Climatic Moisture Deficit Research Articles

Influence of microclimate and forest management on bat species faced with global change.

Climate refugia, areas where climate is expected to remain relatively stable, can offer a near-term safe haven for species sensitive to warming temperatures and drought. Understanding the influence of temperature, moisture, and disturbance on sensitive species is critical during this time of rapid climate change. Coastal habitats can serve as important refugia. Many of these areas consist of working forestlands, and there is a growing recognition that conservation efforts worldwide must consider the habitat value of working lands, in addition to protected areas, to effectively manage large landscapes that support biodiversity. The sensitivity of forest bats to climate and habitat disturbance makes them a useful indicator taxon. We tested how microclimate and forest management influence habitat use for 13 species of insectivorous bats in a large climate refugium in a global biodiversity hotspot. We examined whether bat activity during the summer dry season is greater in forests where coastal fog provides moisture and more stable temperatures across both protected mature stands and those regularly logged. Acoustic monitoring was conducted at a landscape scale with 20 study sites, and generalized linear mixed models were used to examine the influence of habitat variables. Six species were positively associated with warmer nighttime temperature, and 5 species had a negative relationship with humidity or a positive relationship with climatic moisture deficit. Our results suggest that these mammals may have greater climate adaptive capacity than expected, and, for now, that habitat use may be more related to optimal foraging conditions than to avoidance of warming temperatures and drought. We also determined that 12 of the 13 regionally present bat species were regularly detected in commercial timberland stands. Because forest bats are highly mobile, forage over long distances, and frequently change roosts, the stewardship of working forests must be addressed to protect these species.

Tree demographic and neighbourhood responses to regional environmental gradients of the northwestern United States

Abstract Studies of drivers shaping forest communities frequently include abiotic or biotic factors, while their interactive effects remain understudied. Here, we combined data on two prominent abiotic gradients, climatic moisture deficit and wildfire probability, along with tree functional neighbourhoods (i.e. trait differences of close neighbours) to assess variation in survival and growth of 56 tree species in the northwestern US. We asked two questions: (1) How does functional neighbourhood dissimilarity vary with environmental gradients? and (2) How do demographic rates of tree species in the northwestern United States vary with the interactive effects of environmental gradients and functional neighbourhood? We expected functional neighbourhoods to become more similar as environmental stress increased, due to a convergence of species towards an optimum stress tolerance strategy. We also predicted the interactive effects of abiotic and biotic factors on tree demography and high variation in species‐specific responses to these interactive effects due to divergent species life history strategies. Functional neighbourhoods defined by dissimilarities in stem conductivity, litter decomposition, resprouting ability and specific leaf area changed with climate, shifting to more diverse neighbourhoods as climatic moisture deficit and wildfire probability increased. Results supported interactive effects of the functional neighbourhood and climatic moisture deficit or wildfire probability on tree demography, but only when the identity of dominant species was considered. Species‐specific responses were highly variable in their direction and magnitude and often demonstrated opposing effects of climate and the functional neighbourhood and climatic moisture deficit on tree demography. Synthesis. Our findings show that climate and tree neighbourhood functional dissimilarity jointly impact tree demography; however, the effects are species‐specific. Results of this study highlight the need to consider the interactive effects of abiotic and biotic contexts and individual species responses to their environment to adequately understand tree persistence under current and future climate conditions.

Maximizing soil organic carbon stocks under cover cropping: insights from long-term agricultural experiments in North America

Cover crops are widely advocated for increasing soil organic carbon (SOC) levels, thereby benefiting soil health improvement and climate change mitigation. Few regional-scale studies have robustly explored SOC stocks under cover cropping, due to limited long-term experiments. We used the unique experimental data from the North American Project to Evaluate Soil Health Measurements conducted in 2019 to address this issue. This study included 19 agricultural research sites with 36 pairs of cover cropping established between 1896 and 2014. Explanatory variables related to site-specific environmental conditions and management practices were collected to identify and prioritize contributing factors that affect SOC stocks with cover crops, by coupling the Boruta algorithm and structural equation modeling. Overall, cover crops significantly (P < 0.05) improved several indicators of soil health, including greater SOC (concentration: +8%; stock: +7%), total nitrogen (+8%), water-stable aggregates (+15%), and potential carbon mineralization (+34%), on average, compared to no cover crop control. Likewise, on average, cover crops sequestered SOC 3.55 Mg C ha-1 (0–15 cm depth), with a sequestration rate of 0.24 Mg C ha-1 yr-1. In addition, we found climate (Hargreaves climatic moisture deficit) was important in explaining the variation of SOC stocks with cover crops, followed by soil properties (e.g., soil clay content). In terms of management practices, cover crop type had a significant positive (0.36) effect on SOC stocks, with non-legumes showing a greater impact, compared to legumes and mixtures. Crop rotational diversity also had a positive (0.28) effect on SOC accumulation. Our findings suggested that integrating non-legume cover crops into diverse crop rotation is likely to be a promising strategy to maximize SOC stocks with cover crops across North America.

