Hydrologic/water quality models are increasingly used to explore management and policy alternatives for managing water quality and quantity from intensive silvicultural practices with best management practices (BMPs) in forested watersheds due to the limited number of and cost of conducting watershed monitoring. The Agricultural Policy/Environmental eXtender (APEX) model was field-tested using 6 yr of data for flow, sediment, nutrient, and herbicide losses collected from nine small (2.58 to 2.74 ha) forested watersheds located in southwest Cherokee County in East Texas. Simulated annual average stream flow for each of the nine watersheds was within +/- 7% of the corresponding observed values; simulated annual average sediment losses were within +/- 8% of measured values for eight out of nine watersheds. Nash-Sutcliffe efficiency (EF) values ranged from 0.68 to 0.94 based on annual stream flow comparison and from 0.60 to 0.99 based on annual sediment comparison. Similar to what was observed, simulated flow, sediment, organic N, and P were significantly increased on clear-cut watersheds compared with the control watersheds. APEX reasonably simulated herbicide losses, with an EF of 0.73 and R(2) of 0.74 for imazapyr, and EF of 0.65 and R(2) of 0.68 for hexazinone based on annual values. Overall, the results show that APEX was able to predict the effects of silvicultural practices with BMPs on water quantity and quality and that the model is a useful tool for simulating a variety of responses to forest conditions.

Ice storm is a major form of extreme climatic event and may occur more frequently in the future under a changing climate. The 2008 Chinese ice storm provided a natural laboratory to study ecosystem responses and feedbacks to climate variability and extreme events. Four typical subtropical forests (Chinese fir plantation, pine plantation, moso bamboo plantation, and secondary mixed broadleaved forest) were selected to assess the damage caused by the ice storm. The ice damage rate of typical subtropical forests varied between 25% and 81%. The secondary broadleaved forest had most extensive damage while the Chinese fir plantation experienced the most severe damage. Exotic pine species (Pinus elliottii Engelm. and Pinus taeda Linn.) were more severely damaged than the native species, Pinus massoniana Lamb. Ice damage was also affected by tree/culm size, age, stand density, site altitude, and management practices. Large-sized trees/culms were more vulnerable to stem breakage, decapitation, and uprooting, while small-sized trees/culms were more vulnerable to bending and leaning. Younger trees/culms had the highest damage rate, and were more susceptible to bending damage. Ice damage rate increased linearly with the stand density, and higher altitude led to a significant increase of stem breakage. Oleoresin tapping aggravated the damage to pine trees. Resistance of trees to ice damage is an emergent consequence of tree attributes, species origin, site conditions, and human disturbance. Forest silviculture and management practices can play significant roles in controlling forest susceptibility to extreme events. Inappropriate utilization of non-timber forest products can reduce trees' resistance to extreme events. For sustainable forest development, balance needs to be achieved between the high productivity of introduced exotic tree species and the resistance of native species to extreme climatic events.