Great Basin Naturalist
Volume 55 Number 1 Article 6
1-16-1995
Effects of salinity on establishment of Populus fremontii (cottonwood) and Tamarix ramosissima (saltcedar) in southwestern United States
Patrick B. Shafroth National Biological Survey, Midcontinent Ecological Science Center, Fort Collins, Colorado
Jonathan M. Friedman National Biological Survey, Midcontinent Ecological Science Center, Fort Collins, Colorado
Lee S. Ischinger National Biological Survey, Midcontinent Ecological Science Center, Fort Collins, Colorado
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Recommended Citation Shafroth, Patrick B.; Friedman, Jonathan M.; and Ischinger, Lee S. (1995) "Effects of salinity on establishment of Populus fremontii (cottonwood) and Tamarix ramosissima (saltcedar) in southwestern United States," Great Basin Naturalist: Vol. 55 : No. 1 , Article 6. Available at: https://scholarsarchive.byu.edu/gbn/vol55/iss1/6
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 Great Basin Naturalist by an authorized editor of BYU ScholarsArchive. For more information, please contact [email protected], [email protected]. Great Basin Nntur-a1iJ'it 5S(1), © 1995. pp. 58-65
EFFECTS OF SALINITY ON ESTABLISHMENT OF POPULUS FREMONTII (COTTONWOOD) AND TAMARlX RAMOSISSIMA (SALTCEDAR) IN SOUTHWESTERN UNITED STATES
Patrick B. ShafrothL• Jonathan M. Friedmanl, and Lee S. IschingerL
AB!'>"TR.ACT.-The exotic shmb Tamarix ramnsissima (saltcedar) has replaced the native Populusfremont# (cottonwood) along many streams in southwestern United States. We u.sed a controlled outdoor experiment to examine the influence of river salinity on germination and first-year survival of P. fremcnlii var. wisliunii. (Rio Grande cottonwood) and r ratJW$i.ss1ma on freshly deposited alluvial bars. We grew both species from seed in planters ofsand subjected to a declin ing water table and solutions containing 0, 1,3. and 5 times the concentrations of major ions in the Rio Grande at San Marcial, NM (1.2. 10.0.25.7. and 37.4 meq }-l; 0.11, 0.97. 2.37, and 3.45 dS m-J). Germination of P. freuwntii declined hy 35% with increasing salinity (P = .008). Germination of T. rumorissima was not affected. There were no significant elfccts ofsalinity on mortality or above- and belowground growth ofeither species. In labordtory tests the same salini ties had no elrect Oil P. frenwntii germination. P. fremonlii germination is more sensitive to salinity outdoors than in (:ov ered petri dishes, probably because water scarcity resulting from evaporation intensifies the low soil water potentials associated with high salinity. River salinity appears to play only a minor role in dctennining relative numbers of P. }re mnnlii. and 1: ramcsissima seedlings on freshly deposited sandbars. However, over many years salt becomes concelltrat cd on floodplains as a result ofevaporation and salt extmsion from saltcedar leaves. T. ramosissinw is known to be more to]Cr'dnt of the resulting extreme salinities than P. .frenwntU. Therefore, increil.<;es in river salinities could indirectly (lOll tribute to decline of P. fremontii forests by exacerbating salt accumulation on floodplains.
Key words: exotic species, Tamarix ramosissima, Populus fremonlii, rioor salinity, seedling establishment, Rio Grande, riparian oegetation, Bosque del Apache National Wildlife Refuge.