Fire interval and post-fire climate effects on serotinous forest resilience

BackgroundClimate change is eroding forest resilience to disturbance directly through warming climate and indirectly through increasing disturbance activity. Forests characterized by stand-replacing fire regimes and dominated by serotinous species are at risk when the inter-fire period is insufficient for canopy seed bank development and climate conditions for recruitment in the post-fire growing season are unsuitable. Although both factors are critical to serotinous forest persistence, their relative importance for post-fire regeneration in serotinous forests remains poorly understood. To assess the relative effects of each factor, we established plots in severely burned knobcone pine (Pinus attenuata Lemmon) forests in Oregon and California, USA, representing a range of past fire intervals (6 to 31+ years). Specifically, we evaluated effects of fire interval and pre-fire canopy seed bank (proxies for seed supply) and post-fire climate on three metrics of post-fire tree regeneration (seedling density, probability of self-replacement, percent population recovery).ResultsSeed supply consistently had the strongest effect on post-fire regeneration. Between 6- and 31-year fire intervals, post-fire seedling density increased from 1000 to 100,000 seedlings ha−1, while probability of self-replacement increased from ~ 0 to ~ 100% and percent population recovery increased from 20 to 2000% of the pre-fire population, respectively. Similarly, increasing the canopy seed bank by two orders of magnitude increased seedling density and percent population recovery by two orders and one order of magnitude, respectively, and increased the probability of self-replacement by > 50%. Greater post-fire climatic moisture deficit exacerbated the effect of seed supply; an additional 4–6 years between fires was required under high moisture stress conditions to reach similar regeneration levels as under low moisture stress conditions.ConclusionThe overriding effect of seed supply—strongly driven by pre-fire stand age—on post-fire regeneration suggests that altered fire frequency (an indirect effect of climate change) will have a profound impact on serotinous forests. Although direct effects of hot and dry climate are lower in magnitude, they can alter forest recovery where seed supply nears a threshold. These findings reveal how fire interval and climate combine to determine changes in forest cover in the future, informing management and vulnerability mapping.

Prostorna varijabilnost morfoloških obilježja iglica populacija jele (Abies alba Mill.) na Balkanskom poluotoku u odnosu na klimatske čimbenike

Interpopulation and intrapopulation variability of three morphological needle traits (length, width and thickness) was investigated in 16 natural silver fir populations in the Balkan Peninsula. The populations represent refugial areas of silver fir (Abies alba Mill.). This paper aims to provide a comprehensive analysis of the influence of climatic factors (mean annual temperature, number of days with temperatures &amp;lt; 0, &amp;gt; 5, &amp;lt; 18, &amp;gt; 18&lt;sup&gt;o&lt;/sup&gt;C, Hargreaves climatic moisture deficit and De Martonne aridity index, on the pattern of morphological needle traits within each population. Populations showed variation in the analyzed morphological needle traits, which could not be clearly defined by any of the analyzed climatic factors. The De Martonne aridity index and Hargreaves climatic moisture deficit had the greatest impact on the trait values, whereas the mean annual precipitation had the lowest. Evolutionary ecology research of the silver fir needle morphology is a valuable contribution to the comprehention of the present genetic variability as a prerequisite for adaptation to the rapid climate change and conservation of the species area in the Balkan Peninsula region.

Climate Change Effects on Height–Diameter Allometric Relationship Vary with Tree Species and Size for Larch Plantations in Northern and Northeastern China

Tree height–diameter relationship is very important in forest investigation, describing forest structure and estimating carbon storage. Climate change may modify the relationship. However, our understanding of the effects of climate change on the height–diameter allometric relationship is still limited at large scales. In this study, we explored how climate change effects on the relationship varied with tree species and size for larch plantations in northern and northeastern China. Based on the repeated measurement data of 535 plots from the 6th to 8th national forest inventory of China, climate-sensitive tree height–diameter models of larch plantations in north and northeast China were developed using two-level nonlinear mixed effect (NLME) method. The final model was used to analyze the height–diameter relationship of different larch species under RCP2.6, RCP 4.5, and RCP8.5 climate change scenarios from 2010 to 2100. The adjusted coefficient of determination Radj2, mean absolute error (MAE) and root mean squared error (RMSE) of the NLME models for calibration data were 0.92, 0.76 m and 1.06 m, respectively. The inclusion of climate variables mean annual temperature (MAT) and Hargreaves climatic moisture deficit (CMD) with random effects was able to increase Radj2 by 19.5% and reduce the AIC (Akaike’s information criterion), MAE and RMSE by 22.2%, 44.5% and 41.8%, respectively. The climate sensitivity of larch species was ranked as L. gmelinii &gt; the unidentified species group &gt; L. principis &gt; L. kaempferi &gt; L. olgensis under RCP4.5, but L. gmelinii &gt; L. principis &gt; the unidentified species group &gt; L. olgensis &gt; L. kaempferi under RCP2.6 and RCP8.5. Large trees were more sensitive to climate change than small trees.

