The Role of Evolutionary History in Determining Vegetation Dynamics:
A Comparative Study of Mediterranean Ecosystems
in California and in Israel
Second year report
José M. Grünzweig1, Curtis H. Flather2, Ran Lotan1, Pat Regan3, Yohay Carmel1
1
The Lowdermilk Division of Agricultural Engineering,
Faculty of Civil and Environmental Engineering
Technion – Israel Institute of Technology
2
The Rocky Mountain Research Station,
Inventory and Monitoring Institute,
USDA Forest Service
3
Rana Creek Ranch,
Carmel Valley, California
January 2004
1. Introduction
1.1. Report period
This study was started in March 2002, and a First Year Report was issued in January
2003. The current report describes the major steps taken and first results obtained
during the last year from January to December 2003, and documents plans for future
steps of the experiment. For the scientific background of this study, see Appendix 1.
1.2. Summary of the first study year
The core of this study consists of a mutual transplant experiment, where oak species
from California and the eastern Mediterranean Basin are grown together both in
California and Israel to elucidate convergent or divergent evolutionary processes and
their physiological basis. During the first year of this study from March 2002 till
January 2003, study sites were selected in both countries, oak species were chosen,
and the experiments were planned, with the first steps being carried out.
The study sites are the Rana Creek Ranch Nursery in Carmel Valley, California and
the JNF Golany Nursery in northern Israel. Being situated in the Mediterranean-type
climatic zone, the two sites are similar in climate, with the Californian site having
lower mean annual temperature (13.8°C or 56.8°F) but similar mean annual
precipitation (534 mm or 21.4 in) compared to the Israeli site (20.0°C or 68°F, 497
mm or 19.9 in). The following five species were selected: Quercus agrifolia Née, a
Californian evergreen oak with tree stature; Q. douglasii Hook. & Arn., a Californian
deciduous oak with tree stature; Q. berberidifolia Liebm., a Californian evergreen
scrubby oak; Q. calliprinos Webb, an eastern Mediterranean evergreen oak with tree
or shrubby stature; Q. ithaburensis Decaisne, an eastern Mediterranean deciduous oak
with tree stature. Determination of ecological similarity between specific species in
both regions is based on a comparison of the species’ habitats in California (Barbour
& Major 1997) and in Israel (Zohary 1973), and on an earlier comparison conducted
by Naveh (1967). Acorns were collected from two to three sites per species between
late October and mid November 2002. Acorns were bulked and sent for disinfection
in Frances Crim Inspection Station, Linden, NJ.
2. Treatments and growing conditions
2.1. Post-disinfection treatments of acorns
Quarantine: Half of the disinfested acorns of each species were shipped to California
and the other half to Israel. Shipments were accompanied by phytosanitary
certificates. Upon arrival in Israel, the Californian acorns were taken to quarantine at
Beit Dagan station of the Plant Protection and Inspection Services of The Israeli
Ministry of Agriculture. A sample of 100 acorns of each species was tested for the
pathogens Pestalotia spp. and Phytophthora cinnamomi, which were not detected.
Stratification: There are differences between standard practices at the pre-germination
phase of oaks in California and Israel that might reflect possible differences in
physiology of species. Upon arrival to California, acorns of all species were stored at
5°C (41°F) for two weeks, while in Israel, acorns of all species were stored at room
temperature. However, acorns of Q. douglasii and Q. berberidifolia sent to Israel were
stratified during storage after collecting but before being sent to disinfection.
2.2. Sowing and growing conditions
Growing conditions were planned to be similar as much as possible at both sites.
Therefore, we shipped germination trays from Israel to California. The trays consisted
of 24 compartments, with 300 ml (18 in3) bedding per compartment. In California, the
substrate purchased from Sun Land Garden Products, Watsonville, CA was composed
of redwood, sand and quarried filter clay with a wetting agent and slow-release
fertilizer. In Israel, the substrate was purchased from Shacham, Givat Ada, Israel, and
consisted of peat, tuff (porous stone of volcanic origin) and Styrofoam with a wetting
agent and slow-release fertilizer. Acorns were sown in late December 2002 in
California and on January 2, 2003 in Israel.
