Abstract. Acute changes in ecological disturbance regimes can have major consequences for ecosystems and biota, including humans, living within them. Human suppression of fire in the western United States over the last century has caused notable changes to many ecosystems, especially in lower elevation, semiarid forest types dominated historically by fire tolerant taxa like Pinus and Quercus. Recent increases in fire activity in western US forests have highlighted the need for restoration of ecological structure and function, but management targets for restoration in different forest types remain uncertain. Working in the forests of eastern California, we evaluated the direction and magnitude of change in burned area and fire severity between the period prior to Euro-American settlement (;1500-1850) and the ''modern '' period (1984-2009). We compared total annual area burned; proportional area burned at low-moderate severity and high severity; and annual area burned at low-moderate severity and high severity between the two time periods in seven forest types. We also examined modern trends in fire area and severity. We found that modern rates of burning are far below presettlement levels for all forest types. However, there were major differences between low to middle elevation forests and high elevation forests regarding the components of this departure. Low and middle elevation forests are currently burning at much higher severities than during the presettlement period, and the departure in fire area is overwhelmingly expressed in the low to moderate severity categories; in these forest types, mean annual area of high severity fire is not notably different between the modern and presettlement periods. In higher elevation forests on the other hand, the modern departure in fire area is expressed equally across fire severity categories. Our results underline the critical need for forest and fire restoration in the study area, especially in low and middle elevation forests adapted to frequent, low severity fire. Expanded management of naturally ignited fires for resource benefit is clearly needed, but in many parts of our study area, strategic reduction of forest fuels will likely be necessary before large-scale restoration of fire becomes ecologically, politically, and financially feasible.

Ecological theory predicts that the amount of resources available in an ecosystem should affect its response and sensitivity to ecological disturbances like fire, herbivory, and soil disturbance. Plant stature and life form, biomass, rates of growth, and plant palatability are all influenced by habitat productivity, and these factors play key roles in determining disturbance frequencies and intensities (Pickett and White, 1985; Bond and van Wilgen, 1996; Grime, 2001; Table 12.1). Theory and empirical investigations find that site quality is often related to rates of competitive displacement, with relatively unproductive, less competitive environments less reliant on disturbance for diversity regulation (Huston, 1994; Grime, 2001). Because the most significant direct effect of disturbance on vegetation is to increase available space and light (Grace, 1999), the effects of disturbance on plant diversity should correlate positively with productivity, since more productive plant communities are more limited by above-ground competition (Tilman, 1982). Ecologically, a disturbance of a given intensity will cause more change in space and light availability in dense vegetation than in open habitats, where these resources are already more abundant. On evolutionary time scales, species are less likely to specialize on regenerating after disturbance in communities where space and light are less limiting (Grubb, 1977; Bond and van Wilgen, 1996). Given the great differences in productivity between serpentine and nonserpentine habitats, coupled with the heightened presence of endemics and species of Serpentine: The Evolution and Ecology of a Model System, edited by Susan Harrison and Nishanta Rajakaruna. Copyright  by The Regents of the University of California. All rights of reproduction in any form reserved. table 12.1 "Contextual" Features of Serpentine Soil and Vegetation That Influence the Relationship between Disturbance and Plant Diversity Feature Serpentine Effect Ecosystem structure Stunted vegetation; relatively sparse, heterogeneous plant cover; low stem density and woody plant cover; relatively low biomass; significant areas of exposed soil; low canopy height; greater development of understory vegetation. Resource base Infertile soils with high Mg; low Ca, N, P, and K; high heavy metals (Cr, Ni). Available water capacity (AWC) can be higher or lower than normal soils, but many authors refer to low soil moisture of serpentine soils. Species traits Relatively slow growth rates, compared to conspecifics or congeners on more fertile soils. Stress-tolerant life history strategies common. Many endemic plant species. Serpentine plants often exhibit xeromorphic traits traits such as small, thick, hairy, and/or evergreen foliage. In some regions (mostly humid, warm climates), some species hyperaccumulate heavy metals (Cr, Ni, Co), which may act as an herbivore defense. In California, some evidence of higher palatability of serpentine versus nonserpentine grasses. Root systems often deeper and better-developed than in more f...

We isolated and characterized microsatellite loci in the ornamental pampas grass Cortaderia selloana (Schult. & Schult. f.) Asch. & Graebn. for purposes of identifying cultivars and assessing genetic relationships among cultivars. Small insert genomic libraries were enriched for dinucleotide (CT)n and (CA)n repeats. Ninety clones were sequenced of which 76% contained at least one microsatellite with a basic motif greater than six repeat units. Nine primer pairs amplified 10 polymorphic and putatively disomic loci, and were used to genotype 88 individuals representing 17 named cultivars and four selections. In total, 93 alleles were detected with a maximum of two to 19 per locus. Effective number of alleles varied from 1.3 to 9.5. Observed heterozygosity ranged from 0.07 to 0.81. The 10 microsatellite loci distinguished the majority of pampas grass cultivars. An unweighted pair group method with arithmetic mean (UPGMA) cluster analysis, based on proportion of shared alleles among individuals, revealed groups of cultivars corresponding to origin and morphological characteristics. With few exceptions, individuals of a single cultivar clustered together with moderate to strong bootstrap support (greater than 50%). Interestingly, `Pumila' from Europe and the United States formed separate clusters indicating independent origins. A large, diverse cluster with low bootstrap support consisted of selections and cultivars sold as seed, rather than potted or bare-root clonal plants. Primers designed for C. selloana amplified microsatellite loci in other Cortaderia Stapf species concordant with phylogenetic relationships among the species. Cross-amplification was 100% in C. jubata (Lemoine ex Carrière) Stapf; 77% in C. pilosa (d'Urv.) Hack. and C. rudiuscula Stapf; 66% in C. fulvida (Buch.) Zotov; and 55% in C. richardii (Endl.) Zotov and C. toetoe Zotov.

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