Thank you for the question! The focus on pines, versus other evergreens, is simply due to soils and environment. While the western mountains of Virginia can support the likes of spruce and fir (and these are grown for Christmas trees) most of the commonwealth is too hot and low in elevation to grow these other species well. Southern yellow pines also have a lot of research behind them for maximized productivity and will have a good sale-ability for timber with local markets.