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Photos & text

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Photos & texts by Sabina Burrascano is licensed under a Creative Commons Attribution-Noncommercial-No Derivative Works 2.5 Italy License.
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How to assess the conservation status of semi-natural habitats?

The conservation status assessment is one of the most controversial processes that derive from the Habitats Directive and this strongly hampers monitoring and conservation actions.

For a habitat, favourable conservation status should mean that:

  • natural range and areas within that range are stable or increasing;
  • the specific structure and functions which are necessary for its long-term maintenance exist and are likely to continue to exist,
  • the conservation status of its typical species is favourable.

However, many of the concepts included in these criteria are vague and can be applied through a wide range of approaches that are often not consistent. For instance, univocal definitions of “natural range”, “specific structure and functions” should be given in order for these criteria to be read consistently troughout the EU member states and across the broad range of stakeholders that may read and interpret these words.

The interpretation of these concepts is particularly complex when looking at semi-natural habitats, since these, by definition, do not have a natural range, but rather a range that depends on human activities interacting with vegetation dynamics. In fact a semi-natural grassland maintained by grazing livestock has a range depending on the quantity and quality of farming activities and its specific structure and functions also depend on management intensity and objectives.

foto-retro

In a recent study, my colleagues and I contributed to the debate on this topic by proposing to use historical vegetation data to assess the conservation status of semi-natural habitats. Firstly, we quantified the degree of compositional change occurred between the historical sampling and a recent sampling. Since the historical sampling could be assumed as in favourable condition, we used the measure of compositional change as an inverse proxy of conservation status.

Then we quantified ten potential indicators, encompassing proxies of species composition (e.g. number of habitat diagnostic species, relative cover of steppic species), habitat structure/function (e.g. relative cover of woody and graminoid species, ratio between toxic and non-toxic species), and landscape patterns (edge complexity of the polygon, perimeter shared with woody communities).

Finally, we tested these potential indicators against the degree of compositional change.

The two most relevant indicators were the number of diagnostic species and the relative cover of woody species. By combining these two parameters we assessed the conservation status of 132 locations and found out that this assessment was in good agreement with the number of species of conservation concern.

fig-4

We know we are still far from an agreement on standardised methodologies. However, we hope our attempt of looking in the past to drive future actions can be of use in the path towards this goal.

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