Corridors provide both functional connectivity and structural connectivity. While structural connectivity assesses how connected landscape elements are, functional connectivity measures the degree to which landscape elements actually contribute to animal movement.
Both types of connectivity are important in landscapes like commercial timber stands, where corridors often represent the only native habitat in a heavily managed and monotonous matrix of trees. The design of a corridor, in particular its width, can make a big difference in its ability to support biodiversity and allow movement through the landscape. Providing the right structural connectivity can lead to better functional connectivity, making management and conservation goals more attainable.
Davids, L., Pryke, J.S. and Samways, M.J. 2025. Do pinch points in conservation corridors matter? A test case using localized butterflies and grasshoppers. Biological Conservation 305: 111073.
New research looks at how differences in corridor width that lead to constrictive “pinch points” affect corridor effectiveness in a production landscape. Grasshoppers and butterflies were surveyed along natural grassland corridors within four timber estates in South Africa. Corridors were grouped across three types of pinch points: narrow (<50m wide), wide (>50m wide) and cul-de-sac (only one entrance/exit point). Species richness and abundance were then compared to observations in reference sites of large expanses of open grassland that were found among plantation blocks and nearby protected areas.
Results from over 2,500 butterfly observations and over 3,000 grasshopper observations show that cul-de-sacs significantly reduced butterfly and grasshopper abundance, mostly because they severely limited connectivity to surrounding remnant grasslands and also encouraged the spread of non-native species.
However, corridors with either wide and narrow pinch points were still able to support insect abundance: wide pinch points supported the most species-rich butterfly assemblages, while narrow pinch points were preferred by grasshoppers. This suggests that pinch points may not be a major limiting factor for corridor effectiveness, especially when the scale of the pinch point is small compared to the landscape, and large compared to the target species.
It remains challenging to determine how wide a corridor should be. The design of any corridor often represents a balance between conserving natural habitat and meeting the needs of logging, mining, or other commercial productions. Understanding how design influences structural and functional connectivity for target species can make that balance easier to achieve.
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