Artemisia monosperma and its Activity

פורסם: August 7th, 2011 | עודכן: 14/01/15

Germination and growth of Artemisia monosperma starts in sites protected from wind by nebkas of Ammophila arenaria (Fig. 4.1.32/1). It is accompanied by Senecio joppensis, an annual plant adapted to living in sites in the first stages of sand stabilization (Fig. 4.1.32/2). The Artemisia shrub develops, and its crown becomes intricate upon maturation (Fig. 4.1.33).

Fig.4.1.32: Exposed sand among Artemisia monosperma shrubs. Decreased wind velocity enabled germination of A. monosperma (1) and growth of Senecio joppensis (2).

Fig.4.1.33: A young plant of Artemisia monosperma. Due to its morphology, this shrub does not cause sand accumulation around it.

The intricate crown functions as an efficient windbreak against the local wind (Fig. 4.1.34). It builds up a nebka with fine grains and hence has a better moisture regime than plants in the open areas of the sand dune. Qualitative demonstration of this process may be seen when comparing sand grains near- and in nebkas. In Fig. 4.1.35 a Silene succulenta plant is seen on sand with coarse grains at the surface (Fig. 4.1.35/1). At the shrub center (marked #2) there is already a small sand mound which considerably decreases the wind velocity behind it. Fine sand protected from the wind is deposited and forms an elongated crest (#3) on the leeward side. There are places where the Artemisia is covered by sand or buried in it.

Fig.4.1.34: Artemisia monosperma plant builds up a nebka (1) in a dune dominated by Ammophila arenaria and has clear ripples.

Fig.4.1.35: Silene succulenta function as an efficient wind break and accumulate sand among its stems (2). Small sand grains were transported from the surrounding sand and large grains remained. The decreasing wind velocity in the developing nebka enables accumulation of fine-grained sand clearly differing from the surrounding sand.

To its advantage, because of its structure, the plant at a certain stage ceases to accumulate sand and its total burial is prevented (Fig. 4.1.36). In winter, after being covered with sand, the Artemisia plant develops adventitious roots into the wet sand from the buried stems (Fig. 4.1.37/3). In this way the plant may elongate efficiently from the exposed stems with a local supply of water. Artemisia shrubs grow and expand and new individuals grow and develop in the empty spaces between them until the entire area becomes covered (Fig. 4.1.38). At this stage there is efficient trapping of air-borne dust which leads to improvement of the moisture regime. This amelioration is expressed in the increase of the number of the accompanying annual species and the growth of nebkas of all the plants, leading to the formation of hills (as in Fig. 4.1.39).

Fig.4.1.36: A buried shrub of Artemisia monosperma. The projecting stems hardly arrest sand any more.

Fig.4.1.37: A branch of Artemisia monosperma covered by sand to point 1. Leaves that were active and buried (2) died and roots developed from stems (3).

Fig.4.1.38: Artemisia monosperma become denser and accompanied by Retama raetam (1), Polygonum palaestinum(2) and Heterotheca subaxillaris(3).

Fig.4.1.39: A sand hill built up by Artemisia monosperma plants.

The rising of sand hills in the landscape dominated by A. monosperma has an impact on the local winds and leads to sand erosion by the wind. As time passes, the hilly landscape with mounds becomes flat and turns into a plain (Fig. 4.1.40). The exposure of its roots (Figs. 4.1.41-4.1.43) is prominent in areas with high geomorphologic activity. A. monosperma has adapted to the exposure of its roots by developing a layer of cork, which protects the roots from direct desiccation. A plant with exposed root lies on its side (Fig. 4.1.42) and its dense canopy locally decreases wind velocity. Sand trapped near this canopy buries branches, which leads to the formation of adventitious roots (as in Fig. 4.1.37). In areas where A. monosperma dominates, typical biological and geomorphological processes take place. The area becomes flat and its vegetation cover increases. Humus is formed and starts to accumulate in the shade of shrubs; dust is trapped and the accompanying plants assist in improving the nutrient regime and reservoirs.

Fig.4.1.40: A sand field dominated by A. monosperma plants. A local woman collects shrubs for building residential hut and for fire fuel.

Fig.4.1.41: Sandy area after strong wind erosion. Shrubs of Artemisia monosperma remained with exposed roots which became black and were not harmed due to their cork layer protecting them from drought.

Fig.4.1.42: An Artemisia monosperma shrub with exposed root; its above-ground parts "lie" on its side. Stems in contact with the soil will produce roots in the next growth season.

Fig.4.1.43: A hill with exposed Artemisia monosperma roots.