Effects of fine-scale disturbances on the demography and population dynamics of the clonal moss Hylocomium splendens

1 The boreal forest is subject to disturbance but the effects on population dynamics are poorly understood. We investigated how a prominent species of the forest floor, the clonal moss Hylocomium splendens, responded to diffe rent types of fine-scale disturbance. 2 Canopy gap formation was simulated in H. splendens populations by removin g 50% of the bryophyte layer (Removal treatment) and herbivory by clipping all of its growing points (Clipped treatment). Demographic parameters and p opulation dynamics were compared with an unmanipulated reference population (Ref). 3 Both types of disturbance caused a significant decrease in mean segment s ize (particularly following clipping) and an increase in branching rates. B ranching rates in the Removal population were enhanced at all architectural opportunities for enhanced branching, but only the Clipped segments themse lves were affected during the 2 years following disturbance. 4 The population effects of disturbance were analysed by a periodic matrix model, with 3-year as the period, followed by elasticity analysis. The Ref population was approximately stable (growth rate, lambda = 1.012), with the survival of mature segments making an overwhelming contribution to its gro wth rate. The higher lambda (1.740) in the Removal population was associate d with higher elasticities of branching. Clipping reduced lambda to 0.841 b y blocking segment survival, although regeneration of new growing points on the remnant main shoot axis after 1 year, and its subsequent maturation in the next year, then made a major contribution. 5 Life table response experiment analyses revealed that almost all demograp hic processes including branching and the survival of mature segments contr ibuted to the increased lambda in Removal treatment. The relatively small d ecrease in lambda following clipping was mainly due to the absence of matur e segment survival, being almost balanced by the pulse of regeneration of g rowing points the year after disturbance. 6 We conclude that H. splendens populations show a good ability to recover from common types of disturbances in their environment. The general mechani sms behind the responses are discussed.