Massive flows of snow down mountain slopes can clear out dense forest and make way for shrubs and smaller trees, allowing a more diverse range of bird species to live in the affected area
Avalanches create attractive living environments for many bird species, leading to increased bird diversity in mountainous areas where powerful flows of snow have ploughed down larger trees.
The sudden, massive shifts of snow periodically clear out sections of dense, high-canopy forest populated mainly by tits, thrushes and woodpeckers, making way for the growth of shrubs and smaller trees that appeal to whinchats, pipits and buntings. Combined, these landscape “mosaics” host a wide variety of bird species, although these might be altered as climate change affects future avalanche activity, says Riccardo Alba at the University of Turin in Italy.
“I didn’t expect to find such diversity,” he says. “It is crucial to continue studying the interactions between climate change and biodiversity in mountain environments to better understand how these ecosystems are changing and how to protect them for the next generations.”
Avalanches can pose a serious risk to humans. They also play a major role in mountain ecosystems. However, their effects on biodiversity are surprisingly understudied, says Alba.
To better understand their impact on bird communities, Alba and his colleagues surveyed 240 points in the western Italian Alps near Turin during the bird breeding season in spring 2021. Half these points were in areas that had been affected by avalanches, according to previous surveys or historical data – some several decades ago and some within the past few years.
The data revealed that the habitats in areas where avalanches had occurred were more varied – with more rocks, small trees, grass and relatively short plants – compared with areas where they hadn’t. The differences were most pronounced at lower altitudes, which harboured mostly tall trees such as beeches, ashes, and maples, compared with at higher altitudes, where larches and bushes like junipers and alpenroses were more common, says Alba.
Consequently, the researchers also found a greater variety of birds in the tracks of avalanches, with 62 species identified in previous avalanche areas and only 55 in unaffected areas, he says.
Birds seen in dense forest spared by avalanches included great spotted woodpeckers (Dendrocopos major), song thrushes (Turdus philomelos) and Eurasian treecreepers (Certhia familiaris), he says.
By contrast, the avalanche-hit areas included a higher proportion of species that often live at the treeline at higher altitudes, in addition to migratory birds and birds that typically nest in open habitats. These included black grouses (Lyrurus tetrix), tree pipits (Anthus trivialis), common linnets (Linaria cannabina), rock buntings (Emberiza cia), whinchats (Saxicola rubetra), yellowhammers (Emberiza citrinella) and black redstarts (Phoenicurus ochruros).
The make-up of different species varied even further according to how recently – and how often – avalanches had occurred in a particular area, says Alba.
Researchers are still debating whether global warming will make avalanches more or less frequent, but any disturbance in their natural rhythm could have a significant impact on bird diversity, he adds.
“Either of these changes will have consequences for mountain biodiversity at a broader scale, so it’s important to carry on with research,” he says.
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