SHRUB ENCROACHMENT AND GRAZING REGIMES: EFFECTS ON OAK WOODLAND FUNCTIONING

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Effects of grazing exclusion and shrub encroachment on the ecosystem ecology of evergreen oak woodland

Publication . Lecomte, Xavier Jean François; Caldeira, Maria da Conceição Brito; Bugalho, Miguel; Pereira, João Santos

Shrub encroachment, an increase in density and cover of shrub plant communities, is affecting biodiversity and functioning of ecosystems around the world. Through feeding and trampling ungulates affect the structure and species composition of plant communities, including shrublands, and are key drivers in shrub encroachment processes. This thesis, conducted within a long-term browsing exclosure experiment, investigates the effects of ungulates (red deer Cervus elaphus and fallow deer Dama dama) on the encroachment of C. ladanifer, a dominant Mediterranean shrub, into a mixed cork (Quercus suber) and holm (Quercus rotundifolia) evergreen oak woodland in Southern Portugal. Five paired fenced (ungulate-excluded) and unfenced (ungulate-allowed) plots of 25 m x 25 m were established in the study area in July 2001. Fenced plots had a 2.20 m height fence to exclude deer occurring in the site. Data on C. ladanifer reproduction structures (buds, fruits and flowers), soil seed bank, population density and biomass, were collected in fenced and open plots in 2007, 2013 and 2015. Ungulates consumed buds, flowers and fruits and decreased the soil seed bank of C. ladanifer. Plant reproductive costs (loss of fruits) were higher than potential benefits (seed dissemination) and the population density and biomass of C. ladanifer, decreased in the open plots by the end of the experiment. Ungulates decreased above-ground carbon (C) storage but also the amount of fine fuel loads reducing fire hazard and the probability of crown fires, and consequent adult oak mortality, in open plots. Therefore ungulate may potential benefit long-term ecosystem C storage. A drought year during data monitoring allowed quantifying jointly effects of ungulate browsing and drought on C. ladanifer mortality which increased in open plots. Changes in live:dead plant biomass affected fire hazard. Results show that ungulate ecology needs to be considered when investigating shrub encroachment processes

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Fundação para a Ciência e a Tecnologia

Número da atribuição

SFRH/BD/90753/2012