Tree‐ring records provide global high‐resolution information on tree‐species responses to global change, forest carbon and water dynamics, and past climate variability and extremes. The underlying ...assumption is a stationary (time‐stable), quasi‐linear relationship between tree growth and environment, which however conflicts with basic ecological and evolutionary theory. Indeed, our global assessment of the relevant tree‐ring literature demonstrates non‐stationarity in the majority of tested cases, not limited to specific proxies, environmental parameters, regions or species. Non‐stationarity likely represents the general nature of the relationship between tree‐growth proxies and environment. Studies assuming stationarity however score two times more citations influencing other fields of science and the science–policy interface. To reconcile ecological reality with the application of tree‐ring proxies for climate or environmental estimates, we provide a clarification of the stationarity concept, propose a simple confidence framework for the re‐evaluation of existing studies and recommend the use of a new statistical tool to detect non‐stationarity in tree‐ring proxies. Our contribution is meant to stimulate and facilitate discussion in light of our results to help increase confidence in tree‐ring‐based climate and environmental estimates for science, the public and policymakers.
Tree‐ring records provide global high‐resolution information on tree‐species responses to global change, forest carbon and water dynamics, and past climate variability and extremes. The underlying assumption is a stationary (time‐stable), quasi‐linear relationship between tree growth and environment. Our results show that this assumption might be too simplistic. Non‐stationarity between tree growth and climatic or environmental drivers is evident at global scale.
The jaboticaba tree (Plinia peruviana (Poir.) Govaerts) is a native Brazilian species, and its fruits are very popular in Brazil. The purpose of this study was to model the diameter growth, and ...determine the age of jaboticaba trees in four natural populations in Southwest of Paraná State, Brazil. The knowledge of the growth dynamics of this species is essential to assist management and conservation strategies and to discover when this species was established in the region. Core samples were collected to obtain complete growth series by measurement of annual growth rings. The series were crossdated, seven growth models were adjusted, and the best model for each site and a general model were selected using statistics rules. The time series spanned periods of ~75 to ~100 years, and growth ranged between 0.27 and 0.37 cm year-1. Chapman-Richards' model showed better adherence for locations individually, and Monomolecular when grouped. Because to the age reached by the jaboticaba trees and the high density of this species in these natural populations, consequently named "jaboticabais", it was inferred that there was an anthropogenic action in the dispersion and formation of the settlements through the indigenous and caboclos that inhabited the region before 1940. Also, this is the first work to register and verify the fusion of trunks for species of the Plinia genus using double piths found in samples, a feature that must be considered to avoid overestimating the age of jaboticaba trees based solely on measuring tree diameter.
Considerable evidence exists that current global temperatures are higher than at any time during the past millennium. However, the long-term impacts of rising temperatures and associated shifts in ...the hydrological cycle on the productivity of ecosystems remain poorly understood for mid to high northern latitudes. Here, we quantify species-specific spatiotemporal variability in terrestrial aboveground biomass stem growth across Canada’s boreal forests from 1950 to the present. We use 873 newly developed tree-ring chronologies from Canada’s National Forest Inventory, representing an unprecedented degree of sampling standardization for a large-scale dendrochronological study. We find significant regional- and species-related trends in growth, but the positive and negative trends compensate each other to yield no strong overall trend in forest growth when averaged across the Canadian boreal forest. The spatial patterns of growth trends identified in our analysis were to some extent coherent with trends estimated by remote sensing, but there are wide areas where remote-sensing information did not match the forest growth trends. Quantifications of tree growth variability as a function of climate factors and atmospheric CO₂ concentration reveal strong negative temperature and positive moisture controls on spatial patterns of tree growth rates, emphasizing the ecological sensitivity to regime shifts in the hydrological cycle. An enhanced dependence of forest growth on soil moisture during the late-20th century coincides with a rapid rise in summer temperatures and occurs despite potential compensating effects from increased atmospheric CO₂ concentration.
The urban environment features poor air quality and harsher climate conditions that affect the life in the cities. Citizens are especially vulnerable to climate change, because heat island and ...impervious exacerbates extreme climate events. Urban trees are important tools for mitigation and adaptation of cities to climate change because they provide ecosystem services that increase while trees grow. Nonetheless, the growth of trees may be affected by the harsher conditions found in the urban environment. We assessed the impact of air pollution and climate on the spatial/temporal variability of tree growth in São Paulo, Brazil, one of the largest urban conglomerates in the world. For this purpose, we sampled 41 trees of the Tipuana tipu species in a region that includes industrial areas. We built a tree-ring chronology using standard dendrochronological methods. Spatial analyses show that trees grow faster in the warmer parts of the city and under higher concentrations of airborne P, whereas growth is reduced under higher concentrations of Al, Ba, Zn. Particulate matter (PM10) from the industrial cluster also reduce average growth rate of trees, up to 37% in all diameter classes. Similar results were obtained via temporal analyses, suggesting that the annual growth rate is positively associated with temperature, which explain 16% of interannual growth variability. Precipitation, on the other hand, has no association with tree growth. The average concentration of PM10 explains 41% of interannual growth variability, and higher concentrations during the driest months reduce growth rate. Despite heat island effect and water limitation in the soil of the city, this species takes advantage of warmer conditions and it is not limited by water availability as measured by precipitation. On the other hand, air pollution directly impacts the growth of these trees being a major limiting growth factor.
