| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
|
|
|
|||||||
|
|||||||||
Graduate Group in Botany and Department of Environmental Horticulture, University of California, Davis, California 95616 USA
Received for publication March 21, 2000. Accepted for publication July 5, 2000.
 |
ABSTRACT |
|---|
 TOP ABSTRACT INTRODUCTIONSITE CHARACTERISTICS AND METHODSRESULTSANALYSISDISCUSSIONLITERATURE CITED |
|---|
In the Mediterranean climate of the Sierra Nevada, the heavy winter snowpack persists into late spring, after precipitation has effectively stopped. We found the subsequent depletion of soil moisture due to plant water uptake to result in predawn xylem water potentials for conifers more negative by 0.6–1.4 MPa than those for shrubs or inferred soil potentials. Shrubs generally depleted soil moisture more rapidly and ultimately extracted a greater fraction of the available soil moisture than did the conifers. This depletion of soil moisture by shrubs, particularly Arctostaphylos patula, may limit conifer growth and regeneration by prematurely terminating growth on the shallow soils studied. The conifers all generally showed similar patterns of soil moisture use, except that A. magnifica extracted moisture more rapidly early in the season.
Key Words: Abies • Arctostaphylos • competition • conifer • drought • Pinus • shrub • snowpack
|
INTRODUCTION |
|---|
|
TOPABSTRACTINTRODUCTIONSITE CHARACTERISTICS AND METHODSRESULTSANALYSISDISCUSSIONLITERATURE CITED |
|---|
). An ecotone between the midmontane forest and upper montane forest of the Sierra is marked by a major discontinuity in the distribution of tree, shrub, and forb species (Mellmann-Brown and Barbour, 1995
; Barbour and Minnich, 2000
). The overall objective of the work reported in this and in a companion paper in this issue (Royce and Barbour, 2001
) was increased understanding of environmental factors and their interactions affecting conifer species distribution across this ecotone.
The midmontane–upper montane ecotone is typically a 250 m wide zone of elevations. In the southernmost Sierra Nevada (south of Sequoia National Park) and in the Transverse Range (adjoining the Sierra to the southwest) it occurs at elevations where winter precipitation changes from predominantly rain to predominantly snow with increased elevation (Kunz, 1988
; Barbour et al., 1991
; cf. Minnich, 1986
), between 2200 and 2800 m. Snowpack in the upper montane forest is deep (>2 m), but temperatures are mild, compared to continental mountain ranges (Baker, 1944
).
During summer months, a scarcity of precipitation leads to a moisture deficit, particularly in the southern Sierra (Kruse, 1990
; Parker, 1994
)—even at cool, high elevations (Major, 1990
). This drought is a normal event, though its intensity varies with exposure, elevation, and year. It occurs even though total annual precipitation, falling mostly in winter, is well in excess of potential annual evapotranspiration (Major, 1990
). This montane Mediterranean climate occurs in the mountains of Morocco, Spain, and Turkey (Walter, 1984
). It also occurs in the mountains of northwest California and southwest Oregon, but not in other North American mountain ranges (Baker, 1944
).
The midmontane (mixed conifer) forest is a somewhat open four-layer community (Barbour and Minnich, 2000
). On slopes of the southernmost Sierra Nevada both the overstory and understory are dominated by yellow pine (Pinus ponderosa Laws or Pinus jeffreyi Grev. & Balf.), Sierra white fir (Abies concolor Gordon & Glend. var. lowiana (Gordon) Murray), sugar pine (Pinus lambertiana Douglas), incense cedar (Calocedrus decurrens (Torry) Florin), and black oak (Quercus kelloggii Newb.). A patchy shrub canopy includes species of Arctostaphylos, Ceanothus, and Quercus, and numerous understory forbs are seasonally common in open areas. (Nomenclature follows the Jepson Manual [Hickman, 1993
].)
The upper montane (red fir) forest is a simpler, two-layer community (Barbour and Woodward, 1985
). In the southernmost Sierra it is dominated by Shasta red fir (Abies magnifica Murray var. shastensis Lemmon) and western white pine (Pinus monticola Douglas) and includes a minor forb understory. Although commonly a more closed community than the midmontane forest, the upper montane forest canopy opens near the ecotone, and shrubs such as Chrysolepis sempervirens (Kellogg) Hjelmq. may be locally dense.
