Key Points • The Luquillo Mountains are affected by a wide array of environmental processes and disturbances. Events that concurrently alter the environmental space of several different areas of the Luquillo Mountains occur every 2 to 5 years. Events such as hurricanes that cause widespread environmental modification occur once every 20 to 60 years. • The most common disturbance-generating weather systems that affect the Luquillo Mountains are (1) cyclonic systems, (2) noncyclonic intertropical systems, (3) extratropical frontal systems, and (4) large-scale coupled ocean- atmospheric events (e.g., North Atlantic Oscillation, El Niño-Southern Oscilla- tion). Unlike some tropical forests, disturbances associated with the passage of the Inter-Tropical Convergence Zone or monsoonal rains do not occur. • Hurricanes are considered the most important natural disturbance affecting the structure of forests in the Luquillo Mountains. Compared to other humid tropical forests, Luquillo has a high rate of canopy turnover caused by hurricanes but a relatively low rate caused by tree-fall gaps. Historically, pathogenic disturbances have not been uncommon. • Human-induced disturbances have historically included tree harvesting for timber and charcoal, agriculture, and agroforestry. In the past few decades, water diversions, fishing and hunting, and road building have been important disturbances. Present and future human-induced disturbances are related to regional land use change, the disruption of migratory corridors, and forest drying related to coastal plain deforestation and regional climate change. • Hurricane-related storm discharges can cause significant geomorphic modifications to Luquillo stream channels, and stream water concentrations of sediments and nutrients can be elevated for months to years following a major hurricane. However, the largest floods are not necessarily associated with hurricanes, and the annual peak discharge can occur in any month of the year but is most common in the late summer and fall. • Over the entire island of Puerto Rico, 1.2 landslide-producing storms occur each year. In the Luquillo Mountains, landslides are typically covered with herbaceous vegetation within 2 years, have closed canopies of woody vegetation in less than 20 years, and have aboveground biomass of the adjacent forest after several decades.