Expanding native forest in Scotland: small-scale mechanisms, landscape-scale responses

Forest expansion is an increasing UK priority and Scotland, which was historically extensively forested, receives a significant proportion of this. Mature forest remnants in the Scottish Highlands support rare specialist species and many have been continuously forested for millennia. However, current policies and grants incentivise forest creation by planting, leading to under investment in protection of and expansion from forest remnants. Using a combination of designed experiments and data collection across natural gradients, this project will explore aboveground processes of forest establishment and interactions with belowground communities and soil properties, providing evidence on outcomes of forest expansion by natural regeneration vs planting.

In collaboration with Trees for Life, we are collecting data on soil communities and properties across a landscape-scale network of plots within Trees for Life’s Caledonian Recovery Project and Wild Trees Survey. Trees for Life’s pioneering work provides detailed information on the status of mature forest remnants across Scotland and the dynamics of natural tree regeneration within and around these remnants. We will link data on tree regeneration and forest status to a set of variables on soil communities, soil physical properties, and soil chemical properties. Soil communities both facilitate tree establishment and respond to the establishment of trees, driving subsequent changes in soil physical and chemical properties.

Data collection across the natural gradient of forest status represented by Trees for Life’s network of survey plots will be complemented by experimental work in collaboration with Highlands Rewilding. We have co-designed experiments with Highlands Rewilding, exploring mechanisms of forest establishment and soil property/community responses. Experiments consider natural regeneration and tree planting as mechanisms of native forest creation in a clear-fell plantation (Bunloit Estate) and grassland context (Beldorney Estate). In the Bunloit experiment we have an additional treatment assessing the efficacy of mycorrhizal inoculation of tree establishment.