The role of fire in terrestrial vertebrate richness patterns

Productivity is strongly associated with terrestrial species richness patterns, although the mechanisms underpinning such patterns have long been debated. Despite considerable consumption of primary productivity by fire, its influence on global diversity has received relatively little study. Here we examine the sensitivity of terrestrial vertebrate biodiversity (amphibians, birds and mammals) to fire, while accounting for other drivers. We analyse global data on terrestrial vertebrate richness, net primary productivity, fire occurrence (fraction of productivity consumed) and additional influences unrelated to productivity (i.e., historical phylogenetic and area effects) on species richness. For birds, fire is associated with higher diversity, rivalling the effects of productivity on richness, and for mammals, fire's positive association with diversity is even stronger than productivity; for amphibians, in contrast, there are few clear associations. Our findings suggest an underappreciated role for fire in the generation of animal species richness and the conservation of global biodiversity.     

Back to the Future: The Responses of Alpine Treelines to Climate Warming are Constrained by the Current Ecotone Structure

Alpine treeline ecotones are considered early-warning monitors of the effects of climate change on terrestrial ecosystems, but it is still unclear how accurately treeline dynamics may track the expected temperature rises. Site-specific abiotic constraints, such as topography and demographic trends may make treelines less responsive to environmental fluctuations. A better understanding on how local processes modulate treelines’ response to warming is thus required. We developed a model of treeline dynamics based on individual data of growth, mortality and reproduction. Specifically, we modeled growth patterns, mortality rates and reproductive size thresholds as a function of temperature and stand structure to evaluate the influence of climate- and stand-related processes on treeline dynamics. In this study, we analyze the dynamics of four Pyrenean mountain pine treeline sites with contrasting stand structures, and subjected to differing rates of climate warming. Our models indicate that Pyrenean treelines could reach basal areas and reproductive potentials similar to those currently observed in high-elevation subalpine forest by the mid twenty-first century. The fastest paces of treeline densification are forecasted by the late twenty-first century and are associated with higher warming rates. We found a common densification response of Pyrenean treelines to climate warming, but contrasting paces arise due to current size structures. Treelines characterized by a multistratified stand structure and subjected to lower mean annual temperatures were the most responsive to climate warming. In monostratified stands, tree growth was less sensitive to temperature than in multistratified stands and trees reached their reproductive size threshold later. Therefore, our simulations highlight that stand structure is paramount in modulating treeline responsiveness to ongoing climate warming. Synthesis. Treeline densification over the twenty-first century is likely to occur at different rates contingent on current stand structure and its effects on individual-level tree growth responses to warming. Accurate projections of future treeline dynamics must thus incorporate site-specific factors other than climate, specifically those related to stand structure and its influence on tree growth.     

A targeted metabolomic procedure for amino acid analysis in different biological specimens by ultra-high-performance liquid chromatography–tandem mass spectrometry

Introduction

Amino acid analysis in biological fluids is essential for the study of inborn errors of metabolism (IEM) and other diseases.

Objectives

Our aim was to develop a UPLC-MS/MS procedure for the analysis of 25 amino acids and identification of 17 related compounds.

Methods

Sample treatment conditions were optimized for plasma, urine, cerebrospinal fluid (CSF) and dried blood spots. Amino acids and related compounds were analyzed on a Waters ACQUITY UPLC H-class instrument with a reversed-phase C-18 column using water and acetonitrile with 0.1% formic acid as the mobile phases (run time?=?9 min). The detection was performed with a Waters Xevo TQD triple-quadrupole mass spectrometer using positive electrospray ionization in the multiple reaction monitoring mode.

Results

The method linearity, intra-assay and inter-assay precision, detection limit, quantification limit and trueness analysis displayed adequate results in both physiological and pathological conditions. Method comparison was performed between UPLC-MS/MS and ion exchange chromatography (IEC) with ninhydrin derivatization, and the methods showed good agreement, except for 4-hydroxyproline, aspartate and citrulline. Paediatrics age-related reference values in plasma, urine and CSF were established and patients with different IEM were easily identified.

