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SPECIES:  Ostrya knowltonii
Knowlton's hophornbeam. Image by John Ruter, University of Georgia,


SPECIES: Ostrya knowltonii
AUTHORSHIP AND CITATION: Tesky, Julie L. 1994. Ostrya knowltonii. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: []. Revisions: Images were added on 20 July 2018.
ABBREVIATION: OSTKNO SYNONYMS: Ostrya baileyi Rose [9,23] NRCS PLANT CODE: OSKN COMMON NAMES: Knowlton's hophornbeam ironwood western hophornbeam woolly hophornbeam wolf hophornbeam TAXONOMY: The scientific name of Knowlton's hophornbeam is Ostrya knowltonii Coville (Betulaceae) [9,10,7,23]. There are no recognized infrataxa. LIFE FORM: Tree FEDERAL LEGAL STATUS: No special status OTHER STATUS: NO-ENTRY


SPECIES: Ostrya knowltonii
GENERAL DISTRIBUTION: Knowlton's hophornbeam is found in southeastern Utah, northern Arizona, southeastern New Mexico (in the Guadalupe and Sacramento mountains in Eddy County), and northern Trans-Pecos Texas. It is not a common tree and its occurrence is sporadic even in these areas [9,10,18,23].
Distribution of Knowlton's hophornbeam. Map courtesy of USDA, NRCS. 2018. The PLANTS Database. National Plant Data Team, Greensboro, NC [2018, July 20] [21].
   FRES21  Ponderosa pine
   FRES32  Texas savanna
   FRES35  Pinyon - juniper

     AZ  NM  UT  TX

   12  Colorado Plateau
   13  Rocky Mountain Piedmont

   K019  Arizona pine forest 
   K023  Juniper - pinyon woodland
   K031  Oak - juniper woodlands
   K032  Transition between K031 and K037
   K086  Juniper - oak savanna

   210  Interior Douglas-fir
   237  Interior ponderosa pine
   239  Pinyon - juniper
   241  Western live oak

   504 Juniper-pinyon pine
   733 Juniper-oak
   735 Sideoats grama-sumac-juniper 

Knowlton's hophornbeam is commonly found in oak (Quercus spp.) woodlands,
pinyon (Pinus spp.)-juniper (Juniperus spp.) woodlands, and lower
ponderosa pine (Pinus ponderosa) forest zones [9].  In Texas it is a
component of the gray oak (Quercus grisea)-true pinyon (Pinus
edulis)-alligator juniper (Juniperus deppeana) association at 5,000 to
7,000 feet (1,524-2,133 m) and the ponderosa pine-Douglas fir
(Pseudotsuga menziesii) association at 6,000 to 7,500 feet (1,828-2,286
m).  In Texas it is also associated with Texas madrone (Arbutus
texana), southwestern white pine (Pinus strobiformis), chinkapin oak (Q.
muehlenbergii), and bigtooth maple (Acer grandidentatum) [18].  In
deciduous canyon woodlands of Guadalupe Mountains National Park, Texas,
Knowlton's hophornbeam will increasingly replace wavyleaf oak (Q.
undulata), alligator juniper, Riogrande cottonwood (Populus deltoides
ssp. wislizenii) and little walnut (Juglans microcarpa) as the moisture
gradient goes from xeric to mesic.  Knowlton's hophornbeam is replaced by
bigtooth maple and chinkapin oak, especially on upper terraces, around
springs and in canyonheads [6,13].  


SPECIES: Ostrya knowltonii
WOOD PRODUCTS VALUE: Knowlton's hophornbeam wood is thin, fine grained, hard, tough, and durable [4,23]. It is occasionally used for fuel or posts [23]. Because of its density the wood of hophornbeam (Ostrya spp.) can be used for tool handles, mallet heads, and other hard wooden objects [4]. IMPORTANCE TO LIVESTOCK AND WILDLIFE: Several species of breeding birds use canyonland habitats where Knowlton hophornbeam occurs [12]. PALATABILITY: NO-ENTRY NUTRITIONAL VALUE: NO-ENTRY COVER VALUE: NO-ENTRY VALUE FOR REHABILITATION OF DISTURBED SITES: NO-ENTRY OTHER USES AND VALUES: NO-ENTRY OTHER MANAGEMENT CONSIDERATIONS: Hophornbeam species (Ostrya spp.) suffer from few insect pests or diseases, and none of these are regarded to be of economic importance [4].


