Climate on the broad scale, across hundreds of kilometers, brings about the broad-scale distribution of vegetation types (Chapters 1 and 2). However, even looking at the world much more locally, we see that there are also very substantial differences in the average climate. For example, a south-facing slope has a different climate from a north-facing one. The year-round temperature and rainfall conditions under a tree will be different from those just a few meters away in the open. The temperature right at the soil surface is different from the temperature a few centimeters under the surface.
Such local differences make up what are known as "microclimates". These are little climates that exist to some extent everywhere and vary on a scale of a few tens of meters, a few centimeters or even a few millimeters. Such differences are all-important to plants, and also the animals that live amongst them.
Microclimates help to explain part of the patchiness in vegetation that occurs on smaller scales; they determine which plants can grow where. They are also important in understanding how so many different species of plants manage to coexist, without them all being out-competed by one strong species. And microclimates can explain certain features of growth form, leaf shape and physiology of plants.
Furthermore, microclimates are the building blocks of climate. The broad-scale climate is in part the product of these countless little climates, added up and averaged out. If we really want to understand how climate on the global scale is made, including how plants themselves help to form it (Chapters 3 and 4), we have to understand microclimates.
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