The Thaumcraft 2 Wiki has this to say about Silverwood trees and their logs:
|These mystical trees only grow in areas where the Aura is extremely strong.|
Silverwood trees themselves purifies the local aura and helps it grow. They are also the only known tree to shake off the effects of Taint when all around them is slowly being corrupted.
The wood harvested from the trees is extremely magical in nature and is useful in crafting objects of cleansing or purifying nature.
Silverwood trees do not bear seeds or fruit, nor can one find a Silverwood sapling. It is not known how they come to be. On occasion their leaves will drip quicksilver when destroyed - very strange...
Vanilla Shears can be used to harvest Silverwood Leaves. Do note that the shears from Equivalent Exchange (Dark Matter Shears and Red Matter Shears) will not work on the leaves and instead destroy them. The Chainsaw can successfully harvest them so long as it has power.