Towards a framework for understanding the context dependence of impacts of non‐native tree species

Abstract

1. Biological invasions are a major driver of ecosystem change but causes of variation in their environmental impacts over space and time remain poorly understood. Most approaches used to quantify the impacts of non-native species assume there are interactions among per capita (i.e. individual level) effects, species abundance and the area occupied by the species. However, studies rarely evaluate these factors and their interactions and often fail to recognize that the magnitude of impacts can be highly context dependent. Understanding what drives the context dependence of non-native species impacts can improve our understanding and predictions of ecosystem change and better inform options for mitigation.2. Conifers, especially pines, are among the most problematic non-native plant species globally. We use Pinaceae to illustrate how context dependence in biodiversity and environmental impacts of non-native plant species can be generated by at least four processes: nonlinear density effects; intraspecific variation in functional traits; shifts in impacts over time; and persistence of impacts as biological or ecosystem legacies following non-native species removal. Using this understanding, we develop a framework to better quantify interactions of impacts along environmental gradients (e.g. soil fertility, climate, ecosystem age).3. We demonstrate how impacts of non-native species can occur at both low and high density, and that failing to account for intraspecific variation in effect traits can lead to significant errors in the prediction of impacts. By incorporating context dependence in regard to density and functional traits, we can measure how the interaction of this context dependence will shift along environmental gradients. | 945Functional Ecology SAPSFORD et Al.

Limited evidence for a consistent seed mass‐dispersal trade‐off in wind‐dispersed pines

“…However, in contrast to our own findings, a strong trade‐off was found between seed mass and terminal velocity for P. sylvestris in France (Debain et al., 2003). Thus, it is likely that, as with other aspects of Pinus life history, relationships between seed mass and terminal velocity appear strongly context‐dependent (Sapsford et al., 2020). Surprisingly, the relatively few studies that have examined within‐species relationships between seed mass and dispersal potential in other taxa have all found negative relationships (Chen & Giladi, 2020; Larios & Venable, 2015; Skarpaas, Silverman, Jongeians, & Shea, 2011).…”

Impacts of alien tree species on the abundance and diversity of terricolous bryophytes

“…However, lack of difference in soil C:N ratio between invaded and non-invaded poor P. sylvestris forests does not support this suggestion. Different patterns of P. serotina impacts on bryophytes in P. sylvestris plantations and poor forests are an example of the context-dependence of biological invasion (González-Moreno et al 2014; Dyderski and Jagodziński 2019b;Sapsford et al 2020). Here, a mismatch between habitat fertility and forest species composition changed the impact of an invasive tree species on bryophytes.…”

Forest inventory-based assessments of the invasion risk of Pseudotsuga menziesii (Mirb.) Franco and Quercus rubra L. in Germany

“…the ecosystem services provided by NNT, whilst minimising their detrimental impacts (Brundu and Richardson 2016), for example, by identifying ecosystem types or demarcated areas where they can be cultivated with a low risk of invasion (Rouget et al 2002). Invasion risks of NNT strongly depend on the type of ecosystem (Pyšek et al 2012;Sapsford et al 2020;Vor et al 2015) emphasizing the importance for analysing the spatial extent for potential or existing invasive NNT (Hawkins et al 2015;Rouget et al 2002).…”