Country diary: Purple catkins light the way towards spring | Oliver Southall

Hurstpierpoint, West Sussex: Look out for the alders – they’re remarkable trees and one of our first to come to life as winter recedes

A few wet weeks have left the ground here sodden, making walking a challenge. It doesn’t help that my wellies have sprung a leak. On the rainiest days, I find my range reduced to a few splashy circuits of the village fields, the nearby Downs receding into hanging cloud.

Nevertheless, there are signs of drier times to come. Today, my eye is drawn by a line of alders (Alnus glutinosa) that marks the course of a stream. Their graceful silhouettes are bathed in a distinctive maroon haze. Up close, the cause resolves into delicate clarity: purple catkins dangling in bunches from the tip of each twig. Formed at the end of last summer, they have recently begun to lengthen and unclench, coaxed by warming days. Soon (and well before the tree’s round leaves unfurl), they will split open, revealing hundreds of vivid yellow stamens: tiny, lantern guides through the murk and mire of late winter.

Along with its birch-family cousin hazel (Corylus avellana), the alder is one of our first trees to bloom. Its light, wind-blown pollen provides essential forage for emerging bee queens. When fertilised, the female flowers, currently inconspicuous, swell into fleshy grape-sized green cones – casings for seed much loved by hungry finches. I’m always struck by the clusters of spent cones, now darkened and woody, that linger on the branches into the following spring, often right next to the new catkins. Their fragile, rattly presence is an easy way to spot this unshowy but ecologically important species.

Alders are place-making, pioneer trees. They’ll tolerate compacted, infertile soil, creating a more porous and welcoming structure for other plants. Their roots house bacteria that convert atmospheric nitrogen into usable form. Such qualities give the tree a useful role in healing damaged post-industrial landscapes, turning barren mine spoil and toxic tailings into thriving ecosystems.

Alders can also teach us a thing or two about dealing with wet feet. It is strengthened by wetness, making it historically invaluable for aquatic engineering. Much of Venice stands on alder pilings. In the 19th century, coppiced alder was widely used to sole the clogs of factory workers. Water-resistant and grease-proof, it moulds snugly to instep and toes. Ideal, I’d imagine, for a new pair of wellies.

• Under the Changing Skies: The Best of the Guardian’s Country Diary, 2018-2024, is available now at guardianbookshop.com