Western North American Naturalist
Volume 63 Number 3 Article 2
8-6-2003
Plant community patterns in unburned and burned blackbrush (Coleogne ramosissima Torr.) shrublands in the Mojave Desert
Matthew L. Brooks United State Geological Survey, Western Ecological Research Center, Las Vegas, Field Stateion, Henderson, Nevada
John R. Matchett United State Geological Survey, Western Ecological Research Center, Las Vegas, Field Station, Henderson, Nevada
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Recommended Citation Brooks, Matthew L. and Matchett, John R. (2003) "Plant community patterns in unburned and burned blackbrush (Coleogne ramosissima Torr.) shrublands in the Mojave Desert," Western North American Naturalist: Vol. 63 : No. 3 , Article 2. Available at: https://scholarsarchive.byu.edu/wnan/vol63/iss3/2
This Article 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 63(3), ©2003, PI'. 283-298
PLANT CO.\1.\1U TITY PATTERNS IN UNBUfu'lED AND BURl ED BLACKBRUSH (COLEOGYNE RAMOSISSIMA TORR.) SHRUBLANDS IN THE MOJAVE DESERT
Matthew L. Brooks 1 and John R. Matchett]
ABSTRACT.-The blackbrush vegetation type is dominated by Coleogyne ramossisinUl, which is thought to preclude the coexistence of many other plant species. Fire can remove blackbrush cover and possibly increase plant species richness and evenness. Fire also may increase the frequency and cover of alien annual grasses, thereby intensifying landscape flammability. We tested these predictions in unburned and burned (6---14 years postflre) blackbrush at 3 sites spanning the range ofthis vegetation type in the Mojave Desert. Species richness in unburned blackbrush was similar to published values for other vegetation types in western North America, but riclmess varied significantly among the 3 sites and 4 spatial scales (1, 10, 100, and 1000 m2). Richness values declined in order from annual forbs, woody perennials, herbaceous perennials, annual grasses, cacti, to perennial grasses. Fire reduced Coleogyll€ cover, thus boosting species evenness. In contrast, species richness decreased after burning, although the results varied among spatial scales. Total cover was unaffected by fire because cover of woody perennials decreased, while cover of annual forbs, annual grasses, herbaceous perennials, and perennial grasses increased. N'ative species richness and cover decreased, whereas alien richness and cover increased after burning, espe cially where the alien forb Erodillln cicutarillln was present. Fire had no effect on frequency and variable effects on cover ofalien annual grasses. These results indicate that in blackbrush species richness can vary among sites and local spatial scales, and effects offire can vary among plant Iife-fonns and between natives and aliens.
Key words: blackbrush, Coleogyne ramosissima,fire, alien plnllts, plnnt species diversity, Mojave Desert.
The hlackbrush vegetation type occurs at there are only a few associated shrub species, the bioregionaI transition between the Mojave and these occur usually as scattered plants in and Great Basin Deserts, from California an otherwise pure stand of Coleogyne." Thus, through Nevada, Arizona, and Utah (Bowns species richness and evenness of vascular 1973). In the Mojave Desert blackbmsh occu plants is generally thought to be low in black pies the elevational zone from approximately bmsh compared with otller vegetation types 1220 m to 1525 m, above the zone dominated in western North Amercia. by creosote bush (Larrea tridenata) and below ~ost accounts describing the dominance of the zone dominated by sagebrush (Artemisia Coleogyne in blackbmsh indirectly suggest that spp.; Bradley and Deacon 1967, Randall 1972, high cover of this species resuJts in the com Beatley 1976). Blackbmsh is dominated by tl,e petitive exclusion ofother plant species (Bowns type species, Coleogyne ramosissima, which can 1973, Beatley 1976, Bowns and West 1976). If comprise 90-95% of total plant cover (Shreve this is true, then reduction of Coleogyne cover 1942). For clarity in this paper, we refer to the should lead to heightened species richness vegetation type as blackbmsh and the type and evenness. Fire has been used to reduce species as Coleogyne. Coleogyne cover and promote the growth of Although 185 species ofvascular plants have more palatable rangeland species (Bowns been found growing within blackbrush (Vasek 1973), but the effects of fire on plant species and Barbour 1988), tlley are never very abun diversity are unknown. dant except at upper- and lower-elevational Effects of fire on blackbmsh appear to be ecotones (Bowns 1973, Beatley 1976, West long tenn. There is only 1 report of Coleogyne and Young 2000). Beatley (1976) stated that resprouting after fire (Bates 1984), 2 reports "so nearly complete is the dominance of this of seedling establishment by Coleogyne after shrub species that in areas that are not ecotonal fire (Ellison 1950, Lei 1999), and 1 report of
.United States GeoIogX:aI Sun'e)·. Western Ecological Research Centel; Us \'eps f"1dd Station, 160 N. Stephanie s~ HeDderson, NV 89074.
283 284 WESTERN NORTH AMERICAN NATURALIST [Volume 63 autogenic succession back to blackbrush after fire would increase cover and frequency ofalien fire (Thatcher 1975). In the latter case, fire annual plants, grass species in particular. intensity was likely very low and Coleogylle survival very high, resulting in incomplete re ST OY AREA moval of Coleogylle, which allowed the direct reestablishment of the blackbrush vegetation Three study sites were established from the type. ',1ost studies report that blackbrush does northeast to the southwest Mojave Desert, in not reestablish after fire (Bowns 1973, Beatley the middle of the blackbrush zone between 1976, West and Young 2(00), even 37 years post the upper and lower ecotones in each region. fire (Callison et al. 1985). A wide range of The Beaver Drun site (37°11'17"N, 113°56'39"W, m) is in the Bureau of Land Management, species can dominate after Coleogyne is re 1230 St. George Field Office region of southwestern moved by fire (Jenson et al. 1960, Bowns 1973, Dtall. The Spring Mountain site (36°01'40"N, Wright and Bailey 1982, Bates 1984, Callison 115°3'1O''w, 1470 m) is in the Spring ~10untain et al. 1985). Annuals typically dominate during National Recreation Area of the Humboldt the first few postfire years, and early succes Toiyabe National Forest in southern Nevada. sional perennial plants dominate after the first The Joshua Tree site (34°03'23"N, 116°19'45''w, few decades (Jenson et al. 1960, Bates 1984, 1370 m) is located at Joshua Tree :'
TAULE 1. Species richness of higher vascular plllnts at 4 spatial scales in unbul'llcd (U) and burned (B) blilckbrush within each site, and among all sites combined, during spring 200l. Values are averages (±1 $;;" = 4 per site pcr fire hisIOl)') and bum effects for each scale are indicated as not significant (n5), negative (. P s; 0.05, -- P < 0.01, ... ,) S 0.001), or positive (+ P S 0.05, + + P S; 0.01, + + + P < O.(XH); and significant across all scales (. P S; 0.05.•• P S 0.01, ... PS 0.001).
