Loss of nitrogen fixing species. Some plants can ‘fix’ atmospheric nitrogen.  That is they can take nitrogen from the air and use it to make complex nitrogen-containing organic compounds (such as amino acids / proteins).  This fixation of nitrogen is due to the presence of symbiotic bacteria in root nodules.  Gardeners often make use of ‘nitrogen fixers’, such clover, peas and beans to augment soil fertility. A recent study has investigated the changes in the makeup of the flora in European forests (over several decades) from 1940 to 2019.  What they found was that the proportion of nitrogen fixing plants has declined.  The changes did not seem correspond to any changes in temperature  or aridity / rainfall during the time period, but to nitrogen accumulation in the environment.  When nitrogen levels are low, nitrogen fixing plants have an advantage, but when nitrogen levels increase their advantage over other plants is lost. Nitrogen compounds in the soil can result from the intensive use of fertilisers on nearby agricultural land or atmospheric deposition of various pollutants.  Nitrogen levels have increased tenfold since the start date of the surveys.  This loss of nitrogen fixing plants might, in the long term, result in a loss of ecosystem resilience. For further info - visit https://www.science.org/doi/full/10.1126/sciadv.adp7953 The great green wall project. There are a number of large scale tree planting projects, many associated with offsetting global warming.  The great green wall aims to grow a belt of trees some 8000 km in length, and 15 km wide in the Sahara.  The planned route supported trees in the past.  The aim is to ‘stabilise’ the desert, limiting further expansion into the Sahel, as the tree roots help to stabilise the soil, limiting erosion.  Desertification is associated with drought and overgrazing.  The idea of such a barrier was taken up and approved by countries south of the Sahara in 2002, during a special summit.  The trees selected are drought resistant species, that also serve to fertilise the soil and contribute fruits, fodder and fuel wood for local communities. Though millions of trees have been planted, the project needs more funding if it is to succeed. Further details about the great green wall can be found here and here. Dealing with drought ? [caption id="attachment_35526" align="alignleft" width="300"] drought[/caption] Drought is a problem not only for woodlands but also for crops, resulting in substantial food loss across the globe.  The damage to crops is likely to increase as fresh water availability declines.  During drought, the availability of water in the topsoil decreases, leaving water only accessible in the  deeper subsoil.  Plants seek water through their roots and whilst roots generally grow downwards, they also tend to spread outwards to form a network. So, if the roots are mainly located in the upper layer of the soil, they may not be able to absorb water as the soil dries.   Now, research at the University of Nottingham has found that the plant growth regulator abscisic acid plays a critical role in a plant’s response to drought.  The abscisic acid  promotes the production of another growth regulator - auxin.  The two enhance the plant’s geotropic response* - so that the roots permeate deeper into the soil in search of water. Full details in the research paper here : https://www.sciencedirect.com/science/article/abs/pii/S0960982224016439?dgcid=coauthor * Geotropism is a plant’s response to gravity.

Trees come in many shapes and sizes.  Some are tall and thin, like Poplars, others have a ‘rounded’ canopy, like oak and horse chestnut.  Sometimes we ‘persuade’ trees to assume a particular shape or form, perhaps through pollarding or coppicing - or something more extreme - like topiary or bonsai.  However, sometimes nature itself has unusual or dramatic effects on trees.  Wind can leave trees on cliff tops or exposed places distorted and growing almost horizontally along the direction of the prevailing wind. Occasionally, something very strange is seen.  For example, at Gryfino in Western Poland, there is a forest with some very weird looking trees. There are about 400 trees that are bent at the base.  At first, the trunk lies more or less parallel with the ground, then it bends upwards and the stem is erect.  Consequently each trunk of these pines trees has a pronounced bend in it (see photo below).  The rest of the trees in this forest are quite normal, growing upright and straight - like most pines.It is thought that the pines were planted back in the 1930’s though the local town was forsaken by the residents during the second world war (and only repopulated in relatively recent times). The trees are sometime referred to as the Crooked Forest. There has been much speculation as to how the trees came to be so mis-shapen.  The theories run from The landing of alien space craft! This crushed / flattened the trees when young and tender The trees were damaged  by German tanks during the war (but why only a select number of trees?) Genetic mutation(s) which resulted in abnormal growth Fungal infection(s) which resulted in abnormal growth The young trees were flattened by a heavy fall of snow, which perhaps persisted for some time.  The trees were able to right themselves in the Spring, through a normal geotropic response. The trees were part of plantation / forest, in which some were deliberately cut at a young / sapling stage.  The area was a tree farm, where some of the pines were cut / bent for later use in furniture or frames. By bending a young tree down to the ground in this manner (for some time), compression wood is formed. Such wood has higher lignin and lower cellulose content and it is stronger than wood that is bent after a straight tree is felled (for example, by a steaming process).  Indeed, English ‘hedgerow oak’ was known to be the best for the curved timbers needed to internally strengthen a sailing ship.  Trees were even deliberately bent in certain ways so as to " grow" a required set of curved timbers.  Such curved timbers were known as “compass timbers”.  In Gryfino, it is likely that the war interrupted the activities of local foresters / woodworkers, they left and these trees were left to grow on in their rather unusual form. Thanks to Kalasancjusz at Pixabay for the image of the crooked forest.