Sites near and within the ecotone, such as those in this study, are of a woodland character, with 20–30% overstory cover and sometimes with extensive shrub or forb cover where trees are absent. The ecotone forest is marked by the co-occurrence of the dominants P. jeffreyi, A. concolor, A. magnifica, and sometimes P. monticola, together with shrubs from both the mid- and upper montane communities.
The objective of this study was to identify and quantify species-specific differences in patterns of water use in response to the seasonal climate of the Sierra Nevada and to identify how these differences might influence conifer species distribution. We report measurements of the seasonal progression of soil and plant water status in the relatively unstudied southernmost Sierra, where the summer drought is most severe (Parker, 1994
). A Mediterranean climate is unusual for coniferous forests, and most understanding of the ecophysiology of conifers is for climates with wetter summers and/or colder temperatures.
|
SITE CHARACTERISTICS AND METHODS |
|---|
|
TOPABSTRACTINTRODUCTIONSITE CHARACTERISTICS AND METHODSRESULTSANALYSISDISCUSSIONLITERATURE CITED |
|---|
70 km south of Sequoia National Park. Measurements were made through the 1994 and 1995 seasons every 2–3 wk, from the date of local snow melt, typically in May, to the first fall storm, typically in October or November. Fortuitously, these two seasons offered near extreme conditions (based on a subjective review of snow sensor records extending over 20–25 yr, California Data Exchange Center, http://cdec.water.ca.gov). The winter of 1994 began a drought year in California, with a seasonal precipitation 75% of normal and a snowpack on 1 April 55% of normal in the southern Sierra, leading to an early onset of an extended summer drought. The winter of 1995 saw seasonal precipitation 160% of normal and a snowpack on 1 April 185% of normal, leading to an unusually late onset of the summer drought (California Department of Water Resources, 1994–1995; normals based on records extending back up to 50 yr). Approximate boundaries of the ecotone were determined by a vegetation survey of 167 sites, in preparation for the selection of three permanent research sites for the present study. One of these permanent sites was located below (elevation 2230 m) and another above (elevation 2820 m) the ecotone. Site vegetation was typical for their elevation and general location, and sites were selected with as many tree species as possible present. These sites generally showed little sign of human disturbance. However, the frequent heavy shrub cover was, in part, probably the result of many years of fire suppression, and forb and grass coverage was probably reduced from continued cattle grazing. The third permanent site was located at an elevation of 2700 m, within the ecotone. This site had been logged selectively and lightly a number of years earlier, but large trees were still present, and extensive patches of several shrub species were present.
All permanent sites were on level ridge-tops and were typically 100–200 m across. Sites were rocky, with poorly developed soils (sandy to loamy entisols or inceptisols) and with soil parent rock the common southern Sierra granodiorite. The depth to parent rock varied over 50–170 cm at differing locations at each site, based on our experience drilling neutron probe holes. Except immediately near the surface, the soils were quite compact, being formed from in-place decomposition of the parent rock. Some roots probably penetrated fractures in the parent rock (cf. Zwieniecki and Newton, 1994, 1996
), but we could not verify the extent of such fracturing or penetration. (The first two sites are the sites designated "A" and "B," respectively, on Fig. 1 of the companion paper [Royce and Barbour, 2001
], while the third site is located on the ridge separating the two sites designated "Y" on that figure.)
|
Environmental conditions
On-site temperatures were measured using maximum–minimum thermometers, and a funnel-type bulk rain gage was mounted in an open location near the thermometer enclosure at each site (Royce and Barbour, 2001
). Data from a continuous recording weather station (Pascoe) located 2 km from the highest site and at a comparable elevation were used to fix the timing of storms occurring between site visits. The timing of snow melt on each site was fixed with more frequent site visits at critical times in the late spring. Environmental measurements were continued through the 1996 season, a near normal water year.
Soil moisture
Soil water content was monitored with a neutron-scattering probe (CPN Company, Martinez, California, USA, model 503 Hydroprobe; Kramer and Boyer, 1995
; Brady and Weil, 1996
). Access holes were between 50 and 170 cm deep, 5 cm in diameter, and lined with thin-walled aluminum irrigation pipe. Standard probe depths used in the measurements were 20, 40, 70, 100, and 150 cm, where permitted.
