The research presented here demonstrates that in the fir forests on the northeast slopes of Ilgaz Mountain, Abies bornmulleriana Mattf forms tree clumps and that this is especially associated with extreme climatic conditions (Tab. 2). The structure, size and form of the tree clumps, the h/d(1.3) ratio of trees inside them, the spatial distribution of trees inside the clumps, the relationships between this and altitude and the effects of tree clumps on stability and vitality were considered (Tab. 2-4). It was indicated that the foremost characteristic of investigated tree clumps formation of firs is the stabilizing effects on the ecosystem (Tab. 3-4).