The dendroecological potential of shrubs in north Iranian semi-deserts

In deserts and semi-deserts such as in the Irano-Turanian region in northern Iran, forest vegetation is scarce but shrubs are dominant. For this floristic province, placed in a biodiversity hotspot with a cold and dry climate, we provide the first climate-growth study on shrubs. From stems of three wide-spread shrubs (Astragalus, Rhamnus and Ephedra species) annual rings were identified and their widths measured.On average, around 40-year long annual-ring series per stem were obtained, cross-dated and related to meteorological variables. Astragalus and Rhamnus reflected a clear regional climate signal in their ring widths whereas Ephedra showed an only weak association with climate variables. While above-average air humidity in combination with low temperatures in spring and summer favored shrub growth, precipitation had surprisingly only a weak effect on growth. From the abundance of fog events in this area, we concluded that the extreme moisture dependency of the shrubs before and throughout the growing season may have been relieved by the uptake of fog drip through the foliage.As projected by climate models, the deficit in humidity will intensify and temperature will continue to rise in this region. So, the ability of the Irano-Turanian endemic shrubs to infiltrate into neighboring regions could become limited and their current distribution range may be confined to higher elevations which provide a moister and cooler environment.     

Dendrochronological potential of four neotropical dry-forest tree species: Climate-growth correlations in northeast Brazil

Tropical dry forests (TDF) are highly important tropical forest ecosystems. Yet, these forests are highly threatened, usually neglected and only poorly studied. Understanding the long-term influences of environmental conditions on tree growth in these forests is crucial to understand the functioning, carbon dynamics and potential responses to future climate change of these forests. Dendrochronology can be used as a tool to provide these insights but has only scantly been applied in (dry) tropical forests. Here we evaluate the dendrochronological potential of four Caatinga neotropical dry forest tree species – Aspidosperma pyrifolium, Ziziphus joazeiro, Tabebuia aurea, and Libidibia ferrea – collected in two locations in northeastern Brazil (Sergipe state). We provide an anatomical characterization of the ring boundaries for the four species and investigate correlations of their growth with local and regional climatic variables. All four species form annual rings and show high inter-correlation (up to 0.806) and sensitivity (up to 0.565). Growth of all species correlated with local precipitation as well as with sea-surface temperatures in the tropical Atlantic and/or tropical Pacific oceans. We also show teleconnections between growth and the El Niño South Oscillation. The strong dependence of tree on precipitation is worrisome, considering that climate change scenarios forecast increased drought conditions in the Caatinga dry forest. Including more species and expanding dendrochronological studies to more areas would greatly improve our understanding of tree growth and functioning in TDFs. This type of knowledge is essential to assist the conservation, management and restoration of these critical tropical ecosystems.     

Tree ring anatomy indices of Pinus tabuliformis revealed the shifted dominant climate factor influencing potential hydraulic function in western Qinling Mountains

Trees can adjust xylem anatomical structure related with potential hydraulic functions to cope with climate variability. We therefore need a better understanding of how climate variability constrains wood anatomy and tree radial growth. Pinus tabuliformis dominates natural forests and plantations over the western Qinling Mountains, which is one of the ecologically vulnerable areas in China. Here, we investigated the response of P. tabuliformis tree-ring anatomical structure to climate variability by applying wood anatomy analysis, and evaluated the influences of anatomical traits on potential hydraulic functions and the climate significance of intra-annual density fluctuations (IADFs). We found that with the increasing temperature from spring to summer, the negative effect of temperature on the formation and enlargement of earlywood and transition-wood tracheids was gradually enhanced. However, spring precipitation not only had a direct and positive influence on the formation of earlywood, but also had a delaying impact on the transition-wood cell enlargement. Besides, the smaller earlywood tracheid size of P. tabuliformis could be a substantially characteristic reflecting spring drought. The contribution of lumen diameter on conduit wall reinforcement was dominated in earlywood, while the contribution of cell wall thickness was greater than that of lumen diameter in latewood. The different contributions of anatomical traits on conduit wall reinforcement would further affect the response of potential hydraulic function to climate. IADFs of P. tabuliformis could be a potential indicator to reflect the abnormal summer precipitation events in the western Qinling Mountains. IADFs with strong and weak intensity indicated years with high and low rates of change in mid-summer precipitation, respectively. Future warmer and drier climate in the western Qinling Mountains will likely result in the production of smaller tracheids to ensure hydraulic safety, which means the stronger drought resistant of P. tabuliformis in the future. In this study, we linked the xylem anatomy and potential hydraulics functions with intra-seasonal climate variability in the context of climate warming and drying, and proposed some xylem anatomical indices reflecting potential drought events.     

