Landscape Partnership Resources Library
Global warmth with little extra co2
Most climate models consider only short-term processes such as cloud and sea-ice formation when assessing Earth’s sensitivity to greenhouse-gas forcing. Mounting evidence indicates that the response could be stronger if boundary conditions change drastically.
CO2 emissions from forest loss
Deforestation is the second largest anthropogenic source of carbon dioxide to the atmosphere, after fossil fuel combustion. Following a budget reanalysis, the contribution from deforestation is revised downwards, but tropical peatlands emerge as a notable carbon dioxide source.
Acceleration of global warming due to carbon-cycle feedbacks in a coupled climate model
The continued increase in the atmospheric concentration of carbon dioxide due to anthropogenic emissions is predicted to lead to significant changes in climate1. About half of the current emissions are being absorbed by the ocean and by land ecosystems2, but this absorption is sensitive to climate3,4 as well as to atmospheric carbon dioxide concentrations5, creating a feedback loop. General circulation models have generally excluded the feedback between climate and the biosphere, using static vegetation distributions and CO2 concentrations from simple carbon-cycle models that do not include climate change6. Here we present results from a fully coupled, three-dimensional carbon±climate model, indicating that carbon-cycle feedbacks could signi®cantly accelerate climate change over the twenty-®rst century. We ®nd that under a `business as usual' scenario, the terrestrial biosphere acts as an overall carbon sink until about 2050, but turns into a source thereafter. By 2100, the ocean uptake rate of 5 Gt C yr-1 is balanced by the terrestrial carbon source, and atmospheric CO2 concentrations are 250 p.p.m.v. higher in our fully coupled simulation than in uncoupled carbon models2, resulting in a global-mean warming of 5.5 K, as compared to 4 K without the carbon-cycle feedback.
vegetation controlled by tropical sea surface temperatures in the mid-Pleistocene period
The dominant forcing factors for past large-scale changes in vegetation are widely debated. Changes in the distribution of C4 plants—adapted to warm, dry conditions and low atmospheric CO2 concentrations1—have been attributed to marked changes in environmental conditions, but the relative impacts of changes in aridity, temperature2,3 and CO2 concentration4,5 are not well understood. Here, we present a record of African C4 plant abundance between 1.2 and 0.45 million years ago, derived from compound-specific carbon isotope analyses of wind-trans- ported terrigenous plant waxes. We find that large-scale changes in African vegetation are linked closely to sea surface temperatures in the tropical Atlantic Ocean. We conclude that, in the mid- Pleistocene, changes in atmospheric moisture content—driven by tropical sea surface temperature changes and the strength of the African monsoon—controlled aridity on the African continent, and hence large-scale vegetation changes.
Using (brain)temperature to analyse temporal dynamics in the songbird motor pathway
Here we address these issues by using temperature to manipulate the biophysical dynamics in different regions of the songbird forebrain involved in song production. We find that cooling the premotor nucleus HVC (formerly known as the high vocal centre) slows song speed across all timescales by up to 45 per cent but only slightly alters the acoustic structure, whereas cooling the downstream motor nucleus RA (robust nucleus of the arcopallium) has no observable effect on song timing. Our observations suggest that dynamics within HVC are involved in the control of song timing, perhaps through a chain-like organization. Local manipulation of brain temperature should be broadly applicable to the identification of neural circuitry that controls the timing of behavioural sequences and, more generally, to the study of the origin and role of oscillatory and other forms of brain dynamics in neural systems.
Strong effect of dispersal network structure on ecological dynamics
A central question in ecology with great importance for management, conservation and biological control is how changing connectivity affects the persistence and dynamics of interacting species. Researchers in many disciplines have used large systems of coupled oscillators to model the behaviour of a diverse array of fluctuating systems in nature1–4. In the well-studied regime of weak coupling, synchronization is favoured by increases in coupling strength and large-scale network structures (for example ‘small worlds’) that produce short cuts and clustering5–9. Here we show that, by contrast, randomizing the structure of dispersal networks in a model of predators and prey tends to favour asyn- chrony and prolonged transient dynamics, with resulting effects on the amplitudes of population fluctuations. Our results focus on synchronization and dynamics of clusters in models, and on time- scales, more appropriate for ecology, namely smaller systems with strong interactions outside the weak-coupling regime, rather than the better-studied cases of large, weakly coupled systems. In these smaller systems, the dynamics of transients and the effects of changes in connectivity can be well understood using a set of methods including numerical reconstructions of phase dynamics, examinations of cluster formation and the consideration of important aspects of cyclic dynamics, such as amplitude.
