Climatic Window Research Articles

A 60–50 ka African Humid Period modulated by stadial Heinrich events HE6 and HE5a in northwestern Africa

A Late Pleistocene lacustrine sedimentary succession has recently been discovered and investigated in Northwest Africa (Morocco, Anti-Atlas, Agadir-Tissint Feija). By integrating new radiometric 230Th/U and OSL ages and new clay mineral analyses with previous sedimentological evidence, we significantly refine the origin and the timing of this succession and its significance for African paleoenvironments and paleoclimate. The sedimentary succession reflects the evolution of a paleolake, referred to as paleolake Tissint, that indicates the abrupt establishment of a wet period at ∼60 ka and a gradual return to drier conditions at ∼50 ka. Establishment of this paleolake coincides with a peak of precession-forced high summer insolation centered around ∼60 ka suggesting that orbital parameters triggered humid conditions in northwest Africa during this time interval. Comparing this observation with others from the literature, it appears that continental-scale wet conditions prevailed across North, Central and East Africa at that time and add evidence in support of a 60–50 ka African Humid Period (AHP). Given that the Holocene African Humid Period was associated with “Green Sahara” conditions, wet conditions between 60 and 50 ka likely sustained coeval greening, at least partially, of the Sahara region. In northwest Africa, the 60–50 ka AHP is affected by Heinrich Event HE6 which via adjustment of the Atlantic Meridional Ocean Circulation (AMOC) seems to have delayed the onset of this AHP. In a similar way, the younger Heinrich Event 5a resulted in short-term regional aridification about 55 ka ago that briefly interrupted the generally wetter period. Finally, as the AHP between ∼60 ka and ∼ 50 ka coincides with a major Human dispersal out of Africa; these particular conditions may have offered a climatic window of opportunity for Homo sapiens to open migration routes across Africa towards the Levant.

Biological diversification linked to environmental stabilization following the Sturtian Snowball glaciation.

The body fossil and biomarker records hint at an increase in biotic complexity between the two Cryogenian Snowball Earth episodes (ca. 661 million to ≤650 million years ago). Oxygen and nutrient availability can promote biotic complexity, but nutrient (particularly phosphorus) and redox dynamics across this interval remain poorly understood. Here, we present high-resolution paleoredox and phosphorus phase association data from multiple globally distributed drill core records through the non-glacial interval. These data are first correlated regionally by litho- and chemostratigraphy, and then calibrated within a series of global chronostratigraphic frameworks. The combined data show that regional differences in postglacial redox stabilization were partly controlled by the intensity of phosphorus recycling from marine sediments. The apparent increase in biotic complexity followed a global transition to more stable and less reducing conditions in shallow to mid-depth marine environments and occurred within a tolerable climatic window during progressive cooling after post-Snowball super-greenhouse conditions.

Global Geodynamic Control on Phanerozoic Marine Carbonates Sedimentary Systems

AbstractThis pilot study is founded on an exhaustive investigation of representative and well-documented cases (120) of carbonate systems during the Phanerozoic. We investigated the coupling between geodynamic settings and geometry, physiography, and stratigraphic architecture of carbonate platforms. The objective is to identify and quantify the impact of geodynamic controls on carbonate platforms and possible global trends during the Phanerozoic. Carbonate platforms are characterized in terms of geometry, stratigraphic architecture, time duration, preservation rate, progradation and rates of progradation, platform type, and thickness. Geodynamic parameters are characterized in terms of basin physiography, basement depth and type, tectonic setting, and subsidence origin. Relationships between carbonate parameters and geodynamic characteristics are investigated, leading to nine models of Geodynamic Carbonate Platforms. Passive margin is the most favorable geodynamic setting for the development of carbonate platforms in three dimensions. The continental crust hosts most of the carbonate platforms independently of time and geodynamic settings. Carbonate platforms developed above the exhumed mantle or oceanic crust (volcano) are the exception or very small and isolated. Global trends during the Phanerozoic of carbonate platform lateral extend, progradation, or thickness are tentatively interpreted in relation to geodynamic and eustatic parameters. The concept of spatial intersection between geodynamic and climatic windows favorable to carbonate platforms is introduced with its possible retroaction to the global carbon cycle.

