Modelling Spanish black pine seedling emergence: Establishing management strategies for endangered forest areas

Changes in climate may reduce the success of natural regeneration and hence require adjustments to silvicultural practices. Special attention is required for species such as Spanish black pine (Pinus nigra Arn. ssp salzmannii) because of impediments to achieve successful natural regeneration. Spanish black pine seed germination was studied under field conditions at a normal altitude for the species and at the upper altitude limit of its distribution in the Cuenca Mountains (southeastern Spain). The aim was to assess the effect of location, overstory density, soil treatment, sowing date and climatic characteristics on regeneration success. ANOVA results indicated a significant interaction of location by overstory density on germination rates. A logistic model containing the temperature variable TemminAc, the light radiation effect (Rad variable) and the interaction term between soil treatment (Soil Treat) and radiation (Soil Treat × Rad) correctly predicted the germination success in 94% of cases. Moreover, two Poisson regression models (one for each experimental site) showed that the number of germinated seeds depends on stand basal area (G), soil treatment (Soil Treat) and sowing date (Seed Season). Conservation management could increase initial seedling recruitment by promoting soil preparation and higher basal area levels. The populations at higher altitudes are particularly endangered due to the unfavourable environmental conditions for the development of this species, which seriously affect seed rain density and germination rates.

► Germination of Spanish black pine is threatened, mainly at its altitudinal limits.
► Germination success is negatively influenced by solar radiation and air temperature.
► Stand density positively affects the number of germinated seeds.
► Soil scalping promotes success of germination and amount of germinated seeds.
► Germination might be improved through the use of silvicultural prescriptions.