Snowball Earth termination by destabilization of equatorial permafrost methane clathrate
The start of the Ediacaran period is defined by one of the most severe climate change events recorded in Earth history—the recov- ery from the Marinoan ‘snowball’ ice age, ,635 Myr ago (ref. 1). Marinoan glacial-marine deposits occur at equatorial palaeolati- tudes2, and are sharply overlain by a thin interval of carbonate that preserves marine carbon and sulphur isotopic excursions of about 25 and 115 parts per thousand, respectively3–5; these deposits are thought to record widespread oceanic carbonate precipitation during postglacial sea level rise1,3,4. This abrupt transition records a climate system in profound disequilibrium3,6 and contrasts shar- ply with the cyclical stratigraphic signal imparted by the balanced feedbacks modulating Phanerozoic deglaciation. Hypotheses accounting for the abruptness of deglaciation include ice albedo feedback3, deep-ocean out-gassing during post-glacial oceanic overturn7 or methane hydrate destabilization8–10. Here we report the broadest range of oxygen isotope values yet measured in mar- ine sediments (225% to 112%) in methane seeps in Marinoan deglacial sediments underlying the cap carbonate. This range of values is likely to be the result of mixing between ice-sheet-derived meteoric waters and clathrate-derived fluids during the flushing and destabilization of a clathrate field by glacial meltwater. The equatorial palaeolatitude implies a highly volatile shelf permafrost pool that is an order of magnitude larger than that of the present day. A pool of this size could have provided a massive biogeochem- ical feedback capable of triggering deglaciation and accounting for the global postglacial marine carbon and sulphur isotopic excur- sions, abrupt unidirectional warming, cap carbonate deposition, and a marine oxygen crisis. Our findings suggest that methane released from low-latitude permafrost clathrates therefore acted as a trigger and/or strong positive feedback for deglaciation and warming. Methane hydrate destabilization is increasingly suspected as an important positive feedback to climate change11–13 that coincides with critical boundaries in the geological record14,15 and may represent one particularly important mechanism active during conditions of strong climate forcing.
A general integrative model for scaling plant growth, carbon flux, and functional trait spectra
Linking functional traits to plant growth is critical for scaling attributes of organisms to the dynamics of ecosystems (1,2) and for understanding how selection shapes integrated botanical phenotypes (3). However, a general mechanistic theory showing how traits specifically influence carbon and biomass flux within and across plants is needed. Building on foundational work on relative growth rate (4–6), recent work on functional trait spectra (7–9), and metabolic scaling theory (10,11), here we derive a generalized trait-based model of plant growth. In agreement with a wide variety of empirical data, our model uniquely predicts how key functional traits interact to regulate variation in relative growth rate, the allometric growth normalizations for both angiosperms and gymnosperms, and the quantitative form of several functional trait spectra relationships. The model also provides a general quantitative framework to incorporate additional leaf-level trait scaling relationships (7,8) and hence to unite functional trait spectra with theories of relative growth rate, and metabolic scaling. We apply the model to calculate carbon use efficiency. This often ignored trait, which may influence variation in relative growth rate, appears to vary directionally across geographic gradients. Together, our results show how both quantitative plant traits and the geometry of vascular transport networks can be merged into a common scaling theory. Our model provides a framework for predicting not only how traits covary within an integrated allometric phenotype but also how trait variation mechanistically influences plant growth and carbon flux within and across diverse ecosystems.
