Supplemental Information s11

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 pressure- driven 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

1 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.

2 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 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec A. salsola E. actoni E. californ ica E. fascicul atum E. linearif olia J. californ ica P. fascicul ata P. arbores cens P. tridenta

3 ta Q. corneli us- mulleri R. ovata S. mexica na S. greggii T. montan a Z. parryi

4 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.

5 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

6 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.

7 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 desert- chaparral 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.