Ecological Archives A021-007-A1

Kenneth L. Cole, Kirsten Ironside, Jon Eischeid, Gregg Garfin, Phil Duffy, and Chris Toney. 2011. Past and ongoing shifts in Joshua tree distribution support future modeled range contraction. Ecological Applications 21:137–149.

Appendix A. Fossil records documenting late Pleistocene Joshua tree distribution and Holocene migration rates.

Joshua tree fossils have been found frequently in packrat middens from across the Sonoran Desert of southern Arizona, the Colorado Desert of southern California, and the Mojave Desert of California, Nevada, and northwestern Arizona (Fig. 2; TABLE A1).

The southern portions of broad regional late Pleistocene distribution rapidly disappeared after the start of the Holocene, leaving only the northernmost localities intact. However a few Holocene records near what had been these northerly late Pleistocene stands allow some inferences of possible Holocene, post-ground sloth, movements.

One of Joshua tree's most northerly Pleistocene locations is in the Alabama Hills of California's Owens Valley (Koehler and Anderson 1995), about 10 km to the north of its current northern limit within the Owens Valley. These fossils could infer that its distribution has retreated southward sometime during the Holocene at a rate that averaged 0.9 m/yr over the entire period (10 km over 11,700 years). But, the rarity of midden records make it impossible to determine whether this was a slow, steady contraction, an instantaneous change, or the end product of many expansions and contractions through time. Whichever it was, the northern population limit did not change much during this period.

Alternately, a series of fossils from Eureka Valley, CA, near Joshua tree's current northern extent just east of the Owens Valley, could infer a northward Holocene expansion. Joshua tree is contained in one of four recent assemblages from the area, dated at < 200 years (Spaulding, 1980), but not in several older middens. The site is about 35 km northwest of its nearest recorded Pleistocene fossil locality in Death Valley (Wells and Woodcock, 1986). But Joshua tree is not contained in 3 other nearby Eureka Valley assemblages also dating to < 200 years, suggesting that its inclusion into these middens from on rocky slopes is infrequent despite its occurrence on the alluvial slopes well below the site (Spaulding 1980). Even if Joshua tree did migrate northward to this site over the Holocene, it is less than 20 km northwest of portions of Death Valley where it could reasonably be expected to have occurred considering the high elevation (~1500 m) of its Pleistocene occurrences nearby in Owens Valley (FIG. 2). Using this 20 km distance between the northernmost late Holocene midden record in Eureka Valley and the nearest likely Pleistocene occurrence in Death Valley, a maximum migration rate of 1.7 m/yr (20 km over 11,700 years) could be calculated. Thus a range of possible northward Holocene migration rates could be -1 to 2 m/yr, much slower than any other species yet studied (McLachlan et al. 2005; Yansa 2006; Cole et al. 2008a).

TABLE A1. Fossil records of Joshua tree associated with radiocarbon ages > 10,000 yr B.P.

Location Radiocarbon  Age(s)   Lat. Long. Source
Alabama Hills, Owens Valley, CA 13,350
36.63 -118.13 Koehler and Anderson 1995
Death Valley, CA 19,550 36.58 -117.33 Wells and Woodcock 1985
Scodie Mts., CA 12,870
35.58 -117.95 McCarten and Van Devender 1988
Joshua Tree National Park, CA 12,015 33.99 -116.07 Holmgren et al., 2010
Granite Mts., CA 24,400 35.45 -116.54 Koehler et al. 2005
Marble Mts., CA 10,555 34.67 -115.58 Spaulding 1980
Whipple Mts., CA 10,840 34.27 -114.42 Rowlands 1978
Whipple Mts., CA 10,490
34.21 -114.37 Van Devender 1990
Picacho Peak, CA 12,500 32.87 -114.83 Cole 1986
Amargosa Desert, NV 10,010
36.57 -116.09 Spaulding 1985, and Personal Communication
Amargosa Desert, NV 10,240
36.63 -116.27 Spaulding, Personal Communication
Specter Range, NV 28,460 36.66 -116.20 Spaulding 1985
Frenchman Flat, NV > 40,000 36.63 -115.93 Wells 1983
Sheep Range, NV 19,200 36.70 -115.27 Spaulding 1981
Sheep Range, NV 16,490
36.64 -115.28   Spaulding 1981
Sheep Range, NV 11,550
36.47 -115.25 Spaulding 1981
Arrow Canyon Range, NV 10,400
36.77 -114.89 Spaulding 1994
Gypsum Cave, NV 11,360
36.22 -114.90 Laudermilk and Munz  1935, Steadman et al. 2005
Rampart Cave, AZ 16,330
36.10 -113.93 Phillips 1977
Artillery Mts., AZ 18,320   34.37   -113.62   King and Van Devender, 1977
Artillery Mts., AZ 21,000
> 30,000
34.33 -113.58 Van Devender and King 1971.
Kofa Mts., AZ 11,450 33.43   -114.10 Van Devender 1973
Kofa Mts., AZ 13,400 33.40 -114.02 King and Van Devender 1977.
Tinajas Altas Mts., AZ > 43,200 32.35 -114.09 Van Devender 1990
Puerto Blanco Mts., AZ 14,120 31.95 -112.78 Van Devender 1987
Ajo Mts., AZ 13,500
32.12 -112.70 Van Devender 1977
Waterman Mts, AZ 12,530
32.35 -111.46 Van Devender 1990, Anderson and Van Devender 1991.


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