International conference of the Israeli Society of Ecology and Environmental Sciences. Jerusalem, 1999 ROCK AND SOIL SYSTEM AS THE MAJOR ECOLOGICAL FACTOR AFFECTING THE WATER REGIME IN QUERCUS ITHABURENSIS FOREST IN ALONIM-SHFAR’AM REGION N. Herr *, A. Singer *, J. Riov **, E. Sass *** * Department of Soil and Water, The Hebrew University of Jerusalem, 76100 Rehovot, Israel. ** Department of Horticulture, The Hebrew University of Jerusalem, 76100 Rehovot, Israel. *** Institute of Earth Sciences, The Hebrew University of Jerusalem, 91904 Jerusalem, Israel. ABSTRACT Quercus ithaburensis forest in Alonim-Shfar’am region (Lower Galilee, Israel) exists only on specific sites. The structure of the sub-soil in the forested sites consists of chalky rock covered with Nari, brown shallow Rendzina, and soil pockets up to 1.5 meter deep which interrupt the Nari layer. The tree root-system is composed of a dense root mat located at the bottom of the shallow soil layer and deeper root system concentrations that are located in soil pockets. In the adjacent limestone and Terra Rossa area, where the forest doesn’t grow, there are no significant soil pockets and the soil lies above cracked rock. The main factor responsible for the difference between the two soil-rock systems is their different water regimes, due to the structure of the soil layer, the presence of soil pockets and the hydraulic characteristics of the subsoil rock. Differences in nutrient availability are the result of the different water regime in both habitats. Improved water economy as the main factor and improved nutrient supply as a secondary factor, lead to improved conditions which enable growth of trees in the chalk habitat that is covered with Nari and Rendzina soil with its soil pockets. KEWORDS
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International conference of the Israeli Society of Ecology and Environmental
Sciences. Jerusalem, 1999
ROCK AND SOIL SYSTEM AS THE MAJOR ECOLOGICAL
FACTOR AFFECTING THE WATER REGIME IN QUERCUS
ITHABURENSIS FOREST IN ALONIM-SHFAR’AM REGION
N. Herr *, A. Singer *, J. Riov **, E. Sass ***
*Department of Soil and Water, The Hebrew University of Jerusalem,
76100 Rehovot, Israel.
**Department of Horticulture, The Hebrew University of Jerusalem, 76100
Rehovot, Israel.
***Institute of Earth Sciences, The Hebrew University of Jerusalem, 91904
Jerusalem, Israel.
ABSTRACT
Quercus ithaburensis forest in Alonim-Shfar’am region (Lower Galilee, Israel) exists
only on specific sites. The structure of the sub-soil in the forested sites consists of
chalky rock covered with Nari, brown shallow Rendzina, and soil pockets up to 1.5
meter deep which interrupt the Nari layer. The tree root-system is composed of a
dense root mat located at the bottom of the shallow soil layer and deeper root system
concentrations that are located in soil pockets. In the adjacent limestone and Terra
Rossa area, where the forest doesn’t grow, there are no significant soil pockets and
the soil lies above cracked rock.
The main factor responsible for the difference between the two soil-rock systems is
their different water regimes, due to the structure of the soil layer, the presence of soil
pockets and the hydraulic characteristics of the subsoil rock. Differences in nutrient
availability are the result of the different water regime in both habitats. Improved
water economy as the main factor and improved nutrient supply as a secondary
factor, lead to improved conditions which enable growth of trees in the chalk habitat
that is covered with Nari and Rendzina soil with its soil pockets.
KEWORDS
Brown rendzina; chalk; Quercus ithaburensis; soil moisture; soil pockets;
water regime
INTRODUCTION
In the Alonim-Shefar’am region of the Lower Galilee of Israel, the Quercus ithaburensis
forest thrives only in limited areas. The climate and the topographic conditions seem to
be quite similar throughout the region, and preliminary observations suggested that
factors related to soil and rock could be the reason for this phenomenon. The forest exists
on a chalky rock that is covered by Nari hardpan and Rendzina soil, and is absent on
limestone and associated Terra Rossa soil. The objective of this work was to examine in
detail the hypothesis that soil and rock are responsible for the limited distribution of Q.
ithaburensis in this region.