Reef island evolution in a turbid‐water coral reef province of the Indo‐Pacific

AbstractCoral reef islands are vulnerable landforms to environmental change. Constructed of largely unconsolidated reef‐derived sediments, they are highly sensitive to variations in metocean boundary conditions, raising global concern about their future resilience and stability in the face of increased natural hazards, sea‐level rise and anthropogenic climate change. This study examines the evolution of an inshore turbid reef island from the southern Pilbara region of Western Australia (Indo‐Pacific) using detailed analyses of island chronostratigraphy (composition, texture) and geochronology (21 in‐situ radiometric dates) from Eva Island. Downcore, composition of island‐grade (reef‐derived) sediments were homogenous, dominated by molluscan (37%–42%) and coral (32%–37%) constituents. The 14C radiometric dating of island sediments, beachrock and coral microatolls identified five stages of island formation across changing sea‐level regimes over the mid to late Holocene: (1) limestone platform accretion at ca 6,000 cal yr BP, coinciding with reef decline or ‘give‐up’ on neighbouring Exmouth Gulf reefs; (2) sand cay (i.e. core) initiation and vertical aggregation at ca 5,000 cal yr BP during the point of sea‐level regression to current levels; (3) major accretion and lateral progradation of the island between 3,500 cal yr BP and 2,500 cal yr BP including the modification of island shorelines through alongshore reworking of sediment; (4) lateral accretion and minor expansion to the north and formation of beachrock pavement between 2,500 and 650 cal yr BP; and (5) planform adjustment (erosion of the north‐west island) and backstepping under stabilised sea levels over the past 650 years. While this model is comparative to studies on island formation following incremental sea‐level fall following the mid‐Holocene highstand, it demonstrates active landform readjustment under stabilised sea levels over the past 2,000 years, probably the influence of local‐scale metocean boundary conditions within climate windows across the mid to late Holocene period (i.e. independent of sea‐level fluctuations). Importantly, while sediment production rates are predicted to be lower in turbid‐water reef systems than clear water, Eva Island shows no change in carbonate producers (i.e. proportion of mollusc and coral) over the course of island building, indicating the carbonate factory has not experienced significant adjustments in reef ecology, but has remained stable despite low water quality.

Revisiting the agro-climatic zones of Ghana: A re-classification in conformity with climate change and variability

The Ghana Meteorological Agency delineated Ghana’s geographical space into four agro-climatic zones namely the north, transition, forest and coastal zones. Since the demarcation in the 1960s, previous studies have rarely provided a more dis-aggregated agro-climatic zone map in tandem with contemporary climate change and variability. The continued use of this age-old classified zones is a disservice to the public. In this study, therefore, we evaluated the existing agro-climatic zone map of Ghana and reconstructed it to a more appropriate and dis-aggregated map that reflect current climate change and variability impact. This was achieved by quantifying the contrast in rainfall and temperature amount over a 30 year period for different climate windows and mapped out areas with similar rainfall and temperature regimes. Our findings revealed significant changes in the existing agro-climatic zones especially in terms of number, the boundary size and geographical orientation of the zones. The newly proposed map consist of five distinctive climate zones namely: the Sudan Savannah, Guinea Savannah, Transition, Forest and Coastal zones. The Sudan and Guinea Savannah zones showed a southerly expansion. The transition zone shriveled in size as the Guinea Savannah zone took over most of it, notably in the southeast. The forest zone shrank in size with a northwest shift while the coastal belt grew to encompass the whole coast of Ghana. These changes are strong evidence of climate change and possible food production changes. These findings are useful to agriculture sector in planning their activities, the health sector in predicting specific diseases caused by changes in weather and climate, Ghana Meteorological Agency for weather forecasting purposes, and the National Disaster Management in identifying disaster prone zones.