Seedlings at both sites were grown in a shadehouse of approximately 50% shade. In
contrast to substrate and light conditions, water and nutrient availability were
extremely different between sites. In the Californian nursery, seedlings were grown
according to local standards of low irrigation frequency (once a week) and lack of
nutrient addition on top of slow-release fertilizer. Only in early September, seedlings
were transferred to a different site in the nursery to allow two irrigations per week. In
the Israeli nursery, seedlings received local standards of high irrigation frequency (20
L m-2 ground area day-1 or 4.3 gal yd-2 day-1) and fertilizer application (once or twice
a week liquid fertilizer 6-3-6 + microelements; Deshanit, Beer Yaacov, Israel). In
addition to low irrigation frequency, seedlings in the Californian nursery suffered
from a watering failure in July 2003 resulting in an irrigation-free period of 2 weeks.
2.3. Experimental design and measurements
Trays were grouped in blocks of four to eight trays in California and in blocks of two
to five trays in Israel. Trays were randomly assigned to blocks, and blocks were
randomly placed in the nursery.
Measurements for germination, survival and height were performed weekly during the
first 8 weeks after the onset of germination of most species (late February 2003), and
biweekly during the rest of the growing season. Measurements included all seedlings
on some dates, a randomly selected subset of seedlings on others. Physiological
measurements were conducted on one seedling per block and five blocks per species.
2.4. Personnel
Seedlings are being grown by the nursery managers Pat Regan in California and
Hiroy Amara in Israel. Supervision, monitoring and regular morphological
measurements are being conducted by Pat Regan in California and Ran Lotan in
Israel. Because of high work load of Pat Regan in the commercial nursery data
collecting and processing is slow, and thus a substitute for these tasks needs to be
found. No such problems exist in Israel. To improve coordination of the entire study,
José Grünzweig was hired in October 2003. He will synchronize future activities
between California and Israel, and will conduct physiological measurements at both
sites.
3. First results
3.1. Germination and survival
Germination time and rate: Germination in Israel started 4 weeks after sowing in Q.
ithaburensis, 9 weeks after sowing in the Californian species and 10 weeks after
sowing in Q. calliprinos. Eighty percent of the seedlings of all species germinated
within 6 weeks. Mean number of days to germination was about 60 days in Q.
ithaburensis and 85 to 100 in the other species (Table 1). Germination rate was
generally low in the Californian species, with 50% germination in Q. douglasii and
less than 20% in Q. berberidifolia, and was extremely low in the Israeli species (<4%;
Table 1). Acorns of Q. agrifolia and Q. douglasii that were collected at the same sites
in California for commercial use and were not disinfected germinated at much higher
rates than the experimental seed material in the Californian nursery. Similarly, acorns
of Q. calliprinos and Q. ithaburensis sown for common afforestation purposes in the
Israeli nursery germinated at high rates. It seems therefore that disinfection had a
negative impact on germination of seeds from all species. In addition, unfavorable
storage conditions during quarantine in Israel appeared to have severly damaged the
acorns of Q. calliprinos and Q. ithaburensis. As a consequence of the very low
germination success of the eastern Mediterranean species in Israel, seedlings that were
grown for afforestation purposes in the same nursery were used as a replacement.
However, since those seeds did not undergo disinfection, shipment and quarantine, the
few original seedlings, particularly those of Q. ithaburensis, served as a control in
most measurements (see below).
Survival rate: Survival rate was high at around 90% in all species (Table 2), and
seedling death was caused by drought (California), disease and herbivory (insects,
jays, mice).
3.2. Seedling growth
Q. ithaburensis not only germinated first, but also showed highest growth rate among
all species, particularly during the first months after germination (Figure 1). The other
four species had similar growth rates during those first months, but while the other
species seem to have slowed down during summer 2003, Q. agrifolia continued
height accumulation at a similar rate until fall, thus reaching a final height similar to
that of Q. ithaburensis. The replacement for Q. ithaburensis seedlings showed equal
growth patterns to the original ones (open and closed circles in Figure 1). However,
the replacement for Q. calliprinos (open squares) grew considerably better than the
original ones (closed squares), suggesting that the eight germinated seeds out of
almost 600 that were sown were damaged to some degree and had low vigor.
