The Long Fall

Back in mid-November I wrote a post about the local signs of climate change. I mentioned that leaf fall seems to be getting later each year, and speculated that "it could be another two weeks before all the leaves are gone."

So, was my speculation correct?

This week's blast of stormy weather has stripped many deciduous trees of their remaining foliage. However, as I walked into central Sheffield this morning, I noticed quite a few trees that still have some leaves. Moreover, a significant proportion of their leaves are still green.

The species with verdant foliage included hazel (Corylus avellana), silver birch (Betula pendula), sycamore (Acer pseudoplatanus), goat willow (Salix caprea) and alder (Alnus glutinosa). I even spotted an ash (Fraxinus excelsior) with a smattering of green leaves; this is usually one of the earliest trees to shed its foliage. 

Later in the day, I cut through Meersbrook Park on my way to the Ecology Unit. A mistle thrush (Turdus viscivorus) was in full song and a pair of woodpigeons (Columba palumbus) were inspecting a half built (or half demolished) nest. Not the sort of behaviour you expect in the second week of December!

The effects of climate change are magnified in cities because they are generally warmer than the surrounding countryside (due to the urban heat island effect). The quirky phenomena we observe in urban environments today may give an indication of what we can expect across the British Isles tomorrow as global warming progresses.

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The science dealing with the influence of climate on the recurrence of annual phenomena, such as leaf fall, is known as phenology (not be confused with phrenology, the study of cranial lumps and bumps).

I recently signed up as a volunteer recorder with the Nature's Calendar project run by The UK Phenology Network, which is monitoring the timing of a wide variety of spring and autumn events. You can download a copy of the network's report on autumn 2006 here.

Comments

[John]

As of last Sunday, some trees in one of my local birding haunts still bore leaves. I did not get up close to ID them, but they did not look like oaks or beeches from a distance.