Influence of concurrence of extreme drought and heat events on carbon and energy fluxes in dominant ecosystems in the Pacific Northwest region

Abstract

Abstract. The impacts of drought intensity and vapor pressure deficit (VPD) beyond historic norms in PacificNorthwest (PNW), USA, are critical in understanding the potential future function and resilience of ecosystems in the region. While ecosystems in this region are adapted to seasonal droughts, June 2015 temperatures were the highest 10 recorded in the region and strongly coupled with relatively low soil moisture. June is usually the best month for growth in the PNW. Here, we examined the impact of the June 2015 climate extremes on carbon and energy fluxes at sagebrush in the high desert, young and mature ponderosa pine in the semi-arid Great Basin, and Douglas-fir in the mesic ecoregion compared to an average climate year (2014). We assessed if the ecosystems recover from extreme climate stress within the growing season. The monthly anomalies in temperature and VPD were 3 standard deviations, 15 and precipitation was 1standard deviationoutside the 30-year mean at all sites. In sagebrush, the carry-over effect of precipitation (i.e., intensive precipitation prior to the drought and heat) mitigated the immediate impact of extreme climate stress, leading to 25-40% increase in net ecosystem production (NEP) and gross primary production (GPP), with little change in ecosystem respiration (RE) and 65% increase in latent heat flux, compared to the June 2014. The drought and heat lowered NEP by 35-65% and GPP by 15-33% in ponderosa pine and Douglas-fir. A greater increase 20 in latent heat flux was observed in Douglas-fir (110%) than in ponderosa pine (<10%) driven by increased evaporation. were corresponding with 30-40% decline and were greater than in mature ponderosa pine (5-20% decline), when compared to the long-term seasonal means (2002)(2003)(2004)(2005)(2006)(2007)(2008)(2009)(2010)(2011)(2012)(2013)(2014)(2015), respectively. Our results suggest that the responses of carbon and energy fluxes to climate extremes differ depending on site-and species-specific characteristics. Douglas-fir is likely to experience more constraints on carbon fluxes than ponderosa pine if the hot and dry season intensifies in the PNW. Given the likelihood of future drought and heat extremes, identifying these anomalous ecological responses to 30 anomalous climate (e.g., the combination of VPD, heat, and dry soil) is critical to improve predictions of physiological thresholds and tolerance of different tree species.Biogeosciences Discuss., https://doi

Analysis on water use efficiency of Populus euphratica forest ecosystem in arid area

“…Except for the wetland ecosystem, WUE of crop land was the lowest, which might be affected by the unproductive stage, and the soil evaporation was higher than that of permanent vegetation. Tang et al [2014], Tan et al [2014], Kwon et al [2018], Quansah et al [2015], Gang et al [2016], Chatterjee et al…”