Reparation ecology and climate risk in Latin-America: Experiences from four countries

IPCC's Sixth Assessment is a landmark in recognizing social justice and local knowledge as imperative for successful climate adaptation; however, taking this new scientific consensus seriously has profound implications. While narratives of fossil fuel companies and closing climate windows often dominate climate politics, there is an urgent need for new thinking frames, especially given that everyday adaptations by the most vulnerable are often hindered by incumbent actors at more local scales. In response, this paper tackles the issue of climate risk and human wellbeing in Latin America from an emerging and innovative perspective: reparation ecology. Reparation is a heuristic category by means of which we systematize converging evidence about the responses of local Latin-American communities to severe socio-environmental crises that are closely connected to climate risks and to long-lasting threats to the wellbeing of human societies and ecosystems. The results focus on a comparative analysis of five case studies on nature-based urban adaptation in two low-income settlements in Brazil; local ecological governance led by actors from the organized civil society in Colombia; agroecological and just innovative food production systems in Ecuador and sustainable urban-rural food markets in Guatemala. Assuming the complexity of climate change from a culturally and geographically located perspective, the paper unveils the non-doomed, ecologically reparative character of these initiatives. It therefore contributes to the recent turn in the debate on climate risk, claiming that diverse groups of people and communities around the world are contributing to radical change, tuning their behaviors and social arrangements in what an emerging scholarship defines as reparation ecology.

Climate windows of opportunity for plant expansion during the Phanerozoic

Earth’s long-term climate may have profoundly influenced plant evolution. Local climatic factors, including water availability, light, and temperature, play a key role in plant physiology and growth, and have fluctuated substantially over geological time. However, the impact of these key climate variables on global plant biomass across the Phanerozoic has not yet been established. Linking climate and dynamic vegetation modelling, we identify two key ‘windows of opportunity’ during the Ordovician and Jurassic-Paleogene capable of supporting dramatic expansions of potential plant biomass. These conditions are driven by continental dispersion, paleolatitude of continental area and a lack of glaciation, allowing for an intense hydrological cycle and greater water availability. These windows coincide with the initial expansion of land plants and the later angiosperm radiation. Our findings suggest that the timing and expansion of habitable space for plants played an important role in plant evolution and diversification.

Plasticity in female timing may explain earlier breeding in a North American songbird.

Many species have shifted their breeding phenology in response to climate change. Identifying the magnitude of phenological shifts and whether climate-mediated selection drives these shifts is key for determining species' resilience to climate change. Birds are a strong model for studying phenological shifts due to numerous long-term research studies; however, generalities pertaining to drivers of phenological shifts will emerge only as we add study species that differ in life history and geography. We investigated 32 years of reproductive timing in a non-migratory population of dark-eyed juncos Junco hyemalis. We predicted that plasticity in reproductive timing would allow females to breed earlier in warmer springs. We also predicted that selection would favour earlier breeding and asked whether the temperatures throughout the breeding season would predict the strength of selection. To test these predictions, we examined temporal changes in the annual median date for reproductive onset (i.e. first egg date) and we used a sliding window analysis to identify spring temperatures driving these patterns. Next, we explored plasticity in reproductive timing and asked whether selection favoured earlier breeding. Lastly, we used a sliding window analysis to identify the time during the breeding season that temperature was most associated with selection favouring earlier breeding. First egg dates occurred earlier over time and strongly covaried with April temperatures. Furthermore, individual females that bred in at least3 years typically bred earlier in warmer Aprils, exhibiting plastic responses to April temperature. We also found significant overall selection favouring earlier breeding (i.e. higher relative fitness with earlier first egg dates) and variation in selection for earlier breeding over time. However, temperature across diverse climatic windows did not predict the strength of selection. Our findings provide further evidence for the role of phenotypic plasticity in shifting phenology in response to earlier springs. We also provide evidence for the role of selection favouring earlier breeding, regardless of temperature, thus setting the stage for adaptive changes in female breeding phenology. We suggest for multi-brooded birds that advancing first egg dates likely increase the length of the breeding season, and therefore, reproductive success.