Consequently, seedling height after the first growing season was about 40 cm (16 in)
for Q. agrifolia, Q. calliprinos and Q. ithaburensis, and about 20 cm (8 in) for Q.
douglasii and Q. calliprinos.
As a consequence of the difference in growing conditions between nurseries,
particularly differences in irrigation frequencies and fertilizer applications, seedlings
reached considerably greater height in Israel compared to California (Table 2).
Seedlings of most species were 2-3 times higher in Israel than in California, seedlings
of Q. calliprinos were almost 5 times higher in Israel. Despite the dry conditions in
the Californian nursery, seedlings that survived the drought did not show greater
drought damage than in Israel, except for Q. douglasii which had considerably larger
leaf loss in California (Table 2). Q. ithaburensis, the other deciduous species, lost
about 25% of its leaves at both sites. Although deciduous species show greater
drought damage than evergreen species, seedling height was largest in the deciduous
Q. ithaburensis in California and in Q. ithaburensis and the evergreen Q. agrifolia in
Israel.
3.3. Seedling physiology
Leaf gas exchange was measured at both sites for all species, except for Q.
berberidifolia because of small leaf size and difficulties in accessibility of leaves by
the measuring chamber. We used Q. calliprinos and Q. ithaburensis seedlings of the
replacement set in Israel, and compared performance of original and replacement
seedlings of Q. ithaburensis. Gas exchange was measured with a portable
photosynthesis system (LI-6400, LI-COR, Lincoln, NE) during morning (8:00-10:30)
and midday hours (12:00-14:30). Measurements were carried out in California on two
days in mid September and in Israel on one day in early July and one day in mid
September. Climatic conditions were generally similar between the two days of
measurement at both sites (Table 3). However, there were some differences between
California and Israel, with lower temperatures and higher afternoon vapor pressure
deficit in California. The particularly low morning temperatures in California were
caused by shading of seedlings by a large tree during most of the morning hours. Leaf
gas exchange was measured at ambient conditions, except for photosynthetically
active photon flux density that was kept constant at 1200 μmol m-2 s-1 with artificial
light.
Photosynthesis was higher in morning hours than at midday in Q. agrifolia at both
sites and in the other three species only in Israel (Figure 2). The lack of response to
the more stressful midday conditions in Q. douglasii, Q. calliprinos and Q.
ithaburensis in California might be related to adaptation of these species to the dry
conditions induced by low irrigation frequency in the Californian nursery. Highest
photosynthetic rates were measured for Q. douglasii (average 8.7 μmol m-2 s-1 over
both days and time of measurement) in California and Q. calliprinos (7.7 μmol m-2
s-1) and Q. ithaburensis (8.1 μmol m-2 s-1) in Israel. Interestingly, a Californian
species performed best in California, while the two eastern Mediterranean species
performed best in Israel. Leaf-diffusive (stomatal) conductance is a measure for
stomata aperture and potential water loss. Conductance was highest in all species at
the September measurement in Israel, and decreased from morning to midday in all
species and at all sites, except for Q. douglasii and Q. calliprinos in California (Figure
3). Transpiration, the actual water loss, was highest in all species at the September
measurement in Israel, and was also high in Q. douglasii at the midday measurements
in California (Figure 4). The original seedlings of Q. ithaburensis showed
photosythetic rates, stomatal conductances and transpiration rates almost identical to
seedlings of the replacement set.
Plotting photosynthesis against stomatal conductance produces a measure for intrinsic
water-use efficiency (WUE), i.e. carbon assimulation per potential water loss which is
supposed to be independent of environmental conditions. Intrinsic WUE was
relatively high in the two eastern Mediterranean species and considerably lower in the
Californian Q. agrifolia (Figure 5). Moreover, the photosynthesis/conductance
relationship for the eastern Mediterranean species fitted one line, irrespective of
where and when the measurements were taken, whereas this relationship was much
less evident or inexistent for the Californian species. This indicates a better internal
regulation of photosynthetic and hydrological processes in the eastern Mediterranean
compared to the Californian species. Plotting photosynthesis against transpiration is a
measure for actual or instantaneous WUE, i.e. carbon assimilation per water actually
lost. This measure is dependent on plant mechanisms for water regulation
(conductance) and on the environmental conditions during the measurement. It is
therefore a less stable parameter in a varying environment. Consequently, the
photosynthesis/transpiration relationship in the eastern Mediterranean species could
be described by a regression line of lower significance than that for intrinsic WUE,
and was not significant at all in the Californian species (Figure 6). This means that
carbon assimilation per water lost in the latter is subjected to large variation in
changing environments, while in the former, WUE varies less because of better
internal regulation.
