The next time you get the chance to look across a valley to a high peak, make sure to enjoy your view of nature’s altimeter.
There will be no trees on the highest parts of any great hills, as they cannot survive the low temperatures and high winds. The altitude at which they give up is called the treeline. It is never perfectly horizontal, because the shape and aspect of mountains influences the conditions; trees can survive in sheltered gullies much higher than in nearby exposed spots.
Low in the valley there will be generous offering of deciduous trees, but as your eyes range up the hillside there will come a point where the broadleaved trees give up and the hardier conifers take over. This species change continues above the treeline as well, where we find tougher smaller plants, like heather.
For a finer reading of the altimeter we need to walk amongst the trees. When hiking up a hill through a woodland, keep an eye on both the tree species you pass and their height. Before each tree gives up and hands over to a tougher species, notice how they become steadily shorter.
We are ready to study the gauge in more detail now. From bottom to top of a big hill we find: tall deciduous trees seguing to shorter ones, which yield to tall conifers that in turn give way to shorter ones. The conifers capitulate at the treeline, handing over to the heather, bracken and grasses.
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