Evaluation of pinyon sapwood to phytomass relationships over different site conditions

Abstract

Detailed studies of competitive interactions in the pinyon/juniper (Pinus monophylla Torr. & Frem., Juniperus osteosperma (Torr.) (Little) ecosystem require accurate estimates of biomass from physical measurements of the plant species involved. Relationships between green leaf biomass (phytomass) and trunk sapwood area were evaluated on 6 plots on a western Nevada mountain range. Four of the plots covered a range of environmental conditions from the lower to the upper edge of the woodland belt in 100-m elevation increments. The remaining 2 covered canyon and mountain top environments. The sapwood area to phytomass relationship was first individually analyzed for each of the 6 plots and the results compared. The ratio for grams of phytomass per cm2 of sapwood area for the tree in each plot with the highest value ranged from 1.5 to over 2 times the tree with the lowest value. The highest average plot ratio was only 10% greater than the lowest average plot ratio. Individual regression slopes for the 6 plots did not significantly differ and the data were combined for the remaining analyses. The regression relationship for trees with less than 40-cm2 sapwood area differed from the overall relationship. The slope values for the sapwood area to foliage biomass relationship for the western Nevada data averaged about 2/3 the slope values for a data set from a mountain range in southwestern Utah. These differences were significant between a subset of young trees from each site with up to 40-cm2 sapwood area (P less than or equal to 0.01) and for an analysis between all the sampled trees from each site (P less than or equal to 0.10).