I m2 10 m2 100 m2 1000 m2 U Il U Il U Il U Il
ALL VASCUI..hll 1'J..... NTS Beaver Darn •• 12.7 (0.28) 10.8 (0.49) - 18.9 (0.46) 14.3 (0.93) -- 27.0 (0.89) 20.9 (0.38) --- 42.\ (2.45) 32.4 (1.34) ~ Joshua 'Ih:e Il.l \2.6 (0.30) 12.9 (0.24) ns 21.9 (I.O\J) 20.4 (0.95) ns 31.4 (1.55) 28.0 (1.08) ns 47.9 (0.75) 43.6 (2.47) ns ~ Spring ML liS 7.8 (0.57) 9.0 (0.30) ns 18.0 (1.08) 14.0 (0.88) ns 31.1 (1.66) 30.8 (l.75) ns 55.8 (2.88) 49.5 (1.77) ns '"..., Sites c:..'ombined .. 11.0 (0.72) 10.9 (0.52) ns \9.6 (0.70) 16.2 (1.01) --- 29.8 (0.95) 26.5 (1.40) -- 48.6 (2.05) 41.8 (2.36) --- '"'" ALIENS "Z Beaver Dam ns 2.9 (0.04) 3.0(0.01) ns 3.0 (0.00) 3.0 (0.00) ns 3.0 (0.00) 3.0 (0.00) ns 3.1 (0.13) 3.0 (0.00) os 0 Joshua Tree 11,\ 1.2(0.11) 1.8 (0.08) + + 1.8 (0.33) 2.1 (0.24) ns 2.0 (0.35) 2.6 (0.13) ns 2.9 (0.32) 3.8 (0.14) + :l Spring Mt. • 1.2 (0.07) 1.6 (0.30) 4.1(0.06) +++ 2.0 (0.29) 2.8 (0.25) 4.3 (0.\4) ++ :c 3.3(0.19) +++ 4.0 (0.00) ++ + ;> Sites combined ••• 1.8 (0.24) 2.7 (0.20) +++ 2.2 (0.23) 3.1 (0.25) ++ + 2.3 (0.20) 3.2 (0.18) +++ 2.9 (0.14) 3.7(0.17) +++ 3: NATIVES '"~ Beaver Darn •• 9.7 (0.32) 7.8 (0.50) - 15.9 (0.46) 11.3 (0.93) -- 24.0 (0.89) 17.9 (0.38) --- 39.0 (2.44) 29.4 (1.34) - () Joshua Ti'ee us 11.3 (0.29) 11 .I (0.30) ns 20.1 (0.86) \8.3 (0.73) ns 29.4 (1.52) 25.4 (1.20) ns 45.0 (0.89) 39.9 (2.40) 0' I! Spring Mt. liS 53.0 (2.79) 45.3 (1.85) ns Z 6.6 (0.52) 5.7 (0.46) ns 16.4 (0.83) 9.9 (0.94) -- 29.2 (1.49) 26.8 (1.75) ns ~ Sites <:ombined ••• 9.2 (0.63) 8.2(0.71) -- 17.4 (0.68) 13.2 (1.19) --- 27.5 (1.02) 23.3 (1.34) --- 45.7 (2.08) 38.2 (2.23) --- c WOODY I'EHENN'AU~ Beaver Dam tiS 1.5 (0.04) 1.3 (0.12) ns 3.3 (0.47) 2.8 (0.45) ns 6.3 (0.97) 5.4 (0.13) ns 11.3 (1.42) 8.8 (0.78) ns ~ ~ Joshua Trcc •• 1.2 (0.02) 0.2 (0.07) --- 2.1 (0.16) 0.6 (0.13) --- 5.1 (0.66) 1.6 (0.13) -- 10.1 (0.55) 5.8 (0.63) -- ..., Spring Mt. liS 2.4 (0.16) 1.3 (0.13) -- 5.3 (0.33) 2.5 (0.37) -- 10.4 (0.66) 7.5 (0.54) - 17.9 (0.88) 14.8 (0.52) Sites combined ••• 1.7 (0.16) 0.9 (0.17) --- 3.6 (0.44) 2.0 (0.34) --- 7.3 (0.79) 4.8 (0.75) --- 13.1(1.16) 9.8 (1.18)
1-1 EIIIJACEOUS I'EIIENN1AUi Beaver Dam liS 1.2 (0.16) 1.0 (0.09) ns 1.8 (0.20) 1.6 (0.28) ns 3.0 (0.20) 2.8 (0.25) ns 5.9 (0.47) 5.4 (0.24) ns Joshua Tree liS 0.4 (0.05) 0.3 (O.O\J) '" 1.6 (0.22) 1.6 (0.30) ns 2.6 (0.32) 2.\ (0.24) ns 4.9 (0.52) 4.4 (0.24) ns Spring Mt. ns 0.5 (0.10) 1.1(0.11) ++ 1.8 (0.23) 1.4 (0,16) ns 4.0 (0.74) 4.4 (0.75) ns 9.0(1.21) 7.4 (0.24) ns Sites combined liS 0.7(0.11) 0.8 (0.11) ns 1.7 (0.11) 1.5 (0.14) ns 3.2 (0.30) 3.1 (0.38) ns 6.6 (0.68) 5.7 (0.40) os --<: 0 -~ 3 '"Zl j
TAI)LE 1. Continued.
