The use of chemicals to control insect pests of crops has a long history. One of the most concerning episodes was the extensive use of DDT, an organochlorine compound. Initially used to control outbreaks of malaria and typhus, it was then used as an agricultural insecticide. Within a few years there were warning signs of its adverse effects, and in 1962 Rachel Carson published Silent Spring which questioned the indiscriminate use of insecticides. The use of these chemicals continued despite evidence of bioaccumulation in ecosystems and  Identification of specific effects such as the thinning of the eggshells of birds of prey. Consequently, populations of eagles and sparrowhawks declined. It was not until a decade later that the use of DDT was banned or severely restricted. Now the use of insecticides such as the neonicotinoids is being questioned. These are still used for seed dressings of oilseed rape and maize. Even in very low concentrations, there is evidence that these chemicals are damaging to pollinators such as bees and bumblebees. Various studies indicate that these chemicals affect the  bees ability to navigate, so that some do not return home. The chemicals also affect the number of bumblebee queens produced by a colony. Much of the pesticide research has focused on the physiology of honeybees. This research has indicated that worker bees can help protect the queen from chemical contamination by filtering out certain substances in the food provided for her, some of which may pass to the honeycomb.  Recent studies suggest that this ability to sequester chemicals may be overwhelmed and that pesticides can accumulate in the queen over time. To offset this build-up it seems that the queen can offload toxic chemicals into the eggs she produces. A queen may produce several hundred eggs each day which ultimately develop into the workers required to sustain the colony. However, eggs containing these chemicals such as methyl parathion [an organophosphate insecticide] may not develop fully. Consequently, there may come a point when the chemical burden means the colony is no longer viable. [caption id="attachment_21584" align="aligncenter" width="600"] Honey bee - wings beating furiously[/caption] Honeybees are responsible for the pollination of approximately one-third of the world’s food crops including oilseed rape, mustard, cabbage, peppers, citrus fruits, coffee, sunflowers, avocados and raspberries. The rapid decline of these pollinators threatens agricultural productivity and ecosystem stability. Details of the most recent work on pesticides and honeybees : https://www.sciencedirect.com/science/article/abs/pii/S0960982226008195

Changing tree lines. Research led by the University of Leeds provides a picture of how mountain tree lines are shifting upward in response to rising temperatures. The tree line is the upper ecological limit for tree growth. The study reveals that the world's tree lines are moving to higher altitudes as the planet warms. The research team used advanced satellite imagery to study a million kilometres of closed-loop treelines across the world. Closed-loop treelines are distinct rings around the upper slopes of mountains. Because these high-altitude zones are largely isolated from human land-use activities, they offer scientists an opportunity to measure the direct impacts of climate change on vegetation patterns without the interference of farming activities or other forms of development . The main findings of the study were: There was an upward shift of tree lines across the Earth.  Roughly 70% of the treelines surveyed moved upward. The most noticeable shifts occurred in tropical regions. This was particularly true in the mountains of Malawi, Papua New Guinea, and Indonesia.  There was considerable variation in the amount of movement of the tree lines.  Tropical treelines advanced more rapidly than those in temperate areas, where a retreat could sometimes be seen. In some areas, such as the western United States, wildfires have resulted in a retreat of the tree lines.  This retreat might be due to heat and drought, but also changing management practices. The upward migration of mountain tree lines poses challenges to high-altitude ecosystems that exist above the trees. While an expanding forest can increase carbon sequestration by removing more carbon dioxide from the atmosphere, it can also trigger a series of unwanted consequences.  For example, As trees and wooded areas advance, they encroach upon unique ecosystems, such as alpine tundra and meadows. Consequently, alpine plants and animals that are adapted to cold and windy conditions are confined to ever smaller areas. Having reached the mountain peak, they have nowhere else to go and face the risk of localised extinction. The result of this tree line advance is to reduce biodiversity. Remote upland ecosystems are at risk. In the longer term, the trees may affect the hydrology of the area, changing the pattern of water runoff to areas below. The leads study highlights the vulnerability of remote upland ecosystems and the changing position of treelines across the world. Further information on this study here : https://onlinelibrary.wiley.com/doi/abs/10.1111/gcb.16885 Thanks to Angus for images

