Redistribution of forest carbon caused by patch blowdowns in subalpine forests of the Southern Rocky Mountains, USA

Abstract

Patch blowdowns varying in size from 0.1 to 33 ha affected several areas in Rocky Mountain National Park, Colorado, USA, during the winter of 2011–2012. These blowdowns resulted in substantial redistribution of forest carbon by snapping and uprooting trees, thereby increasing instream wood recruitment, recruitment of dead wood to the forest floor, and exposure of organic soil on uprooted tree plates. Estimates of carbon redistribution at five sites in Rocky Mountain National Park range as high as 308 Mg C/ha in high‐severity patches to 106 Mg C/ha in low‐severity patches, of which typically 10–30% is soil C and the remainder is downed wood. Masses of carbon redistributed from living to dead biomass at high‐severity sites represent a substantial portion of average total biomass in old‐growth subalpine forests in the region. Consequently, the potential for increasing frequency and/or severity of blowdowns under a warming climate represents a significant potential source of terrestrial carbon to the atmosphere. The majority of this carbon is in the form of downed wood that becomes a carbon source to the atmosphere, although interactions between downed wood and river processes can locally increase carbon storage in floodplain soil. Predictions of changes in precipitation and wind patterns, and associated changes in wildfire and insect infestation, suggest that blowdowns may become more common in future in the Southern Rockies, but the consequences for carbon dynamics depend on site‐specific interactions between blowdowns and other processes such as floodplain storage of organic matter.

Sources and interpretation of channel complexity in forested subalpine streams of the Southern Rocky Mountains

“…Ongoing changes to forest ecosystems associated with warming climate have the potential to alter the magnitude of geomorphic complexity of subalpine forest streams by changing the recruitment of wood to channels via wildfire, insect infestations, and blowdowns [ Wohl , ; Dennison et al ., ], as well as the ability of streams to transport wood via changes in flow and sediment regimes [ Goode et al ., ]. Consequently, it is particularly important to document existing levels of geomorphic complexity and relations between complexity and potential driver variables.…”

Stand dynamics and topographic setting influence changes in live tree biomass over a 34-year permanent plot record in a subalpine forest in the Colorado Front Range

“…Annual examinations of all the plots revealed only two noteworthy disturbance events since the date of plot installation. Some of the tallest trees in stand MRS4 were windthrown by a series of winter storms in 2011-12 which caused widespread treefalls in the northern Front Range (Wohl 2013). SFD caused sharp increases in the numbers of dead subalpine fir in stand BL6, with minor effects in other stands.…”

“…The current trajectory towards warmer, drier conditions (a climatic "press") is affecting tree mortality and recruitment dynamics in the subalpine forests of the Southern Rocky Mountains Ecoregion (Smith et al 2015, Conlisk et al 2017, Andrus et al 2018). Likewise, relatively discrete extreme climatic events ("pulses") such as windstorms (Veblen et al 1991, Wohl 2013), droughts (Bigler et al 2007), wildfires (Schoennagel et al 2007, and climatically-induced outbreaks of bark beetles (Chapman et al 2012, Hart et al 2014 are well-documented sources of pulsed increases in tree mortality in subalpine forests throughout the Southern Rocky Mountains Ecoregion. Substantial empirical evidence as well as modelingbased studies indicate that climatic presses and pulses are likely to significantly affect future biomass patterns of subalpine forests in the Southern Rocky Mountains Ecoregion (Temperli et al 2015, Conlisk et al 2017, Foster et al 2018.…”

Fire effects on soils: the human dimension

“…Finally, particularly where fires cause high tree mortality (stand-replacing fires), the accelerated uprooting of trees brings regolith or deep soil to the surface and exposes it to accelerated weathering. For example, following winter storms in a subalpine forest in the southern Rocky Mountains, local soil distribution of 450-600 Mg ha 21 has been reported within patches of uprooted trees [68]. Thus, while the soil degradational impacts of fire are often those that are at the forefront of the debate, it is also clear that fire can increase soil fertility, organic carbon content, weathering and, ultimately, soil formation, particularly in areas where limited topography or rapid vegetation cover limit post-fire erosion.…”