How do different competing species influence the response of Betula pubescens Ehrh. to browsing?

When attempting to expand existing woodland through natural regeneration, herbivory and competition from the existing vegetation may impede the regenerating saplings. This work addresses how browsing and competition with other vegetation interact to drive sapling growth and morphology of the widespread tree species B. pubescens. We took above-ground morphological measurements of B. pubescens saplings within an intimate mosaic of Calluna vulgaris and Molinia caerulea, comparing saplings growing with each of the two plant species under three different red deer (Cervus elaphus) densities, allowing comparison of different levels of both past and present levels of browsing damage. Saplings growing in M. caerulea dominated vegetation responded to reduced browsing with faster growth than those growing in C. vulgaris dominated vegetation. However, we found that when natural browsing levels were high, browsing masked any differences in inter-specific interactions between plant species. We propose that, in regeneration schemes where deer densities are reduced, these differences should confer a competitive advantage to saplings growing with M. caerulea over those growing with C. vulgaris. Additionally, our results highlight the importance of browsing history, rather than just current browsing levels, in determining sapling growth responses under different herbivore management regimes. This study highlights the importance of multi-factor interactions in determining plant growth and morphology under different conditions. In particular we identify the prevalence of interactions between competition, herbivory and time, as determining the potential growth and morphology of B. pubescens saplings in regeneration areas. This has important implications for the management of sites where browsing impedes the natural regeneration of trees and shrubs, or where herbivore densities have been reduced to encourage woodland regeneration.