Reproductive performance of the invasive tree Ligustrum lucidum in a subtropical dry forest: does habitat fragmentation boost or limit invasion?

Abstract

The spread of non-native invasive plants is closely linked to land use changes imposed by human activities such as the expansion of urbanizations and agricultural activities that result in the loss and fragmentation of native forests. While the conditions generated in fragmented forests may provide suitable new habitat for the arrival and establishment of invasive plant propagules, we know little about the reproductive performance of established invasive populations growing in fragmented conditions. We assess sexual reproduction of Ligustrum lucidum in continuous and fragmented forests across 2 years. We also measure soil quality parameters in 1 year to determine their relative influence in shaping its reproduction in both landscape conditions. We observed a strong decrease in reproductive success at the population level in fragmented habitats. However, reproduction at the individual level showed no differences in seed production per tree between landscape conditions, implying no changes in pollination service. Simultaneously, soils of continuous forests had higher water content, total nitrogen, organic matter and carbon. These soil quality parameters were positively correlated with seed production and seedling number per plot within the same year. Thus, reproductive failure in fragmented forests would not be the result of Allee effects but the consequence of less favorable abiotic soil conditions. In current dynamic and changing climatic scenarios imposed by human activities, water and nutrient demanding invasive plants like L. lucidum might be as likely as or even more susceptible to these changes than native ones. Climatic shifts acting in concert with land use changes may either ameliorate invasion spread in abiotically eroded fragmented habitats or boost invasion into novel environments, resulting in new distribution spread patterns.

A Global Review of Ligustrum Lucidum (OLEACEAE) Invasion

“…1 Percentage of studies about L. lucidum invasion carried out in each continent tubular in shape to 1.5 mm long, with lobes that are 2-4 mm long. The flowers are hermaphrodite and pollinated by insects Aguirre-Acosta et al 2014). The inflorescences are 100-250 mm long, 200 mm wide, and are broadly pyramid-to cone-shaped.…”

“…In the introduced area, L. lucidum was widely planted for hedge, shade, shelter and probably garden purposes because it is an attractive tree that gives good shade, grows rapidly and it produces fragrant flowers (Johnson 1953 ; Johnson 2009 ; Hoyos et al 2010 ; Aguirre-Acosta et al 2014 ; Hummel et al 2014 ; Rodrigues et al 2015 ). A study performed in New Zealand found that L. lucidum has a good wood for barbecue charcoal producing persistent heat (Wilcox 2000 ).…”

Community Attributes Predict the Relationship between Habitat Invasibility and Land Use Types in an Agricultural and Forest Landscape

“…Alterations in species composition and community structure may change the availability of environmental resources for alien plants. Changes in land use types and forest management regimes may also bring alien propagules to the resident community, raising possibilities of alien plant invasion [65]. Our study has identified indicators for habitat and community invasibility; however, further work such as control experiments still needs to be done to enhance our mechanistic understanding of the interactions between plant invasion and the biotic and abiotic indicators of habitat invasibility.…”

Effects of tree size and park maintenance on soil seed bank of Gleditsia triacanthos, an exotic tree in urban green areas

“…Under park maintenance of either moderate or perfect intensity, seed density did not correlate with tree circumference. Lack of correlation can be caused either by habitat effects on seed production of honey locust specimens, as it has already been described for other species (Rocha and Aguilar 2001;Aguirre-Acosta et al 2014), or by the park maintenance itself. The latter seems to be the more obvious reason because in neglected parks, where more or less natural accumulation of soil seed bank could take place, significantly higher seed density was observed under big trees than under small ones, and also in the direct correlation between tree circumference and seed density we obtained positive and significant relationship in a linear regression test.…”

“…Increasing density of soil seed bank under the canopy of woody species parallel with the age of the specimens is a plausible assumption, although rarely documented by published studies (but see Allen et al 1995;Cseresnyés and Csontos 2012;Aguirre-Acosta et al 2014). The accumulation of seed bank should be more pronounced for trees known about considerable survival of their seeds, retaining germinability for long periods in the soil, like the case of honey locust (Ferreras et al 2015).…”