The Soil and Water Assessment Tool (SWAT) was used to quantify the potential impacts of clearcutting on hydrologic and water quality components, and assess potential forest biomass production and perform sensitivity analysis of crop parameters to predict forest biomass in the Upper Pearl River Watershed. Results based on clearcutting indicated that the hydrologic and water quality components increases with increase in percentage of forest area harvested. The most significant effect was observed from 55% and 75% harvesting scenarios. The results based on SWAT’s performance to simulate potential forest biomass production showed satisfactory performance and revealed that the watershed has the potential to produce approximately 49 tons/ha of annual forest biomass. The results also revealed that predicted forest biomass was sensitive to three out of the seven crop parameters: Fraction of maximum leaf area index, corresponding to 1stpoint on the optimal leaf area development curve, Radiation use efficiency and maximum LAI.