Woodland regeneration on grazed former arable land: A question of tolerance, defence or protection?

作者：Van Uytvanck Jan^*; Van Noyen Anke; Milotic Tanja; Decleer Kris; Hoffmann Maurice

来源：Journal for Nature Conservation, 2010, 18(3): 206-214.

DOI：10.1016/j.jnc.2009.10.001

• Associational resistance
• Browse line
• Large herbivores
• Low intensity grazing
• Pioneer tree assemblages
• Resistance traits
• Spatial heterogeneity
• Tree and shrub recruitment and establishment

Ecological restoration of native woodlands and wooded pastures on former agricultural land is an important topic in modern conservation practice. The introduction of large herbivores is increasingly used to achieve these aims. We investigated how grazing, resistance traits of plants( concerning herbivory) and associational resistance interact and affect the establishment pattern of woody species on abandoned arable land (N-Belgium, W-Europe). In these early successional tree assemblages, we tested whether grazing increased or decreased spatial heterogeneity, which is supposed to be a crucial factor for biodiversity.
With repeated measurements, 2-3 and 5-7 years after the cessation of agricultural use, we sampled 87 grazed and 56 ungrazed plots (314 m(2)) in 14 sampling areas (former arable land) on nutrient rich, ( sandy) loam soils. We recorded established tree frequencies, related to grazing, time, resistance traits and unpalatable/spiny vegetation cover in the herb and low shrub layer. We investigated horizontal and vertical heterogeneity using variances in establishment frequencies and variances in frequencies of trees that were able to grow beyond the browse line, respectively.
We found massive colonisation of grazing tolerant and resistant woody species in early successional stages. Grazing decreased frequencies and height of the most abundant tolerant species( mainly Salix caprea L.). After 5-7 years, frequencies of defensive and tolerant species were equal, but the former ( mainly Betula pendula Roth) were able to grow beyond the browse line. When the cover of unpalatable/spiny vegetation was high enough (460% of plot size), it also provided suitable nurse sites for tolerant species to grow out. In early assemblages, grazing increased horizontal and vertical heterogeneity, resulting in intermediate successional stages. In the long-term, the mechanism of associational resistance will also allow non-resistant and tolerant species to grow beyond the browse line and promote forest succession and the order of species establishment and replacement.

• 出版日期2010-8