In the Iberian Peninsula, the evergreen oak woodlands are of great ecological and socio-economic importance. In Portugal, these so-called montados cover 736,700 ha, representing 23% of the forested area. They are considered a national heritage, key to biodiversity conservation and provision of ecosystem services. Dominated by Quercus species, these open woodlands form an agro-silvo-pastoral system. The herbaceous layer, key to these systems’ multi-functionality, is dominated by a diverse community of C3 annual species. It plays a significant role in carbon fixation and ecosystem productivity, as well as influencing nutrient cycling and water balance, these variables being highly dependent on timing and magnitude of precipitation.
Climate change scenarios for the Iberian Peninsula predict increasing temperatures and increasingly variable precipitation regimes, which will challenge the sustainability and biodiversity of semi-natural ecosystems such as cork oak woodlands.
To assess the effects of precipitation variability on the understorey vegetation in a managed cork oak woodland, large ‘rain-out shelters’ were constructed. The water manipulation treatment is based on historical precipitation data for the experimental site, with average annual precipitation of 680 mm. The median number of rain events during the growing season (October to May) is 24, with the median length of the dry period being 7 days. During the growing season of October 2010 - June 2011, 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 three-fold to 21 days. The aim was to assess the effects of prolonged dry periods, without altering total annual precipitation inputs, on productivity, species composition, leaf-level photosynthesis and gas exchange of the herbaceous understorey.
Results/Conclusions
Increasing the dry period between precipitation events from 1 to 3 weeks had no significant affect on the productivity, species composition nor gas exchange of the understorey vegetation. Incorporating soil water content data in the conceptual ‘bucket model’ shows that the soil water content during the life-cycle of these annual plants did not reach severe water stress conditions. In addition, the annual plant community is adapted to short-term droughts. The effects of prolonged droughts within the growing period of the herbaceous understorey are currently being investigated by increasing the experimental dry period to 6 weeks.