Tree Circumference Changes and Species-Specific Growth Recovery After Extreme Dry Events in a Montane Rainforest in Southern Ecuador

Abstract

Under drought conditions, even tropical rainforests might turn from carbon sinks to sources, and tree species composition might be altered by increased mortality. We monitored stem diameter variations of 40 tree individuals with stem diameters above 10 cm belonging to eleven different tree genera and three tree life forms with high-resolution dendrometers from July 2007 to November 2010 and additionally March 2015 to December 2017 in a tropical mountain rainforest in South Ecuador, a biodiversity hotspot with more than 300 different tree species belonging to different functional types. Although our study area receives around 2200 mm of annual rainfall, dry spells occur regularly during so-called “Veranillo del Niño” (VdN) periods in October-November. In climate change scenarios, droughts are expected with higher frequency and intensity as today. We selected dry intervals with a minimum of four consecutive days to examine how different tree species respond to drought stress, raising the question if some species are better adapted to a possible higher frequency and increasing duration of dry periods. We analyzed the averaged species-specific stem shrinkage rates and recovery times during and after dry periods. The two deciduous broadleaved species Cedrela montana and Handroanthus chrysanthus showed the biggest stem shrinkage of up to 2 mm after 10 consecutive dry days. A comparison of daily circumference changes over 600 consecutive days revealed different drought responses between the families concerning the percentage of days with stem shrinkage/increment, ranging from 27.5 to 72.5% for Graffenrieda emarginata to 45–55% for Podocarpus oleifolius under same climate conditions. Moreover, we found great difference of recovery times after longer-lasting (i.e., eight to ten days) VdN drought events between the two evergreen broadleaved species Vismia cavanillesiana and Tapirira guianensis. While Vismia replenished to pre-VdN stem circumference after only 5 days, Tapirira needed 52 days on average to restore its circumference. Hence, a higher frequency of droughts might increase inter-species competition and species-specific mortality and might finally alter the species composition of the ecosystem.

Indigenous use of fire in the paramo ecosystem of southern Ecuador: a case study using remote sensing methods and ancestral knowledge of the Kichwa Saraguro people

“…This coincides with other studies which have observed that Indigenous people from other areas use diverse seasonal calendars according to their cosmovision and ecological parameters based on where they inhabit (McKemey et al 2021 ). Regarding the VdN phenomenon, Raffelsbauer et al ( 2019 ) showed that it is characterized by a pronounced low-pressure system east of the Andes that weakens the dominant trade winds. This causes a reduction in cloudiness and the presence of higher outgoing longwave solar irradiance (OLR) under clear skies during the night, and the daily temperature range increases to approximately 25°C, from 2.4°C during the night to 27.1°C during the day (Bendix et al 2008 ; Rollenbeck and Bendix 2011a , 2011b ).…”

“…This causes a reduction in cloudiness and the presence of higher outgoing longwave solar irradiance (OLR) under clear skies during the night, and the daily temperature range increases to approximately 25°C, from 2.4°C during the night to 27.1°C during the day (Bendix et al 2008 ; Rollenbeck and Bendix 2011a , 2011b ). Taking advantage of the VdN phenomenon, and under paramo conditions (Raffelsbauer et al 2019 ), the Saraguro produce the low-severity burns (Fig. 4 ).…”

INTRAGRO: A machine learning approach to predict future growth of trees under climate change

“…The course of daily stem circumference variation patterns (DSCCs) shows typical cycles, with stem shrinkage during daytime, when trees transpire more water than is replenished by the root system, and stem increment during nighttime due to stem water replenishment and irreversible growth caused by cambial activity (Deslauriers et al., 2007; Zweifel, 2016). Besides the leaf phenological status of the tree, its DSCCs depend on the short‐term weather conditions, showing characteristic diurnal patterns of stem increment and shrinkage, with variable amplitudes of DCC and radial growth during different seasons, but also during short‐term climatic episodes within one season (Raffelsbauer et al., 2019). The advantage of clustering DSCC patterns is that patterns occurring during different seasons of the year but representing similar plant physiological responses to the weather conditions are merged in one group of data, whereas in conventional time series analyses, tree responses are interpreted within the seasonal climate pattern (e.g.…”

The Dry and the Wet Case: Tree Growth Response in Climatologically Contrasting Years on the Island of Corsica

“…Electric point or band dendrometers are valuable tools for monitoring continuous stem radial variations (SRV) and quantifying radial tree growth in high resolution [15,[27][28][29]. Dendrometer measurements allow the investigation of the influence of site conditions and meteorological factors on growth, as well as species-specific responses to changing climate conditions [30][31][32]. However, not all SRV are caused by radial growth, i.e., cambial division and cell expansion.…”