Summary1 Although plants of Equisetum spp. are generally thought to be of little value to ecosystems, a study of a cold-temperate Alaskan shrub wetland showed that they acquired and cycled phosphorus and other nutrients more eciently than other plant community members. While Equisetum plants represented only 5% of the above-and below-ground biomass in the community, they contained 16% of the P and 24% of the K. 2 Equisetum plants accounted for 29% of the P and 39% of the K in annual community foliage litterfall. Over a 2-year period, losses from Equisetum litter contributed 55, 41, and 75% of the P, K and Ca litter inputs into soil nutrient pools. 3 The ability of dierent species of Equisetum to acquire nutrients is linked to their deep rooting habit. While the majority of their roots and rhizomes, and particularly the ®ne roots, were located in the C horizon, the majority of roots and rhizomes of other species were located in the overlying O horizon. The biomass of Equisetum plants was also correlated with edaphic characteristics of the C horizon. 4 The absorption of nutrients from the C horizon by Equisetum helped bring P and other minerals to the soil surface, increasing the amount of minerals in the O horizon and thus making them potentially available to other species, including Myrica gale, Salix spp., and Carex spp. Productivity in this community is limited by P and N, and the ability of Equisetum to act as a nutrient pump may help explain why its net primary productivity is high for a cold-temperate wetland.

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Abstract. In this study, we used once-plowed lands that have returned to forest for over 50 years to study the vertical distribution of meteorologically-deposited lead. These mineral soils were an essentially homogeneous 20 cm-thick layer when last plowed. As such, they were effectively a "clean slate" upon which pollutants deposited since the last plowing can be measured without the confounding aspects of well-developed natural soil horizons and the spatial heterogeneity of native forest soils. The concentration and amount of lead as well as copper and zinc, biologically active metals, were measured at five sites in New England. In the mineral soil, copper content ranged from 25 mg cm depth-t m -2 at 0-2 cm depth to 37 nag cm depth-J m -'~ at 6-8 cm depth, but showed no consistent patteru with depth at all sites. Zinc concentrations and amounts increased with depth in the mineral soil to 14 ttg g-t and 167 mg cm depth J m -e, respectively. In contrast, lead showed a decrease with depth from 350 mg cm depth -t m -e at 0-2 cm depth to 102-108 mg cm depth -~ m -~" between 10 and 20 cm depth. At all five sites, decreases in lead concentration with depth were correlated with decreases in the amount of organic mater. Amounts of total lead deposited since the abandonment from plowing have been estimated at 1.4 g m -2 in rural sites. Thirty-five percent of this presumably anthropogenically-derived lead was in the forest floor; the remaining 65 % was in the upper mineral soil.

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Invasive species have a major effect on many sectors of the U.S. economy and on the well-being of its citizens. Their presence impacts animal and human health, military readiness, urban vegetation and infrastructure, water, energy and transportations systems, and indigenous peoples in the United States (Table 9.1). They alter bio-physical systems and cultural practices and require significant public and private expenditure for control. This chapter provides examples of the impacts to human systems and explains mechanisms of invasive species’ establishment and spread within sectors of the U.S. economy. The chapter is not intended to be comprehensive but rather to provide insight into the range and severity of impacts. Examples provide context for ongoing Federal programs and initiatives and support State and private efforts to prevent the introduction and spread of invasive species and eradicate and control established invasive species.

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