杏吧原创

Ivy is multiplying across European forests, riding a perfect storm of environmental changes, say scientists.

Michael Perring, an ecologist at Ghent University in Belgium, and his colleagues spotted the trend while working on a study of more than 1800 research plots in 40 forest regions across temperate Europe, from Ireland in the west to Hungary in the east. The study compared data gathered between 1933 and 2015.

The research reveals that common ivy (Hedera helix) has become even more common. During the study interval it has spread, reaching on average 14 per cent more of the study sites in each forest region than at the outset. Most other plant species haven鈥檛 spread to more study sites, and some species are now found at fewer of the sites.

It is 鈥渜uite dramatic鈥�, says Perring. 鈥淚t鈥檚 a coherent signal across multiple forests in Europe.鈥�

Local temperature rise was the biggest predictor of where common ivy would flourish, followed by shade and nitrogen levels, although these didn鈥檛 fully explain the plant鈥檚 spread.

Forests are becoming darker as management practices change. Common ivy then outcompetes other plants because its evergreen leaves allow it to photosynthesise through the winter, when more light gets through.

Nitrogen pollution, caused by agriculture and the burning of fossil fuels, also seems to accelerate ivy growth, says co-author Pieter De Frenne, a bioscientist at Ghent University.

The results echo predictions in that rising temperatures would make 鈥渁ggressive鈥� woodland plants such as ivy behave like invasive species, suppressing woodland flowers.

鈥淚t might mean that you don鈥檛 get big clumps of primroses or violets鈥� [though] it probably won鈥檛 eliminate them,鈥� says Keith Kirby, a woodland ecologist at the University of Oxford, who co-authored the 2013 study.

鈥淎n increase is鈥� not necessarily a bad thing,鈥� according to a statement from the UK鈥檚 Woodland Trust. 鈥淚t鈥檚 great habitat for birds, bats, invertebrates and small mammals, and therefore a key part of a forest ecosystem. The autumn flowers on ivy are a great late season nectar source for insects and then berries for the birds.鈥