Massive and effective acorn dispersal into agroforestry systems by an overlooked vector, the Eurasian magpie (Pica pica)

Loreto Martínez‐Baroja,Mercedes Molina‐Morales,Daniel Gómez‐Sánchez,Salvador Rebollo,Pedro Villar‐Salvador,José María Rey‐Benayas,Pablo Quiles,Alexandro B Leverkus,Lorenzo Pérez‐Camacho,Jorge Castro

doi:10.1002/ecs2.2989

Loreto Martínez‐Baroja, Mercedes Molina‐Morales + Show 8 more

Open Access

https://doi.org/10.1002/ecs2.2989

Copy DOI

Abstract

AbstractOak regeneration and the expansion of forested sites in Eurasia rely on acorn dispersal by animals, especially the Eurasian jay (Garrulus glandarius). However, in open agroforestry systems where jays are absent, such as old fields far from acorn sources, oak recruitment still occurs. We hypothesize that the Eurasian magpie (Pica pica), an abundant corvid in this system, substitutes the jay in its seed dispersal function. By ringing 169 magpies, video recording >7500 acorn removal events with trail cameras, and radio‐tagging 337 acorns, we quantified that (1) magpies cached 41–56% of the annual acorn production of Quercus ilex trees in single caches on the ground; (2) breeding pairs, and especially males, were the main acorn dispersers; (3) each breeding magpie cached 169–1372 acorns in 6 weeks; and (4) the effectiveness of dispersal (percentage of cached acorns resulting in seedlings) was 0.6–2.4%, which (5) yielded a high density of emerged seedlings (56–439 seedlings/ha). We evidence that magpie could be a key species in the regeneration of oak agroforestry mosaics because they massively and effectively dispersed acorns. However, in our particular study site, effectiveness was low probably due to herbivory and summer drought stress (i.e., a context limitation rather than an intrinsic limitation of the disperser). As the distributions of magpies and oaks overlap widely in Eurasia, effective acorn dispersal by magpies could have a significant role in large‐scale oak forest recovery in strongly fragmented landscapes.

Highlights

Forest regeneration is paramount to counteract centuries of land degradation (Chazdon 2017), combat climate change (Nabuurs et al 2007), and attain the Sustainable Development Goals (U.N. 2017)
This study confirms our hypothesis that magpies, one of the most common corvids in Eurasia, are effective and long-distance dispersers of acorns in open agroforestry systems
Magpies produced hundreds to thousands of scattered caches of one single acorn. This resembles the strategy shown by the Eurasian jay, which maximizes the potential for seedling emergence (Kurek et al 2018), among other reasons

Summary

Introduction

Forest regeneration is paramount to counteract centuries of land degradation (Chazdon 2017), combat climate change (Nabuurs et al 2007), and attain the Sustainable Development Goals (U.N. 2017). Natural forest regeneration is limited by the ability of tree species to spread naturally (Rey Benayas et al 2008, 2015). Animal-mediated seed dispersal of large-seeded trees, like acorns, constitutes a major ecosystem service that allows the regeneration, densification, and expansion of forests (Whelan et al 2008). More than 60% of tree species in communities of temperate biomes are zoochorous (Howe and Smallwood 1982). Synzoochory, seed dispersal by seed-caching seed predators (Gomez et al 2019), is especially relevant in Quercus species ( “oaks”) and other large-seeded trees (Pesendorfer et al 2016a).

Methods

Results

Discussion

Conclusion