DECISION TREE FOR CROPPED HABITATS
Gavin Siriwardena
British Trust for Ornithology
Introduction
The aim of this decision tree is to provide a guide to the process for reaching an evidence-based decision on the feasibility of including cropped habitats within an SPA boundary. It considers only species that have been identified as using cropped habitats elsewhere in the SPA framework and “sites” (population centres) that have been identified as important for the species’ populations (i.e. supporting more than 1% of the UK population or more than 20,000 individuals). This is important because SPAs are a key conservation tool for species whose UK populations are (a) internationally important at the European level and (b) found in definable concentrations each comprising more than 1% of the total population, yet current SPA boundaries fail to include the full range of UK habitats used by some such species. The habitats that are not included are generally cropped in some way, i.e. managed for some commercial product (arable crops, livestock or forestry). This produces several challenges for site-based conservation, including potential conflicts with commercial land managers, whose priorities may conflict with conservation goals, and the difficulty inherent in defining site boundaries in what is essentially the “matrix”, or background, habitat, which explain why these habitats have been under-represented in the SPA suite to date. Nevertheless, there is a real problem for species like wintering geese, whose roost sites tend to be more definable and designated as SPAs, but whose feeding sites in cropped habitats are equally (if not more) important for their persistence, yet are mostly not included within SPA boundaries. The general issues that need to be considered in making decisions about including cropped habitats in SPAs are reasonably clear and species-specific summaries of the importance of doing so have been collated by Stroud et al., Baker & Stroud and Stroud & Baker. However, there is a gap in terms of guidance for policy-makers as to how to interpret the great depth of information and how to reach consistent decisions across the wide range of species and sites involved. The decision tree presented here aims to fill this gap by providing a simple guide to aid evidence-based decision-making that is applicable to all sites and species.
The starting point for this decision tree is that the focal species has been identified as using cropped habitats and suitable for site-based protection. It is also assumed that a candidate set of SPA locations have been identified from pre-existing survey data or observations, each meeting the standard guidelines for SPA designation (e.g. more than 1% of the UK population is found locally: These sites may or may not already have been designated as SPAs for the species, so the issues of interest relate both to the extent to which the species uses cropped habitats as well as land within existing local SPA boundaries and to whether new SPAs consisting wholly or partly of cropped land should be designated. The tree should be considered in the context of the terms-of-reference framework for SPAs produced by JNCC.
The legal requirement for SPA designation rests entirely on data on population size and distribution, whereas the practicalities of successful conservation management in the context of limited resources often require factors such as economics and population health to be taken in to account. For example, species with increasing populations are less in need of active management than declining or threatened ones and voluntary schemes can be more effective for long-term management than obligatory, “top-down” policy measures. Increasing populations are also likely to need ever-increasing areas of habitat. Consideration of these issues has been commonplace in previous SPA designation processes, in practice, and is still likely to be so in the future. However, European Court of Justice judgements specifically preclude consideration of such factors in the designation of SPAs for a species, so they cannot be included here. An important part of the science of habitat management for conservation is the design of effective, practically feasible (and not just theoretically appropriate) mechanisms. For SPA species, SPA designation is clearly an appropriate part of the “toolkit”, but it is recommended that they are used advisedly, carefully considering the context in which they would work.
Notes on the decision tree
Numbers and letters index boxes in the decision tree (Fig. 1), divided in to Questions (Decisions), Actions and Outcomes. The tree begins with Action A, in the top left corner.
QUESTIONS (DECISIONS)
1. Does the SPA network provide all the resources needed by a sufficient proportion of the national population, e.g. as measured by the SPI?
This might actually duplicate part of the Framework, but is included for completeness, asking whether extra SPA designation is required, considering the indications of the Site Provision Index for the species. Additional protection might then be achieved via additional sites or via extension of the habitat and geographical scope of existing SPAs. It is important to note that “sufficient” here is a subjective, policy decision – either within the SPA framework or elsewhere – there is no scientific basis for it unless an over-arching (also subjective) decision is made regarding desired population growth rates or security from extinction risk, for example.
