Pinus ponderosa / Juniperus horizontalis Community Type 



PINPON / JUNHOR; ponderosa pine / creeping juniper 

 MTNHP rank G3/S3 



Environment: This is a woodland type restricted to one comer of the county, sampled in two plots, 

 and noted only in a small area of arid hills east of Mill Iron in northeastern Carter County. Here it is 

 the predominant woodland type on BLM tracts and occupies slopes, usually with northerly aspects 

 but extending to protected easterly and westerly positions, of the side ridges of dissected sandstone 

 capped tablelands. It has been noted elsewhere in southeastern Montana in similar settings. 



Vegetation: The sampled stands have a relatively open canopy (about 30% cover) of relatively 

 small trees (estimated largest trees about 12" dbh, 40 ft. tall) and a low shrub layer clearly dominated 

 by Juniperus horizontalis (70-80% cover). It is hypothesized that this ground hugging evergreen 

 shrub becomes established in thinsoil settings, possibly "blowouts," and serves as nursery cover for 

 seedlings of Pinus ponderosa. This is supported by the many pine seedlings and saplings observed 

 in patches of creeping juniper outside the forest canopy. It is provisionally treated as a community 

 type (successional community) rather than a plant association (climax community) because no 

 mature stands were observed or have been reported of this type, and on-site observations are 

 consistent with succession to other local Pinus ponderosa types, e.g., with Pseudoroegneria spicata 

 ox Juniperus communis. Presence of the shrub Rhus trilobata in both plots, although only in trace 

 amounts, provides continuity with stands of PINPON/JUNHOR described from northeastern 

 Montana (DeVelice et al. 1995), where this species was constant and sometimes an understory 

 codominant. Cover values of other understory graminoids and forbs are low, composed mostly of 

 species found in neighboring range communities. 



Warmer aspect slopes of the side ridges may be occupied by Schizachyrium scoparium communities 

 (SCHSCO/CARFIL) which may also be serai to Pinus ponderosa communities (also see discussion 

 of PINPON/SCHSCO). The ridge tops are occupied by grasslands (mostly STICOM/CARFIL) on 

 well-drained soils, and sagebrush steppe (ARTTSW/PASSMI) on shallow, poorly drained soils on 

 level bedrock. Alluvial terraces below the ridges are occupied by silver sagebrush communities 

 (ARTCAN/CALLON). More mesic higher elevation stands of ponderosa pine in the vicinity lack 

 Juniperus horizontalis. Dusek (1980) described ponderosa pine communities of the Custer National 

 Forest Long Pines unit and noted a PINPON/JUNHOR community type confined to "coulee heads 

 and sidehills with very coarse textured soils" in the adjacent to the BLM tracts sampled by our plots. 



Soils: Within Carter Co. and throughout the eastern-most portion of Montana this type is found on 

 well-drained soils derived from sandstone or sandstone mixed with porcellainite ("scoria"), which 

 weather to sandy loams and loams. 



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