In the last century the exotic shlUh saltcedar channeliZing southwestern watercourses. (Tamarix ramosissima Ledebour) has spread Reductions in the magnitude ofhigh flows and tbroughout southwestern United States, where associated reductions in channel movements it now dominates many riparian ecosystems decreased the formation of bare, moist alluvial (Bowser 1958, Robinson 1965). In many areas bars, which provide ideal P. frernontii seedling T. ramosissima has replaced stands dominated habitat (Ohmart et al. 1977, Stromberg et a!. by the native Fremont cottonwood (Popultls 1991). Smaller peak Ilows have also reduced fremontii Wats.; Campbell and Dick-Peddie leaching of salts from floodplain soils (Busch 1964, Ohmart et al. 1977), decreasing the habi and Smith in press), perhaps favoring the salt tat of Neotropical migrant birds (Anderson et al. tolerant Tamarix (Everitt 1980, Brotherson 1977, Cohan et al. 1978) and altering fluvial and Winkel 1986, Jackson et a!. 1990). Flow processes (eraf 1978, Blackburn et al. 1982). regulations that have altered the historical Understanding the factors controlling estab timing of peak flows may have inhibited P. fre lishment of T. ranwsissima and P. fremontii can m.ontii regeneration because ofits short period aid in managing these species. ofseed dispersal and viability in early summer Successful invasion by Tamarix in the South (Horton 1977, Everitt 1980), but tbey have west has been attributed to many mctors. Much enhanced Tamarix regeneration because of its of the early spread probably resulted from the abundant seed production throughout the coincidental timing of clearing of P. frerrwntii growing season (Merkel and Hopkins 1957, stands by early settlers and the availability of Tomanek and Ziegler 1962, Warren and Tnrner Tamarix seed (Campbell and Dick-Peddie 1975, Horton 1977). Finally, successful inva 1964, Harris 1966, Horton and Campbell sion of T. ramosissima has been atbibuted to 1974, Ohmart et a!. 1977). Subsequent spread its superior ability to resprollt following Bre resulted largely from effects of damming and (Busch and Smith 1993).
IN~lionnllli"II~1 Survey, Midcolll;neut JI'.coJogiclll Science Center, furl Collin¥, CO 805$3400.
58 1995] SALINITY EFFECTS ON POPULUS AND TAMARIX ,59
We conducted experiments to examine the filled to 92 cm with washed coarse sand influence of river salinity on germination, sur (approximately 6% gravel [>2000 !Lm], 78% vival, and growth of Populus fremontii var, wis sand [>300-2000 !Lm], 16% fine sand lizenii (Rio Grande cottonwood) and T. ramo [>7,5-300!Lm], and <1% silt and clay), sissima on freshly deposited alluvial hars, the Four salinity treatments were each replicat principal habitat for seedling establishment of ed in three tanks (12 tanks total), Each tank hoth species, Field observations have snggest contained three planters of P. fremontii var, ed that P. fremontii is more negatively affected wislizenii and three of T. rarnosissima. Thus, by high salt concentrations than T. rarnosissi the experimental unit for each species was a rna (Brotherson and Winkel 1986, Anderson group ofthree planters within a tank. To avoid 1989), Laboratory studies have confirmed this pseudoreplication, responses were measured difference by exposing seedlings and cuttings as the mean value of the three planters. The of these species to varying concentrations of results for the two species were analyzed as NaCI and CaCI2 (Jackson et a1. 1990, Siegel separate, completely randomized experiments and Brock 1990), Two factors potentially con with four treatments and three replicates per found the relationship of results of laboratory treatment. studies to field conditions, First, the mix of The tanks were filled with water from the salts found in riparian ecosystems typically Cache la Poudre River (a snowmelt stream low includes many constituents other than Na, Ca, in dissolved solids), and solutions containing and C1. In many plants, salinity effects result mnltiples (0, 1,3, and 5 times) ofthe mean con from toxicity of specific ions as opposed to centration of all major ions in the middle Rio osmotic stress (Greenway and Munns 1980), Grande were made. These four solutions con Second, moisture availability is lower and