Predicting Potential Habitat of a Plant Species with Small Populations under Climate Change: Ostryarehderiana

Ostrya rehderiana is a famous plant species with extremely small populations. With ongoing global climate change, the extremely small populations would face more uncertainties and risks, including the loss of genetic diversity and extirpation. Thus, assessing the impact of climate change on suitable habitat of O. rehderiana is particularly important for its conservation and restoration. Here, we built niche models with climate variables and soil and human footprint variables. Furthermore, new methods were applied to avoid confounding effects between climate and soil and human footprint variables to simulate the potential habitats of O. rehderiana in current and future climates. We found that the Hargreaves climatic moisture deficit, degree-days below 0 °C, chilling degree-days, and the temperature difference between mean warmest month temperature and mean coldest month temperature, or continentality, were the most important climate factors. The topsoil USDA texture classification, topsoil cation exchange capacity of (clay), and topsoil sodicity (ESP) were the key soil factors determining the suitable distribution of O. rehderiana. Compared with soil factors, human footprint has less influence on the suitable distribution of O. rehderiana. The niche range of this species was projected to expand and shift to north in the Representative Concentration Pathway (RCP) 4.5 scenario for the 2050s. Our study results could be referenced in further extremely small populations ecological restoration studies and provide the scientific strategies for the conservation and restoration of O. rehderiana.

Corrigendum

Methods in Ecology and EvolutionVolume 13, Issue 2 p. 528-530 CORRIGENDUMFree Access Corrigendum This article corrects the following: Redundancy analysis: A Swiss Army Knife for landscape genomics Thibaut Capblancq, Brenna R. Forester, Volume 12Issue 12Methods in Ecology and Evolution pages: 2298-2309 First Published online: October 18, 2021 First published: 24 December 2021 https://doi.org/10.1111/2041-210X.13782AboutSectionsPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat In the article by Capblancq and Forester (2021) ‘Redundancy analysis: A Swiss Army Knife for landscape genomics’, the function used to re-encode the genotypes from the lodgepole pine genomic datasets (C. Mahony et al., 2019; C. R. Mahony et al., 2020) contained an error. The authors have corrected the function and the core results and interpretations of the lodgepole pine data remain unchanged. There were some small changes to the results, including in the number of retained SNPs after filtering and the number of identified outlier loci, resulting in small changes in the following tables and figures: Table 1, Table 2, Figure 1 and Supporting information 3 and 4. The corrected tables and figures are given below and the R tutorial that accompanies the paper has been updated with the correct re-encoding function and with the new version of the results, tables and figures. The updated version of the R tutorial can be found at this link: https://github.com/Capblancq/RDA-landscape-genomics or from Zenodo (Capblancq & Forester, 2021). The journal editors and authors are satisfied that this error does not affect the results or conclusions of the article. The authors apologize for any confusion or inconvenience caused by this error. TABLE 1. Climatic variables identified as significantly associated with genetic variation using forward variable selection with RDA (redundancy analysis) Variables Cum F-value p-value MAR—Mean Annual solar Radiation 0.0222 0.022 7.35 0.002** EMT—Extreme Minimum Temp. 0.0223 0.045 7.53 0.002** MWMT—Mean Warmest Month Temp. 0.0099 0.054 3.92 0.002** CMD—Climatic Moisture Deficit 0.0087 0.063 3.56 0.002** Tavg wt—Winter Mean Temp. 0.0041 0.067 2.21 0.002** DD_18—Degree Days below 18°C 0.0030 0.070 1.88 0.002** MAP—Mean Annual Prec. 0.0017 0.072 1.52 0.002** Eref—Potential Evaporation (Hargreave) 0.0016 0.074 1.47 0.002** PAS—Prec. As Snow 0.0018 0.075 1.53 0.002** TABLE 2. The influence of climate, geography and neutral genetic structure on genetic variation decomposed with pRDA (partial redundancy analysis). Inertia is analogous to variance. The proportion of explainable variance represents the total constrained variation explained by the full model Partial RDA models Inertia R 2 p(>F) Proportion of explainablevariance Proportion of total variance Full model: F ~ clim. + geog. + struct. 84.6 0.146 0.001*** 1 0.17 Pure climate: F ~ clim. | (geog. + struct.) 22.5 0.039 0.001*** 0.27 0.05 Pure structure: F ~ struct. | (clim. + geog.) 17.5 0.030 0.001*** 0.21 0.04 Pure geography: F ~ geog. | (clim. + struct.) 4.2 0.007 0.003*** 0.05 0.01 Confounded climate/structure/geography 40.2 0.48 0.08 Total unexpected 408.8 0.83 Total inertia 493.4 1.00 FIGURE 1Open in figure viewerPowerPoint Results of the genotype–environment association using partial RDA (redundancy analysis). (a) The projection of loci and environmental variables along the first two RDA axes. The locus scores are rescaled to an unshown axis for better visibility. (b) A Manhattan plot with the distribution of −log10(p-values). Loci identified as outliers (p-value < 3.4 × 10−7 and the lowest p-value per contig) are coloured for both panels Supporting information 3: Venn diagram showing the degree of overlap between the genetic outliers identified with the unconstrained RDA-based genome scan and the outliers identified by Mahony and colleagues (2020) using Bayenv2 and a genotype–phenotype association (GPA) method Supporting information 4: Venn diagram showing the degree of overlap between the genetic outliers identified with the constrained or unconstrained RDA-based genome scans REFERENCES Capblancq, T., & Forester, B. R. (2021). Capblancq/RDA-landscape-genomics: v2.0.0 (v2.0.0). Zenodo, https://doi.org/10.5281/zenodo.5747827Google Scholar Mahony, C., MacLachlan, I., Lind, B., Yoder, J., Wang, T., & Aitken, S. (2019). Data from: Evaluating genomic data for management of local adaptation in a changing climate: A lodgepole pine case study. Dryad Digital Repository, https://doi.org/10.5061/dryad.56j8vq8Google Scholar Mahony, C. R., MacLachlan, I. R., Lind, B. M., Yoder, J. B., Wang, T., & Aitken, S. N. (2020). Evaluating genomic data for management of local adaptation in a changing climate: A lodgepole pine case study. Evolutionary Applications, 13(1), 116– 131. https://doi.org/10.1111/eva.12871Wiley Online LibraryPubMedWeb of Science®Google Scholar Volume13, Issue2February 2022Pages 528-530 FiguresReferencesRelatedInformation