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•Spatial/temporal variability of urban climate and air pollution affect tree growth.•Despite heat island effects, trees grow faster under warmer conditions•Despite water limitation by impervious cover, precipitation does not affect growth.•Air pollution (Al, Zn, Ba, PM10) has a stronger influence than climate on growth.•Cities can affect tree development and interfere with adaptation to climate change.
Understanding impacts of drought on tree growth and forest health is of major concern given projected climate change. Droughts may become more common in the Southwest due to extreme temperatures that ...will drive increased evapotranspiration and lower soil moisture, in combination with uncertain precipitation changes. Utilizing ~1.3 million tree-ring widths from the International Tree Ring Data Bank representing 10 species (eight conifers, two oaks) in the Southwest, we evaluated the effects of drought on tree growth. We categorized ring widths by formation year in relation to drought (pre-drought, drought year, and post-drought), and we used a mixed-effects model to estimate the effects of current and antecedent precipitation and temperature on tree growth during the post-drought recovery period. This allowed us to assess changes in sensitivity of tree growth to precipitation and temperature at multiple timescales following multiple droughts, and to evaluate drought resistance and recovery in these species. The effects of precipitation and temperature on ring widths following drought varied among species and time since drought. Across species, 16% of the climate effects (i.e., "sensitivities") were significantly different from their pre-drought values. Species differed, with some showing increased sensitivities to precipitation and temperature following drought, and others showing decreased sensitivities. Furthermore, some species (e.g., Abies concolor and Pinus ponderosa) showed low resistance and slow recovery, with changes in growth sensitivities persisting up to 5 yr; others (e.g., Juniper spp.) showed high resistance, such that their climatic sensitivities did not change. Among species, the importance of different antecedent climate variables changed with time since drought. Though a majority of species responded positively to same-year precipitation pre-drought, all 10 species were positively affected by same-year precipitation the second year after drought. Our results demonstrate tree growth sensitivities vary among species and with time since drought, raising questions about physiological mechanisms and implications for forest health under future drought.
Severe drought can cause lagged effects on tree physiology that negatively impact forest functioning for years. These “drought legacy effects” have been widely documented in tree‐ring records and ...could have important implications for our understanding of broader scale forest carbon cycling. However, legacy effects in tree‐ring increments may be decoupled from ecosystem fluxes due to (a) postdrought alterations in carbon allocation patterns; (b) temporal asynchrony between radial growth and carbon uptake; and (c) dendrochronological sampling biases. In order to link legacy effects from tree rings to whole forests, we leveraged a rich dataset from a Midwestern US forest that was severely impacted by a drought in 2012. At this site, we compiled tree‐ring records, leaf‐level gas exchange, eddy flux measurements, dendrometer band data, and satellite remote sensing estimates of greenness and leaf area before, during, and after the 2012 drought. After accounting for the relative abundance of tree species in the stand, we estimate that legacy effects led to ~10% reductions in tree‐ring width increments in the year following the severe drought. Despite this stand‐scale reduction in radial growth, we found that leaf‐level photosynthesis, gross primary productivity (GPP), and vegetation greenness were not suppressed in the year following the 2012 drought. Neither temporal asynchrony between radial growth and carbon uptake nor sampling biases could explain our observations of legacy effects in tree rings but not in GPP. Instead, elevated leaf‐level photosynthesis co‐occurred with reduced leaf area in early 2013, indicating that resources may have been allocated away from radial growth in conjunction with postdrought upregulation of photosynthesis and repair of canopy damage. Collectively, our results indicate that tree‐ring legacy effects were not observed in other canopy processes, and that postdrought canopy allocation could be an important mechanism that decouples tree‐ring signals from GPP.
Legacy effects in tree rings were large in response to a severe drought in a temperate forest. Despite this postdrought suppression of tree growth, ecosystem fluxes were not affected, likely due to dynamic C allocation away from stem growth towards the canopy.
•Drought-induced dieback in A. glutinosa was detected 20 years before signs of dieback.•Co-occurring defoliated trees area more sensitive to climate than non-defoliated.•Non-defoliated trees are more ...sensitive to the hydrology regime than defoliated.•Under drought defoliated trees took subsurface water and non-defoliated vadose water.•Analyses of tree growth allow anticipating shifts in tree vigour.
Progressive death of twigs and branches (i.e. dieback) may happen in response to biotic and abiotic agents thereby reducing tree growth and eventually death. Drought-induced dieback has been seldom studied in riparian habitats. We used retrospective tree-ring and oxygen isotope analyses to determine whether growth patterns, sensitivity to climate and hydrology, as well as access to deep subsurface water and microhabitat river variables, are related to Alnus glutinosa L. Gaertn. decline. Tree-ring sampling was conducted on A. glutinosa individuals showing dieback ‘declining’ (defoliated) and compared with paired ‘non‐declining’ (not defoliated) individuals in one slow-running stream. Radial growth of declining trees responded to the rate of precipitation-evapotranspiration from February to July more than non-declining. In contrast, the growth of non-declining trees positively correlated with the October river discharge of the year preceding tree-ring formation. After the severe 1998 drought, the growth of declining trees decreased in comparison to non‐declining trees, showing, since then, early warning signals of dieback. Since 1998, resilience decreased as drought events accumulate in declining trees, but not in non-declining trees. Also, trees situated near to the active river channel recover better from drought. In the 1998 tree ring, we found differences in δ18O between vigour classes suggesting that non-declining trees had access to deeper water pools in drought years. Our findings provide new information that could be used to forecast changes in black alder dynamics under the current climate change scenario, especially at the species’ xeric range edges, and assist managers in designing riparian forest adaptation strategies.
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