L3 Earth's Major Biomes I (Fall 2024-25) PDF

L3: Earth’s Major Biomes I Dr. Cynthia Yau OCES1030 Environmental Science Fall 2024-25 1 Cheetah in African Savanna. Photo: USA Today Lecture Outline Levels of Organization of Ecological Systems...

L3: Earth’s Major Biomes I Dr. Cynthia Yau OCES1030 Environmental Science Fall 2024-25 1 Cheetah in African Savanna. Photo: USA Today Lecture Outline Levels of Organization of Ecological Systems The Biome Concept Terrestrial Biomes World’s Climate Zones & Climate Graphs Major Types of Terrestrial Biomes Tropical Rainforests and Tropical Seasonal Forests Tropical Savanna and Grasslands Deserts Temperate Grasslands Temperate Forests Boreal Forests or Taiga Tundra Reference: Cunningham et al. (2022): Chapter 5 2  Levels of Organization of Ecological Systems The biosphere is an ecological system composed of individuals, populations, communities, and ecosystems. 3 Level of Description Organization An individual organism (e.g. plant, animal, or single- Individual celled life form) A group of individuals of one species living in a Population given area Different populations of different species all living Community and interacting in a given area A system of interacting communities and its non- Ecosystem living environment Large geographical areas on Earth with similar Biome climates and similar communities The parts of the land, ocean, and atmosphere in Biosphere which organisms are able to live 4  The Biome Concept Ecologists call interacting populations of different species living in the same location communities. A series of biological communities or ecosystems over a large geographical area are termed biomes: – plants and animals that have common characteristics for the particular environment they exist in; – biomes are not restricted to a specific continent, instead are adaptations to a shared abiotic environment. Biomes can be broadly divided into: – Terrestrial biomes: those on land – Aquatic biomes: those in freshwater and marine habitats 5 Examples of Major Biomes 6  TERRESTRIAL BIOMES Terrestrial biomes can be defined as: Broad, regional types of ecosystems characterized by distinctive climate and soil conditions, and distinctive kinds of biological communities adapted to those conditions. Terrestrial biomes are mainly defined by: Climatic conditions – abiotic factors (temperatures, precipitation) Predominant vegetation – primarily distinguished by their vegetation, although animals are also included, i.e. flora (plants) and fauna (animals).  World’s Major Terrestrial Biomes Biomes are based primarily on dominant vegetation types We will cover only some major biomes, not all these listed here The number of biomes vary depending on the authority or source: Range of 5-13 terrestrial + freshwater biomes are often given Plus around 4+ marine biomes Biome type can be predicted based on two key factors of a region: Temperature, and Precipitation – water that falls from the clouds towards the ground Note: biomes are most likely to occur in the absence of human disturbance or other disruptions. 9  World’s Climate Zones Equator: 0° latitude Tropic of Cancer: 23°26’ N Tropic of Capricorn: 23°26’ S Polar Temperate Tropics 10  Differential Heating of Earth’s Surface By The Sun The amount of solar radiation reaching a given area varies with latitude due to curvature of the Earth. Low angle of incoming solar radiation: more diffuse heating - > cooler climate Curvature of Earth Solar radiation directly overhead at Equator: more concentrated heating -> warmer climate  Annual Mean Global Temperatures Annual Mean Temperatures More in later lecture on Atmosphere: Air Circulation & Climate 12  Global Distribution of Precipitation Precipitation is any liquid or frozen water that forms in the atmosphere and falls back to the Earth; e.g. as rain, sleet, hail, and snow Precipitation is highest Annual Total Precipitation (cm) around the equator 20  Cold Hot Biomes Vary Wet With Temperature and Precipitation This diagram does Average Precipitation (cm) not consider other factors, such as soil type and shape of the land (e.g. mountains) Dry Average Temperature (°Celsius)  Biomes Vary with Latitude Many temperature‐controlled terrestrial biomes occur in approximately latitudinal bands Examples: Boreal forests: Canada, Europe, Siberia Tropical forests: near the equator Deserts: around latitudes 30°N and S Some biomes are named for their latitudes, such as: Tropical rainforests: between Tropic of Cancer and Tropic of Capricorn Arctic tundra: near/above Arctic Circle (66.6°N) Biomes are not exactly the same as climate zones – as there are factors other than temperature, plus adaptations by different plants to their particular region.  Vertical Zonation by Elevation Temperature and precipitation change with elevation, as well as with latitude. Elevation = the height above sea level Barren rocks Mountains are cooler and often wetter than low elevations. Mosses & lichens → Vertical zonation of vegetation Alpine tundra types is defined by elevation. Grassland Coniferous forest Deciduous forest Vertical Zonation on a Mountain16  How To Interpret Climate Graphs Examples from Cunningham et al. (2022) X-axis - months of the year Left y-axis – temperature (C) Right y-axis – precipitation (mm). The number of dry months (shaded yellow) and wetter months (mid- blue) varies with geographic location Horizontal = x-axis Average annual temperature and Vertical = y-axis total precipitation at top of graph  Not ALL climate graphs show the information in the same way! Another example: Here, precipitation is given as a bar histogram while temperature is shown by a line graph Months above freezing are not indicated Total annual precipitation is not given Comparing climate graphs helps us to understand the different conditions that influence plant and animal growth in the various biomes. 