The effect of individual genetic heterozygosity on general homeostasis,heterosis and resilience in Siberian larch (Larix sibirica Ledeb.) using dendrochronology and microsatellite loci genotyping

The genetic mechanisms underlying the relationship of individual heterozygosity (IndHet) with heterosis and homeostasis are not fully understood. Such an understanding, however, would have enormous value as it could be used to identify trees better adapted to environmental stress. Dendrochronology data, in particular the individual average radial increment growth of wood measured as the average tree ring width (AvTRW) and the variance of tree ring width (VarTRW) were used as proxies for heterosis (growth rate measured as AvTRW) and homeostasis (stability of the radial growth of individual trees measured as VarTRW), respectively. These traits were then used to test the hypothesis that IndHet can be used to predict heterosis and homeostasis of individual trees. Wood core and needle samples were collected from 100 trees of Siberian larch (Larix sibirica Ledeb.) across two populations located in Eastern Siberia. DNA samples were obtained from the needles of each individual tree and genotyped for eight highly polymorphic microsatellite loci. Then mean IndHet calculated based on the genotypes of eight loci for each tree was correlated with the statistical characteristics of the measured radial growth (AvTRW and VarTRW) and the individual standardized chronologies. The analysis did not reveal significant relationships between the studied parameters. In order to account for the strong dependence of the radial growth on tree age the age curves were examined. An original approach was employed to sort trees into groups based on the distance between these age curves. No relationship was found between these groups and the groups formed based on heterozygosity. However, further work with more genetic markers and increased sample sizes is needed to test this novel approach for estimating heterosis and homeostasis.     

Estimates of leaf-area index for the territory of Russia using State Forest Inventory data

The 2007 State Forest Inventory (SFI) data have been used at two scales of spatial resolution: the datasets of the forest regions (31) and the forest-management basic units (1900) to estimate the leafarea index (LAI, m² m^–2) of forests in Russia. The area and yield data on all 66 tree species recorded in the SFI offer the opportunity to obtain the wood specific gravity values U (m³ ha^–1) for all these tree species. The conversion coefficients of yield to leaf phytomass per unit area (t m^–3) and the projected specific leaf areas (SLAs) (cm² g^–1) are used to estimate the LAI. The obtained LAI values are similar to the average ground and remote-sensing estimates (the given review for July includes eighteen literature sources). The highest LAI values can be observed in the middle taiga subzone in the European part of Russia and in the Angara River regions. The LAI estimates may be used to compute the productivity of the forest ecosystems at different scales of analysis and to extrapolate the calibrated data acquired with remote control techniques.     

Climate change and the potential for range expansion of the Lyme disease vector Ixodes scapularis in Canada

We used an Ixodes scapularis population model to investigate potential northward spread of the tick associated with climate change. Annual degree-days >0 degrees C limits for I. scapularis establishment, obtained from tick population model simulations, were mapped using temperatures projected for the 2020s, 2050s and 2080s by two Global Climate Models (the Canadian CGCM2 and the UK HadCM3) for two greenhouse gas emission scenario enforcings 'A2'and 'B2' of the Intergovernmental Panel on Climate Change. Under scenario 'A2' using either climate model, the theoretical range for I. scapularis establishment moved northwards by approximately 200 km by the 2020s and 1000 km by the 2080s. Reductions in emissions (scenario 'B2') had little effect on projected range expansion up to the 2050s, but the range expansion projected to occur between the 2050s and 2080s was less than that under scenario 'A2'. When the tick population model was driven by projected annual temperature cycles (obtained using CGCM2 under scenario 'A2'), tick abundance almost doubled by the 2020s at the current northern limit of I. scapularis, suggesting that the threshold numbers of immigrating ticks needed to establish new populations will fall during the coming decades. The projected degrees of theoretical range expansion and increased tick survival by the 2020s, suggest that actual range expansion of I. scapularis may be detectable within the next two decades. Seasonal tick activity under climate change scenarios was consistent with maintenance of endemic cycles of the Lyme disease agent in newly established tick populations. The geographic range of I. scapularis-borne zoonoses may, therefore, expand significantly northwards as a consequence of climate change this century.     