1 m2 10 m2 100 m2 1000 m2 U B U B U B U B
PEHENNIAL CllASSES Beaver Dam '" 0.1 (0.08) 0.2 (0.07) "' 0.2 (0.06) 0.1 (0.06) ns 0.3 (0. L4) 0.9 (0.13) + 0.6 (0.32) 1.8 (0.25) + Joshua Tree liS 0.3 (0.06) 0.3 (0.07) ns 1.3 (0.16) 0.8 (0. (8) ns 1.9 (0.13) 2. I (0.55) us 2.6 (0.38) 3.6 (0.32) us "'l- Spring Mt. .. 0.2 (0.04) 0.6 (0.06) ++ 0.5 (0.27) 1.0 (0.18) m 2.0 (0.20) 2.6 (0.32) liS 2.6 (0.38) 3.6 (0.13) + " Sites combined '" 0.2 (0.04) 0.3 (0.06) + 0.7 (0.17) 0.6 (0.14) ns 1.4 (0.2(;) 1.9 (0.30) + 2.0 (0.34) 3.0 (0.30) +++ 1'1'" ." CACTI ." Beaver Dam liS 0.0 (0.00) 0.0 (0.00) ns 0.3 (0.19) 0.0 (0.00) ns 0.9 (0.31) 0.6 (0.24) ns 2.6 (0.72) 1.5 (OA1) us g'" Joshua Tree .. 0.0 (0.01) 0.0 (0.00) ns 0.0 (0.00) 0.0 (O.OO) ns 0.8 (0.14) 0.0 (0.00) •• 1.3 (0.14) 0.5 (0.20) • Spring Mt.·· 0.1 (0.03) 0.0 (0.01) . 0.3 (0.12) 0.0 (0.00) I.l (0.24) 0.3 (0.30) • 3.4 (0.13) 1.1 (0.13) ••• -Z Sites combined .. 0.0 (0.02) 0.0 (0.00) •• 0.2 (0.08) 0.0 (0.00) . 0.9(0.14) 0.3 (0.13) .. 2.4 (0.35) 1.0 (0.19) ... tl:l i: ANNUAL CHASSES n Beaver Dam· 3.3 (0.17) 3.1 (0.11) ns 3.8 (0.18) 3.4 (0.24) ns 4.0 (O.OO) 3.4 (0.13) •• 4.3 (0. L4) 4.0 (0.20) ns '" Joshua Tree ns J.2 (0.11) 1.5 (0.12) ns 1.8 (0.31) 1.7 (0.06) ns 1.8 (0.48) 2.3 (0.25) ns 2.5 (0.35) 2.9 (0.24) liS c "~ Spring Mt. .. 1.1 (0.24) 2.0(0.07) +++ 1.6 (0. L6) 2.4 (0.07) ++ 1.6 (0.13) 2.3 (0.25) ns 2.4 (0.24) 3.3(0.14) + Sites l.'ombined '" 1.9 (0.3 L) 2.2 (0.21) ++ 2.4 (0.32) 2.5 (0.22) 115 2.5 (0.36) 2.6 (0.20) ns 3.0 (0.29) 3.4 (0.18) ns '"<:
ANNUAL FOHBS '" ":-' Beaver Dam· 6.6 (0.32) 5.3 (0.32) 9.6 (0.24) 6.6 (0.16) ••• 12.6 (0.75) 7.9 (0.24) ••• J7.5 (0.84) 11.0 (0.74) •• '"~ Joshua Tree ns 9.4 (0.28) 10.7 (0.40) + 15.1 (0.81) 15.7 (1.02) ns 19.3 (0.78) 19.9 (0.72) liS 26.3 (0.66) 26.5 (1.00) ns 0- Spring Mt. os 3.5 (0.45) 4.2 (0.26) ns 8.5 (1.00) 6.8 (0.51) ns 12.0 (0.61) 13.8 (0.63) ns 20.5 (J .06) 19.5 (1.36) us Z Sites l.:ombined • 6.5 (0.75) 6.7 (0.88) JlS 11.1 (0.96) 9.7 (1.33) • 14.6 (1.06) 13.8 (1.51) ns 21.4 (1.19) 19.0(1.99) ••
~ •
288 "VESTERN NORTH AMERICA.1\' NATURALlST [Volume 63
Species richness increased 446% between 35 ;;;- the 1- and 1000-m2 spatial scales (Fig. 1), but • • 30 c::::J Unburned the percent increase differed between natives ~- - ,,",,' (497%) and aliens (160%; Table 1). As a result, ..g 25 there was a decline in the percentage of alien "~ 20 species at progressively larger spatial scales • (16%, 11%, 8%, and 6% alien species; Fig. 2). • ~- ,. * The percent increase in richness between l ."or 2 * and 1000-m scales also varied among plant ~-,. life-forms: cacti (6000%), perennial grasses (1000%), herbaceous perennials (943%), woody -•~ • ~ perennials (771%), annual forbs (320%), and • annual grasses (158%). , '000 Species evenness in unburned blackbrush did not differ significantly among sites (X 2 = 0.9583, P = 0.6193), due to the high domi Fig. 2. Percent of total species richness comprising nance ofColeogyne cover at all sites (Fig. 3). aliens in unburned and burned blackbrush. Asterisks indi cate statistically significant (P :0:;; 0.5) differences between BURl\ED BLACKBRUSH.-Species in richness burned and unburned values at a given scale. burned blackbrush was 20%, 10%, and 14% lower than in unburned blackbrush at the 10-, 100-, and 1000-m2 spatial scales (Table 1). Richness did oot decline significantly after fire Total cover in burned blackbrush was 50% at the 1_m2 scale, except at the Beaver Dam (41-,51% range), virtually the same as unburned site. The effects of burning on richness varied blackbrush, but Coleogyne was almost com among sites (site-by·fire interaction, F416, = pletely removed by fire. In the absence of 4.34, P = 0.0145) and was strongest at Beaver Coleogyne, a variety of species dominated the Dam (Table 1). cover of burned areas. At Beaver Dam the Effects of fire on species richness differed burned area was dominated by Erodium cicu between aliens and natives and among plant tarill1n, Gutierrezia sarothrae, Thamnosma mon life-forms. Alien richness increased. whereas tana, Astragalus nuttalianus ssp. imperfectus, native richness decreased, after fire (Table 1). and Bromus madrilensis ssp. rubens (Fig. 3a). Accordingly, the percentage of alien species At Joshua Tree the burned area was dominaled increased after fire (F4,15 = 