in Thoreau’s Journal:  

Every part of nature teaches us that the passing away of one life is the making room for another.  The oak dies down to the ground, leaving within its rind a rich virgin mould, which will impart a vigorous life to an infant forest – – The pine leaves a sandy and sterile soil—the harder woods a strong and fruitful mould. – – 

So this constant abrasion and decay makes the soil of my future growth. As I live now so shall I reap. If I grow pines and birches, my virgin mould will not sustain the oak, but pines and birches, or, perchance, weeds and brambles, will constitute my second growth. – –