Characterisation of Woody Necromass in Beech Forests with Different Anthropic Accessibility: The Case of La Rioja (Spain)

In this study, a comprehensive analysis of deadwood was conducted in four macro-areas located in two beech forests of public utility in Enciso (La Rioja, Spain). Dendrometric data, as well as qualitative and quantitative characteristics of deadwood, were collected and analysed with respect to the degree of accessibility to the forest to determine the effect of different levels of forest accessibility on deadwood volume and carbon stocks. All decomposition classes were present except the first, highlighting the development of natural degradation dynamics. Deadwood stored 6.9 t/ha of C in the easy accessibility class, 5.7 t/ha of C in the medium accessibility class and 2.2 t/ha of C in the difficult accessibility class. The average volume of deadwood and carbon stored calculated in this study were higher than the values reported in the Spanish and Italian national forest inventories, including one developed for Riojan beech forests. Deadwood volume was on average 22.5 m3/ha, showing an unequal distribution, with the lowest values found far from the access roads, despite forest accessibility generally being considered a factor that facilitates the human collection of deadwood. The distribution patterns of deadwood in beech forests of La Rioja, apparently counterintuitive, were due to a combination of different factors, including slope, cattle grazing, and weather conditions which might have favoured downward movement of the deadwoodThis research was funded by the Spanish Ministry of Science, Innovation and Universities, AGL2016-76769-C2-2-RS

Shifts in wood anatomical traits after a major hurricane

•1. Trait variation across individuals and species influences the resistance and resilience of ecosystems to disturbance, and the ability of individuals to capitalize on postdisturbance conditions. In trees, the anatomical structure of xylem directly affects plant function and, consequently, it is a valuable lens through which to understand resistance and resilience to disturbance. •2. To determine how hurricanes affect wood anatomy of tropical trees, we characterized a set of anatomical traits in wood produced before and after a major hurricane for 65 individuals of 10 Puerto Rican tree species. We quantified variation at different scales (among and within species, and within individuals) and determined trait shifts between the pre- and posthurricane periods. We also assessed correlations between traits and growth rates. •3. While the majority of anatomical trait variation occurred among species, we also observed substantial variation within species and individuals. Within individuals, we found significant shifts for some traits that generally reflected increased hydraulic conductivity in the posthurricane period. We found weak evidence for an association between individual xylem anatomical traits and diameter growth rates. •4. Ultimately, within-individual variation of xylem anatomical traits observed in our study could be related to posthurricane recovery and overall growth (e.g. canopy filling). Other factors, however, likely decouple a relationship between xylem anatomy and diameter growth. While adjustments of wood anatomy may enable individual trees to capitalize on favourable postdisturbance conditions, these may also influence their future responses or vulnerability to subsequent disturbances

STRUCTURAL PATTERNS, GROWTH PROCESSES, CARBON STOCKS IN AN ITALIAN NETWORK OF OLD-GROWTH BEECH FORESTS

In the framework of the Project of National Interest (PRIN) “Climate change and forests - Dendroecological and ecophysiological responses, productivity and carbon balance on the Italian network of old-growth beech forests”, 9 old beech (Fagus sylvatica L.) forests were sampled in the eastern Alps and in the central Apennines to assess: i) the degree of ‘old-growthness’ on a structural and dendroecological basis; ii) the carbon (C) stocks in the different ecosystem compartments; iii) some ecophysiological traits using stable isotopes. Live and dead tree structure, soil features and C stocks were examined in some among the oldest and less disturbed beech forests in Italy. Furthermore, leaves, litter and wood cores were sampled for concurrent dendroecological, nutrient and stable isotope analysis, to study age structure, disturbance history and medium- and long-term response to climate and ecophysiological traits. In all sampled stands, values of basal area, volume and large trees density reached or exceeded control values reported for European and North American old-growth forests, while total amount of deadwood was generally low, except in two sites. Diameter distribution showed a remarkable differentiation from bimodal to ‘rotated-sigmoid’ curve. In accordance with structural analyses, disturbance chronologies revealed the importance of frequent low-to-moderate events in generating a fine-scale structure, confirming previous results on beech forests. Different degrees of ‘old-growthness’ were identified for Alpine and Apennine beech stands through the ‘structural-based approach’, which proved to be a valid tool for old-growth forests detection. Preliminary results on carbon stocks on a subset of sites indicate that these old-growth forests are relevant carbon reservoirs, with 192-268 MgC ha-1 of total biomass (67-73% aboveground; 27-33% belowground, 4 stands) and 7-21 MgC ha-1 of deadwood. In these stands, also forest floor (excluding deadwood) and soils are stores of relevant amount of carbon (5-9 MgC ha-1 litter layer, 4 stands; 168-420 MgC ha-1 mineral soil, 3 stands). Finally, carbon isotope discrimination (Δ) analysis, a proxy of wateruse efficiency, was applied on tree-ring cores from a subset of sites. The perspectives of this technique for a retrospective ecophysiological interpretation of climate-change impact on old-growth forests were described. Preliminary results obtained within this PRIN project indicate that the reported ecological indicators can be used to produce a description of forest structures and processes driving stand dynamics (‘structural-based approach’). Furthermore, the use of multiple sampling and research techniques and the integration of research groups with complementary expertise can foster deeper understanding of the ecology and dynamics of old-growth forests.L'articolo è disponibile sul sito dell'editore http://www.aisf.it

Stem Circadian Phenology of Four Pine Species in Naturally Contrasting Climates from Sky-Island Forests of the Western USA

