A lot of research work now focuses on the resilience of woodlands and forests in the light of climate change, that is their ability to cope with conditions like drier, hotter summers and/or  warmer/wetter winters. It has generally been assumed that trees at the limit of their range in dry regions would be most affected by climate change (with rising temperatures and less water).  However, a major study of some six million tree annual ring samples, (involving 120+ species) coupled with analysis of historical climate data has shown that trees in drier regions show a certain resilience to drought.  Trees seemingly become less sensitive to drought as they approach the edge of their range.  Trees in wetter climates are less resilient when they experience drier conditions or drought.  It seems probable that many species in wetter woodland and forest ecosystems will face significant challenges if the climate does move to a drier and warmer state. Assisted migration may be needed.  One idea is to ‘exploit’ the genetic diversity found at the edge of a species range.  The slow natural migration of trees may not be able to keep pace with the speed of climate change. Full details of this study by the University of California can be found here : Drought sensitivity in mesic forests heightens their vulnerability to climate change The effects of climate change have become very clear in recent times.  This last year witnessed:- Record breaking wild fires in Canada, with the smoke extending across to the East coast of the States. [caption id="attachment_40597" align="aligncenter" width="675"] Canadian forest fire[/caption] Heat waves in parts of America , for example, Phoenix (Arizona) suffers the best part of a month with temperatures of 43oC. Parts of the North Atlantic Ocean saw unprecedented temperatures The global temperature in July was 1.5oC above the pre-industrial average, September saw temperatures 1.8oC above the pre-industrial average. Parts of Chile and Argentina saw a ‘heatwave’ in the middle of their winter. It is clear that ‘unchartered waters’ lie ahead.

Rapid onset climate change, and the spread of new pests and diseases are creating unprecedented challenges to the long-term survivability of UK woodlands.  This looming threat is becoming ever more tangible, and the need for strategies of resilience building is urgent. Promoting diversification within and amongst woodlands has been identified as one such strategy with the potential for significant, positive impact. DiversiTree is a UKRI-funded project led by the James Hutton Institute which is measuring the impact a more diverse mixture of tree species has on building resilient woodland ecosystems, as well as how woodland managers and others understand woodland diversity, and what they are CURRENTLY doing to promote resilient woodlands. The project also hopes to generate practical advice and results which managers can use to make better informed decisions regarding the species mix of their woodlands, especially with regard to conifers. A key question which often accompanies discussions of woodland diversity is the planting of non-native species within British woodlands. The DiversiTree project is taking an evidence-focussed approach to its assessment and are investigating how ecological resilience interacts with woodlands with different priorities or objectives and what this might mean for the longer-term ecological sustainability of the forests of the UK. In actuality, many native woodlands are rather species poor, and could potentially benefit from a period of managed diversification with native species, non-natives, or a mixture depending on local objectives and context. What is critical here, is understanding the ecological role ANY tree can serve in a complex landscape, and planting in a manner which enhances and strengthens a woodland’s biodiversity.   If you’d like to learn more about our work and keep updated with our progress, please follow us on Twitter @DiversiTree_UK (https://twitter.com/DiversiTree_UK?s=20) or email [email protected] with any questions.  Seumas Bates (Environmental Anthropologist, Bangor University)  

