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Changing forests and woodlands.

Changing forests and woodlands.

by blogs at woodlands, 18 March, 2022, 2 comments

For millions of years, forests and woodlands have been changing - as a result of natural regeneration, storms, fires and climate change.  However, with the expansion of human populations, woodlands and forests have been cut down to make way for towns, cities and the infra-structure of ‘modern’ life.  Sadly forests, and woodlands such as those in the path of HS2,  are still disappearing. ‘Untouched’ rain / tropical forest is being cut down to make way for cash crops; plus vast wooded areas have been destroyed by fire in Australia, Sweden and on the West Coast of the United States in recent years. Clearfell of any forested area for timber or agriculture involves the removal of all trees / vegetation and is sometimes followed by burning of the remaining debris. Clearfell can also have unintended consequences (beyond the loss of entire animal communities.  An Australian study has shown that it lowers soil nutrient levels - notably nitrate and phosphate.  Furthermore, the use of heavy machinery in clearfelling can compact the soil and its consequent exposure to the elements can lead to erosion (rain runoff).   When an area is subject to intense fire, there is a drop in the organic carbon content of the soil and structural damage to the soil; it can take many years for such fire-damaged soil to ‘recover’. Forests and woodlands support the vast majority of land-based species. However,  the species that we see today on a woodland walk may be different to those our ancestors might have seen five hundred or a thousand years ago.  Certain species only survive in relatively undisturbed (and ancient) forests / woodlands.  There are species that can ‘deal’ with disturbance and are adaptable, indeed opportunitistic,  such as red deer and fox.  The same can be said for certain plants species, which can become invasive.   Changes in species make-up and biodiversity do not always immediately follow loss of forest or woodland.  Generally speaking, the longer the life span of a species then the longer for the effects of forest loss to become apparent.  It may be that the effects ‘span’ generations, raptors / birds of prey may manage to raise their young in the immediate period following loss of forest or woodland. But their offspring may struggle to survive in a depleted environment. It might be that with limited resources an animal might simply not reproduce for years, if ever again.  Consequently, the impact of forest destruction / loss that species depletion might not be apparent for many years. The loss of forests and woodlands has lead to many local, national and inter-national initiatives to offset these losses: for example, New Zealand’s ‘One Billion Trees” project and the Nature Conservancy’s “plant a billion trees’ campaign.  Broadly speaking, reforestation involves the planting of native trees in an area, whereas planting with new (non-native) species is afforestation. Recent research suggests that whilst non-native plants often grow faster than native species, they also have less dense tissues (think: oak versus larch) and decompose more readily, which can contribute to more rapid cycling of carbon.  This will not help to mitigate climate change. It is also important to consider which trees might prosper and offer resilience in the light of climate change. Our climate is changing and will be different in the future, with summer temperatures being higher.  We have already seen more extreme weather events (leading to flooding and wild fires).  Forestry England has a number of tools to help plan which tree species will be suited to a site, now and in future.   There is ESC4 which offers a means to help forest managers and planners select tree species that are ecologically suited to particular sites; and there is also the climate matching tool.  As Forestry England says this is “so that we can see which places in the world currently experience the climate we are projected to have in future. We can compare these different places to help us plan which tree species will be suited to a site, now and in future”.  One strategy is to create woodlands that are more diverse, as it thought that diversity helps woods more resilient to climate change. This can be through encouraging a range of different, but carefully selected trees to grow, and being aware of the provenance of seeds or saplings.
Woodlands web updates : 13

Woodlands web updates : 13

by blogs at woodlands, 2 February, 2022, 0 comments

Wetlands. In the past, many areas of wetlands have been drained and ‘dried out’.  Now it is recognised that this is counter-productive in terms of carbon storage / sequestration and biodiversity, so there are now measures to restore wetlands. The hope has been that restoration of wetlands will do much to restore the variety of plants and animals (and help carbon storage).  However, research by the University of Copenhagen suggests that such projects might be ‘struggling’. The study examined ten wetlands (near the River Odense) that were restored between 2001 and 2011.  The restoration involved the removal of drains and ditches, and allowed streams to meander again instead of flowing in ‘straight channels’.  The aim of the project was primarily to reduce the leaching of nitrogen and phosphorus from adjacent farmlands, and hope to see greater diversity of plants (e.g. marsh orchids, globeflower, tussock-sedge and ragged-robin).   The ‘restored’ wetlands were botanically poor (whether restored in 2001 or 2011), they had only a quarter of the plant species compared to natural wetlands.  This may be due to  the continued input of nutrients (from agriculture), which encourages species that are ‘nutrient hungry’ at the expense of others. the ‘difficulty’ of wetland species to disperse from one area to another. It may be that future restoration programs will need to include planting / seeding of additional wetland species. It has been suggested  that it could take the best part of a hundred years for the restored wetlands to resemble natural wetlands. Redwoods and relatives. Previous posts have talked about the special features of the giant redwoods (their height, age etc).  Over the last 150 years, they have ben subject to the pressures of commercial logging, clear felling and more recently high intensity fires.  Indeed, the fires have been of such an intensity that seed banks in the soil have been destroyed. Now they have been subject to genomic analysis, that is their DNA has been analysed and sequenced.  The first conifer genome to be sequenced was that of Norway Spruce, then that of loblolly pine.  These suggested that conifer genomes are large (3 to 10 times larger than the human genome), with repetitive sequences.  Coast Redwoods are hexaploid, that is, they ave six copies of each chromosome (we are diploid, that is, have only two copies of each chromosome).   The DNA of a coast redwood has  27 billion base pairs of DNA, the giant sequoia has 8 billion; by contrast we have circa 3 billion.   It is hoped that the Redwood Genome project will see the restoration of areas of coast redwood and giant sequoia that have been lost over the years. The genomic analysis will help inform and guide management strategies, ensuring genetic diversity in the newly planted tree seedlings. Such a strategy will (hopefully) enable newly planted areas to survive and thrive — in the Anthropocene. More on chromosomes Just as it has recently been shown that Coast redwoods are polyploids (i.e. have extra sets of chromosomes), so recent research in the Czech Republic has shown that the common nettle [Urtica dioica] has different ecological ‘preferences’ depending on its chromosomal status.  Nettles can be diploid (2n = 26) or tetraploid (2n = 52).  The tetraploid nettles seemingly have a broader ecological tolerance and a wide geographical distribution, whilst the diploid nettles occur in a narrower range of ecological conditions. Details of this research can be accessed here (note link opens a PDF) and Plants for a future has lots of information on nettles.    

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