Fig 1.
Location of the study region in southern Ecuador (top right) and of the study area in the valley of the San Francisco river (Reserva Biológica San Francisco, RBSF) with the research station Estación Cientifica San Francisco (ECSF) and the position of the core research area between two canopy towers. The Ministerio de Agricultura, Ganadería, Acuacultura y Pesca—Ecuador has kindly provided the SIGTIERRAS (Sistema Nacional de Información y Gestión de Tierras Rurales e Infraestructura Tecnológica) orthophoto, which is the basis of the figure.
Fig 2.
Climate diagram of the Reserva Biológica San Francisco (RBSF) during the study period (2015–2019, 1950 m a.s.l.).
Table 1.
Characterization of the investigated trees: Height, diameter at breast height (DBH), projected crown area, specific leaf area (SLA), and leaf exposition.
SLA data from personal communication by Jürgen Homeier (Dept. Resource Management, University of Applied Sciences and Arts (HAWK) Göttingen, Germany).
Fig 3.
Soil water content at 1980 m a.s.l. in the research area at various soil depths over a wet (May 2020) and 3 weeks of an exceptionally dry month (August 2020).
The vertical bars represent precipitation events of different intensities.
Fig 4.
Diurnal courses of above-canopy air temperature (TA,°C), evapotranspiration (ET, mm h-1), vapor pressure deficit (VPD, kPa), and sap flux (g cm-2 min-1).
The left column shows the time period November 2019 –October 2020, right column August 1–20, 2020.
Fig 5.
Normalized sap flux (g cm-2 min-1 at a depth of 2.8 cm) of individuals of nine tree species growing on the research plot in the evergreen mountain rainforest in the Reserva Biológica San Francisco.
The data are means of the recordings of three sensors per tree. The grey background shows the atmospheric water vapor pressure deficit (VPD). Vertical light grey bars indicate night hours. (n = 9).
Table 2.
Distribution of the diurnal sap flux in eight evergreen tree species over day and night and average water potential of the leaves.
n.m. = not measured. ± indicates standard errors.
Fig 6.
Gas exchange on the background of microclimate parameters (VPD–shadowed in grey, PAR–red area) of a leaf in the sun crown of Tapirira guianensis, measured over 2 days (November 5–7, 2015) under simulated natural atmospheric conditions with the IRGA.
Simultaneously, sap flux was measured in the stem at breast height (lower panel).
Fig 7.
Stem circumference changes of different tree species during a short spell of dry weather.
The grey background shows the atmospheric water vapor pressure deficit (VPD). The time span shown in Fig 5 is shaded (n = 29).
Table 3.
Parameters characterizing leaf transpiration over two nights and two days of Tapirira and Ocotea as representatives of the two groups of differing hydrological performance. *p < 0.05.
Fig 8.
Leaf gas exchange on the background of microclimate parameters (VPD and PAR) of Ocotea aciphylla, measured over 2 days (November 21–23, 2015) under atmospheric conditions simulated as close to natural as possible with the IRGA.
Fig 9.
Nighttime (19:00 to 6:00) response of leaf conductance (gleaf) to lnVPD (following Oren et al. 1999) of Tapirira and Ocotea, respectively.