Niche separation and weak interactions in the high tidal zone of saltmarsh‐mangrove mixing communities

1. Saltmarsh‐mangrove ecotones occur at the boundary of the natural geographic distribution of mangroves and salt marshes. Climate warming and species invasion can also drive the formation of saltmarsh‐mangrove mixing communities. How these coastal species live together in a “new” mixed community is important in predicting the dynamic of saltmarsh‐mangrove ecosystems as affected by ongoing climate change or human activities. To date, the understanding of species interactions has been rare on adult species in these ecotones.
2. Two typical coastal wetlands were selected as cases to understand how mangrove and saltmarsh species living together in the ecotones. The leaves of seven species were sampled from these coastal wetlands based on their distribution patterns (living alone or coexisting) in the high tidal zone, and seven commonly used functional traits of these species were analyzed.
3. We found niche separation between saltmarsh and mangrove species, which is probably due to the different adaptive strategies they adopted to deal with intertidal environments.
4. Weak interactions between coexisting species were dominated in the high tidal zone of the two saltmarsh‐mangrove communities, which could be driven by both niche differentiation and neutral theory.
5. Synthesis. Our field study implies a potential opportunity to establish a multispecies community in the high tidal zone of saltmarsh‐mangrove ecotones, where the sediment was characterized by low salinity and high nitrogen.

     

Growth form and leaf habit drive contrasting effects of Arctic amplification in long-lived woody species

Current global change is inducing heterogeneous warming trends worldwide, with faster rates at higher latitudes in the Northern Hemisphere. Consequently, tundra vegetation is experiencing an increase in growth rate and uneven but expanding distribution. Yet, the drivers of this heterogeneity in woody species responses are still unclear. Here, applying a retrospective approach and focusing on long-term responses, we aim to get insight into growth trends and climate sensitivity of long-lived woody species belonging to different functional types with contrasting growth forms and leaf habits (shrub vs. tree and deciduous vs. evergreen). A total of 530 samples from 7 species (common juniper, dwarf birch, woolly willow, Norway spruce, lodgepole pine, rowan, and downy birch) were collected in 10 sites across Iceland. We modelled growth trends and contrasted yearly ring-width measurements, filtering in high- and low-frequency components, with precipitation, land- and sea-surface temperature records (1967–2018). Shrubs and trees showed divergent growth trends, with shrubs closely tracking the recent warming, whereas trees, especially broadleaved, showed strong fluctuations but no long-term growth trends. Secondary growth, particularly the high-frequency component, was positively correlated with summer temperatures for most of the species. On the contrary, growth responses to sea surface temperature, especially in the low frequency, were highly diverging between growth forms, with a strong positive association for shrubs and a negative for trees. Within comparable vegetation assemblage, long-lived woody species could show contrasting responses to similar climatic conditions. Given the predominant role of oceanic masses in shaping climate patterns in the Arctic and Low Arctic, further investigations are needed to deepen the knowledge on the complex interplay between coastal tundra ecosystems and land-sea surface temperature dynamics.     

Comparative dendroecological characterisation of Ailanthus altissima (Mill.) Swingle in its native and introduced range

Knowledge on the ecology of tree species in both their native and introduced range can increase the understanding of their successful establishment and spread outside the native range. Here, we analysed radial growth patterns of Ailanthus altissima (Mill.) Swingle in two sites in its native range in eastern China and in two sites in the introduced range in southern Switzerland, where it started to disperse into forests in the 1950s. Growth rates were similar despite lower amounts of growing season precipitation in China. Furthermore, we found negative correlations between annual radial growth and average temperatures in the growing season at the warmest of the four sites, which suggest that radial growth of A. altissima starts to be limited by average growing season temperatures above 21 °C. Regarding wood anatomy, we did not find clear correlations between vessel lumen area and monthly temperature or precipitation at the time of tissue formation in spring. Overall, our results demonstrate that A. altissima has the potential to grow in drier conditions than currently found in Switzerland, which is in line with previous studies.     

xRing—An R package to identify and measure tree-ring features using X-ray microdensity profiles

Climate influences tree-ring density and ring-density variables extracted from X-ray images have been widely used for climate reconstructions. The R package xRing was developed to identify and measure tree rings on X-ray microdensity profiles automatically. This package is available for free and it offers functions to visualize and calibrate X-ray images, to detect tree-ring borders and to identify earlywood-latewood transition using wood density variations at the inter- and the intra-ring scale. The most important functions are calibrateFilm, detectRings, correctRings, detectEwLw, and getDensity. Outputs of these functions are S3 objects, for which specific methods are provided, including plot and print. The non-linear relationship between optical density of the film and wood density is defined by the function calibrateFilm. The function detectRings detects tree rings using wood density profiles as input. This function uses the difference between local maximum and minimum values to identify tree-ring borders automatically. The correctRings function is used to call a Graphical User Interface (GUI) to visualize and to correct tree-ring borders manually. After correcting tree-ring borders, the detectEwLw function is used to compute earlywood and latewood widths by dividing rings according to relative intra-ring density changes. The getDensity function computes for each tree ring the minimum (maximum) density and the mean earlywood, latewood and whole-ring density. Finally, a list with dataframes with tree-ring width and density variables can be obtained using the function getRwls. One of the major advantages of xRing package is that requires little knowledge of R language, but at the same time it can be easily changed or adapted by experienced users.     

