The importance of tropical tree-ring chronologies for global change research

Quaternary Science Reviews · 2025-03-06 · 24 citations

Tropical forests and woodlands are key components of the global carbon and water cycles. Yet, how climate change affects these biogeochemical cycles is poorly understood because of scarce long-term observations of tropical tree growth. The recent rise in tropical tree-ring studies may help to fill this gap, but a large-scale quantitative analysis of their potential in global change research is missing. We compiled a list of all tropical tree species known to form annual tree rings and built a network encompassing 492 tropical ring-width chronologies to evaluate the potential to generate insights on climate sensitivity of woody productivity and to build centuries-long reconstructions of climate variability. We assess chronology quality, length, and climatic representativeness and explore how these change along climatic gradients. Finally, we applied species-distribution modeling to identify regions with potential for tree-ring studies in ecological and climatic studies. The number of tropical chronologies has rapidly increased, with ∼400 added over the past two decades. Yet, tree-ring studies are biased towards high-elevation locations, with gaps in warmer and wetter climates, on the African continent, and for angiosperm species. The longest chronologies with strongest climate signals (i.e., synchronous growth variations among trees) are from cool regions. In wet regions, climate signals and precipitation sensitivity decrease. Most tropical regions harbor 5–15 (and up to 80) species with proven potential to generate chronologies. The potential for long climate reconstructions is particularly high in drier high elevation sites. Our findings support strategies to effectively expand tree-ring research in the tropics, by targeting specific species and regions. Tropical dendrochronology can importantly contribute to global change research by generating historical context of climate extremes, quantifying climate sensitivity of woody productivity and benchmarking vegetation models.

Climate reconstruction for Dalat city, Lamdong province, Vietnam using tree rings of Keleeteria Evelyniana Mast

2025-06-02

Keteleeria evelyniana Mast., a long-lived conifer species, has high timber and non-timber values. It is also listed in the Red List of the International Union for Conservation of Nature (VU - IUCN, 2024). It is mainly distributed in the mixed broad-leaved and coniferous forests in the Central Highlands of Vietnam and some other areas of Vietnam, such as Vu Quang National Park, Ha Tinh province. This study aimed to identify the impacts of climatic factors and climatic dynamics on the tree ring width of Keteleeria evelyniana Mast., at the main different sites of the Central Highlands. Haglöf Sweden®

Pantropical tree rings show small effects of drought on stem growth

Science · 2025-07-31 · 14 citations

Increasing drought pressure under anthropogenic climate change may jeopardize the potential of tropical forests to capture carbon in woody biomass and act as a long-term carbon dioxide sink. To evaluate this risk, we assessed drought impacts in 483 tree-ring chronologies from across the tropics and found an overall modest stem growth decline (2.5% with a 95% confidence interval of 2.2 to 2.7%) during the 10% driest years since 1930. Stem growth declines exceeded 10% in 25% of cases and were larger at hotter and drier sites and for gymnosperms compared with angiosperms. Growth declines generally did not outlast drought years and were partially mitigated by growth stimulation in wet years. Thus, pantropical forest carbon sequestration through stem growth has hitherto shown drought resilience that may, however, diminish under future climate change.

<i>Robinia pseudoacacia,</i> a nitrogen-fixing tree, facilitates the future growth of neighboring trees in Black Rock Forest

Canadian Journal of Forest Research · 2025-01-01

Trees that form symbioses with nitrogen (N)-fixing bacteria (N fixers) have long been thought to facilitate neighbors’ growth by providing new N, but some data do not show facilitation. Two hypotheses to explain the lack of facilitation are that (1) N fixers may decrease the amount of N they fix over time, reducing the N supply to their neighbors and (2) the effect of facilitation might take longer than the 1–5-year interval of most studies. In this study, we tested these hypotheses with the N-fixing tree Robinia pseudoacacia L. and its nonfixing neighbors, using tree ring N isotopes to estimate past N fixation and tree ring width to estimate past size and growth. Where the isotopes allowed a constrained estimate of N fixation, we did not find support for the first hypothesis: 51% of Robinia’s N came from fixation throughout its 60-year lifespan, with little variation across age. In support of the second hypothesis, we found that Robinia enhanced growth of neighboring trees in the future (up to 14 years) more than in the present. This delayed effect matches the expected timing of facilitation by N fixers and indicates that single-census studies might underestimate the degree to which N fixers facilitate forest growth.

