Responses of Fraxinus excelsior seedlings to grass-induced above- and below-ground competition

Abstract

The competitive interactions between woody seedlings and herbaceous vegetation have received increasing interest in recent years. However, little is known about the relative contributions and underlying mechanisms of above-and below-ground competition between species. We used a novel experimental approach to assess the responses of Fraxinus excelsior seedlings to different combinations of root and shoot competition imposed by the grass Dactylis glomerata under greenhouse conditions. Seedling growth was significantly reduced by competition for soil resources, but neither biomass nor height were significantly affected by shoot competition for light. Competitive response indices based on biomass confirmed that below-ground competition was more important than above-ground competition, and indicated that root and shoot competition did not interact to influence plant growth. Fraxinus biomass allocation and seedling traits were almost all significantly affected by root competition; these responses varied depending on the trait examined. In contrast, morphological responses to shoot competition were limited. In the absence of root competition, seedlings showed a significant increase in the biomass allocated to leaves and a greater leaf area ratio in response to shoot competition. Our findings suggest that morphological modifications help to mitigate the negative effects of competition, but the expression of plasticity may be suboptimal due to resource constraints. The present study also highlights the importance of appropriate experimental controls and analysis to avoid confounding effects of experimental design and ontogeny on the interpretation of competitive responses.

White‐tailed deer (Odocoileus virginianus) positively affect the growth of mature northern red oak (Quercus rubra) trees

“…Belowground competition can be intense (Casper andJackson 1997, Bloor et al 2008) and has been demonstrated for both saplings and adult trees in other contexts (Bloor et al 2008, Montgomery et al 2010. Because understory vegetation represents an important fraction of forest biomass (Knight et al 2009, Heckel et al 2010 and is a substantial contributor to ecosystem transpiration (Yepez et al 2003), competition for water and nutrients may be important in structuring forest communities and could be strongly influenced by deer herbivory.…”

Root spatial distribution and biomass partitioning in Quercus robur L. seedlings: the effects of mounding site preparation in oak plantations

“…Since root development plays a major role in competition among tree individuals (e.g. Leuschner et al 2004;Bloor et al 2008) and in competition between young trees and herbaceous vegetation for limited soil resources (Löf 2000;Coll et al 2003Coll et al , 2004, information about biomass partitioning to roots and root system extension forms the basis for appropriate evaluations of regeneration success.…”

Effect of nitrogen availability on forest understorey cover and its consequences for tree regeneration in the Austrian limestone Alps

“…Van Dobben et al 1999;Beckage and Clark 2003;Ladd and Facelli 2005). These interactions may involve both competitive and facilitative components, and the indirect impact of eutrophication on tree recruitment may hence vary from negative over neutral to positive (Paluch 2005;Baier et al 2007;Bloor et al 2008).…”