Pink Floyd’s Grantchester Meadows features some unusual instrumentation: the rolling whistles of a skylark, a honking goose, a buzzing insect. Recordings of blackbirds feature prominently in Kate Bush’s Aerial Tal, not to mention, of course, in the Beatles’ Blackbird, and field recordings of farmyard animals, rushing rivers and harsh winds have been used by other musicians over the years. Now, however, soundscape artists are blurring the division between music and the natural world further, with many taking to Britain's woodlands in search of their natural notes and melodies. For some, it’s not only a meditative experience, but a way of enhancing their perception of the natural world. “Listening, if you give it time, can be transformative to one’s sense of place,” sound artist Jez Riley French told Sound UK. “You have to give up control in a way. At least give up the idea that you know what a forest sounds like.” The quantity and variety of different sounds to be discovered in even a small patch of British woodland can be almost endless for the committed listener. Here are some you might not have noticed before: Caterpillar Business You may, on a June day, notice the sound of raindrops pattering on the forest floor, then look up to discover there’s not a cloud in the sky. When large numbers of caterpillars feed on the canopies of oak trees during early summer, a sound not unlike rainfall can be heard. This is actually the sound of frass (caterpillar droppings) landing on the forest floor. The Inner Workings of Trees This one requires a bit of specialist kit, but is worth the effort. By attaching a contact microphone to the trunk of a tree, you can record the whispering movement of water through the tree’s xylem and the crackling sound of the sap rising up the trunk during spring, as well as the tiny pops and cracks of the growing and shifting wood fibres. Wasps Taking a Bite Did you know wasps have a penchant for wood? Carefully approach a dry log or a bit of old fencepost on a summer’s day and you may hear a social or paper wasp hard at work. These wasps scrape away wood fibres, chew them into a pulp, and take them back to their nests to build new walls. The sound is a faint scrabbling, like fingernails on a tabletop. Gorse Bombshells  Some compare it to gunshots, though the more temperate say the sound is closer to popcorn. As the sun heats the seed pods of a gorse plant during summer, the pressure inside them gradually builds and eventually, they burst, launching their seeds into the air, and letting off a loud pop. When dozens are going off at once on a hot day, the sounds combine into a satisfying crackle. How to Have a Go Though a clutch of soundscape artists have made their passion into a profession by creating albums of natural sound or providing accompaniment to exhibitions, most use field recording as a relaxing weekend hobby, and an excuse to spend time in the woods. The price and complexity of recording setups can range depending on the user’s commitment.  Hobbyists might want to invest in an omnidirectional microphone, such as a Lom mikroUsi, a Clippy EM272, or a Sennheiser MKH 8020, in order to capture the entire forest atmosphere at once. Contact microphones that capture those gurgling tree sounds, or hydrophones for recording activity below the surface of ponds and brooks, can also be worthy investments for the truly dedicated.  But for those just starting out, a basic plug-in microphone or even a phone recording can provide a fine place to start. Often it is the act of paying acute attention to the woodland around you, rather than the recording itself, which is most valuable. “The key is to be aware of your individual role in the collective quietness,” French explained. “Allow time for the sounds to take us beyond our usual, short attention spans.” Thanks to David Alty for the wasp image.

During a drought, the trees in a woodland or forest become 'stressed' and may die.  The  reason for their death is not immediately obvious (beyond lack of water), and  it is not possible to ‘transplant’ a mature tree and its complete root system to a lab for detailed investigations.  However, recently, researchers at the University of Innsbruck have taken ‘the lab’ to a set of mature pine and pine trees. The trees were fitted with rugged and waterproof ultra-sound detectors.  Some of the trees had their canopies covered by a ‘roof’ so that the summer rain was denied to the trees, and they essentially experienced a ‘drought’.   Drought stressed trees produce ultrasound ‘clicks’ (faint acoustic waves that bounce off of air bubbles) that can be picked up by the detectors.  Air bubbles or emboli form in the vascular system of the trees when they are struggling for water.  Water is drawn up the xylem vessels by the evaporation of water (via the stomata) from the leaves, there is a continuous column of water.  When the column of water breaks, bubbles form with the xylem vessels and the transport of water to the leaves is reduced.  If the flow of water is substantially reduced the tree will die. The sound detectors found that the spruces produced more clicks than the beeches when water stressed, suggesting more emboli were formed within their xylem tissues.  It may be that the beeches were able to access the deeper reserves of water in the soil, whereas the spruces had a shallower root system. Trees can, of course, reduce water loss from their leaves by closing down their stomates.  But when their stomates are closed, they cannot take in carbon dioxide for photosynthesis and make the sugars / starch that they need for their metabolism.  At the end of the experiment, the trees that experienced ‘drought’ were drenched with water and most recovered well, and their rates of photosynthesis caught up with the ‘control’ groups of trees (those with summer rain).  However, the spruces’ water reserves were somewhat depleted; this was determined by measuring the resistance the tissues offered to an electrical current. The ability to withstand / recover from drought could over time affect the make up of woodlands and forests,  particularly if the trend for hotter and drier summers continues. Interestingly, some work in the United States (at University of Wisconsin–Madison) suggests that young tree saplings that have experienced drought or heat are more likely to survive when transplanted into more challenging areas.  It seems that the soil microbes that young saplings experience can help young trees establish themselves.  Saplings grown in soil (and microbes) that have experienced drought / cold / heat are more likely to survive when later transplanted and faced with similar conditions.  Trees with ‘cold-adapted’ microbes survived better when experiencing Wisconsin’s winter temperatures. The work was conducted with different species of tree in a variety of locations in Wisconsin and Illinois. The transplant locations varied in temperature and rainfall.  It may be that fungi that inhabit the roots of the saplings are involved in these ‘responses’, though the microbial population of the soil is diverse. For more details of this work, follow the link here.

Whilst it is not possible to attribute a particular weather event to climate change alone, what is clear is that climate change / global warming intensifies certain meteorological events. High temperatures and reduced rainfall have lead to the extreme fires seen recently in Australia and on the pacific coast of America.  Floods and periods of drought are now more common and the last two decades have seen some of the warmest years on record - in the U.K. .  Whilst too much water can result in the death of trees and plants as the soil becomes water-logged - so oxygen cannot reach the root -  drought also stresses trees and other plants. Drought-induced death of trees is associated with the failure of the water transporting system (xylem), but the process is poorly understood. Tree, indeed plant survival, is dependent on a continuous supply of water to the leaves. Read more...

Climate change is now a fact of life and one aspect of this is the occurrence of more extreme weather events.  These can take the form of high winds / hurricanes, extended periods of heavy rainfall or conversely periods of drought.  Clearly extreme weather can affect all ecosystems; woodlands and forests are no exceptions.   Consequently in recent years, a number of organisations have been looking at different tree species in order to understand more about drought resistance (or the ability to withstand prolonged flooding - when the roots are deprived of oxygen). INRA (French National Institute for Agricultural Research) has been looking at a small tree of the cypress Family (Cupressaceae) - Callitris tuberculata.   This grows as a small evergreen tree or shrub in Western Australia.  It can survive extreme drought and has been described as “the most drought resistant tree in the world”. Read more...