Diversification of UK’s Sitka spruce forests would provide biodiversity benefits, new paper shows
A recent paper authored by scientists at some of the UK’s top environmental research groups has shown that diversifying the nation’s Sitka spruce forests would provide biodiversity benefits as well as potentially increasing their resilience to pests, diseases and climate change.
Originating in North America, the Sitka spruce was introduced to Britain in 1831 and has since become the most common tree species in the UK’s commercial forests.
Used for both timber and paper production, the imported spruce was historically planted in monocultures – creating substantial forests with little to no other tree species.
Our forests currently face a range of threats including climate change and an increasing number of new pests and pathogens. To increase the resilience of our forests to these threats tree species diversification is often promoted – the idea being that if one tree species declines, other tree species might survive increasing the resilience of our forests. However, the impact of tree species diversification on tree associated biodiversity is rarely considered.
The new paper, titled Sprucing up the UK’s Sitka spruce (Picea sitchensis) forests: can tree species diversification benefit biodiversity?, was published as part of DiversiTree – a collaborative project aimed at increasing woodland resilience through greater tree species diversity.
Authored by scientists from The James Hutton Institute, the RSPB, the Royal Botanic Garden Edinburgh and the University of Aberdeen, the publication explains how adding other tree species to the nation’s Sitka forests would not only provide better resilience for species that currently use Sitka spruce but also increase the biodiversity supported by our commercial forests and promote a healthier ecosystem overall.
“As our forestry adapts to a changing climate and new tree pests and pathogens, it is crucial that we understand how this may impact forest associated biodiversity.”
Dr Ruth Mitchell, The James Hutton Institute
To begin the study, the researchers conducted a literature review and identified 564 species (12 birds, 147 bryophytes, 28 non-lichen-forming fungi, 123 invertebrates, 243 lichens and 11 mammals) which use the Sitka spruce for feeding or as a living space; however, many of these are non-specialists and can survive on a wide range of trees.
The authors then assessed 34 tree species which could be planted with Sitka spruce for their impacts on both biodiversity and ecosystem function. Tree species were assessed for their leaf litter decomposition traits, influence on the soil and leaf litter chemistry, as well as their ability to grow alongside Sitka spruce, support Sitka spruce-associated species and nurture additional biodiversity.
It was found that diversification of Sitka spruce forests with oak, sycamore, Scots pine, birch, beech and Norway spruce would provide the greatest biodiversity benefits, supporting both the species found on Sitka spruce and additional biodiversity not currently found in these forests. However, all these tree species, except sycamore, are unable to grow in the long-term when planted in mixtures with Sitka spruce.
To remedy this, the scientists behind the paper suggest planting ‘blocky mixes’ – small blocks of single tree species which connect the forest like a patchwork quilt – to diversify Sitka spruce plantations without major impact to timber production. Further research is needed to decide the optimal size and arrangement of these ‘blocks’.
Dr Ruth Mitchell, a Plant Soil Ecologist at the Hutton and the paper’s lead author, said, “As our forestry adapts to a changing climate and new tree pests and pathogens, it is crucial that we understand how this may impact forest associated biodiversity.
“This work shows how diversification of our Sitka spruce plantations with other tree species can bring many biodiversity benefits.”
“However, we have also found that those tree species that would provide the greatest biodiversity benefits will not grow in the long-term with Sitka as they would be shaded out. We therefore need careful thought around how we spatially plant mixed species forests to get a range of benefits.”