Single neutron probe holes were drilled at the drip line under mature trees: A. concolor, P. jeffreyi, P. lambertiana, C. decurrens, and Q. kelloggii at the low site; A. magnifica and P. monticola at the high site; and A. concolor, A. magnifica, and P. jeffreyi at the ecotone site. Holes were drilled beneath a patch of the shrub Arctostaphylos patula Greene (greenleaf manzanita) at the low site, beneath a patch of the shrub C. sempervirens (bush chinquapin) at the high site, and beneath patches of the shrubs A. patula, C. sempervirens, Ceanothus cordulatus Kellogg (mountain whitethorn), and Cercocarpus ledifolius Nutt. (curl-leaf mountain-mahogany) at the ecotone site.
The presence of numerous rocks and stones in the immediate vicinity of each access hole resulted in neutron counts varying by as much as 50% at different depths in the same hole or between holes, under what should have been water saturation conditions. This variation required that the probe be calibrated in situ at each depth station in each hole. This was accomplished by assuming that the soil was saturated with water as the snow melted and that rapid draining of gravitational water at the end of snowmelt led to a field capacity some 3 d after that date. All moisture measurements were then reported in terms of this field capacity, as a soil moisture fraction (SMF), rather than in absolute terms. This calibration was estimated to have an uncertainty 5%.
Xylem water potential
Predawn xylem water potential was monitored for all trees studied in 1994 and 1995 and for all shrub species studied in 1995. In addition to the trees and shrub species for which soil moisture was measured, water potentials were measured on the shrubs Ceanothus pinetorum Cov. (Kern ceanothus) and C. cordulatus at the low site and C. pintorum and Ribes cerium Douglas (squaw or wax current) at the ecotone site. Midday xylem water potential was also monitored on trees in 1994.
Measurements in the field used a Scholander pressure chamber and were made on needle- or leaf-covered twigs for the firs, incense cedar, and shrubs, and on single fascicles for the pines. Change in measured water potential resulting from transpiration from these small specimens was prevented by sealing the specimen in the pressure chamber within 30 sec after cutting. Additionally, mid-day cuttings were bagged in plastic covered with aluminum foil at least an hour before cutting, to induce stomatal closure. Bleeding from resin canals was distinguished from the emergence of xylem water by its location on the stem cross section. Otherwise, the recommendations of Ritchie and Hinckley (1975)
were generally followed. The accuracy of these measurements was estimated as ±0.1 MPa (cf. Waring and Cleary, 1967
).
Water potential measurements were also made on trees and shrubs at four additional permanent sites within the ecotone, in conjunction with growth measurements reported in the companion paper (Royce and Barbour, 2001
). Summary statistics on water potentials reported here include data from these sites and data from saplings and pole-sized trees at all permanent sites, in order to improve the strength of the statistical analyses. Analyses were carried out using JMP (SAS Institute, 1995
). Method details are given elsewhere (Royce, 1997
).
|
RESULTS |
|---|
|
TOPABSTRACTINTRODUCTIONSITE CHARACTERISTICS AND METHODSRESULTSANALYSISDISCUSSIONLITERATURE CITED |
|---|
30 d, compared to 1994. Spring temperatures in 1995, particularly minima, were depressed compared to 1994, and the entire progression of temperatures was shifted later by 30 d (Fig. 3 and discussion in the companion paper [Royce and Barbour, 2001
]).
|
A less sharply defined low-moisture date, typically 60 d after the last-water date, marked the transition from a spring growth period to the summer drought period. Appreciable precipitation between the no-snow and low-moisture dates, the growth period, fell at the low-elevation site with its early no-snow date. For the higher elevation sites, with later snow melt, most of this precipitation fell before their no-snow dates and did not contribute to a growth-period total. As a result, the total growth-period precipitation was strongly correlated with no-snow date (r = -0.69). This growth-period precipitation extended the growth period by delaying the onset of the summer drought. Total drought period precipitation, falling between the low-moisture date and the first major fall storm, was only 23 mm averaged over all sites (precipitation data for 1994–1996, six sites, N = 18).
Soil moisture
Soil moisture (SMF) approximately followed an exponential depletion curve (Fig. 1). Soil at shallow depth (20 cm) was more rapidly and completely depleted of water than were deeper layers. Early in the season there was sometimes a more rapid depletion of water at the 40- and 70-cm levels, as compared to water from 100 cm and below. (Cf. Ziemer, 1978
; Running, 1980
; or Arkley, 1981
.)
