Grassland to shrubland state transitions enhance carbon sequestration in the northern Chihuahuan Desert

Abstract

The replacement of native C4 -dominated grassland by C3 -dominated shrubland is considered an ecological state transition where different ecological communities can exist under similar environmental conditions. These state transitions are occurring globally, and may be exacerbated by climate change. One consequence of the global increase in woody vegetation may be enhanced ecosystem carbon sequestration, although the responses of arid and semiarid ecosystems may be highly variable. During a drier than average period from 2007 to 2011 in the northern Chihuahuan Desert, we found established shrubland to sequester 49 g C m(-2) yr(-1) on average, while nearby native C4 grassland was a net source of 31 g C m(-2) yr(-1) over this same period. Differences in C exchange between these ecosystems were pronounced--grassland had similar productivity compared to shrubland but experienced higher C efflux via ecosystem respiration, while shrubland was a consistent C sink because of a longer growing season and lower ecosystem respiration. At daily timescales, rates of carbon exchange were more sensitive to soil moisture variation in grassland than shrubland, such that grassland had a net uptake of C when wet but lost C when dry. Thus, even under unfavorable, drier than average climate conditions, the state transition from grassland to shrubland resulted in a substantial increase in terrestrial C sequestration. These results illustrate the inherent tradeoffs in quantifying ecosystem services that result from ecological state transitions, such as shrub encroachment. In this case, the deleterious changes to ecosystem services often linked to grassland to shrubland state transitions may at least be partially offset by increased ecosystem carbon sequestration.

Enhanced gross primary production and evapotranspiration in juniper‐encroached grasslands

“…Over the past century, woody plants have been observed worldwide to be increasing in abundance and density in grasslands and savannas, a process termed "woody plant encroachment" (WPE; Archer, Vavra, Laycock, & Pieper, 1994;Archer, 2010;Scott, Jenerette, Potts, & Huxman, 2009). Ecological succession of grasslands to woodlands may alter ecosystem structure and function and can threaten ecosystem services (Msanne et al, 2017;Petrie, Collins, Swann, Ford, & Litvak, 2015). For example, an increase of woody plants in grasslands has been reported to alter animal habitats (Coppedge, Engle, Masters, & Gregory, 2004) and reduce biological diversity (Ratajczak, Nippert, & Collins, 2012;Van Els, Will, Palmer, & Hickman, 2010), forage, and livestock production (Anadon, Sala, Turner, & Bennett, 2014).…”

Simulated climate effects of desert irrigation geoengineering

“…We may validate our simulations by comparison with some previous published work on the regional climatic impacts of irrigation13141516; and with irrigation impacts on carbon storage62425. The models we use have also been thoroughly validated against observations (see Methods), and via model intercomparisons of future greenhouse and geoengineered climates262728.…”

“…2a,b,g,h), which are both consistent with net uptake of carbon ranging from 0.033 to 0.127 kg C m −2 yr −1 in field experiments in the Tengger Desert by Yang et al 6,. northern Chihuahuan Desert by Petrie et al 24. and Mojave Desert by Jasoni et al 25…”

Fire Severity and Regeneration Strategy Influence Shrub Patch Size and Structure Following Disturbance

“…Considerable literature on shrub dynamics in the NAM region has focused on shrub encroachment into grasslands (e.g., [27][28][29][30]), and on impacts of shrub evapotranspiration on desert hydrology (e.g., [31,32]). Less research has focused on the dynamics of shrub species in montane forest ecosystems, particularly as those shrub species are affected by wildfire disturbance.…”