Q. ithaburensis in Israel occurs discontinuously in specific regions from the Golan Hights in
the north to the Sharon Plain in the center of the country. This species probably reached
Israel about 10,000 years ago, after the last Ice period, from south Turkey (Zohari, 1973;
Stiller et al., 1984; Bar-Matthews et al., 1998). Its distribution in the past was broader than
today. Cutting, grazing and temporary utilization of the land for cultivation of olives and
vineyards probably affected the distribution of Q. ithaburensis. It seems that the forest
(especially in the research region) regenerated again in the same boundaries after each
disturbance of the natural situation. This is due to good regeneration by stump sprouts as
well as regeneration from seed in the same suitable niches. Most of the forest in the region
was cut during World War I, regenerated (Eig, 1933), partly cut during World War II, and
regenerated in the same boundaries.
METHODS
The research region
Alonim-Shefar’am is a region of moderate hills up to 250 m above sea level. The geological
base consists of chalky rocks of the Maresha formation (middle Eocene) in the west, changing to
the west by interfingering with limestone of Timrat formation (Greenberg, 1963; Sneh, 1988).
The chalk is covered by Nari calcrete hardpan (Greenberg, 1963; Yaalon & Singer, 1974; Wieder
et al, 1994) and brown Rendzina soil, while the limestone is covered with Terra Rossa soil
(Singer, 1969).
On the chalk that is homogenous in the west, natural vegetation consists of a maquis, while on the heterogeneous chalk in the transition zone grows a park-forest of Q. ithaburensis (without any accompanying species of trees and shrubs). On the limestone landscape there are no trees at al. In this research the park-forest is compared to the bare area.
Methods of research
A comparative mapping of rock, soil and vegetation was carried out by projecting the tree area from areal photographs on topographic map, and the forest distribution was analyzed using topographic, geologic and pedologic data by GIS. Sub-soil structure and location of
roots in relation to this structure were examined in hundreds of field sections. Moisture regime in the Rendzina and Terra Rossa soil was measured continuously for 3 years using gypsum soil moisture sensors and data loggers. There were two measurement stations in each of the two soil systems studied, one on a hill top and the other on the southern slope. In each station there were 5 sensors at a depth of 20 cm. The soil moisture data complemented by periodical gravimetric measurements at 10 sites in the research region. Gravimetric soil water content in soil pockets was measured at the end of the summer. Soil temperature was measured near each of the soil moisture sensors in the same system. Air temperature, humidity and precipitation were measured in the same stations. Other aspects that were examined included soil and rock characteristics, chemical composition of the soil and soil solution, tree water tension in trees, transpiration and stomatal conductance.
RESULTS AND DISCUSSION
Forest distribution has been found to be largely dependent on the rock and soil
characteristics. The topographic effect is minor and is in evidence only by the fact that in
the northern aspect the percentage of the tree coverage increases with increase in slope
up to an optimal degree, but the average percentage of coverage in the northern aspect is
not higher than that in the other slopes, and the forest borders cross various aspects and
slopes.
The structure of the sub-soil in the forest sites consists of chalky rock covered with Nari,
brown or red-brown shallow Rendzina, and soil pockets up to 1.5 meter deep which
interrupt the Nari layer. The tree root-system is composed of a dense root mat located at the
bottom of the shallow soil layer and a deeper root system which is concentrated in soil
pockets. Each tree occupies at least one soil pocket. In the limestone and Terra Rossa areas,
where the forest does not grow, there are no significant soil pockets but the soil is somewhat
deeper and lies above cracked rock. The soil-rock system varies greatly due to rock
variations that were caused by the original sedimentation process and subsequent sliding,
bending of layers and many faults. The rock variation leads to variations in the Nari
structure and development of soil pockets. As a consequence, the root environment may
differ considerably from one tree to another.
Water regime in the shallow soil. There were notable differences between the desiccation
processes of the Terra Rossa and Rendzina soils during spring and summer (Fig. 1). The
desiccation process in Terra Rosa was enhanced by events of hot and dry weather. The
effect of spring showers on delaying the drying of this soil was short and limited. Terra
Rossa usually reached complete dryness (a situation close to “air dryness”) by the end of
August. In Rendzina, soils, in contrast, the desiccation rate was more moderate. The
effect of spring showers in slowing down the drying process was more noticeable and
lasted longer after each rain, while the effect of hot and dry weather was less pronounced
compared with the Terra Rossa. Soil moisture persisted in Rendzina until the end of the
summer and was observed at depths of 20 cm with tensions of about 20-40 bar. At this
tension, tree roots are able to survive.
