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[2] The region forms a transition zone between the temperate forests to the north, and the steppe to the south. The forest-steppe is an area of Russia in which precipitation and evaporation are approximately equal. [2] The ecoregion is in the Palearctic realm, with a Humid Continental climate.
[1] [3] Many migratory birds and butterflies spend winter in tropical and subtropical conifer forests. This biome features a thick, closed canopy which blocks light to the floor and allows little underbrush. As a result, the ground is often covered with fungi and ferns. Shrubs and small trees compose a diverse understory. [1]
The herb layer is very rich and, in undisturbed areas, the trees can grow very large. Typical trees include sugar maple ( Acer saccharum ), beech ( Fagus grandifolia ), tuliptree ( Liriodendron tulipifera ), basswood ( Tilia americana ), northern red oak ( Quercus rubra ), cucumber tree ( Magnolia acuminata ), and black walnut ( Juglans nigra ).
The top layer of the understory is the sub-canopy composed of smaller mature trees, saplings, and suppressed juvenile canopy layer trees awaiting an opening in the canopy. Below the sub-canopy is the shrub layer, composed of low growing woody plants. Typically the lowest growing (and most diverse) layer is the ground cover or herbaceous layer.
A megasporocyte is divided by meiosis in each ovule. Each winged pollen grain is a four celled male gametophyte. Three of the four cells break down leaving only a single surviving cell which will develop into a female multicellular gametophyte. The female gametophytes grow to produce two or more archegonia, each of which
The leaves are usually 9 to 11 cm (3 + 1 ⁄ 2 to 4 + 1 ⁄ 4 in) long on a full-grown tree. The trunk diameter often ranges from 46 to 88 cm (18 to 35 in); depending on the growing conditions, however, open-grown trees can attain diameters of up to 153 cm (60 in).
[1] The perpetually warm, wet climate makes these environments more productive than any other terrestrial environment on Earth and promotes explosive plant growth. [2] A tree here may grow over 23 m (75 ft) in height in just 5 years. From above, the forest appears as an unending sea of green, broken only by occasional, taller "emergent" trees.
Populus deltoides is a large tree growing to 20–30 m (65–100 ft) tall and with a trunk up to 2.8 m (9 ft 2 in) diameter, one of the largest North American hardwood trees. The bark is silvery-white, smooth or lightly fissured when young, becoming dark gray and deeply fissured on old trees.