What about the small woods, individual trees and hedgerows in the Chew Valley?

posted in: Chew Valley, LiDAR, Small Woods, Woodland | 0

The existing “woodland” in the Chew Valley covers some 7% of the land area. This figure is derived from the National Forest Inventory (NFI) 2018, compared to 10% cover for England and 13% for the UK as a whole. These figures are based on the NFI and allow standard comparisons to be made between time periods and between countries. The figures are for “Woodland” – i.e. areas more than 0.5 hectares in size. But what about the many small patches of trees that are less than 0.5 hectares and individual trees in fields and hedgerows? These small areas are ecologically different to the larger woodland patches but they add up and clearly have value as habitats and as carbon stores. But what to they add up to?

Using airborne LiDAR from the Environment Agency it is possible to identify and measure these small woods and even lone trees to get a more realistic idea about the tree canopy cover in the valley – within both the larger woodland and the small patches not accounted for by the official NFI survey. The map and table below are a first pass at doing this.

CategoryCanopy Cover (Ha)%
Small Woods and Trees6864.8%
Hedgerows and Shrubs2001.4%

The tiny specs of lighter green on the map below are the small woods, lone trees and hedgerows. It is hard to see them on a map at this scale.

Contains data from Ordnance Survey, Environment Agency, Forestry Commission, DEFRA, OGL 2021

The canopy cover of 883 Ha for Woodland, as measured by LiDAR, is less than the 945 Ha of Woodland area calculated from NFI. This is not surprising as woodland isn’t completely uniform and has gaps in it, young trees don’t have a closed canopy and some woodlands include areas without any trees at all, including grassland.

Across the valley the canopy of small woods and individual trees covers 686 Ha of land. All of those little bits add up. This is considerable and represents an additional 75% of tree canopy cover in addition to the trees within Woodland. Hedgerows and shrubs, including plants in people’s gardens, cover an additional 200 ha.

This does not mean that we need to create less new woodland. The criteria for measuring woodland cover have not changed and the figure of 7% woodland cover will be broadly similar at the next national inventory, hopefully a bit more. What is does show is that there are a significant number of trees in the landscape outside of Woodland proper. However, we also know that the number of hedges and the number of hedgerow trees in the Valley is measurably less than it was in 1880. What these statistics tell us is not that we need to make less effort on tree planting but that we need to make more effort to increase not only Woodland but also the number of trees outside woodland, including in hedgerows.

Ordnance Survey 1880 with EA LiDAR tree cover. It is clearly evident that trees, hedges and orchards have been lots since that date, although there have been some limited gains.

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