In September, five seedlings per species (three seedlings of Q. berberidifolia) were
harvested for carbohydrate, nutrient and stable isotope analyses (see Table 2). Those
analyses are under way at present.
4. Future plans
4.1. Transplantation
During the first half of February, the 200 most vigorous seedlings of each species will
be transplanted to 15-liter bags containing the same potting mixture as in the
germination trays. Bags will be shipped from Israel to California as has been done
with the trays a year earlier, so that seedlings at both sites will be transferred into the
same volume. In contrary to earlier plans, we decided to postpone the transplantation
until the end of the inactive winter season. We also decided against use of local soil as
a substrate because of unknown response of the exotic species. For example,
Californian species in Israeli soil would have been subjected to high pH and an exotic
microflora, both potentially resulting in poor seedling performance. Moreover,
gardening substrate could result in better plant performance than native soil. The
small seedlings in California need to grow substantially to reach enough height for the
planned treatments. The seedlings will be organized in the shade house in randomized
blocks.
4.2. Measurements
Seedlings will be monitored for height growth and branching every two months
during winter and once every month during the growing season. Measurements of leaf
gas exchange and leaf water relations will be conducted once during the growing
season in California and three times during the growing season in Israel. Immediately
prior to treatments, several plants will be harvested for destructive analyses of
biomass, biomass partitioning, carbohydrates, nutrients and stable isotopes.
4.3. Treatments
In late summer or fall 2004, seedlings will be subjected to various treatments. Thirty
replication are planned per each treatment and each species:

Simulated heavy grazing: 90% of the limbs will be pruned.

Simulated moderate grazing: 50% of the limbs will be pruned.

Simulated fire: the boughs of the saplings will be burned with a burner (fire
temperature can be monitored with termocoupels).

Control: no treatment.
4.4. Regeneration
Following treatments regeneration will be monitored every two weeks, and later in
longer intervals according to regeneration time of the saplings. Five indices will be
recorded:

Stem diameter at the base of the stem.

Sapling height.

Cumulative stem + branches length (approximated biomass, Teper 1997).

Height of regenerating buds.

Area / width of representative leaf (10 replications per sapling).
5. Appendix 1: Scientific background
An underlying assumption of many global change models (e.g., Prentice et al. 1992)
is that structural and functional attributes of ecosystems have similar environmental
controls, in climatically similar regions. This assumption, based on the concept of
ecological convergence, implies that it is possible to predict ecosystem attributes for a
region using relationships between ecosystem attributes and environmental variables
developed for geographically and evolutionarily unrelated regions. This concept has
important applied significance for evaluating large-scale ecosystem processes in areas
of the world where data availability is limiting. If this hypothesis is proved (i.e.
convergence exits), we may confidently apply global change simulations to such areas
using ecological parameters derived from other, similar ecosystems for which
extensive data exist. An alternative hypothesis is that the unique evolutionary history
of each specific region largely affects traits of its current ecosystems. Under this latter
hypothesis, it is expected that while ecological convergence may be apparent for some
traits (presumably those that are primarily affected by climate, such as plant
physiognomy), ecological divergence would be found for other traits (those that are
likely to be affected by evolutionary history, such as plant response to disturbance).
Convergence in ecosystem structural traits (e.g., species richness, distribution of plant
functional types, plant physiognomy etc.) has been documented for several biomes
(e.g., Orians & Solbrig 1977; Mooney 1977; Mares et al. 1985; Armesto et al. 1995).
A recent study (Paruelo et al. 1998) has shown convergence not only in ecosystem
structure (distribution of C3 and C4 grasses and shrubs), but also in important
ecosystem functional traits (primary production and soil organic carbon) between
grasslands in North America and South America.
