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This chapter explores the controls over nutrient pools and fluxes across different California grassland types, beginning by discussing exotic-dominated annual grasslands, where most biogeochemical studies have occurred. Patterns in these annual grasslands are compared to those in native grasslands and oak-grassland matrices. Finally, the chapter examines the roles of organisms other than plants in influencing nutrient dynamics.

In this chapter, we explore birds as drivers of nutrient dynamics across ecosystems. For example, seabirds transport nutrients from pelagic regions to land areas. We explain why nutrient transport by birds is important and how the characteristics of birds are especially effective for nutrient transport. In the case of seabirds, birds link distant ecosystems by transporting nutrients that otherwise would remain in a certain place, in ways that few other animals can. We present case studies that show the direct and indirect ecological effects of avian nutrient transport, and describe provisioning services provided by those ecological interactions. Globally, seabirds transfer an estimated 10,000 to 100,000 tons of phosphorus from sea to land annually, making up an extremely important supporting ecosystem service, due to humans' excessive use of phosphorus. Lastly, we discuss some negative effects of bird nutrient transport on people and environments, e.g. excessive nitrogen and phosphorus can pose threats to certain habitats, underlining the importance of assessing the costs and benefits of bird-mediated nutrient dynamics in human-dominated ecosystems. We must consider the diversity of ways in which humans value habitats and ecosystem services of birds, in order to find ways to balance the various ecological functions of birds.

This chapter discusses the attributes of deciduous forest herbs that significantly contribute to ecosystem-level nutrient dynamics. It attempts to distinguish among characteristics that are unique to some or all herbaceous species. It compares nutrient content and seasonal patterns of nutrient accumulation among groups of deciduous forest herbs and with overstory species. It considers site quality (nutrient availability) as a determinant of herbaceous nutrient accumulation and discusses patterns of internal cycling (retranslocation) and decomposition of ephemeral materials. Finally, the chapter offers a fresh outlook on the influence of herbaceous populations on ecosystem-level nutrient cycling. In particular, it discusses the idea that spring ephemerals function to retard nutrient loss during spring runoff with regard to its potential use and limitations in understanding the complex nature of deciduous forest ecosystems.

The southern Yucatán peninsular region contains the largest and most rapidly disappearing continuous tract of tropical forest in Mexico (Flores and Espejel Carvajal 1994; Delfín Gonzales, Parra, and Echazarreta 1995; Acopa and Boege 1998). Vegetation in the region is a mosaic of forest types with different structural appearances (Flores and Espejel Carvajal 1994; Hernández-Xolocotzi 1959; Miranda 1958) that primarily reflect variation in environmental and edaphic conditions (Ibarra-Manríquez 1996). However, the structure and tree composition of forests in the region, as elsewhere in the central Maya lowlands, has been and remains strongly influenced by human activity (Ch. 2). In spite of the abundance of botanical work throughout the Yucatán peninsula, little attention has been devoted to characterizing the forests in this frontier region quantitatively, and the variation and distribution of forests remain poorly documented. Yet, it is precisely this kind of documentation that is required for integrated land studies of the kind that the SYPR project is undertaking (Turner et al. 2001). Since the third decade of the twentieth century, botanical interest has focused on the flora of the Yucatán Peninsula, especially that located in the historically more accessible portion of the peninsula (Ibarra-Manríquez 1996). Early twentieth-century studies (Lundell 1938; Standley 1930) led to a broad classification of the primary vegetation as deciduous tropical forests (Miranda 1958), or evergreen tropical forests (Rzedowski 1981), controlled in distribution by the northwest to southeast precipitation gradient, distinctive dry season, and karstic terrain (Ch. 2). Today, the entire region is appropriately labeled a seasonally dry tropical forest (Bullock, Mooney, and Medina 1995). During the rainy season (May–October) most species have their canopies fully displayed and light is a limiting factor in the forest understory (Martínez-Ramos 1985, 1994). For the remainder of the year, monthly precipitation usually does not exceed 100mm. During the lowest rainfall months (February–April), water may become limiting and considerable defoliation takes place, especially in the north and west. Other factors controlling forest structure and composition include topography, twentieth-century land-use history, and hurricanes (Brokaw and Walker 1991; Cooper-Ellis et al. 1999).