Ecological significance of common nonarboreal pollen: examples from drylands of the Middle East

Abstract

Surface pollen assemblages within the continental Middle East and the ecology of the common pollen-producers provide the basis for analyzing pollen assemblages of the past. Sparse psammophilous vegetation is found within the hyperarid zone. It primarily produces pollen of Cyperus conglomeratus and Calligonum. Within the arid zone pollen of Chenopodiaceae, Plantago and insect-pollinated herbaceous vegetation dominates. Artemisia pollen becomes important within semi-arid climates. Both Artemisia and Chenopodiaceae are characteristic of highly continental climates with cold winters and dry summers. Because Artemisia pollen increases and Chenopodiaceae decreases with decreasing aridity the ratio of their pollen ( C/ A) is used as a moisture indicator. This ratio should be applied within narrow geographical limits and within non-forested areas. Grasses (Poaceae) are not well-adapted to climates with summer drought and their pollen percentages are low in most of the region. They are somewhat higher where favorable edaphic conditions occur or where summers are less arid. A low C/ A during the pleniglacial suggests moist conditions with a rainfall regime similar to today. Increases in Chenopodiaceae pollen at the expense of Artemisia indicate intense aridity during late glacial times. An early Holocene phase of summer rainfall is evident in the region-wide replacement of Chenopodiaceae/ Artemisia vegetation by grasses and in the spread of deciduous trees in less arid sites.