28.40, P < 0.0001; by Mentzelia affinis and BrornliS tectorwn, fol Fig. 2). Richness of annual and perennial lowed by Amsinckia tesselata, Chael1actis ste grasses increased, whereas richness or woody viodes, $phaeralcea ambiglla, Erodium cicu perennials and annual forbs diminished after lariwn, and Achnatherom speciosa (Fig. 3b). At burning (Table 1), but the responses of all life Spring Mountain, Encelia virginensis, Erodium forms varied among sites (Fs,IS = 5.98, P = cicutariwn and Baileya multiradiata dominated 0.0031). the burned area, followed in abundance by Burning extended evenness from 0.54 + 0.04 Pnmus fasciculata, Gutierrezia sarothrae, and (1 sx) in unburned to 0.65 +0.01 in burned plots, Bromus madriteus;" ssp. rubens (Fig. 3c). and the effect was strongest at Spring ~10un Although total cover returned to prefire tain where there was a 56% increase. Fire en levels 6--14 years postfire, patterns of recovery hanced species evenness by decreasing cover varied significant.ly among plant life-forms. ofColeogyne and increasing the equitability of Cover of woody perennials was 60% lower, cover among other species (Fig. 3). and cover of all otller plant life-forms was 170-450% higher, in burned than unburned Plant Cover and blackbrush (Table 2). Annual forb cover in Alien Frequency creased 266% after burning, was higher than Total plant cover in unburned blackbrush that of any other life-form in burned areas averaged 49% (46-,51% range). Coleogyne was (21 %), and increased significantly after burn by far the most dominant plant species at 26% ing at all 3 sites. Responses to fire by other absolute cover, comprising 53% of total cover plant life-forms varied among sites. Cover of and 73% of woody perennial cover (Fig. 3). annual grasses increased significantly only at 2003] FIRE EFFECTS IN BLACKBRUSH VECETATION 289
A. Beaver Dam
30
25 I Unbumed Bumed 20 ~ -0
5
0
25
20
~ -0 - '5
5
o r I-.n n~~c-. c-.~
c. Spring Mountain 35
30
25 -~ -0 20
Fig. 3. Percent cover distribution of species in unburned and burned blackbrush. Species were arranged along the abscissa in their rank order ofcover dominance in the unburned plots. Additional species were added to the right of an axis break if any of the top 15 species in burned plots were not among those plotted for the unburned plots. Species codes are listed in the Appendix. !S
TABLE 2. Pen::cnl cover of higher vascular plant's in unburned (U) and burned (8) blackbrush within each study site. and llmong all sites combined, during spring 2001. Values are averages (±1 8,; II = 4 pCI' site pCI' firc history) lind burn effects for each group are indicated as not significant (n5), negative (- P S 0.05, -- P S 0.01, --- P S 0.(01), or positive (+ P S 0.05, + + P S om, + ++ P S 0.001); lind signillclIllt across ull groups (* P S 0.05, ** P S 0.01, ... P S 0.001). Alien species :E ~ BrOIllIl$ lIl11dritIJIIsis'/'I1heus Bromlls teclo/"wn Erodiwn cicutarium Others '"... U Il U Il U Il U Il '"z Z Beaver Dam •• 6.5 (2.24) 4.7 (0.22) TIS 1.4 (0.29) 1.9 (0.36) "' 2.0 (0.20) 11.8 (3.48) ++ 0.0 (0.00) 0.0 (0.00) ns 0 Joshua Tree tiS 0.4 (0.18) 0.8 (0.34) ns 3.4 (0.63) 12.0 (2.10) ++ 0.0 (0.01) 1.4 (1.06) ns 0.3 (0.18) 0.3 (0.08) ns ::j Spring Mt. .. 1.0 (0.11) 1.9 (0.17) ++ 0.0 (0.01) 1.0(0.11) +++ 0.2 (0.08) 7.8 (2.38) ++ 0.0 (0.03) 0.6 (0.13) ++ X ;.- Sites combined ... 2.6 (1.07) 2.5 (0.51) '" 1.6 (0.48) 5.0(1.63) +++ 0.7 (0.28) 7.0 (1.84) +++ 0.1 (0.07) 0.3 (0.09) ++ ::: a '" Lifc·forms ()-'" > Woody perennials Ilerbuccaus perennials Perennial grasses Annual grasses Annual forbs Z Z U Il U Il U Il U Il U Il ~ c Beaver Dam liS 32.4 (2.94) 20.5 (3.73) • 0.7 (0.09) 0.7 (0.11) ns 0.4 (0.33) 0.1 (0.08) ns 8.7 (2.44) 7.7 (0.58) ns 8.6 (0.34) 20.2 (4.10) + s: Joshua Tree' 30.6 (4.15) 1.9 (0.86) ••• 0.7 (0.22) 2.1 (0.91) '" 1.0 (0.31) 2.3 (0.54) ns 4.1 (0.65) 13.1(2.21) ++ 12.9 (1.18) 31.2 (3.66) ++ t: ~ Spring Ml.· 41.4 (1.57) 19.4 (3.72) •• 0.3 (0.05) 5.2(0.99) +++ 0.3 (0.13) 1.9 (0.64) + 1.0 (0.10) 3.0 (0.22) +++ 2.2 (0.28) 11.5(1.99) +++ ... Sites combined ... 34.8 (3.04) 13.9 (3.04) --- 0.6 (0.09) 2.7(0.70) +++ 0.6 (0.17) 1.5 (0.38) + 4.6 (1.22) 7.9 (1.42) +++ 7.9 (1.38) 21.0 (3.00) +++
"Cadi un:; c~c111dcd 1M,'t'll.ll.W ofmillinml (.~JVcr nllllllo slntl.~II(.'Il.II)' '~'gnlllClLnt difTcl'cll(.1)s.