Rates of Disturbance vary by data resolution: implications for conservation schedules using the Alberta Boreal Forest as a case study

Investigations of biophysical changes on earth caused by anthropogenic disturbance provide governments with tools to generate sustainable development policy. Canada currently experiences one of the fastest rates of boreal forest disturbance in the world. Plans to conserve the 330 000 km² boreal forest in the province of Alberta exist but conservation targets and schedules must be aligned with rates of forest disturbance. We explore how disturbance rate, and the accuracy with which we detect it, may affect conservation success. We performed a change detection analysis from 1992 to 2008 using Landsat and SPOT satellite image data processing. Canada's recovery strategy for boreal caribou (Rangifer tarandus caribou) states that ≤35% of a caribou range can be either burned or within 500 m of a man‐made feature for caribou to recover. Our analyses show that by 2008 78% of the boreal forest was disturbed and that, if the current rate continues, 100% would be disturbed by 2028. Alberta plans to set aside 22% for conservation in a region encompassing oil sands development to balance economic, environmental, and traditional indigenous land‐use goals. Contrary to the federal caribou recovery strategy, provincial conservation plans do not consider wildfire a disturbance. Based on analyses used in the provincial plan, we apply a 250 m buffer around anthropogenic footprints. Landsat image analysis indicates that the yearly addition of disturbance is 714 km² (0.8%). The higher resolution SPOT images show fine‐scale disturbance indicating that actual disturbance was 1.28 times greater than detected by Landsat. If the SPOT image based disturbance rates continue, the 22% threshold may be exceeded within the next decade, up to 20 years earlier than indicated by Landsat‐based analysis. Our results show that policies for sustainable development will likely fail if governments do not develop time frames that are grounded by accurate calculations of disturbance rates.     

The importance of phenology for the evaluation of impact of climate change on growth of boreal, temperate and Mediterranean forests ecosystems: an overview

An overview is presented of the phenological models relevant for boreal coniferous, temperate-zone deciduous and Mediterranean coniferous forest ecosystems. The phenology of the boreal forests is mainly driven by temperature, affecting the timing of the start of the growing season and thereby its duration, and the level of frost hardiness and thereby the reduction of foliage area and photosynthetic capacity by severe frost events. The phenology of temperate-zone forests is also mainly driven by temperature. Since temperate-zone forests are mostly mixed-species deciduous forests, differences in phenological response may affect competition between tree species. The phenology of Mediterranean coniferous forests is mainly driven by water availability, affecting the development of leaf area, rather than the timing of phenological events. These phenological models were subsequently coupled to the process-based forest model FORGRO to evaluate the effect of different climate change scenarios on growth. The results indicate that the phenology of each of the forest types significantly affects the growth response to a given climate change scenario. The absolute responses presented in this study should, however, be used with caution as there are still uncertainties in the phenological models, the growth models, the parameter values obtained and the climate change scenarios used. Future research should attempt to reduce these uncertainties. It is recommended that phenological models that describe the mechanisms by which seasonality in climatic drivers affects the phenological aspects of trees should be developed and carefully tested. Only by using such models may we make an assessment of the impact of climate change on the functioning and productivity of different forest ecosystems. Received: 21 October 1999 / Revised: 10 May 2000 / Accepted: 10 May 2000     

Managing for naturalness alone is not an effective way to preserve all the valuable natural features of the Białowieża Forest – a reply to Jaroszewicz et al.

