The Go-Between

Tree bumblebees collecting nectar from sallow blossom this morning, beside the river Tyne at Wylam in Northumberland. They seem to be hardier than other bumblebee species, foraging despite the fact that it was cold and very windy.

Most trees that produce catkins in spring are wind pollinated but sallow relies on insect pollinators (and occasionally, perhaps, birds like blue tits that have a liking for nectar). Both male and female catkins of sallow produce nectar to attract the first bumblebees, flies and butterflies of spring. There are separate male and female sallow trees so these insect go-betweens are essential for successful seed set. The catkin above is a female and ...

..........this one is a male sallow, producing nectar and pollen. The bee has just withdrawn its proboscis from the flower (it's the brown tube with the knee-bend) and it has yet to withdraw it between the two protective sheaths that also give it rigidity: you can see the sheaths pointing upwards in a V-shape (double click image for a larger, clearer view).

A Force of Nature ....

The whole country is gripped by snow and ice - our transport network grinds to a halt - schools close - panic buying in supermarkets. 

Meanwhile, along the river Wear near Durham city this morning, these sallow catkins were shrugging off their bud scales, ready to bloom as soon as it warms up a little bit. 



Nature is irrepressible......

Is Sallow Britain's only Native Bird-Pollinated Plant?

It’s been a slow spring in North East England and there still aren’t many flowers around, so the blooming of sallow catkins must provide a real lifeline for newly emerged pollen-eating insects like this hoverfly. Sallow – aka goat willow, aka pussy willow – is unusual in that it exists as separate male and female trees and pollen must be transferred between the two - which may be some distance apart - for seeds to be produced. Catkins of both sexes produce nectar, which is what attracts butterfly and bee pollinators, but it’s mainly pollen that most hoverflies are looking for; visiting and cross-pollinating female trees isn’t high on their agenda.

But blue tits are attracted by the nectar too and they visit trees of both sexes. Quentin Kay at Swansea University first noted this, back in 1985 (you can read his original research paper in Bird Study here) and it may be that goat willow is our only native bird-pollinated plant. Bird pollination is common in the tropics and sub-tropics, where hummingbirds have become nectar specialists, but it’s rare in cooler climates.

For more posts on tree ID click here

A Tree-Spotter's Guide to Buds: part 4

Aspen Populus tremula twigs are tipped with these sharply pointed buds that sometimes have a slight stickiness about their bud scales. This is quite common in poplar species and is most pronounced in balsam poplars, where the resin that's responsible has a wonderful fragrance. Poplars have a tendency to hybridise, sometimes making identification tricky, but aspen is easy to identify when it's in leaf because of a peculiarity of the leaf stalks; they're flattened from side to side, so the leaves tremble from side to side in the slightest breeze - hence the Latin epithet tremula. They also turn a wonderful shade of lemon yellow in autumn, and the sight of a whole tree of lemon yellow foliage trembling in the wind is something to behold.

Apple Malus domestica buds are blunt and downy, with few bud scales. The knobbly, scarred twigs have a character all of their own, especially........

...in old trees that have acquired their own epiphytic flora of lichens. Old orchards, now fast disappearing, are wonderful resources for people and wildlife and their cause has been vigorously championed by that admirable organisation Common Ground - see http://www.commonground.org.uk/

Most hedgerow apples are likely to be descendants of discarded cores of domesticated apples, rather than the native crab apple Malus sylvestris

The buds on the main twigs of wild cherry or gean Prunus avium are not particularly distinctive but a little way down the twig from these you'll find....

... the fruiting spurs that will carry those clusters of dazzling white flowers in spring - and in summer the cherries. Over the last couple of years I've tasted quite a lot of wild cherries and this particular tree bears unusually juicy and large deep red fruits, that make excellent cherry sauce for pouring over ice cream. Unfortunately, someone else has made the same discovery and this year raided all the low branches on the tree before I could get to it. All I can say is that I hope they suffered the same fate as the badger that had over-endulged in the fallen fruits: the ground nearby carried the purplish-red telltale signs of a badger with a severe stomach upset, along with a mass of cherry stones that had passed unharmed through its digestive system.

Sallow (aka pussy willow aka goat willow) Salix caprea carries green buds with no apparent bud scales, The single scale that sheaths the whole bud deepen in colour through the winter, taking on a brownnish hue, and when the leaf and flower tissue inside swells in spring the whole covering is shrugged off.

For part 3 see http://cabinetofcuriosities-greenfingers.blogspot.com/2009/12/tree-spotters-guide-to-buds-part-3.html

For more posts on tree ID click here