Above-ground biomass and N, P and S capital in singleleaf pinyon woodlands

Abstract

Above-ground biomass on 11 singleleaf pinyon ( Pinus monophylla Torr. & Frem) woodland sites average 150·5 Mg/ha, of which 60% is tree biomass and 40% the forest floor. The majority of tree biomass (53%) constitutes slash, thus only 28% of the above-ground biomass and 6% of its nitrogen (N) capital is removed as fuelwood. Nitrogen concentration in the forest floor (1·85% N) exceeds that in live pinyon tissue including foliage (1·04% N). Because of its large biomass and high N concentration, the forest floor contains 77% of the above-ground N capital. Site N in soil and above-ground biomass are approximately equal (1178 to 1326 kg/ha), whereas 85 to 87% of phosphorus and sulfur occurs in soils. The nitrogen capital is more at risk from tree harvest and residue management activities than phosphorous or sulfur. In a 100-year rotation, traditional stem wood or whole tree harvest would not appear to adversely impact the N, P and S capital of these sites, but if greater than one-third of the forest floor is lost in burning post-harvest slash, a negative N balance may occur.