Plant Ecology - Chapter 18

1. Plant Ecology - Chapter 18 Biomes

2. Terrestrial biomes • Defined by the physiognomy of the predominant vegetation

3. Boundaries? • No sharp boundaries between biomes • Intergrades

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

5. Desert biomes • <10 inches (<25.4 cm) of rain per year • Cool • Temperate • Tropical

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

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

8. Climatograph

9. 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)

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

11. 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

13. 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

14. Desert life • Plants are either drought evaders or drought resistors

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

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

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

18. 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

19. 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

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

21. 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

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

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

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

25. 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

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

27. Tropical forests • Equatorial, mean temp. ~25°C, 12 hrs sunlight per day • Rainfall highly variable-determines type of tropical forest present

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

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

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

31. 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

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

33. Tropical rain forest soil • Very poor - little or no topsoil • Easily weathered • Subsoil with iron-based clay - laterite • Major problems with slash-and-burn agriculture

34. Tropical rain forests today • Deforestation

35. 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

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

37. 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

38. Taiga • Boreal forest, coniferous forest • Harsh winters with lots of snow

39. 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

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

41. 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