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

Ökologische Informationen von Ringbreiten, stabilen Kohlenstoff-Isotopen und holzanatomischen Variablen in tropischen Jahresringen – Ein Beitrag zur Dendrochronologie in den Tropen

Bäume sind langlebige Organismen und speichern ökologisch relevante Informationen in ihren Jahresringen. Untersuchungen des Baumwachstums auf der Grundlage von Jahresringen können dazu beitragen, wichtige Information über Alter und Zuwachs zu erlangen, aber auch wichtige Fragen bezüglich ihrer Reaktionen auf sich ändernde Umweltbedingungen zu beantworten. Tropische Waldökosysteme weisen eine sehr große Artenvielfalt und ein breites Spektrum an klimatischen Zonen auf. Diese große Variabilität äußert sich auch in einer Vielzahl von möglichen holzanatomischen Strukturen und entsprechenden Beziehungen zu ökologischen und umgebungsbedingten Faktoren. Die erfolgreiche Anwendung dendrochronologischer Methoden in den Tropen bedingt daher ausführliche Kenntnisse holzanatomischer Strukturen und deren Variabilität zur eindeutigen Bestimmung von Jahresringen in tropischen Bäumen. In Kapitel 2 wird der holzanatomische Hintergrund der makroskopischen Sichtbarkeit von Ringstrukturen behandelt. Traditionelle Methoden der Altersbestimmung wie die Radiokarbondatierung des Stammzentrums, Schätzungen auf der Grundlage wiederholter Durchmesserbestimmungen oder Modellrechnungen auf der Grundlage von Sterblichkeitsraten. Diese Methoden werden diskutiert und leiten über zu den Vorteilen der Jahrringanalyse zur Bestimmung von Alter und Zuwachs tropischer Bäume. In Kapitel 3 wird das dendroklimatologische Potenzial von zwei dominanten Baumarten aus Trockenwäldern in Namibia untersucht. Für beide Arten kann eine starke Korrelation zwischen Baumwachstum und Klimazeitreihen sowie mit El Niño Indizes festgestellt werden. Alle signifikanten Korrelationen zum Niederschlag sind positiv, was bedeutet, dass höhere Niederschlagsraten einen positiven Einfluss auf das Baumwachstum haben. In Kapitel 4 werden Bäume verschiedener hydrologischer Standorte verglichen, um festzustellen, welchen Einfluss Niederschlagsunterschiede auf 13C-Diskriminierung in tropischen Bäumen haben. Die Korrelation zwischen Niederschlags-Zeitreihen und den Isotopenwerten der Jahresringe sind signifikant negativ. Die Ergebnisse dieser Studie zeigen, dass tropische Bäume, wie Bäume gemäßigter Zonen, Kohlenstoffisotopensignaturen im Holz speichern, die mit externen Faktoren in Verbindung gebracht werden und zur Altersbestimmung tropischer Bäume genutzt werden können. Zum besseren Verständnis der Beziehungen zwischen externen Faktoren und der Holzstruktur wurden in Kapitel 5 holzanatomische Merkmale tropischer Bäume verschiedener Taxa entlang eines weiten Klimagradienten analysiert. Der Gefäßdurchmesser zeigt die stärkste Korrelation mit generellen Klimamerkmalen, sowie Baumwachstum und –gestalt. Ein bemerkenswertes Ergebnis lieferte die Analyse der relativen Flächenanteile von Gefäßen, Faserzellen und Parenchym, da bis heute ist nur wenig über die Ursachen der Aufteilung in verschiedene Zelltypen bekannt ist: generell zeigt sich, dass die Morphologie des Baumes einen stärkeren Einfluss auf die holzanatomische Struktur hat als die Klimabedingungen Dennoch können sich diese Wechselbeziehungen aufgrund von phylogenetischen Grenzen, individueller Wuchsleistung und aufgrund klimatischer Veränderungen verschieben. Die Analyse der Jahresringe in Bezug auf deren Ringbreiten, stabilen Kohlenstoffisotopen-Gehalt und quantitative holzanatomische Merkmale zeigt, dass tropische Jahresringe vielfältige ökologische Informationen speichern. Die Untersuchungen dieser Dissertation leisten damit einen wichtigen Beitrag zur Weiterentwicklung der tropischen Dendrochronologie. Die Anwendung der vorgestellten Methoden kann somit künftig dazu beitragen, wichtige Forschungslücken auf dem Gebiet der Ökologie tropischer Wälder und des Klimawandels zu schließen, sowie waldbauliche Fragestellungen zu beantworten

