Response of forest tree samplings to experimental mechanical damage in lowland Panama

Physical damage to saplings is considered an important factor that affects tree population dynamics in tropical forests, but interspecific differences in post-damage vegetative recovery and survival have been rarely quantified. Over 4 years, the vegetative and demographic responses to experimental mechanical damage were monitored in naturally-growing saplings of four coexisting tree species, under comparable overhead illumination conditions, in a lowland moist forest in Central Panama. Inflicted damage mimicked both crown loss and stem breaage ('snapped') and stem pinning by fallen debris ('bent') in individuals (1.0-2.5 m tall) of Alseis blackiana (Rubiaceae), Protium panamense, P. tenuifolium, and Tetragastris panamensis (all Burseraceae). For all species combined, 4-year percent mortality was significantly different between bent (21%), snapped (13%), and undamaged controls (6%). Species differed in their capacity to survive damage. Saplings of A. blackiana showed the highest resilience, expressed as a high ability to regain pre-damage height in snapped individuals, production of adventitious roots in bent individuals, and very high survival. A previous classification of the study species fit them into a large 'generalist' guild, after no illumination preferences were obvious for their juvenile growth and survival at the study site. In contracts, this study suggests that tree vegetative behavior should be incorporated in future tropical forest research that attempts to detect species differentiation in regeneration potential at the saplings phase