Water potential
When water was plentiful shortly after snow melt, predawn xylem water potentials were roughly independent of soil moisture. Predawn potentials declined more rapidly than soil moisture after there had been depletion of soil moisture, typically to SMF 
0.6. By this time, moisture depletion had slowed markedly. In late summer, when soil moisture depletion had nearly stopped, predawn water potentials continued to become more negative, minimum values (Fig. 2) occurring just before the first fall storm.
|
|
ANALYSIS |
|---|
|
TOPABSTRACTINTRODUCTIONSITE CHARACTERISTICS AND METHODSRESULTSANALYSISDISCUSSIONLITERATURE CITED |
|---|
has also shown data that are most consistent with soil moisture depletion at depth being due almost entirely to forest plant water uptake. (Cf. Oren and Sheriff, 1995
.)
In order to compare soil-moisture depletion rates between individuals and species, the depletion rate was modeled by the quadratic expression
 |
40 cm. The change in the depletion rate with soil moisture is then
 |
 |
 |
In this model, SMF is initially unity on the date t = t0 and declines to a limiting value given by the parameter c. If the shape-controlling parameter q is large, the model reduces to one of simple exponential decay, where the depletion rate is proportional to the available moisture remaining (x - c), constantly declining as moisture is depleted. The quantity s(1 - c) is then the initial rate of depletion, and s is the coefficient appearing in the exponent of the exponential. For q = 1, on the other hand, the depletion rate is initially constant, then declining more slowly than in the exponential case as moisture depletion takes place. A constant depletion rate might correspond to evaporation or transpiration from a free water surface of constant area, as would be the case in the absence of stomatal control.
The model assumes that there is no substantial input of moisture due to precipitation during the depletion cycle. Since daily evapotranspiration in the absence of drought stress was probably 2 mm/d with transpiration reduced by stomatal closure during the summer (Royce, 1997
), at most the observed average drought-period total precipitation of 23 mm could have made only a minor contribution to replenishing deep soil moisture. Furthermore, during the period of our observations, summer storms each yielded only a few millimeters of precipitation, this precipitation only wetted the surface of leaves or soil, and most appeared to have been lost to direct evaporation by the next day. Localized heavier summer rainfall does occur, but only rarely on any particular site. Its importance may be diminished, because subsequent evaporation during warm days should be enhanced, as the radiatively cooled night time surface attracts moisture from warmer deep soil.
Soil moisture fraction (SMF) data for dates after the last spring rain and before the first fall rain were fitted to Eq. 3 with the use of a nonlinear least-square routine. The resulting parameters, s, c, and q, were then used in Eq. 1 to calculate the depletion rate. This procedure allowed the determination of the depletion rate without the data scatter that would have resulted from the numerical differentiation of the original data. Parameter values (except t0) for individual trees or shrub patches typically showed insignificant differences when determined from the 1994 or 1995 data. In most cases, the best fits were obtained with q = 1, consistent with plant limitation of water use only after some soil moisture depletion had taken place. However, in a few cases best fits were found for larger values of q (2), reflecting more immediate plant regulation or other restriction of water use. These differences were sometimes seen between trees of the same species and, so, cannot be attributed to interspecies differences.
Values of c showed small differences (5%) between individual trees or shrub patches of the same species. These differences may have been due to errors in the neutron probe calibration between holes or to minor differences in soils. The data for each tree or shrub patch were normalized, so that c values were the same for all individuals of each species. The resulting SMF depletion-rate values for different individuals of a species then differed typically by 20%, whether individuals were on the same site or one at the ecotone site and one at a nonecotone site. These depletion rates were averaged over all individuals at each SMF value (Fig. 4).
|
15%, but at later times (SMF < 0.7), the shrub moisture depletion rates averaged 35% more than rates for the low-elevation conifers. Residual (asymptotic) values of SMF when depletion had stopped, the parameter c, show no significant (P < 0.05) differences for different species within the conifer or shrub groups. However, means for each of these groups were significantly different from each other, and the mean surface depletion value was significantly different from the mean conifer value. (Mean values of final SMF: Conifers = 0.48 [depth 40 cm, SD = 0.02]; Shrubs = 0.42 [depth 40 cm, SD = 0.03]; Surface = 0.39 [depth = 20 cm, conifers or shrubs, SD = 0.03]. P < 0.001.)
