▁red ▁al ders ▁which ▁excel ▁at ▁nit ro gen - fix ation ▁but ▁lack ▁the ▁storage ▁capacity ▁that ▁the ▁Douglas - fir ▁can ▁offer . ▁In ▁early ▁April ▁of ▁every ▁year , ▁a ▁new ▁layer ▁grows ▁between ▁the ▁b ark ▁and ▁wood . ▁As ▁this ▁new ▁layer ▁takes ▁over ▁transport ation ▁of ▁flu ids ▁throughout ▁the ▁tree , ▁last ▁year ' s ▁layer ▁of ▁cells ▁die ▁and ▁form ▁a ▁ring ▁in ▁the ▁wood . ▁ ▁After ▁about ▁ 2 0   year s , ▁the ▁tree ▁begins ▁to ▁develop ▁fert ile ▁con es . ▁Bud s ▁form ▁where ▁aux ins ▁accum ulate ; ▁these ▁become ▁either ▁new ▁need les ▁or ▁con es . ▁The ▁bud s ▁remain ▁und iffer enti ated ▁until ▁July ▁and ▁continue ▁to ▁develop ▁throughout ▁the ▁fall ▁and ▁winter . ▁The ▁next ▁year , ▁some ▁bud s ▁will ▁open ▁in ▁mid - May ▁expos ing ▁a ▁new ▁set ▁of ▁need les . ▁The ▁cone ▁bud s ▁on ▁the ▁lower ▁end ▁of ▁the ▁tree ▁ ▁while ▁other ▁bud s ▁burst ▁open ▁in ▁April ▁re le asing ▁a ▁mist ▁of ▁pol len . ▁The ▁con es ▁at ▁the ▁top ▁of ▁the ▁tree ▁open ▁their ▁scales ▁for ▁wind - bor ne ▁pol len ▁to ▁enter . ▁Within ▁the ▁cone , ▁the ▁pol len ▁fert il izes ▁a ▁seed ▁which ▁is ▁released ▁in ▁September . ▁The ▁quantity ▁and ▁quality ▁of ▁seed ▁production ▁var ies ▁year - to - year ▁but ▁a ▁particularly ▁effective ▁c rop ▁is ▁produced ▁about ▁every ▁ 1 0   year