TEMPERATE FORESTS |
I. TemperateCool Rainforests
A. Climate ('maritime')
The temperate cool rainforests occur poleward of the Mediterranean region, 40°- 60° N and S latitude, along the western coast of continents under the influence of the westerlies (roaring forties, furious fifties, screaming sixties; latter doesn't hit the southern continents)
Rainfall occurs principally in winter but has no summer-drought as does the Mediterranean region found adjacent to it and towards the equator
B. Biome Regions
1. northern California - southern Canada
12 ft of rain! Mosses and ferns dominate understory; 20 species of conifers!, long-lived, 50-80 meters tall, 2-3 m dbh
Sequoia sempervirens (coastal redwood), Picea sitchensis (sitka spruce), Tsuga heterophylla (western hemlock), Thuja plicata (western red cedar), Pseudotsuga menziesii (Douglas fir), Abies amabilis (silver fir)
2. [Europe - gone! Why?]fossils of gymnosperms seen in western North America
Sequoia sempervirens grown in Wales and Kew since 1889 and nicely survives3. southern Chile
a. Valdivian rain forest: 41° - 43° S
b. Magellanic rain forest: 43°- 56°lianas and epiphytes common;
Nothofagus (southern or silver beeches), Araucaria araucana (monkey puzzle), Fitzroya (Patagonian cypress); also Aextoxicon punctatum (monotypic endemic family), Eucryphia (Eucryphiaceae -- 1 species here, 4 in SE Australia), Laurelia sempervirens (Monimiaceae -- 1 species here, 1 in New Zealand)4. SE tip of Australia, Tasmania, South Island of New Zealand
lianas and ferns and mosses
Nothofagus solandri (mountain beech, most widespread), Eucalyptus coccifera (Myrtaceae), Eucalyptus regnans (mountain ash), Metrosideros (Myrtaceae), Podocarpus dacrydioides ('kahikatea'), Dacrydium (Podocarpaceae, red pine), Dicksonia antarctica (tree fern; Jurassic fossil to England!), Weinmannia racemosa (Cunoniaceae -- genus pantropical, Madag., Andes), Eucryphia (Eucryphiaceae -- 4 species here, 1 in Chile), Laurelia novae-zelandiae (Monimiaceae -- 1 species here, 1 in Chile)
II. MoistSubtropical Forests
A. Climate
The moist subtropical forests form on eastern edges of continents between 30° and 35° under the influence of moist and warm air moving out from the western sides of the oceanic subtropical high pressure systems (i.e., the easterly trades and monsoons).
Rainfall occurs all year round. Summers brings copious amounts of rainfall and is oppressively humid and warm; summer cyclones (hurricanes or typhoons) bring especially huge rainfalls. Winters bring cooler, sometimes subfreezing weather, but still wet.
B. Biome Regions
Broadleaf evergreen forest (most places): "laurel" or "laurel-oak" forest in Northern Hemisph., "laurel" and conifer dominated in Southern Hemisp.; often valuable timber trees, dense wood.
1. SE United States (extends into Mexico at higher elevations!)
Quercus virginiana (live oak), Persea (Lauraceae), Magnolia (magnolia), Taxodium (bald cypress)southern pine forest (interior to coastal SE United States)
Pinus echinata (yellow pine), P. taeda (loblolly pine)2. southern China, Taiwan, southern Japan
Quercus (oaks), Lithocarpus (tanoaks), Castanopsis (chinquapins), Ardisia (Myrsinaceae), Persea (Lauraceae, coffin wood), Camellia (Theaceae), Cryptomeria (Japanese cedar), Metasequoia (dawn redwood), Ginkgo biloba (ginkgo, maidenhair tree)
3. Uruguay and southernmost Brazil
Podocarpus (podocarps)
4. eastern coast of Australia, North Island of New Zealand
Eucalyptus, Agathis australis ('kauri', Araucariaceae), Podocarpus (podocarps)
5. SE African coast (only remnants left)
Podocarpus, Ocotea (Lauraceae, stinkboom: used to make locks in Panama Canal)
III. Temperate DeciduousForests
A. Evolution of the 'deciduous' habit
1. The deciduous habit is generally believed to be a drought-avoidance adaptation which evolved in dry subtriopical regions (Axelrod, 1966). Deciduous trees reduce their demand for water by shedding leaves during the dry season.
