Shrubs protect oak seedlings against ungulate browsing in temperate broadleaved forests of conservation interest: A field experiment
Anna M. Jensen, Frank Götmark, Magnus Löf
Forest Ecology and Management, 266; 187-193, doi:10.1016/j.foreco.2011.11.022
In many oak-rich temperate broadleaved forests of conservation value, high ungulate browsing pressure restricts oak regeneration. We examined the protection of oak (Quercus sp.) seedlings from browsing provided by naturally occurring shrubs in ten forests across southern Sweden over three years. We planted oak seedlings in four plots in each forest; two with naturally regenerated shrubs and two with no shrubs. Ungulate browsers (e.g. moose and deer) were excluded from two plots at each site, one with and one without shrubs.
The probability of a seedling being browsed was 20 % lower for oaks growing among shrubs than in the absence of shrubs. When browsing did occur, the intensity was lower for seedlings in shrubs. Regression analyses showed that browsing frequency increased on seedlings in tall shrubs, and decreased on seedlings that had been browsed previously. Browsing intensity decreased if the seedling grew in tall and dense shrubs. Browsing frequency and intensity on the oak seedlings were both increased by over-topping of the shrub canopy. Increased abundance of the prickled Rubus idaeus and R. fruticosus in plots with shrubs did not affect browsing frequency and intensity. Two and a half years after planting, oak seedling mortality increased by the presence of shrubs.
Although, shrubs restricted oak seedling growth, we conclude that shrubs initially facilitated oak regeneration by concealment, and subsequently by numeric dilution. Shrubs maybe used to reduce browsing damages if long-term evaluation indicates a net positive outcome for oak survival and growth.
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