Sarah West

 Last week I visited the beautiful Strensall Common to set up a project with Natural England who run the site. It's a SSSI, a Site of Special Scientific Interest, which means that it has rare plants or animals on it so it gets special protection. Julian from Natural England showed us around the site. It's a lowland heath, a rare type of habitat (see OPAL East Midlands pages for more information as they're doing research on these habitats)

Here's a picture I took on the site, you can see where the birch trees have been cut down in the foreground. If these types of sites were left alone, they are likely to become completely wooded - you can see the white bark of the birch trees in the woodland at the back of the picture.

This occurs due to a process known as succession. Starting from bare ground, the first things to arrive in an area (known as colonists) are often lichens or bryophytes (mosses and liverworts) which cn thrive in bare, low nutrient environments. Once these are in place, they create a little sheltered area out of the wind, so soil and water can start to build up, allowing other species like grasses to gain a foothold. Then, larger species like heather move in, and eventually trees like the birch here are able to grow.

So why is this a problem, aren't trees great? Well, they are, but lowland heath itself is a very important habitat. Plants like petty whin (Genista angelica) (see Encylopaeida of Life photo below) aren't able to compete with the birch trees, so if the birch trees were allowed to grow up then plants like this wouldn't be able to survive there.

And the habitats provided by the lowland heath, with its heather, grasses, sedges and many other plants are great places for invertebrates to live. The problem in a relatively small area like the UK is that if we just let everything carry on naturally, we'd end up with only trees and then all the plant and animal species that need lowland heaths for example would become locally extinct.

It's a complicated issue, and I'm not sure how well I've explained it, but if you want more info then the Offwell Woodland and Wildlife Trust site on succession is a good place to start.