Enhanced gross primary production and evapotranspiration in juniper‐encroached grasslands

Abstract

Woody plant encroachment (WPE) into grasslands has been occurring globally and may be accelerated by climate change in the future. This land cover change is expected to alter the carbon and water cycles, but it remains uncertain how and to what extent the carbon and water cycles may change with WPE into grasslands under current climate. In this study, we examined the difference of vegetation indices (VIs), evapotranspiration (ET), gross primary production (GPP), and solar-induced chlorophyll fluorescence (SIF) during 2000-2010 between grasslands and juniper-encroached grasslands. We also quantitatively assessed the changes of GPP and ET for grasslands with different proportions of juniper encroachment (JWPE). Our results suggested that JWPE increased the GPP, ET, greenness-related VIs, and SIF of grasslands. Mean annual GPP and ET were, respectively, ~55% and ~45% higher when grasslands were completely converted into juniper forests under contemporary climate during 2000-2010. The enhancement of annual GPP and ET for grasslands with JWPE varied over years ranging from about +20% GPP (~+30% for ET) in the wettest year (2007) to about twice as much GPP (~+55% for ET) in the severe drought year (2006) relative to grasslands without encroachment. Additionally, the differences in GPP and ET showed significant seasonal dynamics. During the peak growing season (May-August), GPP and ET for grasslands with JWPE were ~30% and ~40% higher on average. This analysis provided insights into how and to what degree carbon and water cycles were impacted by JWPE, which is vital to understanding how JWPE and ecological succession will affect the regional and global carbon and water budgets in the future.

Remote sensing of solar-induced chlorophyll fluorescence (SIF) in vegetation: 50 years of progress

“…Several satellite-based trials have reported the potential of far-red SIF to indicate drought and temperature stress at ecosystem scales (Berkelhammer et al, 2017;Koren et al, 2018;Song et al, 2018;Sun et al, 2015;Wang et al, 2018Wang et al, , 2016Wu et al, 2018;Yoshida et al, 2015;Zuromski et al, 2018). Others have used far-red SIF to monitor the dynamics of photosynthesis in the Amazon forest (e.g., Alden et al, 2016;Guan et al, 2015;Köhler et al, 2018b;Koren et al, 2018;Lee et al, 2013;Parazoo et al, 2013;Yang et al, 2018a), high-latitude forests (Jeong et al, 2017;Walther et al, 2016), tundra ecosystems (Luus et al, 2017;Walther et al, 2018), dryland ecosystems of southwestern North America (Smith et al, 2018;Zhang et al, 2016c), and across Australia (Ma et al, 2016;Sanders et al, 2016).…”

The effects of woody plant encroachment and wildfire on plant species richness and composition: Temporal changes in a forest–steppe mosaic

“…Increasing fire frequencies are expected during the 21st century at mid to high latitudes, depending on the productivity in grassland and savanna communities (Moritz et al, 2012; Fusco et al, 2019). Juniper encroachment changes the carbon cycle and increases productivity in US grasslands (Wang et al, 2018), and thus it moves the grassland into a more fire‐prone state. When these ecosystems are dominated by fire‐sensitive species such as the non‐resprouters Ashe or common junipers ( Juniperus ashei , Juniperus communis ) (Fuhlendorf et al, 1997; Marozas et al, 2007), wildfire may cause marked changes in plant species composition due to complete dieback of formerly abundant woody species and an immediate decrease of shaded microhabitats (Ónodi et al, 2014; Kertész et al, 2017).…”

Impact of Eastern Redcedar Proliferation on Water Resources in the Great Plains USA—Current State of Knowledge

“…Counties with redcedar documented in the Great Plains and studies conducted in the Great Plains that document changes in the hydrology of the system as a result of redcedar encroachment. The majority of hydrological studies have employed experimental manipulations in locations where grasslands have undergone regime shifts to juniper woodland (e.g., Oklahoma) [23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38]. Fewer studies have employed simulations or scenario analyses to assess the relative vulnerability of regions where grasslands are still intact, but at the early stages of redcedar encroachment (e.g., states in the Northern Great Plains), to delineate potential impacts to water resources with future spread and grassland conversion [39][40][41][42][43][44][45].…”

“…Direct comparison of stand-level transpiration between grassland and redcedar is usually unavailable. For grassland, transpiration was mostly measured together with evaporation as evapotranspiration based on energy balance, remote sensing, or eddy flux techniques [28]. Partitioning evapotranspiration into transpiration and evaporation remains a formidable challenge in the tallgrass prairie [49].…”