Explaining the larger seed bank of an invasive shrub in non-native versus native environments by differences in seed predation and plant size

Abstract

Background and aims-Large, persistent seed banks contribute to the invasiveness of non-native plants, and maternal plant size is an important contributory factor. We explored the relationships between plant vegetative size (V) and soil seed bank size (S) for the invasive shrub (Ulex europaeus) in its native range and in non-native populations, and identified which other factors may contribute to seed bank variation between native and invaded regions.  Methods-We compared the native region (France) with two regions where Ulex is invasive, one with seed predators introduced for biological control (New Zealand) and another where seed predators are absent (La Réunion). We quantified seed bank size, plant dimensions, seed predation, and soil fertility for six stands in each of the three regions.  Key results-Seed banks were 9 to 14 times larger in the two invaded regions compared to native France. We found a positive relationship between current seed bank size and actual plant size, and that any deviation from this relationship was probably due to large differences in seed predation and/or soil fertility. We further identified three possible factors explaining larger seed banks in non-native environments: larger maternal plant size, lower activity of seed predators and higher soil fertility.  Conclusions-In highlighting a positive relationship between maternal plant size and seed bank size, and identifying additional factors that regulate soil seed bank dynamics in non-native ranges, our data offer a number of opportunities for invasive weed control. For non-native Ulex populations specifically, management focusing on 'S' (i.e. the reduction of the seed bank by stimulating germination, or the introduction of seed predators as biological control agents), and/or 'V' (i.e. by cutting mature stands to reduce maternal plant biomass) offers the most probable combination of effective control options.

Native and invasive seedling drought-resistance under elevated temperature in common gorse populations

“…In terms of vegetative growth, our study showed an increase in height and leaf area for invasive gorse populations as compared to native populations in the early phases of the invasive process (seedling establishment) under warm conditions. This observation is in accordance with previous studies showing an increase in vegetative growth (Hornoy et al 2011) and reproductive output (Udo et al 2017;Bakker et al 2019) in introduced Ulex europaeus populations compared to native ones under non-limiting conditions.…”

A mini-review on the impact of common gorse in its introduced ranges

“…This study reported that salinity tolerance ability of U. europaeus is relatively less in its native range than when it is co-occurring with the invasive Acacia longifolia . Moreover, a comparative study done to compare the plant vegetative size and soil seed bank of U. europaeus in its native range and the invaded ranges showed that relatively larger seed banks in invaded ranges than on the native range (Bakker et al 2019 ). Larger maternal plant size, lower activity of seed predators, and higher soil fertility in the invaded areas were suggested as the potential reasons for these variations.…”