Western North American Naturalist

Volume 60 Number 2 Article 14

5-24-2000

Sexual reproduction of Gambel oak (Quercus gambelii) near its northeastern limit

Jamie L. Reynolds College, Colorado Springs, Colorado

Timothy N. Feintstein Colorado College, Colorado Springs, Colorado

James J. Ebersole Colorado College, Colorado Springs, Colorado

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Recommended Citation Reynolds, Jamie L.; Feintstein, Timothy N.; and Ebersole, James J. (2000) "Sexual reproduction of Gambel oak (Quercus gambelii) near its northeastern limit," Western North American Naturalist: Vol. 60 : No. 2 , Article 14. Available at: https://scholarsarchive.byu.edu/wnan/vol60/iss2/14

This Note is brought to you for free and open access by the Western North American Naturalist Publications at BYU ScholarsArchive. It has been accepted for inclusion in Western North American Naturalist by an authorized editor of BYU ScholarsArchive. For more information, please contact [email protected], [email protected]. Western North American Naturalist 60(2), © 2000, pp. 225–227

SEXUAL REPRODUCTION OF GAMBEL OAK (QUERCUS GAMBELII) NEAR ITS NORTHEASTERN LIMIT

Jamie L. Reynolds1, Timothy N. Feinstein1, and James J. Ebersole1,2

Key words: Quercus gambelii, Gambel oak, saplings, seedlings, sexual reproduction, Colorado.

Gambel oak (Quercus gambelii Nutt.) is a Colorado, Brown (1958) found sexual reproduc- , clonal, white oak that ranges in tion “less evident” than vegetative reproduction. size from to small (Harper et al. There is no published information on occur- 1985). It occurs throughout much of , rence of sexual reproduction in northeastern , , and Colorado, with small parts of Q. gambelii’s range. In this study we ranges in , , Oklahoma, and asked whether sexual reproduction occurs northern Mexico (Little 1971). In the southern near the northeastern limit of the species, and part of its range the oak has wide elevational we discuss ages and microhabitat preferences limits, and these limits narrow in the north of individuals we did find. (Neilson and Wullstein 1983). It generally We searched for seedlings (<1 yr old) and grows with ponderosa pine (; saplings (small stems >1 yr old) in areas with Harper et al. 1985), pinyon pine (Pinus edulis; mature oaks in October 1997 at 3 sites from Neilson and Wullstein 1986), or just below the Colorado Springs to Canon City, Colorado. lower limit of pinyons and junipers (personal Site 1 is immediately west of Colorado Springs observation). along Lower Gold Camp Road (38°48′N, Neilson and Wullstein (1983) showed that 104°53′W, 2440 m elevation), about 70 km Gambel oak in northern Utah likely migrated south of the northern limit of the species in to its present range using sexual reproduction this portion of its range. Colorado pinyon (Pinus during the mid-Holocene hypsithermal and edulis), one-seed juniper ( Juniperus mono- that the species now persists there through sperma), and mountain-mahogany (Cercocar- asexual reproduction. They found mortality of pus montanus) mix with Gambel oak on steep planted 1-yr-old Q. gambelii to be very high in (40°–45°) colluvial slopes with many large northern Utah and low in Arizona and New boulders. Site 2 is in Aiken Canyon Preserve Mexico. Neilson and Wullstein (1983) found (38°37.5′N, 104°52.5′W, elevation 2070 m), no more than 20 natural seedlings in northern about 30 km south of Colorado Springs. We Utah in 4 yr of fieldwork, but reported a high searched gentle slopes several hundred meters density in Arizona and New Mexico (range east of the abrupt transition between the 120–1320 ha–1, generally 300–900 ha–1 [Neil- Great Plains and the Front Range where clear- son and Wullstein 1986]). Neilson and Wull- ly defined groups of Q. gambelii stems are sep- stein (1983) concluded that young, sexually arated by meadows. Site 3 lies 4 km north of reproduced individuals in northern Utah died Canon City (38°24′N, 105°15′W, 1710 m). due to late spring freezes and especially sum- Moderate oak cover occurs among J. mono- mer/fall drought caused by absence of Arizona sperma and P. edulis on 15°–20° slopes. summer monsoons in northern Utah. This When searching for seedlings and saplings, explanation is consistent with relatively high we walked all habitats within 20–30 m of survival of individuals planted at and north of mature oaks and pushed vegetation aside when Q. gambelii limits in Wyoming, where summer necessary to ensure no individuals were missed. monsoons extend farther north than in Utah Small stems beneath mature oaks were not (Neilson and Wullstein 1983). In west central examined due to the very large number of

1Department of Biology, Colorado College, Colorado Springs, CO 80903-3294. 2Author to whom reprint requests should be addressed.

