This week I am looking at Alder, one of the sacred trees of the Celts, though it is not mentnioned in the Rede. 

Our local alders are many-trunked scrub alders that favour ditches and other moist places.  They often colonize disturbed ground and mineral soils in pure, clonal stands.  One of the significant things about their colonizing habit is that their rootlets work with Frankia bacteria to fix nitrogen from the air into the soil, in a form available to other plants, which can then succeed them.  The bark is often home to lichens, which require clean air, and give the trunks a blotchy appearance.

Alder leaves, crimped like paper muffin-tin liners, stay green until they drop off, quickly decomposing into a rich, black muck with an exhilaratingly earthy smell, while the cones stay on over winter, eventually falling and staining the snow, as does the meltwater dripping off them.  In early spring, both male and female catkins precede the leaves. 

The wood is orangey when freshly cut.  I have used the bark to make a brown dye, although related species can yield an orange dye.  The bark has strong antibiotic properties, and can be used on skin, and has been used for respiratory complaints.  Although not good as firewood, the wood is used locally for smoking salmon, as it has little resin and imparts a pleasant flavour.  Local tribes have carved the wood into feast gear items.

Taking the above into consideration, I see the qualities of an envoy and stabilizer in alder's colonization; and those of a diplomat and peacemaker in linking the air to the earth.  Alder works with some microbes, and but against others, so it judges.  The bark yields a cheerful colour, and the leaves keep up a good appearance until the end.  And it preserves food in good taste.  So, I say this tree has "jovial" qualities (qualities of Jupiter/Zeus).  This male deity was ruler of the gods, lawgiver, dispute-settler, sky-god, and generally considered generous and beneficent (though he had his moments).  Alder is linked with air, earth, and water, most obviously; but I have read that it makes excellent charcoal, connecting it with fire and the fouth element.