Surprising Drought Tolerance of Fir (Abies) Species between Past Climatic Adaptation and Future Projections Reveals New Chances for Adaptive Forest Management

Research Highlights: Data of advanced-age provenance tests were reanalyzed applying a new approach, to directly estimate the growth of populations at their original sites under individually generated future climates. The results revealed the high resilience potential of fir species. Background and Objectives: The growth and survival of silver fir under future climatic scenarios are insufficiently investigated at the xeric limits. The selective signature of past climate determining the current and projected growth was investigated to analyze the prospects of adaptive silviculture and assisted transfer of silver fir populations, and the introduction of non-autochthonous species. Materials and Methods: Hargreaves’ climatic moisture deficit was selected to model height responses of adult populations. Climatic transfer distance was used to assess the relative drought stress of populations at the test site, relating these to the past conditions to which the populations had adapted. ClimateEU and ClimateWNA pathway RCP8.5 data served to determine individually past, current, and future moisture deficit conditions. Besides silver fir, other fir species from South Europe and the American Northwest were also tested. Results: Drought tolerance profiles explained the responses of transferred provenances and predicted their future performance and survival. Silver fir displayed significant within-species differentiation regarding drought stress response. Applying the assumed drought tolerance limit of 100 mm relative moisture deficit, most of the tested silver fir populations seem to survive their projected climate at their origin until the end of the century. Survival is likely also for transferred Balkan fir species and for grand fir populations, but not for the Mediterranean species. Conclusions: The projections are less dramatic than provided by usual inventory assessments, considering also the resilience of populations. The method fills the existing gap between experimentally determined adaptive response and the predictions needed for management decisions. It also underscores the unique potential of provenance tests.