225 226 WESTERN NORTH AMERICAN NATURALIST [Volume 60 small, vegetatively produced stems there. experience the same competition with herba- Candidate stems were identified as being sex- ceous vegetation as another oak in southwest- ually reproduced by the spent, attached ern North America (Weltzin and McPherson or by long, tapering taproots and lack of hori- 1997). However, even if this were an impor- zontal rhizomes (Neilson and Wullstein 1986). tant limiting factor, it seems likely we would For each seedling/sapling or cluster of these, have found at least some seedlings or saplings we noted its relative shading during summer within herbaceous vegetation. It is likely that and early fall in 3 categories: little shade animals dispersing to bare soil con- (<20% of the day), intermediate shade, and tribute to the pattern we found. nearly continuous shade (>80%). We esti- Means of acorn dispersal for Q. gambelii mated ages of individuals by counting termi- are not clear from our data and likely include nal bud scale scars. We generally could do this more than 1 vector. More research is neces- with high confidence to about 4 yr and with sary to definitively determine vectors, but pos- reasonable confidence on older stems. sibilities will be considered here. Acorns that All seedlings and saplings occurred in bare germinated on the soil surface may be simply soil, and none were within herbaceous vegeta- gravity-dispersed. Several animal species tion. Sexual reproduction occurred close to could bury acorns in soil. Western Scrub Jays edges of mature clones, with 64% of seedlings (Aphelocoma californica) were commonly ob- and saplings within 3 m, 30% within 3.1–5.0 served caching Gambel oak acorns, and 96% m, and the remainder within 7.7 m. Seedlings of 211 caches were of single acorns on the and saplings generally showed strong prefer- west side of Colorado Springs in 1983–1986 ence for sites receiving partial summer shade; (R. Bunn unpublished data). Western Scrub at Aiken Canyon and Canon City 80% of clus- Jays usually pushed acorns into the soil until ters or single individuals occurred in this type they were from just below the surface to 1.5 of microsite. At the Colorado Springs site all cm deep. They most often chose to place individuals were in full sun and were 1–2 yr acorns into the soil in small bare areas within old in a recently eroded area. clumps of the short-grass blue grama/hairy For all individuals with acorns still attached grama (Bouteloua gracilis/B. hirsuta), but (roughly 50% of those found), acorns were sev- when caching near mid-grasses jays tended to eral cm below the surface. Seventy-three per- place them in bare soil at the edges of clumps cent of seedlings and saplings occurred in (R. Bunn unpublished data). It is these caches, clusters of >1 stem with stems <1 cm from when not recovered, which seem likely to pro- each other (Table 1). These originated from duce some of the single seedlings and saplings groups of 2–20 acorns that were touching each we observed. Steller’s Jays (Cyanocitta stel- other several cm below the soil surface. leri), which also disperse acorns (Vander Wall Most individuals from sexual reproduction 1990), are markedly less common at our study (71%) were 1–2 yr old, and only 1 sapling was sites then Western Scrub Jays. >7 yr old (Table 1). Heights for seedlings Based on ranges and information on foods ranged from 2 to 15 cm, and for 2-yr-old and storage habits (Fitzgerald et al. 1994), sev- saplings from 2 to 20 cm. The tallest sapling eral small mammals could bury acorns in clus- found was a 60-cm-tall, 6-yr-old stem. Occa- ters. Rock (Spermophilus variegatus) sional short, old saplings were found, e.g., a commonly eat acorns when they are available 15-yr-old, 16-cm-tall stem. (Ortega 1987) and carry large stores of acorns Occurrence of seedlings and saplings in in cheek pouches (J. Ortega written communi- partially shaded sites agrees with results of cation). Other mammals that eat seeds and Neilson and Wullstein (1986), who found most might bury clusters of acorns include golden- seedlings on the northeast side of sheltering mantled ground squirrels (Spermophilus later- objects. In most situations apparently only alis), Colorado (Tamias quadrivitta- individuals experiencing moderate shade can tus), least chipmunks (T. minimus), and withstand summer drought stress (Neilson and mice (Peromyscus maniculatus). Wullstein 1983). Sexual reproduction does occur in the north- Competition with herbaceous vegetation eastern portion of the range of Q. gambelii, could conceivably limit sexual reproduction to though apparently it is not common. We cau- bare soil since young Q. gambelii presumably tion against inferring from our limited data on 2000] NOTES 227

TABLE 1. Gambel oak (Quercus gambelii) seedling and sapling numbers by site, by occurrence singly or in clusters, and by age.

