Biological invasions in ancient woodlands

Overview

Biological invasions by alien species are regarded as one of the top five direct drivers (together with habitat destruction, over-exploitation, climate change and pollution) of recent global biodiversity loss, according to the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services. The impacts of alien species are linked to the declining conservation status of threatened species, and their accelerated spread into protected and biodiverse habitats are a major global concern. Ancient woodlands are the richest and most complex terrestrial habitat in the UK, home to more threatened species than any other. However, encroachment and establishment of invasive alien species pose additional challenges to the unique flora and fauna, as well as ecosystem function, of ancient woodlands.

Ancient woodlands are areas of woodland that have persisted since 1600 in England and Wales, and 1750 in Scotland. Only 2.5% of the UK land is covered in ancient woodland. Ancient woodlands are valued as being among the most complex and diverse of ecosystems, and as having plants and animals that do not occur in woodlands of recent origin. Ancient woodlands are often isolated sites, having a characteristic flora which do not easily migrate between woodlands. Bluebells, Hyacinthoides non-scripta, are an iconic feature of UK ancient woodlands, currently under threat from hybridisation with non-native bluebells, Hyacinthoides hispanica. Other indicator species, including birds such as hawfinch and wood warbler, and understory plants such as herb paris, often feature in ancient woodland sites. As well as monitoring the status of indicator species within ancient woodlands, the regeneration of ancient woodland trees is also important in maintaining longevity of these ecosystems.

Up to 70% of ancient woodland has been lost or damaged due to conifer plantations, overgrazing and the spread of invasive species. Currently, 1207 ancient woodlands remain under threat in Britain. Himalayan balsam, Impatiens glandulifera, is an annual plant native to the western Himalayas, prolific along waterways but now thriving in woodland areas. It is listed under Schedule 9 of the Wildlife and Countryside Act 1981, therefore it is an offence to plant or otherwise cause this species to grow in the wild. Himalayan balsam, by forming tall, dense colonies, shades out and results in the extirpation of native vegetation. This species is notoriously difficult to manage, particularly if an adjacent water way provides a constant input of viable seeds.

Although much research has been done on the impacts of Himalayan balsam within riparian habitats, little is known of its impacts in woodlands, particularly ancient woodland sites. Alongside this, managing this invasive alien species in protected habitats such as ancient woodlands are challenging, as traditional control methods (for e.g. chemical and mechanical), may not be feasible due to indirect impacts on threatened and specialist native species.

In the North East of England, The Woodland Trust have a protected 100Ha ancient woodland site Pontburn Wood situated alongside an invaded river, the River Derwent. Establishment of Himalayan balsam in the adjacent woodland has increased exponentially over the last 5 years, with further encroachment apparent.
The overall aim of this project is to understand the impact of Himalayan balsam on ancient woodland biodiversity and determine an effective management strategy to control and mitigate further invasion.
Specifically, the project objectives are to:
1) Undertake a baseline assessment of the impacts of Himalayan balsam on ancient woodland flora both on above-ground vegetation and below-ground soil seed bank,
2) Determine how Himalayan balsam impacts native tree sapling growth and establishment due to potential preferential herbivory of native vegetation and competition dynamics of early growing Himalayan balsam seedlings,
3) Undertake an assessment of effective management strategies for reducing the abundance of Himalayan balsam in the woodland, and
4) Assess the viability of mitigation methods for reducing further colonisation from the river

Methodology

The project will be carried out in collaboration with the Woodland Trust. Therefore, the student will be working in partnership with colleagues from the Woodland Trust when designing and implementing management protocols for ancient woodlands. This partnership will also be working to establish a long-term monitoring regime which will extend beyond the PhD.

Methods:
1) The student will undertake a full site assessment, mapping key topographical features of the woodland and catalogue fauna and flora present at the site using botanical survey methodology and camera traps. Variation in environmental conditions and native community composition will be compared across the gradient of invasion.
2) In order to understand the potential for natural forest regeneration from the seed bank, the student will conduct a germination trial. Soil cores will be taken across the invasion gradient in the woodland and germinated in polytunnels at Newcastle University.
3) To assess whether mammalian herbivores preferentially graze native vegetation, thus facilitating invasion success of Himalayan balsam, fenced exclusion experiments will be set up and seasonally monitored.
4) A variety of management options will be employed to determine the best control protocol for managing Himalayan balsam invasion in ancient woodlands. Management options will include: exclosures will be installed to assess grazing control; Hand pulling, an effective but time-consuming strategy, will be trialled; soil saturation in spring, known to reduce Himalayan abundance in along river banks, will be administered.
5) Invasion pathways will also be assessed in order to create a risk management protocol and inform mitigation from further invasion.

Project Timeline

Year 1

Literature review as a topic model to gain understanding of key themes within invasions of ancient woodlands (months1-4); prepping for fieldwork, mapping site features and installing enclosures/exclosures, soil core collection (months 5-6); spring community survey (month 7); implement informed management strategies (months 8-10); summer community survey (months 11-12)

Year 2

Data management and modelling method assessment (months 13-16); soil core collection, set up germination experiment months (months 17-18); spring community assessment (month 19); implement informed management strategies (months 20-22); summer community survey (months 23-24)

Year 3

Data collection from germination experiment (Months 25); Data analyses, writing up results (months 26-30); Writing thesis chapters, attendance at an international conference (months 31-36)

Year 3.5

Writing publications and thesis submission (months 37-42)

Training
& Skills

The student will receive training from an interdisciplinary supervisory team, particularly in some of the key NERC most wanted skills:
*Fieldwork: the large fieldwork element of this PhD means the student will be exposed to a variety of sampling and experimental techniques in the field
*Taxonomic Identification: to create an inventory of fauna and flora the student will receive species ID training, particularly botanical.
*Data management and modelling: the student will be part of the Modelling, Evidence and Policy Research group at Newcastle and as such will have the opportunity to learn an array of modelling methods best suited to their data.
*Translating research into practice: As the output of this PhD will be integral to management of invasive species, the student will receive training in science communication to multiple audiences (e.g. policy makers, non-governmental organisations (NGOs) and the wider public).

The student will also participate in IAPETUS training and events. A training budget is included for any external training required by the student.

References & further reading

Ancient Woodlands: Modern Threats doi: 10.1111/j.1469-8137.2008.02579.x
Scientists’ warning on invasive alien species dx.doi.org/10.1111/brv.12627

Further Information

For further information please contact Dr Zarah Pattison, zarah.pattison@newcastle.ac.uk

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