The dead leaf on the sycamore stump opened its wings and revealed itself to be a comma butterfly (Polygonia c-album). Their orange pattern was a little worn after a long winter’s hibernation, but still glowed like hot embers in the spring sunshine.
As I watched, it dipped its proboscis into a river of leaking sap, trickling down a leafless, broken twig. It had found a convenient nectar substitute and showed no inclination to fly away. With few wild flowers out, this was most likely the best energy source available. The twig must have been leaking for several days; some sap had solidified into a white crust, but still it trickled downwards and dripped on to the soil.
The pressure of rising sap in trees has been building for weeks. I noticed the first hint about a month ago, in the silver birches on Baal hill. It was manifested as a faint purple watercolour wash in the tips of twigs, where a million buds had swelled, each imperceptibly, but collectively enough to tint the crowns.
Then, in the last days of freezing weather before winter loosened its grip, I found a birch that was bleeding sap profusely. A limb had been sawn off about six feet above ground and its lifeblood, dripping from the wound, had frozen into long icicles. When I broke one and tasted it, there was a hint of sweetness on the tongue that the butterfly feeding on today’s leaking sycamore might have tasted too.
Unless a tree is wounded and bleeds, it is hard to imagine the hydraulic forces that build under the bark as spring approaches, but today it was plain to see in the avenue of horse chestnuts beside the lane here. The rotund, glossy “sticky buds” could no longer contain the pressure as tightly folded leaves within swelled. They were pushing against bud scales that were sliding apart, lubricated by resin that had protected them all winter and was melting in the warmth of a spring afternoon. The force is irresistible, the process inexorable. Another day or two and the leaves, like furry clenched fists, will punch their way out and extend their fingers towards the sun.
