The impact of changes in the timing of precipitation on the herbaceous understorey of Mediterranean evergreen oak woodlands

Abstract

Climate change scenarios for the Iberian Peninsula predict increasing temperatures and increasingly variable precipitation regimes, which will challenge the sustainability and biodiversity of Mediterranean ecosystems such as the semi-natural evergreen oak woodlands. To assess the effects of precipitation variability on productivity, species composition and vegetation gas exchange of the understorey vegetation in a typical managed cork oak woodland, a large-scale rainfall manipulation experiment was established. We studied the impacts of a change in the timing of precipitation events on this ecosystem, without altering total annual precipitation inputs. The two water manipulation treatments were: 'weekly watering treatment', where natural conditions were simulated with a normal dry period of 7 days, and '3-weekly watering treatment', with the normal dry period increased threefold to 21 days. Our experimental precipitation patterns resulted in significant differences in temporal soil moisture dynamics between the two treatments. Average soil water content (SWC) at 3 cm depth during the growing season was 16.1 ± 0.17% and 15.8 ± 0.18% in the weekly and 3-weekly watering treatments, respectively, with a mere 5% increase in the variability of SWC when extending the dry period from one to three weeks. Water infiltration into deeper soil layers (>50 cm) was significantly higher in the 3-weekly watering treatment as compared to the weekly watering treatment. This might be beneficial to Quercus suber, the tree component in this ecosystem, as its extensive tree root system enables water acquisition from deeper soil layers. However, manipulation of the within-season precipitation variability, with a shift to fewer, but larger rain events, without change in total precipitation amount, had no significant effect on aboveground net primary productivity (ANPP), belowground net primary productivity (BNPP) and species composition, with average values of peak biomass of 385 g m −2 and 222 g m −2 for ANPP and BNPP, respectively. The experimental precipitation patterns did not result in significant differences in the vegetation gas exchange between the two watering treatments. The CO 2 and H 2 O exchange parameters correlated well with air temperature. In addition, evapotranspiration showed a good correlation with SWC. Incorporating the data of SWC in the conceptual 'bucket model' showed that, independently of the watering regime, soil water availability during the life-cycle of these annual plants did not reach severe water stress conditions, which can explain the lack of a significant treatment effect in our study. In addition, our results showed that the annual plant community in these Mediterranean ecosystems is well adapted to short-term drought, through their phenological patterns and physiological adaptations.

Consequences of Changing Precipitation Patterns for Ecosystem Functioning in Grasslands: A Review

“…In comparison to closed shelters, alterations in microclimate are reduced, with wind convection, temperature, and solar radiation less affected (Gherardi and Sala 2013). Experimental designs to study the effects of precipitation manipulation: (a) closed shelters after Jongen et al (2013b); (b) throughfall shelters, after Yahdjian and Sala (2002), picture from K. Tielbörger; and (c) movable shelters, after Báez et al (2013), picture from S. Collins 3. 'Movable shelters' (Fig.…”

Drought impact on carbon and water cycling in a Mediterranean <i>Quercus suber</i> L. woodland during the extreme drought event in 2012

“…The longterm mean annual temperature is about 15.9 • C, and the annual sum of precipitation is about 680 mm (Jongen et al, 2013b), with a characteristic annual pattern of high winter precipitation (November to January) and summer drought from June to September (Paredes et al, 2006). The relevance of the winter precipitation for the Portuguese hydrological cycle can be easily explained by the prevailing Mediterranean-type climate that concentrates most of the precipitation during the winter half of the year, with little to no precipitation in summer.…”

“…The Q. suber trees likely have deep soil water and groundwater access. Native annual grasses and herbs form the understorey vegetation (Jongen et al, 2013b;Dubbert et al, 2014a), which emerges after the first rains in autumn, has a peak stand height in spring (March-April), and becomes senescent at the beginning of the summer period (late May), with a maximum LAI of 0.70±0.05 m 2 leaf m −2…”

“…The local understorey vegetation consists of native annual grasses and herbs (Jongen et al, 2013b;Dubbert et al, 2014a). The species are adapted to regular summer droughts by seed formation in spring before the onset of the summer droughts.…”

Overgrazing in the Montado? The need for monitoring grazing pressure at paddock scale

“…The variability of precipitation and the length of the summer drought are among the most important drives for vegetation quality and availability (Joffre et al 1999;Jongen et al 2013). The overall pattern of pasture biomass production is characterized by a production peak in late spring, around the month of June despite the great inter-annual variation (Fig.…”