Demographic and net primary productivity dynamics of primary and secondary tropical forests in Southwest China under a changing climate

Tropical forests are major carbon sinks on the Earth's land surface. However, our understanding of how the demographic rate and carbon sink capacities of tropical forests respond to climate change remains limited. In this study, we investigated the impacts of environmental drivers on forest growth, mortality, recruitment, and stem net primary productivity (NPPstem) over 16 years at five tropical forest plots in Xishuangbanna, Southwest China. These plots are along a successional gradient spanning three tropical secondary forests (tropical secondary forest‐1 [TSF‐1], tropical secondary forest‐2 [TSF‐2], and tropical secondary forest‐3 [TSF‐3]) and two primary forests (tropical rainforest [TRF] and tropical karst forest [TKF]). Our results showed that early successional secondary forests (TSF‐2 and TSF‐3) had higher diameter growth rates and relative mortality rates. An extreme drought event during 2009–2010 reduced the growth rate, relative recruitment rate, and NPPstem for most plots while increasing mortality in early successional forest plots. We observed significant negative effects of maximum temperature (Tmax) on NPPstem and diameter growth rate across all plots. Additionally, we found that precipitation had significant positive effects on diameter growth rate across all plots. Furthermore, tree mortality increased with rising Tmax, whereas precipitation significantly enhanced tree recruitment. Our findings highlight the vulnerability of tree growth, mortality, recruitment, and productivity in tropical forests to extreme drought events in Southwest China. Continued climate warming and more frequent droughts will induce higher mortality rates and impede growth, thus reducing the carbon sink capacity of tropical forests, especially in early successional stage tropical secondary forests