stitute treatments Ox, lx, 3x, and 5x. Mean ion more variable in the field than in these labora concentrations were derived from eight mea tory studies. This factor is important because surements from the conveyance channel at low soil water potential caused by high salinity San Marcial, NM, between October 1989 and is exacerbated by low soil moisture content. September 1991 (U,S, Geological Snrvey 1991, We addressed these concerns by exposing T. 1992), The following salts were added to make rarnosissirna and P. frernontii seedlings to four treatment lx: 309,9 mg I-I CaS04*2HzO; 302.4 different concentrations of a mix of salts mg 1-1 NaHC03; 122,0 mg I-I MgCI2*6H20; designed to mimic ion concentrations in the 70,1 mg 1-1 NaCI; 13,9 mg 1-1 K2S04, Because Rio Grande. The experiment was conducted the coarse sand substrate was low in nutrients outdoors in planters subjected to a controlled (cf Segelquist et ai, 1993), 15 mg I-I of Fisons water-table drawdown. Experimental condi Technigro fertilizer (16% N, 17% P, 17% K) was tions were designed to simulate alluvial bars added to every tank. along the Rio Grande in central New Mexico, At the time of planting and for 1 wk there where once-extensive P frernontii forests have alter, the water level was 10 cm below the soil largely been replaced by T rarnosissima thick surface, A 3,5-cm-week-1 drawdown rate was ets (Campbell and Dick-Peddie 1964), Our applied for the remainder of the growing sea outdoor experiments were supplemented by son (17 June to late September), Water-table studies of germination under similar salinity drawdowns are associated with summer treatments in the laboratory. declines in discharge along western streams. The 3.5-cm-wcek-1 drawdown rate was select METHODS ed hecause a previous study (Segelquist et ai, 1993) indicated that it is within the optimal Seedling establishment experiments were range for establishment and growth of plains conducted outdoors in 1993 near Fort Collins, cottonwood (Populus deltoides ssp, monilifera), CO, at latitude 40°35' north, longitude 105°5' Flowering panicles of T. ramosissima were west, and elevation 1524 m, Twelve 122 X 92 collected on 17 May at the Bosque del Apache cm (diameter X depth) epoxy-lined steel tanks National Wildlife Refuge (latitude 33°46' contained six 30 X IOO-cm planters made of north, longitude 106°54' west, elevation 1375 PVC pipe. Holes 1.26 em in diameter were m), The panieles were air-dried for 48 h to drilled into the lower 10 em of each planter to enhance opening of seed capsules. Collected allow water exchange, and the planters were material was sifted through a series of soil 60 GREAT BASIN NATURALIST [Volume 55 screens until clean samples of seeds were ob the substrate column and seedlings in the tained. Catkins of P. fremontii were collected basin. We gently separated seedlings from the at the Bosque del Apache on 1 June. The cat sand and water and measured total length of kins were air-dried for 72 h to enhance open every harvested seedling. Mean root lengths ing of seed capsules. Capsules were placed were determined by subtracting the mean between soil screens and seeds were separat shoot length for a planter from the mean total ed from the cotton and capsules using forced length in that planter. Roots and shoots were aiI: Seeds of both species were sealed in plas separated for both species, and P. frernontii tic containers and refrigerated at 5" C (Zasada leaves were stripped from the stems. Roots, and Densmore 1977). On 10 June, 100 P. fre shoots, and leaves were dried at 60"C for 72 h montii seeds were planted in each of three and weighed. planters per tank, and 200 T. ramosissima One-way analysis ofvariance (SAS Institute, seeds were planted in each of the other three Inc. 1990) was used to assess the significance oftreatment differences within the two species planters. for five variables: percent ofplanted seeds alive Electrical conductivity (EC) and tempera at the end of the experiment ("end-of-season ture were measured using a Yellow Springs survival"), shoot length, root length, per-plant Instrument Co., Inc., Model 33 S-C-T meter, aboveground biomass, and per-plant root bio and pH was measured using a Corning 105 mass. For all variables the mean value of the hand-held pH meter in conjunction with a three planters in a tank was the unit ofanalysis. Coruing ATC temperature probe and a Coming The arcsine transfOlTIlation was applied to end general purpose combination electrode. EC of-season survival values to meet the equal vari was measured weekly in every tank begining ance assumption (Snedecor and Cochran 1980). 