Asymmetry in community regulation: effects of predators and productivity

Eutrophication and predator additions and extinctions are occurring in ecosystems worldwide. Although theory predicts that both will strongly alter the distribution of biomass in whole communities, empirical evidence has not been consolidated to quantitatively determine whether these theoretical predictions are generally borne out in real ecosystems. Here we analyze data from two types of trophic cascade studies, predator removals in factorial combination with fertilization and observed productivity gradients, to assess the role of top-down and bottom-up forces in structuring multi-trophic communities and compare results from these analyses to those from an extensive database of trophic cascade studies. We find that herbivore biomass declines and plant biomass increases in the presence of predators, regardless of system productivity. In contrast, while plants are increased by fertilization, this effect does not significantly increase herbivores in either the presence or absence of predators. These patterns are consistent among marine, freshwater, and terrestrial ecosystems and are largely independent of study size and duration. Thus, top-down effects of predation are transferred through more trophic levels than are bottom-up effects of eutrophication, showing strong asymmetry in the direction of control of biomass distribution in communities.     

Indoor/Outdoor Air Pollution Exposure Continuity Relationships

The indoor/outdoor air pollution exposure continuity relationships are considered in an attempt to define the major parameters determining the relation. The widely accepted hypothesis of a homeostatic balance between indoor and outdoor pollutant levels has been disclaimed using particulate lead as an index contaminant. A serial filtration collection technique was employed and analysis was performed by atomic absorption spectrophotometry. The results of this study demonstrate the importance of considering parameters other than outdoor pollutant levels in determining indoor air quality.     

The Challenges of Incorporating Cultural Ecosystem Services into Environmental Assessment

The ecosystem services concept is used to make explicit the diverse benefits ecosystems provide to people, with the goal of improving assessment and, ultimately, decision-making. Alongside material benefits such as natural resources (e.g., clean water, timber), this concept includes—through the ‘cultural’ category of ecosystem services—diverse non-material benefits that people obtain through interactions with ecosystems (e.g., spiritual inspiration, cultural identity, recreation). Despite the longstanding focus of ecosystem services research on measurement, most cultural ecosystem services have defined measurement and inclusion alongside other more ‘material’ services. This gap in measurement of cultural ecosystem services is a product of several perceived problems, some of which are not real problems and some of which can be mitigated or even solved without undue difficulty. Because of the fractured nature of the literature, these problems continue to plague the discussion of cultural services. In this paper we discuss several such problems, which although they have been addressed singly, have not been brought together in a single discussion. There is a need for a single, accessible treatment of the importance and feasibility of integrating cultural ecosystem services alongside others.     

Variation in responses of late-seral herbs to disturbance and environmental stress

Clonal herbs that attain maximum development in late-seral forest are often assumed to have similar responses to disturbance and to be functionally equivalent. However, little is known about the demographic or physiological responses of these plants to disturbance or to the altered conditions of the post-disturbance environment. Following harvest of a mature coniferous forest, we compared abundance, demographic changes, and physiological acclimation of three clonal herbs (Asarum caudatum, Clintonia uniflora, and Pyrola picta) that differ in belowground morphology and leaf longevity. We measured ramet density, leaf area, and demographic variables (survival, clonal growth, flowering, and seedling establishment) before and for two years after harvest, and in adjacent undisturbed forest. Acclimation to increased solar radiation was assessed two years after harvest by measuring leaf mass per unit area (LMA) and chlorophyll a:b ratios of leaves produced in the current year. Although initial declines in abundance were similar, demographic responses indicate that patterns of recovery varied greatly among species. Two years after logging, ramet survival and clonal growth (production of new ramets) of Clintonia were greater in the harvest area than in the forest. Asarum had lower survival in the harvest area, but greater clonal growth, and Pyrola showed no difference in either survival or growth between environments. Only Asarum produced seedlings, although their survival was low in the harvest area. All species had higher LMA in the harvest area, but only Clintonia (with annual leaves) had a higher chlorophyll a:b ratio, suggesting the greatest potential for acclimation to increased light. Our results demonstrate that forest herbs with greater rhizome plasticity and shorter leaf duration have greater potential to acclimate after disturbance than those with rigid architectures and persistent leaves. Thus, species with comparable successional roles can vary substantially in their demographic and physiological responses to disturbance, with potential consequences for long-term recovery.     

Exploring Patterns of Seafood Provision Revealed in the Global Ocean Health Index

Sustainable provision of seafood from wild-capture fisheries and mariculture is a fundamental component of healthy marine ecosystems and a major component of the Ocean Health Index. Here we critically review the food provision model of the Ocean Health Index, and explore the implications of knowledge gaps, scale of analysis, choice of reference points, measures of sustainability, and quality of input data. Global patterns for fisheries are positively related to human development and latitude, whereas patterns for mariculture are most closely associated with economic importance of seafood. Sensitivity analyses show that scores are robust to several model assumptions, but highly sensitive to choice of reference points and, for fisheries, extent of time series available to estimate landings. We show how results for sustainable seafood may be interpreted and used, and we evaluate which modifications show the greatest potential for improvements.     

