A report outlining the results of a large 18-year habitat study published on 27 September in Science highlights the immense value of habitat connectivity and biodiversity (1). The authors suggest the benefits of reconnecting fragmented habitats may be underestimated.
Loss of habitat is the biggest driver of extinction. However, reconnecting patches of habitat could potentially save many species, according to the study. And far more effectively than previously thought. Rates of plant extinction were reduced by 2 per cent annually in connected habitats compared to isolated patches. Moreover, the colonization of new plant species increased by 5 per cent each year.
Perhaps most importantly, these numbers were consistent year after year, suggesting that the number of species will continue to increase each year. The scientists don’t yet know when this will cease to be the case.
The team of researchers studied a type of grassland habitat — the longleaf pine savanna — that once existed across the US. Now, a mere 3 per cent of the ecosystem remains and only in small fragments. Yet, these grasslands are still home to many plant species like blazing stars and the butterfly milkweed, as well as the endangered red-cockaded woodpecker and gopher tortoises.
To study the effects of habitat connectivity, the researchers were able to create new patches of savanna inside — 2.5-acre squares — a pine plantation in South Carolina and then created corridors of the savanna —more than 150 meters long by about 25 meters wide — between the plots. New habitats were connected to existing ones via these so-called landscape corridors — thin strips of habitat that connect isolated patches of habitat — and the results were even better than expected.
Each year, the scientists monitored the number of native plant species. They counted individual species and whether or not they were seen that year in a certain patch. At the end of the 18 year period, the connected patches had 14 per cent more species — on average, 200 species — compared to unconnected areas. The scientists observed a massive boost in annual colonisation of 5 per cent, showing that the benefits continue to grow over time. The restored habitats are now replete with butterflies, vibrant flowers, and many other species.
Habitat loss and fragmentation are leading threats to biodiversity in ecosystems around the globe, the authors write. The world now mainly consists of small isolated fragments resulting in a rapid and ongoing decline in biodiversity. But the idea of reconnecting habitats is not new.
For example, the Yellowstone to Yukon Conservation Initiative was initiated in 1993 to strengthen connections between wild landscapes of northern Canada all the way to the US Rocky Mountains through various rewilding programmes. However, until now, biodiversity and extinction rates were only examined on a small scale.
The researchers are now certain of the long-running effects of connectivity. So, the sooner more habitats are reconnected, the better off they may be. As the authors conclude, efforts to increase connectivity will pay off over the long-term and conservation plans that ignore connectivity, such as plans that focus solely on habitat area, could miss out on the immense gains in biodiversity specifically attributed to landscape connectivity.
(1) Damschen, E.I. et al. Ongoing accumulation of plant diversity through habitat connectivity in an 18-year experiment. Science (2019). DOI: 10.1126/science.aax8992