We have again reached out to our PGR members to tell us about their current research and its implications for landscape ecology. The highlights this month centre around invertebrates and the health of wooded landscapes. Each these research projects can inform forest management decisions to conserve populations of “good” invertebrates and identify management options to control the “bad”. Each project serves as a piece in the puzzle to figure out how to better protect and enhance forest ecosystem health.
The impacts of tree disease on functional connectivity for woodland invertebrates
Fiona Plenderleith, Postgraduate Researcher at the University of Aberdeen and the James Hutton Institute.
There is increasing concern about the loss of trees outside woodlands to diseases. European ash (Fraxinus excelsior) for example is common outside woodlands in the UK but is threatened by the fungal disease ash dieback (Hymenoscyphus fraxineus). This loss of ash trees outside of woodlands could lead to a loss in structural connectivity,impacting the ability of individuals to move between woodlands (defined functional connectivity) and maintain gene flow (defined genetic connectivity). However, the consequences of this for the invertebrates that rely on ash trees remain relatively unexplored.
As part of my PhD, I applied an individual-based modelling platform called RangeShifter to explore the impacts of tree loss on the spatial dynamics of ‘virtual’ ash-reliant insects. We simulated the loss of individual trees both inside and out of woodlands in sites in the Southeast of the UK and modelled species dispersal in relation to the cost of movement across non-woodland habitat, to estimate both the functional and genetic connectivity.
The removal of 10 % of ash trees resulted in a reduction of up to 14.6 % in dispersers that reach and settle in new woodlands, and an increase in isolated woodlands by up to 2.9 %. This resulted in a reduction in gene flow. Overall, the consequences of tree loss for woodland connectivity were influenced by the species dispersal traits, but the consequences for gene flow depended on the arrangement of trees within the landscape.
This research highlights the use of individual based models as a tool to assess tree disease impacts on connectivity at a landscape scale for multiple species. This approach will be extended to inform management options for improving connectivity. It may also be useful for informing repopulation of resistant individuals of tree species, such as Elm that have been lost from landscapes.
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Integrated Pest Management in UK Forestry
Katrina Dainton, Postgraduate Researcher at Forest Research and the University of Edinburgh
Forests are essential to the health of the planet. They support biodiversity, provide ecosystem services, sequester carbon, mitigate climate change, and promote human health and wellbeing (Sing et al., 2018). Insect pests that damage and kill trees can drastically alter landscapes and ecosystems. Bark beetles, for example, have killed millions of hectares of forest across Europe and North America (Hlásny et al., 2019). In the UK, where forests are smaller and less contiguous, tree damage and mortality tend to be more localised, although several diseases (i.e. Dutch elm disease, Ash dieback and Phytophthora ramorum) have had widescale impacts on specific tree species.
To mitigate the negative effects on trees and landscapes it is necessary to manage these tree health threats. Different management options are available, some of which can themselves directly impact landscape scale change, e.g. felling and removing trees. An integrated pest management (IPM) approach promotes taking preventative measures to protect trees from pests whilst reducing the need for more drastic reactive methods.
I am undertaking a PhD (supervised by University of Edinburgh, Scotland’s Rural College and Forest Research) to evaluate IPM awareness and use in UK forestry. This research will assess the methods being used to manage insect pests in UK forestry. It will also investigate forest manager perspectives on the opportunities and challenges of taking an IPM approach. The aim being that current challenges are identified including if there is a gap for new practices, which can then be tested in a case study approach.
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Hlásny, T. et al. (2019) Living with bark beetles: impacts , outlook and management options., From Science to Policy 8. European Forest Institute.
Sing, L. et al. (2018) ‘A review of the effects of forest management intensity on ecosystem services for northern European temperate forests with a focus on the UK’, Forestry, 91(2), pp. 151–164. doi: 10.1093/forestry/cpx042.
Understanding and protecting the biodiversity of decaying wood
Stephanie Skipp, Postgraduate Researcher at University of East London
Over their extensive lives, ancient trees accumulate many decay related features such as peeling bark, sap runs, dead branches and tree hollows. It is due to this structural complexity that ancient trees can provide habitat for thousands of other species. In the UK alone, over 1700 species of invertebrate are known to require ancient trees to complete their life cycle (Alexander, 2002). With this in mind, it is clear that ancient trees constitute incredibly valuable structures for biodiversity within a landscape.
Unfortunately, past woodland management has resulted in a suboptimal current situation for ancient trees. Historical deforestation and land use change has resulted in the loss of much of the UK’s ancient woodland, and many woodlands that remain have been subjected to management practices that do not effectively conserve a healthy tree age structure. As a result of this, The Woodland Trust (2021) designated only 7% of woodlands in the UK as being of ‘good ecological condition’ with sufficient volumes of deadwood, ancient trees and structural diversity. This is a situation that urgently needs to be addressed, especially as woodland planting for climate change becomes an increasingly popular topic.
My PhD research aims to learn more about the specific habitat requirements of decaying-wood associated (saproxylic) beetles and to investigate novel methods that may be used to aid their conservation in future. To do this, I have surveyed the beetle populations of two important pasture woodland sites. I intend to use these results to link the presence of beetle species to local features such as tree density and available microhabitats. In addition, I have set up ‘beetle boxes’ in two ancient woodland sites. These aim to provide additional habitat for species of beetle that thrive on the unique conditions found inside the basal rot holes of ancient trees. After one year, the beetle boxes have been found to host 25 species of saproxylic beetle, with several of these known to specifically prefer ancient tree hollows. These promising results provide an encouraging starting point for future investigations into deadwood habitat supplementation in vulnerable forests.
Alexander, K. N. (2002). The Invertebrates of Living & Decaying Timber in Britain and Ireland: A Provisional Annotated Checklist. English Nature.
The Woodland Trust. (2021). State of the UK’s Woods and Trees 2021. https://www.woodlandtrust.org.uk/state-of-uk-woods-and-trees/