Vegetation dynamics is an important component of dynamic models of global change
(Neilson 1995; Peng 2000) and yet, very few studies have addressed the question of
ecological convergence in vegetation dynamics. Currently, there are at least two
indications that ecological convergence is not prevailing when it comes to ecosystem
dynamics. The first one is a study of the response of grasslands to grazing in
ecosystems worldwide (Milchunas & Lauenroth 1993). Analyzing studies of grazing
effects, they concluded that grasslands in regions with a long history of intensive
grazing (e.g., Southern Europe) are more resilient than grasslands in regions with a
short history of livestock grazing (e.g., North America). The second indication stems
from our recent comparative study of vegetation changes in California and in Israel
(Carmel & Kadmon 1999, Carmel, Flather and Dean in preparation). We found a
major dissimilarity between response of vegetation in California and in Israel to
disturbance. This dissimilarity may be attributed to various factors, including
differences in evolutionary history of the respective ecosystems. If ecosystem
dynamics is indeed dependent on its evolutionary history, than some premises of
global change simulations may be unrealistic. This research examines experimentally
the existence of ecological convergence in vegetation dynamics.
Mediterranean-type ecosystems are the most commonly used systems for comparative
studies of ecological convergence (Naveh 1967; Aschmann 1973; Zinke 1973;
Kummerow 1973; Cody & Mooney 1978; Specht & Moll 1983; Miller 1983;
Hustinger et al. 1991; Armesto et al. 1995). Several studies compared specifically the
Mediterranean ecosystems of California and Israel (Naveh 1967, Naveh and
Whittaker 1979, Shmida 1981, Barbour and Minnich 1990). These two systems share
similar general climatic patterns (although some important differences exit, Naveh
1967) as well as general physiographic features (e.g. Shmida 1981). The dominant
trees in Mediterranean type ecosystems of both California and Israel are deciduous
and evergreen oak species (Quercus spp).
One of the goals of our previous study (Carmel and Kadmon 1999, Carmel, Kadmon
and Nirel In Press, Carmel, Flather and Dean In Preparation) was to assess if
convergent evolution, shown previously for vegetation structure, exits also for
vegetation dynamics. The two sites that were chosen for the study share a similar
history of land use changes in recent decades (abandonment of agricultural practices
and removal of livestock some fifty to sixty years ago), in addition to similarities in
topography and climate. Landscape scale vegetation changes over a period of several
decades were analyzed in relation to environmental factors in both systems, using
historical aerial photographs. Results of this study showed that cover of both
deciduous and evergreen trees in Hastings Nature Reserve, California, changed very
little during 60 years, in comparison to changes in tree cover on Mt. Meron, Israel.
We then analyzed results from previous landscape scale studies of vegetation
dynamics in California (Callaway and Davis 1993, Plant et al. 1999, Brooks and
Merenlender In Press) and in Israel (Samocha et al. 1980, Kadmon and Harari-Kremer
1999) and other Mediterranean basin countries (Debussche et al. 1999, Preiss et al.
1997). We found that re-colonization by trees of lands where woody vegetation cover
had been removed (e.g., agricultural land, logging, or fire) was much slower than was
observed in the Mediterranean basin. These fast changes in the Mediterranean basin
seem to involve mostly vegetative regeneration.
There are at least two possible explanations for this contrast between landscape-scale
dynamics in the two regions.
(1) Lower recruitment in California caused by local environmental factors. A lack of
recruitment in many parts of California has been long noticed for several species (e.g.
Standiford et al. 1997). A number of factors, such as cattle grazing, invasion of exotic
annual grasses, and increased deer and gopher populations, have been suggested as
possible explanations to this phenomena (e.g. Muick and Bartolome 1987, Borchert et
al. 1989, Hall et al. 1992, Gordon and Rice 1993, Standiford et al. 1997, Swiecki et al.
1997). Taking this argument further, it may be claimed that local unfavorable
conditions in California are responsible for the difference between the two regions. A
variant of this explanation (1b) argues that lower soil quality in California depresses
regeneration capacity. Naveh (1967) writes: ‘Most non-cultivated soils within the
California province are coarse structured non-calcic, Brown Upland soils and
lithosols, inferior in fertility and water-holding capacity… [compared with the typical
calcareous soils of the Mediterranean region in Israel]’ (Naveh 1967). Conversely,
soils in the Mediterranean basin are typically derived from limestone, dolomite and
other calcareous rocks (Yaalon 1997), which are uncommon in California.
