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Size matters when it comes to preserving biodiversity in natural areas. Larger and strictly protected areas are clearly more effective, according to biologists from Utrecht University and international colleagues. Examining the biodiversity of more than 700 natural areas worldwide, their study could help pinpoint the most suitable areas for protection.

Protecting habitats is increasingly used as a means of preserving biodiversity. But to what extent is this approach effective? A new study shows that the effect of protecting forest areas depends on both their size and protection status. The study was led by biologists Robert Timmers and Merel Soons of Utrecht University. Their findings are published in the journal Frontiers in Ecology and the Environment.

Birds as indicator for biodiversity

The researchers collected data from bird observations in more than 700 forest areas worldwide. The areas varied in size and protection status. "Birds are a good indicator of the effectiveness of protection," said Timmers. "This is due to the large number of bird species, their global distribution, and the important roles they play within ecosystems. In addition, there are many high-quality measurements available on birds."

Smaller forest fragments, fewer bird species

The research shows that fragmentation and the loss of habitat does indeed have major consequences for the preservation of biodiversity. Smaller forest areas clearly carry far fewer bird species. This is especially visible with large birds of prey. For example, the researchers noted that the African long-tailed hawk (Urotriorchis macrourus) was only observed in forest fragments measuring over 100 hectares.

Small but well protected

Yet, smaller natural areas can also be effective as a biodiversity preserve, according to the researchers. However, this is only the case when the area is highly protected. In smaller forest fragments from 50 hectares and up, strict protection already leads to more bird species, compared to unprotected areas. When the area is only moderately protected, the positive effect starts to appear when the area measured at least 175 hectares.

Vulnerable species benefit from protected areas

Moreover, endangered bird species are more likely to occur in protected areas. This indicates that protection is effectively helping to protect these vulnerable species. For example, the black-fronted piping guan (Pipile jacutinga), which exclusively occurs in the Atlantic rainforest in South America, was only found in strictly protected areas.

Identifying suitable areas for protection

The results could help identify suitable areas for protection, according to the researchers. "Up until now, conservation measures have been applied mainly in large areas and intact areas," said Timmers. "Our results indicate that this is most effective. But we also show that it makes sense to protect smaller areas in fragmented landscapes, especially when preserving endangered bird species. In smaller areas, however, strict protection is most effective."

More diverse nature reserves

Since the establishment of world's first national park, Yellowstone National Park in 1872, the number of protected natural areas has increased dramatically. In the past thirty years only, the total surface of protected areas nearly doubled. However, differences between the protected areas, for example in their degree of protection, have also grown.

Fragmented landscapes

But even though the number of protected areas has increased, researchers see the total surface of natural areas has diminished. Protected areas are therefore becoming increasingly isolated, closely surrounded by agricultural or urban areas. This raises the question of whether protected areas in fragmented landscapes can effectively protect species.

Timmers: "We're clearly seeing that fragmentation limits the distribution of plants and animals. Small areas have a relatively larger perimeter, making them more vulnerable to external influences. It is therefore important to counteract this fragmentation and to connect nature areas with each other as much as possible. In addition, our study provides evidence that protection is an effective means of preserving species, even in small fragmented areas."

Unique study

The study by Timmers and colleagues offers a much broader scope than previous ones. It registers the effectiveness of large and small protected areas in fragmented landscapes based on biodiversity, and includes the degree of protection. "Previous studies on the effectiveness of protected areas focused on large areas in relatively intact landscapes," said Timmers.