Why Assessing the Effectiveness of Protected Areas Is More Difficult Than It Seems

Source: French to English Tester   Published on: 2026-04-26

Source: The Conversation – in French– By Paul Rouveyrol, Ecologist, expert in the evaluation of protected area policies, National Museum of Natural History (MNHN)

It is not enough to create protected areas: it is also necessary to ensure that they have a positive effect on biodiversity. How can this monitoring be carried out? The difficulties are methodological: how can we be certain that what we observe is indeed, and only, related to the creation of the protected area? And how can we compensate for the absence of monitoring data from several decades ago? Elements of an answer.

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As early as 2020, France committed internationally to cover30% of its territory by protected areas, which was one of the objectives set by international negotiations on biodiversity. Today, the target figure has been reached: protected areas represented, in 2025,33.5% of the territoryFrench land and maritime.

However, beyond the covered area, international texts explicitly require that these areas be“effectively preserved and managed”, understand: that protected areas are truly protected. Indeed, designating a space is not enough to guarantee that it will have positive effects on biodiversity.

But how to evaluate the effectiveness of protected areas? Intuitively, one might be tempted to compare the state of ecosystems inside protected areas with that of the rest of the territory. If the protected areas are “effective”, then we can expect this state to be better within them.

The problem is that one can certainly consider that a protected area is only effective if this difference exists, but the converse is not true: protected areas are never allocated at random. Statistical methods based on monitoring protected and unprotected areas over time (control sites) allow bypassing this limitation, but they are not perfect either. It is therefore urgent to multiply approaches to ensure the robustness of monitoring.

When comparing with unprotected areas is not enough

Comparing the interior and exterior of protected areas is necessary but not sufficient. This may seem paradoxical, but there are several explanations for this:

• On the one hand, protected areas are generally created to allow the conservation of a natural heritage considered remarkable, consequently endowed with richer biodiversity or sheltering more rare species than the rest of the territory. It is therefore logical that, from their creation, and even before they have had an effect, the ecosystems thrive better there than elsewhere.

• On the other hand, the creation of a protected area often generates conflicts with certain categories of stakeholders, particularly economic ones, who expect their activities to be restricted there. These difficulties in acceptance result in avoiding, during the establishment of protected areas, zones with a high level of human activities. It has beendemonstratedthat protected areas were more present in remote or sparsely populated areas, such as mountainous regions.

This second bias also results in less degraded biodiversity within protected areas from the moment of their creation, reinforcing the difficulty in drawing conclusions from a simple comparison inside/outside.

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Also to read:
To preserve biodiversity, let us not abandon the unprotected areas

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What the evolution of habitats says about the effectiveness of protected areas

How to overcome biases related to the location of protected areas when evaluating their effectiveness? In experimental sciences, this difficulty is addressed with a specific design, called BACI, an acronym forBefore After Control Impact(that is in French: “before after treated control”)

The principle is simple: it is not about comparing the current state of a protected site with that of an unprotected site, but about monitoring the evolution over time of each of these two sites, and this, since the creation of the protected area.

Thus, a protected site will be considered “effective” if its evolution since its creation is more favorable than that of the unprotected site, called the “control.” Since it would make no sense to compare, for example, a protected forest area with a control site in a cereal plain, care is also taken that the monitored protected area and the control zone are as similar as possible. The objective is to limit the impact of influencing factors other than the creation and management of the protected area.

By applying this model to the Natura 2000 network in France, it has been shown that the evolution of populations of common birds in agricultural environments wasmore favorable inside the network than outside.

We already knew, thanks to aprevious study, that these populations were more abundant in the network. As previously explained, this mainly showed that the Natura 2000 sites had been located in areas richer in birds than average. This is, moreover, an essential prerequisite for these sites to be able to play a role in the conservation of these species.

It is interesting to note that the study using the BACI approach for the Natura 2000 network did not conclude that bird populations linked to agricultural environments increased within the sites labeled Natura 2000. It is only when comparing with the rest of the territory, where the decline of these same populations wasdizzying over the period, which the analysis concluded to have an “effectiveness” of the Natura 2000 sites.

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Also to read:
Protection of biodiversity: a look back at the evolution of “protected areas” around the world

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Know how to cross-check sources and take a step back on the figures

However, even when it uses BACI, this type of study is not without its limitations. Often, there is no data going far enough back in time to accurately describe the evolution of biodiversity. Even the data used to select the “control” sites, which must be similar to the protected sites at the time of their creation, are too fragmentary and lack precision.

However, French protected areas are, for the most part, very old. They often existfor several decades, sometimes a hundred years, which further complicates matters.

Under these conditions, it is difficult to establish a true BACI:

• firstly because the “before” image rarely dates back to the creation date of the protected area and therefore does not completely escape localization biases,

• but also because the “witness” is only vaguely similar to the protected area, and that, at a time too recent, not necessarily at its creation.

These difficulties are hard to overcome. In most cases, the absence of historical environmental data cannot be compensated for.

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Also to read:
The classified “natural” sites: going beyond the idea of a nature museum?

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Are these imperfect results therefore useless? No. Certainly, they must be interpreted with caution, but they provide valuable information, for example on a more marked effect in a certain type of natural environment or protected area. Thus, the effect of Natura 2000 demonstrated on birds linked to agricultural environments was not observed on forest species, which may indicate insufficient management effort in these environments.

They therefore constitute only a part of the evaluation and can usefully be complemented with other approaches, notably qualitative ones. Still within the Natura 2000 network, in a counterintuitive way, it has been measured that the more the sites were initially subjected to human pressures likely to degrade them,the less significant were the resources put in place regarding these pressures.

This result does not fully predict the effect of the policy, but it provides information on what might explain why it is not as significant as expected. Beyond the question of the produced effect, it is thus possible to assess the relevance of management efforts carried out in protected areas.

Evaluating the effectiveness of protected areas is therefore difficult. This task must contend with the full complexity of ecosystems, as well as that of the societies with which they interact. Nevertheless, it is an essential job.

Rather than relying on a single, necessarily limited, model, everything would be gained by multiplying approaches, questions, data, and scientific disciplines. It is by building up a body of evidence by cross-referencing sources that one can draw the most accurate, but also the most useful, picture of the effect protected areas have on biodiversity.

Paul Rouveyrol does not work for, advise, own shares in, or receive funds from any organization that could benefit from this article, and has declared no other affiliation than his research organization.

–ref. Why evaluating the effectiveness of protected areas is more difficult than it seems –https://theconversation.com/why-evaluating-the-effectiveness-of-protected-areas-is-more-difficult-than-it-seems-278818