2. Leaf-shedding in the temperate zone, is an adaptation to the cold season. Loss of thin deciduous leaves in winter and protection of the buds represents a saving of material as compared with the freezing of thick evergreen leaves. It is not facultative but obligatory (placed in greenhouse they still shed).
3. Hardwood species have efficient water conducting cells called vessels. With efficient water conduction, hardwoods can maintain high rates of photosynthesis and so shade out competitors, but this advantage is lost in seasonally dry climates and in areas where growth is restricted by long and very cold winters. At this extreme, conifers with tracheids (less susceptible to breakage of the water column) are selected for.
4. Thus, broad-leaved evergreens have the advantage in mild, moist climates where year-round photosynthesis is possible; deciduous hardwoods have the advantage in drier and winter cold climates; and conifers have the advantage in very cold climates. This tracks the major forest biomes, for example, from SE United States to Canada.
B. Climate
Alternate between warm, moist summers and mild winters. 250 days to 125-150 days in growing season (frost free). Trees resume growth in spring in response to increasing temperature; numerous herbs flower before canopy coast forest floor in deep shade; autumn color change and leaf drops.
C. Biome Regions [more on the floristic links later!]
1. Eastern North America (north of evergreen and pine forests of the south)
Fagus (beech), Liriodendron (tulip tree), Tilia (basswood), Acer (maple), Aesculus (horse chestnut), Ulmus (elm), Fraxinus (ash), Quercus (oaks), Carya (hickory) & Pinus strobus (white pine)
Shrub and herbaceous diversity varied but spectacular [Ranunculaceae, Berberidaceae, Liliaceae, Umbelliferae]
2. Eastern Asia: similar genera in common, different species and more diverse [more on this later]
3. Europe: alot lower diversity, native forests very few
IV. Boreal Coniferous Forest ('Taiga'in Eurasia)
A. Location and Ecology
Coniferous forests are mainly found in broad circumpolar belt across the northern hemisphere and on mountain ranges where low temperatures limit the growing season to a few months each year; thus too unfavorable for most hardwoods.
Extends from Alaska to New Foundland. Furthest north extension at 69° in NW Canada. Extends from eastern Scandinavia across northern Asia to the Pacific Ocean. Furthest north extension at 72° in Siberia. The geographic position of the southern continents precludes the development of similar forests at high latitude.
Almost all of the coniferous species are evergreen with the exception of Larix (larch); subshrubs (often scandent) are common.
Soil is 'spodozol' [podzol], heavily leached and acidic.
Many of these areas have been recently glaciated so the boreal forest is very young and intimately connected with fens and bogs. The boreal forest is connected to cold montane coniferous forests even south of the boreal forest, but the species are often quite distinct. There is a poleward decrease in species diversity, as expected.
B. Climate
Average daily temperature of 10°C is found in fewer than 120 days and cold seasons last 6 months. Tundra will form at the northern edge when there are 30 days only of average daily temperature of 10°C and cold season lasts up to 8 months.
Considerable variation is climate from location to location. Cold oceanic boreal forests show considerably less fluctuation in seasonal temperature relative to cold continental boreal forests of Eurasia.
C. Biome Regions
1. North America
a. boreal forest
Picea glauca (white spruce) : only species to range across N. America
Picea mariana (black spruce), Pinus (pines), Abies (fir), Larix (larch), Tsuga (hemlock), Thuja (white cedar), Juniperus (junipers)
non-conifers: Alnus (alder: N2 fixing!), Betula (birch), Populus (aspen)
subshrubs/herbs: Vaccinium (blueberries), Maianthemum (wild lily of the valley), Linnaea (twinleaf), Pyrola (shinleaf), Rubus (raspberry), Lycopodium (club moss), Pteridium (bracken fern)b. sub-alpine forest
Picea glauca (white spruce) extends into Rocky Mts.
Pinus contorta (lodgepole pine), Pinus ponderosa (ponderosa pine), Abies lasiocarpa (subalpine fir)2. Eurasia
a. taiga
floristically poorer than North America with 2 species dominate (Picea abies: Norway spruce, Pinus sylvestris: Scot's pine). species pairs with North America common: (e.g., Larix decidua, larch).
