Talking trees and Wilting Woods

This looks like a scene from a BBC wildlife program and it is just as exciting! You will have to imagine the sounds of the jungle at night just beyond the circle of light, the rustling of invisible small creatures in the dry leaves, constant chirping, whining, stridulation of insects that sound like frogs and frogs that sound like insects. Then there is the forest itself, still and cool down here but sighing with the breeze far overhead in the canopy, creaking and cracking as the weight of vines slowly topple a strangled tree, the loud ‘ker-plunk’ of ripe fruit dropping and the continual patter of leaves falling in to make way for the new ones and to release their nitrogen back into the sparse soil. Spring and Autumn simultaneously. 
The two scientists come from Brazil and the USA and are used to forests with either jaguar or brown bear lurking in them so extra loud noises make them jump and look warily over their shoulders as they conduct their research. Here though, the scuffles in the leaf litter are usually small native rats, or the pair of big skinks that have their home under a rock behind the shed or the red-bellied snake that lives in the drought tunnel nearby.

The drought tunnels are long tent-like structures that keep the rain from directly falling onto some of the trees’ roots. These can then be compared with those that get their full complement of water. This means a lot of research can be done on how longer periods of drought effect the rain forest – something that is at the forefront of concern as there is increasing incidence of tropical trees dying world-wide because of climate change caused by global warming.

Here the American team are testing stress levels in trees that have less water than normal ones (although the rainfall overall in the Daintree this year has been very low ). Less water means trees have to modify their circulatory system, xylem and veins, so the pressure within the tree rises. It is harder to get the water from the roots up to the transpirating leaves. The pressure within the tree rises. This is measured in the leaf by a ‘leaf-bomb’ machine, a nifty piece of apparatus that involves holding a leaf within a nitrogen pressurised compartment and increasing the pressure until a bead of water is extruded from the exposed stalk. It is a bit like a cold pressure-cooker. We commented hopefully that it would not be as temperamental as the kitchen variety with their record of tomato sauce blow-outs hitting the ceiling.
 The drought-ridden leaves demonstrate significantly raised pressure before the water droplet appears. Over time that extra struggle to circulate moisture through the plant leads to weakness and susceptibility to disease and death.

The Brazilian team are looking at the way in which the trees communicate through chemical signals, that is oils and vapours released by individual trees into the atmosphere. Each test-tube of air collected from near the tree or from a frond of leaves contained in a jiffy bag has a complex chemical signature which changes constantly depending on species, age, weather and climate conditions, flowering and fruiting, health, damage, who the next door neighbour is and, at the moment, drought stress. It has long been known that scent signals go out to pollinators and fruit eaters, but the analysis here is much deeper, as complicated as unravelling an incredibly subtle language without words or grammar. Tiyana may well spend the rest of her life trying to interpret how trees talk and what they are saying.

And my job as a volunteer, an evening spent writing down results, being fascinated with both projects and increasingly understanding the worrying impact of the sudden degree or two rise in global temperature. 
‘Help!’ would seem to be the overriding plea from the trees at this moment.