Comparing the Sexual Reproductive Success of Two Exotic Trees Invading Spanish Riparian Forests vs. a Native Reference

Abstract

A widely accepted hypothesis in invasion ecology is that invasive species have higher survival through the early stages of establishment than do non-invasive species. In this study we explore the hypothesis that the sexual reproductive success of the invasive trees Ailanthus altissima (Mill.) Swingle and Robinia pseudoacacia L. is higher than that of the native Fraxinus angustifolia Vahl., all three species coexisting within the riparian forests of Central Spain. We compared different stages of the early life cycle, namely seed rain, seed infestation by insects, seed removal by local fauna, seed germination under optimal conditions and seedling abundance between the two invasive trees and the native, in order to assess their sexual reproductive success. The exotic species did not differ from the native reference (all three species displaying high seed rain and undergoing seed losses up to 50% due to seed removal by the local fauna). Even if the exotic R. pseudoacacia showed a high percentage of empty and insect-parasited seeds along with a low seedling emergence and the exotic A. altissima was the species with more viable seeds and of higher germinability, no differences were found regarding these variables when comparing them with the native F. angustifolia. Unsuitable conditions might have hampered either seedling emergence and survival, as seedling abundance in the field was lower than expected in all species -especially in R. pseudoacacia-. Our results rather suggest that the sexual reproductive success was not higher in the exotic trees than in the native reference, but studies focusing on long-term recruitment would help to shed light on this issue.

Effects of litter mixing on litter decomposition and soil properties along simulated invasion gradients of non-native trees

“…For each model, we assessed the residual deviance and the Akaike information criterion (AIC). The quadratic model was considered to improve the linear model if its AIC was at least two units lower than that of the linear model (Burnham and Anderson 2002).…”

Seed Production, Viability, and Reproductive Limits of the Invasive Ailanthus altissima (Tree-of-Heaven) within Invaded Environments

“…Martin and Canham [18] reported Ailanthus out-produced other exotic invasive counterparts (e.g., Acer platanoides L.) and co-occurring native tree species by several orders of magnitude, but without the periodic seed crop failures common among many native species. Similarly, Cabra-Rivas and Castro-Diez [16] reported that Ailanthus showed greater seed viability than the invasive Robinia pseudoacacia L. and native Fraxinus angustifolia Vahl in Spain. Moreover, Ailanthus is unexpectedly fecund even in environments presumably less favorable for invasion such as closed canopy forests [9,18] or as germinants following submergence in water [19,20].…”

“…Previous studies on Ailanthus seed production have reported reproductive outputs from several hundred thousand [15,16] to several million seeds in a single year, with large inter-annual variation and tree size-dependent effects [17,18]. Martin and Canham [18] reported Ailanthus out-produced other exotic invasive counterparts (e.g., Acer platanoides L.) and co-occurring native tree species by several orders of magnitude, but without the periodic seed crop failures common among many native species.…”