It may not be necessary to know exactly what resources a species finds in a cropped habitat: protecting a species’ habitat could be sufficient, regardless of whether the value of that habitat is actually known. However, this is critical information if measures are needed to mitigate habitat impacts or if the value of the habitat for the species in practice needs to be assessed to make management or policy decisions. The substrate might be less important for the value of a roosting site than for a foraging site, for example, thus affecting the changes in management that might be acceptable while preserving site value, or a given cropped habitat might be preferred, but not essential, i.e. the resources provided there might also be obtainable elsewhere with a negligible (or a measurable, acceptable) change in carrying capacity. Again, this is critical information to inform management decisions.
If insufficient data are available to answer this question, there is a clear need for further research before decisions as the appropriateness of following the route of SPA designation or expansion can be made.
2. Does the SPA boundary encompass all the resources needed by a sufficient proportion of the local population?
For an individual site, the existing or proposed SPA designation may already protect enough of the cropped habitats used by the focal species, either deliberately or by accident (e.g. if protection is focused on roost sites, but most feeding happens to take place in the same area). If so, no extension of the area being considered is necessary. Again, “sufficient” here reflects a subjective, policy decision.
3. Does the proposed boundary include cropped habitat?
For new sites, specific consideration of cropped habitats may not be necessary, even for acknowledged CHIP species.
4. Are the resources outside the boundary significant (or negligible)*?
It is likely that, in some cases, there will be records of the focal species at a given site that are in cropped habitats, but that these are unlikely to reflect a significant influence of cropped habitat on the local population. Alternatively, the legislative and practical difficulties inherent in protecting the cropped habitat for the species concerned might outweigh the population benefits. In such cases, this use of cropped habitat can be treated as negligible. In practice, this sort of decision will be made commonly, but, again, there is no way to define “significant” or “negligible” on a scientific basis: thresholds can only be set as policy decisions. Note that if “negligible” just means “undetectable”, it is important to remember that detectability depends on data quality. Nevertheless, guidelines could be more sophisticated, for example considering different (lower) threshold levels if the cropped habitat is used all year, as opposed to in one season only, for resident species.
5. Is the important habitat outside the boundary cropped?
Just because the species is a CHIP one and has requirements outside an existing SPA boundary, it does not necessarily mean that those are on cropped land. If they are not (at least locally), the decision process can again ignore cropped habitats.
6. Does the cropped habitat fulfil an irreplaceable function of the ecological requirements of the species in question (or is it a top-up of existing semi-natural habitat)?
This question is designed to tease out the information important for informed management decisions. If the use of cropped habitat is basically an overspill from existing semi-natural habitat that is not managed commercially, a solution that is more sustainable in the long term and easier logistically might be to restore, to enhance or to extend the semi-natural habitat that is present already, where it is clear that it would fulfil the same ecological requirements of the species in question as the cropped habitat it currently uses.
7. Can semi-natural habitat be enhanced or increased to replace the resources provided by cropped habitats?
Following on from (6), a more sustainable solution to supplying the resources provided by the cropped habitat might be to promote semi-natural habitats, if possible.
8. Can the precise cropped areas being used be defined effectively within the matrix in the long term (i.e. from year to year)?
Whether particular parts of a cropped habitat matrix can be identified as being valuable in the long term is critical for the logistics of designing site protection. It might be feasible to protect defined landscape units (e.g. fields) with particular, controlled management, while other habitats are, by their nature, rotational or successional and so not associated with particular locations in the long term. These would require different approaches for protection. Whether habitats can be defined will depend both on the physical features of the habitat and on bird behavioural factors such as site fidelity: areas might be identified solely through proximity to the existing SPA, in combination with a broad habitat definition (e.g. arable “farmland”) and species-specific data on key parameters such as home range size or distances travelled from roosts, or through fine-scale habitat features such as vegetation composition in grassland.
9. Is this because insufficient data on bird use of areas around SPAs are available?
An obvious reason why precise areas might not be definable would be a lack of appropriate data. Systematic surveys of cropped areas in and around existing or potential SPAs throughout the season(s) of interest and over multiple years would provide the ideal information, but standardized and complete records of flock locations, for example, would probably be adequate.
