surveyed and/or evaluated for presence of bur oak (Quercus macrocarpa). Survey was not 

 conducted outside of the Thompson Creek tract but it is possible that there are scattered trees 

 if not oak groves elsewhere in the drainage. 



HABITAT: The Montana population of bur oak {Quercus macrocarpa) occurs in two, relatively 

 discrete settings. Most of the population occurs on bentonitic shale ridges trending WNW to ESE 

 that extend south into Wyoming. They form solid stands or mixed stands on slopes, and are widely 

 scattered in a savanna-like association on the ridgetops. The bur oak {Quercus macrocarpa) is 

 codominant in various proportions with Rocky Mountain juniper {Juniperus scopulorum) and 

 ponderosa pine {Pinus ponderosa). The undergrowth is relatively depauperate even under 

 continuous canopy cover. Openings are often dominated by the rhizomatous sedge, sun sedge {Carex 

 inops; syn. C heliophila). Shrubs are confined to the more wooded stands. The grass and forb 

 components have a high proportion of and cover by exotic species. There is a high diversity of 

 annuals in the undergrowth including blue toadflax {Linaria canadensis). 



A small portion of the Montana oaks grow on alluvial terraces along the Thompson Creek, tributary 

 of the Little Missouri River, where they are the dominant tree or occasional in stands of green ash 

 {Fraxinus pensylvanica). These habitats have understories dominated by introduced hay grasses, in 

 many places a near monoculture of smooth brome (Bromus inermis). There are three BLM tracts 

 with oaks present in upland woodlands and one tract with riparian oak woodland. Vegetation was 

 sampled by plots at two sites on BLM land, one representing a Quercus macrocarpa/Juniperus 

 scopulorum community on the toeslope of the shale ridge setting, and one representing a Q. 

 macrocarpa/Bromus inermis community type in the alluvial terrace setting. Elsewhere, it grows on 

 limestone escarpments and woody draws (Girard et al. 1988). 



SPECIES BIOLOGY: This is a peculiar case in which a state-significant plant association is 

 dominated by a state-significant species. The single Montana population is estimated to consist of 

 5,000-10,000 trees, present on over 1,000 acres; with densities ranging from 1 to 20 trees per acre 

 (Heidel 1993). Much of the 360 acres of BLM-administered land in the area has oak trees, while 

 only a small fraction have oak-dominated vegetation (Heidel 1993). 



Bur oak can grow to be an extremely big, long-lived tree elsewhere in its range (over 300 years old, 

 1 m DBH, 30 m high and twice as wide). Bur oak in the Black Hills area shows some of the genetic 

 traits of Garry's oak {Quercus Gerri), perhaps reflecting an overlap in their range under different 

 climates (source). In Carter County, mature oak trees which were bored were estimated to be 60 

 years old (average tree of app. 0.15 m DBH in upland stand) to 1 10 years old (largest tree of riparian 

 stand; Heidel 1993). It may be short-lived under the stress at the edge of its range, dependent on 

 resprouting for persistence, or showing affects of land use. Low acorn production was reported in 

 1992 and no acorns were seen in the two BLM stands visited in 1997. Few seedlings were seen in the 

 1997 vegetative sampling plots, but reproduction by suckers growing from dying (uncommon) and 

 healthy trees was noted. Many trees are multi-trunked. This is explained either by resprouting of 

 trees when the tops were killed in the past by, e.g., fire, browsing, or logging; the suckering noted, or 

 patterns of seed dispersal by fox squirrels caching acorns underground. 



OTHER COMMENTS: The "Alzada Oaks" are Montana's only stand of bur oak {Quercus 

 macrocarpa), and part of the westernmost natural occurrences of the species. They have been 



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