Seeding Causes Long-Term Increases in Grass Forage Production in Invaded Rangelands

Matthew J Rinella,Alan D Knudsen,James S Jacobs,Jane M Mangold

doi:10.1016/j.rama.2019.10.008

Abstract

Seeding is sometimes used in attempts to increase grass forage production in invaded rangelands, but insufficient long-term data prevent determining if seeded grasses are likely to become and remain productive enough to justify this expensive practice. We quantified long-term seeding outcomes in a widespread Rocky Mountain foothill habitat invaded by leafy spurge (Euphorbia esula L.) and several exotic grasses. Fourteen yr after seeding, the most productive grass (bluebunch wheatgrass [Pseudoroegneria spicata (Pursh) Á. Löve]) produced 900 (100, 12 000) kg ha−1 [mean (95% CI)], which was about 70% of total plant community biomass. This result was not greatly altered by grazing according to an unreplicated, grazed experiment adjacent to our replicated ungrazed experiment. Regardless of treatment, E. esula gradually became less productive and seeded and unseeded plots produced similar E. esula biomass 14 yr after seeding. P. spicata reduced exotic grasses about 85%. Our results resemble those of another foothills study of another invasive forb (Centaurea stoebe L. ssp. micranthos [Gugler] Hayek) and a Great Plains study of E. esula, so foothills seeding outcomes seem somewhat insensitive to invader composition, and seeding can increase forage across much of E. esula’s range. While there is always some risk seeded grasses will fail to establish, our study combined with past studies identifies invaded habitats where seeded grasses have a good possibility of forming persistent, productive stands.

Highlights

Invasive plants with poor forage characteristics have replaced forage grasses on millions of hectares of western US rangelands (Duncan et al 2004)
Examples include leafy spurge (Euphorbia esula L.), an invasive forb not typically heavily consumed by cattle, elk, and deer (Trammell and Butler 1995), and downy brome (Bromus tectorum L.), an invasive annual grass lacking palatability and protein content beyond early growth stages (Cook and Harris 1952)
In areas infested with sulfur cinquefoil (Potentilla recta L.), seeded grass cover jumped from 8% to 50% between 3 and 6 yr after seeding (Endress et al 2007; Endress et al 2012), and in areas invaded by spotted knapweed (Centaurea stoebe L. ssp. micranthos [Gugler] Hayek), seeded grasses went from sparse to dominant between 2 and 15 yr after seeding (Rinella et al 2012)

Summary

Introduction

Invasive plants with poor forage characteristics have replaced forage grasses on millions of hectares of western US rangelands (Duncan et al 2004). Long-term research indicates seeding can return forage production to foothills invaded by the short-lived, tap-rooted perennial forb spotted knapweed Micranthos [Gugler] Hayek) (Rinella et al 2012), and if this is true for the long-lived, rhizomatous weed of this study (E. esula), it will suggest seeding outcomes are somewhat consistent across invader species. Grasses were sown with and without herbicide, and based on Rinella et al (2012), we hypothesized seeded biomass would remain greater where herbicide was applied 14 yr earlier

Methods

Study Design

Results

Discussion