Reconstructing temporal changes in diversity from pollen assemblages is potentially important both palaeoecologically and ecologically because community diversity may, in part, result from historical processes. The use of diversity indices such as Shannon's information index or Simpson's index is not appropriate with pollen percentage data because such indices consider both the numbers of different taxa and their relative frequencies or representation. The latter aspect in pollen data is inevitably influenced by inherent differences in pollen production and dispersal. The total number of taxa present in a sample is a robust and useful measure of palynological richness if, and only if, all the pollen counts are standardized to a fixed number of grains. Rarefaction analysis implements such a standardization and provides minimum variance unbiased estimates of the expected number of taxa ( t) in a random sample of n individuals taken from a larger collection of N individuals containing T taxa. The underlying mathematical theory of rarefaction analysis and its important biological and palaeoecological assumptions are discussed. The use of rarefaction analysis is illustrated with three data-sets: Crose Mere, central England (0-c. 12 500 BP); Abernethy Forest, eastern Scotland (5500-12 100 BP); and three sites (Lochs Ashik, Cleat, Meodal) on the Isle of Skye, western Scotland, all covering the last 10 500 years. Palynological richness, as estimated by rarefaction analysis, is high in the protocratic phase (c. 9500-12 500 BP), low in the mesocratic phase (c. 5500-9500 BP), low in the oligocratic phase (0-c. 5500 BP), and high in the Homo sapiens phase (0-c. 5000 BP) of the Holocene. Although factors such as local site characteristics and pollen production, dispersal, and input may influence temporal changes in richness, changes in palynological richness are interpreted as reflecting predominantly the changing floristic richness of the vegetation types in the pollen-source area of a lake and the changing mosaic structure of the landscape through time. Intermediate levels of disturbance, either natural in the protocratic phase or anthropogenic in the Homo sapiens phase appear to be important in maximizing richness at the landscape scale by preventing (he dominance of any single component but insufficient to cause extinction of components at the landscape scale.

Ecosystems change in response to factors such as climate variability, invasions, and wildfires. Most records used to assess such change are based on short-term ecological data or satellite imagery spanning only a few decades. In many instances it is impossible to disentangle natural variability from other, potentially significant trends in these records, partly because of their short time scale. We summarize recent studies that show how paleoecological records can be used to provide a longer temporal perspective to address specific conservation issues relating to biological invasions, wildfires, climate change, and determination of natural variability. The use of such records can reduce much of the uncertainty surrounding the question of what is "natural" and thereby start to provide important guidance for long-term management and conservation. P aleoecological records (e.g., fossil pollen, seeds and fruits, animal remains, tree rings, charcoal) spanning tens to millions of years provide a valuable long-term perspective on the dynamics of contemporary ecological systems (1). Such studies are increasingly becoming part of community and landscape ecological research (2). In contrast, conservationrelated research largely ignores paleoecological records. For example, there are no temporal records spanning more than 50 years included in any of the key biodiversity assessments published over the past 7 years (3). Paleoecological records have been considered too descriptive and imprecise, and therefore of little relevance to the actual processes of conservation and management. Such criticisms may have been valid 30 years ago, but there is now a wealth of information in paleoecological records providing detailed spatial and temporal resolutions (1, 4-7) that match in detail most records currently used in conservation research.The potential of paleoecological records in conservation biology has been highlighted several times, including their application to biodiversity maintenance, ecosystem naturalness, conservation evaluation, habitat alteration, changing disturbance regimes, and invasions [e.g., (8)(9)(10)(11)(12)(13)(14)]. Conservation of biodiversity in a changing climate (15) and the relevant temporal and spatial scales for ecological restoration (16) have also been considered to warrant a longer-term temporal perspective. Most of these studies are descriptive and provide little practical application. A number of recent applied paleoecological studies, however, have begun to provide direct management information for biodiversity conservation at local, regional, and global scales. These include recommendations relating to biological invasions, wildfires, climate change, and conservation management within thresholds of natural variability. The overriding message from these studies is that such temporal perspectives are essential for meaningful modeling, prediction, and development of conservation strategies in our rapidly changing Earth. Biological InvasionsBiological invasions are of critical concern to conservation...