Seasonal water availability drives trait variation in isolated Basin and Range Pinus ponderosa

Tree species resistant to drought stress are likely to be more successful under the moisture-limited conditions predicted with climate change, and variation in drought-resistant traits can influence a species’ sensitivity to change. Trait variation is often tied to the timing, amount, and type of precipitation a given forest stand is exposed to, and local topographic heterogeneity may exacerbate or mitigate soil moisture stress. Although drought resistance is well-studied in widespread tree species, knowledge is limited on trait variation in drought-resistant conifers with more narrow distributions or isolated populations.Pinus ponderosa is amongst the most widespread conifers in semi-arid forests of western North America, and var. scopulorum occurs in some of the most arid portions of the species’ range. In the Northern Basin and Range physiographic province of western North America, scopulorum is isolated to montane sky islands, making it a model system for testing the effects of climate and topography on trait variation in drought-resistant conifers. To investigate the relationship between interacting climatic and topographic conditions and drought-resistant traits, we sampled 55 stands across six ranges in Nevada and Utah to quantify trait variation in cone volume, wood density, latewood to earlywood ratio (LER), specific leaf area (SLA), and needle lifespan and asked how these traits vary across the regional climate gradient. We then used linear mixed models to explore whether seasonal climatic moisture deficit (CMD), monsoonality, aspect, elevation, or tree-level attributes are associated with trait variation.Traits varied widely both within and among ranges, with trait responses strongly linked to seasonal water availability. Cone volumes and SLA increased with increasing summer (July-Aug) CMD, while cone volume decreased with increasing winter (Nov-Jan) CMD. Winter moisture stress was also tied to wood formation, as wood densities increased under greater cold season (Oct-Feb) CMD. Needle lifespan and LER were not shaped by seasonal CMD but rather by the degree of monsoonality, indicating that drought-resistant conifers may be able to take advantage of late-summer precipitation. Contrary to our expectations, local topographic variation had no influence on trait variation in the stands sampled here, while elevation and tree diameters were significant for wood traits alone. These findings suggest that both seasonal moisture stress and the timing of precipitation influence drought-resistant conifer trait variation in semi-arid environments and highlight the potential for these conifers to withstand extreme fluctuations in seasonal water availability, which is predicted to become more common as the climate continues to change.

A climatic dipole drives short- and long-term patterns of postfire forest recovery in the western United States

Researchers are increasingly examining patterns and drivers of postfire forest recovery amid growing concern that climate change and intensifying fires will trigger ecosystem transformations. Diminished seed availability and postfire drought have emerged as key constraints on conifer recruitment. However, the spatial and temporal extent to which recurring modes of climatic variability shape patterns of postfire recovery remain largely unexplored. Here, we identify a north-south dipole in annual climatic moisture deficit anomalies across the Interior West of the US and characterize its influence on forest recovery from fire. We use annually resolved establishment models from dendrochronological records to correlate this climatic dipole with short-term postfire juvenile recruitment. We also examine longer-term recovery trajectories using Forest Inventory and Analysis data from 989 burned plots. We show that annual postfire ponderosa pine recruitment probabilities in the northern Rocky Mountains (NR) and the southwestern US (SW) track the strength of the dipole, while declining overall due to increasing aridity. This indicates that divergent recovery trajectories may be triggered concurrently across large spatial scales: favorable conditions in the SW can correspond to drought in the NR that inhibits ponderosa pine establishment, and vice versa. The imprint of this climatic dipole is manifest for years postfire, as evidenced by dampened long-term likelihoods of juvenile ponderosa pine presence in areas that experienced postfire drought. These findings underscore the importance of climatic variability at multiple spatiotemporal scales in driving cross-regional patterns of forest recovery and have implications for understanding ecosystem transformations and species range dynamics under global change.

Plant community type is an indicator of the seasonal moisture deficit in a disturbed raised bog

AbstractDepth to water table is a simple, commonly used measure of hydrological function in raised bogs. The maximum depth of the water table or the average annual water table is often monitored over the long term to track the hydrological trajectory of the ecosystem. These measures, however, may not take into account the duration of the moisture deficit period. The annual water table moisture deficit (WTMD) at 67 sites in a single disturbed raised bog was calculated using the amount of time that the water table was at each depth below the surface during the moisture deficit season. The calculated value estimates a linearly developing deficit that dewaters the acrotelm during the moisture deficit season. At each site, plant species composition was assigned to one of eight plant community types. The approximate threshold above which bog plant communities will begin transitioning into drier types with taller shrubs and trees was a WTMD of 62 m‐days. An annual climatic moisture deficit (CMD) was calculated using daily air temperature, spatially interpolated precipitation and estimated potential evapotranspiration for each site. Mixed‐effects modelling of WTMD as a function CMD indicated a positive linear relation for most vegetation types, which was affected by the presence of drainage ditches, ditch blocking, fire and evapotranspiration by shrubs and trees. Tracking the WTMD and its relation to CMD may be useful for assessing ecosystem health and serve as a basis for estimating moisture deficit thresholds for bogs of conservation concern.