Currently, Brzeziecki et al. 2016 (Journal of Vegetation Science 27: 460–467.) are using data from permanent study plots established in 1936 in Bia?owie?a National Park (NE Poland) to develop theoretical equilibrium tree size distributions and to then compare modelled and actual distributions with a view to assessing the population dynamics of the species involved. As part of their discussion, the authors address the question of possible consequences for the overall diversity of forest ecosystems under strict protection if long‐term trends relating to tree population densities and size structures are maintained. In the overall context of the above, the goal of the present paper is to respond to Jaroszewicz et al. (Journal of Vegetation Science 28: 218–222.) who suggest that the paper of Brzeziecki et al. (2016) is not representative for the whole Bia?owie?a National Park, and that – in this connection – strict protection should not be seen as a cause for concern. In this paper, we show that the data analysed by Brzeziecki et al. (2016) adequately characterize conditions in the wider Park. We also point out that the thorough scientific understanding of the long‐term dynamics of woodland communities under strict protection should indeed be taken into account as efforts are made to arrive at an effective conservation strategy capable of ensuring that the uniquely valuable features of the Bia?owie?a Forest are retained.     

Evaluating within‐population variability in behavior and demography for the adaptive potential of a dispersal‐limited species to climate change

Multiple pathways exist for species to respond to changing climates. However, responses of dispersal‐limited species will be more strongly tied to ability to adapt within existing populations as rates of environmental change will likely exceed movement rates. Here, we assess adaptive capacity in Plethodon cinereus, a dispersal‐limited woodland salamander. We quantify plasticity in behavior and variation in demography to observed variation in environmental variables over a 5‐year period. We found strong evidence that temperature and rainfall influence P. cinereus surface presence, indicating changes in climate are likely to affect seasonal activity patterns. We also found that warmer summer temperatures reduced individual growth rates into the autumn, which is likely to have negative demographic consequences. Reduced growth rates may delay reproductive maturity and lead to reductions in size‐specific fecundity, potentially reducing population‐level persistence. To better understand within‐population variability in responses, we examined differences between two common color morphs. Previous evidence suggests that the color polymorphism may be linked to physiological differences in heat and moisture tolerance. We found only moderate support for morph‐specific differences for the relationship between individual growth and temperature. Measuring environmental sensitivity to climatic variability is the first step in predicting species' responses to climate change. Our results suggest phenological shifts and changes in growth rates are likely responses under scenarios where further warming occurs, and we discuss possible adaptive strategies for resulting selective pressures.     

Experimental investigations into the feasibility ofex situ preservation of palm seeds; an alternative strategy for biological conservation of this economically important plant family

Given the widespread belief that the conservation of palms, especially the large-trunked species, is only accomplished throughin situ preservation or in plantations, this paper explores the feasibility of a third approach, i.e. cryogenic preservation of their seedsex situ. Seeds of the following palm species were subjected to air-drying to assess their tolerance of dessication:Washingtonia filifera (L. Linden) H. Wendl.;Sabal mexicana Mart. (syn. S. texana; Zong, 1990);Schippia concolor Burret;Orbignya cohune (Mart.) Dahlgren ex Standley;Acoelorraphe wrightii (Griseb. & H. Wendl.) H. Wendl. ex Becc.;Desmoncus orthacanthos Mart.;Attalea crassispatha (Mart.) Burret;Zambia antillarum (Desc.) L.H. Bailey;Pinanga malaiana (Mart.) Scheff.;Pinanga aff. polymorpha Becc.;Daemonorops verticillaris (Griff.) Mart. Of these, only two (W. filifera andS. mexicana) survived drying to moisture contents around 5% (fresh weight basis). Seeds of the remaining spp. would be difficult or impossible to conserveex situ in seedbanks or cryostores. Data are presented to show that the response ofO. cohune embryos to drying is similar to other recalcitrant (dessication intolerant) seeds, while seeds ofA. wrightii may belong to an intermediate seed storage category with limited tolerance of drying. The results are discussed in relation to the inadequacy of current knowledge as a basis for decisions on the broad scaleex situ conservation of palm germplasm.