Moisture levels in soil pockets were high (tension of 1-4 bar), mainly at the bottom of the
pockets, in cracks inside the walls and under large stones. This situation allows the tree
to continue water uptake during the whole summer. In response to the first fall showers,
the Rendzina soils become wet more quickly and fully, and stayed wet longer than Terra
Rossa. Therefore, the dry period of the upper soil layer ends earlier.
The reasons for the quicker and more thorough wetting of the Rendzina, and
subsequently, its saturation over longer periods of time compared with Terra Rossa are:
Relatively large Nari areas on the surface, which extend into the shallow
subsoil, lead to formation of runoff water even after light rains, that allow the
wetting of the root environment at the bottom of this layer. Continued downward
penetration of water is probably limited by the laminar crust of the Nari hardpan.
The chalky rock and the Nari hardpan maintain a high level of water saturation
during the whole summer due to their high water holding capacity. The high
effective saturation of the chalk and the Nari, their low water tension and
moderate hydraulic conductivity permit water to move from the rock to the drying
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Average soil temperature
Terra Rossa 1: top of the hill
Rendzina 1: top of the hill
Terra Rossa 2: southern slope
Rendzina 2: southern slope
Hourly rain (mm)
Terra rossa 2
Terra rossa 1
Rendzina 1
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S o i l t e m p r e t u r e
Spring rain Outomn-winter rain
Soil water content, soil temperature and precipitation
in Terra Rossa on limestone and Rendzina on chalk with Nari
measured continuously from spring to winter, 1995
Fig. 1 :
Date, 1995 . The points are every hour
soil, and thus retard the process of drying of the shallow soil and allow to maintain
high levels of moisture in the soil pockets (Fig. 2). Thus the soil pockets function
as a “plant-pot” that is almost saturated with water.
Fig 2: Water flow in the rock-soil-tree system. Calculated by using data of soil and rock moisture
measurements, retention curves of soil and rock hydraulic conductivity. Transpiration rate and water
tension in leaf measured directly. The main water storage and main water flow is coming from the
chalk under the soil pocket.
In contrast, the Terra Rossa has no continuous rock exposure next to the
surface, and the subsoil rock is cracked and dense. Soil pockets do not exist and
the limestone does not absorb moisture.
The Rendzina has a higher water holding capacity than Terra Rossa.
Tree responses to the soil water regime. Soil moisture, water availability in the soils at
different sites, and tree responses are all related. In a habitat where soil moisture is high, the
water tension in the leaves will be lower and stomatal conductance, growth parameters,
acorn formation and the timing of leaf shedding are indicative of a better situation. When
soil moisture is low, the tree water tension rises and tree activity decreases to a minimum. In
general, due to dry soil conditions, the stomata closing mechanism is activated in order to
regulate the water tension in the trees during the day and during the season (Tenhunen et al.,
1987; Davies and Zhang, 1992). Transpiration rate decreases with the advancement of the
summer, and is compatible with water movement from the rock to the soil pockets.
Nutrient availability – a secondary factor. The type of moisture regime of the soil-rock
system leads to differences in mineral availability in the different soils. During winter the
chalky rock is saturated with water and therefore aeration conditions in the soil pockets
and the Rendzina are impaired. The nitrification process of the decomposable organic
matter slows down, and because of the limited leaching in this system, the accumulated
ammonium is not removed. In spring, when temperatures rise and the aeration conditions
improve, the nitrification process is more complete, and the concentration of available
nitrogen rises. The ratio ammonium/nitrate, that is high in winter, and high levels of
nitrogen in spring, make the Rendzina habitat superior. In contrast, in the drying Terra
Rossa, it can be assumed that the mobility of potassium and phosphorus decreases, and
therefore absorption of these elements decreases toward the end of summer (as it found
in the leaf chemical composition of seedlings). The drying up process apparently
damages the selective uptake of the roots and leads to uncontrolled uptake of damaging
elements.
CONCLUSIONS
In summary, it seems that the main cause of variation that is responsible for the difference
between the two soil-rock systems is their different water regimes, due to the structure of
the soil layer, soil pockets and the hydraulic characters of the subsoil rock. The differences
in the mineral availability are the result of the water regime in both habitats. Improved
water economy as the main factor and improved nutrient element supply as a secondary
cause, lead to improved conditions for tree growth in the chalk habitat that is covered with
Nari and Rendzina soil with its soil pockets.
REFERENCES
Bar-Mattews M., Ayalon M., Kaufman A. (1998). Eastern Mediterranean paleoclimate
during the last 60,000 years as derived from cave deposits. In: Israel Geological Society,