Nonlinear spatial and temporal decomposition provides insight for climate change effects on sub-Arctic herbivore populations

Global temperatures are increasing, affecting timing and availability of vegetation along with relationships between plants and their consumers. We examined the effect of population density, herd body condition in the previous year, elevation, plant productivity and phenology, snow, and winter onset on juvenile body mass in 63 semi-domesticated populations of Rangifer tarandus throughout Norway using spatiotemporal generalized additive models (GAMs) and varying coefficient models (VCMs). Optimal climate windows were calculated at both the regional and national level using a novel nonlinear climate window algorithm optimized for prediction. Spatial and temporal variation in effects of population and environmental predictors were considered using a model including covariates decomposed into spatial, temporal, and residual components. The performance of this decomposed model was compared to spatiotemporal GAMs and VCMs. The decomposed model provided the best fit and lowest prediction errors. A positive effect of herd body condition in the previous year explained most of the deviance in calf body mass, followed by a more complex effect of population density. A negative effect of timing of spring and positive effect of winter onset on juvenile body mass suggested that a snow free season was positive for juvenile body mass growth. Our findings suggest early spring onset and later winter permanent snow cover as reinforcers of early-life conditions which support more robust reindeer populations. Our methodological improvements for climate window analyses and effect size measures for decomposed variables provide important contributions to account for, measure, and interpret nonlinear relationships between climate and animal populations at large scales.

Climatic windows for human migration out of Africa in the past 300,000 years

Whilst an African origin of modern humans is well established, the timings and routes of their expansions into Eurasia are the subject of heated debate, due to the scarcity of fossils and the lack of suitably old ancient DNA. Here, we use high-resolution palaeoclimate reconstructions to estimate how difficult it would have been for humans in terms of rainfall availability to leave the African continent in the past 300k years. We then combine these results with an anthropologically and ecologically motivated estimate of the minimum level of rainfall required by hunter-gatherers to survive, allowing us to reconstruct when, and along which geographic paths, expansions out of Africa would have been climatically feasible. The estimated timings and routes of potential contact with Eurasia are compatible with archaeological and genetic evidence of human expansions out of Africa, highlighting the key role of palaeoclimate variability for modern human dispersals.

Climate windows of intra-annual growth and post-drought recovery in Mediterranean trees

Forests store large amounts of carbon as wood, but this storage potential depends on seasonal radial growth and how it is driven by climate. Therefore, we need a better understanding on how intra-annual radial increment rates determine growth responses to climate variability. There is a large gap of knowledge on the climate windows, i.e. the effective climatic time-window for tree growth, and predictors of intra-annual growth, particularly in seasonally dry biomes such as Mediterranean forests where growth may show several seasonal peaks. We described the radial increment rates of five tree species inhabiting mesic (Quercus ilex, Quercus faginea, Arbutus unedo) and xeric (Pinus halepensis, Juniperus thurifera) sites using dendrometers. Then, we related those rates and tree-ring width to climate data using correlations and model selection. All species presented bimodal patterns of radial increment rates with a major peak in spring and a minor peak in autumn, being this pattern most marked in Q. ilex, A. unedo and J. thurifera. Differences in climate-rates relationships were greater between species than between sites. Wet and cool conditions in winter and spring increased spring rates, but the climatic time-windows were longer in some species (Q. ilex, J. thurifera) and shorter in others (Q. faginea, P. halepensis). Similarly, wet and cool conditions also enhanced autumn rates in the xeric site, but warm conditions did it in the mesic site. Rainy autumn conditions reduced A. unedo rates. Climate-growth associations at intra- and inter-annual scales were consistent in species showing long intra-annual climatic time-windows such as Q. ilex. Our findings confirm the importance of wet winters and cool springs for radial growth in some species, and the relevance of autumn growth in A. unedo. Similar studies on intra-annual radial increment rates and climatic time-windows of forest growth and productivity can reveal which will be the species most impacted by drought.

