10. The Meads
As you stand on the new bridge built in 1974 over the river Cherwell, you see beyond the ancient meads owned by the College since 1982; we were fortunate to be able to purchase them from the Oxford Preservation Trust. They are a site of special scientific interest (SSSI). They have been managed in the same way for over 500 years. No ploughing has occurred during this period. No fertilisers, herbicides, or pesticides have ever been used. The rich and diverse meadow flora has developed because of the traditional farming methods. The herbage is allowed to grow up from the end of winter; it is cut for hay in July after the flowering plants have seeded. Cutting and removing the aftermath balances the nutrient level which favours a large number of native flowering species growing within the meadow turf. The grassland is allowed a short recovery period.
On Lammas Day, the 1st of August, cattle are turned out onto the meadows to graze the grass; they are hungry grazers and keep the grass short. This actually helps the broadleaved flowering plants, since reduction of the grass by grazing allows improved light levels for the other plant material growing in the meadow turf. Cattle grazing ceases on All Soul’s Day on the 1st of November, when the ground conditions become too wet and the cattle can degrade the meadow turf during the winter months. At the end of the winter the meadows will provide a suitable habitat for ground nesting birds like skylarks which will nest in the meads in early summer in the increasingly long grass. This type of meadow is now extremely rare in England, and meadows of this type continue to be threatened by changes to their surrounding environment, farming practices, and other environmental factors. Our grassland is extraordinarily diverse. We are fortunate to have a pool of expertise within the College community (Dr Alison McDonald & Dr Tim King) who are monitoring changes and adapting meadow management to maintain and improve the diversity that already exists.
Over the last twenty years or so the College had not been able to find the funds to manage the willows along the river bank properly. They had grown too big, and their roots and branches were encroaching into the river and onto the meadows, endangering more delicate species and posing potential risks to passers by. But we are delighted that, thanks to a generous five-year grant from the Aspen Trust which began in 2022, we were able to launch a programme to bring the meads and riverside back to their proper standards.
Work began with pollarding the willow trees along the river bank. For non-specialists, that involved cutting the trees back sharply, allowing smaller and less invasive branches to grow back, and to ensure the presence of willows in this ancient meadow is sustainable.
We also now know that the meads are not simply a remarkable source of biodiversity; they are also second only to peat bogs as the landscape which sequesters the most carbon from the atmosphere.
As part of a group of Oxford Colleges keen to improve biodiversity across the Collegiate University, we ran a series of measurements and experiments in 2021 to track precisely what our contribution to environmental health is. A selection of students, Fellows, families and friends undertook a biodiversity audit. It showed how much we are taking carbon out of the environment naturally; hinted at how biodiversity helps cushion the worst of the climate change effects; and was a reminder of how important for our wellbeing biodiversity around us is. We looked at every single one of our 475 trees (second only in Oxford to Magdalen College, with its deer park) and measured their width and height. This gave us a calculation of how much carbon they were storing and capturing. Trees are one of nature’s most effective carbon capture and storage. We also identified that we have 128 different species of trees growing in our grounds. Across 3.3 hectares, they store over 98% of our carbon in their trunks, branches, leaves and roots – about 428 tonnes of carbon in all.
We then undertook a number of surveys of our earthworm population. Earthworms are an excellent indicator of the health of soil (if it is too compacted, it will neither capture as much carbon nor provide a home to as many earthworms). The deeper they are, the better the soil health. 85% of the earthworms we surveyed are soil feeding, 15% are surface feeding. We used satellite data to analyse our land use, including the meads. Of our 14.27 hectares (35 acres) of land, about 30% is built estate, with the remainder being grounds and garden. 3.3 hectares are trees, 4.03 are meadow and uncut grass, 1.25 are wetlands, water meadow and water, and 1.38 are mowed lawn.And we know that there is a direct connection between biodiversity and sustainability, so we used experimental techniques to assess our insect and bird variety, strong indicators of our biodiversity in general. At the time of counting we had at least 49 different bird species, including seven RSPB Birds of Red Conservation Concern. We identified 1394 insects, the third ranked among Oxford colleges, and the allotments at College were especially rich for pollinating bees and wasps.
All told, these calculations suggested that, leaving the meads and marshes to one side, in 2021 the College was taking around 434 tonnes of carbon out of the atmosphere through our natural habitat, to set against the annual average of 1,200 tonnes we would have been emitting from our main estate over the coming twenty years if we had not completed our Zero Carbon works.
But we also now know that the meads are even better than our trees as a carbon sink, and they probably store another 431 tonnes of carbon, with our marshes storing another 57 tonnes. Calculations continue, but it looks like the carbon preserved in our trees, plus the carbon preserved in our meads and marshes, is worth at least 918 tonnes of carbon.
Tim Hitchens
