How Trees Reclaimed a Frozen Land The British landscape we know today, its rolling hills, hedgerows and scattered woodlands, is the product of thousands of years of change. But rewind far enough and none of it existed. After the last Ice Age, Britain was a treeless, frozen expanse. What followed was one of the most remarkable transformations in the natural history of these islands: the slow, steady return of the forests. A land emerging from ice About fifteen thousand years ago, the climate began to warm and the ice sheets that had smothered much of Britain started retreating northward. The southern parts of the country may have supported a sparse arctic grassland, but trees were entirely absent.  Sea levels remained low, vast quantities of water were still locked up in ice, so Britain was physically connected to mainland Europe. A broad plain of meandering rivers linked present-day East Anglia with the Netherlands and northern Germany, across a region now submerged beneath the North Sea and often referred to as Doggerland. This land bridge allowed plants, animals, and eventually human settlers to make their way into Britain from the continent, setting in motion changes that would reshape the landscape dramatically. The pioneer trees arrive Trees gradually colonised the bare ground. The first wooded areas were likely dominated by birch — species such as Betula nana and B. pubescens that tolerate extreme cold. Although the climate was warming, conditions were still too harsh for many pollinating insects. Birch is wind-pollinated, making it an ideal pioneer species: one that can establish itself on immature or disturbed soils in challenging environments. In doing so, pioneer species modify their surroundings and 'open the door' for others to follow, a process known as succession. Over time, pine, aspen and hazel arrived and took hold, followed later by elm, oak and small-leaved lime. Forests spread across Britain, covering the land except for the highest, wettest and coldest areas. Reading the past through pollen How do we know what grew where, and when? Pollen analysis of peat bogs and other sedimentary deposits can reveal which species were present over different periods. The outer wall of a pollen grain — the exine — is extraordinarily resistant to decay, so its distinctive structure remains intact for millennia, allowing researchers to identify species long after the trees themselves have vanished. The wildwood takes shape By around six thousand years ago, forest covered most of the British countryside. This great expanse of woodland is often called the “wildwood”, a term popularised by Oliver Rackham in Trees and Woodlands in the British Landscape. The wildwood was at its most abundant during this period: a complex, tangled mosaic of trees, many of them dead or dying from the effects of wind, fire sparked by lightning, and flooding. It would have offered a rich variety of habitats and niches for plants, insects and mammals alike. Not as dense as you might think Recent research and pollen analysis published in the Journal of Ecology suggests that Europe’s post-glacial wildwoods were rich in hazel, oak and yew; species that tend to flourish in more open woodland where light reaches the ground, rather than in dense, closed-canopy forest. Hazel produces more pollen and flowers freely in sunlit conditions. Yew, while sensitive to fire, is shade-tolerant and needs some space and light to avoid being outcompeted by taller trees. Its leaves are toxic to most mammals (including humans), which protects it from grazing. The persistence of yew in ancient woodlands, along with its sensitivity to fire, points to a relatively open woodland structure; one maintained, it is thought, by the grazing activity of large herbivores. Oak, too, is a light-demanding species whose seeds germinate best on disturbed ground. Large herbivores consume huge quantities of vegetation, altering plant biomass and community composition. They also cause physical damage through trampling and bark-stripping. These processes can help create clearings and maintain open areas within the woodland. The resulting light reaching the forest floor would have encouraged a rich ground flora to flourish beneath the canopy. A living legacy Britain’s wildwood may be largely gone, but its legacy runs through the landscape. The oaks, hazels and yews that define many of our oldest woodlands are living links to those post-glacial forests. Understanding how they established themselves and how grazing, fire and climate shaped the woodland around them isn’t just a matter of historical curiosity. It offers practical insight for anyone involved in woodland conservation and restoration today. The wildwood reminds us that British forests were never static or uniform; they were dynamic, open and shaped  by many animals,  and the elements. 

