Abstract
Planted woodland islets can provide seeds for restoring forest ecosystems in Mediterranean old fields lacking seed sources, but other factors than seed arrival can also hinder the establishment of woody species. We experimentally examined factors affecting the emergence, survival, growth and recruitment of holm oak (Quercus ilex) seedlings juveniles from 25-year-old 100-m2 oak woodland islets planted in a Mediterranean old field. Wet springs and summers increased seedling emergence and survival. Distance to the islets per se did not affect seedling performance. However, emergence and survival increased in microsites close to the islets in less sun-exposed orientations of the islets and far from the islets in more sun-exposed orientations. Damage by wild boar reduced emergence, and unsheltered seedlings had 26% lower survival than sheltered ones, reflecting herbivory. Herb community biomass and light reduction by herbs increased with distance from nearest islet; the sparse herb cover around islets was due to competition from woodland islets, not to herbivory. There was a mismatch between the pattern of seedling survival and how the abundance of naturally recruited oaks varied with distance from the nearest islet; this suggests that other drivers can counteract the spatial pattern of seedling survival. We conclude that natural regeneration of Q. ilex in old fields from planted woodland islets is slow (5.7 seedlings ha−1 yr−1) due to acorn and seedling predation, and drought during spring and summer. Despite their small size, planted islets affected survival of oak juveniles depending on the orientation and distance relative to the islets.
Highlights
Natural regeneration, called passive or spontaneous restoration, has restored many woodland and forest areas (Chazdon et al 2020); for instance, 133 million ha in Europe have been recovered through natural regeneration up to 2010 (FAO 2015)
The goal of the present study was to assess the spatial effects of holm oak (Quercus ilex L.) woodland islets on oak recruitment outside the islets 25 years after islets establishment in Mediterranean old fields and to identify factors that influence that recruitment
In a previous study (Rey-Benayas et al 2015), we analysed long-term recruitment at this site, and we experimentally showed that high acorn predation or removal, seedling herbivory and stressful microclimatic conditions slow down oak seedling establishment from the woodland islets
Summary
Called passive or spontaneous restoration, has restored many woodland and forest areas (Chazdon et al 2020); for instance, 133 million ha in Europe have been recovered through natural regeneration up to 2010 (FAO 2015). Insufficient seed dispersal, reduces the effectiveness of passive forest restoration (Jordano et al 2008; Navarro and Pereira 2012; Rey-Benayas and Bullock 2012). Various strategic revegetation actions have been applied to accelerate forest restoration in areas without forest remnants such as farmed landscapes (Rey-Benayas and Bullock 2015). These actions differ in their intensity of intervention, from high-intensity intervention named “reconstructive restoration” to lower-intensity “assisted restoration” (Gann et al 2019; Atkinson and Bonser 2020). The less intensive actions include several forms of nucleation techniques such as planting tree clusters, hedgerows and even isolated trees, all of which promote regeneration and enhance wildlife, agricultural production and other ecosystem services (Manning et al 2006; Rey-Benayas et al 2008; Van Vooren et al 2017)
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