Ramat Bet Hakerem: Invasive Plants; Harvesting Ants

Published: September 12th, 2010 | Updated: 14/01/15

1.14. Invasive plants following man-made land disturbance

Invasive plants grow successfully at the margin of the rock reserve and especially in sites in the proximity of irrigated lawns (Fig. 2.1.63). The invasive plants cannot compete with the local flora unless the equilibrium is disturbed. An example of an invasive plant belonging to the indigenous flora of Israel is Dittrichia viscosa (Fig. 2.1.64). The natural habitat of D. viscosa, is on the banks of fresh-water rivers, near swamps and near springs, where it grows without human interference. It blooms in summer and uses water resources available in these habitats in that season. During the first rain showers seed dispersal takes place; each seed is assisted by a pappus enabling it to travel long distances. The airborne seeds land on the ground and seeds that arrive at a suitable habitat germinate and have to withstand the first dry summer. Disturbed soils where vegetation was artificially removed function as such a habitat. Plants using the water in winter were removed and D. viscosa can sustain there in summer.

The fresh green color of D. viscosa is seen in Figs. 2.1.63 and 2.1.64 near the rock reserve. The water is available there as a result of disturbance and irrigation of the lawn. Any kind of disturbance brings in its wake the invasion of plants which do not belong to the area and arrive there in a way similar to that of D. viscosa. Each of the following invasive plants has many tales of wandering, which are beyond the scope of the present chapter. We may list them here and remember that they are found in a belt of 1-2 m around the rock reserve boundaries. The cosmopolitan representatives are: Ecballium elaterium (Fig. 2.1.65), Portulaca oleracea (Fig. 62.1.66), Conyza bonariensis, Amaranthus retroflexus, and Euphorbia lasiocarpa. Plants of local origin, common in disturbed ground are: Convolvulus arvensis, Hirschfeldia incana, Sinapis alba, Isatis lusitanica, Silybum marianum, Foeniculum vulgare, Lactuca serriola, Capparis spinosa, Malvella sherardiana, Antirrhinum majus and Urospermum picroides. It is worth protecting the reserve from disturbance so that these invaders do not succeed in establishing themselves.

Fig. 2.1.63: Irrigated lawn at the margin of the rock reserve is one of the first promoters of the Dittrichia viscosa – the fresh green shrub at the rock reserve margins.

Fig. 2.1.64: Dittrichia viscosa is a plant of swamps and fresh water springs but also grows in human-disturbed sites.

Fig. 2.1.65: Ecballium elaterium is an invasive plant growing in Israel in human-disturbed sites.

Fig. 2.1.66: Portulaca oleracea is a cosmopolitan group of closely related species growing in all continents between the latitudes 40 degrees north and south of the equator. Confined to disturbed sites and margins of ornamental plots irrigated in summer.

1.15. Nests of harvesting ants

I am expanding a little into zoology because of the intimate relationships of plants and harvesting ants. There are at least three large nests of harvesting ants in the rock reserve. They are easily recognized by the presence of plant parts which accompany seeds in plant diaspores (e.g. bracts, valves, awns, glumes), around holes in the soil. The diameter of the remnants collection (known as “threshing zone”) is 1-2 m. Large seeds of wheat, oats, and barley are much desired by ants as can be seen from the abundance of their parts. Studies of ant nests in various places in the country led to the well known statement that the depth of chambers containing seeds may be 3 m. There are always interesting things to be observed near the ant nest all year round. The devoted observer will soon come to understand the Biblical Proverb: “Go to the ant, thou sluggard; consider her ways and be wise.” When studying plant adaptations to the Mediterranean biome, one must pay attention to ant-induced processes, properties, or adaptations. Diaspores penetrate into soil fissures, and are anchored inside the soil by means of hairs and bristles turned up, to prevent easy removal. Thus hairiness, awns, and minute teeth are properties of the grasses with large seeds, which may be related to ants. These properties are part of the syndrome of living with ants in the Mediterranean zone during evolutionary time and processes.

A thorough discussion of ants and Silybum marianum and Notobasis syriaca relationships is presented in “Plant Stories” chapter H, sections 3 & 4. Part of the observations I made on the way to publishing articles on these issues, took place at Ramat Bet HaKerem before urbanization. Observing plant remains from two nests at the rock reserve I listed the following species: Triticum dicoccoides, Hordeum spontaneum, Hordeum glaucum, Avena sterilis, Echinops adenocaulos, Sinapis alba, Malva parviflora, Medicago polymorpha, Medicago rotata, Hymenocarpos circinnatus, Sarcopoterium spinosum, Calendula arvensis, Erodium gruinum and Lolium rigidum.

Part of the ants’ life cycle is a phenomenon worth watching every year. During the summer, the main activity seen in the nest and around it is the collection of plant diaspores. The workers inside the nest process the food and throw out the non-seed remains onto the threshing zone around the nest. After the first rain shower, on a warm, sunny day there is interesting activity. Winged male and female ants come out of the nest, climb onto tall places, plant remains and stones around the nest, and after warming up, they fly. During their flight, male and female meet, copulate and are often seen as ants with two pairs of wings. The fertilized female ants try to establish new nests.