During the last Ice Age, much of the UK was covered with a layer of ice up to kilometre deep, or by enormous glacial lakes. Certainly in northern parts, there was no vegetation as glaciers scraped their way across the landscape.  So much water was locked up in the glaciers that sea levels dropped dramatically; we were connected to Europe by areas such as Doggerland.  Details of the glaciation and its effect can be found on the BRITICE site.  When the ice age came to an end some eleven thousand years ago, plants, animals and humans migrated back to the previously frozen and inhospitable land.  Over time, large forests and woodland areas developed.  In the North, boreal forest grew up - represented today by the remaining Caledonian Forest.  Further south, there was the wildwood (as described by Rackham and others). The wildwood was probably a complex and tangled mixture of different trees, with many of the trees either dead or dying through the effects of wind, fire (lightning strikes) and flooding. It would have offered a vast variety of habitats and niches for plants, insects and mammals. Read more...

pollardAfter the last Ice Age, plants, animals and humans moved back into the vast areas vacated by the retreating ice.  Plant, and then, animal communities became established and much of the area was covered by what has been termed ‘wildwood’ – see previous Wildwood blogs.  These areas would also have been home to human populations migrating from the hinterland of Europe and Doggerland.  Communities developed and we may suppose that areas of forest/woodland/wild wood would have been cleared - for housing, the grazing of animals, to provide firewood/timber.  Such forest / woodland would have been managed to a greater or lesser degree. Read more...

We British like our hedges - perhaps it's part of the British reserve, keeping people at arms' length, or maybe it's because they are very functional for keeping stock in fields and marking boundaries. For wildlife, hedgerows have long been important avenues of local migration and hedges represent their own distinct habitat. The attitude of the authorities towards hedges has undergone a roller coaster ride over the last 50 years. In the 1970s, the government were paying grants for the removal of hedges with the objective of encouraging the creation of larger fields to make agriculture more efficient - these were bad times for conservation - Oliver Rackham describes these as "the locust years".  More recently grants have been available for planting hedges and their unauthorised removal in the countryside has become a criminal offence with the Hedgerow Regulations of 1997. Read more...

Why do hedgerows exist?  Many were originally planted to contain livestock (sheep, cattle, pigs, chickens), others existed to define boundaries – who owned which parcels of land.  Hedges often delineate fields; field is derived from the old English feld which means an area of felled trees.  However, hedge construction and management was particularly associated with the process of enclosure, which transformed the landscape of England.  This was often connected with the change of land use - from arable to pasture for sheep.  Read more...

The wholesale destruction of ancient woodland through farming and forestry has diminished but new roads,  bypasses and the installation of infra-structure & services (such as utilities & power lines) can still be a problem.  In recent times, new or different threats to ancient woodlands have emerged to upset the balance of woodland ecosystems. In the 1960’s and early 70’s concern focussed on the effects of air and acid rain pollution .  Such pollution was characterised by the deposition of sulphur dioxide and its derivatives (sulphuric & sulphurous acid), plus various nitrogen oxides. Read more...