Tropical tree growth driven by dry-season climate variability

Interannual variability in the global land carbon sink is strongly related to variations in tropical temperature and rainfall. This association suggests an important role for moisture-driven fluctuations in tropical vegetation productivity, but empirical evidence to quantify the responsible ecological processes is missing. Such evidence can be obtained from tree-ring data that quantify variability in a major vegetation productivity component: woody biomass growth. Here we compile a pantropical tree-ring network to show that annual woody biomass growth increases primarily with dry-season precipitation and decreases with dry-season maximum temperature. The strength of these dry-season climate responses varies among sites, as reflected in four robust and distinct climate response groups of tropical tree growth derived from clustering. Using cluster and regression analyses, we find that dry-season climate responses are amplified in regions that are drier, hotter and more climatically variable. These amplification patterns suggest that projected global warming will probably aggravate drought-induced declines in annual tropical vegetation productivity. Our study reveals a previously underappreciated role of dry-season climate variability in driving the dynamics of tropical vegetation productivity and consequently in influencing the land carbon sink.We acknowledge financial support to the co-authors provided by Agencia Nacional de Promoción Científica y Tecnológica, Argentina (PICT 2014-2797) to M.E.F.; Alberta Mennega Stichting to P.G.; BBVA Foundation to H.A.M. and J.J.C.; Belspo BRAIN project: BR/143/A3/HERBAXYLAREDD to H.B.; Confederação da Agricultura e Pecuária do Brasil - CNA to C.F.; Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES, Brazil (PDSE 15011/13-5 to M.A.P.; 88881.135931/2016-01 to C.F.; 88887.199858/2018-00 to G.A.-P.; Finance Code 001 for all Brazilian collaborators); Conselho Nacional de Desenvolvimento Científico e Tecnológico - CNPq, Brazil (ENV 42 to O.D.; 1009/4785031-2 to G.C.; 311874/2017-7 to J.S.); CONACYT-CB-2016-283134 to J.V.-D.; CONICET to F.A.R.; CUOMO FOUNDATION (IPCC scholarship) to M.M.; Deutsche Forschungsgemeinschaft - DFG (BR 1895/15-1 to A.B.; BR 1895/23-1 to A.B.; BR 1895/29-1 to A.B.; BR 1895/24-1 to M.M.); DGD-RMCA PilotMAB to B.T.; Dirección General de Asuntos del Personal Académico of the UNAM (Mexico) to R.B.; Elsa-Neumann-Scholarship of the Federal State of Berlin to F.S.; EMBRAPA Brazilian Agricultural Research Corporation to C.F.; Equatorian Dirección de Investigación UNL (21-DI-FARNR-2019) to D.P.-C.; São Paulo Research Foundation FAPESP (2009/53951-7 to M.T.-F.; 2012/50457-4 to G.C.; 2018/01847‐0 to P.G.; 2018/24514-7 to J.R.V.A.; 2019/08783-0 to G.M.L.; 2019/27110-7 to C.F.); FAPESP-NERC 18/50080-4 to G.C.; FAPITEC/SE/FUNTEC no. 01/2011 to M.A.P.; Fulbright Fellowship to B.J.E.; German Academic Exchange Service (DAAD) to M.I. and M.R.; German Ministry of Education, Science, Research, and Technology (FRG 0339638) to O.D.; ICRAF through the Forests, Trees, and Agroforestry research programme of the CGIAR to M.M.; Inter-American Institute for Global Change Research (IAI-SGP-CRA 2047) to J.V.-D.; International Foundation for Science (D/5466-1) to M.I.; Lamont Climate Center to B.M.B.; Miquelfonds to P.G.; National Geographic Global Exploration Fund (GEFNE80-13) to I.R.; USA’s National Science Foundation NSF (IBN-9801287 to A.J.L.; GER 9553623 and a postdoctoral fellowship to B.J.E.); NSF P2C2 (AGS-1501321) to A.C.B., D.G.-S. and G.A.-P.; NSF-FAPESP PIRE 2017/50085-3 to M.T.-F., G.C. and G.M.L.; NUFFIC-NICHE programme (HEART project) to B.K., E.M., J.H.S., J.N. and R. Vinya; Peru ‘s CONCYTEC and World Bank (043-2019-FONDECYT-BM-INC.INV.) to J.G.I.; Peru’s Fondo Nacional de Desarrollo Científico, Tecnológico y de Innovación Tecnológica (FONDECYT-BM-INC.INV 039-2019) to E.J.R.-R. and M.E.F.; Programa Bosques Andinos - HELVETAS Swiss Intercooperation to M.E.F.; Programa Nacional de Becas y Crédito Educativo - PRONABEC to J.G.I.; Schlumberger Foundation Faculty for the Future to J.N.; Sigma Xi to A.J.L.; Smithsonian Tropical Research Institute to R. Alfaro-Sánchez.; Spanish Ministry of Foreign Affairs AECID (11-CAP2-1730) to H.A.M. and J.J.C.; UK NERC grant NE/K01353X/1 to E.G.Peer reviewe

Site-specific climate sensitivity of tree-ring width and vessel anatomical features of Juglans regia L. in Bhutan Himalaya

Climate change significantly impacts tree growth in the Himalayas, however, there is little information on how broadleaved tree species in Himalayan regions respond to climate change. Juglans regia L. (Common or Persian walnut) plays a vital economic and ecological role across the Himalayas, but little is known about how environmental changes influence the growth and wood anatomical traits of this species. In this study, we developed chronologies of tree-ring width (TRW) and six quantitative vessel anatomical features of Persian walnut trees from two sites in the Bhutan Himalayas. We evaluated how TRW and vessel anatomical features respond to climatic conditions and extreme climate events for the period 1960–2020. We found the climate sensitivity of tree growth differed at the two study sites, with the southwest-facing Dodeyna site (DOD) exhibiting higher moisture sensitivity than the north-facing Chimithangka site (CHI). The climate sensitivity of vessel traits was much stronger than that of tree-ring widths, particularly at the DOD. Hydraulic efficiency-related vessel traits (Mean vessel area, MVA; theoretical hydraulic conductivity, Kh; and hydraulic diameter, Dh) were positively sensitive to moisture availability, whereas the hydraulic safety-related vessel traits (vessel density, VD; and vessel grouping index, RVGI) were negatively sensitive to moisture availability at the DOD site. We further observed that MVA and Kh were significantly higher during extreme dry events at CHI site but displayed opposite directions at DOD site. Notably higher RVGI at the DOD site during dry years indicated an enhancement of hydraulic safety against drought. These findings highlight that the climate sensitivity of tree-ring width and vessel traits of walnuts were site-specific and mediated by aspects with the drier site (south-facing slope) being more sensitive. Whilst consideration of the aspects and site-specific climate sensitivity of tree species is crucial to developing robust forest conservation strategies at a larger spatial scale in the Himalayan region which is more vulnerable to climate change