Earth system sensitivity inferred from Pliocene modelling and data
Here we use a coupled atmosphere–ocean general circulation model to simulate the climate of the mid-Pliocene warm period (about three million years ago), and analyse the forcings and feedbacks that contributed to the relatively warm temperatures. Furthermore, we compare our simulation with proxy records of mid-Pliocene sea surface temperature. Taking these lines of evidence together, we estimate that the response of the Earth system to elevated atmospheric carbon dioxide concentrations is 30–50% greater than the response based on those fast-adjusting components of the climate system that are used traditionally to estimate climate sensitivity. We conclude that targets for the long-term stabilization of atmospheric greenhouse gas concentrations aimed at preventing a dangerous human interference with the climate system should take into account this higher sensitivity of the Earth system.
First signs of carbon sink saturation in European forest biomass
European forests are seen as a clear example of vegetation rebound in the Northern Hemisphere; recovering in area and growing stock since the 1950s, after centuries of stock decline and deforestation. These regrowing forests have shown to be a persistent carbon sink, projected to continue for decades, however, there are early signs of saturation. Forest policies and management strategies need revision if we want to sustain the sink.
CARBON CYCLE : Fertilizing change
Carbon cycle–climate feedbacks are expected to diminish the size of the terrestrial carbon sink over the next century. Model simulations suggest that nitrogen availability is likely to play a key role in mediating this response.
Temperature Mediated Moose Survival in Northeastern Minnesota
The earth is in the midst of a pronounced warming trend and temperatures in Minnesota, USA, as elsewhere, are projected to increase. Northern Minnesota represents the southern edge to the circumpolar distribution of moose (Alces alces), a species intolerant of heat. Moose increase their metabolic rate to regulate their core body temperature as temperatures rise. We hypothesized that moose survival rates would be a function of the frequency and magnitude that ambient temperatures exceeded the upper critical temperature of moose. We compared annual and seasonal moose survival in northeastern Minnesota between 2002 and 2008 with a temperature metric. We found that models based on January temperatures above the critical threshold were inversely correlated with subsequent survival and explained .78% of variability in spring, fall, and annual survival. Models based on late-spring temperatures also explained a high proportion of survival during the subsequent fall. A model based on warm-season temperatures was important in explaining survival during the subsequent winter. Our analyses suggest that temperatures may have a cumulative influence on survival. We expect that continuation or acceleration of current climate trends will result in decreased survival, a decrease in moose density, and ultimately, a retreat of moose northward from their current distribution.
On the Hydrologic Adjustment of Climate-Model Projections: The Potential Pitfall of Potential Evapotranspiration
Hydrologic models often are applied to adjust projections of hydroclimatic change that come from climate models. Such adjustment includes climate-bias correction, spatial refinement (‘‘downscaling’’), and consideration of the roles of hydrologic processes that were neglected in the climate model. Described herein is a quantitative analysis of the effects of hydrologic adjustment on the projections of runoff change associated with projected twenty-first-century climate change. In a case study including three climate models and 10 river basins in the contiguous United States, the authors find that relative (i.e., fractional or percentage) runoff change computed with hydrologic adjustment more often than not was less positive (or, equivalently, more negative) than what was pro- jected by the climate models. The dominant contributor to this decrease in runoff was a ubiquitous change in runoff (median 211%) caused by the hydrologic model’s apparent amplification of the climate-model-implied growth in potential evapotranspiration. Analysis suggests that the hydrologic model, on the basis of the empirical, temperature-based modified Jensen–Haise formula, calculates a change in potential evapotranspiration that is typically 3 times the change implied by the climate models, which explicitly track surface energy budgets. In com- parison with the amplification of potential evapotranspiration, central tendencies of other contributions from hydrologic adjustment (spatial refinement, climate-bias adjustment, and process refinement) were relatively small. The authors’ findings highlight the need for caution when projecting changes in potential evapotranspiration for use in hydrologic models or drought indices to evaluate climate change impacts on water. KEYWORDS: Hydrologic model; Climate change; Potential evapotranspi- ration
Migration and Dispersal: Science Special Section
