Complex sentence: Conifers dominate the climax forests of the Coastal Douglas-fir, and all of the climax-forming conifers that exist alongside Douglas-fir can live for centuries, with a few species capable of living for over a millennium.
Split into simpler sentences: Conifers dominate the climax forests of the Coastal Douglas-fir. All of the climax conifers that grow alongside Douglas-fir can live for centuries, with a few species capable of living for over a millennium.