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We present the first Greenlandic tree ring oxygen isotope record (δ18OGTR), derived from four birch trees collected from the Qinguadalen Valley in southwestern Greenland in 1999. Our δ18O record spans from 1950–1999 and is significantly and positively correlated with winter ice core δ18O from southern Greenland. δ18OGTR records are positively correlated with southwestern Greenland January–August mean temperatures. North Atlantic Oscillation (NAO) reconstructions have been developed from a variety of proxies, but never with Greenlandic tree rings, and our δ18OGTR record is significantly correlated with NAO (r = −0.64), and spatial correlations with sea-level pressure indicate a classic NAO pressure seesaw pattern. These results may facilitate a longer NAO reconstruction based on long time series of tree ring δ18O records from Greenland, provided that subfossil wood can be found in areas vacated by melting glaciers.

The absence of pines from tropical forests is a puzzling biogeographical oddity potentially explained by traits of shade intolerance. Pinus krempfii (Lecomte), a flat-leaved pine endemic to the Central Highlands of Vietnam, provides a notable exception as it seems to compete successfully with shade-tolerant tropical species. Here, we test the hypothesis that successful conifer performance at the juvenile stage depends on physiological traits of shade tolerance by comparing the physiological characteristics of P. krempfii to coexisting species from two taxa: the genus Pinus, and a relatively abundant and shade-tolerant conifer family found in pantropical forests, the Podocarpaceae. We examined leaf photosynthetic, respiratory and biochemical traits. Additionally, we compiled attainable maximum photosynthesis, maximum RuBP carboxylation (Vcmax) and maximum electron transport (Jmax) values for Pinus and Podocarpaceae species from the literature. In our literature compilation, P. krempfii was intermediate between Pinus and Podocarpaceae in its maximum photosynthesis and its Vcmax. Pinus exhibited a higher Vcmax than Podocarpaceae, resulting in a less steep slope in the linear relationship between Jmax and Vcmax. These results suggest that Pinus may be more shade intolerant than Podocarpaceae, with P. krempfii falling between the two taxa. However, in contrast, Vietnamese conifers’ leaf mass per areas andmore »biochemical traits did not highlight the same intermediate nature of P. krempfii. Furthermore, regardless of leaf morphology or family assignation, all species demonstrated a common and extremely high carbon gain efficiency. Overall, our findings highlight the importance of shade-tolerant photosynthetic traits for conifer survival in tropical forests. However, they also demonstrate a diversity of shade tolerance strategies, all of which lead to the persistence of Vietnamese juvenile conifers in low-light tropical understories.

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