Abstract
AbstractForest disturbances are major sources of carbon dioxide to the atmosphere, and therefore impact global climate. Biogeophysical attributes, such as surface albedo (reflectivity), further control the climate‐regulating properties of forests. Using both tower‐based and remotely sensed data sets, we show that natural disturbances from wildfire, beetle outbreaks, and hurricane wind throw can significantly alter surface albedo, and the associated radiative forcing either offsets or enhances the CO2 forcing caused by reducing ecosystem carbon sequestration over multiple years. In the examined cases, the radiative forcing from albedo change is on the same order of magnitude as the CO2 forcing. The net radiative forcing resulting from these two factors leads to a local heating effect in a hurricane‐damaged mangrove forest in the subtropics, and a cooling effect following wildfire and mountain pine beetle attack in boreal forests with winter snow. Although natural forest disturbances currently represent less than half of gross forest cover loss, that area will probably increase in the future under climate change, making it imperative to represent these processes accurately in global climate models.
Highlights
Terrestrial disturbances are primary regulators of the global carbon cycle (Running, 2008), and can switch entire ecosystems from carbon sinks to sources (Luysseart et al, 2008)
Over the 5 years following the hurricane the sum of the two positive forcings results in an average net radiative forcing of 5.3 ± 1.0 W mÀ2 that is still increasing with time (Fig. 5a), where the albedo forcing accounted for 45% of the total forcing
Albedo can decrease after a disturbance, as demonstrated by our hurricane-defoliated mangrove case
Summary
Terrestrial disturbances are primary regulators of the global carbon cycle (Running, 2008), and can switch entire ecosystems from carbon sinks to sources (Luysseart et al, 2008). Increasing evidence suggests major natural forest disturbances are increasing in frequency and/or intensity under climate change, including fire (Westerling et al, 2006), insect outbreaks (Raffa et al, 2008), and landfalling hurricanes (Bender et al, 2010). 2–4 million ha of forest annually in the United States alone (Forest Service USDA, 2008; Schwind, 2008; Zeng et al, 2009). In British Columbia (BC), the extent of forest mortality caused by mountain pine beetle (MPB) has reached unprecedented levels. In 2007, the affected area surpassed 10 million ha (Westfall & Ebata, 2009). A warming and drying in the region associated with climate change has allowed the beetle to expand its range to these exceptional limits
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