A sediment core 7.2 m long from Lake Mirabad, Iran, was examined for loss-on-ignition, mineralogy, oxygen-isotopic composition of authigenic calcite, and trace-element composition of ostracodes to complement earlier pollen and ostracode-assemblage studies. Pollen, ostracode-inferred lake level, and high Sr/Ca ratios indicate that the early Holocene (10000 to 6500 cal yr BP) was drier than the late Holocene. Low δ18O values during this interval are interpreted as resulting from winter-dominated precipitation, characteristic of a Mediterranean climate. Increasing δ18O values after 6500 cal yr BP signal a gradual increase in spring rains, which are present today. A severe 600-yr drought occurred at ca. 5500 cal yr BP, shortly after the transition from pistachio-almond to oak forest. During the late Holocene, two milder droughts occurred at about 1500 and 500 cal yr BP. Within the resolution of the record, no drought is evident during the collapse of the Akkadian empire (4200–3900 cal yr BP). Rather, a decrease in δ18O values to early-Holocene levels may indicate the return to a Mediterranean precipitation regime.

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Summary AimUsing a large database that has been created over the past 5 years with the RECORDER package, presence/absence data for 829 species of vascular plants in the 103 1‐km2 squares that cover the city of Plymouth (pop. 243,373) have been analysed by two‐way indicator species analysis (TWINSPAN) and canonical correspondence analysis (CCA) to establish the major species assemblages and to examine their spatial distribution across the city in relation to variation in land use. LocationThe City of Plymouth. MethodsNine groupings of squares emerged and their distribution was mapped across the city. Interpretation of those groups and their variation in relation to the land use ordination axes showed that TWINSPAN groups lying along the first axis of variation correlated floristic variation with the process of urban development and the historical evolution of urban structure. The second axis appeared to be related to particular remnant semi‐natural habitats within the city that could be regarded as ‘hot‐spots’ for survival of many plant species. Species were categorized into four types on the basis of their recency and mode of arrival in the city and by using the historical flora of Plymouth produced by T. R. Archer‐Briggs in 1880. Variations in the sources of species in relation to the TWINSPAN classification groups were then examined. A second ordination was also computed; this time with geological, altitudinal and distance variables. TWINSPAN groups were then superimposed on the ordinations using polygons to assist with biogeographical interpretation. Results and conclusions The results of both the multivariate analyses and distribution of species by source are then discussed in the context of previous research into urban plant ecology, particularly in Central Europe. The problems of inferring process from pattern in this meso‐scale study are reviewed and suggestions are made for further research into urban ecology and biogeography in the city.

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