~ 6- -c 3 "~ 2003] FIRE EFFECTS IN BLACKBRUSH VEGETATION 291
Joshua Tree and SpIing Mountain, and cover of 50 herbaceous perennials and perennial grasses • c::::J Unbumed increased significantly only at Spring Mountain. 40 - Burned Fire boosted cover of aliens 191% (F118, = 32.22, P < 0.0001) and reduced cover of natives 26% (F1,18 = 16.15, P = 0.0008; Fig. 4), and these trends did not differ significantly among sites (F2.18 = 0.13, P = 0.74). As a result, the proportion of total cover compris • ing aliens increased from 10% before fire to 10 31% after fire (FUS = 38.22, P < 0.0001). Alien plant species that increased the most o'-----L-~ in cover differed significantly among sites Aliens Natives (F416 = 4.33, P = 0.0146). At Beaver Dam and Spring Mountain the enhanced alien cover was mainly due to Fig. 4. Percent cover of alien and native species in un Erodium cicutarium, burned and burned blackbrush. Alien and native species whereas at Joshua Tree the increase was are listed in the Appendix. Asterisks indicate statistically mainly caused by Bromus tectorum (Table 2). significant (P :S: 0.5) differences between burned and Cover of the relatively uncommon alien species unburned values for aliens or natives. Sa/sola tragus, Bromus trinH, and Schismus spp. collectively increased after fire, due to their strong positive response at the Spring blackbrush is not lower than other vegetation Mountain site. Bromus madritensis ssp. rubens types in western North America, as we had cover exhibited a slight increase at Spring predicted it would be. In the current study we Mountain, but the overall effect of fire across reported 11 total plant species per 1 m2, which all sites was not significant. is comparable to 7 species per 1 m 2 reported Total frequency of aliens did not increase in ponderosa pine and shortgrass steppe, 8 in significantly due to fire (F1,18 = 1.57, P = tallgrass prairie, 9 in aspen, and 12 in mixed 0.2266), but there was a significant site-by-fire grasslands (Stohlgren et al. 1999a). We reported effect (F2,18 = 4.01, P = 0.0363), and alien fre- an average of 7 woody perennial species per quency did increase significantly from 54% to 100 m2 (10 at Spring Mountain), which com 78% at Spring Mountain (F1,6 = 14.99, P < pares closely with 6 woody perennial species 0.0083). Responses varied among alien species, per 100 m2 reported in pinyon/juniper/sage with Erodi-um cieutarium exhibiting the great brush, 8 in creosote bushlbursage, and 8-10 est increase in frequency, from 37% in unburned reported for unburned blackbrush near our to 67% in burned areas (FIlS, = 30.69, P Spring Mountain study site (Lei and Walker <0.0001). The response of Erodium Gieutarium 1995). We reported 47 total species per 1000 frequency to burning varied among sites (F2,18 m2, compared to 38 species per 1000 m 2 in = 10.44, P = 0.0010), increasing from 1% to chaparral (Schluter and Ricklefs 1993),45 spe 29% at Joshua Tree (F = 5.22, P = 0.0623), 16, cies in the Colorado Rocky Mountains (Stohl 13% to 75% at Spring Mountain (F16 = 32.89, , gren et al. 1999a), 50 species in Mediterranean P = 0.0012), and 96% to 98% at Beaver D,m regions with rainfall similar to the sites in the (F1,6 = 0.20, P = 0.6704). The overall combin~d current study (150 mm; Rosenzweig and Abram frequency of the alien annual grasses Bromus madritensis ssp. rubens and Bromus tectorum sky 1993), and 65-70 species in semiarid grass lands and shrublands (Schluter and Ricklefs did not differ significantly (FIlS, = 0.79, P < 0.4410) between unburned 79% (+7) and 1993). We also reported 46 native species and 2 burned 84% (+5) areas. 3 alien species per 1000 m , which compared favorably with 32 native species and 3 alien DISCUSSION species in Rocky Mountain grasslands (Stohl gren et al. 1999b). Thus, species richness ofall Species Richness in higher vascular plants, woody perennial species, Unburned Blackbrush and alien species at our Mojave Desert black Results from our 3 study sites suggest that brush sites was comparable to other major species richness in unburned Mojave Desert vegetation types. 292 \VESTER'-J NORTH A1IERICAN NATURALIST [Volume 63
Species richness increased logarithmically conclusion that species lichness at our 3 Mojave between the 1- and 1000-m2 scales, but this Desert blackbrush sites was comparable to increase was much higher for natives than other vegetation types. aliens. This pattern suggests that native rich Effects ofFire on B1ackbrush ness was more closely related to increased Community Structure environmental heterogeneity at successively larger spatial scales. Apparently, the spatial Fire removed virtuany all Coleogyne cover, distribution of the few alien species in this which is consistent with most other reports study was influenced more by environmental (Jenson et al. 1960, Bowns 1973, Beatley 1976, heterogeneity at the smaller scales, whereas Callison et al. 1985, West and Young 2000). distribution of the many native species was The loss of Coleogyne as the single dominant affected more equitably by heterogeneity at all species, and its replacement by 2 to 5 other scales. The greater richness at higher spatial co-dominant species 6-14 years postfire, re scales also varied among plant life-forms. sulted in increased species evenness but de Perennials increased proportionally more than creased species richness. Decreased richness annuals, indicating that the former were re after Coleogyne removal and the finding that sponding more to environmental variation at species richness in blackbrush was similar to successively higher spatial scales. Hetero other vegetation types were inconsistent \vith geneity at 1 m2 was due to the shrub-inter the assertion that Coleogyne has a strong neg shrub gradient, and at 1000 m2 it was due to ative effect on the number of other coexisting the microtopographic gradient from finer-tex species (Bowns 1973, Beatley 1976, Bowns tured soils of rainfall runoff areas (hummocks) and West 1976). Thus, the cover dominance of to coarser-textured soils ofrun-on areas (wash Coleogyne may not prevent the coexistence of lets; Brooks 1999). These results demonstrate a wide range ofother plant species. that different spatial scales can produce differ Loss ofColeogyne cover is not the only effect ent relative estimates of species richness offire and therefore not the only potential fac between natives and aliens, and