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Doctoral thesis, 2020

Forest restoration using direct seeding of oak – Odor cues from predators as a seed protection strategy against foraging rodents

Villalobos, Adrian

Abstract

In forest restoration of oak, planting nursery-growth seedlings is related to high operational costs. One cost-efficient alternative is the application of direct seeding. However, acorn removal by rodents is one of the major drawbacks in its implementation. As rodents rely on their sense of smell to allocate their predators and show fear/defense related behaviors, there is a strong potential for the application of predator odor cues as a seed protection strategy. Therefore, the overall goal of this thesis was to investigate to which extent predator odors could be used as a seed protection strategy against foraging rodents. To reach this goal, I established laboratory and field experiments to investigate natural-based treatments and synthetic odor compounds from predators. The first laboratory study (paper I) revealed mink excrement as the most efficient treatment, because it reduced seed consumption and seed touch by rodents, but did not have negative effects on germination. Based on this results, we established a direct seeding field experiment (paper II) were the acorn removal rates were monitored under the application of two mink excrement treatments and other factors such as distance to forest edge and acorn size. Here, in contrast to the laboratory study, the mink excrement did not reduce acorn removal. Factors such as loss of efficiency over time due to excrement desiccation or animal habituation after a long odor exposure were accounted as possible explanations. The results further confirm the importance of reducing suitable habitats for rodents such as post-harvest slash piles, and to select acorn sizes with caution, because although bigger acorns produce better seedlings, they are also removed in higher quantities. Finally, the laboratory and field studies (paper III and IV, respectively) regarding synthetic predator odor compounds showed for the first time that the compound 2-propylthietane was avoided by bank voles in laboratory settings and reduced the acorn removal rates in natural conditions. This result further supports the behavioral relevance of single compounds, which may elucidate fear responses as strong as for complex odor mixtures. In conclusion, this thesis highlights the relevance of synergies between laboratory and field studies with the goal to direct research efforts in finding a better protection strategy during direct seeding.

Keywords

rodent pest management; Quercus; Apodemus; Myodes; seed protection; volatile compounds; predator-prey dynamics; clear-cut; regeneration; repellent

Published in

Acta Universitatis Agriculturae Sueciae
2020, number: 2020:35
ISBN: 978-91-7760-588-1, eISBN: 978-91-7760-589-8
Publisher: Southern Swedish Forest Research Centre, Swedish University of Agricultural Sciences