Lecture 18 Thursday, November 1, 2007 • What is a biome?o Large (global patterns), stable terrestrial ecosystem characterize by a specific plant and animal communitieso Named after dominant vegetationo E.g. Forest, savanna, grassland, shrublands, desert, and tundra o Biomes can have disjunctive or separate distributionso Assemblages of different, but similar looking specieso Rooted in the idea of “climax vegetation” **Climax = final steady stateo Today, most ecologists think of ecosystems as dynamic, rather than reaching a stable state• Towards a new concept of Biomeso We can think of biomes as complex and dynamic: “constantly changing”o Integrate concepts like disturbance and the modification of disturbance regimes by humanso Realize that there is still much to learn• Criteria and/or Characteristics in different biomeso Vegetation structure: shape, layerso Productivity (Biomass)o Biodiversityo Distribution: geographic extento Climate: temperature and precipitation trendso Soilso Disturbance regimes• Biomeso Forested Tropical Rainforest Midlatitude Deciduous Forest Needle leaf Forest Temperate Rain Foresto Non-Forested Mediterranean Shrublands Grasslands Deserts Tundra• Equatorial and Tropical Rain Forestso Veg Structure Trees: large bases, shallow roots Solid canopy cover Multiple canopy layers (sub-canopy) Sparse understory (not much light) Epiphytes and Lianas Very high biomass and productivity Very high in biodiversityo Distribution ~0-20 N & S lato Climate Low daylight variation High insolation Lots of precipitation Year round warm temperatures No distinct seasons Tropical Seasonal Forest and Scrubo Disturbance Natural• blow-down, not much fire Human: Forest clearing• Slash and burn agriculture• Lots of erosion• Forested Vegetation tends not to come back (only after hundreds to couple of thousands of year)• Mid-latitude Broadleaf Deciduous Forestso Adapted to distinct seasons, plentiful moisture, summer high precipitationo Structure Moderately complex Mainly deciduous trees Species: Maple, Oak, Beech, pine, hemlock A few vines and shrubs Many herbs (spring ephemerals)• Ephemeral means brief• Concentrate growth and flowering in early spring before leaves come out• Takes advantage of sunlighto High biomass and biodiversity, but less than tropical rain forestso Soils are “average”. Fairly nutrient poor.o Distributiono Climate Distinct, predictable seasons Cold winters, warm summers Max precipitation in summero Disturbance Treefall Gaps Infrequent fires Floods (Floodplain forests) Insects and disease Humans: logging, clearing for agriculture, development• Needle-leaf Evergreen Forestso Adapted to harsh conditions: cold, snow, and periods of droughto Structure Not complex Lacks sub-canopy Canopy is open to dense Species: Spruce/Fir, Pine, Larch Understory: dense to little or none, shrubs, herbs and small trees Low diversity, Low productivity Biomass varies: (Sequoias vs. lodgepole pine)o Two types of Needle-leaf Forests Montane Forests• Found at higher elevations• Range of types from open pine forests to denser spruce/fir• Growing season may or may not be long Boreal Forests• Found only in northern hemisphere• 45-65 North Latitudes• Band across the globe: circumboreal• Short growing season• Mainly spruce/firo Distributiono Climate Climate can be harsh: cold, lots of snow, periods of drought Climate can be variable, especially in montane forests (warm days in winter, early/late season snowso Disturbance Natural Disturbance• Wind (big blow down events)• Fire (varies in intensity and frequency)• Insect outbreaks Human Disturbance• Logging• Changes in Fire regime (accelerating or slowing down)• Development (housing, mining) Fire• Intensity and Frequency are inversely related• Suppression may decrease frequency• Only if “normal” frequency is less than the time of
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