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The Valency Valley

Woodlands

Why do deciduous trees shed their leaves? Through photosynthesis leaves feed trees. However in autumn and winter frost damage to leaves would leave a tree open to infection by disease. Also precious water would be lost through evaporation at a time when the tree’s roots cannot gain sufficient moisture from the cold ground. Broad leaves would also act as traps for snow, which would weigh down and snap limbs and act as extra ‘sail’ in high winds, making the tree even more vulnerable. As the leaves disappear photosynthesis can no longer take place via the sun – green chlorophyll is not produced and hence the myriad of autumn colours are produced – browns, reds, yellows – as the leaves die and fall. Each species of tree has different shaped and patterned leaf scars on its twigs where leaves have dropped. In this way, even in winter, it is possible to identify tree species fairly easily.
Tree seed dispersal. Some tree fruits fall straight to the ground – acorns, beechnuts, and conkers. Others like maple, ash and sycamore have ‘wings’ and can flutter and blow some distance. Acorns and hazelnuts will also be buried by jays and squirrels, offering further chances for germination.
Fungi.  Without fungi, life would choke on its own waste products – they are the natural world’s essential rotters as they break down dead leaves, rotten wood, feathers etc, reducing them to humous and returning nutrients to the soil. The mushrooms and toadstools we see in autumn are only the fruiting bodies – like an apple on a tree. The main part consists of nutrient absorbing threads underground which exist all year round. The warm, damp weather often associated with autumn provides the ideal conditions for the fruits to grow. The fruits are short-lived but will release millions of spores to ensure that the underground mass of threads – or mycelium – live on for decades.

Galls. People often ask me what the strange growths are, which look like fruits, growing on the leaves of trees. These are called galls. They are formed when a plant’s cells are hijacked by an intruder, e.g. an insect grub or an egg laying insect – often wasps. Chemicals are exuded into the cells which cause them to divide and mutate and the plant forms a tumour-like growth. Oak trees are particularly vulnerable to this and will produce ‘knopper’ and ‘marble’ galls amongst others.

Butterflies

We have been surveying butterflies along the Valency Valley once again this summer. This year has been a good year for butterflies, and we have recorded the rare pearl and small pearl-bordered fritillaries once more. There is a healthy population of the more widespread silver-washed fritillary which is probably the largest British species and can’t be missed despite its rapid flight.

Both here and on the cliffs I have noticed large numbers of the clouded yellow butterfly this year (dark yellow with black wing tips). This is a migrant summer species from southern Europe and as such numbers fluctuate from year to year. In its warm native countries this strong, fast flyer is a prolific breeder producing up to four broods a year. Occasionally there is a big influx into Britain when the European population has swollen in favourable conditions. Eggs are laid in great numbers on clover, lucerne and trefoils. Spring migrants will have time to breed in the UK producing a single brood in the autumn, but none can survive the cold damp November weather.

Invasive plants

Ever since the flood, we have been keeping a watchful eye on the appearance of invasive plants along the valleys. We all know about Japanese knotweed, and this hasn’t emerged as a problem. What have turned up though, especially this summer, are large quantities of Himalayan balsam.

This garden escape has found its way into the Valency catchment, and has begun to spring up all over the place. It spreads prolifically and can soon take over an area, much like knotweed. It is a tall very fleshy stemmed plant that likes streamsides and damp grassland. It has a very ornate pink flower and the ability to fling its seed a great distance once the ripened seed pods explode – some of you may have seen this filmed on BBC Wildlife shows!

Because of this we have been pulling up the plant whenever we see it in the Valley before this occurs! I have seen whole fields of the stuff when out walking in other parts of the country, where it’s obviously not been managed, so would hate it to get out of control here.

 small pearl bordered fratillery