12 June (17 measuring dates). Whenever EC Data from the Colorado Climate Center was measured, a representative water temper were used to determine the difference be ature for that day was determined by averag tween precipitation and open-pan evaporation ing the temperature values from five randomly (adjusted with pan coefficient = 0.73) for the selected tanks. All EC measurements were period 1 June-30 September 1993 in Fort corrected for temperature and reported at Collins. Evaporation at Fort Collins exceeded 25 °C. Fourteen weekly measurements of pH precipitation by 26.2 em during this period. The were made beginning 30 June. On 16 June, 14 same calculation was made for the Bosque del July, 18 August, and 17 September, water sam Apache using data from the Western Regional ples from one randomly selected tank per Climate Center for the years 1975 through treatment were analyzed to determine con 1990. Precipitation data are from the Bosque centrations of Ca, Mg, Na, K, C03, HC03, Cl, del Apache National Wildlife Refuge, and S04, and N03. Ca, Mg, Na, and K were deter open-pan evaporation data are from Socorro, mined by inductively coupled plasma emis NM (latitude 34"5' north, longitude 106"53' sion spectroscopy (ICP; EPA method 200.0, west, elevation 1399 m; pan coefficient = 0.73). United States Environmental Protection Growing-season evaporation at the Bosque del Agency 1983); C03 and HC03 were deter Apache exceeded precipitation by an average mined by titration (EPA method 310.1, United of 40.6 em; n = 16, maximum = 51.0 em, and States Environmental Protection Agency minimum = 32.3 em during these 16 years. 1983); Cl, S04, and N03 were determined by We perfonned laboratory gennination exper ion chromatography. Concentrations are iments in January 1994. Five 25-seed repli reported in meq 1-1 to facilitate comparison of cates of £lve salinity treatments were com our solutions to solutions in other studies and pletely randomized for both T. ramosissima and because meq 1-1 can be related easily to elec P. fremontii. Seeds were sowed in 7.5-cm petri trical conductivity, which is commonly report dishes containing a Whatman #3 filter and 7 ed in the context ofsalinity studies. ml of a treatment solution. Petri dishes were On 29 September 1993 (day 112) we mea placed in a Percival Model 1-35 biological sured the shoot length ofevery living seedling. incuhator after sealing the dish tops with Para We harvested all live seedlings in early October. film. Temperature in the incubator was 20°C To harvest, we lifted a planter and laid it hori throughout the experiment, and petri dishes zontally in a water-filled basin. The planter were exposed to 16 h of light and 8 h of dark was then slowly lifted upside down, leaving ness each day. Four of the treatment solutions 1995] SALINITY EFFECTS ON POPULUS AND TAMARIX 61 were the same as those used in the establish 21.7" C (standard error = 0.8, n = 17). Concen ment experiment (0, 1, 3, and 5 times the con trations of measured chemical constituents in centration of the Rio Grande at San Marcial, different treatments did not increase propor NM); the fifth solution contained 7 times the tionally to the quantities of salt originally concentration ofthe Rio Grande. Genninants in added, indicating that salts (especially CaC03) every petri dish were counted after seven days. precipitated at higher concentrations (Table 1). A seed was considered genninated ifit exhibited Nevertheless, concentrations increased across expanded cotyledons and an elongated radicle. treatments, with total concentrations ranging The arcsine transformation was applied to per from 0.7 meq 1-1 (0.11 dS m-I ) in treatment Ox cent germination values to meet the equal to 37.4 meq 1-1 (3.45 dS m-l ) in treatment 5x variance assumption, and one-way analysis of (Table 1). variance was performed on the transformed For P. fremontii