Each plot is 30 m square with an area of 900 m (0.22 acre). All plot trees are 

 singleleaf pinyon; a few juniper (Juniperus osteosperma) are in the study area but none 

 are on or near the plots. Several Jeffrey pine (Pinus jeffreyi) are in the vicinity of 

 the highest plot (Monte Cristo), but none are on or immediately adjacent to the plot. 



Closed stands were deliberately chosen so that the influence of understory vegeta- 

 tion on tree growth would be negligible. The understory was sparse and of low vigor, 

 especially on the lower two plots. Ephedra (Ephedra viridis) , bitterbrush (Purshia 

 tridentata), and mountain mahogany (Ceraocarpus ledifolius) were the principal under- 

 story species on the Monte Cristo plot. Sagebrush (Artemisia tridentata) and gooseberry 

 (Ribes velutinum) were the principal understory species on the other two plots. 



METHODS 



The boundaries of the 30 m by 30 m plots were laid out with staff compass and tape. 

 Control lines at 5 m intervals parallel to the lower boundary were used in the mapping 

 of tree stem locations and crown outlines. The foliage class of all trees taller than 

 1 m was estimated on a scale of 1 to 9. A vigorous tree with dense foliage on all sides 

 was rated 9, and a tree with very sparse foliage was rated 1. 



All trees taller than 1 m were felled and their total height (including stump) was 

 measured with a tape. Stump height was about 15 cm for all but a few trees that could 

 not be cut at that height because of large limbs or other irregularities. 



From 6 to 9 trees on each plot, representative of the range in stump diameters, 

 were selected for weighing. Each of these trees was separated into four components 

 that were weighed with a load cell on a boom mounted on a pickup truck. The four com- 

 ponents were: 



1) live material larger that 76 mm diameter outside bark (d.o.b.), 



2) live material 25 to 76 mm d.o.b., 



3) foliage and other live material smaller that 25 mm d.o.b., 



4) deadwood. 



The relative proportions of foliage, twigs less than 6.4 mm d.o.b., and branches 

 6.4 to 25 mm were determined by subsampling about 10 percent of the <25 mm component. 

 Cross-sectional disks were taken of each of the components and, along with samples of 

 foliage and twigs, were analyzed in the laboratory for moisture content and bark per- 

 centage. These data were used to calculate ovendry mass of foliage, ovendry mass of 

 wood larger than 76 mm, and total aboveground ovendry biomass in each tree. 



On the weighed trees, stem sections were taken at stump height and at approximately 

 1-m intervals on the dominant stem up to a 3-cm diameter on the dominant leader. On 

 the unweighed trees, stem sections were taken at the stump, at 3 cm on the dominant 

 leader, and at one or two intermediate points on the dominant stem. The annual rings 

 on all of these sections were counted and height-age curves were plotted for each tree. 

 These curves were extrapolated to ground level to estimate tree age, and interpolated 

 to determine past height at any particular time. False rings and missing rings are 

 known to occur in pinyon and can make age determinations difficult, but comparisons of 

 ring width patterns among trees and with Bridgeport precipitation data failed to 

 indicate either false or missing rings in the trees on the Sweetwater plots. 



Stump diameters, both inside- and outside-bark, were measured with a diameter tape. 

 If there was more than one stem at stump height, the diameter of each stem was measured 

 and the equivalent stump diameter was calculated by: 



3 