INTRODUCTION: When to Go, Where to Stop THE ABILITY TO MOVE, AT SOME STAGE IN THE LIFE CYCLE, IS FUNDAMENTAL TO SUCCESS in life. Passive drift in water columns conferred a selective advantage for early life, offering an escape from starvation and genetic uniformity. Since then, organisms have evolved many ways to disperse and migrate in response to the pressures of finding resources, escaping predators, seeking out mates and suitable breeding grounds, and distancing themselves from family. Dispersal in its broadest sense means movement away from the birthplace. Strictly speaking, migration involves travel in a periodically and geographically predictable way, whether it occurs just once or many times. In this issue, Science deals with what we know, what we need to know, and how we are going to find out more about both of these movement types. In plants, the spore, seed, or fruit is typically the unit of dispersal. Although the many morphological adaptations for their dispersal are known, until now, researchers have been unable to determine the distances traveled or the proportion of dispersal events that lead to seedlings. In one Perspective (p. 786), Nathan describes recent developments in the modeling and measurement of the long-distance dispersal of plants. A News story by Holden (p. 779) discusses the push to come up with a theoretical framework, not just for plants, but for all moving organisms. Organisms also disperse in reaction to changing habitats and climate. The Perspective by Kokko and López-Sepulcre (p. 789) discusses the selective forces affecting this ability in animals and how dispersal translates into range expansions and contractions. Kintisch (p. 776) describes the challenges for marine scientists assessing how climate change may affect oceangoing species. Humans have been great dispersers. Colonizing new habitat has been a hallmark of human ecology over the past million years or so. In a Review (p. 796), Mellars considers recent advances in archaeology and genetics that are illuminating the controversies over the routes taken by ancient peoples in the colonization of Asia 40,000 to 60,000 years ago. Two Perspectives consider migration: Holland et al. (p. 794) focus on migrating insects, which tend to travel in established geographical patterns across several generations rather than returning to their birthplace, and Alerstam (p. 791) discusses the accumulating and sometimes conflicting evidence about the navigational mechanisms used by animals (particularly birds) in long-distance annual migrations. In a related Report (p. 837), Muheim et al. describe the role of polarized light at dawn and sunset in calibrating the magnetic compasses of migrating birds. A News story by Morell (p. 783) describes a new model that will clarify the mix of genes and environmental responses underlying successful bird migration. As News stories by Blackburn and Holden (p. 780) and Unger (p. 784) point out, ingenuity and persistence are beginning to pay off in new techniques for following organisms, be they fish, crabs, jellyfish, rhinos, or polar bears. Thanks to these advances, the study of the ecology and evolution of movement is charging ahead and unearthing the challenges faced by organisms in dispersing and migrating in a world undergoing anthropogenic change.
Millennium Ecosystem Assessment: Research Needs
The research community needs to develop analytical tools for projecting future trends and evaluating the success of interventions as well as indicators to monitor biological, physical, and social changes.
Effects of grazing on grassland soil carbon: a global review
Soils of grasslands represent a large potential reservoir for storing CO2, but this potential likely depends on how grasslands are managed for large mammal grazing. Previous studies found both strong positive and negative grazing effects on soil organic carbon (SOC) but explanations for this variation are poorly developed. Expanding on previous reviews, we performed a multifactorial meta-analysis of grazer effects on SOC density on 47 independent experimen- tal contrasts from 17 studies. We explicitly tested hypotheses that grazer effects would shift from negative to positive with decreasing precipitation, increasing fineness of soil texture, transition from dominant grass species with C3 to C4 photosynthesis, and decreasing grazing intensity, after controlling for study duration and sampling depth. The six variables of soil texture, precipitation, grass type, grazing intensity, study duration, and sampling depth explained 85% of a large variation (`150 g m␣2 yr␣1) in grazing effects, and the best model included significant interactions between precipitation and soil texture (P = 0.002), grass type, and grazing intensity (P = 0.012), and study duration and soil sampling depth (P = 0.020). Specifically, an increase in mean annual precipitation of 600 mm resulted in a 24% decrease in grazer effect size on finer textured soils, while on sandy soils the same increase in precipitation pro- duced a 22% increase in grazer effect on SOC. Increasing grazing intensity increased SOC by 6–7% on C4-dominated and C4–C3 mixed grasslands, but decreased SOC by an average 18% in C3-dominated grasslands. We discovered these patterns despite a lack of studies in natural, wildlife-dominated ecosystems, and tropical grasslands. Our results, which suggest a future focus on why C3 vs. C4-dominated grasslands differ so strongly in their response of SOC to grazing, show that grazer effects on SOC are highly context-specific and imply that grazers in different regions might be managed differently to help mitigate greenhouse gas emissions. Keywords: carbon sequestration, grasslands, grazing, grazing intensity, precipitation, soil organic carbon, soil texture