10. Can a “management zone” be defined around which the key cropped habitats rotate?
If individual, stable landscape units for management cannot be identified, the next step is to identify, if possible, a larger area within which the habitats that are important in any given year are always found. This might be a region with suitable land-use practices or an area delimited with reference to known movement distances, for example. As with attempts to identify precise areas to protect, defining a wider area will depend on the behaviour of the species of interest, specifically factors such as site fidelity. Within such a “management zone”, it would be most appropriate to consider conditional protection or compensation for impacts (i.e. only if landscape units are used in a given year or season) or to apply protective measures or to award compensation based on probabilities of use by the target species (based on research evidence). However, such measures are not permitted under SPA rules, so designation of discontinuous SPA land parcels might be more appropriate, i.e. identifying the suitable habitat within the landscape and designating only broadly or potentially suitable areas, e.g. fields that might provide suitable habitat. If none of this is feasible, the answer to the question has to be “no”, leading to Outcome (vii).
11. Could permanent sub-areas be managed easily to control/focus the species’ use of themanagement zone?
It could be advantageous to concentrate a species’ use of the broader management zone into particular areas, which could, for example, be sown with sacrificial crops and be managed as reserves. This could secure habitat quality indefinitely and prevent conflicts with land managers.
12. Can the management zone feasibly be managed as an additional part of the SPA?
SPAs vary considerably in size, but very large terrestrial areas, for example, are likely to be impractical to manage, which could be a key consideration in determining whether they are a feasible means to protect a species in the local context. Although there is no legislative upper limit to SPA size, feasibility must be affected in practice by factors such as numbers of landowners and diversity of land-use, which will affect whether the area can be treated as a single unit for management effectively.
ACTIONS
A. The species uses cropped habitats
This is the link to the framework and the rest of the SPA decision process
B. Consider individual focal actual or potential SPA sites with known or proposed boundaries
From here on, actual or virtual SPA boundaries are considered. In other words, for existing SPAs, their existing boundaries and the potential for extension are considered, while for potential new sites, a particular proposed boundary and whether that might need to be extended is considered. In this context, actual and virtual SPAs are the areas meeting the standard rules for SPA designation ( Where appropriate, separate decision pathways are provided for the contexts of new and existing SPAs.
C. Re-draw boundary to include this additional habitat
This simply reflects the adjustment of incorrectly drawn boundaries for SPAs that do not need to consider cropped areas.
D. Conduct surveys to identify areas used
Some survey data must exist for the decision process to reach this stage, but more might be required to make a complete inventory of the use of relevant habitats so that areas for protection can be defined accurately. A key caveat, however, is that decisions should not necessarily be held hostage to data quality: conservation decisions need to be made using the best available data. If data quality is poor, decisions should still be made using the data, perhaps using the precautionary principle such that decisions err on the side of providing more protection than might be needed. However, in such cases it is also critical that data inadequacy is not glossed over and that efforts to collect better information continue.
E. Define cropped area for protection
This definition should make use of appropriate data on birds and habitats, as used in reaching Decision (8). The area should then be considered as an addition to the existing SPA or the boundary for a proposed new one.
F. Consider creating/extending natural habitat and protecting by extending SPA
Restored or enhanced semi-natural habitats (perhaps successional habitats “arrested” by management at the stage where they have most value for the species of interest) could be more sustainable in the long term than commercially cropped habitats for logistical reasons. In addition, they would support the Stage 2 SPA selection guideline to designate “more natural” areas preferentially, where possible. They would also provide clearly definable habitat features that would facilitate SPA (re-)designation to cover the smallest possible areas.
I. Define the “management zone”
This definition needs to make use of the data used to make Decision (10).
G. Consider using such managed sub-areas
This process would probably form a feasibility study and consultation as to whether the necessary management could be provided in practice.
H. If successful, conduct the necessary management of the sub-areas
This is then simply the result of the consultation under Action (G), applied in the field.
J. Proceed considering the whole management zone as a potential SPA, noting that conditional protection of (discontinuous) land parcels might be more effective than firm boundaries
Given knowledge that bird use of a given habitat type is not readily predictable, such that only that use itself defines the habitat, protection conditional on bird use or on particular field contents in rotational systems, might be desirable. However, if this is not allowed within SPA rules, protection might instead be applied to discontinuous parts of the “management zone” on the basis of the habitat content there. The SPA for a given local population would then consist of multiple, discontinuous patches within a larger area. If none of this is feasible, the answers to Decisions (10) or (12) should lead to Outcome (vii).
OUTCOMES
i No additional protection necessary
The national SPA network is already sufficient for the focal species, as assessed by currently available data.
ii No additional protection necessary – seek to protect other sites elsewhere