If you thin some its sure to benifit the other if they are fighting for sunlight ,but it can also work the other way too . My neighbor cut down all of his oak trees so the fir trees could do better .Well all the extra sunlight dried out the ground and all the fir trees died then. Now the land is mostly brush and not good for anything without a lot of work . The only good thing is it has a lot of deer and turkeys on it .