Israel is situated at the juxtaposition of several major environmental domains: the Euro-Siberian, Irano-Turanian, Mediterranean, Saharian and Sudanese. Longitudinally, the country is divided into three different zones: the coastal plain to the west, the mountainous backbone and the Jordan Rift Valley. The interrelationships of these environmental belts and the topography create a great variability of biotopes and local environments, which, being in a border zone, are very sensitive to climatic changes. The climatic changes, and the ensuing environmental changes, are best exposed by the vegetational composition (presently displaying the entire spectrum from a Mediterranean forest to the north through a bare desert to the south).
Any change in the climatic conditions, minor as it might be, would have greatly influenced the distribution of environments in Israel, thereby influencing human life, economy and settlement patterns.
The best technique for following paleoclimatic changes seems to be the analysis of pollen grains, which represent the vegetation at the time of deposition. Pollen grains of wind-pollinated plants are produced in great numbers and, consisting of a very resistant substance—sporopollenin—are generally quite well preserved in the sediments of inhabited sites and depositional basins. Morphologically, pollen grains of different plants vary considerably (Figs. 2-7) and, being in the size range of 20-80 microns, can easily be identified through the microscope. Pollen grains carried by the winds, are incorporated in the sediments, and in the case of aquatic depositional basins, also by streams. Therefore, the ensuing pollen spectrum of each sample, generally consisting of about 150-200 individuals, represents the regional vegetation. Pollen derived from plants which grow near an inhabited site is somewhat overrepresented, and a comparison of spectra recovered from such sites with spectra found in other synchronous sediments, preferably lacustrine, helps to differentiate the regional and local vegetations. This enables us to draw conclusions on both the regional vegetational and climatic conditions and the local flora, some of which may have been cultivated.
Not all plants are represented by their pollen in the sediments. The insect-pollinated are much less likely to be present than the wind-pollinated, and within the latter group some plants produce larger quantities of pollen than others. Several plants are underrepresented due to differential destruction of the pollen grains in the process of fossilization. Prior to drawing conclusions from fossil pollen spectra, it is therefore necessary to compare them with recent pollen spectra from regions of known vegetation, climate and directions of transporting agents.
In order to isolate the individual pollen grains, the samples of sediment are processed by rather complicated physicochemical methods. The required sample size is about 50 grams when collected from a borehole, and about ten times as much from an archeological site, due to the more rapid rate of sedimentation. The sample is first washed in hydrochloric acid to remove any carbonates which may have cemented the particles together. Hydrofluoric acid is used to dissolve some of the clay minerals, and flotation in a heavy liquid then separates the mineral from the organic matter. The organic matter containing the pollen is further treated by acetolysis and oxidation to minimize the amount of “dirt.” The residue is then mounted on a glass and studied under a microscope. For ordinary work a light microscope is sufficient, but when detailed morphological study of the pollen is carried out, the scanning electron microscope is a great help. Figs. 2-7 were photographed by the SEM of the Division of Paleontology, Geological Survey of Israel, by Mr. M. Dvorachek. The pollen grains are identified and counted, and the percentages of each of the constituents of the spectrum is calculated. When successive samples are available, a pollen diagram can be drawn, so that any changes may be followed consecutively as a function of time. Since this is quite difficult to achieve
with material from archaeological sites, it is preferable to first obtain pollen diagrams from boreholes in the same area which can then be compared with samples from such sites.
For example, Fig. 1 shows schematically the results of rather detailed palynological analyses of boreholes from the Hula Valley and the Mediterranean offshore, covering the time-span of the last 6000 years (measured by radiocarbon). The archaeological periods of Israel are correlated with the pollen diagrams according to the radiocarbon ages. The diagrams sum up and compare the arboreal with the non-arboreal pollen distribution. Almost no influence of cultivation is reflected by these diagrams, since the boreholes were drilled far from the land—in the middle of Lake Hula and in Haifa Bay, some ten kilometers offshore. This gives a basic picture of the regional vegetation, with no “noise” of the local components. Indeed, the similarity of the pollen diagrams from the Hula and the Mediterranean is striking, and could therefore be used as a sound basis for making conclusions on the natural vegetation and development of the climate throughout the last 6000 years.
The recent pollen spectrum for northern Israel comprises a mixture of Mediterranean elements, the most important being pollen of oak, pine, olive and pistachio, none of which is especially prevalent today. Some zones along the diagrams are totally different in the composition of the pollen spectra. The main difference lies in the considerably higher percentages of arboreal pollen, especially displayed by increases in oak and olive percentages. These increases are conspicuous from the bottom of the curves up to about 2400-2300 B.C.; from about 2100 up to about 1100 B.C., and a shallower peak from 700600 B.C. up to A.D. 800-900. These periods are separated by intervals in which the arboreal share is considerably lower. The bottoms of these “lows” occur around 2250 B.C. and again about 950 B.C., after which the arboreal pollen curve remains low until the present day. Some minor “lows” are around 3000 B.C., A.D. 300 and A.D. 1100-1300.
It seems that in periods corresponding to the high peaks of the arboreal pollen curve the Levant enjoyed a more humid climate than it does today, involving two factors: rains reaching the Levant from the Atlantic Ocean as warm fronts, and the occurrence of occasional summer rains. This is quite in contrast to precipitation patterns of today when only winter rains are known in the Levant, coming as thunderstorms originating in the Aegean Sea. As a result, the previous humid periods enjoyed a richer vegetation and considerably less erosion and wind deflation.
The different climates had a very strong influence on the settlement pattern of Israel. During the Chalcolithic period and Early Bronze Age, settlements existed much further south than in later periods. There was some difference between the two cultures, in spite of similar climatic environment, but this may be attributed to cultural factors, the Chalcolithic economy being purely pastoral while the Early Bronze Age people were both farmers and shepherds. The end of the Early Bronze Age is marked by invasions of nomadic tribes coming out of the desert and settling in the now non-agricultural areas. A more favorable climate returned during Middle Bronze Age II and to some extent also during the Late Bronze Age when, it may be recalled, Israel was regarded as a “land of milk and honey.”
The paradise, however, did not last, and the deteriorating climate towards the first millennium B.C. forced the Israelites to develop agricultural techniques suited to the new, drier environment. The development of agricultural terraces was an important innovation contributing to the prosperity of these times. An interesting parallel may be noted: the Israelis of today, like the Israelites of the Biblical period, have settled in previously unoccupied parts of the country, and have been able to make the land flourish only by adapting agricultural techniques to the environment and developing sophisticated methods of cultivation.