there was a significant values (SAS Institute, Inc. 1990). When germi treatment effect (P = .003) on end-of-season nation equaled 100%, the proportion was survival, but not on any of the four measured counted as (n - 0.25)/n, where n = the num growth variables (Table 2). End-of-season sur ber of seeds planted (Snedecor and Cochran vival was negatively associated with increasing 1980). salinity: survival was greatest in treatment Ox and lowest in treatment 5x. Because the end RESULTS of-season survival variable combines germina tion and mortality, we analyzed the arcsine EC and pH in the tanks varied little within transfonned number ofseedlings 7 d after plant treatments over the course of the experiment ing (gennination), and the arcsine-transformed (Table 1). Mean temperature in the tanks was difference between germination and end-of-
TABLE L Chemical analysis oftank water for four treatments in the outdoor establishment experiment in FOrt Collins, CO. For ion concentrations (n = 4), minimum and maximum values are presented in parentheses below treatment means. For electri.cal conductivity (n = 51) and pH (n = 42), means + 1 standard error are presented. Treatment Factor Ox Ix 3x 5x
Ca (mmoll-l ) 0.36 1.82 4.02 4.54 (0.20,0.52) (1.71, 2.00) (3.49, 4.83) (3.02,7.02) Mg (mmol I-J) 0.11 0.60 1.65 2.62 (0.08,0.16) (0.46,0.75) (1.47, 1.97) (2.28, 2.97) Na (mmol I-J) 0.17 4.85 13.87 22.24 (0.09,0.28) (4.41,5.11) (11.91,15.49) (19.33,24.65)
K (mmoll-1) 0.08 0.26 0.51 0.79 (0.06,0.09) (0.20,0.34) (0.44,0.55) (0.72,0.90)
HC03 (mmol I-J) 1.04 3.92 8.34 9.60 (0.62, 1.44) (3.24,4.44) (729,9.96) (5.87, 15.74) Cl (mmol I-J) 0.10 2.47 7.10 12.12 (0.07,0.14) (1.88.2.82) (6.96, 7.31) (10.88, 13.21) S04 (mmol I-J) 0.04 1.66 5.06 7.73 (0.04,0.05) (1.32, 1.86) (4.76,5.32) (7.13. 8.33) N03 (mmol I-J) 0.03 0.03 0.05 0.06 (0.002,0.08) (0.006,0.09) (0.01,0.08) (0.02.0.15) Total cations (meq I-I) 1.2 10.0 'l5.7 37.4 (0.7,1.6) (9.2, 10.8) (23.8, 26.7) (34.5. 41.5)
EC (dS m· l ) 1.09 + 0.03 0.97 + 0.11 2.37 + 0.23 3.45 ± 0.39 pH 7.54 ±0.03 8.10 ± 0.02 8.29 + 0.02 8.05 +0.03 62 CHEAT BASIN NATUHALIST [Volume 55
TABLE 2. Survival and growth of Populus fremontii and Tamarix ramosissima seedlings exposed to four diHerent salini- ty treatments for one growing season outdoors in Fort Collins, CO. High and low replicate means are given in parenthe- ses below the treatment means (n = 3). Treatment efl'eets were analyzed by completely randomized one-way ANOVA. Survival AN OVA was performed on arcsine~transformed data. Treatment Species Variable Ox Ix 3x 5x F F Cottonwood Survival 57.0 49.3 46.6 29.0 11.4 .003 (% ofplanted seed) (50.0,63.0) (45.7,54.0) (41.0,51.0) (20.7,35.0)
Shoot height (mm) 33.9 36.3 39.6 38.3 2.6 .13 (32.8,34.5) (34.5, 38.5) (36.5,43.9) (34.7,40.8)
Root length (mm) 239.2 280.9 286.9 247.4 2.1 .17 (227.1,258.4) (257.8,309.3) (253.6,311.7) (206.3,274.6)
Per-plant shoot 14.1 14.6 21.4 19.8 2.8 .11 biomass (mg) (13.7,14.4) (11.2, 16.6) (18.9,25.8) (14.3,25.9)
Per-plant root 26.8 19.6 31.8 31.2 1.1 .41 biomass (mg) (21.2,35.5) (16.4,21.3) (21.6,43.2) (17.2,42.9)
Sultcedar Survival 42.3 37.8 37.3 29.5 1.6 .26 (% ofplanted seed) (29.5, 51.6) (33.8,42.0) (31.8,40.8) (22.8,35.2)
Shoot height (mm) 18.1 17.7 18.2 18.3 0.04 .99 (17.3, 18.8) (15.5, 19.8) (15.6,22.2) (18.2,18.3)
Root length (mm) 174.4 173.6 179.0 162.0 0.15 .92 (166.4, 184.9) (154.8, 192.9) (128.1,243.6) (147.2,169.5)
Per-plant shoot 5.5 5.5 6.3 6.2 0.22 .88 biomass (mg) (4.8, 6.2) (4.1,6.4) (4.3,9.6) (.5.8,6.4)
Per-plant root 7.7 7.3 9.9 9.5 0.74 .56 biomass (mg) (7.1, 8.9) (5.5,9.2) (7.0,14.7) (7.6,12.1)
season survival (mortality). There was a signif dS m-I ) is consistent with results of earlier icant treatment effect on germination (P = studies. Jacksou et al. (1990) found that P. fre .008), but not on mortality (P ~ .45), iudicat montU germinated in the laboratory at salini iug that the effect on end-of-seasou survival ties of 0, 27, and 106 meq 1-1 using a mixture was predominantly due to lower germination of NaCI aud CaCI2, but not at 319 meq I-lor at higher salt concentrations. For T. ramosissima above. Siegel and Brock (1990) observed high there were no significant treatment effects er percent germination of P. fremontii in the (Table 