Conclusion

We report a modified UPLC-MS/MS procedure for the analysis of 42 amino acids and related compounds in different specimens. The method is fast, sensitive and robust, and it has been validated to be an alternative to the traditional IEC procedure as the routine method used in metabolic laboratories. The method greatly decreases the run time of the analysis while displaying good metrological results.

     

Incorporating Anthropogenic Influences into Fire Probability Models: Effects of Human Activity and Climate Change on Fire Activity in California

The costly interactions between humans and wildfires throughout California demonstrate the need to understand the relationships between them, especially in the face of a changing climate and expanding human communities. Although a number of statistical and process-based wildfire models exist for California, there is enormous uncertainty about the location and number of future fires, with previously published estimates of increases ranging from nine to fifty-three percent by the end of the century. Our goal is to assess the role of climate and anthropogenic influences on the state’s fire regimes from 1975 to 2050. We develop an empirical model that integrates estimates of biophysical indicators relevant to plant communities and anthropogenic influences at each forecast time step. Historically, we find that anthropogenic influences account for up to fifty percent of explanatory power in the model. We also find that the total area burned is likely to increase, with burned area expected to increase by 2.2 and 5.0 percent by 2050 under climatic bookends (PCM and GFDL climate models, respectively). Our two climate models show considerable agreement, but due to potential shifts in rainfall patterns, substantial uncertainty remains for the semiarid inland deserts and coastal areas of the south. Given the strength of human-related variables in some regions, however, it is clear that comprehensive projections of future fire activity should include both anthropogenic and biophysical influences. Previous findings of substantially increased numbers of fires and burned area for California may be tied to omitted variable bias from the exclusion of human influences. The omission of anthropogenic variables in our model would overstate the importance of climatic ones by at least 24%. As such, the failure to include anthropogenic effects in many models likely overstates the response of wildfire to climatic change.     

Species Climatic Suitability Explains Insect–Host Dynamics in the Southern Rocky Mountains,USA

Ecosystems - Recent extreme events of drought and heat have been associated with insect-driven tree mortality. However, there is substantial uncertainty about the impact of climate variability and...     

Seedling recruitment, survival and facilitation in alpine Pinus uncinata tree line ecotones. Implications and potential responses to climate warming

Aims Alpine tree line ecotones are harsh environments where low temperatures constrain tree regeneration and growth. However, the expected upward shift of tree line ecotones in response to climate warming has not been ubiquitous. The lack of coupling between tree line dynamics and climate warming might be explained by factors other than climate variation that determine seedling recruitment in these ecotones. We want to assess how the availability of suitable habitat for establishment and the effects of facilitation on seedling survival and growth affect tree recruitment within tree line ecotones and modulate their responses to climate. Location We evaluate the relevance of these factors for Pinus uncinata tree line ecotones in the Catalan Pyrenees (north‐east Spain) and Andorra. Methods We analysed the microhabitat of naturally established seedlings in rectangular plots at the tree line ecotone, assessing the habitat type and the proximity to potentially protective elements that may improve microsite conditions. We tested whether krummholz individuals influence regeneration at the tree line by performing a transplantation field experiment to evaluate the extent of facilitation on seedling survival and growth in height. A total of 820 seedlings were transplanted at different distances and orientations (resulting in 12 positions) from krummholz mats and monitored over 2 years. Results Safe sites for P. uncinata recruits consisted of sparse vegetation covering bare soil, gravel or litter, and close to protective elements that may ameliorate microsite conditions. The field experiment showed that directional positive interactions enhance seedling survival and growth, altering the spatial patterns of recruit survivorship, especially during harsh winter conditions (shallow and irregular snowpack). Main conclusions Our results suggest that scarce availability of safe sites and uneven facilitation by krummholz control seedling recruitment patterns within alpine tree line ecotones. Such constraints may distort or counter the response of tree line ecotones to climate warming at local and regional scales.     