Water potential
With plentiful soil moisture (SMF > 0.65), predawn water potentials showed considerable variation, between -0.4 and -0.7 MPa for conifers and between -0.2 and -0.3 MPa for the shrubs, but appeared roughly independent of SMF (cross-hatched areas on Fig. 5).
|
) was fitted to a function exponential in the SMF. Such an exponential relationship was suggested by data on soil water potentials (Kozlowski, Kramer, and Pallardy, 1991
; Kramer and Boyer, 1995
; Brady and Weil, 1996
). Conifers entered this regime at higher SMF values than did the shrubs. (At -1 MPa, mean values of SMF were conifers = 0.50 [SD = 0.04] and shrubs = 0.43 [SD = 0.04]. P < 0.001.) However, with further increased soil moisture depletion, the distinction between conifers and shrubs was no longer significant. (At -2 MPa, mean values of SMF were conifers = 0.46 [SD = 0.04] and shrubs = 0.41 [SD = 0.04]. P > 0.13.) Toward the end of summer, some shrubs reached more negative predawn water potentials than did any of the conifers (Fig. 2). While differences in performance among shrub species were not significant at a high confidence level, the data do suggest important differences between A. patula and C. sempervirens, the most common shrubs found on the study sites. For A. patula, soil moisture depletion led to an average residual SMF value of 0.41, next to the lowest value found under any tree or shrub. For C. sempervirens, on the other hand, the residual soil moisture was 0.44, the highest value for any shrub. Late-summer predawn xylem water potentials were more negative than -4 MPa for A. patula but no more negative than -1.5 MPa for C. sempervirens. Arctostaphylos patula often forms monospecific stands, suggesting a strong capability of excluding other species, but C. sempervirens does not. (The less common C. cordulatus, with the lowest residual SMF observed [0.39] also forms similar monospecific stands.)
|
DISCUSSION |
|---|
|
TOPABSTRACTINTRODUCTIONSITE CHARACTERISTICS AND METHODSRESULTSANALYSISDISCUSSIONLITERATURE CITED |
|---|
; DeLucia and Heckathorn, 1989
; DeLucia and Schlesinger, 1991
; Jaindl, Doescher, and Eddleman, 1993
), making more extensive osmotic adjustments (Bowman and Roberts, 1985
) and developing a more extensive root system to support this continued transpiration (Hellmers et al., 1955
). Shrub and forb competition for water has been widely cited as a major negative influence on young conifers (e.g., Tappeiner and Radosevich, 1982
; Lanini and Radosevich, 1986
; Drivas and Everett, 1988
; Parker and Yoder-Williams, 1989
; Callaway et al., 1996
) and appears to be particularly strong for shrubs of the Ericaceae (Conard and Radosevich, 1982
; Radosevich, 1984
; White, 1985
; Shainsky and Radosevich, 1986
; Anderson and Helms, 1994
) such as A. patula. However, Rejmánek and co-workers found that water is not the dominant factor in this competition on deep soils in the Sierra Nevada (Rejmánek and Messina, 1989
; Randall and Rejmánek, 1993
).
In our study, on relatively shallow soils (50–170 cm deep), we found that the low-elevation conifers reduced their water uptake more than did the shrubs at moderate drought conditions (Fig. 4, SMF 0.5–0.55), and that predawn xylem water potentials in conifers, but not in shrubs, became increasingly negative at these SMF values (Fig. 5). Abies magnifica showed an initial water uptake rate larger than the other conifers and most shrubs, but this rate declined rapidly, to values similar to those for the other conifers. The high initial depletion rate for A. magnifica is consistent with the observation that A. magnifica seedlings in a growth chamber developed a more extensive root system than did A. concolor seedlings (Barbour, Pavlik, and Antos, 1990
). We presume that changes in water uptake, as inferred from soil moisture depletion, reflect primarily changes in transpiration. (Cf. Whitehead and Jarvis, 1981
; Kramer and Boyer, 1995
; or Oren and Sheriff, 1995
.) This is consistent with Kunz' (1988)
central-Sierra measurement of higher June leaf conductances in A. magnifica than in A. concolor, but similar conductances for the two species at later dates.
Conifer predawn water potentials under drought conditions were substantially more negative than shrub predawn water potentials. But soil water potentials cannot be more negative than shrub predawn water potentials, or shrubs could not extract soil moisture. Hence, conifer water potentials must have been substantially more negative than soil water potentials, demonstrating an apparent inability of the conifers to recharge depleted water storage over a single night. This inability could have been due to an inadequate root system and/or the limited conduction capability of conifer tracheids, compared to shrub xylem vessels. (Cf. Oren and Sheriff, 1995
; or Pallardy et al., 1995
.)
