Soil scarification favors natural regeneration of Pinus pinea in Lebanon forests: Evidences from field and laboratory experiments

Abstract

Pinus pinea is an important species for ecological and economic reasons in the Mediterranean area and especially in Lebanon. However, conditions of its natural regeneration have received little attention. Our study aimed to test the influence of soil disturbances, predation and autotoxicity on pine regeneration. A seed sowing field experiment was conducted in a mature stand in which two types of soil disturbances were tested (soil scarification and litter burning) in presence or absence of predation. In addition, a laboratory experiment evaluating the influence of litter (present, absent or burned) and green needle leachates (i.e. in order to mimic potential autotoxicity) on seed germination and seedling growth was conducted. Results showed a strong effect of soil disturbance, in particular soil scarification which promoted seedling emergence and early survival, whereas the role of predation was low. Forty to sixty days after seed installation, seedling density peaked at 14.9 ± 0.4 seedling.m-2 in the scarification treatment, 13.1 ± 0.4 in the burning treatment and 8.4 ± 0.4 in the control treatment. However, an unexpected high mortality rate was recorded at the end of the field experiment in all treatments, as after seven months seedling density dropped to 0.2 ± 0.02. In the laboratory experiment, we emphasized an autotoxic effect of green needle aqueous extract on seed germination and seedling growth in the presence of litter. This allelopathic effect could be potentially linked to the presence of quinic acid which was measured as the major metabolite detected in needle aqueous extracts. In conclusion, we recommend soil preparation treatments to favor seedling emergence in combination with thinning to achieve seedling development on the long term.

Forest fire survival in young, denseBetula ermaniistands on soil scarification sites

“…Soil scarification is a commonly used ‘close to nature’ forest management method that assists the natural regeneration of woody plants in various forest biomes, with widespread research globally, including Europe (Hynynen et al , 2010; Nilsson et al , 2010; Jäärats et al , 2012), the United States (Woolley et al , 2012), and Canada (Beaudry et al , 1997; Giasson et al , 2006), with recent reports from South–Central Chile (Soto and Puettmann, 2018), Lebanon (Nakhoul et al , 2020), and Japan (Umeki, 2003). Globally, the concept of ‘close to nature’ has garnered attention, and it aims to reconcile wood production and ecological resilience (Messier et al , 2013; O’Hara, 2016).…”

Litter facilitates plant development but restricts seedling establishment during vegetation regeneration

“…Litter cover provides some suitable conditions for seed germination, and these conditions are key to seed germination (Sonkoly et al, 2020). On the positive side, litter protects seeds from herbivores (Hu et al, 2016; Nakhoul et al, 2020), enables seed germination by controlling soil temperature fluctuations (Xia et al, 2015), alleviates seed desiccation by shielding the soil surface from ultraviolet light (Visscher et al, 2016) and promotes seed vigour by creating water diffusion barriers for dry grasslands and microclimates for shady forests (Chen, Ma, et al, 2018; Ruprecht et al, 2010). Conversely, litter input can also make certain constraints stronger, such as negatively impacting seeds by placing them in deep shade or darkness (Rotundo & Aguiar, 2005), or by releasing allelochemicals from coniferous (Kainulainen et al, 2003) and broadleaved litter (Lang et al, 2021).…”

“…Litter cover provides some suitable conditions for seed germination, and these conditions are key to seed germination (Sonkoly et al, 2020). On the positive side, litter protects seeds from herbivores (Hu et al, 2016;Nakhoul et al, 2020), enables seed germination by controlling soil temperature fluctuations (Xia et al, 2015), alleviates seed desiccation by shielding the soil surface from ultraviolet light (Visscher et al, 2016) and promotes seed vigour by creating water diffusion barriers for dry grasslands and microclimates for shady forests (Chen, Ma, et al, 2018;Ruprecht et al, 2010).…”