among plant tor related to postfire plant community patterns. life-forms in blackbrush. Fire also can kill mature plants and seeds and Species evenness in unburned blackbrush alter soil characteristics (Whelan 1995). It is appeared to be low, with Coleogyne dominat likely that many native plant species recover ing that landscape. Howevel~ comparisons with slowly after blackbrush fires because they values from other studies were confounded by evolved in a desert ecosystem where fire is in a wide range ofevenness metrics and sampling frequent. Reduced species richness 6--14 years designs, or insufficient published descriptions postfire may result from slow recovery ofthese of the methods that we used. As a result, we native species, especially woody perennials. were unable to include any reliable compar Alien species are often invasive, responding isons in this paper. rapidly to increased availability of limiting The single year of plant community data resources created by disturbances such as fire reported in this study should be sufficient to (Grime 1977, Chapin et al. 1986). It is there evaluate general diversity patterns in black fore not surprising that fire increased alien brush. Winter rainfall from October through richness and cover in this study, as we pre March ranged from 88% to 111% of the 30 dicted it would. The single site where alien year average at the study sites, resulting in a richness and cover of either Bromus tectorum moderately diverse display of native annuals or B. madritensis ssp. rubens did not increase (MLB personal observation). These rainfall significantly after fire was Beaver Dam, where estimates are based on data from the closest moderate levels of past and current cattle graz weather stations to each site that had the nec ing may have allowed aliens to establish rela essary weather data for calculating 30-year tively high levels of richness and annual grass averages (1 to 3 stations per site; National Cli cover in unbumed blackbrush. The other 2 sites matic Data Center). There may have been some had not been grazed by livestock for many annual plant species that remained donnant as decades and had much lower levels of alien seeds anel were not detected, but this would richness and cover. These results suggest that only have caused species richness to be under relatively undisturbed blackbrush may be some estimated and would not have affected the what resistant to invasion by alien species, and 2003] FIRE EFFECTS IN BLACKBRUSH VEGETATION 293 the effects offire on previously disturbed black States Department of the Interior and Depart brush may not modify dominance of alien ment of Agriculture, and the Park Oriented annual plants if disturbance levels are already Biological Support Program of the United States high. Geological Survey and National Park Service. Although alien richness and cover were Logistical support and permission to conduct consistently higher in burned than unburned this study were provided by Tom Patterson, blackbrush, no single alien plant life-form or Hank McCutcheon, and Jane Rodgers at Joshua species dominated all sites. Alien annual grass Tree National Park; Tim Duck at the Bureau of cover increased the most after fire at Joshua Land Management, St. George Field Office; Tree, whereas the alien annual forb Erodium and Deborah Couche at the Spring Mountain cicutarium increased the most at the other 2 National Recreation Area of the Humboldt sites. Frequency of alien annual grasses did Toiyabe National Forest. Ileene Anderson and not differ between burned and unburned areas, Susan Hobbs performed the fieldwork. Jim indicating that tl,e continuity of annual grass Callison, Jeffrey Lovicb, and 2 anonymous re fuels was not affected by burning 6-14 years viewers provided comments on the manuscript. postfire. These results do not support the con clusions ofothers that alien annual grasses are LITERATURE CITED typically among the most dominant postfire BATES, P.A. 1984. The role and use of 6re in blackbrush species in burned blackbrush (Jenson et al. (Coleogyne ramosissima Torr.) communities in Cali 1960, West 1983, Callison et al. 1985) and that fornia Master's thesis, University ofCalifornia, Davis. their heightened dominance after fire may 56pp. increase landscape flammability (Holmgren BEATLEY, J.C. 1975. Climates and vegetation patterns across 1960). However, these results are from a single the Mojave/Creat Basin Desert transition area. American Midland Naturalist 93:53--70. year of annual plant sampling and must be ___. 1976. Vascular plants of the Nevada Test Site and interpreted cautiously. central-southern Nevada: ecological and geographic Annual plant cover can vary dramatically distributions. Energy Research and Development among years of contrasting rainfall, especially Administration TID-2688!. Technical Information for alien species in the Mojave Desert (Brooks Center, Office ofTechnical Information, Springfield, VA. 308 pp. 1999, 2000). Before plants were sampled in BOWNS, lE. 1973. An autecological study of blackbrush the current study, 2 of the previous 3 winter (Coleogyne ramosissima Torr.) in southwestern Utah. rainfall seasons experieuced less than half of Doctoral dissertation, Utah State University, Logan. the long-term average rainfall in the Mojave 115 pp. BO\VNs, JE., AND N.E. WEST. 1976. Blackbrush (Coleogyne Desert. In 1999 rainfall ranged from 16% to ramosissima Torr.) on southwestern Utah rangelands. 54%, in 2000 it was 30% to 68%, and in 2001 Research Report 27, Utah Agricultural Experiment rainfall averaged 88% to 111% of the 30-year Station, Utah State University, Logan. 27 pp. average at rainfall stations near the 3 study BRADLEY, W.C., AND J.E. DEACON. 1967. The biotic com sites (1 to 3 stations per site; National Climatic munities ofsouthern Nevada. Nevada State Museum Anthropological Papers 13:202-295. Data Center). It is probable that the seed bank BROOKS, M.L. 1999. Alien annual grasses and fire in the of alien annual grasses, Bromus spp. in partic Mojave Desert. Madrono 46:13-19. ular (Brooks 2000), was depleted during this __. 2000. Competition between alien annual grasses drought. The dominance of alien annual and native annual plants in the Mojave Desert. grasses reported in the current study was American Midland Naturalist 144:92-108. _--,' 2003. Effects of increased soil nitrogen on the therefore on the low end of the interannual dominance by alien annual plants in the Mojave range. It is likely that a few years of high rain Desert. Journal ofApplied Ecology 40:344-353. fall would increase cover, and possibly fre BROOKS, M.L., AND T.e. ESQuE. 