FINE-ROOT DYNAMICS FOLLOWING SINGLE AND MULTIPLE DISTURBANCES IN A SUBTROPICAL WET FOREST ECOSYSTEM

1 Live and dead fine root biomass and rates of root decomposition were studied prior to and immediately following a localized disturbance (experimental gap creation) and a landscape-level disturbance (Hurricane Hugo) in a lower montane subtropical wet forest in Puerto Rico. The effects of the hurricane on the previously disturbed environment ( experimental gaps) were also examined to determine the effects of a multiple disturbance regime. 2 A 40% decline in fine live roots occurred two months following gap creation. Six months following the hurricane, high fine root mortality resulted in a decline of 70-77% of the initial fine live root biomass in the experimental gaps; a similar decline occurred in the control forest. Root decay was slow and 48-65% of the fine root necromass still remained in trench plots after one year. 3 Concentrations of Ca, Mg, K, P and N in fine roots (live plus dead) changed little over the course of one year. The loss of nutrients in live fine roots (kg ha-1) was equivalent to the loss of biomass. 4 In the trench plot experiment, high root mortality resulted in lower concentrations of exchangeable cations in the soil, and a lower pH when compared to soil outside the trench plots. Concentrations of NO3-N were higher in the trench plot soils than in the surrounding soil environment and may have contributed to cation losses. 5 Fine roots in this forest were not greatly diminished following localized disturbances and contributed to nutrient conservation. These root systems were more adversely affected by a landscape-level disturbance and by a multiple disturbance regime. High root mortality following these disturbances may result in significant declines in nutrient availability.