Direct seeding success of four threatened oak species in a peri-urban forest: effects of microhabitat and rodent exclusion

Abstract

Cloud forest degradation leads to the loss of foundational species, including oak trees, with negative and cascading effects on biodiversity. The relatively simple and inexpensive technique of direct seeding could help recover focal species in degraded peri-urban forests, but the success of this technique may be limited by mammalian seed predation. In this study, we evaluated the success of direct seeding of four sympatric and threatened oak species (Quercus germana, Q. lancifolia, Q. xalapensis, and Q. sartorii) in the cloud forest of central Veracruz. We considered the effects of planting microhabitat (low vs. high vegetation cover) and predator/disperser exclusion (total exclusion, partial exclusion, and open access to all predators) on the probability of acorn removal and germination, and on seedling emergence. Total germination was highest in Q. germana, followed by Q. lancifolia, Q. xalapensis, and Q. sartorii (52%, 32%, 29.33%, and 8.67%, respectively). Total emergence was highest in Q. lancifolia, followed by Q. xalapensis, Q. germana, and Q. sartorii (17.33%, 14.67%, 10.7%, and 2%, respectively). When acorns were exposed and unprotected in the microhabitat with high vegetation cover, removal and predation were higher (74%) than in the microhabitat with low vegetation cover (52%). Intermediate-sized acorns of Quercus xalapensis were the most frequently removed (43.33%), followed by Q. lancifolia (40%), Q. sartorii (28%), and Q. germana (26%). Seed removal was null with total exclusion of mammals, and this treatment presented the highest values of germination and emergence (54% and 22.5%, respectively), followed by partial exclusion (25.5% and 7.5%, respectively) and open access to all predators (12% and 3.5%, respectively). Microhabitat had no effect on germination and emergence. The direct seeding technique is useful for enriching degraded forests; however, its cost-efficiency depends on species attributes and predator/disperser preference. When using unprotected seeds, planting in microhabitats with low vegetation cover (<50% of vegetation cover above 30 cm) will reduce the removal and predation of acorns by 13%. To increase the success of direct seeding of oaks in degraded or secondary forests, protection of the seeds is recommended, particularly for the intermediate-sized acorns of Q. lancifolia and Q. xalapensis.