Effect of Projected Land Use and Climate Change on Water Quality of Old Woman Creek Watershed, Ohio

The separate and synergistic effects of land use and climate change on water quality variables in Old Woman Creek (OWC) watershed were evaluated using a hydrological model set up in Soil and Water Assessment Tool (SWAT) for the OWC watershed. Model calibration was done using a multi-objective evolutionary algorithm and pareto optimization. The Parameter-Elevation Regressions on Independent Slopes Model (PRISM) climate data and the 20 different Global Circulation Models (GCMs) developed by the Coupled Model Intercomparison Project Phase five (CMIP5) were used. Validation was done using the streamflow data from USGS gaging station and water quality data from the water quality lab, Heidelberg University. The simulation was divided into two land use scenarios: Scenario 1 for constant land use and Scenario 2 where land use was varied. Both land use simulations were run in four time periods to account for climate change: historical (1985–2014), current to near future (2018–2045), mid-century (2046–2075), and late-century (2076–2100) climate windows. For the historical period, the average of all the simulations made from the 20 different CMIP5 GCMs shows good agreement with the PRISM results for flow and the water quality variables of interest with smaller inter-model variability compared to PRISM results. For the other three climate windows, the results of Scenario 1 show an increase in flow and eight water quality variables (sediment (total suspended sediment), organic nitrogen, organic phosphorus (particulate p), mineral phosphorus (soluble reactive p), chlorophyll a, carbonaceous biochemical oxygen demand (CBOD), dissolved oxygen, total nitrogen) across the climate windows but a slight decrease in one water quality variable, mineral phosphorus in the mid-century. The results of Scenario 2 show a greater increase in flow, and the eight water quality variables across the climate windows show a relatively larger decrease in one water quality variable (mineral phosphorus). The projected land use change has little impact compared to the projected climate change on OWC watershed in the 21st century.

Impact of Seasonal Variation in Climate on Water Quality of Old Woman Creek Watershed Ohio Using SWAT

The effect of the projected 21st century climate change on water quality in Old Woman Creek (OWC) watershed was evaluated using the Soil and Water Assessment Tool (SWAT) and the precipitation and temperature projections from three best Global Climate Circulation Model (GCM)l ensemble downloaded from the Coupled Model Intercomparison Project Phase 5 (CMIP5). These three best GCMs (GFDL-ESM2M, MPI-ESM-MR, EC-EARTH) were identified as those closest to the multivariate ensemble average of twenty different GCM-driven SWAT simulations. Seasonal analysis was undertaken in historical (1985–2014), current to near future (2018–2045), mid-century (2046–2075), and late-century (2076–2100) climate windows. The hydrological model calibration was carried out using a multi-objective evolutionary algorithm and pareto optimization. Simulations were made for stream flow and nine water quality variables (sediment, organic nitrogen, organic phosphorus, mineral phosphorus, chlorophyll a, carbonaceous biochemical oxygen demand, dissolved oxygen, total nitrogen, and total phosphorus) of interest. The average of twenty different CMIP5-driven SWAT simulation results showed good correlation for all the 10 variables with the PRISM-driven SWAT simulation results in the historical climate window (1985–2014). For the historical period, the result shows an over-estimation of flow, sediment, and organic nitrogen from January to March in simulations with CMIP5 inputs, relative to simulations with PRISM input. For the other climate windows, the simulation results show a progressive increase in stream flow with peak flow month shifting from April to March. The expected seasonal changes in each water quality variable have implications for the OWC estuary and Lake Erie water quality.

