How do invasive trees impact shrub layer diversity and productivity in temperate forests?

Marcin K Dyderski,Andrzej M Jagodziński

doi:10.1007/s13595-021-01033-8

Abstract

• Key messageInvasive tree species alter taxonomic diversity and functioning of forest shrub layers: Prunus serotina increases shrub layer biomass two to three times but decreases its biodiversity, Robinia pseudoacacia slightly increases shrub layer biomass and has no effect on its biodiversity, while Quercus rubra both biomass and biodiversity of the shrub layer.• ContextAlthough the impact of invasive trees on understory biodiversity is known, very little data exist about their influence on shrub layer biodiversity and productivity.• AimsTo assess impacts of Prunus serotina Ehrh., Quercus rubra L., and Robinia pseudoacacia L. on shrub layer aboveground biomass, species composition, and alpha diversity.• MethodsWe measured stand structures in a set of 168 study plots established in Wielkopolski National Park (W Poland), and we compared biomass and diversity metrics using generalized mixed-effects linear models.• ResultsWe found the lowest aboveground biomass of shrub layers in Q. rubra forests. P. sylvestris forests invaded by P. serotina had two to three times higher aboveground biomass than non-invaded forests. R. pseudoacacia forests had 27.8% higher shrub layer biomass than Quercus-Acer-Tilia forests. We found negative impacts of Q. rubra and negligible impacts of R. pseudoacacia on shrub layer alpha diversity metrics. However, the effect of Q. rubra was similar to native F. sylvatica. P. serotina negatively affected functional diversity, but its effects were lower in rich P. sylvestris forests than in poor P. sylvestris forests.• ConclusionThe introduction of alien tree species alters ecosystem services and species diversity of shrub layers. The direction and magnitude of these alterations are alien species-specific and context-dependent. Therefore, their management should account for their impacts.

Highlights

Shrubs play an important role in forest ecosystems
We found the lowest mean aboveground biomass of shrub layers in Q. rubra forests (0.52 ± 0.14 Mg ha−1), which was about one-third of that in F. sylvatica forests (1.43 ± 0.43 Mg ha−1) and one-fourth of that in Q. petraea forests (2.17 ± 0.54 Mg ha−1)
In both types of P. sylvestris forests we found approximately 2.5-times higher aboveground shrub biomass in P. serotina invaded than non-invaded forests (8.11 ± 1.87 vs. 3.50 ± 0.59 Mg ha−1 in rich and 5.59 ± 1.23 vs 2.09 ± 0.78 Mg ha−1 in poor P. sylvestris forests); these differences were statistically insignificant in a pairwise comparison

Summary

Introduction

Invasive tree species significantly alter ecosystem services (Castro‐Díez et al 2019) and biodiversity (Terwei et al 2016; Šibíková et al 2019). We aimed to quantify the impact of three invasive woody species: Prunus serotina Ehrh., Quercus rubra L., and Robinia pseudoacacia L. on shrub layer biomass and functional, phylogenetic, and taxonomic diversity. We hypothesized that (1) the impact of P. serotina will differ from Q. rubra and R. pseudoacacia, as P. serotina occupies the shrub layer niche, in contrast to the canopy-dominants Q. rubra and R. pseudoacacia, and (2) the invasive species studied will decrease both biomass and taxonomic, phylogenetic, and functional alpha diversity of shrub layers

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Conclusion