IAP-25-090

The legacy of lost woods: soil microbial communities and the regeneration of the Caledonian Forest

Deforestation – and associated losses of biodiversity and ecosystem function – is a global problem (Hansen et al., 2013). The loss of old-growth forests is particularly damaging because these habitats are highly biodiverse and store huge quantities of carbon (Luyssaert et al., 2008), characteristics that are not replicated by younger forest stands. Consequently, there is a pressing need to conserve old-growth forest. In the UK, the old-growth Caledonian Forest is an internationally important ecosystem. The Forest formerly covered much of Scotland, but centuries of deforestation and have confined it to a few locations in the Scottish Highlands. Due to its high ecological and cultural value, conservation agencies are keen to expand and connect the remaining fragments of the Forest by removing plantations of non-native conifers and planting unwooded sites with indigenous tree species (Wilson, 2015). However, the success of these schemes is highly variable, for unknown reasons.

The composition of soil microbial communities may provide an explanation for the unpredictable fate of reforestation projects. Trees are known to depend on symbiotic relationships with certain soil microbes, notably mycorrhizal fungi; thus, it is likely that that the successful establishment of indigenous saplings is only possible when these microbes are present (Selosse et al., 2006). The natural assembly of the soil microbial communities associated with old growth forests most likely occurs on timescales that are impractical for restoration efforts (de la Peña et al., 2016). However, beneficial microbes may persist in the soil after the clearance of old growth forest, i.e., there could be a legacy effect (Johnson et al., 2014). If this is the case, recruitment of indigenous tree species in areas that retain a legacy of past forest cover is likely to be higher than in areas that do not. It follows that areas with suitable soil microbiology are prime targets for restoration efforts, if these areas can be identified. Unfortunately, very little is known about long-term changes in soil microbial communities: if there is a legacy effect, we don’t know how long it lasts, nor if subsequent exploitation of the land (e.g., for coniferous plantations) hastens its demise. Understanding these factors is clearly important to land managers when it comes to planning the conservation and gradual restoration of ancient woodland.

This project aims to determine if a microbial legacy of old growth forest is present in areas that were formerly part of the Caledonian Forest, and if there is a link between the soil microbial community and the success of restoration projects. The IAPETUS student will do this by profiling the microbial communities present on deforested sites of different ages and comparing these communities to those in extant fragments of the Caledonian Forest, as well as more recent plantations of non-indigenous conifers. The microbial communities will be profiled using molecular (DNA) techniques, specifically DNA metabarcoding.

The study will focus on sites in the Cairngorms National Park, Scotland (CNP). The Cairngorms National Park contains fragments of old-growth Scots pine woodland, along with deforested areas and plantations of non-native conifers. The PhD student will build on research conducted by the CASE partner, Zulu Ecosystems, to identify and restore areas in CNP where old-growth forest was cleared in the historical era (from decades to centuries ago). The student will then sample soils along a gradient of increasing age since deforestation, keeping other factors relevant to soil microbial composition (e.g., bedrock geology) as constant as possible. Soil from extant ancient woodland and plantations of non-indigenous conifers will also be collected for comparison. The soil samples will then undergo molecular (DNA) analysis targeting fungi and bacteria along with the analysis of physical and chemical properties (pH, nutrient and soil organic matter content, etc.) The student will a) profile the soil microbial communities on each site, using old-growth communities as a reference point and b) identify genes associated with key ecosystem functions (e.g., the cycling of carbon and nitrogen). The student will receive practical training in field survey techniques and applied ecological restoration at the CASE partner’s Scottish HQ in Inverness.

Year 1

Preparatory research into the soil microbial ecology of forested ecosystems; identification and dating of deforested sites; site selection and design of sampling strategy, including negotiating permissions; training in field skills

Year 2

Field survey and sampling; training in lab-based skills; soil analysis (physical and chemical properties); molecular analysis (DNA metabarcoding)

Year 3

Data analysis: quantification of changes in soil microbial communities with time since deforestation; thesis writing

Year 3.5

Manuscript preparation

Fieldwork skills: training in seedling surveys, grazing impact surveys, soil surveys, other biodiversity field skills. Training in planning and developing restoration projects. Health and safety in the field, including outdoor first aid; training in off-road driving using a 4-wheel drive vehicle.
Use of molecular (DNA) methods, specifically DNA metabarcoding, to characterise soil microbial communities (fungi and bacteria).
Lab-based analysis of physical and chemical properties of soil.
Statistical techniques, specifically statistical modelling of biological communities.
Use of GIS in restoration ecology.