La progression du Pin sylvestre et du Pin noir dans le paysage des Grands Causses : impact des activités humaines et des facteurs naturels

In the Grands Causses region (Aveyron, Lozere, Gard, Herault), Scots pine (Pinus sylvestris L.), a native species, and Black pine (Pinus nigra Arn. subsp. nigra), which was introduced for timber production, invades grasslands. To understand landscape evolution, we characterised the conditions of seedling recruitment for both species. We showed that recruitment is affected by factors that are both abiotic (summer drought, geology) and biotic (grazing, interactions with herbs and shrubs). These effects translate into demographic growth and speed of invasion. Black pine produces more saplings and spreads faster than Scots pine. It is also less affected by droughts but more susceptible to grazing than Scots pine. Management measures should thus concentrate on Black pine, which could potentially spread very fast and dominate Scots pine.