fir and spruce repopulate the site contemporaneously, although most of the initial biomass is dominated by fir and later on the dominance shifts to spruce. Recurrent high-intensity crown fire also helps spruce and fir forests by preventing fir from overtaking spruce through competitive exclusion. Because spruce is shade-intolerant, it requires an open canopy to be established. This means that without fire to wipe out fir trees, thus creating holes in the canopy, spruce would be outcompeted by fir. Fire, insect, fungus and worm threats Fire has an interesting relationship with micro fauna in forests. Damage done to trees by fire hurts the vascular cambium, thus leaving trees more susceptible to insectivorous and fungal attacks. Fungal infections are not as common as insect attacks, but can be just as deadly. The fungus Amylostereum areolatum weakens trees and allows insects such as the Sirex noctilio (European wood wasp) to take over massive numbers of forests. The most common problems in spruce and fir forests are bark beetles, budworms, and gall-forming insects, to which spruce is extremely susceptible. Several gall-forming insects are present in spruce forests, including the Eastern Spruce gall adelgid and the Cooley's Spruce gall adelgid, which normally would not harm forests, unless the trees are unusually vulnerable to them, as they are after a fire. Budworm larvae feed on the leaves of spruce and fir trees, and can become present in large amounts, which is when they become detrimental to a forest. Bark beetles are the most common insect killer of spruce and fir forests because they can spread quickly, breed rapidly, and can easily devour thousands of acres before actions can be taken against them. During the 1990s, the bark beetles affected almost three million acres (12,000 km2) of spruce forests. The attacks of these insects, in turn, raise the mortality rate of trees in the burn area, which provides even more fuel for the next fire. Fauna A number of larger animals are supported by fir and spruce forests, such as moose, deer, elk, birds, snowshoe hares, and other small mammals. Effects on bird populations after fire in fir and spruce forests varied. Of the 41 avian species observed in 3 or more studies comparing post fire and adjacent unburned forests, 22% are consistently more abundant in burned forests and 34% are more abundant in unburned forests. In general, woodpeckers and aerial foragers are more abundant in burned