Pistacia lentiscus; Ceratonia siliqua; Change in Annual Vegetation
7. Pistacia lentiscus and Its Activity
In the area marked 4 in Fig. 4.1.58, sand tongues covered the Ceratonia – Pistacia lentiscus association that existed there in the past. The depth of sand in these areas is more than 5 meters, thus, the mobile sand killed the plants covered by it. At the margin of the dunes, where sand depth was one meter or less, maquis plants survived. The maquis remnants function as a source of seeds for their re-establishment via bird transportation. The number of sites where Pistacia lentiscus seedling may survive the first years after germination is very small. Germination and establishment is possible in the islands of fertile soil below the Retama shrubs. I observed a P. lentiscus seedling for more than five years in the Caesarea sands east of Highway 4, until it died after two consecutive dry years. Two surviving P. lentiscus shrubs on the upper part of a Helianthemum – Retama dune help me in further research and when teaching students and other interested people. Their position testifies that they must have germinated and established themselves at the top of the dune and not as shrubs that survived the sand cover. At the periphery of these Pistacia shrubs are H. stipulatum shrubs that are dying due to the lateral extension of the Pistacia branches that over-shadow the small shrubs. The soil below the Pistacia bush becomes black with time due to the more efficient formation of humus than under the Retama shrubs.
Young plants of Rhamnus lycioides and Rhamnus alaternus and vines of the maquis, such as Asparagus aphyllus and Rubia tenuifolia grow in the shade of the Pistacia shrubs. In this habitat it is rather surprising to find Phagnalon rupestre which is typical of rocky habitats around the country. Not less surprising is the occurrence of Cyclamen persicum, Umbilicus intermedius and Aetheorhiza bulbosa below most of the Pistacia bushes in this area.
In another dune there are four Pistacia bushes on a small area in a Helianthemum – Retama association, with shrubs of Calicotome villosa and Thymelaea hirsuta. These testify to further improvement of soil conditions during the plant succession. Soil and vegetation tests we have carried out (see in the following chapters 4.11 and 4.12) seem to prove that the Pistacia lentiscus – Calicotome villosa association out-competed the Helianthemum – Retama association and should be regarded as an advanced stage towards the climax.
8. Ceratonia siliqua and its activity
Not all the carob trees present in the study area are old and therefore, we should search for a habitat suited to the germination and establishment of carob trees. Carob seedlings are always found in the shade of adult carob trees. In site 9 (Fig. 4.1.59/4), I would show my students 1, 2, or 3-year-old carob seedlings situated in the shade of an old carob tree. Unfortunately, during the last few dozen years there have not been enough consecutive rainy years, hence none of the carob seedlings survived the early stages of growth. It is possible that several rainy years will lead to the development of new carob trees that will germinate in the shade of adult P. lentiscus and C. siliqua plants.
9. Changes in the Annual Vegetation
Prior to the establishment of Ammophila arenaria annuals do not grow on the sands. The first companions of A. arenaria are mainly Senecio joppensis (Figs. 4.1.52, 4.1.54/3). Its seeds are wind-dispersed and are available in high quantities in many places along the coastal plain. Later, Ifloga spicata develops in many places. It is also wind-dispersed and adapted to sand mobility by gluing sand grains to its epidermis. Sand grains moving in saltation hit the attached sand grains and not the epidermal cells.
In more protected sites, where sand is more stable, the dominants are accompanied by sand plants (psammophytes) which succeed to sustain in nutrient-poor soils. The most common are Plantago sarcophylla (Fig. 4.1.53), Rumex occultans (Fig. 4.1.55/1), Rumex pictus (Fig. 4.1.55/2), Maresia pulchella (Fig. 4.1.54/1), and Crepis aculeata (Fig. 4.1.54/4). They occur in the "young" Helianthemum – Retama association but absent in the "old" Helianthemum – Retama association, which faced longer processes of soil amelioration. In the advanced aspect of this vegetation the annuals have higher cover values.
The common species are: Trifolium palaestinum, Aegilops sharonensis (Fig. 4.1.56), and Bromus rigidus. In the stage where Pistacia lentiscus and Calicotome villosa cover most of the area, there are very small opened sites and there are only few annuals at the shrubs' shade.