SPECIES: Ostrya knowltonii
GENERAL BOTANICAL CHARACTERISTICS: Knowlton's hophornbeam is a native, deciduous, small tree 10 to 40 feet (3-12 m) tall with a 6- to 18-inch (15.2-45.7 cm) trunk diameter [9,23]. The trunk is usually short and divided into a number of slender, crooked branches to form a round-topped crown [23]. The leaves are 1 to 2.5 inches (2.5-6.3 cm) long and short-pointed or rounded at the apex [7,9,23]. The twigs are slender, tomentose at first to glabrous and lustrous later [l9,23]. The bark is 0.125 inch (0.31 cm) thick, shallowly furrowed and breaking into loose, small scales 1 to 2 inches (2.5-5 cm) long [23].
Knowlton's hophornbeam leaves and fruit. Image by Steven Katovich, USDA Forest Service,

Male and female flowers are in catkins [9,23].  The staminate catkins
form singly or in groups of two to three at the tips of the previous
year's branches.  They are slender, cylindrical, pendulous and 0.5 to
1.25 inch (1.3-3.2 cm) long [15,23].  The pistillate catkins are about
0.25 inch (0.6 cm) long, generally with two flowers in the axil of each
bract [23].  The fruit is a compressed ovoid nutlet [4].  The nutlet is
about 0.25 inch (0.6 cm) long, solitary, and sessile [23].


Knowlton's hophornbeam reproduces by seed.  The flowers are wind
pollinated and the fruit is wind dispersed [14].  Germination is epigeal
[4].  Unless seeds are sown soon after maturity or are stratified, they
will not germinate until the second year [23].  No specific information
was available on germination rates or viability of Knowlton's hophornbeam
seeds; however, information is available on eastern hophornbeam (Ostrya
virginiana) [17].  Eastern hophornbeam seeds usually germinate in the
spring the year after they are shed.  Germination capacity of eastern
hophornbeam seed is 27 to 65 percent [11].  Eastern hophornbeam trees do not
produce seeds abundantly until they are about 25 years old [17].

Knowlton's hophornbeam can be regenerated by grafting [23].  Other species
of hophornbeam will sprout from the stump if cut or burned; however, no
specific information was available regarding the ability of Knowlton
hophornbeam to do so [11].

Knowlton's hophornbeam is commonly found on sunny, dry, well-drained sites
in mountains and canyons and at the bases of monoliths in sandstone
areas [15,22,23,24].  Knowlton's hophornbeam commonly occurs between 4,200
and 7,000 feet (1,280-2,133 m) in elevation [7,9,15,23,24].

Specific information regarding Knowlton's hophornbeam's successional
status was not available in the literature.  Eastern hophornbeam
typically occurs in late seral to climax forests.  It is shade tolerant
and will reproduce well under full shade [11].  How closely this applies
to Knowlton's hophornbeam is unknown.

Knowlton's hophornbeam flowers are produced from March through May before
or with the leaves [15,23].  The fruit of hophornbeam species matures
and is dispersed during the same season as pollination.  In most
hophornbeam species, the staminate catkins are produced the growing
season before anthesis and are exposed during the winter.  The
pistillate catkins develop in the spring with the new shoots, with
anthesis occurring as the leaves are forming [4].


SPECIES: Ostrya knowltonii
FIRE ECOLOGY OR ADAPTATIONS: Specific information was not available regarding the fire ecology and adaptations of Knowlton's hophornbeam as of 1994. Knowlton's hophornbeam may sprout after top-kill by fire, as do other species of hophornbeam [11]. Knowlton's hophornbeam probably also colonizes burned sites via wind-dispersed seeds. Pinyon-juniper communities where Knowlton hophornbeam commonly occurs have historically burned every 10 to 30 years. Where livestock grazing has reduced grass cover and accelerated erosion, fire frequency has decreased [25]. FIRE REGIMES: Find fire regime information for the plant communities in which this species may occur by entering the species name in the FEIS home page under "Find Fire Regimes". POSTFIRE REGENERATION STRATEGY: NO-ENTRY


SPECIES: Ostrya knowltonii
IMMEDIATE FIRE EFFECT ON PLANT: Information was not available regarding the immediate effects of fire on Knowlton's hophornbeam; however, this tree is probably top-killed or killed by most fires. PLANT RESPONSE TO FIRE: NO-ENTRY FIRE MANAGEMENT CONSIDERATIONS: NO-ENTRY