______Seedlings and Saplings Search No. / Age in yr time Total In cluster No. ______Site (h) no. Single clusters (min, max) clusters 1–2 3–7 >7 Colorado Springs 4 31 8 23 3, 20 2 10 0 0 Aiken Canyon 25 33 9 24 2, 4 6 12 3 0 Canon City 6 25 7 18 2, 11 3 3 6 1

age structures (Table 1) that essentially no sex- Colorado Nature Conservancy for access to ually reproduced individuals successfully Aiken Canyon and Richard Bunn for provid- mature. Larger stems, which may have origi- ing his unpublished data. nated from acorns, were less likely to be exca- vated by us to determine seedling status. Vari- LITERATURE CITED ation through time in successful sexual repro- duction is also unknown based on our obser- BROWN, H.E. 1958. Gambel oak in west-central Colorado. vations in a single season. In spring 1998 a Ecology 39:317–327. FITZGERALD, J.P., C.A. MEANEY, AND D.M. ARMSTRONG. small number of Gambel oak seedlings were 1994. Mammals of Colorado. University Press of observed in an area ca 0.3 ha of western Col- Colorado, Niwot. 467 pp. orado Springs while none were observed in HARPER, K.T., F.J. WAGSTAFF, AND L.M. KUNZLER. 1985. unirrigated parts of the same area the previous Biology and management of the Gambel oak vegeta- 8 yr (personal observation). Since sexual repro- tive type: a literature review. USDA Intermountain Forest and Range Experiment Station GTR INT-179, duction of Q. gambelii in northern Utah is lim- Ogden, UT. 31 pp. ited primarily by late summer and fall drought LITTLE, E.L. 1971. Atlas of United States . Volume 1. (Neilson and Wullstein 1983), the above-aver- Conifers and important hardwoods. USDA Forest age precipitation for June through October Service, Miscellaneous Publication 1146, Washing- 1997 at Colorado Springs (NOAA 1997) caused ton, DC. Unpaginated, ca 400 pp. NEILSON, R.P., AND L.H. WULLSTEIN. 1983. Biogeography by an El Niño event (Webster and Palmer of two southwest American oaks in relation to atmos- 1997) may have increased seedling survival pheric dynamics. Journal of Biogeography 10:275–297. compared to most years. Thus, while sexual ______. 1986. Microhabitat affinities of Gambel oak seed- reproduction commonly occurs in the south- lings. Great Basin Naturalist 46:294–298. ern part of the Q. gambelii range (Neilson and NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION. 1997. Climatological data, annual summary, Colorado. Wullstein 1986), sexual reproduction is rare, Volume 102, No. 13. National Climatic Data Center, or possibly episodic, in the northwestern Asheville, NC. (Neilson and Wullstein 1983) and northeastern ORTEGA, J. 1987. Den site selection by the rock (this study) portions of the range. The species (Spermophilus variegatus) in southeastern Arizona. apparently maintains itself in the northern Journal of Mammalogy 68:792–798. VANDER WALL, S.B. 1990. Food hoarding in animals. Uni- part of its range primarily vegetatively; and versity of Chicago Press, Chicago. 445 pp. occasional sexual reproduction creates possi- WEBSTER, P.J., AND T.N. P ALMER. 1997. The past and the bilities of new clones, genetic variation, and future of El Niño. Nature 390:562–564. dispersal to new areas. WELTZIN, J.F., AND G.R. MCPHERSON. 1997. Spatial and temporal soil moisture resource partitioning by trees and grasses in a temperate savanna, Arizona, USA. ACKNOWLEDGMENTS Oecologia 112:156–164.

This research was done as a class project at Received 26 October 1998 Colorado College, and we appreciate the input Accepted 15 June 1999 of other students in the class. We thank The