2000. Alien grasses in the quency, of alien annual grasses, thus increas Mojave and Sonoran Deserts. Pages 39-44 in M. Kelly, M. Howe, and B. Neill, editors, Proceedings of ing landscape flammability (Rogers and Vint the California exotic plant pest council symposium. 1987, Schmid and Rogers 1988, Brooks 1999). California Exotic Plant Pest Council, San Diego. CALLISON, J., J.D. BROTI-IERSON, AND J.E. BOWNS. 1985. The ACKNOWLEDGMENTS effects of fire on the blackbrush (Coleogyne mmosis· sima) community of southwestern Utah. Journal of Range Management 38:535--538. Financial support was provided by the CHAPIN, £S., P.M. VlTOUSEK, A.ND K. VAN CLEVE. 1986. The National Park Service-Pacific West Region, nature of nutrient limitation in plant communities. the Joint Fire Sciences Program of the United American Naturalist 127:48-88. 294 WESTERN NORTH AMERICAN NATURALIST [Volume 63
D'ANTONIO, C.M., AND P.M. VITOUSEK. 1992. Biological Pages 230-240 in D. Schluter and R.E. Ricklefs, edi invasions by exotic grasses, the grass/fire cycle, and tors, Species diversity in ecological communities: global change. Annual Review of Ecology and Sys historical and geographical perspectives. University tematics 3:63-87. ofChicago Press, Chicago, IL. ELLISON, L. 1950. Blackbrush burning. Unpublished report, SCHMID, M.K., AND G.R ROGERS. 1988. Trer> u.s. Forest Service, Intennountain Forest and Range occurrence in the Arizona Upland subdiv Experiment Station, Ogden, VI 5 pp. Sonoran Desert, 1955 to 1983. Southwes GRIME, J.P 1977. Evidence for the coexistence of three ralist 33:437-444. primary strategies in plants and its relevance to eco SHREVE, F. 1942. The desert vegetation of North America. logical and evolutionary theory. American Naturalist Botanical Review 8:195-246. 11 UI69-1194. SOKAL, RR., AND R]. ROHLF. 1995. Biometry. W.H. Free HICKMAN, j.e. 1993. The Jepson manual-higher plants of man and Company, New York. 887 pp. California. University of California Press, Berkeley. STOHLGREN, T.]., D. BINKLEY, G.w. CHONG, M.A. K....LKHAN, 1400 pp. L.D. SCHELL, K.A. BULL, Y. OTSUKI, ET AL. 1999a. HOLMGREN, R.C. 1960. Inspection tour of old blackbrush Exotic plant species invade hot spots of native plant bums in BLM District N-5, southern Nevada. Unpub diversity. Ecological Monographs 69;25-46. lished report, U.S. Forest Service, Intermountain STOHLGREN, T.J., M.B. FALKNER, A.\'D L.D. SCHELL. 1995. Forest and Range Experiment Station, Reno Research A modified-\Vhittaker nested vegetation sampling Center, Reno, NV 8 pp. method. Vegetatio 117:113--121. JENSON, D.E., M.E. BUZAN, D.E. DIMOCK, AND R HOL1'.I STOHLGREN, T.J., L.D. SCHELL, AND B. VANDEN HEUVEL. GREN. 1960. Report on field examinations, black 1999b. How grazing and soil quality affect native brush burns, Las Vegas Grazing District (Nev 5), and exotic plant diversity in Rocky Mountain grass April 1960. Unpublished report, Bureau of Land lands. Ecological Applications 9:45-64. Management, Nevada State Office. 10 pp. THATCHER, A.P. 1975. The amount of blackbrush in the LEI, SA 1999. Postfire woody vegetation recovery and soil natural plant community is largely controlled by properties in blackbrush (Coleogyne ramosissima edaphic conditions. Pages 155--156 in H.C. Stutz, Torr.) shrubland ecotones. Arizona-Nevada Academy editor, Proceedings, wildland shrubs; symposium ofSciences 32;105--115. and workshop, u.s. Forest Service, Shrub Sciences LEI, SA, AND L.R WALKER. 1995. Composition and dis Laboratory, Provo, UT. tribution of blackbrush (Coleogyne ramosissima) VASEK, C., Al\'D M.G. BARBOUR. 1988. Mojave Desert scrub communities in southern Nevada. Pages 192-195 in vegetation. Pages 835-867 in M.C. Barbour and J. B.A. Roundy, E.D. McArthur, J.S. Haley, D.K. Mann, Major, editors, Terrestrial vegetation of California. editors, Proceedings; wildland shrub and arid land California Native Plant Society Special Publication 9. restoration symposium. General Technical Report WELSH, S.L., N.D. AlWOOD, S. GOODRICH, AND L.C. HIG INT-GTR-315, U.S. Forest Service, Intermountain GINS. 1987. A Utah flora. Brigham Young University, Research Station, Provo, UT. 894 pp. LUDWIG, J.A., AND J.R REYNOLDS. 1988. Statistical ecology; WHElAN, R]. 1995. The ecology of fire. Cambridge Uni a primer on methods and computing. John Wiley versity Press, Cambridge, UK. 346 pp. and Sons, New York. 337 pp. WEST, N.E. 1983. Colorado Plateau-Mohavian blackbrush MORTENSEN, v.L., ].A. CARELY, G.C. CRANDALL, K.M. semi-desert. Pages 399-411 in N.E. West, editor, Eco DONALDSON, JR., AND G.w. LEISHMAN. 1977. Soil systems of the world 5; temperate deserts and semi survey of Washington County area, Utah. United deserts. Elsevier, Amsterdam. States Department of Agriculture, Soil Conservation WEST, N.E., AND J.A. YOUNG. 2()()(). lntennountain valleys Service, Washington, DC. 140 pp. and lower mountain slopes. Pages 255-284 in M.G. RANDALL, D.C. 1972. An analysis of some desert shrub Barbour and WD. Billings, editors, North American vegetation of Saline Valley, California. Doctoral dis terrestrial vegetation. 2nd edition. Cambridge Uni sertation, University ofCalifornia, Davis. 186 pp. versity Press, Cambridge, UK. ROGERS, C.R, AND M.K. VINT. 1987. Winter precipitation WHISENANT, S.G. 1990. Postfire population dynamics of and fire in the Sonoran Desert. Journal ofArid Envi Bromus japonicus. American Midland Naturalist ronments 13:47-52. 123,301-308. ROSENZWEIG, M.L., AND S. ABRAMSKY. 1993. How are diver WRIGHT, H.A., AND A.W BAILEY. 1982. Fire ecology. Wiley sity and productivity related? Pages 52-65 in D. and Sons, New York. 501 pp. Schluter and RE. Ricklefs, editors, Species diversity in ecological communities: historical and geographical Received 20 December 2001 perspectives. University of Chicago Press, Chicago, Accepted 10 June 2002 IL. SCHLUTER, D., AND R.E. RICKLEFS. 1993. Convergence and the regional component of species diversity. 2003] FIRE EFFECTS IN BLACKBRUSH VECETATION 295
APPENDIX. Higher vascular plant species sampled in unburned (U) and burned (B) blackbrush within each study site during spring 2001 (x = present). Nomenclature follows Hickman (1999) and Welsh et aI. (1987).
