The role of mycorrhizae, site preparation, and organic amendment in the afforestation of a semi-arid mediterranean site with Pinus halepensis

Abstract

A factorial field experiment was conducted in a degraded semi-arid site of Southeastern Spain to test the effectiveness of mycorrhization and several soil preparation techniques on afforestation with Pinus halepensis. The mycorrhizal treatments were nursery inoculation with Pisolithus arhizus and forest soil addition to the planting holes. The soil preparation treatments were terracing (mechanical and manual) and the addition of an organic amendment (urban solid refuse). One year after planting, the study revealed significant differences in mycorrhization levels, frequency of mycorrhizal species, fine root production and growth between the inoculated seedlings and the noninoculated controls. Inoculation with P. arhizus gave better pine growth and mycorrhization rates than the addition of forest soil. Both mycorrhization treatments were particularly effective in combination with mechanical terracing. The organic amendment had no apparent negative influence on the mycorrhization level of the seedlings and significantly improved pine growth. The beneficial effects of mycorrhization treatments on P. halepensis growth persisted 2 yr after planting. The increase in growth of the seedlings due to the treatments could be attributed to the change in soil conditions (increased fertility and soil aeration) and probably to a mycorrhization effect on water relations, although it has not been clearly demonstrated.