Looking around the garden this morning one might be forgiven for thinking that autumn is already here.  Several trees seem to think the short days of autumn have arrived and are preparing to shed their leaves. Certainly the walnut and hazel are of this opinion.  However, other signs indicate that this is not the case, my twenty year old cedar has died, as have several Cryptomerias and other conifers - this despite assiduous trips with the water can.  In fact, the plants are responding to this summer’s weather, a long period without rain (or very little) plus the very hot weather that we have experienced; particularly in the South and South East.  The plants are not reacting to any changes in day length but to drought. Plants detect changes in the photoperiod they experience through their phytochrome system; under normal circumstances their biological clock will tell them when to prepare for winter.   Whilst many well established trees and plants with extensive root systems can withstand a period of drought, younger plants or those in poor or freely draining soil are likely to die.  Such plants simply cannot take up enough water to replace that lost through transpiration; that is, water evaporation through the stomates (pores) in the leaves.    The intensity of the heat this year coupled with the reduced rainfall has affected many plants and trees and it may be some time before we see the full effect of this summer’s weather.  Beech trees suffer more during periods of droughts because they have shallower roots, while oaks reach moisture deeper in the soil and continue to grow.  In the drought of 1976, many beech trees died and survivors often exhibited reduced growth some 40 years on*. Some plants respond to drought stress by bringing forward their reproductive process, so that fruits and seeds are produced early.  This is an attempt to ensure the survival of the species for when conditions are more favourable to growth.  The Woodland Trust, noted for its phenology records, recorded ripe blackberries in late July (lots of reports on its page on Facebook).  Hawthorn, Rowan, Holly and Elder have all been recorded as fruiting earlier this year.  This was true of the filbert in my garden this summer.  This earlier production of fruits and seeds may have ‘knock on’ effects on the wildlife that feed upon them.   Whilst the effects of the extreme weather are obvious in our parks, gardens etc, the effects on rivers and streams are dramatic.   Chalk streams, in particular, have been affected; they are unique habitats.  The River Ver is a chalk stream in Hertfordshire.  The summer has seen large sections of its upper reaches reduced by several kilometres due to the hot weather (and water abstraction).  The effects in and around such streams may be felt for many years as the water levels fall so the habitats for fish, amphibians and invertebrates (such as dragonflies / mayflies) are reduced or lost.  Recolonisation of such drought impacted systems can be slow and prolonged.   An accessible and detailed paper on Beech trees and drought is available here : research gate.net [caption id="attachment_22186" align="alignright" width="300"] Mature Beech on Box Hill, Surrey.[/caption] [caption id="attachment_10575" align="alignleft" width="300"] Mature beech[/caption]

Shade and stress. Shade (low light intensity) causes plants to elongate, reach up to the light to ‘outgrow’ the competition.  Such ‘elongated plants’ are said to exhibit etiolation.  However, there is a point when this strategy is counterproductive.  The plant simply cannot outgrow its taller neighbours, it is wasting resources and becoming weaker.  So plants in deep shade do not generally use this strategy.  Deep shade is detected by the phytochrome pigment system and ‘relayed' onto the plant’s circadian clock, the internal ‘daily time piece’.  This internal clock has various components and particular genes, some of which have an additional role in suppressing stem elongation (that would normally occur when shaded). Welsh woodlands and insect pollinators. A recent study across many different sites in Wales has revealed the habitats favoured by pollinators such as bees, overflies and butterflies.  The research found twice as many insects in broad leaved woodlands as compared to grassland areas.  They also found that farmlands without hedgerows had significantly fewer insects.  Both hedgerows and woodlands include trees such as oak and maple, which offer varied niches for pollinators.  They provide food (leaves) for larval stages, pollen and nectar for adults, plus egg laying sites and shelter. In Wales, there are plentiful grassland areas (mainly due to farming) with woodland only contributing 15% of land cover.  However, the Welsh Government aims to plant 180,000 hectares of new woodland by 2050.  New woodland will not only contribute to tackling climate change (through carbon sequestration) but will also do much to promote insect biodiversity. Sludge as fertiliser Sewage sludge is commonly spread across farmland as a form of fertiliser (throughout Europe).  Sewage sludge is the residual, semi-solid material that is the ‘by-product’ of sewage treatment of industrial and / or domestic wastewater. Sometimes, referred to as biosolids. It is a sustainable / renewable source of nutrients and reduces material going to landfill or incineration. The use of sludge has attracted attention as it can contain: Breakdown products of various medical / pharmaceutical that have been excreted / eliminated from us and / or animals, such as hormones, antibiotics, various drugs Heavy metals such as lead, cadmium, arsenic  Industrial chemicals / breakdown products PCB’s, dioxin Now, research at Cardiff University has shown that micro plastics in sludge are a problem; these are plastic particles less than 5 mm in size. It estimates that between 31,000 and 42,000 tonnes of micro-plastics are applied to European soils each year.  They are a threat to wildlife as they are easily ingested and can carry / contain toxic chemicals and may pass along the food chain.  The UK was shown to potentially have the highest level of microplastics in its soils, followed by Spain, Portugal and Germany.  

