Botany and Geology

Understanding out local botany

David Beeson

As we all wander the local terrain plants come to our notice. Some people record these and dump their data onto spreadsheets. I do the same with mammal sightings. Only when this information is amassed onto a map do those sightings have real meaning. Then one can see how organisms are often only found in one area, perhaps on a single soil / geology type – in their ecological niche.

For each and every plant, animal, bacterium or fungus they have an ecological niche in which they can survive.

An ecological niche is the role and position a species has in its environment; how it meets its needs for food and shelter, how it survives, and how it reproduces.

For example, a garden spider is a carnivore of small invertebrates that it finds amongst vegetation, possibly employing a web to help trap its prey.

In our gardens we can push a plant’s ecological niche to its extreme. For example, common ling, a heather found growing in acidic soils, can be encouraged to grow in an alkaline soil (for a while!) by adding masses of garden compost. This will not happen ‘in the wild’.

A look at the Andover Geology Map (Sheet  283) will show you that we are dominated by an underlying rock called Upper Chalk (green on map). However, the hill tops have this covered by either clay (Northern part of Harewood) or gravels (Harewood Forest towards Longparish). One has to travel towards Kingsclere before that geology changes.

For a plant, growing in a thin, chalky soil is quite different from a sticky clay that is soggy in winter and baked hard in summer. Hence, the surface botany of upper chalky areas will be markedly unlike that found in the northern parts of Harewood.

Also, living in the top centimetre of the soil will be a contrast to deeper growing plants, for the topsoil is enhance with leaf litter and will be more acidic or less alkaline.

 In the river valley water content will be higher and more constant and, from that you’ll correctly guess the botany will be unique as well.

Suggestion.

Leave your car in the layby on the B3400 at the Whitchurch end of Andover Down. Walk the footpath south through the forest (Clay over upper chalk geology). At the open field it changes to a gravellier soil and is open to sunlight. Take the path, leading off the Middleway towards Forton. At Forton explore the field leading towards Longparish. You should spot dramatic changes in plant distribution.

Return to your car. A walk of 5.3 miles.

A complex series of geological features.

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