In the U.K. about 11.8% of the land is covered by forest, (Thomas and Packham, Ecology of Woodlands and Forests). The amount of ancient woodland within this is very low.  Ancient woodland is also fragmented and dispersed.   Ancient woodland is a term that is applied to areas where trees have been present in the landscape for many hundreds of years, not necessarily as great continuous tracts but as discrete plots or areas.  Such ancient woodlands (in the U.K.) usually have a long history of being ‘managed’ by local communities. This contrasts with the woodland in a  country, such as New Zealand,  where there are large areas of well-preserved and largely ‘natural forest’. The term ‘ancient woodland’ should not be confused with ‘wildwood’.  Wildwood refers to the woodland that developed  after the last glaciatio, in the UK and across Europe.  The nature of ‘the wildwood’ is the subject of some debate. Was it a dense, dark forest or open savannah with trees?  Whatever its nature, wildwood was never managed as such. Ancient woodlands are valued as they are complex and diverse ecosystems.  The diversity of plant (and animal) species in such woodlands is a function of: their continuity (which may extend back many hundreds if not thousands of years), and the human interaction with the woodland (through coppicing, woodcutting, and the management of animals – especially herbivores). The Nature Conservancy Council (now Natural England) recognised the importance of these woodlands some time back and published 1:50,000 maps identifying woodland that had existed since 1600 A.D.  Details of the various divisions of ancient woodland as defined by Natural England may be found here . There are a number of features that are associated with ancient woodland.  Many were subject to coppicing; a program that is characterised by regular felling and subsequent re-growth of the trees.  This makes use of the ability of certain trees to sprout from the stump or base, or grow from root suckers.  Hazel and beech may be managed in this way. In consequence, ancient woodland may have coppice stools (multi-stemmed trees) of great age but may not contain ancient or veteran trees (tall, upstanding and very old trees). Ancient woodlands are usually isolated and have been so for many years.  They have not arisen by recent fragmentation, due to farming or felling.  Beneath the layer of trees, there are a number of plants, which have come to be termed ‘ancient woodland plants’. Some typical examples of ancient woodland indicators are: golden saxifrage, wood sorrel, wood anemone and wild daffodils.  Such plants seldom occur outside woodland and do not easily disperse; that is, they cannot migrate from one woodland to the next. The plants may be clonal, that is, they make use of vegetative / asexual reproduction. There is a long history of an association between ants and plants,  one example of which is the seed dispersal of some species by ants.  In Cow Wheat, (or Melampyrum pratense), the seed looks like an ant’s egg or cocoon in terms of its size, colour, shape, smell and weight.  Some seeds have special structures called elaiosomes – oily appendages, which attract ants.  The ants then carry off the seeds, they eat the oily structure and discard the rest; in consequence the seed is dispersed. Working out which species are associated with ancient woodland is very specialised work. If you find a particular 'indicator species', you should not assume that in itself is proof of ancient woodland ‘status’.  These species are only indicators.  Amongst the ground flora, there is what might be termed a number of “coppicing plants”.  These are plants that cannot tolerate dense or continuous shade.  They tend to appear in greater numbers when some of the trees have been cut down during the coppicing cycle; an example of such a plant is the oxlip, Primula elatior.  Within ancient woods, there may also be grassland species such as the Devil's-bit Scabious in open grassland areas. It has been suggested that there are ‘forest interior’ species – which require large tracts of un-fragmented forest.  Such species (often mammals or birds) are sensitive to the introduction of roads, which dissect woodlands. The creation of such ‘edges’ can have dramatic effects in terms of temperature and humidity.   ‘Openness’ can mean that the temperature increases, whilst humidity decreases; consequently the transpiration (water loss) of trees, shrubs and herbs also increases.  These effects may be felt up to 300 metres into the forest / woodland from the road. In the twentieth century, the greatest threat was the destruction and fragmentation of ancient woodland mainly due to the pressures of more land for farming, forestry and road construction.  Rackham (see below) has suggested that perhaps some 40% of ancient woodland was lost to farming and forestry in the post-war period of the last century.  The process of fragmentation may amplify such loss.  If a 100 hectare wood is reduced to a 50 hectare site, then this remaining area may not be able to support the full fauna and flora of the original woodland.  This is especially true if the 50 hectares is split further by fields or agriculture.  Such fragmentation can have significant effects on bird and mammal populations, which need a certain 'minimum' area for the establishment and maintenance of territory. As the threat to ancient woodland from farming and road construction has diminished though not disappeared, so other threats have become apparent - which will be addressed in another post. Note : The Woodland Trust has produced a number of guides to identifying and managing ancient woodland. Rackham, O.  Woodlands, Collins, 2010 P Thomas and J Packham, Ecology of Woodlands and Forests, Cambridge University Press, 2007 Rackham, O.  Ancient Woodlands: modern threats.  New Phytologist,  2008.

The New Stone Age or Neolithic Period saw the development of settlements and farming. The transition from hunter-gatherer to farmer began and gradually spread across Britain. The construction of settlements and the adoption of farming (a practice that probably began some 10,000 years earlier in the Fertile Crescent) involved the clearing of woodland or forest. It was achieved with fire and the use of flint and polished stone axes. Pollen records suggest a decline between 4000 and 3000 BC in tree species such as ash and an increase in plants such as nettles and plantains.  As ash tends to grow on the edges of woods, its decline could well be associated with the clearance of parts of the wildwood for agriculture, though it may also have disappeared because of disease. Read more...