Correcting the heartwood-sapwood transition in blue intensity measurements with change point detection methods

Dendrochronologia · 2025-04-14 · 1 citations

Delta blue intensity is a commonly used method to correct for the heartwood-sapwood color change in blue intensity (BI) measurements. It is based on the assumption that the heartwood-sapwood color change is similar in both earlywood and latewood. This assumption has not been supported physiologically. Furthermore, delta BI may confound the climate signals in earlywood and latewood BI as it is technically a linear combination of the other two. Here, instead of using delta BI, we used change point detection to identify the heartwood-sapwood transition, and corrected for the color change by rescaling the mean and variance of BI measurements after the transition to those immediately before. We tested three different change point detection methods and found that they agreed well with one another. Importantly, our approach preserves the climate signals in both earlywood and latewood BI data, while delta BI causes a total loss of climate signals in our test case. Therefore, we suggest that change point detection should be used instead of delta BI to account for the heartwood-sapwood color change. • Multiple methods for change point detection in blue intensity (BI) data agree well with one another. • After color change adjustment, earlywood and latewood BI capture temperature signals much better than unadjusted delta BI. • Change point detection should be used instead of delta blue intensity to correct for the heartwood-sapwood color change.

Monsoon climatic signal is stronger in wood anatomical traits than in ring widths of Fokienia hodginsii in central Vietnam

Dendrochronologia · 2025-06-24

Dendrochronological studies conducted in tropical regions in recent decades revealed that some species exhibit annual rings. In Southeast Asia, several ring-width chronologies of Fokienia hodginsii (Dunn) A. Henry & H H.Thomas were established to reconstruct past climatic conditions. Nevertheless, despite the strong correlations with meteorological data, the climate signal in the ring-width chronologies is robust for the shoulder season of the monsoon. For those interested in intra-annual climate signals, other parameters might prove useful. Information on intra-annual variability is crucial for understanding tree growth processes and climate dynamics in tropical regions. In this study, we explore the potential of wood anatomical parameters for climate reconstruction and for gaining a better understanding of the current climate of Southeast Asia. Microslides from cores of F. hodginsii in central Vietnam were analyzed. Notably, average lumen perimeter and lumen length demonstrated the most robust climate signals. They exhibit stronger correlations than ring width with maximum temperature, precipitation, and the Standardized Precipitation Evapotranspiration Index. The highest correlation (r=0.5) was observed between lumen area and October-November-December precipitation. Furthermore, earlywood parameters show higher correlations with precipitation than whole ring parameters. The growth of earlywood in F. hodginsii appears to be influenced by climatic conditions during September-October-November of the previous year and April of the current year. Thus, earlywood is generally produced around April, whereas latewood grows during or after April-May-June. This study is the first attempt to use anatomical parameters to reconstruct climate in Southeast Asia and provides valuable insights into the intra-annual growth dynamics of tropical tree rings.

Quantifying the internal and external drivers of Southeast Asian rainfall extremes on decadal timescales

Climate Dynamics · 2024-09-12 · 2 citations

Abstract Rainfall over mainland Southeast Asia experiences variability on seasonal to decadal timescales in response to a multitude of climate phenomena. Historical records and paleoclimate archives that span the last millennium reveal extreme multi-year rainfall variations that significantly affected the societies of mainland Southeast Asia. Here we utilize the Community Earth System Model Last Millennium Ensemble (CESM-LME) to quantify the contributions of internal and external drivers to decadal-scale rainfall extremes in the Southeast Asia region. We find that internal variability was dominant in driving both Southeast Asian drought and pluvial extremes on decadal timescales although external forcing impacts are also detectable. Specifically, rainfall extremes are more sensitive to Pacific Ocean internal variability than the state of the Indian Ocean. This discrepancy is greater for droughts than pluvials which we suggest is attributable to external forcing impacts that counteract the forced Indian Ocean teleconnections to Southeast Asia. Volcanic aerosols, the most effective radiative forcing during the last millennium, contributed to both the Ming Dynasty Drought (1637–1643) and the Strange Parallels Drought (1756–1768). From the Medieval Climate Anomaly to the Little Ice Age, we observe a shift in Indo-Pacific teleconnection strength to Southeast Asia consistent with enhanced volcanism during the latter interval. This work not only highlights asymmetries in the drivers of rainfall extremes but also presents a framework for quantifying multivariate drivers of decadal-scale variability and hydroclimatic extremes.

