We developed a methodology to assess
the habitat quality of field margins in a set of more intensively managed farms
in Ireland. Overall, we found that over half of the field margins surveyed had
low or very low levels of habitat quality.
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| Field margin with very low habitat quality (dominated by negative indicator species) |
Highlights
- Quality of field margins on intensively managed farms was assessed by plant indicator species that indicated high to low quality of plant diversity in field margins.
- Positive indicator species occurred in 77% of margins and had an average cover of 10%.
- Negative indicator species occurred in 93% of margins with 55% cover.
- We developed an approach to assess the quality of field margins; over half of the margins surveyed did not attain an ‘acceptable’ quality level.
- There is a need to improve the habitat quality of existing field margins.
Introduction
Field margins consist of strips of
herbaceous vegetation that are typically located between field boundary
features such as hedgerows and the main grassland or arable field. However,
little is known about their extent or ecological quality on intensively managed
farmland in Ireland. This lack of knowledge can only be addressed through the
application of a standardised assessment methodology, which we developed and
implemented in this 2022 study by Julie Larkin and colleagues.
Research
approach
We surveyed 92 intensively managed farms across three farming enterprises (tillage, beef and dairy) in Ireland to estimate the percentage of EFA and other farmland habitats occurring within these farms. The *median* farm habitat area was 5% for tillage, 6% for intensive beef and 6.55% for intensive dairy (see a previous blog post, and Fig. 1 from the supplementary information in Larkin et al. 2019). Linear features such as hedgerows, field margins and drainage ditches accounted for 43% of the total area of wildlife habitat surveyed. Here, we look more closely at the habitat quality of the field margins on this sample of farms.
A survey of field margins was conducted
on 92 intensively managed farms, across three enterprise types (arable, beef
and dairy farms) in Ireland. We described the botanical composition and
assessed the habitat quality of field margins based on threshold levels of the
percentage cover of positive, neutral and negative botanical indicator
species) that are predominantly informed by existing EU accepted methods for
vegetation classification.
Results & Discussion
We developed a standardised methodology to assess the conservation value of field margins. This methodology depended on the indicator status of species (positive, neutral, negative), and the proportions of these categories measure in field margins (Table 1).
A fair comment is that the threshold
values for percentage cover appear somewhat arbitrary. However, this is the
case for many such approaches, including habitat reporting for the Habitats
Directive and many other vegetation assessments that we model this approach on.
This specific approach is not a biodiversity inventory (although the
species-level data underpin the methodology); instead we are aiming to develop
a (rapid) assessment of overall field margin quality. When we apply these same
thresholds across field margins we get a spectrum of quality (which shows that
our method can differentiate from high to low quality), and can detect
differences among farm enterprises (Fig. 1).
Positive indicator species occurred in 77% of margins and had an average cover of 10%. There was a high incidence of negative indicator species, occurring in 93% of margins with an average cover of 55%. Using our quality appraisal system, 15% of field margins were of high or very high quality, and the majority (56%) were of low or very low quality (Fig. 1).
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| Fig. 1: The distribution of sampled field margins across each quality grade (very high, high, acceptable, low, very low) across the three enterprises (arable, beef and dairy). |
Compared to either arable or dairy farms, beef farms had a greater percentage of higher quality margins, higher species richness and greater percentage of positive indicator species (Fig. 2, Table 2).
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| Fig. 2: The distribution of sampled field margins across each quality grade (very high, high, acceptable, low, very low) for each of the three enterprises (arable (white), beef (light grey) and dairy (dark grey)). |
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| Field margin area with very high habitat quality. |
Retaining areas of high quality
farmland habitat, and enhancing those areas that have become ecologically
degraded, will be key to achieving the Common Agricultural Policy (CAP)
objective of protecting landscapes and biodiversity. However, the
implementation of appropriate management decisions requires effective
evaluation of the current ecological condition of these habitats. We show that
the majority of field margins in more intensively managed systems in Ireland are
in a botanically impoverished condition. Although this study demonstrated low
abundance of positive indicator species, their frequency of occurrence was
relatively high
Our standardised field margin quality
assessment technique may offer an appropriate method of tracking change in
habitat quality in response to conservation actions to improve habitat quality.
A results-based approach could be considered that would link farmers’ payments
for biodiversity objectives to the quality of habitats; in this case, the
higher the habitat quality of a field margin, the higher the payment received.
Such an approach would better incentivise the improvement of low quality
habitats, and also better reward the supply of higher quality habitats.
References
Larkin, J., Sheridan, H., Finn,
J.A. and Denniston, H., 2019. Semi-natural
habitats and Ecological Focus Areas on cereal, beef and dairy farms in Ireland. Land Use Policy, 88: p.104096.
Larkin et al. 2022. Field
margin botanical diversity, composition and quality on intensively managed
farming systems. Irish Journal of Agricultural and Food Research.
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