Phenological tracking of a seasonal climate window in a recovering tropical island bird species

Constraints on evolutionary adaptation and range shifts mean that phenotypic plasticity, which includes physiological, developmental or behavioural responses to environmental conditions, could be an important mode of adaptation to a changing climate for many species with small insular populations. While there is evidence to suggest adaptive plasticity to climate in some island populations, little is known about this capacity in species that have experienced a severe population bottleneck. In a changing climate, plasticity in the timing of life-history events, such as in breeding phenology, is adaptive if timing is optimised in seasonal environments, although these processes are poorly understood for tropical species. Here, we quantify the effects of climate on the breeding phenology and success of the Mauritius kestrel (Falco punctatus), a tropical raptor whose extinction has been averted by conservation management. We show that the timing of egg-laying is advancing in response to warming, at rates similar to temperate bird populations. Individual females show plasticity to temperature, although there is limited variation among individual responses. We show that advances in breeding phenology are likely to be adaptive, as they track changes in a seasonal climate window of favourable conditions, defined by late winter-early spring temperatures and the onset of the summer rainy season. Our results provide a rare example of a small and bottlenecked insular population that has adjusted to recent climate change through phenotypic plasticity. Furthermore, seasonal climate windows and their dynamics may be widespread mechanisms through which tropical species are impacted by and respond to climate change.

Relating Climate, Drought and Radial Growth in Broadleaf Mediterranean Tree and Shrub Species: A New Approach to Quantify Climate-Growth Relationships

The quantification of climate–growth relationships is a fundamental step in tree-ring sciences. This allows the assessment of functional responses to climate warming, particularly in biodiversity and climate-change hotspots including the Mediterranean Basin. In this region, broadleaf tree and shrub species of pre-Mediterranean, subtropical origin, have to withstand increased aridification trends. However, they have not been widely studied to assess their long-term growth responses to climate and drought. Since these species evolved under less seasonal and wetter conditions than strictly Mediterranean species, we hypothesized that their growth would mainly respond to higher precipitation and water availability from spring to early summer. Here, we quantified climate–growth relationships in five of these broadleaf species showing different leaf phenology and wood type (Pistacia terebinthus L., Pistacia lentiscus L., Arbutus unedo L., Celtis australis L., and Laurus nobilis L.) by using dendrochronology. We calculated Pearson correlations between crossdated, indexed, mean ring width series of each species (chronologies) and monthly climate variables (mean temperature, total precipitation). We also calculated correlations between the species’ chronologies and a drought index on 7-day scales. Lastly, we compared the correlation analyses with “climwin” analyses based on an information-theoretic approach and subjected to cross-validation and randomization tests. As expected, the growth of all species was enhanced in response to wet and cool conditions during spring and early summer. In some species (P. lentiscus, A. unedo, C. australis,) high prior-winter precipitation also enhanced growth. Growth of most species strongly responded to 9-month droughts and the correlations peaked from May to July, except in L. nobilis which showed moderate responses. The “climwin” analyses refined the correlation analyses by (i) showing the higher explanatory power of precipitation (30%) vs. temperature (7%) models, (ii) selecting the most influential climate windows with June as the median month, and (iii) providing significant support to the precipitation model in the case of P. terebinthus confirming that the radial growth of this species is a robust proxy of hydroclimate variability. We argue that “climwin” and similar frameworks based on information-theoretic approaches should be applied by dendroecologists to critically assess and quantify climate–growth relationships in woody plants with dendrochronological potential.

