Temporal changes in climatic limitation of tree-growth at upper treeline forests: Contrasted responses along the west-to-east humidity gradient in Northern Patagonia

Lavergne, Aliénor; Daux, Valérie; Villalba, Ricardo; Barichivich, Jonathan

doi:10.1016/j.dendro.2015.09.001

Cited by 40 publications

(37 citation statements)

References 60 publications

(72 reference statements)

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“…Indeed, when photosynthesis decreases in response to light limitation, the leaf internal CO 2 concentration ( c i ) increases, which in turn increases the carbon discrimination against 12 C (Δ 13 C proportional to c i / c a ratio) leading to a decrease of δ 13 C (Farquhar et al, ). This hypothesis is in agreement with the decreasing trend in cloud fraction (−4%) and increasing trend in photosynthetically active radiations (+3.5%) observed in the region over the 1984–2007 period (data retrieved from NASA/GEWEX Surface Radiation Budget; see Lavergne et al, ). Thus, in line with the literature, environmental conditions favorable to forest productivity (here, cool summers with less sunlight) result in higher Δ 13 C during carbon assimilation and therefore lower δ 13 C, than do conditions unfavorable to growth (Raczka et al, ).…”

Section: Discussionsupporting

confidence: 87%

Past Summer Temperatures Inferred From Dendrochronological Records of Fitzroya cupressoides on the Eastern Slope of the Northern Patagonian Andes

et al. 2018

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Estimating summer temperature fluctuations over long timescales in southern South America is essential for better understanding the past climate variations in the Southern Hemisphere. Here we developed robust 212 year long basal area increment (BAI) and δ13C chronologies from living temperature‐sensitive Fitzroya cupressoides on the eastern slope of the northern Patagonian Andes (41°S). After removing the increasing trend from the growth records likely due to the CO2 fertilization effect, we tested the potential to reconstruct past summer temperature variations using BAI and δ13C as predictors. The reconstruction based on δ13C records has the strongest predictive skills and explains as much as 62% of the total variance in instrumental summer temperature (n = 81, p < 0.001). The temperature signal recorded in tree‐ring growth is not substantially different to that present in δ13C and consequently does not provide additional information to improve the regression models. Our δ13C‐based reconstruction shows cold summer temperatures in the second part of the 19th century and in the mid‐20th century followed by a warmer period. Notably, the 20th and the early 21st centuries were warmer (+0.6°C) than the 19th century. Reconstructed summer temperature variations are modulated by low‐latitude (El Niño–Southern Oscillation) and high‐latitude (Southern Annular Mode) climate forcings. Our reconstruction based on δ13C agrees well with previous ring width based temperature reconstructions in the region and comparatively enhances the low‐frequency variations in the records. The present study provides the first reconstruction of summer temperature in South America south of 40°S for the period 1800–2011 entirely based on isotopic records.

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Section: Discussionsupporting

confidence: 87%

Past Summer Temperatures Inferred From Dendrochronological Records of Fitzroya cupressoides on the Eastern Slope of the Northern Patagonian Andes

et al. 2018

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“…() and Lavergne et al. (), who compared growth responses in N. pumilio across a precipitation gradient, as well as this study, have led us to assert that trees located in harsh environments, be these dry or cold, should show declines in growth, whereas trees located in more mesic and humid conditions should therefore show an enhancement in growth (for other species showing a positive trend, see Camarero et al., ; Urrutia‐Jalabert et al., ).…”

Section: Discussionsupporting

confidence: 53%

“…Site represents the different tree lines, elevation level represents the different sampled elevations from the closed and tall lowest‐elevation forest (E1) to the tree line (E4), calendar year accounts for TRW trends over time, and tree age and DBH control for potential differences in growth trajectories for trees of different age and sizes. In addition, based on prior studies (Alvarez et al., ; Lavergne et al., ), we chose to work with the November–January temperature and precipitation period, which represents the climate conditions during the beginning of the growing season, which have proven to have a direct effect on tree growth, in particular, precipitation. To account for the potentially different patterns in growth trends among sites and elevations, we included interactions among site, elevation and calendar year in the model.…”

Section: Methodsmentioning

confidence: 99%

Recent decadal drought reverts warming‐triggered growth enhancement in contrasting climates in the southern Andes tree line