(2) Differences in evolutionary history have lead to the development of different
strategies for responding to disturbance. The long history of intense human impact in
the Mediterranean Basin (Naveh and Dan 1973, Le Houerou 1981) induced strong
selective pressures for persisting under heavy grazing and logging regime.
Presumably, Mediterranean basin vegetation was selected for strong regeneration
capabilities, which are expressed when released from periods of heavy grazing and
logging. Californian ecosystems have not experienced any intense human impact until
some 150 years ago (Axelrod 1977). Presumably, Californian trees never faced
selective pressures to adapt to intense grazing and logging, and are thus not as capable
of responding to such disturbances. It should be noted that fire was an important
factor in both California and the Mediterranean basin for at least 10,000 years (Fox
and Fox 1986, Naveh 1994), although the nature, intensity and return intervals were
probably different.
These hypotheses are not exclusive. Local ecological conditions and soils are likely to
affect vegetation regeneration. The important question here is – does evolutionary
history have a net contribution in shaping species’ regeneration strategies, and
vegetation recovery potential at the landscape level. An experiment that may
validate/reject each of these hypotheses will be of interest from a theoretical point of
view – it will address the question of the relative importance of evolutionary history
in determining ecosystem properties. Furthermore, it will be very relevant to current
management and restoration efforts of oak woodlands in both countries, since it is
expected that an understanding of the underlying causes of vegetation dynamics in
these ecosystems may be gained. For example, if hypothesis (2) is correct, i.e. the
slow regeneration in California’s woodlands is largely a result of genetic traits related
to a specific evolutionary history, then these ecosystems are much more fragile and
endangered than currently conceived. If this is indeed the case, then research effort
and management programs for these ecosystems should be re-thought, and new
directions should gain priority. An example of such directions may be a plan of statewide network of refuges, in which active management (planting, pruning, deer- and
gopher exclusion) will ensure the continuation of these ecosystems. On the other
hand, if hypotheses (1b) and (2) are not supported by such an experiment, then it may
be concluded that some combination of local environmental conditions is responsible
for the observed slow dynamics California. In this case, it is suggested that further
research effort should be directed towards identifying the specific factors affecting
seedling regeneration and sapling recruitment in California woodlands.
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Table 1.Germination and survival rates of oak species in Israel.
Species
Origin of
species
Life form
Q. agrifolia
Q.berberidifolia
Q. douglasii
Q. calliprinos
Q. ithaburensis
California
California
California
Israel
Israel
evergreen
evergreen
deciduous
evergreen
deciduous
Germination Survival
rate (%)
rate (%)
39.5
17.8
50.0
1.4
3.4
95.5
89.8
95.8
87.5
92.9
Mean no.
of days to
germination
85
89
84
98
57
Table 2. Seedling height and drought damage at sampling date in September 2003.
Site
Origin of
species
Life form
Seedling
height
(cm)
Leaf death
from drought
(% of all
foliage)a
California Q. agrifolia
Q.berberidifolia
Q. douglasii
Q. calliprinos
Q. ithaburensis
California
California
California
Israel
Israel
evergreen
evergreen
deciduous
evergreen
deciduous
14.2 (1.4)
8.7 (0.7)
7.8 (1.2)
7.5 (0.8)
21.5 (2.1)
0.0 (0.0)
3.0 (2.0)
32.0 (6.6)
4.0 (4.0)
26.0 (9.3)
Israel
California
California
California
Israel
Israel
evergreen
evergreen
deciduous
evergreen
deciduous
41.6 (7.3)
19.0 (5.0)
17.7 (1.8)
36.4 (3.7)
41.4 (7.8)
9.0 (5.6)
0.0 (0.0)
7.0 (2.0)
1.0 (1.0)
25.0 (9.2)
a
Species
Q. agrifolia
Q.berberidifolia
Q. douglasii
Q. calliprinos
Q. ithaburensis
Visual estimates
Table 3. Climatic conditions during leaf gas exchange measurements
(VPDL = leaf vapor pressure deficit).
