VEGETATION PATTERNS
Introduction
This is the last of the 3 classes dealing with the processes creating the vegetation cover of the Earth's surface:
1 - The factors affecting the development of individual plants
2 - Factors affecting plants as they grow together in communities
3 - The spatial distribution of vegetation
In considering patterns of vegetation we have a similar problem to that when we considered soil - there are various scales to consider. In this class we look briefly at the global scale.
Bear in mind that all of the various biomes we discuss have the same kind of variability as that associated with our own forest biome here in North Carolina. So there are always going to be areas which do not seem to 'fit' even if they appear to be in the middle of a biome.
The Global Picture
| The global-scale divisions (akin to the 'Soil Orders') are
the Biomes. In general the most complex of these are
the forests - which some people consider to be one biome with lots of
sub-divisions, some consider to be several separate biomes.
Nevertheless, each of the biomes - or the sub-biomes - are an expression
of the vegetation response to the conditions in the area.
On a global scale it often seems that climate - and partly through climate, the soil also - dictate the patterns. Indeed, it is a good idea to compare Fig 10-5 (the global climate map which we have not looked at before); Fig 18-9 (the soil taxonomy) and Fig 20-3 (the biomes - as seen on the thumbnail at the right) |
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A long-leaf pine seedling has a very distinctive shape. |
The global map indicates that North Carolina is in the 'Midlatitude broadleaf and mixed forest' biome. This is the case - a look at the trees around us confirms this. However, until the deforestation brought about by logging at the end of the nineteenth century, the dominant forest type for the state outside the mountains (and especially on the coastal Plain) was the long-leaf pine. There are few of them left - they were a major source of tar when sea-going vessels needed a great deal of tar. |
A mature long-leaf pine forest, near Southern Pines |
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Most forests not only have a 'layer' of large trees, but
also vegetation on the forest floor. The broadleaf evergreens of the
equatorial region is unusual in that it is dark almost continuously under
the canopy. Most forests have a time when light can penetrate -
either because there are few leaves on the trees, or because the
needleleaf trees let light pass. During that time forest-floor
vegetation flourishes.
Our own forests are rather unusual in having a middle layer - the dogwoods and red-buds are examples. In part this is a result of having a rather open canopy as the forest crown. |
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Remember, however, that there are a great range of forest types. They cover a great latitude range, from the equator to the Arctic Circle. |
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Trees require great amounts of water. As precipitation amount decrease, forest gives way to shrub land and eventually to grassland. An finally to desert |  |
| Moving poleward (or upward) within the forest biome, the trees get smaller and smaller as it gets colder. Eventually we get to the Tundra, where only low-growing vegetation survives both the cold and the wind. |  |