18  1. Tropical Rainforests Warm and wet year‐round Rainfall Abundant, >200 cm per year Temperatures Uniform warm to hot year‐round Biodiversity High biodiversity 1/2 to 2/3 of all species of terrestrial plants and insects  Tropical Rainforests (& Seasonal Forests) Southeast Asian Equator rainforest Amazon Congo rainforest Tropical rainforests occur where rainfall is the highest - i.e. around the equator Seasonal forests are more temperate in latitude 20  Sunlight Tropical Emergent Layer (50-80 m) Rainforest Layers Canopy Layer Canopy = tree crowns Understorey Layer Forest Floor ~2% Dark forest floor 21 Tropical Rainforests − Occur in equatorial zones − Experience warm temperatures year-round − Day length 11-12 hours year-round − Abundant rainfall supporting lush growth of vegetation − Soil tends to be thin, poor in nutrients, acidic Tropical forests have enormous numbers of species Species richness = a simple count of number of species in an area Species diversity = the number of different species in an area and their relative abundance About 90% of all nutrients are contained in the bodies of the living organisms as biomass (biological mass); – heavy rainfall washes nutrients out of the soil quickly – tight recycling of nutrients 22  2. Tropical Seasonal Forest Many tropical regions have distinct wet and dry seasons (seasonal variation), though temperatures remain warm-hot year‐round. Open woodlands that grade into savannas (grasslands) Often called dry tropical forests (dry for much of the year) Dry season (cool & dry): brown and dormant Rainy season (warm & wet): vivid green May contain many species of trees and shrubs Include drought‐tolerant deciduous trees, i.e. some or all of the leaves are dropped during the dry season, stop growing when no water is available. Soils have higher levels of nutrients than in tropical rainforests.  Seasonal Tropical Forest Bhawal National Park, Bangladesh Photo: Khalid.hasan.dups (Wikipedia) Photo: Lrb Travel Team Dry season Wet season 24  A Note About Deciduous Versus Evergreen Trees Deciduous = “to fall off” – leaves are all Spring dropped seasonally (to conserve water) Evergreen = remains green all year round (only a few leaves are shed at a time) Winter Evergreen tree Deciduous tree Which type of trees do we mostly have in Hong Kong? 25 3. Tropical Savannas & Grasslands Warm temperatures Dry for most of the year warm year-round, moderate rainfall with a rainy season, but too little rain to support forests dramatic seasonal variation, dominated by grasses and scattered trees - open grasslands with sparse tree cover  Tropical Savannas & Grasslands (cont.) During dry seasons, fires can sweep across a grassland, killing off young trees and keeping the landscape open Plants have many adaptations to survive drought for long periods, and tolerate heat and fires Deep, long‐lived roots seek underground water and persist when above‐ground parts (leaves and stems) die back After a fire or drought, fresh shoots can grow quickly from the roots Africa African savanna, South American pampas Photo: USA Today Cheetahs and other big cats are carnivores (= secondary consumers) Grasses & trees = primary producers Herbivores = primary consumers Termites – dominant herbivores African herbivorous mammals depend on grass for food (primary consumers), but insects (e.g. ants & termites) are the dominant herbivores. 28 4. Deserts Hot or cold, but always very dry Precipitation Very low precipitation  Not all deserts are hot, there are cold deserts too Cold desert in Antarctica The Gobi Desert is also a cold desert 30 5. Temperate Grasslands Warm/seasonal temperatures Enough rain to support abundant grass (but not forests). Plants may have deep roots Thick and rich soils Most are treeless, or trees are sparse except along rivers Are found in regions with relatively cold winter temperatures E.g. Central U.S. and Canada Many regions have been lost to (“prairie”), Eurasia agriculture (“steppe”) 6. Temperate Forests Seasonal temperatures Wide range of precipitation (mainly at latitudes 30°‐ 55°) Grouped by type of tree: Broad‐leaf deciduous forests Shed leaves seasonally Fall (autumn) colors Evergreen forests Coniferous trees (= “cone‐bearing")  Deciduous Forests Broad-leaf forests occur throughout the world where rainfall is plentiful. In mid-latitudes, these forests are deciduous and lose their leaves in winter. The loss of green chlorophyll pigments can produce brilliant colors in these forests in autumn. At lower latitudes, broad-leaf forests may be evergreen (i.e. keep their leaves year-round) or are drought-deciduous. Japanese maples, for example, are broad-leaf deciduous trees. 33 Japanese maple in autumn Coniferous Forests Grow in a wide range of environmental conditions, often occur where moisture is limited Cold climates: moisture is unavailable as it is frozen in winter Hot climates: seasonal drought Pollen cone Sandy soils (do not retain moisture) Conifer trees – do not have flowers, instead have cones. Thin, waxy leaves ('needles') → adaptation to reduce water loss Seed cones of a conifer tree (pine) 7. Boreal Forests or Taiga Vast biome north of the Temperate Zone (subarctic) – extremely cold in winter Low precipitation Characterized by mostly coniferous forests °C can survive winter cold, hence they are dominant slow-growing because of cold temperatures, mostly evergreen species. Siberia (Russia), Canada, and the western U.S. (Alaska) Can reach -50°C  Vast expanse of taiga Taiga – Russian word Boreal forest – ‘boreal’ = ‘northern’ Soil is nutrient poor and very acidic Conifer needles do not decompose readily in the cold temperatures, nutrients remain locked in the leaves. Forest floor of the taiga 36 8. Tundra A harsh treeless landscape that occurs at high latitudes - Arctic tundra, or on mountain tops - alpine tundra Extremely cold, below freezing for most of the year. Very low precipitation.  Short growing season (2‐3 months only)  Low biodiversity °C Can be considered a type of grassland (with dwarf shrubs, grasses & lichens) or a very cold desert  E.g. northern Canada, Siberia Low-growing vegetation, dwarf shrubs Lichen Reindeer Permafrost below ground 38