Species of Salix characterized by particular physiological adaptations and ecological resilience are predisposed to use in conservation and environmental projects in many climatic zones and adverse microsite conditions. The economic importance of Salix is currently increasing and emerging in a wide array of practical applications to restore damaged ecosystems. Here we describe the ecology, physiological characteristics and agricultural requirements of Salix and present an integrated picture based on literature review, of current uses for willows well beyond wetland and riparian situations. These uses include ecosystem restoration, phytoremediation (phytoextraction, phytodegradation, rhizofiltration and phytostabilization), bioengineering (water and wind erosion, and protective structures), and biomass production for both fuel and fiber.

Despite a large body of literature that describes the effects of arbuscular mycorrhizal colonization on plant response to water deficit, reviews of these works have been mainly in narrative form, and it is therefore difficult to quantify the magnitude of the effect. We performed a meta-analysis to examine the effect of mycorrhizal colonization on growth and yield of plants exposed to water deficit stress. Data were compared in the context of annual vs. perennial plants, herbaceous vs. woody plants, field vs. greenhouse conditions, degree of stress, functional group, regions of plant growth, and mycorrhizal and host species. We found that, in terms of biomass measurements, mycorrhizal plants have better growth and reproductive response under water stress compared to non-mycorrhizal plants. When variables such as habit, life cycle, or water stress level are considered, differences in mycorrhizal effect on plant growth between variables are observed. While growth of both annual and perennial plants is improved by symbiosis, perennials respond more favorably to colonization than annuals. Overall, our meta-analysis reveals a quantifiable corroboration of the commonly held view that, under water-deficit conditions, plants colonized by mycorrhizal fungi have better growth and reproductive response than those that are not.

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Forest canopies with leaves shed annually (seasonally deciduous forests) produce a different subcanopy environment than canopies with persistent leaves (evergreen forests). Although causes differ with latitude, seasonality might affect structure and composition of forests similarly. We explored changes in species composition and vertical structure in seasonally deciduous forests from 0°–40° N in the Americas. We measured all woody stems ≥1 cm dbh within replicated 0.0625‐ha plots (16 at each of 9 sites, N > 31 000). Numbers of species, as well as density and basal area, were analyzed parametrically for canopy trees, subcanopy trees, shrubs, and lianas. Numbers of species, especially shrubs and subcanopy trees, were greater in warm (30° N) than cool (40° N) temperate forests. Much larger numbers occurred in subtropical (20° N) and tropical (10° N and 0°) forests, but did not vary in relation to latitude. Higher than expected numbers in areas <0.25 ha in all forests, but especially subtropical forests, indicated local heterogeneity in species composition. Few species occurred exclusively in any structural category, especially at 20° and 30° N. The density of lianas relative to self‐supporting plants was highest at 10° N and declined with increasing latitude. The density of woody plants in the canopy, subcanopy, and shrub layers was higher at 20° N than at other latitudes. In addition, basal area was lowest at 20° N; canopy trees comprised 70% of basal area at 20°, but almost 90% at 0° and 40° N. The subcanopy proportion of basal area was greatest at 30° and least at 40° N. Our study produced general hypotheses. Seasonality influences regeneration dynamics, affecting forest composition and structure along with gap dynamics. Spatial heterogeneity within seasonal forests reflects local regeneration dynamics, including spatial heterogeneity in site conditions, broad tails of dispersal and establishment under a wide range of environmental conditions, as well as recruitment limitations. Structural characteristics of seasonal forests change latitudinally in ways that reflect differences in hurricane frequency. Hurricane effects interact with seasonality to influence the composition and dynamics of seasonal forests at warm temperate and subtropical latitudes, producing seasonal forests that differ from those at both higher and lower latitudes. Corresponding Editor: M. D. Abrams

The efficacy for phytoremediation of five willow species was tested by experimental copper and cadmium uptake in a greenhouse hydroponic system. Five treatments included two concentrations (5 and 25 microM for each metal) and a control. Metal concentrations in solution as well as solution uptake were monitored. Metal resistance was assessed through effects on the dry weight of roots and shoots. The willow species tested were generally resistant of increased Cu and Cd content. Metal accumulation was found in all plant organs of all species. Growth and transpiration were not decreased by 5 microM of copper and 25 microM of cadmium in the solution for most species. 25 microM copper caused injury and reduced the dry weight for all species after 21 d. Salix nigra was highly resistant of both Cu and Cd and accumulated more metals than other species. Future field study should be conducted to confirm the findings and feasibility of the phytoremediation technology using those species.