Generally speaking, leaves are quite small, but collectively they present a massive surface area to the environment.  The total surface of leaves is significantly greater than the surface area of the Earth.  Leaves are the organs of photosynthesis, not only do they make the basic chemicals for the plant, but they replenish the oxygen in the atmosphere. Generally speaking, a leaf has two surfaces.  One surface (the adaxial) is presented to the sun, the other (the abaxial surface) is shielded from the light to some extent.  Both surfaces are covered with a waxy layer (the cuticle), which helps restrict water loss. The underside of the leaf has many tiny pores, the stomates, which can open and close to allow the exchange of gases and water vapour.  The lower surface may be covered in minute 'hairs'.  These create an unstirred layer, so that air next to leaf has a high water content and thus water loss through the stomates is reduced.  The veins of a leaf contain xylem tissue which delivers water and mineral salts, and phloem which transports sugars and other organic compounds from the leaf. [caption id="attachment_43706" align="alignleft" width="300"] adaxial surface[/caption] [caption id="attachment_43705" align="alignright" width="300"] abaxial surface[/caption]   The upper  surface and lower surface  of a foxglove leaf.  Whilst the veins can be seen on the top surface, they are ridged and covered in hairs on the lower surface. [caption id="attachment_13486" align="alignleft" width="240"] galls on sycamore[/caption]   Once a leaf has grown then its size, shape and the veins remain constant, but during the course of the year other things can and will change.  For example, in autumn the coloured pigments in the leaf break down and many compounds are transported out of the leaf as it undergoes senescence. The leaf may be subjected to attack, caterpillars and leaf miners may eat its tissues.  Certain wasps may lay eggs within the leaf so that a gall develops.  Greenfly use their piercing mouthparts to access sugars and other compounds from the phloem.  Bacteria may infect the leaf either through wounds inflicted on the leaf, or by penetrating the stomates. To some micro-organisms, a leaf is ‘home’; it is a habitat.  Rather like it is now common to talk about our gut microbiome or  the microbiome of the skin, so each leaf has a microbiome. Recently, microbiologists from China and Germany have studied the microbiome of oak leaves.  Specifically, they examined the microbiome of the leaves of the pedunculate oak.  They examined how the organisms present changed during the course of a growing season.  They found that the upper and lower sides of the leaves had different communities of micro-organisms.  Both surfaces  shared the same sorts of bacteria, but they varied in the amounts / proportions of the bacteria on the two surfaces.  Furthermore the differences between the upper and lower surfaces changed as the seasons changed.  The diversity of organisms on the lower surface of the leaf fell as the year progressed.  Some of the bacterial DNA on the lower surface was that of bacteria which could be found on / in aphids and whitefly.  Some of the bacteria found were associated with fermentation of sugars.   The study did not investigate fungal species on the leaves, but it does indicate that there are complex microbial communities present on leaves, and that the two surfaces offer different ‘opportunities’ for micro-organisms.  Similarly, it has been established that there is a root microbiome. The root microbiome is a complex community of bacteria, fungi, archaea, and viruses living in and around plant roots. This microbiome helps the plant take in nutrients, fight diseases, and cope with environmental stress. [caption id="attachment_43724" align="alignright" width="350"] Hornbeam - abaxial surface[/caption]   [caption id="attachment_43723" align="alignleft" width="350"] Hornbeam - adaxial surface[/caption]

Non-native species can be a concern if they become invasive.  They can affect or even take over ecosystems.  The effect of Rhododendron ponticum in some woodlands has been disastrous.  Invasive plants can:  lead to the extinction / loss of native species  alter the species diversity of an area change the community structure alter the way in which species interact change the microbiome of the soil The loss of native plants may occur through competition for light, nutrients, water, or space.  Some invasive species have the potential to alter the physical or chemical environment.  They may do this by exuding chemicals that inhibit the growth of other species; such exudates are said to be allelopathic.  The Tree of Heaven (Ailanthus altissima), which was introduced to the U.K. in the eighteenth century from the Western Himalayas, releases a substance [ailanthone] into the soil.  This kills off many native plants and helps the tree take over entire areas.  Another introduced plant is the Himalayan Balsam (Impatiens glandulifera).  As an introduced species, it arrived here without any of its natural ‘enemies', no organisms that either feed on it (insects, caterpillars, etc.) or parasitize it (fungi, bacteria). Also, a single plant can produce between 800 and 2500 seeds. For an annual plant, it is surprisingly tall, sometimes growing to a height of six  feet. It has been able to spread; it did not stay in Victorian gardens. It is now found on waste land, roadsides, railway lines, in damp woodlands, and on river banks and it poses significant problems.  For example, when riverside stands die back in the autumn, it leaves the soil relatively bare and unprotected, which increases the risk of erosion.  Studies have shown that the balsam produces naphthoquinones.  These chemicals leach from the leaves and exude from the roots and are thought to affect : soil fungi associated with mycorrhizal formation  the germination of native plants.   Recently, researchers found that the balsam produces greater amounts of naphthoquinones at the start of the growing season, which would give the plants an advantage over native species by interfering with their germination and early development.  The balsam would then be able to outcompete native plants for light and mineral sources.  When the plants die in the autumn, their decomposition releases significant quantities of nutrients into the soil, which could benefit native plants. If the balsam plants have been growing in riparian environments, then these nutrients may leach into the rivers/streams, increasing the risk of eutrophication. There is an interesting article on the Himalayan Balsam and its possible allelopathic effects here: https://pubmed.ncbi.nlm.nih.gov/41297495/  Thanks to Anton for images.

