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While ecologists involved in management or policy often are advised to learn to deal with uncertainty, there are a number of components of global environmental change of which we are certain–certain that they are going on, and certain that they are human—caused. Some of these are largely ecological changes, and all have important ecological consequences. Three of the well—documented global changes are: increasing concentrations of carbon dioxide in the atmosphere; alterations in the biogeochemistry of the global nitrogen cycle; and ongoing land use/land cover change. Human activity–now primarily fossil fuel combustion– has increased carbon dioxide concentrations from °280 to 355 mL/L since 1800; the increase is unique, at least in the past 160 000 yr, and several lines of evidence demonstrate unequivocally that it is human—caused. This increase is likely to have climatic consequences–and certainly it has direct effects on biota in all Earth's terrestrial ecosystems. The global nitrogen cycle has been altered by human activity to such an extent that more nitrogen is fixed annually by humanity (primarily for nitrogen fertilizer, also by legume crops and as a by product of fossil fuel combustion) than by all natural pathways combined. This added nitrogen alters the chemistry of the atmosphere and of aquatic ecosystems, contributes to eutrophiction of the biosphere, and has substantial regional effects on biological diversity in the most affected areas. Finally, human land use/land cover change has transformed one—their to one—half of Earth's ice—free surface. This in and of itself probably represents the most important component of global change now and will for some decades to come; it has profound effects on biological diversity on land and on ecosystems downwind and downstream of affected areas. Overall, any clear dichotomy between pristine ecosystems and human—altered areas that may have existed in the past has vanished, and ecological research should account for this reality. These three and other equally certain components of global environmental change are the primary causes of anticipated changes in climate, and of ongoing losses of biological diversity. They are caused in turn by the extraordinary growth in size and resource use of the human population. On a broad scale, there is little uncertainty about any of these components of change or their causes. However, much of the public believes the causes–even the existence–of global change to be uncertain and contentious topics. By speaking out effectively, we can help to shift the focus of public discussion towards what can and should be done about global environmental change.

We determined the consequences of systematic changes in nutrient availability during long-term soil development by measuring foliar nutrient concentrations. Sun leaves of the dominant tree Metrosideros polymorpha and of eight other species were sampled in Hawaiian rain forests developed on substrates that were 0.3 @? 10^3, 2.1 @? 10^3, 5 @? 10^3, 20 @? 10^3, 150 @? 10^3, 1400 @? 10^3, and 4100 x 10^3 yr old. Elevation, annual precipitation, parent material, and dominant species were nearly constant along this gradient. Foliar N and P concentrations in Metrosideros were lowest in the youngest site (0.72% and 0.052% for N and P, respectively), increased to a maximum on 20 @? 10^3 and 150 @? 10^3-yr-old substrates (1.45% and 0.108%), and then declined close to the initial concentrations in the oldest site (0.86% and 0.061%); N:P ratios in foliage varied relatively little across the sites. Most other species followed a similar pattern of variation. On a per unit leaf area basis, foliar N and P contents in Metrosideros also peaked on intermediate-aged substrates. Foliar nutrient concentrations in Metrosideros sun leaves were determined across a parallel but wetter substrate age gradient. The pattern of variation was similar on both gradients, but the magnitude of variation was smaller on the wetter sequence of sites. Overall, the pattern of variation in foliar nutrients with substrate age is consistent with conceptual models for the dynamics of soil nutrient availability during long-term soil development, and with measurements of soil properties along this sequence.

