Retaining needles for three years, as conifers do, extends the photosynthesis period but also increases water demand and water loss. Pines and other conifers have a needle structure that is assembled tightly so the vascular tissue is protected and water loss is reduced. Dense foliage reduces air movement around the needles, slowing evaporation. The needle is covered with a waxy cuticle that keeps snow from accumulating and slows transpiration. But the wax is also highly flammable.