Tree mortality and biomass loss in drought-aff ected forests of East Texas,USA

Changes in tree mortality due to severe drought can alter forest structure,composition,dynamics,ecosystem services,carbon fl uxes,and energy interactions between the atmosphere and land surfaces.We utilized long-term(2000‒2017,3 full inventory cycles)Forest Inventory and Analysis(FIA)data to examine tree mortality and biomass loss in drought-aff ected forests for East Texas,USA.Plots that experienced six or more years of droughts during those censuses were selected based on 12-month moderate drought severity[Standardized Precipitation Evaporation Index(SPEI)-1.0].Plots that experienced other disturbances and inconsistent records were excluded from the analysis.In total,222 plots were retained from nearly 4000 plots.Generalized nonlinear mixed models(GNMMs)were used to examine the changes in tree mortality and recruitment rates for selected plots.The results showed that tree mortality rates and biomass loss to mortality increased overall,and across tree sizes,dominant genera,height classes,and ecoregions.An average mortality rate of 5.89%year−1 during the study period could be incited by water stress created by the regional prolonged and episodic drought events.The overall plot and species-group level recruitment rates decreased during the study period.Forest mortality showed mixed results regarding basal area and forest density using all plots together and when analyzed the plots by stand origin and ecoregion.Higher mortality rates of smaller trees were detected and were likely compounded by densitydependent factors.Comparative analysis of drought-induced tree mortality using hydro-meteorological data along with drought severity and length gradient is suggested to better understand the eff ects of drought on tree mortality and biomass loss around and beyond East Texas in the southeastern United States.

Evaluating soil erosion and runoff dynamics in a humid subtropic, low stream order, southern plains watershed from cultivation and solar farm development

Much work has been done to understand and improve soil and water conservation where agriculture has driven land use intensification.Less is known about soil-and water-related impacts from intensification driven by solar farming,especially at watershed-scales.Here we employed Hydrologic Engineering Center's Hydrologic Modeling System(HEC-HMS)to model Pond Creek,a rural watershed in Texas,USA.Land use is primarily crop cultivation and secondarily pasture for cattle grazing.Presently,several industrial-scale projects are planned to convert≈15–30%of Pond Creek from agriculture to solar farms.The model was parameterized using public data sources and information from local stakeholders,then calibrated to several historical precipitation events.Experiments were conducted by varying precipitation depth,duration,and land uses:native vegetation pre-cultivation(control),cultivation(current),current conditions with 15%solar farm conversion(solar),and current conditions with 30%solar farm conversion(solar x2).Shifting to solar farming led to significant increases in cumulative sediment load(+12%–30%),with no significant differences in peak discharge rate changes(+0.38%–4%).Comparison to soil loss tolerance values showed current and solar treatment erosion rates exceeded tolerance values between 0.17 and 2.29 tons per hectare and all treatments were significantly different than the native treatment.We discuss high leverage strategies applicable to solar farm development sites as well as watersheds where they reside.Accelerating demand for land for renewable energy such as solar farming warrants greater attention from the soil and water conservation community to anticipate and mitigate impacts across landscapes.