Once upon a time, the gypsy moth lived only in the Fenlands of eastern England, where its caterpillars fed upon bog myrtle and creeping willow.   As the Fens continued to be drained and agriculture expanded, this native population died out in the early part of the C20th.  However, many years later, a colony of the European form of the moth was found in Epping Forest. This form of the moth is polyphagous, that is, its caterpillars can feed on a variety of plant leaves. They have a particular penchant for the leaves of oak and poplar.  Since its ‘introduction’, this form of the moth has spread to many parts of south-east England. The caterpillars of this moth can denude a tree of its leaves if the infestation is heavy.  Repeated attacks combined with drought can result in the death of trees. The trees do have a defence mechanism which is to increase tannin production, which makes the leaves much more bitter.  But this comes at a cost to a tree, namely an increase in metabolism and energy expenditure to make these materials. [caption id="attachment_43799" align="aligncenter" width="675"] Gypsy moth caterpillar. [Thanks to Bernell MacDonald & Pixabay][/caption] Research has indicated that oak trees have ‘solved’ the problem in a different way.  If a tree has been subject to a significant attack by these caterpillars/moths, then in the succeeding year it delays the opening of its leaves by a few days.  The effect of this is that when the caterpillars emerge, the leaves that they depend upon are still ‘sealed away’ in their buds. So, the caterpillars have little or nothing to eat.  The effect of this is to reduce the damage to the tree by over 50%! The research work was carried out over a large area in Northern Bavaria and made extensive use of radar satellites.  The satellites were able to identify which trees had been stripped bare and how they reacted in the following year.  Further details of this work can be accessed here: https://www.nature.com/articles/s41559-026-03071-9

One of the most intensely studied areas in the country is Wytham Wood, which lies just outside Oxford.  Wytham Wood belongs to Oxford University. The site includes ancient semi-natural woodland, secondary woodland, grassland and ponds. Wytham is a designated SSSI, where some 500+ plant species and 800+ butterfly and moth species have been recorded.  The records of bird populations (like that of the Great Tit) go back some sixty or more years,  initiated by the work of David Lack and others.  Recently this data has been examined in conjunction with detailed weather records over the same period. The Oxford scientists looked to see how the weather affected the growth and development of the chicks of the Great Tit.  Not only did the data cover several decades but also the records of some 80,000 great tits.  The study revealed that Great tits have adjusted to warmer Springs by breeding earlier.  Severe cold weather immediately after hatching was particularly harmful. Older chicks were significantly affected by heavy rainfall. If exposed to very hot weather and heavy rain, the young chicks can lose more than a quarter of their body mass.  This is particularly true for broods raised later in the year. Warm periods were linked to higher fledging weights. The earlier breeding enables the adult birds to take advantage of the earlier appearance of their prey -  caterpillars.  However, this earlier activity can also expose them to cold snaps that can occur in early Spring.  Newly hatched chicks struggle to maintain their body temperature in cold periods as they lack feathers.  They will also need to 'burn' more of their food energy to generate heat, rather than it being used for growth.   Bad weather not only affects their food supply (caterpillars, etc), but also whether the adults can leave the nest to search for and gather food.  The higher fledgling weights during periods of warm weather are probably associated increased insect activity (and visibly), enabling the adults to satisfy the appetites of their young.  As caterpillars have quite a high water content, this helps stave off dehydration in the young chicks. Climate change seems to be throwing more extreme weather events at us, and the seasons are becoming increasingly unpredictable. These weather events (heat, cold, intense rainfall) may well have even greater effects on our bird populations, both woodland and urban. Further details of this study can be found here.

