Woody Plant and Invasive Grass Interactions with Understory Biomass and Soil-Plant Water Dynamics on Three Different Rangelands

• Main Author: Almalki, Yasser Mohammed
• Format: Dissertation
• Language: English
• Published: ProQuest Dissertations & Theses 01-01-2022
• Subjects: Ecology; Hydrologic sciences; Range management; Soil sciences; Wood sciences
• ISBN: 9798374406061

Improving our understanding of vegetation dynamics becomes essential for the proper management of plant communities. Invaded ecosystems and the expansion of unwanted species result in a reduction in ecosystem goods and benefits. Invasive species are currently a significant challenge facing land managers and ranchers. The goal of the research reported within this dissertation was to evaluate the influence of native and introduced invasive species on herbaceous biomass and soil-plant water dynamics on rangelands of the southwestern United States. Our first study was conducted in a semiarid grassland at Elgin, Arizona, we evaluated the influence of Lehman lovegrass (Eragrostis lehamaninana), an introduced warm season invasive grass, on soil moisture dynamics. We measured soil moisture in plots with moderate and high Lehmann lovegrass cover (MLC and HLC, respectively). Average soil moisture at 25 cm depth was greater in MLC vs. HLC plots (11%, and 9%, respectively). Our second study was conducted at a grassland site in Corona, NM with active one seed juniper (Juniperus monosperma) encroachment. We investigated the effects of four one-seed juniper sapling defoliation levels (severe clipping one time (GO) vs. severe clipping twice in consecutive years (GT) vs. herbicide (H) vs. no clipping (C)) on a) soil moisture; b) sapling xylem water potential. We also determined whether the effects of defoliation are contingent on sapling size and stand density. Herbicide treatment increased soil water content and the time during which soil water was available to understory vegetation during monsoon (% 15.3) and dry seasons (% 15.5), while the GT treatment increased soil water content and the time of available water for understory vegetation only during the monsoon season (% 12.1). Saplings in the GT treatment showed lower levels of water stress at midday (-2.3 MPa) relative to C and GO counterparts. Our third study was conducted at pinyon-juniper woodland site close to Santa Fe, NM. We investigated the effects of reducing the number of juniper trees on standing crop and understory cover five and 10 years after treatment at the catchment scale. Reducing one seed juniper trees by thinning promoted a twofold increase in herbaceous understory standing crop. However, tree thinning did not increase herbaceous understory cover. Collectively, our research showed that invasive species at our study sites influenced available soil water thus affecting native plant community dynamics.