The objective of this study was to describe spatial variation (i.e. within interspace [I], as well as under perennial grass [G], deciduous shrub [S] and evergreen tree [E] canopy) in topsoil organic carbon (OC) and nitrogen (ON) of pinon-juniper rangeland differing in juniper (primarily�Juniperus monosperma�and�J. osteosperma) canopy and understory vegetation. Nine macroplots (100m x100m) were established on sites characterized as phase I (31.3 � 5.9 trees/ha), phase II (192.7 � 107.4 trees/ha), or phase III (104.6 � 31.9 trees/ha) juniper canopy. Predominant understory plant species were blue grama (Boutelua gracilis), western wheatgrass (Agropyron smithii), and sideoats grama (B. curtipendula) for phase I,� broom snakeweed (Gutierrezia sarothrae), blue grama, and sideoats grama for phase II, and broom snakeweed, red sprangletop (Leptochloa filiformis), and whitemargin sandmat (Euphorbia albomarginata) for phase III. Above ground dry matter standing crop was 1413.2 � 303.3 kg/ha, 478.3 � 256.9 kg/ha, and 64.2 � 28.7 kg/ha, for phase I, II, and III respectively. At each of the 9 macroplots, 3 soil samples (approximately 250g from top 2.5 cm) each were collected in I, G, S, and E. Samples were dried at 50C, milled to 2mm and OC and ON content was determined using a Teledyne-Tekmar Apollo 9000 C:N analyzer. Differences in OC and ON were determined by Anova. OC and ON (P < 0.05) were 239.35 � 21.44, 20.06 � 2.33; 279.09 � 35.04, 18.39 � 1.79; and 265.48 � 35.22, 22.32 � 2.14 for phase I, II, and III respectively. Similar values (P < 0.05) were 97.23 � 5.66, 9.54 � 0.69; 128.28 � 7.38, 12.63 � 0.62; 422.23 � 36.38, 30.83 � 2.50; and 397.48 � 21.50, 28.03 � 1.92 for I, G, S, and E respectively. Spatial distribution of topsoil OC and ON should be considered when comparing ecosystem sites.
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