Dark Piles in Wheat and Barley Fields of the North Negev
The highway between Lahav junction and Beer Sheva is rich in cultivated wheat or barley fields, especially in a winter with sufficient quantity of rainfall. Large areas of cereals are planted in such a year by the Bedouin. In these fields one may observe what looks like piles of dark plants (Figs. 8.2.1-8.2.3). While talking about it with my colleague Imanuel Noy-Meir, he pointed out an article written by Koyumadzisky, Tzaban, and Offer (1967) “The impact of ant nests on soil fertility in areas of natural vegetation”. Ktavim 17: 195-208. After reading it I stopped my car near such a field on my way to or from Beer Sheva, and observed plant growth near and between ant nests. Worker-ants collected seeds of various plants, snails, beetles, and disposed of their remnants as well as the dead ants of the nest.
An area around the nest, which looks like a circle, is referred to in Hebrew as GOREN, meaning – the “threshing zone”. In this area materials not used by the ants accumulate and increase local soil fertility. These fields belong to Bedouin who did not fertilize the soil. Hence, the wheat among the nests suffered from nutrient deficiency, turned yellow, remained small, and their spikes stayed small (Fig. 8.2.4). Near the nest there were large plants, branched, with dark green leaves and stems, and with large spikes. The car driver on the highway thinks that near the ant nests there are round “piles”. This phenomenon began to form an inseparable part of the lectures of the course “Vegetation of Israel”. It was always emphasized during excursions to the northern Negev. In an area planted with wheat nearby, well managed through fertilization, the ant nests are not recognized at all (Fig. 8.2.5). The latter was near “Philips Farm” and became an olive grove. That landscape remains today only in a picture (Fig. 8.2.5).
In the literature of those days there was no indication that there are plants in Israel that prefer ant nests. The impact of these ants and their nest on the soil and its fertility is dealt with in a Ph.D. thesis carried out at Gilat research station (Offer, J. 1980). My friend, the zoologist Prof. Y. Yom-Tov invited me to join him on an excursion to Ramot Yisachar. He studied gazelle life in that area for many years. He looked upon differences in vegetation density near stations of droppings of male gazelles. Our study of the winter of 1989 was published in an international scientific journal. (Danin & Yom Tov.1990. Nests of harvesting ants as primary habitats of Silybum marianum L. Pl. Syst. Evol. 169: 209 217.) Many of the large plants circles could be well interpreted by the activity of Messor semirufus (harvesting ants; Figs. 8.2.6, 8.2.7). The presence of high quantities of [Silybum marianum] near the ant nests (Fig. 8.2.8, 8.2.9) demanded special attention.