Stand-level drivers of tree-species diversification in Mediterranean pine forests after abandonment of traditional practices

Abstract

a b s t r a c tThe progressive abandonment of traditional forest management over the last few decades has led to significant densification processes in most Mediterranean pine stands. In parallel, some of these stands have also shown tree-species diversification processes, the occurrence of which is considered essential for future adaptability and resilience to change. Here we aim to gain further understanding of the main factors driving these diversification processes via a case-study approach using the long-term-managed black pine (Pinus nigra Arn. ssp. salzmannii) forests of the Catalan Pre-Pyrenees (NE Spain). For this purpose, we sampled 155 plots distributed in 8 different stands and analyzed the role played by a number of microsite factors and stand attributes (including canopy openness and heterogeneity) on the abundance of seedlings (h < 1.3 m) and saplings (h > 1.3 m; dbh < 7.5 cm) of the main tree-species in the area (i.e. black pine, evergreen oak and marcescent oaks). Results revealed ongoing black pine recruitment limitation processes mainly associated to the high canopy cover of the overstory and the increasing abundance of shrubs, which may compete with pines for light resources. In contrast, we found that current environmental and stand-level conditions favor the progressive advance of the recruitment of evergreen and marcescent oaks, which are able to establish successfully under the dominant pine canopy. However, in the absence of canopy openings, light levels may not allow the established oaks (in particular the evergreen Quercus ilex) to grow and progress to higher developmental stages. Our findings bring deeper insight into the role of stand-level factors regulating species diversification, and can be used by forest managers to adjust their practices (e.g. by modifying the spatial and temporal patterns of silvicultural treatments such as thinnings or selection cuttings) in order to favor this natural process and increase stand resilience.

Structure, regeneration and growth of Scots pine (<i>Pinus sylvestris</i> L.) stands with respect to changing climate and environmental pollution

“…Based on the results, by 2015 there was a high increase in the number of recruits compared with 2005 (up to 5.9 times). A comparison of these results with those of Martín-Alcón et al (2015) shows an opposite trend because a decreasing number of recruits is reported in that paper. Such a trend is observed in other studies (Urbieta et al 2011;Carnier et al 2014).…”

“…Such a trend is observed in other studies (Urbieta et al 2011;Carnier et al 2014). Martín-Alcón et al (2015) explain a decreasing number of recruits by the worse availability of light in forest stands. In other works a negative influence of the competition of herbaceous vegetation is mentioned (Lucas-Borja et al 2011;Prévosto et al 2012).…”

How close to nature is close-to-nature pine silviculture?

“…Related to this topic, more information is available from the area of southern and northern Europe (Angelstam, Kuuluvainen 2004;Montes et al 2005;Poyatos et al 2013;Martín-Alcón et al 2015), but in conditions of central Europe researchers paid attention mainly to stands being composed of shade-tolerant species such as spruce, beech and fir.…”

Diversifying sub‐Mediterranean pinewoods with oak species in a context of assisted migration: responses to local climate and light environment

“…; Martín‐Alcón et al. ). Q. coccifera L. and Q. ilex L. are common evergreen sclerophyllous oaks in Mediterranean areas of the Iberian Peninsula, whereas Q. faginea Lam.…”

“…; Martín‐Alcón et al. ). An increase in tree species diversity is generally thought to enhance the forest resilience to environmental changes, including variations in disturbance regimes (e.g.…”