We identified intra-annual climatic drivers of stem water relationships and growth in foundation conifers at a subalpine site in the Great Basin Desert and at a montane site in the Mojave Desert (Nevada, USA). Sites were instrumented to represent naturally different levels of heat and drought stress as part of NevCAN (the Nevada Climate and ecohydrological Assessment Network). We analyzed three years (2013–2015) of sub-hourly dendrometer records for limber (Pinus flexilis) and bristlecone pine (Pinus longaeva) at the subalpine site, and for ponderosa (Pinus ponderosa) and pinyon pine (Pinus monophylla) at the montane site. Multiple logistic regression was used to identify relationships with environmental variables measured in-situ. At both sites, stem expansion occurred during the early morning and late afternoon, and irreversible stem increment was concentrated in the early morning hours. In subalpine species, stem growth started in late spring and continued until August, while at the montane site stem growth was episodic, peaking during summer monsoonal rainstorms. Circadian maximum and minimum stem size during the growing season were reversed during the dormant season at the colder/wetter subalpine site but not at the warmer/drier montane one. Knowledge of intra-annual tree-water relationships and stem growth helps understand how sky island forests grow under highly diverse climatic conditions, including severe drought and heat stress

Wood Cellular Dendroclimatology

Dendroclimatic proxies can be generated from the analysis of wood cellular structures, allowing for a more complete understanding of the physiological mechanisms that control the climatic response of tree species. Century-long (1870–2013) time series of anatomical parameters were developed for Great Basin bristlecone pine (Pinus longaeva D.K. Bailey) by capturing strongly contrasted microscopic images through a Confocal Laser Scanning Microscope. Environmental information embedded in wood anatomical series was analyzed in comparison with ring-width series using measures of empirical signal strength. Response functions were calculated against monthly climatic variables to evaluate climate sensitivity of cellular features (e.g., lumen area; lumen diameter) for the period 1950–2013. Calibration-verification tests were used to determine the potential to generate long climate reconstructions from these anatomical proxies. A total of eight tree-ring parameters (two ring-width and six chronologies of xylem anatomical parameters) were analyzed. Synchronous variability among samples varied among tree-ring parameters, usually decreasing from ring-width to anatomical features. Cellular parameters linked to plant hydraulic performance (e.g., tracheid lumen area and radial lumen diameter) showed empirical signal strength similar to ring-width series, while noise was predominant in chronologies of lumen tangential width and cell wall thickness. Climatic signals were different between anatomical and ring-width chronologies, revealing a positive and temporally stable correlation of tracheid size (i.e., lumen and cell diameter) with monthly (i.e., March) and seasonal precipitation. In particular, tracheid lumen diameter emerged as a reliable moisture indicator and was then used to reconstruct total March–August precipitation from 1870 to 2013. Wood anatomy holds great potential to refine and expand dendroclimatic records by allowing estimates of plant physiological adaptations to external stressors. Integrating xylem cellular features with ring-width chronologies can widen our understanding of past climatic variability (including annual extreme events) and improve the evaluation of long-term plant response to drought, especially in connection with future warming scenarios.Peer Reviewe

Climatic influences on wood anatomy and tree-ring features of Great Basin conifers at a new mountain observatory

Premise of the study: A network of mountain observing stations has been installed in the Great Basin of North America. NevCAN (Nevada Climate-ecohydrological Assessment Network), which spans a latitudinal range of 2.5° and two elevation ranges of about 2000 m each, enabled us to investigate tree growth in relation to climate. Methods: We analyzed wood anatomy and tree-ring characteristics of four conifer species in response to different levels of water availability by comparing a low- and a high-elevation population. Chronologies of earlywood and latewood widths, as well as cellular parameters, were developed from the year 2000 to 2012. Results: At the southern (drier and warmer) sites, Pinus monophylla had smaller cell lumen, tracheid diameter, and cell wall thickness. Pinus monophylla and P. flexilis showed bigger cellular elements at the higher elevations, whereas the opposite pattern was found in Picea engelmannii and Pinus longaeva. When all species and sites were pooled together, stem diameter was positively related with earlywood anatomical parameters. Discussion: We have provided a glimpse of the applications that NevCAN, as a new scientific tool, could allow in the general field of botany. In particular, we were able to investigate how differences in water stress related to elevation lead to changes in xylem anatomy

Water-Use Efficiency of Co-occurring Sky-Island Pine Species in the North American Great Basin

Water-use efficiency (WUE), weighing the balance between plant transpiration and growth, is a key characteristic of ecosystem functioning and a component of tree drought resistance. Seasonal dynamics of tree-level WUE and its connections with drought variability have not been previously explored in sky-island montane forests. We investigated whole-tree transpiration and stem growth of bristlecone (Pinus longaeva) and limber pine (Pinus flexilis) within a high-elevation stand in central-eastern Nevada, United States, using sub-hourly measurements over 5 years (2013-2017). A moderate drought was generally observed early in the growing season, whereas interannual variability of summer rains determined drought levels between years, i.e., reducing drought stress in 2013-2014 while enhancing it in 2015-2017. Transpiration and basal area increment (BAI) of both pines were coupled throughout June-July, resulting in a high but relatively constant early season WUE. In contrast, both pines showed high interannual plasticity in late-season WUE, with a predominant role of stem growth in driving WUE. Overall, bristlecone pine was characterized by a lower WUE compared to limber pine. Dry or wet episodes in the late growing season overrode species differences. Our results suggested thresholds of vapor pressure deficit and soil moisture that would lead to opposite responses of WUE to late-season dry or wet conditions. These findings provide novel insights and clarify potential mechanisms modulating tree-level WUE in sky-island ecosystems of semi-arid regions, thereby helping land managers to design appropriate science-based strategies and reduce uncertainties associated with the impact of future climatic changes