As soil moisture was further depleted, conifers apparently exercised more decisive control of their transpiration. Conifer water uptake was cut off at soil moisture levels (SMF 0.45) where the shrubs were still depleting soil moisture, and the diurnal fall in water potential was not as great as under early-season conditions. When all water use was cut off, conifer water potentials were less negative than shrub water potentials (-1.8 MPa vs. < -4 MPa), further demonstrating the ability of the conifers to control their transpiration and water status. (In general drought-resistant conifers such as P. ponderosa or A. magnifica, and probably others in this study, show only 2–3% residual stomatal conductance under drought conditions, while other conifers show up to 20% residual conductance [Larcher, 1975
; Running, 1976
; Hinckley, Lassoie, and Running, 1978
].)
The shrubs more completely extracted soil moisture than did the conifers (average residual soil moisture, SMF = 0.42 vs. 0.48), consistent with their continued transpiration under low soil moisture conditions. The observations that A. patula final water potentials were extremely negative, that residual soil moisture under A. patula was lower than under most plants, and that A. patula is distributed in monospecific stands are all consistent with identifying it as a particularly strong competitor for water. Arctstaphylos patula was present on only 20% of the higher elevation survey sites dominated by A. magnifica, but was present on 64% of survey sites where A. magnifica was absent. This mutual avoidance between A. patula and A. magnifica may be associated, at least in part, with competition for water between them.
We observed surprisingly little difference in water management between the two years of observation, except that the phenology of water use was uniformly shifted to earlier dates in the drought year.
In conclusion, differences in seasonal water use patterns between conifer species were observed. However, these differences by themselves do not suggest a direct elevation-dependent competitive advantage of one species over another that might explain species distribution across the midmontane upper montane forest ecotone. These water use patterns must be combined with differences in growth phenology between conifer species, as discussed in the companion paper (Royce and Barbour, 2001
), in order to understand species distribution. As compared to the conifers, we found that angiosperm shrubs show water use patterns that may make them particularly effective competitors for moisture from shallow soils, and this is especially true for A. patula. These differences between conifers and shrubs may be important in explaining forest–shrubland ecotones and forest structure changes during post-fire or post-logging succession.
|
FOOTNOTES |
|---|
2 Author for correspondence, current address: Kennedy Meadows Box 2C4, Inyokern, California 93527 USA (ebroyce{at}alumni.caltech.edu
).
|
LITERATURE CITED |
|---|
|
TOPABSTRACTINTRODUCTIONSITE CHARACTERISTICS AND METHODSRESULTSANALYSISDISCUSSIONLITERATURE CITED |
|---|
Arkley, R. J. 1981 Soil moisture use by mixed conifer forest in a summer-dry climate. Soil Science Society of America Journal 45: 423–427
Baker, F. S. 1944 Mountain climates of the western United States. Ecological Monographs 14: 223–254[CrossRef]
Barbour, M. G., N. H. Berg, T. G. F. Kittel, and M. E. Kunz. 1991 Snowpack and the distribution of a major vegetation ecotone in the Sierra Nevada of California. Journal of Biogeography 18: 141–149[CrossRef][ISI]
———, and R. A. Minnich. 2000 California upland forests and woodlands. In M. G. Barbour and W. D. Billings [eds.], North American terrestrial vegetation, 2nd ed., 161–202. Cambridge University Press, Cambridge, UK
———, B. M. Pavlik, and J. A. Antos. 1990 Seedling growth and survival of red and white fir in a Sierra Nevada ecotone. American Journal of Botany 77: 927–938[CrossRef][ISI]
———, and R. A. Woodward. 1985 The Shasta red fir forest of California. Canadian Journal of Forest Research 15: 570–576
Bowman, W. D., and S. W. Roberts. 1985 Seasonal and diurnal water relation adjustments in three evergreen chaparral shrubs. Ecology 66: 738–742[CrossRef][ISI]
