Transcript cold desert
Biomes Major ecosystems found in large geographic regions characterized by a distinct vegetative community --primarily a result of abiotic processes Physiognomy The overall appearance of a biome or community based on the relative density, height, and shape of its dominant vegetation Six major biomes: 1. tropics 2. grasslands/savannah 3. temperate forests 4. coniferous forests or taiga 5. tundra 6. deserts Fig. 24.3 Minor biomes: 1. chaparral 2. temperate rain forest 3. polar regions Fig. 24.4 Tropical Biomes: • Most occur within 10° latitude • Defined by rainfall > 240 cm per year • Temperature and moisture not limiting factors, nutrients and light are Amazon (Neotropics) Congo SE Asia Old World New World Misconceptions about tropics: • Soils are rich • Climate is stable • Jungles are dense Physiognomy of Tropics • high diversity of trees • 400-700 trees per hectare • 100-200 species represented • low population densities for each • dense canopy, stratified up to four levels High light attenuation Humidity ~70% Temperature gradient Humidity 90-95% Fig. 25.6 Leaf litter accumulates rapidly, but decays rapidly Plants in competition for nutrients released in decay Physiognomy of Tropics • shallow, spreading roots and leaves with drip tips Physiognomy of Tropics • shallow, spreading roots and leaves with drip tips • Mycorrhiza fungi and hyphae • buttress and prop roots Physiognomy of Tropics • shallow, spreading roots • Mycorrhiza fungi and hyphae • buttress and prop roots • epiphytes, lianas Gaps and patch dynamics Nurse tree with successional stages of growth to obtain nutrients released from decaying wood Semi-aquatic herbivores Nocturnal frugivores Diurnal herbivores Nocturnal herbivores Ant eaters Parallel Evolution Hammocks in south Florida Temperate rain forest: Olympic National Park, WA Longleaf Pine community of the Southeast http://www.worldwildlife.org/ Deserts are defined by rainfall: • true desert has < 12 cm/yr • extreme desert < 7 cm/yr • semi-desert has up to 40 cm/yr • evaporation exceeds rainfall Deserts also characterized by: • hot days, cool nights from high albedo • sparse plant life • C4 and CAM photosynthesis • xerophytes • more living plant biomass below ground than above, sometimes 1:10 difference Four major North American Deserts 1. 2. 3. 4. Sonoran Mohave Chihuahuan Great Basin Sonoran Desert Lowest, hottest desert up to 120° F in summer Bi-annual rainfall ~18 cm/yr Most diverse desert in NA Saguaro Cactus limited by temperature Sonoran Desert, AZ cholla cactus ocotilla palo verde trees Most precipitation in winter 5-12 cm/yr Higher elevation than Sonoran Plants adapted to cooler temperatures Mohave Desert Joshua Trees Cholla cactus and yucca Most precipitation in summer 15-20 cm/yr Dominated by low shrubs and cactus Chihuahuan desert and creosote Prickly Pear Cactus Largest U.S. desert, considered a cold desert Elevations range from 5000-6000 feet Caused by a series of rainshadow effects Precipitation 15-25 cm/yr Dominated by sagebrush Great Basin Desert Sagebrush dominates All deserts are characterized by slow growth by plants, but also slow decay of litter Very fragile ecosystems because of this Disturbances, even a single car track, may last decades to centuries Archaeological roads, clearings still visible after 1000+ years Kangaroo Rat: Endemic to North America Kangaroo Rat Adaptations No sweat glands and never drink water Kidneys concentrate urine 5X more than humans Nocturnal behavior, with large auditory bulla Stay in burrows during day, plug entrance and cache seeds Use torpor for brief periods, have bare feet to radiate heat, or cover with tail to retain heat Rostrum long, with complex nasal bones, convoluted surfaces cooled by evaporation to capture water in air leaving body Ants in Deserts • high diversity, granivores • Chihuahuan desert: 23 spp. in 30 m2 • 50 spp. in 3 km transect • Australia: 150 spp. in < 1 ha • Sonoran desert exclosure experiment show keystone effect desert grasses dominate