Returning (to) the roots of dendrochronology – Requiem for Jacobus Cornelius Kapteyn (1851–1922)

The need to understand natural climate variability and improve weather forecasts gave birth to the first tree-ring reconstructions more than a century ago in Europe and North America, and still defines a central motivation for modern paleoclimatology: learning from the past to prepare for the future.     

Investigating the potential for Southern Hemisphere climate reconstruction using stable isotopes in Tasmanian tree rings

Few annually dated stable isotope records exist across Oceania. Stable carbon and oxygen isotope ratios have the potential to enhance climate reconstructions currently reliant on tree ring width chronologies. The purpose of this study is to explore the sources of variability in a stable oxygen isotope chronology derived from A. selaginoides from Mount Read, Tasmania. This high elevation site receives abundant rainfall throughout the year and is ∼130 km from the Global Network of Isotopes in Precipitation (GNIP) site at Cape Grim. We crossdated 10 new tree core samples against an existing ring width chronology (954–2011 CE) and analyzed the δ¹⁸O from the individual rings for the period 1960–2018. Using high resolution (0.25 degrees) climate data and ECMWF ERA5 reanalysis data, we disentangled the effects of local climate and source region on the isotopic signatures recorded in the annual rings. In addition, we used HYSPLIT backward trajectory analysis to characterize the source region of precipitation to Mount Read and whether the source region has influence over the δ¹⁸O_TR series. Median δ¹⁸O_TR (n = 10) is correlated with local temperature and vapor pressure deficit in the early growing season. In addition, spatial correlations reveal that median δ¹⁸O_TR is positively correlated with temperature and negatively correlated with precipitation in the source region. However, measurements of δ¹⁸O_TR exhibit high inter-tree variation, particularly between 1960 and 1990. Our results indicate that this δ¹⁸O_TR proxy may provide additional information about past moisture conditions during the growing season, potentially contributing to more robust reconstructions of the Southern Hemisphere climate dynamics; however, additional sampling may be necessary to resolve inter-tree variation in δ¹⁸O_TR.     

Climate signal strength in tree-ring width of spruce growing in the Solovetsky Islands (Russia)

In this study we used 14 spruce tree-ring width local chronologies from sites that are located in different landscape conditions. The climatic response function for the entire period (116 years) shows that all local chronologies without exception have a positive relationship with June temperature (from 0.196 to 0.408) despite quite different local environmental conditions. This finding allowed us to combine all tree-ring width local chronologies into a composite spruce chronology covering the period of 1676–2016 CE with EPS exceeding the 0.85 threshold. The composite chronology was scaled against June air temperatures (CRU TS 4.01) in order to reconstruct it. Monthly air temperature records from the Arkhangelsk weather station were used as an additional source to validate tree-ring based June temperature reconstruction. It is quite remarkable that our reconstruction matches the Archangelsk records not only in the 20th-early 21st centuries but also in the 19th century, confirming the reliability of the reconstruction over more than two centuries. We also used daily records from the nearest Kem’-Port station to identify a more precise target-window. Current research shows that the spruce response to daily temperature is not limited by June, but also extends up to almost half of July. The warmest reconstructed year occurred in 1856 as confirmed by the data published in the local chronicle. The cooling recorded in the historical evidences (describing extremely severe ice conditions in the Arctic seas during the Great Northern Expedition (1733–1743)) was not corroborated by our reconstruction. In the study, we discuss the reasons of the discrepancies found between Solovki June temperature reconstructions and other data such as different seasonality of the compared records, real local climate warming in Solovki, the applied standardization technique, and low of chronologies’ replication. The most reliable part of the reconstruction part lasting from the early 19th to the early 21st centuries is also discussed in terms of its properties like wavelength analyses, and the assessment of influence of volcanic eruptions.     

Variations in the tree-ring structure of Norway spruce (Picea abies) under contrasting climates

Variations in tree-ring structure from pith to bark of mature Norway spruce (Picea abies Karst. (L)) grown under contrasting climate conditions (warm-dry vs. cool-humid) in south-western Germany were investigated. Sample trees were from even-aged stands where no intensive silvicultural treatments had taken place. The cell number (CN), diameter (CD), lumen diameter (CL) and wall thickness (CW) were measured from stem cross-sections taken at breast height. A raw data chronology of each cell parameter was established for the whole annual ring (AR), earlywood (EW), latewood (LW), and transition wood (TW). The long-term trends of the cell parameters were generally non-linear, parameter-specific in AR and EW and similar over sites. Those in LW were site-specific and similar over cell parameters. The variation of the same parameter, expressed by the coefficient of variance (CV), tended to increase from EW towards LW and was clearly higher for CN than for other cell parameters of all tree-ring zones. Trees from the warm-dry site had more LW cells and substantially thicker CW, whereas those from the cool-humid site had larger EW cells. These observed differences are likely due to the hydraulic adaptation mechanisms of trees to different site conditions.