Stable-Carbon Isotope Time Series from Tropical Tree Rings Indicate a Precipitation Signal

Although studies on stable-carbon isotopes in trees from temperate zones provide abundant paleoclimatic data, tropical trees are still understudied in this context. Therefore this study examined the variability of intra- and inter-annual stable-carbon isotopic pattern in several tree species from various tropical climates. The δ13C values of samples of 12 broadleaved trees (seven species) from various paleotropical and neotropical sites along a climatic moisture gradient were investigated. The inter-annual variability between species and sites was studied. Further the relationship between δ13C and precipitation time series was analyzed. Results show that tropical tree species show a similar variability in carbon isotopic composition as temperate tree species. Significant correlations between annual precipitation and tree-ring δ13C time series were negative. Successful crossdating of a tree-ring δ13C time series highlights the potential of carbon isotope measurements for tropical tree-ring analytical studies. Tropical broadleaved trees are able to capture a carbon isotopic signal in their annual rings even under everwet conditions and show good potential for paleoclimatic research

Jaarlijkse groei van Pterocarpus angolensis (Kiaat) en andere boomsoorten in Kavango, Namibië

De meest geprefereerde houtsoort voor zagerij in Namibië en het grootste deel van zuidelijk Afrika, is Pterocarpus angolensis (Kiaat). Er is echter niet genoeg informatie over de jaarlijkse groei van de soort om te bepalen of de oogst duurzaam is. De soort bereikt in Namibië de zuidelijke grens van zijn verspreidingsgebied en men zou kunnen verwachten dat de jaarlijkse groei lager is dan in andere landen waarvoor meer gegevens beschikbaar zijn binnen de literatuur. Deze studie wil bijdragen aan de bepaling van de jaarlijkse diametergroei van Kiaat in Namibië door het meten van de jaarlijkse groei in de regio Kavango. De diametergroei van Kiaat zal worden vergeleken met een paar andere soorten waarvoor boorkernen werden verzameld. Hierbij maakt men gebruik een presslerboor voor het winnen van boorspanen die worden geëgaliseerd met de Core-microtome om ze daaropvolgend met LintabTM software te analyseren. Er werd ook informatie gewonnen uit stamschijven die gedurende het onderzoek te beschikking werden gesteld voor manuele tellingen. Naast Kiaat werd een soortgelijke analyse uitgevoerd op Burkea africana, Baikiaea plurijuga, Terminalia sericea en Schinziophyton rautanenii om na te gaan of ook deze soorten geschikt zijn voor jaarringanalyse op basis van boorspanen. Het onderzoek centraliseert zich binnen de regio Kavango maar beoogt tevens vergelijkingen met naburige regionen binnen en buiten Namibië. Gekeken naar de kwaliteit van boorspanen en de vraag of andere houtsoorten bruikbaar zijn voor jaarringanalyse, merkt men vooral technische problemen door intern rot of holle stammen bij Baikiaea plurijuga en Burkea africana. Voor Terminalia sericea zijn goede boorspanen verzameld maar is het vooral moeilijk om daadwerkelijk tot de kern van de stam te geraken vanwege excentriciteit. Voor Schinziophyton rautanenii vermoedt men geen jaarringen te zien, aangezien het gaat om een stamsucculent. Uit de jaarringanalyse haalt men groeicurven die de relatie tussen diameter en leeftijd weergeven voor stamschijven. Voor boorspanen wordt met LintabTM software de effectieve ringbreedte bepaald en de daaruit volgende groeicurve. Uit een eerste reeks resultaten blijkt de groei in Kavango sneller te verlopen dan drogere gebieden maar trager dan in gebieden met meer neerslag. Terminalia sericea heeft als pioniersoort een snellere groei dan Pterocarpus angolensis, Baikiaea plurijuga en Burkea africana. Analyse toont aan dat de groei van bomen in Kavango onder andere wordt beïnvloed door neerslag en dat de groeipatronen per soort sterkt verschillen

Annual diameter growth of Pterocarpus angolensis (Kiaat) and other woodland species in Namibia

