We found that the dense layers of brash produced by windrowing significantly reduced the amount of natural regeneration. Windrows could be up to a metre high and several metres wide, producing a physical barrier that prevented seedling establishment and creating regions with little or no regeneration. While we might expect seedlings from larger seeded species like rowan (200,000 seeds weigh 1 kg) to have an advantage over seedlings from smaller seeded species such as birch (5.9 million seeds weigh 1 kg) in growing through brash (Leishman and Westoby, 1994) we found no significant difference between the proportion of rowan in windrows and interrows. Furthermore, previous studies have found that where grazing pressure is high, brash (Truscott et al., 2004) and coarse woody debris (Smit et al., 2012) can help protect seedlings from browsing. However, it is difficult to draw any conclusions from our study as only a single site (U15) recorded significant browsing. The low incidence of browsing at our study sites (grazing pressure was controlled) means that grazing is unlikely to limit regeneration (Palmer et al., 2004; Olesen and Madsen, 2008; Yamagawa et al., 2010).
seeds
200,000
200,000 seeds
weigh
1 kg
kg
seeds
5.9 million
5.9 million seeds
weigh
1 kg
kg