Long-term physiological and growth responses of Himalayan fir to environmental change are mediated by mean climate

High-elevation forests are experiencing high rates of warming, in combination with CO2 rise and (sometimes) drying trends. In these montane systems, the effects of environmental changes on tree growth are also modified by elevation itself, thus complicating our ability to predict effects of future climate change. Tree-ring analysis along an elevation gradient allows quantifying effects of gradual and annual environmental changes. Here, we study long-term physiological (ratio of internal to ambient CO2, i.e., Ci/Ca and intrinsic water-use efficiency, iWUE) and growth responses (tree-ring width) of Himalayan fir (Abies spectabilis) trees in response to warming, drying, and CO2 rise. Our study was conducted along elevational gradients in a dry and a wet region in the central Himalaya. We combined dendrochronology and stable carbon isotopes (δ13C) to quantify long-term trends in Ci/Ca ratio and iWUE (δ13C-derived), growth (mixed-effects models), and evaluate climate sensitivity (correlations). We found that iWUE increased over time at all elevations, with stronger increase in the dry region. Climate–growth relations showed growth-limiting effects of spring moisture (dry region) and summer temperature (wet region), and negative effects of temperature (dry region). We found negative growth trends at lower elevations (dry and wet regions), suggesting that continental-scale warming and regional drying reduced tree growth. This interpretation is supported by δ13C-derived long-term physiological responses, which are consistent with responses to reduced moisture and increased vapor pressure deficit. At high elevations (wet region), we found positive growth trends, suggesting that warming has favored tree growth in regions where temperature most strongly limits growth. At lower elevations (dry and wet regions), the positive effects of CO2 rise did not mitigate the negative effects of warming and drying on tree growth. Our results raise concerns on the productivity of Himalayan fir forests at low and middle (<3,300 m) elevations as climate change progresses

Growth-Climate Relationships and Long-Term Growth Trends of the Tropical Forest Tree <i>Choerospondias axillaris</i> (Anacardiaceae) in East-Central Thailand

Tropical forests play important roles in global carbon cycling. Tree-ring analysis can provide important information for understanding long-term trends in carbon-fixation capacity under climate change. However, tree-ring studies in tropical regions are limited. We carried out a tree-ring analysis to investigate the dendrochronological potential of the tropical forest tree Choerospondias axillaris (Anacardiaceae) in east-central Thailand. Our study focused on growth-climate relationships and long-term growth trends. A chronology was constructed covering the period from 1932 to 2019. The tree-ring width index of C.axillaris was positively correlated with precipitation in June, July, and October. Furthermore, growth of C.axillaris was positively correlated with the Standardized Precipitation-Evapotranspiration Index (SPEI) from July to October, indicating that growth of C.axillaris is mainly limited by moisture availability in the late monsoon season. Moving correlation analysis further revealed the consistency and temporal stability of the relationship of tree growth with monsoon season precipitation and SPEI during the period under study. There was a significant increasing trend in long-term growth from 1932 to 2002 (slope = 0.017, p p < 0.001). Our study provides important insight into the growth-climate correlations of a broad-leaved tree species in a dry evergreen forest in tropical Asia