Some flowers are open during the day, ready to receive visitors (pollinators) but close up each night at dusk; for example, crocuses, tulips, poppies.  Other plants move their leaves in response to light and dark. Such movements of flowers and leaves are known as nyctinastic movements. The reasons for these movements are not particularly clear / obvious. A number of suggestions have been advanced : The closing of the petals at night might serve to keep pollen dry.  When wetted, pollen is heavier and less easy for insects to distribute. By closing at night, the nectar and pollen is protected from unwanted visitors.  Some insects are nectar robbers that is they take nectar but do not contribute to pollination. Darwin made the suggestion that the closing might help protect the floral organs from the chill of night time temperature. Leaves may move to help capture rain, closing down at night to allow water to trickle down to the roots (?). Different explanations may apply to different plants but these movements have a common underlying mechanism, namely phytochrome.  Phytochrome is a blue-green light absorbing pigment. It responds to red (in the region of 660 nM) and far red light (>730 nM). Red light is generally abundant during the day, but the balance between red and far red shifts towards the end of the day. This change is detected by phytochrome and it directs the plant’s circadian / daily rhythm.  Phytochrome is involved in many processes during a plant’s life cycle from germination to flowering.  The nyctinastic movements of plant parts is, however, largely controlled by the movement of water into and out of cells - cells can swell or shrink.  Some plants have special structures called pulvini to control the movement of leaves.  Pulvini are found in the bean family (Fabaceae), and plants like the sensitive plant (Mimosa pudica) and the Prayer plant (Maranta sp).  Pulvini are usually located on the leaf stalk (petiole). A pulvinus is a small swelling on the stalk, it has a central core of vascular (water-conducting) tissue surrounded thin-walled cells (parenchyma tissue) with large fluid-filled vacuoles.  The flow of water in and out of the vacuoles of these cells raises or lowers the leaf stalk / leaf. [caption id="attachment_36023" align="aligncenter" width="650"] Pulvinus on sensitive plant[/caption] [caption id="attachment_36032" align="aligncenter" width="650"] Young Mimosa pudica[/caption]  

In early October,  BBC4 screened a 90-minute documentary capturing every aspect of life in an ancient English oak over an entire year  "Oak Tree: Nature's Greatest Survivor" focuses on a single tree in Wytham Woods, just outside Oxford, a site acquired by Oxford University in 1942 for woodland research.   The film, presented by zoologist, entomologist and broadcaster George McGavin, opens with an high-tech assessment of the tree's condition. By firing laser pulses, forestry scientists create a 3-D virtual image of the oak so they can track its size and shape over the 12 months. At the outset, in late August, it's 19 metres tall and 30 metres wide and carries an estimated 700,000 leaves. Read more...

Yew woodland (in Southern England) tends to develop on the thin soils that form over chalk, often on the sides of dry valleys . They can be found along the North Downs, and in West Sussex on parts of the South Downs. Yew woodlands can also be found in the Cotswolds and in the Wye Valley (on limestone). In Ireland, there is a significant Yew wood near Killarney, again growing on top of limestone. Yew woodland may develop from chalk grassland, when grazing by sheep or rabbits is removed. With no grazing, Juniper and / or Hawthorn start to grow.  Then, between these, shade-tolerant Yew seedlings begin to grow.   Eventually, the Yew will overtake the Juniper / Hawthorn, and shade them out. The dead remains of juniper and hawthorn sometimes may be seen on the floor of a Yew woodland. Read more...