Water Availability Is the Main Climate Driver of Neotropical Tree Growth

• Climate models for the coming century predict rainfall reduction in the Amazonian region, including change in water availability for tropical rainforests. Here, we test the extent to which climate variables related to water regime, temperature and irradiance shape the growth trajectories of neotropical trees. • We developed a diameter growth model explicitly designed to work with asynchronous climate and growth data. Growth trajectories of 205 individual trees from 54 neotropical species censused every 2 months over a 4-year period were used to rank 9 climate variables and find the best predictive model. • About 9% of the individual variation in tree growth was imputable to the seasonal variation of climate. Relative extractable water was the main predictor and alone explained more than 60% of the climate effect on tree growth, i.e. 5.4% of the individual variation in tree growth. Furthermore, the global annual tree growth was more dependent on the diameter increment at the onset of the rain season than on the duration of dry season. • The best predictive model included 3 climate variables: relative extractable water, minimum temperature and irradiance. The root mean squared error of prediction (0.035 mm.d–1) was slightly above the mean value of the growth (0.026 mm.d–1). • Amongst climate variables, we highlight the predominant role of water availability in determining seasonal variation in tree growth of neotropical forest trees and the need to include these relationships in forest simulators to test, in silico, the impact of different climate scenarios on the future dynamics of the rainforest

Climate seasonality limits leaf carbon assimilation and wood productivity in tropical forests

The seasonal climate drivers of the carbon cycle in tropical forests remain poorly known, although these forests account for more carbon assimilation and storage than any other terrestrial ecosystem. Based on a unique combination of seasonal pan-tropical data sets from 89 experimental sites (68 include aboveground wood productivity measurements and 35 litter productivity measurements), their associate canopy photosynthetic capacity (enhanced vegetation index, EVI) and climate, we ask how carbon assimilation and aboveground allocation are related to climate seasonality in tropical forests and how they interact in the seasonal carbon cycle. We found that canopy photosynthetic capacity seasonality responds positively to precipitation when rainfall is < 2000 mm.yr−1 (water-limited forests) and to radiation otherwise (light-limited forests); on the other hand, independent of climate limitations, wood productivity and litterfall are driven by seasonal variation in precipitation and evapotranspiration respectively. Consequently, light-limited forests present an asynchronism between canopy photosynthetic capacity and wood productivity. Precipitation first-order control indicates an overall decrease in tropical forest productivity in a drier climate.Peer reviewe

Climate seasonality limits leaf carbon assimilation and wood productivity in tropical forests

The seasonal climate drivers of the carbon cycle in tropical forests remain poorly known, although these forests account for more carbon assimilation and storage than any other terrestrial ecosystem. Based on a unique combination of seasonal pan-tropical data sets from 89 experimental sites (68 include aboveground wood productivity measurements and 35 litter productivity measurements), their associated canopy photosynthetic capacity (enhanced vegetation index, EVI) and climate, we ask how carbon assimilation and aboveground allocation are related to climate seasonality in tropical forests and how they interact in the seasonal carbon cycle. We found that canopy photosynthetic capacity seasonality responds positively to precipitation when rainfall is  < 2000 mm yr⁻¹ (water-limited forests) and to radiation otherwise (light-limited forests). On the other hand, independent of climate limitations, wood productivity and litterfall are driven by seasonal variation in precipitation and evapotranspiration, respectively. Consequently, light-limited forests present an asynchronism between canopy photosynthetic capacity and wood productivity. First-order control by precipitation likely indicates a decrease in tropical forest productivity in a drier climate in water-limited forest, and in current light-limited forest with future rainfall  < 2000 mm yr⁻¹

INFLUENCE OF METEOROLOGICAL CONDITIONS ON CHANGES IN THE VOLUME OF THE PINE STEM AT THE END OF VEGETATION USING HIGH RESOLUTION DENDROMETERS / METEOROLOGINIŲ SĄLYGŲ POVEIKIS DIDELĖS RAIŠKOS DENDROMETRAIS IŠMATUOTAM PINUS SYLVESTRIS KAMIENO APIMTIES POKYČIUI VEGETACIJOS PERIODO PABAIGOJE

