Supplemental Information
Materials and methods
STUDY SITE AND SPECIES
The study was conducted at a woodland site on the lower slopes of the eastern side of the San
Bernardino Mountains, facing the Mojave Desert in Morongo Valley, California, USA
(34°02'12.0”N, 116°37'24.4”W). Desert chaparral forms a more open canopy than other types of
chaparral shrublands, yet individuals often obtain heights (1-3 m) similar to coastal specimens
(Hanes 1971). Dominant chaparral shrub species intermix with Joshua Tree woodland elements
such as Yucca spp., Opuntia spp., and Ephedra spp., as well as piñon-juniper woodland and
mixed evergreen forest elements such as Juniperus californica and Quercus cornelius-mulleri
(Hanes 1971; Minnich 1974; Thorne 1974; Hanes 1977; Baldwin et al. 2002). Additionally,
species such as Ziziphus parryi are endemic to this transitional vegetation type.
HYDRAULIC CONDUCTIVITY AND VULNERABILITY CURVES
Before and after each ‘flow’ measurement, a ‘background’ measurement with no hydraulic head
was recorded to correct for passive stem water uptake (Torres-Ruiz, Sperry & Fernandez 2012).
These two ‘background’ measurements were averaged and then subtracted from the pressuredriven flow to obtain the net flow rate.
Native PLC was measured by collecting stems concurrently with water potential
measurements. Stems were brought back to the lab (>4 hour trip, which allowed tensions in the
stem to “relax” (Wheeler et al. 2013) and cut to 14.2cm under water before measuring native
conductivity. Next stems were flushed, after which maximum conductivity was measured.
Native conductivity versus maximum conductivity allowed the calculation of PLC that
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corresponds to the water potential we measured in the field for that sample. Water potential vs.
PLC was used to verify our vulnerability curves.
References
Baldwin, B.G., Boyd, S., Ertter, B.J., Patterson, R.W., Rosatti, T.J. & Wilken, D.H. (2002) The
Jepson Desert Manual. pp. 624. University of California Press, Berkeley, CA.
Hanes, T.L. (1971) Succession after Fire in Chaparral of Southern California. Ecological
Monographs, 41, 27-52.
Hanes, T.L. (1977) California Chaparral. Terrestrial Vegetation of California (eds M.G. Barbour
& J. Major). Wiley Interscience, New York.
Minnich, R.A. (1974) Vegetation of the San Bernardino Mountains. Symposium Proceedings:
Plant Communities of Southern California (ed. J. Latting), pp. 99-124. California Native
Plant Society, Berkeley, CA.
Thorne, R.F. (1974) The Vascular Plant Communities of California. Symposium Proceedings:
Plant Communities of Southern California (ed. J. Latting), pp. 1-31. California Native
Plant Society, Berkeley, CA.
Torres-Ruiz, J.M., Sperry, J.S. & Fernandez, J.E. (2012) Improving xylem hydraulic
conductivity measurements by correcting the error caused by passive water uptake.
Physiologia Plantarum, 146, 129-135.
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Tables
Supp. Table 1. Phenological chart of 15 study species from a desert-chaparral ecotone in southern California during 2011. Black bars
represent periods with mature leaves, grey bars represent periods of no mature leaves for species with photosynthetic stems, and white
bars represent periods with no mature leaves for species without photosynthetic stems.
Species
A. salsola
E. actoni
E. californica
E. fasciculatum
E. linearifolia
J. californica
P. fasciculata
P. arborescens
P. tridentata
Q. cornelius-mulleri
R. ovata
S. mexicana
S. greggii
T. montana
Z. parryi
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
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Figures
Supp. Figure 1. Representative vulnerability curve replicate for each species. Black circle
symbols represent individual water potential (Ψ) versus percent loss of conductivity (PLC) data
points. Solid line represents the fitted Weibull function. Species code corresponds to Table 1.
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Supp. Figure 2. (a) Leaf area-to-sapwood area ratio (LA:SA), (b) specific leaf area (SLA), (c)
unlogged hydraulic conductivity (Kh), and (d) unlogged xylem water potential at 50% loss of
hydraulic conductivity (Ψ50) as a function of stem midday water potential (Ψstem) during the
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wettest month (March) for co-existing woody plant species from a desert-chaparral ecotone in
southern California. Data for 14 of the 15 study species is shown because S. greggii had no
leaves in March. Each symbol represents a species mean. Corresponding species and symbols are
found in Table 1. Logged plots are shown in Figure 2.
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Supp. Figure 3. (a) Unlogged stem sapwood-specific hydraulic conductivity (KS) and (b)
unlogged xylem water potential at 50% loss of hydraulic conductivity (Ψ50) as a function of leaf
area-to-sapwood area ratio (LA:SA) for 15 co-existing woody plant species from a desertchaparral ecotone in southern California. Each symbols represents a species mean.
Corresponding species and symbols are found in Table 1. Logged plots are shown in Figure 3.
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