ecosystems, an effect occurring during the early 21st century with increased culinary uses for pine nuts. In the United States, millions of hectares of productive pinyon pine woods have been destroyed due to conversion of lands, and in China and Russia, destructive harvesting techniques (such as breaking off whole branches to harvest the cones) and removal of trees for timber have led to losses in production capacity. Elevation and pinecone production The elevation of the pinyon pine is an important determinant of the quantity of pine cone production and, therefore, will largely determine the number of pine nuts the tree will yield. American pinyon pine cone production is most commonly found at an elevation between , and ideally at . This is due to higher temperatures at elevations lower than during the spring, which dry up humidity and moisture content (particularly snow packs) that provide for the tree throughout the spring and summer, causing little nourishment for pine cone maturity. Although several other environmental factors determine the conditions of the ecosystem (such as clouds and rain), the trees tend to abort cones without sufficient water. High humidity encourages cone development. There are certain topographical areas found in lower elevations, such as shaded canyons, where the humidity remains constant throughout the spring and summer, allowing pine cones to fully mature and produce seed. At elevations above , the temperature substantially drops, drastically affecting the state of the dormant cone. During the winter, frequent dramatic changes in temperature, drying, and gusty winds make the cones susceptible to freeze-drying that permanently damages them; in this case, growth is stunted, and the seeds deteriorate. Physical characteristics When first extracted from the pine cone, they are covered with a hard shell (seed coat), thin in some species and thick in others. The nutrition is stored in the embryo (sporophyte) in the center. Although a nut in the culinary sense, in the botanical sense, pine nuts are seeds; being a gymnosperm, they lack a carpel (fruit) outside. The shell must be removed before the pine nut can be eaten. Unshelled pine nuts have a long shelf life if kept dry and refrigerated (); shelled nuts (and unshelled nuts in warm conditions) deteriorate rapidly, becoming rancid within a few weeks or even days in warm, humid conditions. Pine nuts are commercially available in the shelled form, but due to poor storage, they can have poor flavor and