Butterfly Cut

You’ve heard of a buzz cut. How about a butterfly cut? Clear-cutting forests that have grown over old meadows can increase butterfly diversity, new research from Sweden shows. It is one of the first studies, the authors say, to show that the historic use of a forest patch can have a strong influence on a butterfly community — even after nearly a century.

Many species of butterflies thrive in pastures and meadows. But such grasslands have become increasingly rare as farms have dwindled across Western Europe. In Sweden, farm abandonment has led to “large areas previously managed as meadows becoming dense coniferous forest,” Mathias Ibbe of Linkoping University and colleagues report in Forest Ecology and Management. These forests are now routinely logged, creating a patchwork of regrowth. Just what role these clear-cuts – and their historic use – might be playing in providing habitat for butterflies, however, wasn’t clear.

To find out, in 2009 Ibbe’s team surveyed butterflies on 24 two- to four-year-old clear cuts in the county of Östergötland in southeastern Sweden. Historic maps from 1868 and 1877 showed the researchers that half of the patches had once been forest, and half had been meadows. “All the clearcuts historically managed as meadows had been abandoned long enough to allow at least one generation of spruce-dominated coniferous forest to grow to maturity,” the researchers note, which takes 70 to 140 years. Overall, the researchers conducted two butterfly surveys at each site, counting a total of 2,653 flutterers from 44 species.

The surveys revealed “clear differences in the butterfly assemblages between the two types of clearcuts,” they report. Former meadows, for instance, boasted a total of 44 butterfly species, while the former forests had just 30. Former meadows also had a higher number of grassland specialists. And butterfly densities were 2.5 times higher in the grown-over meadows. One reason for the difference, the researchers say, is that the former meadows had “remnant plant communities” that attracted the grassland-loving species.

The results demonstrate “for the first time, to our knowledge, that the legacy of historical land use… can affect butterfly diversity in areas that are once again accessible after a long period of unfavourable conditions,” they write. And although the “transient” butterfly habitat created by regrowing clearcuts isn’t ideal, it could play an important role is sustaining populations, they add. “A significant amount of transient habitat facilitates dispersal,” for example, “and enables recolonization of vacant habitat patches.”

The findings suggest forest managers could do more to help butterflies, the researchers write. They could use historical maps, for instance, to identify one-time meadows due for logging. And to keep those clear cuts butterfly friendlier, they could consider replanting them with deciduous trees instead of conifers, and preserving some open areas. Such steps, the argue, “would make it possible to preserve a greater diversity of habitats for butterflies and other organisms.” David Malakoff | March 13, 2011

Source: Ibbe, M., Milberg, P., Tunér, A., & Bergman, K. (2011). History matters: Impact of historical land use on butterfly diversity in clear-cuts in a boreal landscape. Forest Ecology and Management DOI: 10.1016/j.foreco.2011.02.011

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