Ecosystems

When landscapes are abandoned, do butterflies flee?

Agricultural intensification affects butterfly populations, but so does the abandonment of farmland.
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Amparo Mora and colleagues set out to identify how the abandonment of traditional hay meadows is affecting butterfly communities. Their study in the Soto de Sajambre found a species turnover of around 50% in the first few years of abandonment, rising to about 70% after 18 years of abandonment. The research indicates that butterfly species need connectivity in a landscape to move on from changing habitats.

The research by the Lancaster-based ecologists complements work done elsewhere on the effects of agricultural intensification. However, in the Picos de Europa National Park, land covered by hay meadows has decreased by 70%.

Picos de Europa. Image: Canva.

Mora and colleagues write: “The consequences of this land transformation on biodiversity are still largely unexplored. This is particularly worrying as Picos de Europa is a hotspot of butterfly diversity not only in the Iberian Peninsula, but in the broader European context… There are 137 butterfly species in the National Park, representing 60.6% of the Iberian species…, including several legally protected species at European level (Parnassius apollo, Euphydryas aurinia, Lopinga machine and Phengaris nausithous) and some Iberian endemisms (Erebia palarica, Aricia morronensis and Agriades pyrenaicus).”

The team examined nineteen hay meadows in the area. They walked transects to sample the area for butterflies and studied the landscape’s vegetation. They were not simply looking to see what was there but also to explore the heterogeneity, how diverse the landscape was. They then used data analysis to see how the butterfly community changed depending on how long a site had been abandoned and other factors like plant species richness and diversity, vegetation height and cover, soil humidity, distance to water, elevation and slope.

There was a species turnover of 50% in the first few years. Species with a preference for closed habitats increased in density after abandonment. Forests did not have to replace meadows to have an effect, and meadows surrounded by forest tended to have a lower butterfly community preference index. Where landscapes were heterogeneous, the effect was mitigated, indicating the importance of connectivity in a landscape, allowing species to move through it.

The team found that the plants in a habitat changed rapidly after abandonment, with species richness and diversity peaking three to seven years after abandonment. But, as forest moved in, these figures declined below their initial levels. Strangely, the variation in plant species did not affect variation in butterfly species, unlike previous studies had found, but the ecologists have an explanation.

Mora and colleagues write: “We argue that previous studies were conducted in landscape matrices where remaining grasslands were a small percentage of the total land cover (2–3% as maximum). Such landscapes were very likely below extinction thresholds for species that exhibited long-term negative population trends… In our study, with a remaining mean grassland cover of around 40%, mobility of butterflies across the landscape, among different successional patches of different age, could be buffering the negative effect of plant diversity loss in abandoned meadows. Our results suggest that a matrix with enough suitable habitat remaining, embedded in a more heterogeneous landscape, can slow down the negative effects of plant diversity loss on butterfly communities…”

Heterogeneity is crucial to the wider ecosystem, say the team. As an example, the ecologists conclude with a caution about the increase in woodland specialists. “European woodland butterflies utilise sunny habitats within woodlands, such as sparse stands, bogs, stream sides, clearings, rides or edges. Managing woodlands for many threatened species consists of maintaining relatively low tree density and/or permanent or dynamically managed clearings… Abandoned hay meadows, embedded in forest patches, may be acting as forest clearings for woodland species. For example, Lopinga achine, a rare and endangered woodland species, in Picos de Europa area has taken advantage of hay meadow edges with forests, using them as a suitable habitat for breeding…” This species, they add, did best when forest cover was 70-85%. So while abandonment is an issue for the butterflies in the old environment, management might also be necessary to support biodiversity for the newer species after agriculture has gone.

RESEARCH ARTICLE

Mora, A., Wilby, A. and Menéndez, R. (2021) “Abandonment of cultural landscapes: butterfly communities track the advance of forest over grasslands,” Journal of Insect Conservation. Springer Science and Business Media LLC. doi:10.1007/s10841-021-00365-0.

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