Editorial : Functional Traits as Indicators of Past Environmental Changes

This article is part of the Research Topic - Functional Traits as Indicators of Past Environmental ChangesInternational audienceEditorial on the Research Topic Functional Traits as Indicators of Past Environmental Changes. Paleoecology uses the biological remains in lake and bog sediments to reconstruct past environmental changes and to provide a valuable historical perspective on climatic and ecosystem changes occurring in the present day. Most paleoecological reconstructions are based on the analysis of the relative abundance of sub-fossils of plant and animal remains (e.g., testate amoebae, diatoms, fossil pollen), which are regarded as a proxy for past environmental conditions. Calibration data sets can be used to infer quantitative reconstructions of past environmental variables such as water-table depth, pH, and temperature. One emerging sub-discipline in paleoecology aims to reconstruct past functional diversity patterns of plants (e.g., using pollen and plant macro-remains) and other organisms (e.g., testate amoebae, diatoms, and chironomids) through a focus on functional traits. Such an approach has been argued to offer an alternative perspective from paleoecological archives, especially for understanding how past climate changes and human impacts influenced species' functional diversity and then ecosystem functions over long timescales.The papers in this Research Topic are based around the theme of using functional traits for better understanding past environmental changes from sediments. Across the fossil record, species may appear and disappear through environmental filtering, but certain traits might remain regardless of which species carries the trait (Lamentowicz et al., 2019). Thus, if the aim is to understand how current climate changes influence species and their functions over long-time scales, focusing on functional traits is of paramount importance for gaining insight. Such an approach will allow us to (1) build hypotheses for past and/or future patterns and processers based on different traits and (2) use the fossil record to test the strengths and weaknesses of different modeling approaches in predicting biodiversity patterns in response to current and future climate changes. The papers in this Research Topic demonstrate the potential breadth and scope of functional paleoecology, with contributions related to ecosystem ecology, forest management, peatland conservation, paleoclimatology, paleolimnology, and biogeography

Climate Sensitivity and Ecoclimate Sensitivity: Theory, Usage, and Past Implications for the Future Biospheric Responses

Two usages of ‘climate sensitivity’ co-exist: one climatological and one ecological. The earlier climatological usage quantifies the sensitivity of global mean surface temperature to atmospheric CO2, with formal variants differing by timescale and processes. The ecological usage, renamed here as ecoclimate sensitivity, is defined as a change in an ecological response variable per unit climate change. The two concepts are treated very differently: climatologists have focused on reducing uncertainty of global climate sensitivity estimates, while ecologists have focused on the multivariate processes governing variations in ecoclimate sensitivity across drivers, response variables, and scales. Because radiative forcing scales logarithmically to [CO2]atm, ecological impacts per ppm [CO2]atm often also scale logarithmically, although non-linear ecoclimate sensitivities can alter this expectation. Critically, past estimates of climate and ecoclimate sensitivity carry an implicit tradeoff, in which smaller estimates of climate sensitivity indicate higher ecoclimate sensitivities. For the LGM, estimates of equilibrium climate sensitivity have narrowed to 2.4 to 4.5 °C, while high ecoclimate sensitivity is indicated by post-glacial biome conversions, continental-scale species range shifts, and high community turnover. We introduce a new term, ecocarbon sensitivity, defined as the product of global climate sensitivity, local ecoclimate sensitivity, and a global-to-local climate scaling factor. Given past biospheric transformations, we can expect high sensitivity of the terrestrial biosphere to current rises in [CO2]atm, a conclusion that is insensitive to estimates of climate sensitivity. The next frontier is better quantification of the processes governing the form and variations of ecoclimate and ecocarbon sensitivity across systems and scales

The human–environment nexus and vegetation–rainfall sensitivity in tropical drylands