Radial growth response of two oaks to climate at their disparate distribution limits in semiarid areas, Beijing, China

AbstractImpending climate warming is expected to influence plant growth and distribution, and the distribution range limit of tree species is extremely sensitive to climate change. However, synchronous comparisons of responses of different tree species with overlapping ecological niches to climate at their distribution range limit in the same region have received little attention. In the present study, we assessed the discrepancy in radial growth responses of two dominant oak species to climate at their distribution range limit (southern range limit forQuercus mongolica, northern range limit forQuercus variabilis) in Beijing, China. Furthermore, growth–climate relationships were examined using linear mixed‐effects models, and growth trends up to the year 2100 were forecast based on future climate scenarios (RCP2.6 and RCP8.5). Our results indicated that there were no significant differences in the growth response to climate betweenQ. variabilisat its northern limit andQ. mongolicaat its southern limit, and the growth of the two tree species was positively correlated with the minimum temperature and negatively correlated with the climatic moisture deficit of autumn. However, the growth response to climate variables varied at different sites. Additionally, the model forecast showed an increase in radial growth ofQ. variabilisat its northern limit andQ. mongolicaat its southern limit up to the end of the present century.

Resilience of southern Yukon boreal forests to spruce beetle outbreaks

Changed disturbance regimes could drive biome-level shifts in vegetation structure and have cascading societal consequences. Expanding and intensifying bark beetle outbreaks pose a risk of major changes to large regions of boreal forests in North America. We evaluated the resilience of boreal forests in southwestern Yukon to an unprecedented spruce beetle (Dendroctonus rufipennis Kirby [Coleoptera: Curculionidae) outbreak using data collected from permanent plots, which were measured repeatedly, in 21 stands. We determined basal area (m2/ha) and density (stems/ha) of canopy trees (which are most vulnerable to beetles), density of advance regeneration, and growth response to the outbreak using ring widths from over 800 trees ranging in size from small advance regeneration to canopy trees. Beetle-related reductions in tree canopy basal area averaged 52% across all stands but there was considerable variability among stands. About 68% of variation in basal area reductions among stands was explained by variability in pre-outbreak canopy tree basal area (β = 1.1; p = 0.0021) and a climatic moisture deficit index (β = 0.5; p = 0.0015). Although the percentage of white spruce (Picea glauca (Moench) Voss) in the canopy was reduced in some stands, by 2–29%, white spruce remained the dominant canopy tree species. Almost all stands had more than adequate advance regeneration density (average = 5 448 stems/ha) in 2016 to replace canopy trees killed by beetles. Variability in advance regeneration among stands could partly be explained by pre-outbreak tree canopy basal area (β = −0.4; p = 0.0018), a climate moisture deficit index (β = −0.3; p = 0.0004), and shrub per cent cover (β = −0.3; p = 0.0003), as well as, humus depth (β = 544; p = 0.0186). Over the last two decades, spruce trees, of all size classes, exhibited substantial increases in mean annual radial growth increment, beginning 4–5 years after the start of the outbreak. The proportion of trees in a stand with at least a 50% increase in radial growth increment varied significantly with canopy tree basal area at the end of the outbreak (β = −0.12; p < 0.0001), climatic moisture deficit (β = −0.02; p < 0.0196), and humus depth (β = 0.26, p < 0.0001). Our findings indicate high response diversity to disturbance and suggest that forests of southwestern Yukon have high resilience to the recent spruce beetle outbreak because of the large number of surviving canopy trees, the abundant advance regeneration of spruce that can replace beetle-killed trees, and the increased growth of surviving trees.

Isotopic heterogeneity in whitebark pine (Pinus albicaulis Engelm.) nuts across geographic, edaphic and climatic gradients in the Northern Rockies (USA)