2). laboratory in NaCI solutions of 0, 25, aud 50 Although P. fremontii germination in out meq I-I thau at 100 meq I-I aud above. There door tanks was siguificautly decreased at high fore, P. frernontii is no more sensitive to the salinity, laboratory germination was not simi mix of salts present in the Rio Grande than to larly affected even at seven times the salinity NaCI and CaCI2 solutious of equal streugth. of the Rio Grande, total concentration 48.4 Tests at higher salinities with the same ionic meq I-I (4.56 dS m-l; Table 3). There was a sig ratios were not possible with our Rio Grande nificant positive effect ofincreasing salinity on mix because of low solubilities of some of the T. ramosissima germination (P ~ .03) (Table 3). constituent salts. The decrease in T. rarnosissi rna germination at low salinity in the laborato DISCUSSION ry (Table 3) is consisteut with the finding by Jacksou et al. (1990) that germination iucreas The absence of a negative effect of salinity es between 0 and 106 meq I-I. on P. frerrwntii germination in the laboratory at Our results indicate that a given water salin conceutratious as high as 48.4 meq I-I (4.56 ity may negatively affect germination of P. 1995] SALINITY EFFECTS ON POPULUS AND TAMARIX 63
TABLE 3. Percent gennination of Populw jremOfltii and 1am(lnx ramosi3s1mo seedlings c:\posed to five salinity treat ments in covered petri dishes. High and low replicate values are given below the treatment mean (n = 5). Treatment effects were analyzed by completely randomized one-way ANOVA using arcsinc-tr'dtlsformed data. Treatment
Species Ox Ix 3, 5, 7, F P Cottonwood 90.4 96.0 96.0 92.8 96.0 1.2 .35 (80.0, 100.0) (92.0, 100.0) (92.0, 100.0) (84.0,96.0) (92.0,100.0)
Saltcedar 69.6 68.8 78.4 84.8 84.0 3.3 .03 (60.0,88.0) (56.0, 80.0) (68.0, 92.0) (76.0,92.0) (76.0,92.0) jremQntii seeds under ambient conditions but del Apache (John Taylor, Bosque del Apache not under laboratory conditions. This may have National Wildlife Refuge, personal communica resulted from an interaction between the tion), and soil salinity levels as high as 60,000 effects ofsalinity and soil moisture content. or mg I-I occur on floodplain sites along the from vapor-pressure deficit differences. In lower Colorado River (Jackson et al. 1990), outdoor planters, but not laboratory petri dish Soil EC above 2,0 dS m-1 can reduce the es, evaporation of \V'ater may have resulted in growth ofP. jrernontii pole plantings (Anderson lower soil moisture and higher salt concentra 1989), T ramosissimn has been shown to be tion at the soil surface, These factors would less susceptible than P. fremont;; to many of both tend to reduce soil water potential, the negative effects of higher salinities thereby increasing plant water stress. Because (Brotherson and Winkle 1986, Jackson et aL the difference between evaporation and pre· 1990), Tamar;x species avoid harmful effects of cipitatioll is somewhat greater at the Bosque del salts through extrusion from leaves and cellu Apache than in Fort Collins, the effect of salin lar compartmeotation (Berry 1970, Kleinkopf ity might be stronger at the Bosque, especially and Wallace 1974, WaiseI1991), in dry years. Finally, greater vapor-pressure Our results could be applied to efforts to deficits in the field relative to the laboratory revegetate riparian areas from seed. Riparian may have exacerbated plant water stress, revegetation in the Southwest has largely con Salinity appears to be a relatively minor fac sisted of planting poles or potted shoot cut tor regulating numbers of P. fremontii and T. tings. Although these approaches have been ranwsissima seedlings on freshly deposited successful in some areas (Anderson et al. 1990), sandbars along th~ Rio Grande. The only signif· they can cost op to $10,000 per bectare (Ohmart icant effects ofincreasing salinity were a small et aL 1988), Furthermore, they require the decrease in P. fremontii gennination in out· destruction ofparts ofexisting trees, and often door planters and a small increase in 'f ramo entire trees or stands, Finally, these approach sissima germination in the laboratory. There es may require importing cuttings or poles were no significant effects on survival after adapted to different site