Sidmouth Arboretum is launching its 2024 Tree Survey to assess the tree population of the valley and how much it has changed in the last 10 years.

In 2014, Sidmouth Town Council sponsored the Arboretum to carry out a survey of the valley’s treescape. The survey was designed by the specialist company Treeconomics from Exeter Science Park and involved 200 sites selected to give a representative sample of the whole valley. Arboretum volunteers visited the 200 sites to count and measure all the trees. The final report revealed that there were more than 400,000 trees, Larch, Douglas Fir and Ash being the most common, and the tree canopy shaded 23 per cent of the land, much higher than the average for Devon and the whole country where it is about 16 per cent.

There have been significant changes to the local treescape in the last 10 years, including the felling of large areas of the Larch because of a disease called Phytophthora and the ongoing disaster of Ash Dieback. The Council and the Arboretum have teamed up with Treeconomics, now internationally recognised specialists in tree surveys, and will be revisiting the same 200 sites to quantify the changes.

Several significant landowners have already agreed to repeat visits and all the others will be contacted for permission to access their land and check the trees. The survey visits will take place through June to September. In each of the 200 plots, each a circle with a radius of 11m, the tree species plus their height, trunk girth and canopy spread will be recorded, and their health will be assessed against a standard scale.

The landowners will also be asked if they have any sites for future planting, including sites for hedgerows to contribute to another major study where the River Sid catchment Group is looking to use hedges and trees to slow the run off from farmland of heavy rain into the river system.

As well as helping to smooth the flow of water, trees provide many environmental services including the ability to remove air pollutants, provide shade and cooling in hot weather. Apart from changes to the numbers and size of the trees over the last 10 years, it will be possible to estimate the contribution the trees make to the life amount of carbon that the trees have captured in that time. There will be a balance between trees that have grown and sequestered carbon and those that have been removed through forestry operations and because of disease. A recent follow up survey in Torbay found that, although they had lost many trees in 10 years, the remaining trees had grown enough to show a net gain in canopy cover and carbon sequestration.

The collected data will be processed by Treeconomics and a report will be published by February 2025 with a public event to introduce and explain the significance of the findings.