In recent times, we have heard much about various initiatives to plant more trees, such as The Queen’s Green Canopy tree planting project to mark the platinum jubilee. Tree planting is part of the government’s plan to mitigate certain aspects of climate change as the trees will absorb carbon dioxide from the atmosphere, which is one of the principal greenhouse gases.  Once absorbed and used in photosynthesis, much of this carbon is then locked away for many years in the form of complex compounds, such as cellulose and lignin. The peak of carbon dioxide uptake by UK woodlands and forests was estimated to be just under 20 million tonnes in 2009.  However, since that time the amount has actually declined.  Many of the conifer plantations that were planted back in the 1970’s and 1980’s have now been felled / harvested, so they no longer contribute to the uptake of carbon dioxide.  It is important that these clear felled areas are replanted and tree cover restored; indeed, in places increased.  Planting rates have risen in Scotland but the performance by the rest of the UK is somewhat limited.  Even with new planting, it takes time for such new forests / woodlands to reach the CO2 absorption levels seen in the 2000’s. Continuous cover forestry (CCF) is a different approach to woodland forest management; it seeks to avoid clear felling and  promotes a mosaic of trees by age and species. There are a number of factors that influence new planting, such as the availability of land.  Using high grade agricultural land for tree planting would affect targets for increased agricultural productivity and domestic food supply.  Also, with climate change and the increasing number of extreme weather events (storms, flooding, drought etc) greater thought needs to be given to risks such as forest fires.  Recent months have demonstrated the ferocity of forest fires in France, California and Portugal.  We cannot assume that the UK will be exempt from such events.  Similarly, we have witnessed powerful storms (such as Storm Arwen) which felled many thousands of trees (and impacted on public services such as electricity and train travel).  The warming climate is also associated with ‘new’ diseases and parasites in our woodlands and forests. New planting needs resilience ‘built in’ to the plan. The Environment, Food and Rural Affairs Committee in its recent report (2021/2) has made a number of important comments in relation to tree planting in the UK, notably : It noted that the Forestry Commission had said that nurseries in the UK will struggle to expand production to deliver the number of young trees required for the Government to achieve its planting ambitions. There is a lack of a sufficiently skilled and large workforce to achieve England’s tree planting ambitions. To meet the Government’s tree planting goals, the UK will need to import seeds and young trees (until domestic capacity increases); and this carries the risk of the introduction of pests and diseases.  

If you have planted new trees and there's been a spell of extremely dry weather, as happened in the summer of 2022, you might be very worried for their survival, but there are several things you can do to increase their chances.  This isn't just a problem for the first season because saplings can be at risk for the first three years after planting; it's also not a binary, live or die thing for your planting - usually some trees will survive and some will perish but the challenge is to maximise the percentage that make it through a drought.  Let's first consider how dry conditions affect trees.  The saplings' first response is often to increase root development to take up more water.  Your young plants will also seek to reduce water loss so the leaves will wilt or can even be shed even though it's only July or August, and this can lead to the saplings not having the ability to photosynthesise adequately.  So you need to do what you can to avoid water loss and, if practical, to apply water. So, to increase the chance of your saplings surviving you can, if practical, actually spread water around them but that may have to be done fairly regularly during the period of drought.  Ideally irrigation should happen overnight when evaporation is lower and that will also limit pest problems and "leaf burn" that may be associated with irrigation in full sun. An additional strategy is to weed the young trees thoroughly to reduce the competition for water.  This can be combined with firming up the soil around the base of your saplings to avoid the soil drying out through fissures.  To reduce evaporation and stop the weeds returning you can use a mulch around the base of your young trees - ideally a mulch mat or by spreading some woodchips or bark. A few weeks after the drought has passed but while the leaves are still on the saplings you can assess your losses and order new trees to replace those that have succumbed to the dry weather.  This process is described by foresters as "beating up" but when it comes to the actual planting this needs to be done carefully - only replace trees that you are sure have died rather than those which just lost their leaves early. For urban trees you can be prepared for a period of dry weather by installing watering tubes or bags which reduce surface run-off and make sure that the water reaches the tree roots.   It is unclear how many millions of trees have been lost to the 2022 drought but it certainly includes many mature trees as well as many newly-planted saplings and hedgerow shrubs.  It seems that droughts like this are part of a process of climate change and more such events are probable - so our woodlands will be under increasing stress over the next few years.  For those who are establishing new woodlands a sensible approach would be to plant only a proportion of the area each year and to select a wide variety of tree species.  It also suggests that for new woodlands you should, where possible, include the adopting of areas of natural regeneration - where trees have come up of their own accord - these self-set trees are likely to be very resistant / resilient to periods of extremely dry weather. [caption id="attachment_38870" align="aligncenter" width="600"] Drought - green shoots of recovery?[/caption]  