Fajardo

Gazol

Mayr

et al. 2019

Journal of Biogeography

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Aims Rising temperature and declining summer precipitation due to the 1970s‐climate shift in southern South America have reduced forest productivity at dry sites. Here, we worked with the most widespread Southern Hemisphere tree line species, Nothofagus pumilio, across contrasting climatic conditions and determined whether rising atmospheric CO2 concentrations as well as warmer and drier climatic conditions provoked by the 70s‐climatic shift have been causing systematic changes in tree line growth rates and intrinsic water‐use efficiency (iWUE). Location 36–54°S, southern Andes. Time period 1950–2010. Major taxa studied Nothofagus pumilio. Methods We worked at five disparate climatic tree line locations, spanning 18 degrees of latitude; at each location, we sampled trees at four different elevations, including tree line elevation. We quantified the variation in annual tree‐ring width (TRW) as a function of climate, elevation, tree age, size, annual CO2 concentrations and location, using linear mixed‐effects models and interpreted TRW trends in relation to iWUE and isotope (δ13C and δ18O) signalling. Results Across locations, the patterns of tree line growth occurring in the 1980–2010 period exhibited a clear and significant negative trend, in contrast to the previous 1950–1980 period. We found an increase in iWUE and δ18O across time and locations. Given that an increase in δ18O indicates a decrease in stomatal conductance, we assert that drought‐induced stomatal closure appears to be causing the reduction in growth. Main conclusions We show unequivocal evidence that warmer and drier summer conditions translated into a decrease in growth rates along the elevational tree line of the southern Andes, reverting previous growth improvements linked to climate warming. An improvement in iWUE at all locations is most likely explained by decreased stomatal conductance given the rising δ18O signal. An iWUE–growth decoupling may act as an ecological strategy to respond to drought.

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“…This processbased model simulates radial growth using the principle of limiting factors and nonlinear growth response functions (Fritts, 2001), and it requires the following as input variables: site latitude, monthly mean temperature, and monthly total precipitation. The VS-Lite model has been used to successfully simulate and evaluate regional patterns of climate limitation of tree growth in a range of environments from semi-arid to temperate and boreal regions (Tolwinski-Ward et al, 2011;Breitenmoser et al, 2014;Lavergne et al, 2015;Mina et al, 2016).…”

Section: Introductionmentioning

confidence: 99%

Assessing forest vulnerability to climate warming using a process‐based model of tree growth: bad prospects for rear‐edges

Sánchez‐Salguero

Camarero

Gutiérrez

et al. 2016

Global Change Biology

135

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Growth models can be used to assess forest vulnerability to climate warming. If global warming amplifies water deficit in drought-prone areas, tree populations located at the driest and southernmost distribution limits (rear-edges) should be particularly threatened. Here, we address these statements by analyzing and projecting growth responses to climate of three major tree species (silver fir, Abies alba; Scots pine, Pinus sylvestris; and mountain pine, Pinus uncinata) in mountainous areas of NE Spain. This region is subjected to Mediterranean continental conditions, it encompasses wide climatic, topographic and environmental gradients, and, more importantly, it includes rear-edges of the continuous distributions of these tree species. We used tree-ring width data from a network of 110 forests in combination with the process-based Vaganov-Shashkin-Lite growth model and climate-growth analyses to forecast changes in tree growth during the 21st century. Climatic projections were based on four ensembles CO emission scenarios. Warm and dry conditions during the growing season constrain silver fir and Scots pine growth, particularly at the species rear-edge. By contrast, growth of high-elevation mountain pine forests is enhanced by climate warming. The emission scenario (RCP 8.5) corresponding to the most pronounced warming (+1.4 to 4.8 °C) forecasted mean growth reductions of -10.7% and -16.4% in silver fir and Scots pine, respectively, after 2050. This indicates that rising temperatures could amplify drought stress and thus constrain the growth of silver fir and Scots pine rear-edge populations growing at xeric sites. Contrastingly, mountain pine growth is expected to increase by +12.5% due to a longer and warmer growing season. The projections of growth reduction in silver fir and Scots pine portend dieback and a contraction of their species distribution areas through potential local extinctions of the most vulnerable driest rear-edge stands. Our modeling approach provides accessible tools to evaluate forest vulnerability to warmer conditions.

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Temporal changes in climatic limitation of tree-growth at upper treeline forests: Contrasted responses along the west-to-east humidity gradient in Northern Patagonia

Cited by 40 publications

References 60 publications

Past Summer Temperatures Inferred From Dendrochronological Records of Fitzroya cupressoides on the Eastern Slope of the Northern Patagonian Andes

Past Summer Temperatures Inferred From Dendrochronological Records of Fitzroya cupressoides on the Eastern Slope of the Northern Patagonian Andes

Recent decadal drought reverts warming‐triggered growth enhancement in contrasting climates in the southern Andes tree line

Assessing forest vulnerability to climate warming using a process‐based model of tree growth: bad prospects for rear‐edges

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