Myrica faya, an introduced actinorhizal nitrogen fixer, is invading young volcanic sites in Hawaii Volcanoes National Park. We examined the population biology of the invader and ecosystem-level consequences of its invasion in open-canopied forests resulting from volcanic cinder-fall. Although Myrica faya is nominally dioecious, both males and females produce large amounts of fruit that are utilized by a number of exotic and native birds, particularly the exotic Zosterops japonica. In areas of active colonization, Myrica seed rain under perch trees of the dominant native Metrosideros polymorpha ranged from 6 to 60 seeds@?m^-2@?yr^-^1; no seeds were captured in the open. Planted seeds of Myrica also germinated and established better under isolated individuals of Metrosideros than in the open. Diameter growth of Myrica is >15-fold greater than that of Metrosideros, and the Myrica population is increasing rapidly. Rates of nitrogen fixation were measured using the acetylene reduction assay calibrated with ^1^5N. Myrica nodules reduced acetylene at between 5 and 20 @mmol@?g^-^1@?h^-^1, a rate that extrapolated to nitrogen fixation of 18 kg@?ha^-^1@?yr^-^1 in a densely colonized site. By comparison, all native sources of nitrogen fixation summed to 0.2 kg@?ha^-^1@?yr^-^1, and precipitation added <4 kg@?ha^-^1@?yr^-^1. Measurements of litter decomposition and nitrogen release, soil nitrogen mineralization, and plant growth in bioassays all demonstrated that nitrogen fixed by Myrica becomes available to other organisms as well. We concluded that biological invasion by Myrica faya alters ecosystem-level properties in this young volcanic area; at least in this case, the demography and physiology of one species controls characteristics of a whole ecosystem.

Non-native annual grasses dominate most Californian mediterranean-climate grasslands today. However, native Californian grassland flora persists in grasslands on serpentine-derived soils. We manipulated soil nutrient resources to explore the links between nutrient availability, plant productivity, and the relative abundances of native and non-native species in serpentine grassland. Factorial combinations of nitrogen, phosphorus, and other components of a nutritionally complete formula were added to field plots over two growing seasons. Fertilization with nitrogen and phosphorus increased biomass of the resident vegetation substantially in the first season, and within two years allowed the invasion and dominance of non-native annual grasses in patches originally dominated by native annual forbs. Species richness declined with fertilization, as the increased biomass production by invaders suppressed some native forbs. Increased macronutrient availability can increase production on serpentine-derived soil, even when other serpentine characteristics (such as low Ca/Mg ratios and high heavy-metal concentrations) have not been mitigated. Observed changes in community structure and composition demonstrate that the invasibility of plant communities may be directly influenced by nutrient availability, independent of physical disturbance.

The effects of grass-fueled fires on species composition and structure in the Hawaiian seasonal submontane ecosystem were examined in a recent study.

Tropical forests are major contributors to the composition of the atmosphere, and anthropogenic changes to tropical ecosystems have driven changes in the atmosphere. Tropical biologists can make and have made significant contributions to understanding these effects, but we can also learn a great deal from the atmospheric sciences. In this paper, we show how knowledge about the functioning of tropical ecosystems can contribute to building a global source budget for a greenhouse gas (nitrous oxide), and how accumulating information from atmospheric measurements suggests that increased concentrations of a reactive gas (tropospheric ozone) represent a significant perturbation to tropical ecosystems--even in remote areas.

We tested the hypothesis that, where fire has historically been infrequent, wooded areas that have been invaded by grasses and converted to grassland by fire are predisposed to future fire compared to adjacent areas that remain wooded, thus, an initial forest fire may promote future fires. We compare microclimate between a grass-dominated burned area and a nearby grass-invaded woodland that has not burned in recent history, both located in the submontane dry forest of Hawaii Volcanoes National Park. The results were used to parameterized BEHAVE, a fire behavior prediction model developed by the USDA Forest Service. The model's predictions include probability of ignition, intensity, rate of spread, and tree mortality. Contrary to expectations, daytime hourly mean temperatures were higher and relative humidity was lower in the woodland site. However, the differences in temperature and humidity were not great enough to affect spread rate or probability of ignition. Wind speeds were substantially greater in the grassland, and this was most important in driving differences in modeled fire spread. Given similar synoptic conditions, a fire started in the grassland can be expected to spread an order of magnidute faster than one started in the woodland