Grassland restoration with and without fire: evidence from a tree-removal experiment

Forest encroachment threatens the biological diversity of grasslands globally. Positive feedbacks can reinforce the process, affecting soils and ground vegetation, ultimately leading to replacement of grassland by forest species. We tested whether restoration treatments (tree removal, with or without fire) reversed effects of nearly two centuries of encroachment by Abies grandis and Pinus contorta into dry, montane meadows in the Cascade Range, Oregon, USA. In nine, 1-ha plots containing a patchy mosaic of meadow openings and forests of varying age (20 to > 140 yr), we compared three treatments affecting the ground vegetation: control (no trees removed), unburned (trees removed, slash burned in piles leaving 90% of the area unburned), and burned (trees removed, slash broadcast burned). We quantified changes over 3-4 years in soils, abundance and richness of species with differing habitat associations (meadow, forest, and ruderal), and recruitment of conifers. Except for a transient increase in available N (especially in burn scars), effects of burning on soils were minimal due, in part, to mixing by gophers. Tree removal greatly benefited meadow species at the expense of forest herbs. Cover and richness of meadow species increased by 47% and 38% of initial values in unburned plots, but changed minimally in burned plots. In contrast, cover and richness of forest herbs declined by 44% and 26% in unburned plots and by 79% and 58% in burned plots. Ruderal species and conifer seedlings were uncommon in both treatments. Although vegetation was consumed beneath burn piles, meadow species recovered significantly after three years. Long-term tree presence did not preclude recovery of meadow species; in fact, colonization was greater in older than in younger forests. In sum, temporal trends were positive for most indicators, suggesting strong potential for restoration. Contrary to conventional wisdom, tree removal without fire may be sufficient to shift the balance from forest to meadow species. In meadows characterized by historically infrequent fire, small-scale disturbances and competitive interactions may be more critical to ecosystem maintenance and restoration. Managers facing the worldwide phenomenon of tree invasion should critically evaluate the ecological vs. operational need for fire in ecosystem restoration.     

Thinning and burning result in low-level invasion by nonnative plants but neutral effects on natives.

Many historically fire-adapted forests are now highly susceptible to damage from insects, pathogens, and stand-replacing fires. As a result, managers are employing treatments to reduce fuel loadings and to restore the structure, species, and processes that characterized these forests prior to widespread fire suppression, logging, and grazing. However, the consequences of these activities for understory plant communities are not well understood. We examined the effects of thinning and prescribed fire on plant composition and diversity in Pinus ponderosa forests of eastern Washington (USA). Data on abundance and richness of native and nonnative plants were collected in 70 stands in the Colville, Okanogan, and Wenatchee National Forests. Stands represented one of four treatments: thinning, burning, thinning followed by burning, or control; treatments had been conducted 3-19 years before sampling. Multi-response permutation procedures revealed no significant effect of thinning or burning on understory plant composition. Similarly, there were no significant differences among treatments in cover or richness of native plants. In contrast, nonnative plants showed small, but highly significant, increases in cover and richness in response to both thinning and burning. In the combined treatment, cover of nonnative plants averaged 2% (5% of total plant cover) but did not exceed 7% (16% of total cover) at any site. Cover and richness of nonnative herbs showed small increases with intensity of disturbance and time since treatment. Nonnative plants were significantly less abundant in treated stands than on adjacent roadsides or skid trails, and cover within these potential source areas explained little of the variation in abundance within treated stands. Although thinning and burning may promote invasion of nonnative plants in these forests, our data suggest that their abundance is limited and relatively stable on most sites.     

Global rarity of intact coastal regions

Management of the land–sea interface is essential for global conservation and sustainability objectives because coastal regions maintain natural processes that support biodiversity and the livelihood of billions of people. However, assessments of coastal regions have focused strictly on either the terrestrial or marine realm. Consequently, understanding of the overall state of Earth's coastal regions is poor. We integrated the terrestrial human footprint and marine cumulative human impact maps in a global assessment of the anthropogenic pressures affecting coastal regions. Of coastal regions globally, 15.5% had low anthropogenic pressure, mostly in Canada, Russia, and Greenland. Conversely, 47.9% of coastal regions were heavily affected by humanity, and in most countries (84.1%) >50% of their coastal regions were degraded. Nearly half (43.3%) of protected areas across coastal regions were exposed to high human pressures. To meet global sustainability objectives, all nations must undertake greater actions to preserve and restore the coastal regions within their borders.