SPECIES: Ostrya knowltonii
REFERENCES: 1. Bernard, Stephen R.; Brown, Kenneth F. 1977. Distribution of mammals, reptiles, and amphibians by BLM physiographic regions and A.W. Kuchler's associations for the eleven western states. Tech. Note 301. Denver, CO: U.S. Department of the Interior, Bureau of Land Management. 169 p. [434] 2. Dittberner, Phillip L.; Olson, Michael R. 1983. The plant information network (PIN) data base: Colorado, Montana, North Dakota, Utah, and Wyoming. FWS/OBS-83/86. Washington, DC: U.S. Department of the Interior, Fish and Wildlife Service. 786 p. [806] 3. Eyre, F. H., ed. 1980. Forest cover types of the United States and Canada. Washington, DC: Society of American Foresters. 148 p. [905] 4. Furlow, John J. 1990. The genera of Betulaceae in the southeastern United States. Journal of the Arnold Arboretum. 71(1): 1-67. [15644] 5. Garrison, George A.; Bjugstad, Ardell J.; Duncan, Don A.; [and others]. 1977. Vegetation and environmental features of forest and range ecosystems. Agric. 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Washington, DC: U.S. Department of the Interior, National Park Service: 181-237. [16021] 13. Northington, David K.; Burgess, Tony L. 1979. Summary of the vegetative zones of the Guadalupe Mountains National Park, Texas. In: Genoways, Hugh H.; Baker, Robert J., eds. Biological investigations in the Guadalupe Mountains National Park: Proceedings of a symposium; 1975 April 4-5; Lubbock, TX. Proceedings and Transactions Series No. 4. Washington, DC: U.S. Department of the Interior, National Park Service: 51-57. [16017] 14. Pendleton, Rosemary L.; Pendleton, Burton K.; Harper, Kimball T. 1989. Breeding systems of woody plant species in Utah. In: Wallace, Arthur; McArthur, E. Durant; Haferkamp, Marshall R., compilers. Proceedings--symposium on shrub ecophysiology and biotechnology; 1987 June 30 - July 2; Logan, UT. Gen. Tech. Rep. INT-256. Ogden, UT: U.S. Department of Agriculture, Forest Service, Intermountain Research Station: 5-22. [5918] 15. Powell, A. Michael. 1988. Trees & shrubs of Trans-Pecos Texas including Big Bend and Guadalupe Mountains National Parks. Big Bend National Park, TX: Big Bend Natural History Association. 536 p. [6130] 16. Raunkiaer, C. 1934. The life forms of plants and statistical plant geography. Oxford: Clarendon Press. 632 p. [2843] 17. Schopmeyer, C. S.; Leak, W. B. 1974. Ostrya virginiana (Mill.) K.Koch eastern hophornbeam. In: Schopmeyer, C. S., ed. Seeds of woody plants in the United States. Agriculture Handbook No. 450. Washington, DC: U.S. Department of Agriculture, Forest Service: 564-565. [7718] 18. Simpson, Benny J. 1988. A field guide to Texas trees. Austin, TX: Texas Monthly Press. 372 p. [11708] 19. Stickney, Peter F. 1989. Seral origin of species originating in northern Rocky Mountain forests. Unpublished draft on file at: U.S. Department of Agriculture, Forest Service, Intermountain Research Station, Fire Sciences Laboratory, Missoula, MT; RWU 4403 files. 7 p. [20090] 20. Swan, Frederick R., Jr. 1970. Post-fire response of four plant communities in south-central New York state. Ecology. 51(6): 1074-1082. [3446] 21. U.S. Department of Agriculture, Natural Resources Conservation Service. 2018. PLANTS Database, [Online]. U.S. Department of Agriculture, Natural Resources Conservation Service (Producer). Available: [34262] 22. Van Dersal, William R. 1938. Native woody plants of the United States, their erosion-control and wildlife values. Washington, DC: U.S. Department of Agriculture. 362 p. [4240] 23. Vines, Robert A. 1960. Trees, shrubs, and woody vines of the Southwest. Austin, TX: University of Texas Press. 1104 p. [7707] 24. Welsh, Stanley L.; Atwood, N. Duane; Goodrich, Sherel; Higgins, Larry C., eds. 1987. A Utah flora. Great Basin Naturalist Memoir No. 9. Provo, UT: Brigham Young University. 894 p. [2944] 25. Wright, Henry A.; Bailey, Arthur W. 1982. Fire ecology: United States and southern Canada. New York: John Wiley & Sons. 501 p. [2620]

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