Dear Readers, as you might know I am generally a big fan of ivy as a wildlife habitat, and so the news that ivy is becoming more common right across Europe might be a kind of good news. Michael Perring at Ghent University in Belgium has been looking at more than 1800 research plots in 40 forest regions across temperate Europe. The data covers the period between 1933 and 2015, and by the end of this period, ivy was found in 14% more of the sites than at the beginning. Most other plant species haven’t spread, and some species are found at fewer sites.
The biggest predictor was local temperature rise, so our old friend climate change is implicated yet again. However, two other factors were the amount of shade and nitrogen levels. Many managed forests are becoming shadier, though the article doesn’t say why – in forestry sites I would imagine this is because of higher stocking density, but in other woods it might be due to the decline of techniques such as coppicing. In shady woods, ivy has an immediate advantage because it’s evergreen, and so can photosynthesize when the leaves on the trees are gone in winter. In the uncoppiced parts of Coldfall, it’s mainly the evergreens such as yew and holly that survive in the understorey, along with ivy.
Nitrogen pollution through the burning of fossil fuels and agricultural run-off also seems to encourage the growth of ivy, possibly a reason that it’s one of those plants that still flourishes in cities.
The Woodland Trust agrees that it isn’t all bad news – as we know ivy is a great wildlife plant. But I do worry about the lessening of biodiversity that this study shows. What about species that are disappearing from our woods? It would be good to know about them too.
Let’s stay in the forest for now – a study by Constantin Zohner at ETH Zurich in Switzerland has completed a study that shows that climate change is causing autumn leaves to fall earlier than they used to. Zohner and his colleagues looked at leaf fall data from 1948 to 2015 for six tree species (including the common oak, Quercus robur) across 4000 sites in Central Europe. They also grew trees in chambers containing different amounts of carbon dioxide and different levels of sunlight to see when the leaves fell. Finally, they modelled the data to see what would have happened by 2100 if carbon dioxide levels remained high.
They found that leaf-fall would probably start about three to six days earlier than now. This happens because higher carbon dioxide levels and temperatures mean that the spring leaves grow faster and are more productive, and so the life of the leaf is shortened.
Why does it matter? Leaves are a major way of storing carbon, which they tie up when they photosynthesise. If they fall earlier, that’s less time for them to absorb the carbon. Zohner thinks this could account for about 1 gigatonne of carbon less stored globally each year by temperature forests – this is roughly a tenth of what we currently emit. The way that climate change disrupts the cycles of life are myriad and complex.
And finally, who knew that a little wasp could crash a plane? The keyhole wasp (Pachnodynerus nasidens) is a type of mason wasp who would normally find a tiny hole in a wall and build its nest there. It is native to the Neotropics, but has recently found its way to the northern United States and to some parts of Oceania, including, of all places, Brisbane Airport. At the airport, there were a number of incidents with pilots having problems with their airspeed monitors, which are housed in devices called pitot tubes.
To find out what was going on Alan House, at consulting firm Eco Logical Australia, created some 3D replica pitot tubes and set them up at the airport. After 39 months it was found that 93 of the tubes had become completely blocked by the nests of the keyhole wasps.
For once, the solution wasn’t to spray the whole place with insecticide. Instead, the tubes are now covered when planes arrive at Brisbane airport, so the wasps have to find somewhere else to make their nests. Simple.
Photo One By gailhampshire from Cradley, Malvern, U.K – Mason Wasp inspecting holes, Pachodynerus nasidens, CC BY 2.0, https://commons.wikimedia.org/w/index.php?curid=49860259