Using dendrometers for measuring a radial increment of trees is efficient not only for investigation into the dynamics of the increment but also for changes in the tree stem in general, for a physiological condition of trees during certain periods of time, reliance on meteorological conditions and for tree-ring formation studies. The conducted research has applied to high resolution DRL 26 dendrometers that helped with identifying and distinguishing the impacts of climatic factors on the physiology and growth of trees. Also, the performed investigation assisted in assessing the impact of microclimate conditions on changes in tree stems. The location for installing dendrometers was selected with reference to the criteria such as representative research location, the degree of violation assessment, equal distribution of research sites in Lithuania and the estimation of climatic, hydrologic and anthropogenic conditions. Considering the above mentioned criteria, three raised bogs in which temperature, automatic water level devices in wells and dendrometers installed in measurement areas were chosen. The research period lasted from the end of the vegetation period to the beginning of dormancy season. For research purposes, 5 growing Scots pines (Pinus sylvestris) were used for examining changes in the stem volume. Another objective was to find out how stems were affected by growing in bog surroundings and to analyse the synchronicity of volume changes between trees. The conducted research disclosed specific features of the dynamics of changes in the stem volume at the end of vegetation, and the beginning of dormancy season was found. Santrauka Medžių radialiajam priaugiui tirti taikomas dendrometrų metodas padeda spręsti ne vien apie prieaugio dinamiką, bet ir apie medžio kamieno apimties pokyčius apskritai, fiziologinę medžių būklę tam tikrais laiko periodais, priklausomybę nuo meteorologinių sąlygų ir rievės formavimosi savitumų. Tyrimuose buvo naudoti didelės raiškos DRL 26 dendrometrai, leidžiantys nustatyti ir interpretuoti klimatinių rodiklių įtaką medžio fiziologijai ir augimui, įvertinti mikroklimatinių sąlygų poveikį medžio kamieno pokyčiams. Atsižvelgiant į reprezentatyvią tyrimų vietų imtį, skirtingą pažeidimo laipsnį ir tolygų tyrimo vietų pasiskirstymą Lietuvoje, įvertinant klimatines, hidrologines ir (arba) antropogenines sąlygas, buvo pasirinktos trys aukštapelkės, matavimo aikštelėse įrengti gręžiniai su automatiniais vandens lygio ir temperatūros matuokliais, įrengti dendrometrai. Siekiant išsiaiškinti pušies, augančios pelkinėse augavietėse, kamieno apimties pokyčius formuojančius veiksnius bei vertinant atskirų medžių tarpusavio sinchronizacijos ypatumus, darbe naudota penkių dabartinių augančios paprastosios pušies (Pinus sylvestris) kamienų apimties pokyčių analizė. Tyrimų metu nustatyti kamieno apimties kitimo ypatumai vegetacijos periodo pabaigos – ramybės sezono pradžioje. Reikšminiai žodžiai: kamieno apimties kitimas; paros ciklas; meteorologiniai rodikliai; dendrometrai

Plant-water relationships in the Great Basin Desert of North America derived from Pinus monophylla hourly dendrometer records

Water is the main limiting resource for natural and human systems, but the effect of hydroclimatic variability on woody species in water-limited environments at sub-monthly time scales is not fully understood. Plant-water relationships of single-leaf pinyon pine (Pinus monophylla) were investigated using hourly dendrometer and environmental data from May 2006 to October 2011 in the Great Basin Desert, one of the driest regions of North America. Average radial stem increments showed an annual range of variation below 1.0 mm, with a monotonic steep increase from May to July that yielded a stem enlargement of about 0.5 mm. Stem shrinkage up to 0.2 mm occurred in late summer, followed by an abrupt expansion of up to 0.5 mm in the fall, at the arrival of the new water year precipitation. Subsequent winter shrinkage and enlargement were less than 0.3 mm each. Based on 4 years with continuous data, diel cycles varied in both timing and amplitude between months and years. Phase shifts in circadian stem changes were observed between the growing season and the dormant one, with stem size being linked to precipitation more than to other water-related indices, such as relative humidity or soil moisture. During May–October, the amplitude of the phases of stem contraction, expansion, and increment was positively related to their duration in a nonlinear fashion. Changes in precipitation regime, which affected the diel phases especially when lasting more than 5–6 h, could substantially influence the dynamics of water depletion and replenishment in single-leaf pinyon pine