Trees bursting into leaf in gardens, parks and woodlands is one of the most wonderful signs of spring. But how much do you know about tree budburst and what triggers it? Read on to discover the science behind how and why trees wake up in spring.
It started last summer
The new growth of leaves we see each year in spring is due to a complex programme of changes in a tree. You might assume all the action happens in spring, but if you look closely at twigs during autumn and winter, you’ll see they already contain tiny leaf buds.
These buds are formed at the end of summer while trees still have enough energy to grow, before the days get cooler and shorter. The buds then lie dormant over the winter, waiting for the warmth of spring to arrive.
Trees have hormones too
As the seasons change and temperatures rise, the buds swell. Hormones within each bud - such as cytokinin and auxin - play crucial roles in the budburst process, promoting growth and encouraging cells to divide.
These tiny internal changes have a spectacular impact across our woodlands as trees begin their spring growth.
Bursting into leaf
New spring leaves burst into life to help trees catch as much sunlight as possible during the long summer days. Trees are effectively in a race against time to unfurl their leaves before summer arrives.
The leaves use sunlight, water and carbon dioxide to create sugars that feed the tree while it grows, while also releasing the oxygen we breathe.
This process, called photosynthesis, drives the productivity of our forests and supports the wildlife that depends on them.
Timing is everything
The first leaves will start to emerge from their buds between March and April each year, although long-term monitoring shows the timing can shift with changes in weather and climate.
Fluctuating temperatures can damage buds and vulnerable young leaves, and a warm winter can confuse a tree and make it come out of dormancy too early.
Conifers join in too
Broadleaved trees, such as oak, ash and beech, aren't the only type of trees to form buds - most conifers do as well!
One of the earliest trees to turn green is the Dahurian larch, a deciduous conifer at Bedgebury Pinetum. This rarely-seen tree from north-east Eurasia comes into leaf as early as January in the milder English climate.
Resilient forests for the future
Across the forests and woodlands we care for, our expert teams observe seasonal changes every month. By understanding the science behind tree budburst, we can better protect the nation's trees, support forest wildlife, and help our landscapes thrive in a changing climate.
