Blog - conifers

Plant signals.

Plant signals.

by The blog at woodlands.co.uk, 8 March, 2023, 0 comments

Many plants have a distinctive scent, think of sweet peas, jasmine or honeysuckle, or stand next to a pine tree on a warm, summer’s day.  The scent is due to the release of volatile organic compounds (VOC’s, often oils), produced by specific tissues or glands.  Often it is the nectaries within flowers that produce the scent, apart from their ‘job’ of producing the sugary nectar.  The nectaries may be found on almost any structure within a flower - petals, sepals, stamens, ovary*. The location of nectaries varies from species to species.  There are other structures that can produce scent, for example, trichomes, and osmophores. Osmophores are clusters of cells specialising in scent production.  Any part of a plant can release scent, for example, the leaves of eucalyptus, lavender or myrtle. The scent of a plant may include a variety of VOC’s, indeed there may be dozens of different organic compounds contributing to a particular scent.  Many of these compounds are terpenoids (isoprenoids).  They contribute to the scent of eucalyptus oil, lavender oil and the flavours of cinnamon and ginger. Scent may have a number of functions.  It may be released to attract specific pollinators - moths, butterflies, bees, hoverflies etc. (who have learned to recognise the scent).  The production of VOCs can be modulated, for example,  scent production may be turned off when a flower is pollinated.  A scent may also unfortunately be a signal to herbivorous insects to ‘come and feed’. So, scent have positive or negative effects. A scent may be produced to deter herbivory by certain insects.  Sometimes, plants have a different approach. For example,  when pollen beetles feed on oil seed rape, the rapeseed releases VOCs which attract the attention of other insects.  Specifically, those that will lay their eggs in the larvae of the pollen beetles. These insects are usually from the same family as bees, wasps and ants - the Hymenoptera (insects with membranous wings and a ‘narrow waist’).   The pollen beetle larvae are then ‘eaten’ from the inside by the developing parasitoid larva.  The release of VOC’s is affected by a number of factors temperature, light, circadian rhythms, physical damage and drought.  As the temperature increases so the amount of VOCs released increases (usually). This may be experienced in coniferous woodland.  Conifers give off a variety of volatile oils (i.e. biogenic VOC’s) that contribute to a unique aroma and the formation of aerosols found in the air in and around such woodlands and forests; it is most noticeable in warm weather.  [An aerosol is a ‘mixture’ of very small particles (solid or liquid) in air; other examples of aerosols include mist, cigarette smoke, or car exhaust fumes]. In snapdragons, the most scent is emitted at noon which tends to coincide with pollinator activity, in contrast tobacco plants scent release is in the evening / night when hawkmoth are active.  Drought reduces the ability of plants (like rosemary and thyme) to produce / release VOC’s, this in turn, has been observed to affect which pollinators visit their flowers.  Nectaries located within the flowers of a plant are sometimes referred to as nuptial nectaries, whereas those found in other parts are termed extra-nuptial.  
conifer woodland

Creating diverse woodlands and forests

by The blog at woodlands.co.uk, 14 December, 2021, 2 comments

We know that forests are important to all life on the planet.  They have often been referred to as the ‘lungs of the earth’, a reference to the fact that they produce vast quantities of oxygen - which is essential for respiration for so many forms of life.  They also take up carbon dioxide and ‘fix’ it into complex organic molecules - from starches, to cellulose and lignin.  Thus, the carbon is locked away for months, years or even millennia.  The equatorial forests of Brazil and Sumatra are species rich, incredibly diverse, but deforestation and the expansion of agriculture are threats to many biodiverse, forested areas across the world. As so many forests and woodlands have been felled, there is now a movement to plant millions and millions of trees (across the world) in an attempt to mitigate climate change and in the UK to increase our percentage tree cover from a pretty low base.  Sadly, twentieth century forestry in the U.K was largely based on monocultures (for timber production). The trees planted were large stands or plantations of conifers - using Scots Pine, Larch and Spruce. These plantations not only lacked biodiversity, but were / are susceptible to wide scale pest infestation and extreme weather events.   Woodlands and forests that have a diverse range of tree species are not only healthier but show greater growth and carbon fixation. They are more resilient.  The diversity of trees ensures the each species accesses slightly different resources from the environment  - from soil minerals, water and light.  Diversity means that trees of the same species are less likely to be clustered together so pest and pathogen outbreaks are less common or less severe.  One area that has undergone an extensive and diverse planting regime is Norbury Park Estate (near Stafford).  Since 2009, over 100 different tree species have been planted, and the woodlands can now produce 1500 tonnes of new wood each year, and harvest 5000 tonnes of carbon dioxide from the air.  Not only can diverse woodlands / forests fix carbon, supply harvestable timber but they also offer areas for rest and relaxation. Whilst it is not possible to plant an 'instant' forest or woodland, it is possible to plant a range of tree and shrub species that will in time grow and mature to form a diverse and species-rich area.  As Charles Darwin said many years ago “more living beings can be supported on the same area the more they diverge in structure, habits, and constitution” [On the Origin of Species by means of Natural Selection, 1859] Managing woodlands for wildlife - see here.   N.B.  Opens a PDF.    

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