The overall health and persistence of whitebark pine is of international concern. Extensive tree mortality and loss of vigor due to the non-native pathogen white pine blister rust (Cronartium ribicola A. Dietr.), mountain pine beetle (Dendroctonus ponderosae Hopkins), altered fire regimes, and climate change endanger the existence of whitebark pine, which is an important food source (pine nuts) for several wildlife species. Prior stable isotope analysis revealed variability in intrinsic water-use efficiency and nutritional status; however, small sample sizes prohibited the identification of geo-climatic effects on those isotopes. We summarize carbon isotope discrimination (Δ13C, a measure of intrinsic water-use efficiency) and the natural abundance of δ13C, δ15N and δ34S in whitebark pine nuts in the Northern Rockies. Spatial differences in geography, soil parent material and climate (e.g., summer mean temperature, number of degree-days below 0°C, mean annual precipitation, Hargreaves climatic moisture deficit, and the frost-free period) contributed to the low to moderate spatial resolution in selected models (R2 values ranged from 0.24 to 0.51). The importance of soil parent material in all models demonstrated whitebark pine exhibits previously unknown edaphic variation. Identification of the mechanistic drivers contributing to spatial heterogeneity in Δ13C provides an opportunity to select seed sources better suited to optimize long-term survival, vigor and cone production. Matching genetic resources to sites projected to support whitebark pine in future climates would ensure species persistence, while safeguarding an important wildlife food. Suitable wildlife habitat for projected warmer, drier climates was characterized as low values of Δ13C (<13.5‰) and was concentrated in the southeastern portion of the Northern Rockies. Whitebark pine nuts at the landscape scale exhibited unique δ34S and δ15N values relative to other wildlife foods, but these isotope values can overlap other plant materials in more localized areas. Future applications to determine the proportion of pine nuts in assimilated diets will need to accommodate spatial heterogeneity, potential temporal variation in δ13C, nutrient concentrations, animal tissue turnover rates, and seasonal availability of other foods. Further studies of the abiotic and biotic factors on C, N, and S cycles and the relationship between photosynthetic and heterotrophic tissue are needed for a better mechanistic understanding of the determinants of the natural abundance of δ13C, Δ13C, δ15N and δ34S.

Field Evaluation of Cocksfoot, Tall Fescue and Phalaris for Dry Marginal Environments of South‐Eastern Australia. 2. Persistence

AbstractPerennial grasses provide forage and environmental benefits in the agricultural systems of southern Australia, but persistent cultivars are lacking for the lower rainfall inland margins (&lt;600 mm average annual rainfall). Potential new cultivars of cocksfoot (Dactylis glomerata L.), tall fescue (Festuca arundinacea Schreb. = syn. Lolium arundinaceum (Schreb.) Darbysh.) and phalaris (Phalaris aquatica L.) have been developed in response to this need. These and older cultivars were evaluated for persistence at five sites in south‐eastern Australia from 2009 to 2013. A wide range in rainfall was experienced, but survival was principally reduced by a severe spring–summer–autumn drought in the final year in which all species began to decline in persistence once the spring 2012 to autumn 2013 cumulative climatic moisture deficit became higher than about 700 mm and declined very severely at deficits over 1000 mm. The highly summer‐dormant cocksfoot ssp. hispanica control cultivar Kasbah showed outstanding survival of this event in the cropping zone of southern New South Wales, but not at the drier of two sites with acidic soils in central Victorian where all cocksfoot cultivars showed similar survival. Potential new summer‐active tall fescue cultivars survived well at the higher rainfall Victorian site and under high rainfall in northern NSW. All tall fescue cultivars experienced high mortality during a period of high moisture stress in the spring of the establishment year in southern NSW, but the Mediterranean cultivar Grasslands Flecha MaxP gradually recovered. Differences among phalaris cultivars were not large with new cultivars of North African origin being marginally more persistent at the drier site in southern NSW. Comparisons with results from the Mediterranean Basin are discussed. Although there was no clear evidence of differences in persistence between the new and old cultivars, some of the new cultivars were considered to show potential for commercial release.

Native and exotic plant cover vary inversely along a climate gradient 11 years following stand-replacing wildfire in a dry coniferous forest, Oregon, USA.

Community re-assembly following future disturbances will often occur under warmer and more moisture-limited conditions than when current communities assembled. Because the establishment stage is regularly the most sensitive to climate and competition, the trajectory of recovery from disturbance in a changing environment is uncertain, but has important consequences for future ecosystem functioning. To better understand how ongoing warming and rising moisture limitation may affect recovery, we studied native and exotic plant composition 11 years following complete stand-replacing wildfire in a dry coniferous forest spanning a large gradient in climatic moisture deficit (CMD) from warm and dry low elevation sites to relatively cool and moist higher elevations sites. We then projected future precipitation, temperature and CMD at our study locations for four scenarios selected to encompass a broad range of possible future conditions for the region. Native perennials dominated relatively cool and moist sites 11 years after wildfire, but were very sparse at the warmest and driest (high CMD) sites, particularly when combined with high topographic sun exposure. In contrast, exotic species (primarily annual grasses) were dominant or co-dominant at the warmest and driest sites, especially with high topographic sun exposure. All future scenarios projected increasing temperature and CMD in coming decades (e.g., from 4.5% to 29.5% higher CMD by the 2080's compared to the 1971-2000 average), even in scenarios where growing season (May-September) precipitation increased. These results suggest increasing temperatures and moisture limitation could facilitate longer term (over a decade) transitions toward exotic-dominated communities after severe wildfire when a suitable exotic seed source is present.

