One particular concern of continued climate change and global warming is drought.  Not only will drought affect people but also plants. Droughts can inhibit the growth of trees, or kill them.  Over time, they can change the species make up of woodlands and forests.   If woodlands and forests experience drought then this will seriously impact their ability to absorb carbon dioxide from the atmosphere - they act as carbon sinks and help mitigate climate change. Recently Tom Ovenden et al from Stirling University and Forest research at Roslin have focused on the effects of climate on Scots Pine.  Scots Pine is a widely distributed tree across Europe and often planted for its timber.  It is a ‘favourite’ with red squirrels.  The research team examined the trees in a pine forest that was planted (near Inverness) back in 1935.  They examined tree rings from trees from high and low density stands.  A ring forms each year and the width of the ring is a measure of the growth the tree has achieved in a particular year.  Wide rings indicating substantial growth.  The width of the rings was then correlated with climate records.  The rings formed in ‘drought years’ was compared to growth in average (non drought) years, and to the rings formed in ‘post drought’ years. Read more...

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...

In their natural environment, giant sequoias are to be found only in a high and narrow area on the western slopes of the Sierra Nevada.  Like, bristlecones, giant sequoias (Sequoiadendron giganteum) are a long lived species - their life span can be 3000 years.   However, their most spectacular feature is their sheer size - they can reach heights of 300 feet with a trunk that may be 20 feet  or more in diameter.  Indeed, the world’s largest tree (by volume) is General Sherman - a sequoia estimated to have a volume in excess of 52000 cubic feet. The trees are not only long lived but ‘tough’.  They have protection against fire and rock fall, both of which are hazards in their home habitat.  Protection is afforded by their bark, which is very fibrous and can be up to 3 feet thick. Read more...

The autumnal fall of leaves in deciduous trees is a well recognised event; their changing colours prior to being shed often make for spectacular displays - the New England Fall. Evergreens (with certain exceptions) do not undergo a similar loss of leaves but that is not to say that their leaves are forever green or permanent.  Indeed, each year, evergreens have a seasonal drop of their needle-shaped leaves, it is normal part of the tree’s cycle.  The leaves / needles of conifers have varying life spans; they are not a ‘permanent fixture’.  Many conifer needles will turn yellow then as they age, falling off the tree after one to several years. This change can be gradual or in some species quite rapid.  White Pines (Pinus strobus) typically retain their leaves for 2 to 3 years, whereas Scots Pines (Pinus sylvestris) usually retain their needles for three years. Larches, which are conifers (Larix sp) are somewhat unusual in that they shed their leaves every autumn.  The stress that a tree experiences through drought may result in more rapid browning and greater loss of leaves. Read more...

There is only one living member of the genus Sequoia,   Sequoia sempervirens : the coast redwood.  It is a coniferous trees and belongs to the family Cupressaceae. The redwoods (Sequoia sp) are amongst the largest and oldest living organisms on the planet – some are possibly more than three millennia old. The trees are found along the coastal regions of California and Oregon.  Whilst the trees can live to a great age, recent studies have found that the trees are suffering as a result of beetle attack, prolonged drought and and fire damage.  Several of the long lived trees in the Sierra Nevada of California have died in recent years as a result of these ‘problems’.  It had been thought that such trees could survive fire or beetle attack Read more...

In recent times, new or different threats have emerged to upset the balance of woodland and forest ecosystems.   In the 1960’s and early 70’s concern focussed on the effects of air pollution, particularly the effects of acid rain.  This type of pollution was characterised by the deposition / assimilation of sulphur dioxide and its derivatives (sulphuric & sulphurous acid), plus various nitrogen oxides.  This air pollution was largely due to industry and traffic. Some of the most striking effects of ‘acid rain’ pollution were seen in the coniferous forests of Germany - where it was termed : Waldsterben [Wald=forest plus sterben=to die].  Read more...

Climate change means that we are likely to experience more extreme weather events from intense and prolonged rainfall to severe drought and heat.  The plants and trees of woodlands may experience periods of flooding, during which their roots may be deprived of oxygen (as the soil is waterlogged) and consequently - die.  Similarly trees and other plants may be subject to drought - resulting in the stunting of growth or even death.  It had been thought that most trees had roots that penetrated deep into the soil (in search of water and minerals) but the aftermath of the Great Storm of 1987 revealed that this was not the case for many types of tree.  The root systems of many trees are, in fact, relatively shallow - the root plate may only reach down some five to six feet. Read more...

Over the centuries, our woodlands have experienced (to a degree) a relatively stable environment - both in terms of climate and biological ‘incursions’.  There have been occasional ‘perturbations’ some climate or weather related - such as the Great Storm of 1987 and some biological such as Dutch Elm Disease in the 1970’s. Our woodlands have been managed largely on the basis of this stability - a relatively constant biological and physical environment.  However now, climate change is an established fact and the number of biological threats to our native flora and fauna has increased significantly in recent times.   Climate change has seen the advance of Spring and more ‘extreme weather’ [for example, drought, high winds] plus the large scale movement / importation of trees, timber and plants from many different parts of the world has lead to the introduction of various pathogens and pests.  Read more...