Effect of Tree Shelters and Regeneration Method on Survival and Growth of Cork Oak Plantations in the Maamora Forest, Morocco

Abstract

Forests are under intense human pressure, hindering their restoration. A potential solution to regeneration problems is the adoption of tree shelters, which have demonstrated protective benefits in the early establishment of forest plantations. A 9-year study was conducted in the Maamora forest (Morocco) to evaluate the effects of tube shelters and regeneration methods (direct seeding and seedling) on the growth and survival of cork oak (Quercus suber) plantations. A split-plot design was developed with three replicates of 36 plants for each of the four shelter treatments, including T0 (control), T1 (Tubex 1.20 m), T2 (Tubex 1.50 m), and T3 (Tubex 1.80 m) for a total of 964 plants, where periodic inventories were conducted to assess plant survival and growth. Our results show regeneration methods and shelters significantly influenced the survival of cork oak. Direct-seeded plants were more successful than those from seedlings, presenting survival rates of up to 97%. Despite a minimal shelter effect at the beginning, their positive influence was strong later on. Only plants installed with the 1.20 m shelter had an overall success rate of over 50%. Regeneration method had a strong influence on height and diameter growth, with seedling units showing taller plants initially, which shifted to direct-seeded plants in subsequent years. Conversely, the effect of shelters on growth parameters was generally non-significant. Nonetheless, sheltered trees exhibited greater height and diameter than unsheltered trees, particularly in the latter years. Sheltered plants showed an overall faster rate of vertical growth, while unsheltered plants showed faster radial growth.