conditions, One alter germination or above- Or belowground growth native is regeneration of native cottonwoods for either species, even at water salinities sev and willows using natural seedfall (Friedman eraltimes that ofthe Rio Grande. The presence 1993, John Taylor personal communication), of abundant seedlings of P. fremontii and T. This approach generally involves clearing and ranwsissima on sandbars along the Rio Grande irrigating an area so that seeds from nearby in most years is consistent with our results. trees can colonize it. Our results suggest that Although salinity may play only a minor role water as saline as 37.4 meq I-I (EC 3.45 dS in tbe colonization of newly deposited alluvial m-I ) can be used to grow P. fremontii f..om bars by T. ramosissima and P. fremontii, this seed on sand (Tables 1, 2), However, care must factor can become more important over time, be taken to prevent long-term salt accumula Over many years salt becomes concenh'ated tion through evaporation (e,g" through periud on some floodplains as a result of evaporation ic flooding to flush salts) and to avoid sites and salt extrusion from T. 1-amosissima leaves. witb preexisting high salinity, Use of water EC readings as high as 10.0 dS m-I have been with low salinity can help prevent negative reported in floodplain sediment at the Bosque effects on P. jrenumtii and may decrease the 64 GREAT BASIN NATURALIST [Volume 55
germination rate of 1: ramosissima (Table 3). tion of the United States and comments concerning However, in a restoration effort along the the plants' influence upon the indigenous vegetation. Pages 12-16 in Symposium on Phreatophytes. Ameri Cache la Poudre River, T. ramosissima became can Geophysical Union, Sacramento, CA. established in large numbers along with P. del BROTHERSON, ]. D., AND \Z \;VINKEL. 1986. Habitat rela toides in spite of use of water of low salinity tionships of saltcedar (Tamarix ramosissinw) in cen (Douglas Gladwin, National Biological Survey, tral Utah. Great Basin Naturalist 46; 535-541. personal communication). Therefore, low salin BUSCH, D. E., AND S. D. SMITH. 1993. Effects of fire on water and salinity relations of riparian woody taxa. ity will not prevent establishment of T ramo Oecologia 94: 186-194. sissirna from seed when moisture, a bare sedi ___. In press. Decline, persistence, and competition of ment, and a seed source are present. woody taxa in riparian ecosystems of the southwest~ ern U.S. Submitted to Ecological Monographs. CAMPBELL, C.]., AND w: A. DICK-PEDDIE. 1964. Compari ACKNOWLEDGMENTS son ofphreatophyte communities on the Rio Grande in New Mexico. Ecology 45: 492-502. G. T. Auble, D. E. Busch, and an anonymous COHAN, 1). R, B. W. ANDERSON, AND R. D. OHMART. 1978. reviewer provided constructive comments on Avian population responses to salt cedar along the the manuscript. We thank E. R. Auble, G. T. lower Colorado River. Pages 371-382 in R. R Johnson and J. F. McCormick, technical coordinators, Auble, J. Back, E. D. Eggleston, M. Jordan, Strategies for Protection and Management of Flood and M. L. Scott for invaluable assistance with plain Wetlands and Other Riparian Ecosystems: pro the experiments. D. Smeltzer, B. Upton, and ceedings of the symposium. USDA Forest Service the Colorado Division of Wildlife generously General Technical Report WO-12. Washington, DC. EVERITT, B. L. 1980. Ecology of saltcedar-a plea for provided access to the Bellvue-Watson Fish research. Environmental Geology 3; 77-84. Rearing Unit where the outdoor experiment FRIEDMAN, ]. M. 1993. Vegetation establishment and was conducted. T. Kern and P. Soltanpour pro channel narrowing along a Great-plains stream fol vided useful advice regarding the salinity lowing a catastrophic flood. Unpublished doctoral treatments. Concentrations ofions in solutions dissertation, University ofColorado, Boulder. GRAF, W. L. 1978. Fluvial adjustments to the spread of were measured by the Soil, Plant and Water tamarisk in the Colorado Plateau region. Geological Testing Laboratory at Colorado State University, Society ofAmerica Bulletin 89; 1491-1501. Fort Collins, CO. GREENWAY, H., AND R MUNNS. 1980. Mechanisms of salt tolerance in nonhalophytes. 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