Drawing on a large data set from previous observational studies worldwide, new research indicates that protected fragments of forest can be successful for bird conservation, however, their size is the most important factor – rather than the level of protection. Additionally, protection need not be limited to pristine areas, as ‘moderate protection’ – with some human activity permitted – is also worthwhile in areas over 175 hectares.
Forests are home to 80% of terrestrial biodiversity, yet they are under threat. Increasingly fragmented, up to 70% of forest area worldwide is estimated to be within a kilometre of forest edge. Such habitat loss is a major driver of biodiversity loss, and protected areas (PAs) are increasingly being implemented for conservation. PA coverage has almost doubled over the last 30 years – from 8% of terrestrial land surface in 1990 to 15% in 2020 – although this is short of the Aichi Convention on Biological Diversity target of 17%.
The efficacy of protected areas in landscapes under pressure from human activities remains unclear, however, as most studies have focused on relatively large, pristine PAs where little or no anthropogenic activity is permitted. Many PAs are in fact small and isolated, embedded in fragmented landscapes, and not subject to strict protection. The International Union for Conservation of Nature (IUCN) recognises six categories of PA, four of which are strictly protected and managed solely for ecosystem and species conservation. PAs within ‘culturally modified landscapes’ – those that have been influenced by human activities for many years but, despite this, form semi-natural environments – and PAs that are managed primarily for the sustainable use of natural resources, are said to be under moderate protection – accounting for 42% of the global area allocated to PAs.
Through meta-analysis, researchers aimed to assess how fragment size and protection status were associated with bird-species abundance in 46 sites worldwide. Systematically searching available literature, they compiled a data set with over 60 000 survey records of nearly 2 000 bird species in 741 fragments of mature forest and savanna woodland. The fragments ranged in size from under 0.1 hectares (ha) to over 10 000 ha, mostly adjoining land under anthropogenic use. They used modelling to analyse the relationship between probability of bird occurrence, size and protection status, as well as other variables (such as surrounding land use, bird type and conservation status).
Birds were more frequently found in both moderate and strict PAs than in unprotected areas, but the difference in overall frequency only became significant in larger PAs. Frequency increased with fragment size, regardless of which level of protection. The effect of strict protection was significant for fragments of 50 ha and above; the effect of moderate protection, compared to no protection, was only significant in fragments sized over 175 ha.
The researchers assume that competition for resources limits the carrying capacity of a small area (the number of species it can sustain), and small fragments contain a higher proportion of species that are generalists and, therefore, less reliant on protective measures. Forest-dependent birds were particularly sensitive to fragment size; their probability of occurrence declined strongly with decreasing fragment size. In addition, their response to strict protection was more pronounced than for birds that did not rely on the forest environment.
Strict protection appeared to be most important for threatened species. For example, even small fragments larger than 25 ha are worth strictly protecting to maintain forest-dependent birds – for example those that avoid passing through forest gaps. However, findings suggest larger-sized threatened birds may continue to be more impacted by pressures such as hunting, where fragments are small.
The researchers suggest that protection does not have to be strict to be beneficial – those areas with management that reduces human threats or maintains and restores habitat types, are also worth protecting. They conclude that protecting medium to large areas is crucial, but emphasise that conservation value of small fragments should not be underestimated, although stricter protection is then required.
The researchers acknowledge that there are other factors involved in the efficacy of PAs, such as local capacity to enforce protection. Because their analysis was based on observational studies, they were limited by lack of control for sampling effort across different sized fragments (though the effect on results appeared small), and the variability of detecting species (such as observer error and environmental conditions).
Timmers, R., van Kuijk, M., Verweij, P.A., Ghazoul, J., Hautier, Y., Laurance, W.F., Arriaga‐Weiss, S.L., Askins, R.A., Battisti, C., Berg, Å. and Daily, G.C. (2022) Conservation of birds in fragmented landscapes requires protected areas. Frontiers in Ecology and the Environment 20 (6): 361–369.
To cite this article/service:
“Science for Environment Policy”: European Commission DG Environment News Alert Service, edited by the Science Communication Unit, The University of the West of England, Bristol.
Notes on content:
The contents and views included in Science for Environment Policy are based on independent, peer reviewed research and do not necessarily reflect the position of the European Commission. Please note that this article is a summary of only one study. Other studies may come to other conclusions.
- Publication date
- 10 October 2022
- Directorate-General for Environment