Quercus macrocarpa / Symphoricarpos occidentalis Plant Association 



QUEMAC / SYMOCC; bur oak / western snowberry 

 MTNHPrank:G?Sl 



Environment: This community type is documented solely on alluvial terraces of Arkansas Creek, a 

 Little Missouri River tributary, representing a small valley and a subirrigated site on open plains. It 

 is the only report of it in Montana, where it occurs on a scattered BLM tract about 1 mile south of 

 Alzada and 1 mile north of the Wyoming border. Its extent beyond BLM-administered lands is 

 unknown. 



Vegetation: One plot of this post-settlement community type was sampled. The stand has a 

 relatively open savanna-like tree canopy dominated by bur oak {Quercus macrocarpa) with about 

 30% cover; intermixed with lesser amounts of green ash {Fraxinus pennsylvanica) with about 10% 

 cover. The largest oak trees in the plot are about 30 ft. tall, with 12" diameter at breast height (DBH). 

 Heidel (1993) bored the largest tree found in this stand (18" DBH) and estimated its age to be about 

 1 10 years, dating to pre-settlement times. Sexual reproduction by oak appears to be limited; only 

 one seedling was found in the plot, acorn production was poor in 1993 (MTNHP Element 

 Occurrence Record), and no acorns were seen in 1997. Fraxinus pennsylvanica trees in the plot are 

 smaller (about 1 5 ft. tall), but reproduce more successfully; several seedlings were found in the plot. 

 The most abundant native understory species is the western snowberry {Symphoricarpos 

 occidentalis) with about 20% cover. Although the placement of the plot was chosen to represent 

 maximum diversity of native species in the stand, the entire area is dominated by a dense sward of 

 introduced grasses. Smooth brome {Bromus inermis) is most abundant with about 60% cover, and 

 quack grass {Elytrigia repens; syn. Agropyron repens), timothy {Phleum pratense), and Kentucky 

 bluegrass {Poa pratense) are well represented with about 10% cover each. Native graminoids found 

 in lesser amounts in the plot include the sedge Carex tenera, and thick-spiked wheatgrass {Elymus 

 lanceolatus) . Forbs in the plot are mostly exotic species, the most abundant being Rumex crispus. 



This stand occurs among a mosaic of woodlands dominated by green ash {Fraxinus pennsylvanica) 

 and cultivated hay meadows. Older terraces and surrounding rolling uplands are occupied mostly by 

 greasewood and sagebrush communities (SARVER/ARTTSW and ARTTSW/ELYLAN). The shale 

 ridge system to the southeast, which extends into Wyoming, supports upland juniper, bur oak, and 

 ponderosa pine woodlands (see discussion of QUEMAC/JUNSCO). 



Soils: The alluvial soils in this reach of the Little Missouri River are derived from Cretaceous shales 

 and are dominated by the clay fraction. The high organic matter content of the upper horizon is 

 indicative of a relatively productive site, which is confirmed by the sward of knee-high introduced 

 grasses. 



Comments: The closest locations at which the Quercus macrocarpa/Symphoricarpos occidentalis 

 habitat type have been documented come from the Black Hills of South Dakota and Wyoming 



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