1. Biomes Physiognomy 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

2. Six major biomes:
1. tropics: 0-10º
2. grasslands/savannah: 10-40º
3. deserts: 30º
4. temperate forests: 30-45º
5. coniferous forests or taiga: 60º
6. tundra: 60-90º

3. Fig (EFB)

4. Tropical Biomes: Most occur within 10° latitude of the of the equator
Defined by rainfall > 240 cm per year
Temperature and moisture not limiting
factors, nutrients and light are

5. Amazon
(Neotropics)
SE Asia
Congo
Old World
New World

6. Physiognomy of Tropics
high diversity of trees
trees per hectare (2.47 acres)
species represented
low population densities for each
dense canopy, stratified up to
four levels

7. Fig. 29.27 (EFB) High light attenuation Humidity ~70% Temperature
warmer
cooler
90-95%
Fig (EFB)

8. leaf with drip tip

9. Leaf litter accumulates rapidly, but also decays rapidly
Plants in competition for nutrients released by decay

10. Gaps and patch dynamics

11. Nurse tree with successional stages of growth to obtain
nutrients released from decaying wood

12. Temperate rain forest: Olympic National Park, WA

13. Nurse Tree

15. 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

16. 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

18. Four major North American Deserts
Sonoran

19. 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
Tallest cactus in U.S., grows very slow (1-1.5 inches in 10 yrs), live up to 200 yrs, start growing arms after yrs of growth.

20. Sonoran Desert, AZ cholla cactus ocotilla palo verde trees
Ocotilla with grow small leaves after every rain, then shed them

21. Four major North American Deserts
Mohave
Sonoran

22. Mohave Desert Most precipitation in winter 5-12 cm/yr
Higher elevation than Sonoran
Plants adapted to cooler temperatures
Mohave Desert

23. Joshua Trees

24. Four major North American Deserts
Mohave
Sonoran
Chihuahuan

25. Chihuahuan desert and creosote
Most precipitation in summer
15-20 cm/yr
Dominated by low shrubs and cactus
Creosote widespread, all the way to Chile, has no thorns but secondary compounds that give it a bad taste. Varnish on leaves to help seal in water. After rains, this plant provides a pleasant desert smell.
Chihuahuan desert and creosote

26. Prickly Pear Cactus

27. Great Basin Mohave Sonoran Chihuahuan
Four major North American Deserts
Great Basin
Mohave
Sonoran
Chihuahuan

28. Great Basin Desert Largest U.S. desert, considered a cold desert
Elevations range from feet
Caused by a series of rainshadow effects
Precipitation cm/yr
Dominated by sagebrush
Great Basin Desert

29. Sagebrush dominates

31. Desert ‘pavement’