Objective: To examine the association between aortic arch calcification (AAC) and vascular disease in an older Chinese sample. Methods: For this study, 30,203 Chinese aged 50-85 years were recruited with baseline information on socioeconomic position, lifestyle and vascular risk factors. The presence and severity of AAC were diagnosed independently from chest X-ray by two radiologists. Results: The age-adjusted prevalence of AAC was significantly higher in women than men [34.6% (95% CI 33.9-35.3) vs. 27.9% (95% CI 26.8-28.8), p < 0.001]. Severity of AAC was significantly associated with physician-diagnosed ischemic heart disease (adjusted OR = 1.55, 95% CI 1.35-1.79) and combined vascular disease (OR = 1.48, 95% CI 1.30-1.69) after adjusting for multiple potential confounders. Increasing severity of AAC was associated with increased risk for ischemic heart disease and vascular disease (p for trend = 0.02 to <0.001). No association between AAC and stroke was found. Conclusions: AAC was strongly and independently associated with vascular disease, suggesting that assessment of AAC from chest X-ray, which is noninvasive and relatively inexpensive, can provide useful information for risk stratification of vascular disease, and should be routinely incorporated in chest X-ray examination. Copyright © 2011 S. Karger AG, Basel.link_to_subscribed_fulltex

Predicting site productivity of the timber tree Pterocarpus angolensis

Pterocarpus angolensis is an important timber tree of the miombo woodlands of sub-Saharan Africa. The species only grows in natural mixed forests and little is known about is productivity potential. This study aimed at investigating productivity of P. angolensis on a local scale in Namibia and Angola and on a regional scale in southern Africa. The most commonly accepted productivity indicator is stem diameter increment and this was used to study productivity at a regional scale. Indicators of productivity used at the local scale were basal area, proportional basal area and site form, which were derived from 217 forest inventory plots in Namibia and Angola. The productivity measures were modelled with abiotic site factors; biotic factors were added for the local scale. Results indicated that the most consistent site factors at local and regional scale were not related to climate but to forest cover, with the species having a competitive advantage in more open forests. Mean annual diameter increment in the open forests of Namibia was 0.51 cm after 50 years. Boosted regression tree models at a local scale showed that species presence can be modelled more successfully than species basal area, proportional basal area (correlation of 0.72 vs 0.56 and 0.45, respectively) and site form. The sites with the highest productivity of P. angolensis at the local scale had a temperature seasonality below 34.5 °C, a slope of less than 1.5°, tree cover less than 20% and stand basal area higher than 9 m2 ha−1. The results can assist in establishing a site-dependent growth model for the species and direct forest and fire management towards the most productive areas. © 2017 NISC (Pty) Ltd

A Global analysis of parenchyma tissue fractions in secondary xylem of seed plants

Parenchyma is an important tissue in secondary xylem of seed plants, with functions ranging from storage to defence and with effects on the physical and mechanical properties of wood. Currently, we lack a large-scale quantitative analysis of ray parenchyma (RP) and axial parenchyma (AP) tissue fractions. Here, we use data from the literature on AP and RP fractions to investigate the potential relationships of climate and growth form with total ray and axial parenchyma fractions (RAP). We found a 29-fold variation in RAP fraction, which was more strongly related to temperature than with precipitation. Stem succulents had the highest RAP values (mean ± SD: 70.2 ± 22.0%), followed by lianas (50.1 ± 16.3%), angiosperm trees and shrubs (26.3 ± 12.4%), and conifers (7.6 ± 2.6%). Differences in RAP fraction between temperate and tropical angiosperm trees (21.1 ± 7.9% vs 36.2 ± 13.4%, respectively) are due to differences in the AP fraction, which is typically three times higher in tropical than in temperate trees, but not in RP fraction. Our results illustrate that both temperature and growth form are important drivers of RAP fractions. These findings should help pave the way to better understand the various functions of RAP in plants.13 page(s

Vessel diameter is related to amount and spatial arrangement of axial parenchyma in woody angiosperms

Parenchyma represents a critically important living tissue in the sapwood of the secondary xylem of woody angiosperms. Considering various interactions between parenchyma and water transporting vessels, we hypothesize a structure–function relationship between both cell types. Through a generalized additive mixed model approach based on 2,332 woody angiosperm species derived from the literature, we explored the relationship between the proportion and spatial distribution of ray and axial parenchyma and vessel size, while controlling for maximum plant height and a range of climatic factors. When factoring in maximum plant height, we found that with increasing mean annual temperatures, mean vessel diameter showed a positive correlation with axial parenchyma proportion and arrangement, but not for ray parenchyma. Species with a high axial parenchyma tissue fraction tend to have wide vessels, with most of the parenchyma packed around vessels, whereas species with small diameter vessels show a reduced amount of axial parenchyma that is not directly connected to vessels. This finding provides evidence for independent functions of axial parenchyma and ray parenchyma in large vesselled species and further supports a strong role for axial parenchyma in long-distance xylem water transport