Edinburgh researchers find there is no silver bullet for forests under climate change

Researchers argue that a long term strategy is needed to robustly provide tree stocks in the face of uncertain climate change.

For restoration and expansion of native woodlands, forest managers typically use planting stock which has been grown from locally sourced seed, because it is best adapted to local conditions.

However, under rapid climate change, conditions are expected to alter substantially within the life span of an individual tree. There are concerns that tree populations will not be able to adapt quickly enough. It has therefore been suggested that seeds collected from further south, already adapted to warmer conditions, should be used in place of local seed as a simple solution to pre-adapt forests.

In a study published in Forestry, researchers from the University of Edinburgh, Centre for Ecology and Hydrology and Forest Research have analysed the possible risks and rewards associated with this proposed strategy.

They argue that future climate will differ from present climate in many ways other than temperature, and point out that the frequency and severity of extreme events is set to increase. Therefore young trees raised from seed collected further south which are not adapted to the current climate may struggle to survive initially and actually be rather poorly adapted to future environments, especially in the rugged upland landscapes where most tree planting takes place.

On the other hand existing local tree populations contain substantial genetic variability, and if their offspring are able to establish in future generations, natural selection may allow them to adapt to unpredictable new conditions without the need to bring in seed from further south.

Delivering nursery needs

In a separate study, published in Land Use Policy, the research group have investigated whether the forest nursery sector is well placed to deliver the right trees for our future forests.

They find that, due to the vagaries of woodland grant schemes, forest managers are rarely able to provide nurseries with the 1-3 years notice they require to produce plants of appropriate species and geographic origin.

The majority of trees are therefore grown speculatively, with excess trees being burned, and shortages being overcome by importing from abroad – an activity which has been linked to introduction of exotic pests and diseases into GB.

The researchers conclude that a more stable grant system, that acknowledges the imperative for long term planning, is urgently needed. The aim should be to create and support a strong domestic forest nursery sector that will deliver the social benefits used to justify the public funding of tree planting.

The two studies were supported by Forestry Commission Scotland, Forestry Commission GB, Climate XChange and the Biotechnology and Biological Sciences Research Council.

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