The influences of animal diggings and runoff water on the vegetation in the Negev Desert of Israel

There is interaction between porcupines that create diggings and the vegetation in a desert biome. Dense patches of diggings may be found in large areas in the Negev and other deserts such as those of South Africa. Porcupines create diggings from 5 to 25 cm deep in the Negev in order to consume subterranean organs of about 18 species of geophytes and hemicryptophytes. There are two main strategies of consumption of these plants: (a), destruction by total consumption of only 20 to 25% of a patch of plants, which are then renewed from seeds; (b), partial consumption of almost all the plants in a patch so that parts of the plants remain below the bottom of the digging and later continue to grow there. In addition to porcupines, there are many other creatures in deserts, such as insects, reptiles, birds, rodents, gazelles, and ibex, that create diggings, depressions, or wallows in the soil for the consumption of subterranean parts of plants or as night beds or nests. In desert soils with low water infiltration, even a rainfall of about 7 mm may cause runoff water. In a 25-cm-deep depression the runoff equivalent to a 250-mm rainfall may accumulate, whereas only 2-4 turn may penetrate the soil in the area surrounding the digging. Diggings may act as wind traps for seeds and organic matter, and their accumulation, together with large amounts of runoff water, make them favorable microhabitats. Seeds of plant species that are consumed, as well as seeds of other species, germinate, and the plants develop in these diggings in large numbers. A succession of events relating to the emergence of annuals in the diggings occurs according to the percentage of filling-in of the digging by soil erosion. In the diggings there is a gradual increase in plant density, plant biomass, species diversity, and seed yield, up to 50% of filling-in. Then there is a gradual decrease of all these factors until the digging is 100% filled-in. During the filling-in process, plant species dominance changes from plant species with wind-dispersed seeds to those with rain-dispersed seeds.