A brooms race: Seed ecology may explain differences in spread of two invasive legumes

Aldana M. Ariza; Cristina Sanhueza; Gabriela Brancatelli; Sergio M. Zalba

doi:10.25260/EA.26.36.3.0.2691

Authors

Aldana M. Ariza GEKKO, Grupo de Estudios en Conservación y Manejo, Departamento de Biología, Bioquímica y Farmacia, Universidad Nacional del Sur. Bahía Blanca, Argentina
Cristina Sanhueza GEKKO, Grupo de Estudios en Conservación y Manejo, Departamento de Biología, Bioquímica y Farmacia, Universidad Nacional del Sur. Bahía Blanca, Argentina
Gabriela Brancatelli GEKKO, Grupo de Estudios en Conservación y Manejo, Departamento de Biología, Bioquímica y Farmacia, Universidad Nacional del Sur. Bahía Blanca, Argentina. Comisión de Investigaciones Científicas de la Provincia de Buenos Aires (CIC)
Sergio M. Zalba GEKKO, Grupo de Estudios en Conservación y Manejo, Departamento de Biología, Bioquímica y Farmacia, Universidad Nacional del Sur. Bahía Blanca, Argentina

DOI:

https://doi.org/10.25260/EA.26.36.3.0.2691

Keywords:

invasive species, Genista monspessulana, Spartium junceum, fire, seed bank, pampas grasslands

Abstract

1. Biological invasions represent a major threat to biodiversity and ecological integrity worldwide. Shifts in dominance among invasive species provide valuable opportunities to identify the ecological traits that determine invasion success.
2. In the Southern Pampas grasslands of Argentina, two introduced broom species, French broom (FB, Genista monspessulana) and Spanish broom (SB, Spartium junceum) became prominent invaders and management priorities. Historically, control efforts focused on SB. However, following extensive wildfires (2008 and 2013), FB rapidly expanded and displaced SB.
3. We investigated the demographic and ecological mechanisms that may underlie this shift in species dominance by combining field studies, seed bank assessments, germination experiments under contrasting heat treatments and greenhouse water stress experiments.
4. FB produces ~6 times more seeds/plant and develops seed banks ~5 denser than those of SB. Pre-germination heat treatments resulted in higher germination percentages in both species, but FB maintained faster and greater germination even after severe dry-heat exposure, enhancing post-fire regeneration.
5. FB flowers earlier, providing a temporal advantage in reproduction and seed maturation in relation to seasonal rainfall peaks. It showed only limited changes in growth under reduced irrigation, although overall responses to water availability were similar between species.
6. Implications. Abundant seed production, a high germination rate, a dense seed bank, greater tolerance to fire-related heat, and earlier flowering could explain the rapid spread and predominance of French broom in the grasslands of southwestern Buenos Aires Province. Management strategies should prioritize the early control of plants to prevent seed production, the depletion of the seed bank through prescribed burning and the control of post-fire seedlings to contain further expansion.

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