Last survivors

Despite the fact that we've had several frosts, there are still some wasps around, congregating on the flowers of ivy that provide a last chance for them to find nectar.

I found this wasp, which I think is a tree wasp Vespula sylvestris, crawling over the ivy flowers just as the rising sun melted the frost on the grass.

The dense covering of hairs on the wasp's body must provide some insulation against low temperatures, and it probably spent the night under the glossy, waterproof leaves of the ivy plant, which provides an overwintering site for all manner of invertebrates.

For more on the curious back-to-front life cycle of ivy, flowering in autumn and producing fruits in spring, click here.

A Tree-Spotter's Guide to Bark: Part 2

The grey-brown bark of alder Alnus glutinosa isn't particular distinctive - unlike the wood within. Freshly-felled alder wood turns a startling shade of red, although this quickly oxidises to a pinkish-brown. Understandably, the blood-like shade of the cut timber gave rise to many superstitions but didn't stop the coppicing of the tree for the production of high quality charcoal for gunpowder. Alder wood lasts exceptionally well if it's kept permanently wet or submerged - not surprising really, considering the tree's propensity for growing on riverbanks that frequently flood - and it was sometimes used for piles in bridge construction and also for the soles of clogs.

Wild cherry or gean Prunus avium bark is easily recognised by the long horizontal scars (lenticels) that run across the trunk. These are areas of porous bark that allow gas exchange for the living tissues below that generate new wood each year. Cherry bark also has a tendency to peel away in narrow strips around the circumference of the tree.

From a distance silver birch Betula pendula bark is dazzling white when it catches the sunlight, but a closer look reveals subtle shades of pink, orange and brown showing through from the bark tissues just below the surface. At this stage in the tree's life the birch bark peels away, sometimes in large sheets, as the diameter of the trunk expands (and so is ideal for birch-bark canoes) but as the tree ages....

-- the bark splits vertically, separating the white bark into flakey patches between deep fissures.

For more information on tree identification click here

A Tree-Spotter's Guide to Fruits and Seeds: Part 6

Medlar Mespilus germanica isn't a native tree in Britain and it doesn't seem to produce many viable seeds here, but it has been naturalised in a few hedges in southern counties. It's also quite widely planted in botanic gardens, on account of its large, attractive white flowers in spring, vibrant yellow autumn foliage and these curious fruits. Medlars need to be softened by frosts and a period of natural decay after they ripen - a process known as 'bletting' - before they are ready to eat. They have a slightly resinous flavour and are a bit of an acquired taste but I quite like them. There's a tree loaded with the fruits that I pass every day and as soon as the frost has done its work I'll make some medlar jelly - unless someone gets to the tree before me. I've tried to germinate the seeds from the fruits, with a complete lack of success.

The fruits of common lime Tilia x europaea are unmistakeable, being attached to a leaf like bract that slows their fall and allows them to spin to earth when they're released from the tree. It's not as aerodynamically efficient as the winged seeds of sycamores or ash, judging from the concentration of lime seeds that end up very close to the parent tree. Many of the seeds are sterile.

Folklore has it that a heavy holly berry crop is a sign of a hard winter to come. What it really indicates is that back in late May, when the trees were flowering, conditions were good for pollinating insects to carry pollen between the separate male and female trees. Trees with no berries at this time of year are most likely males, which can't produce berries, or females that were too far from a male to be pollinated. Some cultivated hollies carry flowers that are hermaphrodite and always produce berries. There's also a rather attractive yellow-berried form.

Stately elms that once graced the landscape are now history, thanks to the ravages of Dutch elm disease, but shrubby hedgerow elm is still common enough. Its clusters of crimson flowers produce masses of discus-shaped winged seeds - but they are all sterile. Hedgerow elms were all propagated from cuttings, so they were all genetically identical and all equally susceptible to the lethal fungus - only a few mature trees have survived.

For more on tree identification click here