BeaverDam Joshua Tree Spring l\·It. Code U B U B U B
ALiENS Arumal grasses Bromus madritensi$ ssp. ruben.s bromad x x x x x x Bromm tectorum brotec x x x x x x Bromus lrinii x Schismus arabicus x x Schismus barbatus x Annual forbs Erodil.lm cicutarium erOCIC x x x x x x 500010 tragus x x NATrvES Woody perennials Acampropappus spheroceplwlus x x x x x Ambrosia eriocentra x Artemisia dracunculus x Artemisia tridentata x Atriple:r canescens .trean x Chrysothamnus nauseosus x x x Chrysothamnus panirolotus x Chrysothamnus viscidiflorus var. stenophyllus chrvisste x x x x Coleogyne ramosissimo colram x x x x x x Coleogyne ramosissimo (seedling) x x x x x Encelia virginensi8 encvir x x x x Ephedra californk;o ephcal x x x x Ephedra nevadensis ephnev x x x x x x Ephedra torreyana x Ephedra viridis x x x Ericgonum fasciculatum var. polifolium x x x Fallugia paradoxa falpar x Grayia spinosa x x Cutierrezia sarothrae gutsar x x x x x Hymenoclea salsow x x x x Juniperus ca1ifomicus juncal x x Juniperus osteosperma x x Krascheninnikovia !analo x x x Lycium andersonii Iycand x x x x x x Lycium cooperi x x x x Menodcra spinescens menspi x Pinus monophylla x Prunus fasciculatus prufas x x x x Psilostrophe cooperi x Pursh ill mexicana var. stansburyana x x x Purshia tridentata var. glandulosa x x Salazoria mexicana x x $llivia dorrii x x x x Symphcricarpos kmgif1.oru.s x Tetrooymia arillaris var. longispina x x x T1w.mnosma montana thamon x x x x ThennophyUa pent ApPENDIX. Continued. Beaver Dam Joshua Tree Spring Mt. Code U B U B U B Herbaceous perennials Arobis pukhm x x x x Astragalus bernard-wnw x Astragalus 1entiginosus x Baileya multiradiata bailmul x x x Calochortus flexuosus x x x x Calochortus kermedyi x Castilleja angustifolia x x Cauwnthus crassicaulis x x Chomaesyce albomarginata x Chamaesyce fendleri x x Chenopodium incanwn x Cymopterus multineroatus x x Delphinium nuttalianum x x Delphinium parishii x x x x Dichelostemma capitola x x x x Eriogonum inflatum x Eriogonwn plumateUn x x Ericmeuron pulcheUum x x x Gaura coccinea x Lepidium fremontii x x x linum lewisii x Lomatium mohavense x Lomatium nevadense x Mirabilis bigelovjj x Mirabilis multiflortlS x x Oenothera califomica Penstemon palmeri Penstemon sp. Phlox longifolia Phoradendron jUriiperinum Prenonthella exigua x x Senecio multilobatus x x Sphaeralcea ambigua sphamb x x x x x x Stephanorneria pauciflora x x Streptonthus cordatus x x Tricardw watsonii x Perennial grasses Achnatherum hyrnencides achhym x x x x x Achnatherum specWsum achspe x x x x x Aristidn purpurea x x x Elymw elynwides x x x x x Pleuraphis rigidn x x x Poa secunda poasec x x x x Cacti Echinocerus engelmanii x x x x Echinocerus triglochidiatus x Escobaria oioipara desertii x x Opuntia acanthocarpa x x Opuntia basilaris x x , x x Opl.lntia echinocarpa x x x Opuntia erinacea x x Opuntia seedling x Annual grasses Poo bigelovii x x Poo unknown 1 (annual) x Vulpia microstachys x x Vulpia octojlora vuloct x x x x Annual Forbs Amsinckia teselillta amstes x x x Anisocoma acaulis x 2003] FIRE EFFECfS IN BLACKBRUSH VEGETATION 297 ApPENDIX. Continued. Beaver Dam Joshua Tree Spring Mt. Code U B U B U B Asteraceoe unknown x Asteraceae unknown 1 (annual) x Astragalus nuttalwnus vat. imperfectus astoutimp x x Baileya pleniradiata x x BrickeUia abkmgifalia Iinoides briobllin x x Calyptridium morumdrum calmon x x Camissonia campestris camcam x x x x Camissonia unkno\vo species 1 x Camissonia unknown species 2 x Centrostegro thurberi x x Chaenactis fremontii x C~tis $tevioides chaste x x Cirsium neomexicanum x Cwytemia perfoliatll x Co,-eopsi8 bigelovii x Cryptantha circumcisso x x x x Cryptontlw decipiens crydec x x x x x CryptOlltlw. micrantha x x Cryptantha nevadensis x x CryptQlItlta pterocarya x x x x x x Cryptantha recurvata x x Descurainia pinnata x x x x x x Draba ctmeatus dracun x x x x Eriastrom diffusum x x x Erigeron dioorgens x x x x Eriogonwn annual unknown 1 x x Eriogonwn annual unknown 2 x x Eriogonum annual unknown 1 x Eriogonum nidulariwn x x Eriogonum pusillwn x x Eriogonum reniforme x Eriophyllum pringlei enpn x x Eriophyllum wallacei x x x Eschscholzia minutiflora x x Filago depressum x Gilill brecciarum ssp. brecciarum gilb,e x x Gilw clokeyi gildo x x x x lpmrwpsis polycllldon x x Langloisia setO$$isima x x x x Lappula redowski x x Layia. glanduIosa x x Lepidiurn lasiocarpum lepbs x x x x Lesquerella _Ila x x linonthus aureus linaur x x x linonthw bigelovii x x x x Iinanthus demis8tlS x x x Loeseliastrum scJwttii x x Macheranthera canescens x x Macheranthera canescens vat. leucanthemifolia x Malocothrix glabraw x x x Mentzelia affinis menafT x x x x Mentzelia nitens x x x Mimulw bigelovii x x x x Manop/don bellauJes x Nama demissum x x x x Nenadadus glanduliferus x x Nenuu;kuius kmg!florus var. brevi./l APPE~DLX. Continued. Beaver Dam Joshua Tree Spring Mt. Code U B U B U B Nyctaginaceae Unl'llOWIl 1 x Oenothera deltoides x x Dry/heea peifolwta x Oxytheca lrilobata x Pectocarya platycarpa x Plllu:elia dista,lS x Phacelia fremonUi x x x x PhoceJia tanacetifolia phatan x x Phacelia oolliHnortae x x x Plantago patagonica plapat x x x x Rajinesquia neomexicana x x x Salvia columbariae x x Silene antirrhina x x Stephanomeria erigua steexi x x x x Streptanthella longirostris x x x Syntricopappus fremontii x x Unknown species 2 x Uropappus[indleyi x x Vida ludoviciana x x lobea microcarpa x