Analysis of floodplain forest sensitivity to drought

Abstract

Floodplain forests are very complex, productive ecosystems, capable of storing huge amounts of soil carbon. With the increasing occurrence of extreme events, they are today among the most threatened ecosystems. Our study's main goal was to assess the productivity of a floodplain forest located at Lanžhot in the Czech Republic from two perspectives: carbon uptake (using an eddy covariance method) and stem radius variations (using dendrometers). We aimed to determine which conditions allow for high ecosystem production and what role drought plays in reducing such production potential. Additionally, we were interested to determine the relative soil water content threshold indicating the onset and duration of this event. We hypothesized that summer drought in 2018 had the most significant negative effects on the overall annual carbon and water budgets. In contrast with our original hypothesis, we found that an exceptionally warm spring in 2018 caused a positive gross primary production (GPP) and evapotranspiration (ET) anomaly that consequently led in 2018 to the highest seasonal total GPP and ET from all of the investigated years (2015–2018). The results showed ring-porous species to be the most drought resistant. Relative soil water content threshold of approximately 0.45 was determined as indicating the onset of drought stress. This article is part of the theme issue ‘Impacts of the 2018 severe drought and heatwave in Europe: from site to continental scale’.

A historical, geographical and ecological perspective on the 2018 European summer drought

“…As in previous extreme summers, the productivity of crops and grasslands was more strongly affected by the summer drought in 2018 than forests exposed to the effects of both high soil moisture deficits and high water vapour pressure deficits [33,[47][48][49], even though some forests also registered stomatal closure and reduced GPP, especially those at lower altitudes [48] and more exposed to drought [44]. Wetlands in Scandinavia were also negatively affected by the drought [50], but floodplains in the Czech Republic registered higher than average productivity [43]. The geographical distribution of the negative versus positive impacts on ecosystems' GPP and net ecosystem productivity (NEP) can therefore be partly explained by the dominance of croplands in the southern sector of the drought region (Germany, The Netherlands and Belgium, Poland, southern Sweden), compared with the forest-dominated regions in the higher latitudes.…”

Ambiguous Agricultural Drought: Characterising Soil Moisture and Vegetation Droughts in Europe from Earth Observation

“…In fact, in humid climates, increased incoming solar radiation during meteorological drought periods can even enhance evapotranspiration [35] often leading to positive anomalies in vegetation indices, relative to the mean conditions, despite relatively dry conditions [36][37][38][39], as illustrated in Figure 1.…”

Ambiguous agricultural drought: characterising soil moisture and vegetation droughts in Europe from earth observation

“…Above the so-called critical moisture content, evapotranspiration and plant functioning will not be limited or affected by a lack of precipitation. In fact, increased incoming solar radiation during drought periods can even enhance evapotranspiration (Teuling et al, 2013), leading to positive anomalies in vegetation indices despite prolonged meteorological drought conditions (Jolly et al, 2005;Teuling et al, 2006;Mastrotheodoros et al, 2020;Kowalska et al, 2020). Because of this duality in the drought impacts, the use of the term agricultural drought is ambiguous, even more so as the term drought bears a negative connotation to it, though its impacts are not necessarily negative.…”