Soil organic carbon accumulation rates on Mediterranean abandoned agricultural lands

Secondary succession on abandoned agricultural lands can produce climate change mitigation co-benefits, such as soil carbon sequestration. However, the accumulation of soil organic carbon (SOC) in Mediterranean regions has been difficult to predict and is subject to multiple environmental and land management factors. Gains, losses, and no significant changes have all been reported. Here we compile chronosequence data (n = 113) from published studies and new field sites to assess the response of SOC to agricultural land abandonment in peninsular Spain. We found an overall SOC accumulation rate of +2.3% yr−1 post-abandonment. SOC dynamics are highly variable and context-dependent. Minimal change occurs on abandoned cereal croplands compared to abandoned woody croplands (+4% yr−1). Accumulation is most prevalent within a Goldilocks climatic window of ~13–17 °C and ~450–900 mm precipitation, promoting >100% gains after three decades. Our secondary forest field sites accrued 40.8 Mg C ha−1 (+172%) following abandonment and displayed greater SOC and N depth heterogeneity than natural forests demonstrating the long-lasting impact of agriculture. Although changes in regional climate and crop types abandoned will impact future carbon sequestration, abandonment remains a low-cost, long-term natural climate solution best incorporated in tandem with other multipurpose sustainable land management strategies.

A phenology-based approach to the analysis of conifers intra-annual xylem anatomy in water-limited environments

Xylem structure and cambial phenology (i.e. onset and cessation of cambial cell division) of conifers growing under severe water-limitations can change dramatically in relation to moisture availability. In hyperarid environments, analytical tools commonly used to investigate intra-annual variability of xylem anatomy (i.e. tracheidograms), may fail to capture the complexity of tree phenological responses to environmental conditions. This greatly limits our ability to accurately date the onset of intra-annual density variations, including the transition between earlywood and latewood. I present a new approach for developing phenological tracheidograms (“pheno-tracheidograms”) calibrated to account for the seasonal variations in cell division rates. Pheno-tracheidograms were developed for a population of Pinus ponderosa in the Mojave Desert (Nevada, USA) during the period 2015–2016 in order 1) to determine the onset date of latewood formation and 2) to investigate relationships between environmental conditions, lumen diameter, and cell wall thickness targeting specific climatic windows for each tracheid. Pheno-tracheidograms were standardized at the tree-level, showing more flexibility compared to tracheidograms standardized according to a pre-determined number of cells. By displaying cellular parameters with respect to the date of formation of the tracheid to which each measurement is associated, pheno-tracheidograms allowed to determine the beginning of latewood formation with daily resolution. Lumen diameter was significantly correlated with the onset date of cellular enlargement, while cell wall thickness showed a weaker relationship with the beginning of secondary wall deposition. Soil moisture positively affected the duration of cell enlargement and tracheid lumen diameter, particularly in the earlywood, while cell wall thickness was not significantly influenced by environmental conditions. Pheno-tracheidograms represent an empirical, yet effective way to date intra-annual xylem structures and to investigate high-resolution climate-anatomy relationships in conifer species from arid environments characterized by high phenological plasticity.

Environmental niche adaptation revealed through fine scale phenological niche modelling

AbstractAimPhenology, the temporal response of a population to its climate, is a crucial behavioural trait shared across life on earth. How species adapt their phenologies to climate change is poorly understood but critical in understanding how species will respond to future change. We use a group of flies (Rhaphiomidas) endemic to the North American deserts to understand how species adapt to changing climatic conditions. Here, we explore a novel approach for taxa with constrained phenologies aimed to accurately model their environmental niche and relate this to phenological and morphological adaptations in a phylogenetic context.TaxonInsecta, Diptera, Mydidae, Rhaphiomidas.LocationNorth America, Mojave, Sonoran and Chihuahuan Deserts.MethodsWe gathered geographical and phenological occurrence data for the entire genus Rhaphiomidas, and, estimated a time calibrated phylogeny. We compared Daymet derived temperature values for a species adult occurrence period (phenology) with those derived from WorldClim data that is partitioned by month or quarter to examine what effect using more precise data has on capturing a species’ environmental niche. We then examined to what extent phylogenetic signal in phenological traits, climate tolerance and morphology can inform us about how species adapt to different environmental regimes.ResultsWe found that the Bioclim temperature data, which are averages across monthly intervals, poorly represent the climate windows to which adult flies are actually adapted. Using temporally relevant climate data, we show that many species use a combination of morphological and phenological changes to adapt to different climate regimes. There are also instances where species changed only phenology to track a climate type or only morphology to adapt to different environments.Main ConclusionsWithout using a fine‐scale phenological data approach, identifying environmental adaptations could be misleading because the data do not represent the conditions the animals are actually experiencing. We find that fine‐scale phenological niche models are needed when assessing taxa that have a discrete phenological window that is key to their survival, accurately linking environment to morphology and phenology. Using this approach, we show that Rhaphiomidas use a combination of niche tracking and adaptation to persist in new niches. Modelling the effect of phenology on such species’ niches will be critical for better predictions of how these species might respond to future climate change.