Correcting the Heartwood-Sapwood Transition in Blue Intensity Measurements with Change Point Detection Methods

SSRN Electronic Journal · 2024-01-01

Polb 001, an Oral Broad-Spectrum Anti-Inflammatory with the Potential to Prevent Cytokine Release Syndrome (CRS)

Blood · 2023-11-02 · 3 citations

Background Cytokine Release Syndrome (CRS) is a well-recognized toxicity that occurs with high frequency following treatments such as T-cell engaging antibodies, Chimeric Antigen Receptor (CAR) T cells and other T-cell boosting immunotherapies. In addition to patient mortality and morbidity, the high frequency of CRS associated with these treatments represents a barrier to delivery in the outpatient setting. The need for inpatient management of CRS adds to the costs of these treatments and contributes to restricting their availability. Current treatments are dominated by reactive administration of tocilizumab, steroids or anakinra. POLB 001 is a p38 MAPK inhibitor in development for severe influenza infections and CRS. In vivo, POLB 001 acts as a broad-spectrum anti-inflammatory by potently inhibiting the expression of proinflammatory cytokines such as IL-1β, IL-6, IL-8, IL-10, TNFα, COX-2. Methods In this single-center, randomized, double blinded, placebo-controlled, multiple dose study (NCT05765955), 36 healthy volunteers were orally administered 30, 70 or 150 mg POLB 001 or placebo BD (3:1 active to placebo) for 7 days. Each subject was then challenged with intradermal lipopolysaccharide (LPS) and intravenous LPS which drive local and systemic inflammation, respectively. The study objectives were to study the effect of POLB 001 on inflammatory responses following LPS challenge, including cytokine analysis, exploratory analysis including PK and metabolite profile and the safety and tolerability of POLB 001. Results No deaths or serious adverse events occurred during the study. The most commonly reported AE was headache, with the highest number of participants and events in the placebo group (8 (88.9%) subjects and 14 events) followed by the POLB 001 30 mg group (6 (66.7%) subjects and 11 events). Other reported AEs included chills (also more frequent in placebo group) and dizziness (placebo, POLB001 30, 70, 150 mg groups, frequency 22.2%, 11.1%, 33.3%, 22.2%, respectively). POLB 001 reduced levels of activated p38 (phospho-p38) in circulating monocytes by 32.0-60.9%. Reductions were seen in all cytokines measured. Significant reductions were seen in plasma IL-6, IL-8, IL-10 and TNFα. IL-1β levels were below the LLOQ in active and placebo groups. LPS-driven C-Reactive Protein (CRP) was reduced by 70 and 150 mg doses of POLB 001 (33.1 and 33.3%, respectively). Intravenous LPS challenge elevated body temperature by 1°C and HR by &amp;gt;25 BPM with a peak 3 hours following infusion. POLB 001 significantly reduced HR elevations with an estimated difference in peak HR of -8.8 and -7.8 in the 70 and 150 mg groups respectively. Conclusion POLB 001 is safe and tolerable in healthy volunteers. In a human LPS challenge model driving an acute systemic inflammatory response, POLB 001 showed anti-inflammatory effects and clinically meaningful parameters of inflammation were also reduced. The results support further clinical development of POLB 001 for inflammatory diseases and CRS. POLB 001 is undergoing preclinical evaluation in humanized mouse models (NSG-(KbDb)null (IA)null) of T-cell engaging bispecific antibodies, CD19 CAR-T cell therapy for hematological malignancies and for CD28 induced cytokine storm. A Phase 2 trial of POLB 001 in Multiple Myeloma patients receiving T-cell engaging antibodies is planned.

Nonlinear Growth and Physiological Responses of White Spruce at North American Arctic Treeline

Journal of Geophysical Research Biogeosciences · 2023-04-01 · 6 citations

Abstract Much is still unknown about the growth and physiological responses of trees to global change at the northern treeline. We combined tree‐ring width data with century‐long stable carbon and oxygen isotope records to investigate growth and physiological responses of white spruce at two treeline sites in the Canadian Arctic to concurrent increases in temperature, atmospheric CO 2 concentration ( c a ), and decline in sea ice extent over the past century. The tree‐ring records were assessed during three periods with contrasting climatic conditions: (a) the early 20th century warming, (b) the 1940–1970 cooling period, and (c) the anthropogenic late 20th century warming period. We found opposing growth trends between the two sites, but similar carbon isotope discrimination (Δ 13 C) and intrinsic water‐use efficiency ( i WUE) trajectories. While tree growth (defined as basal area increment) increased at the site nearer to the Arctic Ocean during the 20th century following the rise in temperature and sea ice loss, growth declined after 1950 at the more interior site. At both sites, Δ 13 C slightly increased over these periods. However, trees showed a nonlinear response to increased c a , shifting after 1970 from a passive stomatal response (i.e., no changes in i WUE) to an active response (i.e., a moderate ∼12% increase in i WUE). Further, our isotope‐based findings do not support the idea that temperature‐induced drought stress caused the divergent growth trends at our treeline sites. This study thus highlights nonlinear and complex physiological and growth adjustments to concomitant changes in temperature, sea ice extent, and c a over the last century at the northern treeline.