Site
Date
California September 18
September 19
Israel
July 1
September 11
Time during
the day
Air
temperature
(°C)
VPDL
(kPa)
Morning
Midday
Morning
Midday
26.0
36.4
24.2
36.9
2.9
5.3
2.2
5.3
Morning
Midday
Morning
Midday
34.8
40.1
36.1
39.4
2.6
4.2
2.8
4.1
50
Q. agr.
Height (cm)
40
Q. ber.
Q. dou
Q. cal.
30
Q. ith.
20
10
0
Feb-03
Apr-03
Jun-03
Aug-03
Oct-03
Dec-03
Date
Figure 1. Growth of oak seedlings in the Israeli nursery. Open symbols represent
seedlings of Q. calliprinos (open squares) and Q. ithaburensis (open circles) that
replace the original ones because of low germination rate (see text).
Net photosynthesis (µmol m-2 s-1)
16
morning
14
midday
12
10
8
6
4
2
0
01Jul
11Sep
Israel
18Sep
19Sep
California
Q. agrifolia
01Jul
11Sep
Israel
18Sep
19Sep
California
Q. calliprinos
01Jul
11Sep
Israel
18Sep
19Sep
California
Q. douglasii
01Jul
11Sep
Israel
18Sep
19Sep
California
Q. ithaburensis
Figure 2. Photosynthesis in four oak species in California and Israel during two days
in summer 2003. Mean ± s.e. Black dots indicate mean photosynthetic rates measured
for three Q.ithaburensis seedlings grown from the original seeds.
Leaf-diffusive conductance (mol m-2 s-1)
0.5
morning
midday
0.4
0.3
0.2
0.1
0
01Jul
11Sep
Israel
18Sep
19Sep
California
Q. agrifolia
01Jul
11Sep
Israel
18Sep
19Sep
California
Q. calliprinos
01Jul
11Sep
Israel
18Sep
19Sep
California
Q. douglasii
01Jul
11Sep
Israel
18Sep
19Sep
California
Q. ithaburensis
Figure 3. Leaf-diffusive (stomatal) conductance in four oak species in California and
Israel during two days in summer 2003. Mean ± s.e. Black dots indicate mean
photosynthetic rates measured for three Q.ithaburensis seedlings grown from the
original seeds.
10
Transpiration (mmol m-2 s-1)
morning
midday
8
6
4
2
0
01Jul
11Sep
Israel
18Sep
19Sep
California
Q. agrifolia
01Jul
11Sep
Israel
18Sep
19Sep
California
Q. calliprinos
01Jul
11Sep
Israel
18Sep
19Sep
California
Q. douglasii
01Jul
11Sep
Israel
18Sep
19Sep
California
Q. ithaburensis
Figure 4. Transpiration in four oak species in California and Israel during two days in
summer 2003. Mean ± s.e. Black dots indicate mean photosynthetic rates measured
for three Q.ithaburensis seedlings grown from the original seeds.
Net photosynthesis (µmol m-2 s-1)
14
R2 = 0.83
Q. agr.
12
Q. cal.
R2 = 0.94
Q. dou.
10
Q. ith.
8
6
R2 = 0.56
4
2
0
0
0.1
0.2
0.3
0.4
Leaf-diffusive conductance (mol m-2 s-1)
Figure 5. Relationship between net photosynthesis and leaf-diffusive conductance in
Californian (open symbols) and eastern Mediterranean species (closed symbols). Data
points are means for each time of measurement (morning, midday), date and site.
Curvilinear lines represent logarithmic regressions across all data points of Q.
agrifolia (dashed-dotted line), Q. calliprinos (full line) and Q. ithaburensis (dotted
line). The regression for Q. douglasii was not statistically significant.
Net photosynthesis (µmol m-2 s-1)
14
Q. agr.
12
Q. cal.
R2 = 0.68
Q. dou.
10
Q. ith.
R2 = 0.57
8
6
4
2
0
0
2
4
6
8
10
Transpiration (mmol m-2 s-1)
Figure 6. Relationship between net photosynthesis and transpiration in Californian
(open symbols) and eastern Mediterranean species (closed symbols). Data points are
means for each time of measurement (morning, midday), date and site. Curvilinear
lines represent logarithmic regressions across all data points of Q. calliprinos (full
line) and Q. ithaburensis (dotted line). Regressions for Q. agrifolia and Q. douglasii
were not statistically significant.