Global climate change is projected to lead to an increase in both the areal extent and degree of aridity in the world’s drylands. At the same time, the majority of drylands are located in developing countries where high population densities and rapid population growth place additional pressure on the ecosystem. Thus, drylands are particularly vulnerable to environmental changes and large-scale environmental degradation. However, little is known about the long-term functional response of vegetation to such changes induced by the interplay of complex human–environmental interactions. Here we use time series of satellite data to show how vegetation productivity in relation to water availability, which is a major aspect of vegetation functioning in tropical drylands, has changed over the past two decades. In total, one-third of tropical dryland ecosystems show significant (P < 0.05) changes in vegetation–rainfall sensitivity with pronounced differences between regions and continents. We identify population as the main driver of negative changes, especially for developing countries. This is contrasted by positive changes in vegetation–rainfall sensitivity in richer countries, probably resulting from favourable climatic conditions and/or caused by an intensification and expansion of human land management. Our results highlight geographic and economic differences in the relationship between vegetation–rainfall sensitivity and associated drivers in tropical drylands, marking an important step towards the identification, understanding and mitigation of potential negative effects from a changing world on ecosystems and human well-being

Global acceleration in rates of vegetation change over the past 18,000 years

Global vegetation over the past 18,000 years has been transformed first by the climate changes that accompanied the last deglaciation and again by increasing human pressures; however, the magnitude and patterns of rates of vegetation change are poorly understood globally. Using a compilation of 1181 fossil pollen sequences and newly developed statistical methods, we detect a worldwide acceleration in the rates of vegetation compositional change beginning between 4.6 and 2.9 thousand years ago that is globally unprecedented over the past 18,000 years in both magnitude and extent. Late Holocene rates of change equal or exceed the deglacial rates for all continents, which suggests that the scale of human effects on terrestrial ecosystems exceeds even the climate-driven transformations of the last deglaciation. The acceleration of biodiversity change demonstrated in ecological datasets from the past century began millennia ago

Global acceleration in rates of vegetation change over the past 18,000 years

Global vegetation over the past 18,000 years has been transformed first by the climate changes that accompanied the last deglaciation and again by increasing human pressures; however, the magnitude and patterns of rates of vegetation change are poorly understood globally. Using a compilation of 1181 fossil pollen sequences and newly developed statistical methods, we detect a worldwide acceleration in the rates of vegetation compositional change beginning between 4.6 and 2.9 thousand years ago that is globally unprecedented over the past 18,000 years in both magnitude and extent. Late Holocene rates of change equal or exceed the deglacial rates for all continents, which suggests that the scale of human effects on terrestrial ecosystems exceeds even the climate-driven transformations of the last deglaciation. The acceleration of biodiversity change demonstrated in ecological datasets from the past century began millennia ago

The importance and direction of current and future plant-UV research

International audienc

The importance and direction of current and future plant-UV research

International audienc

Approaches to defining a planetary boundary for biodiversity

The idea that there is an identifiable set of boundaries, beyond which anthropogenic change will put the Earth system outside a safe operating space for humanity, is attracting interest in the scientific community and gaining support in the environmental policy world. Rockstrom et al. (2009) identify nine such boundaries and highlight biodiversity loss as being the single boundary where current rates of extinction put the Earth system furthest outside the safe operating space. Here we review the evidence to support a boundary based on extinction rates and identify weaknesses with this metric and its bearing on humanity's needs. While changes to biodiversity are of undisputed importance, we show that both extinction rate and species richness are weak metrics for this purpose, and they do not scale well from local to regional or global levels. We develop alternative approaches to determine biodiversity loss boundaries and extend our analysis to consider large-scale responses in the Earth system that could affect its suitability for complex human societies which in turn are mediated by the biosphere. We suggest three facets of biodiversity on which a boundary could be based: the genetic library of life; functional type diversity; and biome condition and extent. For each of these we explore the science needed to indicate how it might be measured and how changes would affect human societies. In addition to these three facets, we show how biodiversity's role in supporting a safe operating space for humanity may lie primarily in its interactions with other boundaries, suggesting an immediate area of focus for scientists and policymakers