Abundance and spatial attributes of forest remnants differently influence colonization patterns of contrasting oak species

Abstract

Context Forest remnants in fragmented landscapes may trigger forest recovery after disturbances. Beyond extension of patches and distance to colonization sites, little is known about how the size structure of reproductive trees within patches and past land use/cover shape colonization dynamics in mountainous landscapes.

Objectives To assess the influence of (1) forest remnant abundance, spatial attributes (i.e. distance and altitude difference to colonization sites), and composition of reproductive trees at the individual level, and of (2) past land use/cover on the colonization of two functionally distinct Mediterranean oaks, the evergreen Quercus ilex L. and the deciduous Quercus faginea Lam., in a 55-year-old maritime pine (Pinus pinaster Ait.) plantation.

Methods We assessed oak juvenile density in 153 plots within a Mediterranean pine plantation established on cropland and shrubland. We geolocated and measured the diameter at breast height of reproductive oaks (n = 5020) within a 500 m-radius buffer around each plot.

Results Q. ilex showed higher colonization than Q. faginea after accounting for remnant abundance. For Q. ilex, remnant abundance was the most influential factor, whereas colonization by Q. faginea was primarily driven by distance and altitude difference between reproductive trees and colonization sites. Tree size did not affect recruitment. Former cropland exhibited higher oak colonization than former shrubland.

Conclusions In this study, Q. ilex was a more efficient colonizer than Q. faginea, likely leading to evergreen oak dominance in pine plantations in the mid-term. Spatial attributes influenced recruitment of both oak species differently and independently of tree size. These findings help to identify high-regeneration areas more accurately, which supports the optimization of pine plantation diversification in Mediterranean mountain areas.