Interactions between climate and habitat loss effects on biodiversity: a systematic review and meta-analysis
Climate change and habitat loss are both key threatening processes driving the global loss in biodiversity. Yet little is known about their synergistic effects on biological populations due to the complexity underlying both processes. If the combined effects of habitat loss and climate change are greater than the effects of each threat individually, current conservation management strategies may be inefficient and at worst ineffective. Therefore, there is a pressing need to identify whether interacting effects between climate change and habitat loss exist and, if so, quantify the magnitude of their impact. In this article, we present a meta-analysis of studies that quantify the effect of habitat loss on biologi- cal populations and examine whether the magnitude of these effects depends on current climatic conditions and his- torical rates of climate change. We examined 1319 papers on habitat loss and fragmentation, identified from the past 20 years, representing a range of taxa, landscapes, land-uses, geographic locations and climatic conditions. We find that current climate and climate change are important factors determining the negative effects of habitat loss on spe- cies density and/or diversity. The most important determinant of habitat loss and fragmentation effects, averaged across species and geographic regions, was current maximum temperature, with mean precipitation change over the last 100 years of secondary importance. Habitat loss and fragmentation effects were greatest in areas with high maxi- mum temperatures. Conversely, they were lowest in areas where average rainfall has increased over time. To our knowledge, this is the first study to conduct a global terrestrial analysis of existing data to quantify and test for inter- acting effects between current climate, climatic change and habitat loss on biological populations. Understanding the synergistic effects between climate change and other threatening processes has critical implications for our ability to support and incorporate climate change adaptation measures into policy development and management response. Keywords: climate change, habitat fragmentation, habitat loss, interactions, meta-analysis, mixed-effects logistic regression
Untangling the confusion around land carbon science and climate change mitigation policy
Depletion of ecosystem carbon stocks is a significant source of atmospheric CO2 and reducing land-based emissions and maintaining land carbon stocks contributes to climate change mitigation. We summarize current understanding about human perturbation of the global carbon cycle, examine three scientific issues and consider implications for the interpretation of international climate change policy decisions, concluding that considering carbon storage on land as a means to ‘offset’ CO2 emissions from burning fossil fuels (an idea with wide currency) is scientifically flawed. The capacity of terrestrial ecosystems to store carbon is finite and the current sequestration potential primarily reflects depletion due to past land use. Avoiding emissions from land carbon stocks and refilling depleted stocks reduces atmospheric CO2 concentration, but the maximum amount of this reduction is equivalent to only a small fraction of potential fossil fuel emissions.
Wildfire and forest harvest disturbances in the boreal forest leave different long-lasting spatial signatures
Natural disturbances leave long-term legacies that vary among landscapes and ecosystem types, and which become integral parts of successional pro- cesses at a given location. As humans change land use, not only are immediate post-disturbance patterns altered, but the processes of recovery themselves are likely altered by the disturbance. We assessed whether short-term effects on soil and vegetation that distinguish wildfire from forest harvest persist over 60 years after disturbance in boreal black spruce forests, or post-disturbance processes of recovery promote convergence of the two disturbance types.
Long term climate implications of 2050 emission reduction targets
A coupled atmosphere-ocean-carbon cycle model is used to examine the long term climate implications of various 2050 greenhouse gas emission reduction targets. All emission targets considered with less than 60% global reduction by 2050 break the 2.0°C threshold warming this century, a number that some have argued represents an upper bound on manageable climate warming. Even when emissions are stabilized at 90% below present levels at 2050, this 2.0°C threshold is eventually broken. Our results suggest that if a 2.0°C warming is to be avoided, direct CO2 capture from the air, together with subsequent sequestration, would eventually have to be introduced in addition to sustained 90% global carbon emissions reductions by 2050.