Evidences of wider latewood in Pinus sylvestris from a forest-steppe of Southern Siberia

Climate affects wood formation with consequences for the functioning and survival of trees. Since tree-rings tissues (i.e., earlywood and latewood) are formed at different time in the season, the impact of climate change might differently affect their functions.In this study, we combine quantitative tracheid anatomy with the Vaganov-Shashkin growth model (VS-model) to investigate how summer drought affected the annual ring structure of Pinus sylvestris L. from a forest-steppe zone in Southern Siberia. In particular, we used climate-growth relationships over a 50-year period to identify the timing of climatic signal of early-, transition-, and late-wood tracheid’s diameters (DEW, DTW and DLW). Corresponding daily growth rates (Gr) obtained by the VS-model were applied to calculate the changes in the width of the relative tree-ring sectors considering different levels of aridity.Results indicate that tracheid size is sensitive to drought with temporal shifts among the climatic signal of DEW (in May), DTW (June) and DLW (July). A comparison of modeled daily-growth rate cumulated over the climatic window of each ring sector and grouped by years with different level of aridity, indicated that a release of summer drought mostly affected the widths of the transition (+28.1%) and (+48.6%) latewood sectors, thus matching observations performed on the same cores.These results suggest that current changes in climate seasonality, as occurring in the selected area, are positively impacting both the hydraulic efficiency (by increasing the diameter of the earlywood cells) and the latewood width of the wood produced in the area.

Water availability controls Pinus pinaster xylem growth and density: A multi-proxy approach along its environmental range

Deciphering climatic factors limiting cambial activity is critical to forecast the potential of trees to respond to ongoing climatic change. We explored multiple xylem traits, including tree-ring width, inter-annual microdensity variation and intra-annual density fluctuations (IADF), to unveil the climatic factors constraining cambial activity of a Mediterranean conifer (Pinus pinaster) along a continental-aridity gradient. Secondary growth responded mainly to water availability, explaining as much as 64.7% of earlywood growth variance for earlywood growth. The continuous and non-overlapping timing of the climatic signals of earlywood and latewood growth reflected a continuous water limitation of secondary growth along the growing season. Drought also had an extraordinary impact on minimum (Dmin) and maximum (Dmax) density, with maximal explained variances reaching 47.4% and 39.1%, respectively. Dmin was negatively associated to water availability during the initiation of earlywood formation, whereas Dmax responded positively to water availability during two distinct periods: previous winter and the initiation of latewood formation. IADFs in the latewood were quite common along the gradient, occurred in 21–51% of the rings, and responded to episodes of high rainfall and elevated temperature at different phases of latewood formation. Xylem traits identity outperformed site as a driver of climatic signal, revealing the potential of a multi-proxy approach to unveil multiple facets of the xylogenetic cycle. Cambial plasticity, i.e. the ability to adjust the xylogenesis rate and to arrest and resume cambial activity to exploit favorable climatic windows, was critical for Pinus pinaster to thrive within wide climatic envelopes. Nevertheless, the pervasive effect of water availability on all analyzed traits indicates that forthcoming reduced precipitation and increased evapotranspiration, as predicted by climate change models, will negatively impact P. pinaster secondary growth along its whole environmental range.