Decline of Oak

Oak trees have long had a reputation for supporting a lot of other species but until recently we had no idea just how many and what those species were. Recent work has listed 2300 species associated with oak, of which 320 are only found on oak and a further 229 species are rarely found on species other than oak.

Threats to oak Oak trees are currently at risk from a range of pests and pathogens including Acute Oak Decline, Chronic Oak Decline, Oak Processionary Moth and powdery mildews. In addition, a changing climate is thought to increase the susceptibility of oak trees to pests and diseases.

Not all tree species are equal in terms of the biodiversity they support and how they impact on the functioning of the woodland in terms of shade and nutrient cycling. If oak trees decline in abundance this will impact on associated biodiversity and woodland functioning as other tree species may support different species and provide different ecosystem services. Thus, it is important to know what biodiversity and functions are supported by oak, in order to enable us to assess the impact of declines in oak tree on the wider environment.

Oak biodiversity 

Protecting Oak Ecosystems (PuRpOsE) is a multi-disciplinary team, lead by the University of Reading to PRotect Oak Ecosystems through understanding and forecasting causes and consequences, and adaptation management for future climate projections. This webpage documents the results from Workpackage 3 of this project on Impacts of oak decline on biodiversity and ecosystem function/services and mitigation options.

Oak biodiversity Work led by Dr Ruth Mitchell has used existing data sources to collate and produce the most comprehensive list yet of all species known to use oak trees (Quercus petraea and Q. robur) in the UK. In total 2300 species were listed, this consisted of 38 bird species, 229 bryophytes, 108 fungi, 1178 invertebrates, 716 lichens and 31 mammals. This list does not include any of the bacteria and other micro-organisms that are associated with oak so the real number of species that use oak trees, although unknown, is much greater.

Of these 2300 species, 326 were obligate species (species only found on oak) consisting of 57 fungi, 257 invertebrates and 12 lichens. There were 229 species classified as highly associated with oak (rarely found on species other than oak) consisting of 51 fungi, 104 invertebrates and 74 lichens. These 555 species were considered most at risk from a decline in oak health as they don’t or rarely use other tree species.

Information about all these 2300 species has been collated together in an Excel file called OakEcol which can be downloaded to aid woodland managers conserve oak-associated biodiversity.

Replacement tree species and management options

Although a significant loss of oak is not currently predicted imminently, this could occur in the future with combination of climate change and current or future diseases. It may therefore be desirable to encourage a greater diversity of other tree species to support oak-associated biodiversity. Given as the greatest diversity of oak-associated species is supported by mature and veteran trees it is important to start managing woods for the long-term and thinking now about tree species composition for 200 years time. If oak abundance were to significantly decline due to either climate change or disease it would be those species that are most reliant on oak, that would be at risk of declining in abundance. One method to mitigate such impacts is to establish other tree species that will support oak associated biodiversity. For this to occur we need to know which other tree species might be the most suitable to support oak-associated biodiversity.

Information on each of the 2300 oak-associated species was collated to find out if they will or will not use each of 30 other tree species. This information is available in the Excel file OakEcol. The information made available in OakEcol can be used to guide management to conserve oak-associated biodiversity. Using site specific species lists it is possible to refine the list of potentially suitable tree species to support the oak-associated species known to be present at the site and identify management options.

OakEcol OakEcol is a database containing information on the 2300 oak-associated species, their ecology, and if they will use 30 other tree species.The full database was originally developed as a Microsoft office Access database and the tables from this database are now held as separate csv files by EIDC together with detailed metadata. The file here is a simplified Excel file to provide more immediate access to the data in a more familar format for woodland managers.  Instructions on how to use OakEcol are available here.

Case studies

Thirty oak woodland sites across the UK were visited to assess how they could be managed to maximize support for oak associated biodiversity. Firstly, management practices that would maintain oak abundance into the future were identified. Secondly, other tree species that would establish at the site and support the maximum number of oak associated species possible were identified. Each of the sites has been written up as a short case study which can be downloaded on the links below. These case studies consider how best to maintain native woodland containing oak given the current condition of the woodland, other characteristics and constraints of the sites and the future climate driven pressures. However, it is stressed that the suggestions for alternative tree species given in Annex A in each case study are designed to demonstrate how OakEcol can be used to consider management for species that would be affected by a decline in oak. We have not assessed the impact of these suggestions on the wider ecology of the woodland, or on other species present, nor have we considered how this fits into the wider balance of threats and risks to oak woodland. These wider issues should be considered in developing comprehensive resilience approaches. A document detailing the methodology used to create these case studies is available here.

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