop slowly Pine needles break down slowly in cool climate

Taiga animals Primarily seed, insect eaters, or those that feed on plants in or near water Squirrels, birds, elk, moose, deer, beaver, porcupine, grizzlies, wolves