Ecological Monographs最新文献

Peatlands store large amounts of carbon (C), a function potentially threatened by climate change. Peatlands composed of vascular cushion plants are widespread in the northern and central high Andes (páramo, wet and dry puna), but their C dynamics are hardly known. To understand the interplay of the main drivers of peatland C dynamics and to infer geographic patterns across the Andean regions, we addressed the following question: How do topography, hydrology, temperature, past climate variability, and vegetation influence the C dynamics of these peatlands? We summarize the available information on observed spatial and inferred temporal patterns of cushion peatland development in the tropical and subtropical Andes. Based on this, we recognize the following emerging patterns, which all need testing in further studies addressing spatial and temporal patterns of C accumulation: (1) Peatlands in dry climates and those in larger catchments receive higher sediment inputs than peatlands from wet puna and páramo and in small catchments. This results in peat stratigraphies intercalated with mineral layers and affects C accumulation by triggering vegetation changes. (2) High and constant water tables favor C accumulation. Seasonal water level fluctuations are higher in wet and dry puna, in comparison with páramo, leading to more frequent episodes of C loss in puna. (3) Higher temperatures favor C gain under high and constant water availability but also increase C loss under low and fluctuating water levels. (4) C accumulation has been variable through the Holocene, but several peatlands show a recent increase in C accumulation rates. (5) Vegetation affects C dynamics through species-specific differences in productivity and decomposition rate. Because of predicted regional differences in global climate change manifestations (seasonality, permafrost behavior, temperature, precipitation regimes), cushion peatlands from the páramo are expected to mostly continue as C sinks for now, whereas those of the dry puna are more likely to turn to C sources as a consequence of increasing aridification.

Because of the first observations in the 1900s of the oligotrophic and eutrophic states of lakes, researchers have been interested in the process that makes lakes become turbid because of high phytoplankton biomass. Definitions of eutrophication have multiplied and diversified since the mid-20th century, more than for any other ecological process. Reasons for the high number of definitions might be that the former ones did not sufficiently describe their causes and/or consequences. Global change is bringing eutrophication more into the spotlight than ever, highlighting the need to find consensus on a common definition, or at least to explain and clarify why there are different meanings of the term eutrophication. To find common patterns, we analyzed 138 definitions that were classified by a multiple correspondence factor analysis (MCA) into three groups. The first group contains the most generic scientific definitions but many of these limit the causes to increased nutrient availability. A single definition takes into account all causes but would require additional work to clarify the process itself. Nutrient pollution, which is by far the primary cause of eutrophication in the Anthropocene, has generated a second group of environmental definitions that often specify the primary producers involved. Those definitions often mention the iconic consequences of nutrient pollution, such as increased algal biomass, anoxia/hypoxia and reduced biodiversity. The third group contains operational definitions, focusing on the consequences of nutrient pollution, for ecosystem services and therefore associated with ecosystem management issues. This group contains definitions related to regulations, mainly US laws and European directives. These numerous definitions, directly derived from the problem of nutrient pollution, have enlarged the landscape of definitions, and reflect the need to warn, legislate and implement a solution to remedy it. Satisfying this demand should not be confused with scientific research on eutrophication and must be based on communicating knowledge to as many people as possible using the simplest possible vocabulary. We propose that operational definitions (groups 2 and 3) should name the process “nutrient pollution,” making it possible to refine (scientific) definitions of eutrophication and to expand on other challenges such as climate warming, overfishing, and other nonnutrient-related chemical pollutions.

Climate-driven alterations to disturbance regimes are increasingly disrupting patterns of recovery in many biomes. Here, we examine the impact of disturbance and subsequent level of recovery in live hard coral cover on the Great Barrier Reef (GBR) across the last three decades. We demonstrate that a preexisting pattern of infrequent disturbances of limited spatial extent has changed to larger and more frequent disturbances, dominated by marine heatwaves and severe tropical cyclones. We detected an increase in the impact (measured as coral loss) across 265 individual disturbance impacts on 131 reefs in a 36-year dataset (1985–2022). Additionally, the number of survey reefs impacted by disturbance has increased each decade from 6% in the 1980s to 44% in the 2010s, as has the frequency of mass coral bleaching across the GBR, which has increased between 19% and 28% per year, and cyclones (3%–5% per year), resulting in less time for recovery. Of the 265 disturbance impacts we recorded, complete recovery to the highest levels of coral cover recorded earlier in this study (the “historical benchmark”) occurred only 62 (23%) times. Of the 23% of disturbance impacts that resulted in complete recovery to historical benchmarks, 34/62 recovered to their benchmark in 2021 or 2022. Complete recovery was more likely when the historical benchmark was <25% live hard coral cover. The lack of recovery was attributed to recovery time windows becoming shorter due to increases in the frequency of cyclones and of thermal stress events that result in mass coral bleaching episodes. These results confirm that climate change is contributing to ecosystem-wide changes in the ability of coral reefs to recover.