Deciduous trees breaking their winter dormancy and bursting bud is something that we all look forward to. It marks the beginning of a transformation from open, light and airy undergrowth to what will eventually become a shadier and more humid forest floor, allowing only dappled light to pattern the ground. Yet, despite the annual descent of darkness, these deciduous woodlands have a remarkable capacity to remain ungloomy all year round.
Hawthorn and hazel are amongst the first each year to produce leaves; these two species are generally thought of as part of the understorey of an open woodland and it is of great benefit to them to leaf before larger trees such as oak and ash. They can take advantage of the spring light conditions, with the weaker sunlight at this time of year being able to penetrate the bare canopy above into the lower levels of the woodland – hazel can also have remarkably large leaves helping to absorb as much light as possible.
Small and large deciduous trees have evolved to stir at different times, allowing each to find the light and nutrients they need to survive and grow – it is a form of temporal niche separation. After so long being dormant, early spring is the time in which the smaller trees get to replenish their stock of nutrients. Large, canopy trees can shift vast volumes of soil water through there massive roots via evapotranspiration, and with it they take up many minerals from the soil, if the smaller trees don’t get in there early, they may struggle to find the nutrients they require before the canopy closes over them.
You may also notice that not all the small trees burst into life at once. This is partly down to genetic variation, which is invisible to the naked eye, but it is suddenly apparent in these moments of seasonal change. Each tree species, each individual tree, and indeed every bud on each individual, has a slightly different requirement for light and temperature before bursting into leaf – this is hugely important for a tree if there is an unusually late frost for instance, meaning at least some buds should survive unscathed, rather than suddenly suffering a catastrophic leaf fall and losing their ability to photosynthesise.
Obviously, all these changes going on above ground level has a huge effect on the ground flora. Already some of the earliest flowering plants have bloomed and gone over again, having taken advantage of the lack of competition in the coldest months. Now we are starting to see some slightly larger and more spreading plants coming up – ramsons, common comfrey, bluebells – they survive underground as bulbs or tubers and are kept relatively warm by a covering of fallen leaves on the ground. The lengthening daylight and warming temperatures provide signals for the new growth to push through the surface – before long the woodland floor will be alive with colours and buzzing bumblebees looking for early food sources to feed their new colonies.
Ranger Bryan Smith