Question: How to improve reforestation success of Quercus pyrenaica.

Location: 1800 m a.s.l., southern Spain.

Methods: One-year-old Quercus pyrenaica seedlings were planted using two treatments: (1) bare soil, using a 30-cm diameter augur bit (conventional technique) and (2) under the canopy of a pioneer shrub, Salvia lavandulifolia, using a 12-cm diameter augur bit. Survival and growth were monitored for six years. Our hypothesis is that the use of shrubs as nurse plants is an alternative technique of reforestation with higher success than traditional techniques, in which pre-existing vegetation is usually considered a source of competition. The rationale for the study was that for environments with a dry season, pre-existing vegetation buffers summer drought stress, ameliorates the water status of seedlings and thus usually increases seedling recruitment.

Results: Quercus survival was 6.3 × higher when planted under individuals of the pioneer shrub as compared to open areas. Quercus seedlings under shrubs also had shoots 1.8 × longer, while the number of shoots per plant did not differ among treatments. The first summer was the period with the highest mortality (49.1% of seedlings). Summer drought was the main cause of mortality.

Conclusions: The use of shrubs as nurse plants for Q. pyrenaica reforestation is a viable technique to increase establishment success. The technique could be similarly useful in other environments with a dry period and for other Quercus species. In addition, this technique offers the advantage of following natural succession, thus minimizing the impact in the community.