Brady, N. C., and R. R. Weil. 1996 The nature and properties of soils. Prentice Hall, Upper Saddle River, New Jersey, USA
California Department of Water Resources. 1994–1995 Water conditions in California, April 1 and May 1 issues of each year. State of California, Department of Water Resources, Sacramento, California, USA
Callaway, R. M., E. H. DeLucia, D. Moore, R. Wowak, and W. H. Schlesinger. 1996 Competition and facilitation: contrasting effects of Artemisia tridentata on desert vs. montane pines. Ecology 77: 2130–2141[CrossRef][ISI]
Conard, S. G., and S. R. Radosevich. 1981 Photosynthesis, xylem pressure potential, and leaf conductance of three montane chaparral species in California. Forest Science 27: 627–639[ISI]
———, and ———. 1982 Growth responses of white fir to decreased shading and root competition by montane chaparral shrubs. Forest Science 28: 309–319
DeLucia, E. H., and S. A. Heckathorn. 1989 The effect of soil drought on water-use efficiency in a contrasting Great Basin desert and Sierran montane species. Plant Cell Environment 12: 935[CrossRef]
———, and W. H. Schlesinger. 1991 Resource-use efficiency and drought tolerance in adjacent Great Basin and Sierran plants. Ecology 72: 51–58
Drivas, E. P., and R. L. Everett. 1988 Water relation characteristics of competing singleleaf pinyon seedlings and sagebrush nurse plants. Forest Ecology and Management 23: 27–37[CrossRef][ISI]
Hallgren, S. W., and J. A. Helms. 1988 Control of height growth components in seedlings of California red and white fir by seed source and water stress. Canadian Journal of Forest Research 18: 521–529[CrossRef]
Hellmers, H., J. S. Horton, G. Juhren, and J. O'Keefe. 1955 Root systems of some chaparral plants in southern California. Ecology 36: 667–678
Hickman, J. C. 1993 The Jepson manual, higher plants of California. University of California Press, Berkeley, California, USA
Hinckley, T. M., J. P. Lassoie, and W. W. Running. 1978 Temporal and spatial variation in the water status of forest trees. Forest Science, Supplement Number 20
Jaindl, R. G., P. S. Doescher, and L. E. Eddleman. 1993 Influence of water relations on the limited expansion of Pinus monophylla into adjacent Cercocarpus ledifolius communities in the Central Great Basin. Forest Science 39: 629–643[ISI]
Kozlowski, T. T., P. J. Kramer, and S. G. Pallardy. 1991 The physiological ecology of woody plants. Academic Press, San Diego, California, USA
Kramer, P. J., and J. S. Boyer. 1995 Water relations of plants and soils. Academic Press, San Diego, California, USA
Kruse, S. M. 1990 Climatic water budgets, effective moisture, and elevation in the southern Sierra Nevada, California 1951–1980. Cooperative National Park Resources Study Unit, Technical Report Number 41. University of California, Davis, California, USA
Kunz, M. E. 1988 Pattern of distribution, growth, and seedling survival of red fir and white fir in the Sierra Nevada. Ph.D. dissertation, University of California, Davis, California, USA
Lanini, W. T., and S. R. Radosevich. 1986 Response of three conifer species to site preparation and shrub control. Forest Science 32: 61–77
Larcher, W. 1975 Physiological plant ecology. Springer-Verlag, Berlin, Germany
Major, J. 1990 California climate in relation to vegetation. In M. G. Barbour and J. Major [eds.], Terrestrial vegetation of California, 11–74. California Native Plant Society, Sacramento, California, USA
Mellmann-Brown, S., and M. G. Barbour. 1995 Understory/overstory species pattern through a Sierra Nevada ecotone. Phytocoenologia 25: 89–106
Minnich, R. A. 1986 Snow levels and amounts in the mountains of southern California. Journal of Hydrology 86: 37–58[CrossRef]
Oren, R., and D. W. Sheriff. 1995 Water and nutrient acquisition by roots and canopies. In W. K. Smith and T. M. Hinckley [eds.], Resource physiology of conifers, 39–74. Academic Press, San Diego, California, USA
Pallardy, S. G., J. Cermák, F. W. Ewers, M. R. Kaufmann, W. C. Parker, and J. S. Sperry. 1995 Water transport dynamics in trees and stands. In W. K. Smith and T. M. Hinckley [eds.], Resource physiology of conifers, 301–390. Academic Press, San Diego, California, USA
Parker, A. J. 1994 Latitudinal gradients of coniferous tree species, vegetation, and climate in the Sierran–Cascade axis of northern California. Vegetatio 115: 145–155[ISI]