Emergent freeze and fire disturbance dynamics in temperate rainforests

The coastal temperate rainforests of South and North America are part of the most biomass dense forest biome on the planet. They are also subject to rapid climatic shifts and, subsequently, new disturbance processes – snow loss‐driven mortality and the emergence of fire in historically non‐fire‐exposed areas. Here, we compare and contrast Southern and Northern Hemisphere coastal temperate rainforests of the Americas, two of the largest examples of the biome, via synthesis of current literature, future climate expectations and new downscaling of a global fire model. In terms of snow loss, a rapid decline in winter snow is leading to mass mortality of certain conifer species in the Northern Hemisphere rainforests. High‐elevation Southern Hemisphere forests, which are beginning to see similar declines in snow, may be vulnerable in the future, especially bogs and high‐water content soils. Southern Hemisphere forests are seeing the invasion of fire as an ecological force at mid‐to‐high latitudes, a shift not yet observed in the north but which may become more prominent with ongoing climate change. We suggest that research should focus on the flammability of seral vegetation and bogs under future climate scenarios in both regions. By comparing these two drivers of change across similar gradients in the Northern and Southern Hemispheres, this work points to the potential for emerging change in unexpected places in both regions. There is a clear benefit to conceptualising the coastal temperate rainforests of the Americas as two examples of the biome which can inform the other, as change is proceeding in similar directions but at different rates in each region.     

Current regeneration patterns at the tree line in the Pyrenees indicate similar recruitment processes irrespective of the past disturbance regime

Aim Impacts of global change, such as land‐use and climate changes, could produce significant alterations in the elevational patterns of alpine tree line ecotones and their adjacent vegetation zones. Because the responses of the tree line to environmental variations are directly related to successful tree regeneration, understanding recruitment dynamics is an indispensable step in tree line research. We aimed to compare potential ecological limitations on recent tree line regeneration in undisturbed and disturbed sites by analysing the demographic structure and spatiotemporal patterns of recruits and large trees. Location Alpine tree line ecotones comprising Pinus uncinata in the Catalan Pyrenees (north‐east Spain) and Andorra. Methods We assessed the demographic structure and spatial pattern of recent recruitment using techniques of point‐pattern and autocorrelation analyses. A total of 3639 P. uncinata individuals were mapped, measured and aged at 12 sites. To evaluate the effects of past disturbances on recent tree line response we compared tree lines that had either been recently affected by human‐induced disturbances or had remained undisturbed for many years. Results The age structure of the tree lines, together with the lack of an age gap between seedlings and saplings, did not indicate recent episodes of high seedling mortality and suggest that recruitment has been frequent under current climate conditions. Seedlings appeared highly aggregated at short distances (up to 3 m), irrespective of disturbance history, and were spatially segregated with respect to large trees. However, we found no evidence of patches of even‐aged seedlings, and our results suggest that dispersal events at intermediate distances (10–17 m) may be frequent. Autocorrelation analyses revealed different patterns of density and age of recruits between disturbed and undisturbed tree lines, but the strength and small‐scale clustering of seedlings and saplings were very similar between sites. Main conclusions We found no recruitment limitation on recent tree line dynamics in the Pyrenees. Furthermore, processes affecting tree recruitment seem to be similar among populations regardless of their past disturbance regime. Our results suggest that constraints on tree line dynamics causing differential responses between sites may operate on older life stages and not upon recruits, and that such constraints may be more contingent on local site conditions than on disturbance history.     

Disentangling the formation of contrasting tree-line physiognomies combining model selection and Bayesian parameterization for simulation models

Alpine tree-line ecotones are characterized by marked changes at small spatial scales that may result in a variety of physiognomies. A set of alternative individual-based models was tested with data from four contrasting Pinus uncinata ecotones in the central Spanish Pyrenees to reveal the minimal subset of processes required for tree-line formation. A Bayesian approach combined with Markov chain Monte Carlo methods was employed to obtain the posterior distribution of model parameters, allowing the use of model selection procedures. The main features of real tree lines emerged only in models considering nonlinear responses in individual rates of growth or mortality with respect to the altitudinal gradient. Variation in tree-line physiognomy reflected mainly changes in the relative importance of these nonlinear responses, while other processes, such as dispersal limitation and facilitation, played a secondary role. Different nonlinear responses also determined the presence or absence of krummholz, in agreement with recent findings highlighting a different response of diffuse and abrupt or krummholz tree lines to climate change. The method presented here can be widely applied in individual-based simulation models and will turn model selection and evaluation in this type of models into a more transparent, effective, and efficient exercise.