Sadly, the world is losing species, both plant and animal, at a significant rate.  Indeed, some claim that we are now experiencing the sixth mass extinction.  In contrast to previous extinctions (the Permian extinction is thought to be due to an asteroid impact), the present loss of species is largely associated with a mix of direct and indirect human activities. These include :- destruction and fragmentation of habitats,  Exploitation fishing stocks and hunting (think dodo),  chemical pollution,  invasive / introduced species, and  human-caused global warming The loss of animal species has knock-on effects in terms of food chains and biodiversity. Plants are also affected as many rely on animals for the dispersal of their fruits and seeds.  In times of global warming, it is essential that plants can reach new areas that are suitable for their growth.  If not, they are stuck in areas where they may not be able to survive in the changed / changing conditions.  This could mean that plant species are lost, together with the ‘ecosystem services’ that they provide (be it food, timber, carbon storage, flood mitigation etc).  Seed dispersal is also important in terms of recovery from ecological disasters, like wildfires.  Natural forest regrowth usually happens through seed dispersal. If an ecosystem is rich in species, it is generally more resilient to environmental change.  The relationship between fruit / seed dispersal and animals has been significantly affected by the creation of roads, motorways, farms, and the development of cities - essentially habitat fragmentation.  Animal dispersal is often associated with fleshy fruits.  Whilst this is particularly true / obvious for many tropical fruits, it is also the case for many plants in temperate regions.  Berries, hips and haws are dispersed by animal means, with birds being particularly important agents. Several pines produce large seeds and attract corvids such as nutcrackers and jays. The birds, sometimes called scatter hoarders, collect seeds and bury them in areas away from the parent trees but in habitats suitable for the next generation of trees  Mammals also play significant roles.  In Africa, elephants are important  seed  dispersers  for  numerous  species; they  have an extra-ordinary sense of smell and will search out ripe, fleshy fruits. Some seeds have been shown to be distributed 60+ kilometres from a parent plant. Not only this, but the journey through the gut of the elephant seemingly increases the chance of germination, and being deposited in the dung reduces the chance of the seed being eaten by beetles.  Some monkeys in South and Central America eat as many as fifty different types of fruit in a day. carrying some off in their stomachs and dropping others to the ground. In Britain, as part of their diet, foxes will eat various wild fruits, like blackberries; squirrels eat nuts; and mice / voles eat grass and other seeds.  Even invertebrates, like ants, disperse seeds. This may be through the activity of harvester ants, which, like squirrels and other ‘gatherers’,  forage the ground of the wood or forest (collectively) gathering large quantities of seeds and  then transport them back to their nests / colonies.  As they transport the seeds, some get dropped or lost on the way.  Others may be ‘cached’ in or near the nest for later consumption but then are ‘forgotten’ or ignored. Some fruits contain seeds covered with a sticky substance as is the case of Mistletoe. When birds feed on the fruits, the seeds often stick to the beaks of birds.  Then, they may wipe the sticky seed off on a branch;  or it may be eaten and pass out in the bird’s droppings. The ‘glue’ (viscin) around the seed helps fasten the seed in place. Even humans carry seeds far away for plants, for example, by taking an apple on a picnic and throwing the core with its seeds into the bushes. Or seeds may transported in the mud sticking to boots and shoes, or indeed on tractors, cars or other machinery. The loss / extinction of animal species from any given habitat will sooner or later effect the plants.  We are only beginning to fully appreciate the interdependence of life.    The loss of any species - plant or animal - will undoubtedly have unintended and unforeseen consequences which can only be to the detriment of all life on earth.  

Ecology is concerned with understanding the relationships between organisms, and their relationship with their environment.  This can involve how climate and soil influence the growth and development of organisms. Ecological studies may focus on a particular organism (autecology) or specific areas. One area that has been intensely studied is Wytham Wood, which lies just outside Oxford.   The area includes ancient semi-natural woodland, secondary woodland, grassland and ponds. It is a designated SSSI, where some 500+ plant species and 800+ lepidopteran (butterfly and moth) species have been recorded. Records of bird populations go back some sixty or more years (with the work of David Lack and others); other ecological studies with long-term data include those on badgers,  and also work on climate change. Wytham Wood belongs to Oxford University. Historically speaking, it is possibly the most intensely studied woodland in the world.  Read more...

Monks Wood is an area of woodland in Cambridgeshire.   It has been subject to extensive and intensive ecological studies for many years.  The site is described by Natural England as one of our essential lowland woods with ash and field maple trees; also to be found is the rather rare wild service tree.  The ground flora is typical of that of ancient woodland, within the wood there are also ponds and streams.  Monks Wood is a National Nature Reserve. Next to the reserve there is former agricultural land.  Two fields have been studied to understand the process of natural woodland development.  One field was formerly two acres of grassland that was ‘abandoned’ (in 1996), the other was a four acre barley field (that was left to stand in 1961).  For natural regeneration of woodland to occur there needs to be existing woodland nearby.  The transition of these fields to ‘new’ woodland has been monitored over the intervening years - through field surveys of trees, measurement of vegetation height, remote sensing via LIDAR.  Read more...

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...