She discovered that Douglas Firs provide carbon to baby firs. The taiga forest is densely populated with spruces, firs, pines and larch. The most common trees are oak, beech, pines and firs. In the lower forested zone, birch, juniper, blue pines, firs, bamboo and rhododendron grow. Pollen grains of pines, firs, and spruces are winged. Among these are giant sequoias, redwoods, great firs, and sugar pines. Mainly pines, firs and birches can be found here. In the United States, pilings are mainly cut from southern yellow pines and Douglas firs. The remains of the green firs and pines are scattered around its edges. In the forest the evergreen tends to form stands with other firs and beeches. They were two Scotch Firs and two oak trees. Other firs can grow anywhere between tall. The female cones are pendulous, with persistent scales, unlike those of true firs. The bark is grey-green to grey-brown and smooth with resin blisters typical of most firs.