Things have really started to green up over the last few days; the vibrant fresh greens of new growth add a sense of life to a previously dull canvas. Look closely and you will see that there is a clear succession to much of this greening. Trees in particular provide an opportunity to spot which species come into leaf first and which are more sluggish. Over the last few days the rowan in my garden has come into leaf, while the hazel is only just bursting through from its buds. The buds of beech on the other hand, remain firmly sealed, the leaves inside yet to put in appearance.
Many of the newly emerged leaves clearly have quite a bit of growing still to do; look at those of horse chestnut for instance, miniature versions of their final form. On the other hand, the beech leaves will emerge almost fully-formed, raising the question of just how they can be packed into such a small bud. It seems that the key to this trick lies in the way in which the new leaves are folded. Researchers have discovered that the angle between the mid-rib of the leaf and the lateral veins that emerge from it determines how the leaf will unfold. This angles varies between different tree species, ranging from 10 degrees to almost 90; the bigger the angle the more compactly a leaf can be folded and, hence, crammed into a smaller bud. However, this space-saving option comes at a price, since the larger the angle the more slowly the leaf expands. Beech has an angle of roughly 40 degrees (ranging from 50 near the stalk to 30 near the tip), allowing it to expand to its full area that much more rapidly. This strategy lies behind the long leaf buds that you see on beech, each containing a virtually fully-formed leaf, folded ready for rapid deployment.
That we know all this is down to work carried out by a team of scientists working in Japan. They have spent time studying the mechanics of leaf emergence, even using paper to replicate the nature of the unfolding process. An understanding of the principles of leaf emergence and, in particular, how you cram a large flat object into a much smaller three dimensional space, has value elsewhere in science by highlighting how we might overcome particular design problems. This area of science is known as biomimetics and has been used to look to nature for solutions to design issues relating to as wide a range of subjects as folding tents through to deploying the solar panels of satellites and other space-craft. The mechanics of nature are something that we can all learn from.