Unravelling associations between tree-seedling performance, herbivory, competition, and facilitation in high nature value farmlands

Pedro G Vaz; Miguel N Bugalho; José M Fedriani; Manuela Branco; Xavier Lecomte; Carla Nogueira; Maria C Caldeira

doi:10.1016/j.jenvman.2018.11.082

Unravelling associations between tree-seedling performance, herbivory, competition, and facilitation in high nature value farmlands

J Environ Manage. 2019 Feb 15:232:1066-1074. doi: 10.1016/j.jenvman.2018.11.082. Epub 2018 Dec 27.

Authors

Pedro G Vaz¹, Miguel N Bugalho², José M Fedriani³, Manuela Branco⁴, Xavier Lecomte⁴, Carla Nogueira⁴, Maria C Caldeira⁴

Affiliations

¹ Centre of Applied Ecology "Prof. Baeta Neves" (CEABN- InBIO), School of Agriculture, University of Lisbon, Tapada da Ajuda, 1349-017, Lisbon, Portugal. Electronic address: pjgvaz@isa.ulisboa.pt.
² Centre of Applied Ecology "Prof. Baeta Neves" (CEABN- InBIO), School of Agriculture, University of Lisbon, Tapada da Ajuda, 1349-017, Lisbon, Portugal.
³ Centre of Applied Ecology "Prof. Baeta Neves" (CEABN- InBIO), School of Agriculture, University of Lisbon, Tapada da Ajuda, 1349-017, Lisbon, Portugal; Estación Biológica de Doñana (EBD-CSIC), c/Américo Vespucio s/n, 41092, Seville, Spain.
⁴ Forest Research Centre (CEF), School of Agriculture, University of Lisbon, Tapada da Ajuda, 1349-017, Lisbon, Portugal.

PMID: 33395758
DOI: 10.1016/j.jenvman.2018.11.082

Abstract

Herbivory, plant facilitation, and competition have complex impacts on tree regeneration which are seldom investigated together. Grazing exclosure experiments have allowed quantification of the effects of large herbivores on tree regeneration dynamics but have often ignored the effect of herbivorous insects. We experimentally tested how folivory (percentage of leaf damaged by insects) and microenvironment (tree canopy cover and herbs) jointly alter performance (growth and survival) of seedlings of two dominant Mediterranean oak-species within ungulate exclosures in a 3-year field study. An agroforestry system dominated by cork oak (Quercus suber) and holm oak (Q. rotundifolia) was assessed in south-east Portugal. We aimed also to determine whether the two oak species differed in the interdependences between folivory, microenvironment, covaring factors, and seedling performance. Unexpectedly, under the low-moderate insect defoliation, growth and survival of cork and holm oak seedlings were positively associated with herbivore damage. Herb removal increased oak folivory by 1.4 times. Herb removal was also positively associated with growth, directly and indirectly through its negative effect on oak folivory. Tree canopy favored insect folivory upon cork oak seedlings directly and upon holm oak indirectly via decreasing light availability. Folivory was threefold greater upon cork than upon holm oak-seedlings. Our study shows that tree canopy, herbs, and covarying factors can affect cork and holm oak-seedling performances through complex pathways, which markedly differ for the two species. The combined effect of insect herbivory and positive and negative plant-plant interactions need to be integrated into future tree regeneration efforts toward tackling the regeneration crisis of oak agroforestry systems of the Mediterranean.

Keywords: Leaf herbivores; Mediterranean ecosystem; Path analysis; Plant fitness; Plant–animal interactions; Tree mortality.