Constant gardeners: Endozoochory promotes repeated seedling recruitment in clonal plants

Abstract

Paradoxically, seedlings of clonal plants are rarely observed in nature, despite many of these species producing large amounts of seeds every fruiting season. Studies about clonal plants' recruitment strategies are usually based on experiments carried out under controlled conditions (e.g., laboratory) and rarely consider frugivores' effects. We tested the role of endozoochory in the seedling recruitment in natural conditions of the bilberry Vaccinium myrtillus, a widely distributed clonal species and a key resource in temperate and boreal regions of Eurasia, which has been suggested to recruit at occasional windows of opportunity (unpredictable conditions in which seedling recruitment may occur within conspecific adult stands). We marked brown bear Ursus arctos, mesocarnivore (red foxes Vulpes vulpes and martens Martes spp.) and passerine feces containing bilberry seeds in the Tatra Mountains (Carpathian Mountains, Southern Poland) and followed the fate of the embedded seeds during two years. We detected bilberry germination associated with 100%, 87.5%, and 50% of brown bear, mesocarnivore, and passerine feces, and also in 43.6%, 41.2%, and 23.1% of the control plots located 5, 10, and 30 m away from the bear scats, respectively. In bear scats, investigated in more detail, 15.7% of the seedlings survived at least one year. The largest numbers of seedlings were associated with bear scats (154.4 AE 237.3 seedlings/m 2 ), especially to those defecated upon the soil disturbances these animals create next to their resting sites. Our results demonstrate that endozoochory facilitates repeated bilberry seedling recruitment in nature, suggesting that studies on the reproductive strategies of clonal plants must consider the role of frugivores. Some frugivores' behaviors, such as the defecation by bears in the vicinity of their resting sites, may in fact be crucial for the reproduction of clonal plants and for the adaptation of these species to the current changing climatic conditions.

From death comes life: Large vertebrate carrion enhances seedling establishment in clonal ericaceous shrubs

“…Our results tie into several recent studies that highlight that seedling establishment of berry‐producing ericaceous plants is closely linked with non‐exclusive pathways of directed endozoochory. For example, passerine birds direct seed dispersal towards decaying wood (Arnberg et al., 2023) and brown bears towards resting sites (García‐Rodríguez & Selva, 2021), both providing favourable conditions for seedling establishment (Arnberg et al., 2023; García‐Rodríguez et al., 2022). Indeed, Vaccinium populations have shown higher genetic diversity than expected for clonal populations (Albert et al., 2004, 2005; Persson & Gustavsson, 2001).…”

Use climatic space‐for‐time substitutions with care: Not only climate, but also local environment affect performance of the key forest species bilberry along elevation gradient

“…Bilberry's alpine expansion, on the contrary, may be due to influx of berries and seeds from the boreal zone. Despite large seed production, bilberry seedlings are surprisingly rarely observed at the forest floor(García-Rodríguez & Selva, 2021;Welch et al, 2000).This may be due to limited amounts of microsites with bare soil, bilberry's preferred germination substrate. Such microsites become increasingly abundant above the tree line.…”