Multi‐scale spatial controls of understory vegetation in Douglas‐fir–western hemlock forests of western Oregon, USA

Forest understory vegetation is influenced by broad‐scale variation in climate, intermediate‐scale variation in topography, disturbance and neighborhood interactions. However, little is known about how these multi‐scale controls interact to influence observed spatial patterns. We examined relationships between the aggregated cover of understory plant species (%CU) and multi‐scale controls using a large‐scale experiment including treatments of low (LS), moderate (MS) and variable (VS) disturbance severity replicated in second‐growth Douglas‐fir (Pseudotsuga meziesii)–western hemlock (Tsuga heterophylla) forests spanning climate and topographic gradients. We developed hierarchical models using a multi‐step selection process, assessing changes residual spatial autocorrelation associated with progressively broader spatial scales of influence and interaction. To examine the role of plant traits in mediating multi‐scale controls, we contrasted effects for early‐ (%CES) and late‐seral (%CLS) species cover.At neighborhood scales, decreases in %CU with overstory density were accelerated with increases in the relative importance of hemlock in the overstory in the in all but the LS treatment. At intermediate scales, %CU was lower in areas with higher potential radiation in undisturbed control treatments but that trend was reversed in the harvested, disturbed areas. When separated, effects of multi‐scale controls differed between %CES and %CLS. Rates of increases in %CES with reductions in density increased with disturbance severity and decreased with increases in %CLS. At broader scales, %CES increased with climatic moisture deficit where potential radiation was high, and %CLS low. Similarly to %CU, %CLS was related to a three‐way interaction between overstory density, disturbance and hemlock abundance. %CLS declined with increases in climatic moisture deficit where overstory density and the relative abundance of hemlock was high, and decreased with local increases in %CES. Multi‐scale controls explained a portion of the observed spatial autocorrelation for %CES but not %CLS, suggesting the spatial patterning of %CLS is related primarily to unmeasured processes. Results show how understory responses to overstory density and disturbance severity vary across the landscape with moisture and potential radiation, at fine scales with neighborhood structure, and with species traits. Hence, understory responses to climate change likely depend on overstory composition and structure, disturbance and species traits.

Dissecting indices of aridity for assessing the impacts of global climate change

There is great interest in understanding how climate change will impact aridity through the interaction of precipitation changes with rising temperatures. The Aridity Index (AI), Climatic Moisture Deficit (CMD), and Climatic Moisture Surplus (CMS) are metrics commonly used to quantify and map patterns in aridity and water cycling. Here we show that these metrics have different patterns of change under future climate—based on an ensemble of nine general circulation climate models—and the different metrics are appropriate for different purposes. Based on these differences between the metrics, we propose that aridity can be dissected into three different types—hydrological (CMS), agricultural (CMD), and meteorological. In doing this, we propose a novel modified version of the Aridity Index, called AI+, that can be useful for assessing changes in meteorological aridity. The AI + is based on the same ratio between precipitation and evapotranspiration as the traditional AI, but unlike the traditional AI, the AI + only accounts for changes to precipitation during months when precipitation is less than reference/potential evapotranspiration (i.e. there is a deficit). Moreover, we show that the traditional AI provides a better estimate of change in moisture surplus driven by changes to precipitation during the wet season, rather than changes in deficit that occur during the drier seasons. These results show that it is important to select the most appropriate metric for assessing climate driven changes in aridity.

Modeling regional and climatic variation of wood density and ring width in intensively managed Douglas-fir

Characteristics of annual rings are reliable indicators of growth and wood quality in trees. The main objective of our study was to model the variation in annual ring attributes due to intensive silviculture and inherent regional differences in climate and site across a wide geographic range of Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco). Ring specific gravity and ring width of Douglas-fir were examined at five long-term Levels-Of-Growing-Stock (LOGS) installations, three in the US and two in Canada, covering a latitudinal gradient between 43°N and 50°N. At each location, increment cores were collected from replicated plots with three levels of stocking: control (unthinned), lightly thinned (70% basal area retention), and heavily thinned (30% basal area retention). X-ray densitometry analysis provided ring specific gravity and width profiles for 5676 rings from 134 trees. The reduction of stand density through repeated entries resulted in decreased ring specific gravity and increased ring width. A four-parameter mixed-effects logistic model was used to predict ring specific gravity using cambial age, stand density (as number of stems per hectare), and two climatic variables: average temperature from March to May and total precipitation from April to August. A three-parameter mixed-effects logistic model was used to predict ring width using cambial age, stand density (as stand density index), and total climatic moisture deficit of June and July. Both models indicated significant site differences that were included in the models through indicator variables. Ring specific gravity increased slightly with increasing average temperature from March to May and decreasing total precipitation from April to August. Predictions of ring specific gravity of Douglas-fir appear to be more sensitive to changes in temperature compared with changes in precipitation.