Growth-Climate Relationships and Long-Term Growth Trends of the Tropical Forest Tree Choerospondias axillaris (Anacardiaceae) in East-Central Thailand

Tropical forests play important roles in global carbon cycling. Tree-ring analysis can provide important information for understanding long-term trends in carbon-fixation capacity under climate change. However, tree-ring studies in tropical regions are limited. We carried out a tree-ring analysis to investigate the dendrochronological potential of the tropical forest tree Choerospondias axillaris (Anacardiaceae) in east-central Thailand. Our study focused on growth-climate relationships and long-term growth trends. A chronology was constructed covering the period from 1932 to 2019. The tree-ring width index of C.axillaris was positively correlated with precipitation in June, July, and October. Furthermore, growth of C.axillaris was positively correlated with the Standardized Precipitation-Evapotranspiration Index (SPEI) from July to October, indicating that growth of C.axillaris is mainly limited by moisture availability in the late monsoon season. Moving correlation analysis further revealed the consistency and temporal stability of the relationship of tree growth with monsoon season precipitation and SPEI during the period under study. There was a significant increasing trend in long-term growth from 1932 to 2002 (slope = 0.017, p &lt; 0.001); however, long-term growth decreased from 2003 to 2019 (slope = &minus;0.014, p &lt; 0.001). Our study provides important insight into the growth-climate correlations of a broad-leaved tree species in a dry evergreen forest in tropical Asia

Association of geographic distribution and birth weight with sociodemographic factors of the maternal and newborn child of hilly and mountain regions of eastern Nepal: a cross-sectional study.

OBJECTIVES: To determine the association of geographic distribution, and birth weight with sociodemographic factors of the maternal and newborn child of hilly region (lower altitude) and mountain region (high altitude) of eastern Nepal as well as the prevalence of low birth weight (LBW) and large for gestational age (LGA) among term singleton deliveries in eastern Nepal. METHODOLOGY: A cross-sectional study was conducted in the district-level hospitals of Dhankuta, Tehrathum, Solukhumbu and Taplejung districts of eastern Nepal of Province 1. Mothers with preterm or post-term delivery, multiple pregnancies, stillbirth/intrauterine fetal death and incomplete records were excluded from the study with only 1386 term pregnancies (37-42 weeks) delivered at the respective facilities between 17 July 2019 and 16 July 2020 were included. The appropriate data were entered in Microsoft Excel 2019 V.16.0 and statistical analysis was performed by using the statistical package for social sciences, IBM SPSS V.29. RESULTS: The low maternal age, Dalit ethnic group, low gravidity, low parity, higher antenatal care (ANC) visits (≥4), incomplete deworming and dT vaccination status, breech deliveries and LBW newborns were significantly attributed to hilly region (lower altitude) (p value CONCLUSIONS: The local organisations should focus on adequate antenatal care visits in mountain region and coverage of dT vaccine and deworming medications in hilly region. Appropriate measures and programmes should be initiated to bring down LBW in hilly region

Tropical tree growth driven by dry-season climate variability

Interannual variability in the global land carbon sink is strongly related to variations in tropical temperature and rainfall. This association suggests an important role for moisture-driven fluctuations in tropical vegetation productivity, but empirical evidence to quantify the responsible ecological processes is missing. Such evidence can be obtained from tree-ring data that quantify variability in a major vegetation productivity component: woody biomass growth. Here we compile a pantropical tree-ring network to show that annual woody biomass growth increases primarily with dry-season precipitation and decreases with dry-season maximum temperature. The strength of these dry-season climate responses varies among sites, as reflected in four robust and distinct climate response groups of tropical tree growth derived from clustering. Using cluster and regression analyses, we find that dry-season climate responses are amplified in regions that are drier, hotter and more climatically variable. These amplification patterns suggest that projected global warming will probably aggravate drought-induced declines in annual tropical vegetation productivity. Our study reveals a previously underappreciated role of dry-season climate variability in driving the dynamics of tropical vegetation productivity and consequently in influencing the land carbon sink