Natural habitats have been disappearing for a long time - as a result of human activity.  The last century saw hundreds of miles of hedgerow disappear, and the same is true for ponds and wild flower meadows.  Agriculture, transport networks and cities have expanded - woodlands have become fragmented.   Now, sadly we have seemingly daily reports of our rivers and seashores being polluted with sewage.  Indeed, thousands of such incidents have been reported and many rivers and seaside resorts are now unsafe places to swim (or row?).  Clearly, the infrastructure (much of it victorian) is unable to cope with the demands placed upon it.  Surfers against sewage have collected and collated information about sewage, and on their web site there is a map of coastal areas experiencing sewage discharge. If this situation was not bad enough,  run-off from major motorways is also being discharged into our rivers and streams.  Indeed, the Environment Agency has acknowledged this as a serious issue, accounting for some 18% of ‘water quality failures’ in England.  Like sewage, it is damaging. So what does this road run-off water contain?  It seems to be a mix of particles from tyres, clutch and brake pads, motor oil, transmission fluid, coolant, gear oil, and power-steering fluid. In addition, rust or corrosion from the car / vehicle body and galvanised parts can release iron, zinc, and aluminium. Modern tyres contain natural rubber, synthetic rubber etc. so when you brake, or speed up, the tyres shed thousands of tiny rubber and plastic fragments. They form as a result of the friction between the tyre and the road; they are referred to as ‘Tyre Wear Particles’ or (TWPs)*; and are a significant source of microplastics.  Microplastic are seemingly everywhere, in the oceans, in habitats across the world and even in us.  Scientists have found even microplastics in human semen, and also follicular fluid ( the fluid that surrounds a developing egg in the ovary). During and after heavy rain, TWPs and other materials are washed off the roads, with most entering stormwater networks, which channel the run-off into rivers, streams etc. Due to their density,  the TWPs etc sink and form a sediment layer.  The BBC has reported on the ‘black gunk’ in the River Lambourn (Berkshire).  The Lambourn is a chalk stream with crystal clear water as it makes it way through Welford Park, before passing underneath the M4.  Thereafter, it turns brown and murky. This has consequences for the invertebrate animals that live in the waters of the stream or on the stream bed. It is possible to mitigate some of the effects of this run-off / stormwater. For example,  near the A38 in Devon the National Highways have built a reed bed . This filters the run-off from the busy road. There are only 210 true chalk streams worldwide, and most of them are in England.   For example, the Test and Itchen in Hampshire, the Wensum in Norfolk and the Piddle in Dorset.   They are a unique contribution to global ecosystems. The National Highways is aware of the pollution problem across the road network and is using a computer model to identify which stormwater outfalls to tackle. More than a thousand locations that are "potentially high risk" have been identified.  Under its current plans, a limited number of high-risk sites will have had a mitigation in place by the end of last year. *TWPs may be swept up into the atmosphere and transported to remote regions like the Arctic.

Like the monkey puzzle tree, the horsetails (Equisetum spp) are sometimes referred to as ‘living fossils’.  Some of their ‘relatives’ date back to the late Devonian period - about 380 million years ago.  Some were  huge and tree like, reaching a height of some 30 metres, about 98 feet.  These plants formed 'forests' and were abundant in the carboniferous period.  These ancient species persisted for some 100 million years, with some contributing to the formation of coal deposits.  Modern horsetails first appeared during the Jurassic period. Present day forms are much smaller than those of the past..  Equisetum arvense is a species that is widespread across Northern Europe and parts of America. It is a nonflowering plant, multiplying through spores. It can absorb silicon from the soil, which is unusual.  It also has the ability to take up and accumulate heavy metals such as copper, zinc, lead and cadmium.  It grows and spreads by underground rhizomes.  These rhizomes can form an extensive network, penetrating deep into the soil (sometimes to a depth of six feet).  This means the plant can be very difficult to eradicate if it appears in your garden. Techniques for removing the plant can be found on the RHS site : here.  Unchecked, Equisetum can spread extensively and smother / outcompete smaller plants. In Spring, the rhizomes produce pale, fertile shoots, topped with strobili.  Strobili are cone shaped structures that release spores. Once the spores have been released, these shoots wither and die.  Somewhat later, the non-reproductive shoots appear.  These have fine branches that appear in whorls around the ‘segmented’ stems. The whorls form at various ‘nodes’ along the stem.  These branches give the plant is characteristic form.  The name Equisetum comes from the latin Equus for horse, and setae for bristles, as the shoots have a vague resemblance to a horse’s tail.  The word arvense is also derived from the Latin where "arvum", means “ploughed”.  This references the growth of the plant in arable soil and disturbed areas.  Horsetails commonly occur in damp and open woodlands, and may also been found near the edges of streams (which may have been their original habitat). The plant has been used in herbal medicine to make a ‘tea’ or used in baths to treat skin complaints, chilblains and wounds.