Continued disruption of seasonal weather is causing spring activities in autumn

by Michael Smith (Veshengro)

The Woodland Trust warns that continued disruption of seasonal weather may be causing confusion for wildlife.

After a year which saw a ‘split spring’, heatwaves, droughts and a false autumn, the UK’s wildlife may be starting to confuse its seasonal activities as spring sightings are reported in October. 

There have been reports of second flowering for horse chestnut trees, new leaves on species like ash, and plenty of active amphibians and butterflies, and the two former I can verify myself as a professional groundsman aside from a writer. Also at the Park for which I am responsible a bird cherry tree (more like a shrub as it keeps being coppiced) is again in flower and is sprouting new leaves.

We would normally expect butterflies and newts to be going into hibernation around now, and we would also not expect trees to regrow their leaves and flower or flower and then get new leaves, as in the case of prunus species, of which birch cherry is one. 

Warmer weather in autumn can extend the growing periods for plants and allows more foraging time for animals, which in the short term gives them a chance to recover from the summer heatwaves and drought. And while we can expect, after heat and drought as we have been experiencing especially in the southern parts of the UK this summer with trees shedding their leaves as a protection mechanism, some new leaves forming prior to them being shed in autumn in some cases the trees are so confused that they seem to believe spring having arrived already. 

Squirrels too, seeing that many females appear to be suckling, seem to have decided that either it is nowhere near autumn yet or that spring has arrived already, appear to have another litter. Not that there weren't enough of those gray menaces around already who, this year, have taken their toll on the trees in that this year they have done a lot more bark stripping that usual and even on species that they not normally strip. 

However, if extreme weather like we have had this summer becomes increasingly common, disruption to natural cycles may throw species out of sync. Butterflies, for example, rely on a period of dormancy during winter to save energy while food is scarce, and many plants require a spell of cold weather in winter to drive germination in spring.

It’s not just animals that struggle with rising autumn temperatures longer-term as tree’s rely on cold spells to help kill off and stall the spread of pests and diseases.  

Alisha Anstee, Lead Policy Advocate for Tree Health and Invasive Species at Woodland Trust said, “Climate change is likely to lead to a multitude of challenges for our trees and woodlands. One area that is not exempt is the threats posed to trees by pests and diseases. 

As our climate changes over time our trees are likely to be more stressed which means they will be more susceptible to the impacts of pests and diseases. Warmer temperatures will likely lead to more pests and diseases being able to thrive in the UK. These species may previously have been unable to survive in the cooler UK but an increase of up to 2 degrees could reverse this.”

Dr Lewthwaite continues, “A changing climate means changing seasons. We already know that spring is arriving an average of 8.4 days earlier each year, but not so much is known about autumn.”

Whether we can lay all the blame at the door of climate change is a question but the truth is that the UK, at least the southern parts, have not been experiencing a proper set of seasons, as there used to be for some decades by now. 

This year's events could be due, to some extent to the, and that already for some tens of years, wobbling, for lack of a better word, of the jet stream. One could almost assume it to be rather drunk. And in addition to that we seem to be having a serious La NiƱa pattern this summer. 

However, who, at least in the southern parts of the UK, can remember having even remotely have had a proper autumn and winter in the last couple of years. I doubt that anyone can. Snow has become – and, as far as I am concerned good that is too, as I do not like snow – restricted to a couple of days, maybe and the same is true for any real frost. I am old enough to remember real winters in this part of the country lasting for weeks and months. No wonder, therefore, that the natural world is confused because, unlike us humans, it takes them all much longer to adapt. 

As far as tree pests and diseases are concerned we have seen the arrival of Horse Chestnut bleeding canker about a little over 20+ years ago and then the Horse Chestnut leaf miner (Cameraria ohridella), the latter being a pest that likes it a little on the mild side. For its larvae to be killed off it requires a good frost that reaches well into the leaf litter. One can but wonder whether the reason we have so many new tree diseases arriving on our shores, aside from bad biosecurity, is the fact that those pathogen actually thrive now in our much milder “seasons.”

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