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