Parker, V. T., and M. P. Yoder-Williams. 1989 Reduction of survival and growth of young Pinus jeffreyi by an herbaceous perennial, Wyethia mollis. American Midland Naturalist 121: 105–111[CrossRef][ISI]
Radosevich, S. R. 1984 Interference between greenleaf manzanita (Arctostaphylos patula) and ponderosa pine (Pinus ponderosa). In M. L. Duryea and G. N. Brown [eds.], Seedling physiology and reforestation success, 259–270. Martinus Nijhoff/Dr. W. Junk, Dordrecht, The Netherlands
Randall, J. M., and M. Rejmánek. 1993 Interference of bull thistle (Cirsium vulgare) with growth of ponderosa pine (Pinus ponderosa) seedlings in a forest plantation. Canadian Journal of Forest Research 23: 1507–1513[CrossRef]
Rejmánek, M., and J. J. Messina. 1989 Quantification and prediction of woody weed competition in ponderosa pine plantations. In A. Tecle, W. W. Covington, and R. H. Hamre [eds.], Proceedings, Conference on multiresource management of ponderosa pine forests, Flagstaff, Arizona, 97–102. U.S. Forest Service, General Technical Report RM-185
Ritchie, G. A., and T. M. Hinckley. 1975 The pressure chamber as an instrument for ecological research. Advances in Ecological Research 9: 166–254
Royce, E. B. 1997 Xeric effects on the distribution of conifer species in a southern Sierra Nevada ecotone. Ph.D. dissertation, University of California, Davis, California, USA
———, and M. G. Barbour. 2001 Mediterranean climate effects. II. Conifer growth phenology across a Sierra Nevada ecotone. American Journal of Botany 88: 919–932
Running, S. W. 1976 Environmental control of leaf water conductance in conifers. Canadian Journal of Forest Research 6: 104–112
———. 1980 Environmental and physiological control of water flux through Pinus contorta. Canadian Journal of Forest Research 10: 82–91
SAS Institute. 1995 JMP user's guide and statistical and graphics guide, version 3.1. SAS Institute, Cary, North Carolina, USA
Shainsky, L. J., and S. R. Radosevich. 1986 Growth and water relations of Pinus ponderosa seedlings in competitive regimes with Arctyostaphylos patula seedlings. Journal of Applied Ecology 23: 957–966[CrossRef][ISI]
Tappeiner, J. C., II, and S. R. Radosevich. 1982 Effect of bearmat (Chamaebatia foliolosa) on soil moisture and ponderosa pine (Pinus ponderosa) growth. Weed Science 30: 98–101
Walter, H. 1984 Vegetation of the Earth. Springer-Verlag, Berlin, Germany
Waring, R. H., and B. D. Cleary. 1967 Plant moisture stress: evaluation by pressure bomb. Science 155: 1248–1254
White, D. E. 1985 Effects of whiteleaf manzanita on douglas fir and ponderosa pine: water use strategies and growth. In Proceedings, Seventh annual forest vegetation management conference, 86–90. Forest Vegetation Management Conferences, Eureka, California, USA
Whitehead, D., and P. G. Jarvis. 1981 Coniferous forests and plantations. In T. T. Kozlowski [ed.], Water deficits and plant growth, vol. VI, 49–152. Academic Press, New York, New York, USA
Ziemer, R. R. 1963 Summer evapotranspiration trends as related to time following logging of high elevation forest stands in Sierra Nevada. M.S. thesis, University of California, Berkeley, California, USA
———. 1964 Summer evapotranspiration trends as related to time after logging of forests in the Sierra Nevada. Journal of Geophysical Research 69: 615–620[CrossRef]
———. 1978 Logging effects on soil moisture losses. Ph.D. dissertation, Colorado State University, Fort Collins, Colorado, USA
Zwieniecki, M. A., and M. Newton. 1994 Root distribution of 12-year-old forests at rocky sites in southwestern Oregon: effects of rock physical properties. Canadian Journal of Forest Research 24: 1791[CrossRef]
———, and ———. 1996 Seasonal pattern of water depletion from soil–rock profiles in a Mediterranean climate in southwestern Oregon. Canadian Journal of Forest Research 26: 1346–1352[CrossRef]
This article has been cited by other articles:
|
|
 |
|
  E. B. Royce and M. G. Barbour Mediterranean climate effects. II. Conifer growth phenology across a Sierra Nevada ecotone Am. J. Botany, May 1, 2001; 88(5): 919 - 932. [Abstract] [Full Text] [PDF]
|
|
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
