Cover–biomass relationships of an invasive annual grass, Bromus rubens, in the Mojave Desert

Abstract

Estimates of plant biomass are helpful for many applications in invasive plant science and management, but measuring biomass can be time consuming, costly, or impractical if destructive sampling is inappropriate. The objective of this study was to assess feasibility of developing regression equations using a fast, non-destructive measure (cover) to estimate aboveground biomass for red brome (Bromus rubens L.), a widespread non-native annual grass in the Mojave Desert, USA. At three study sites, including one measured for three consecutive years, B. rubens cover spanned 0.1-85% and aboveground biomass 1-321 g m-2. In log10-transformed linear regressions, B. rubens cover accounted for 68-96% of the variance in B. rubens biomass among sites, with all coefficients of determination significant at P < 0.05. For every doubling of percent cover, biomass was predicted to increase by 78, 83, and 144% among the three sites. At the site measured for three consecutive years, which ranged in rainfall from 65-159% of the long-term average, regression slopes each year differed from other years. Regression results among sites were insensitive to using cover classes (10 classes encompassing 0-100% cover) compared with simulated random distribution of integer cover within classes. Biomass of B. rubens was amenable to estimation in the field using cover, and such estimates may have applications for modeling invasive annual plant fuel loads and ecosystem carbon storage. Management Implications By altering biomass structure, invasion of non-native grasses has changed fuels and fire behavior in drylands. Modeling fuels and many other features of non-native plants requires estimates of biomass, which can be time consuming or infeasible to measure directly. As an alternative, this study developed regression equations to estimate biomass from the rapid, non-destructive measure of plant cover for red brome (Bromus rubens L.), a pervasive, non-native annual grass in the Mojave Desert, USA. For every doubling of B. rubens cover, predicted B. rubens biomass increased by 78-144% among sites. In applying the equations to estimate fire-risk thresholds of hazardous fuels using cover, a provisional threshold of 100 g m-2 of B. rubens biomass required for fire spread was exceeded at 19, 25, and 45% B. rubens cover among sites. The equations, and suggested refinements in future work, may be helpful for rapidly estimating fuel loads and assessing effectiveness of invasive plant management, including levels required to keep fuels below wildfire spread risk thresholds. Accompanying the equations, a photographic guide showing cover classes and their associated biomass is provided.

Weed Biology and Ecology Studies: Diversity, Dominance, Population and Weed Growth and Land Use Efficiency in Intercropping Corn (Zea mays l.) with Leguminous Crops in Dryland

“…Monorope treatment and intercropping of peanuts and cowpeas with corn causes a significant increase in the growth of the plants themselves so that their retention is stronger in suppressing the growth and population of weeds. Scott (2020), reported similar results that biomass from cover crops can effectively suppress the growth of the annual weed Gulongan Poaceae. Legume biomass also increases varying soil porosity, due to increased levels of organic matter and increased activity of microorganisms such as phosphorus solubilizing bacteria and Rhizobium (Chieppa et al, 2020).…”

“…According to Kara et al (2020), these four weeds have high competitive power in various types of agricultural land management so they are also called invasive weeds. Scott (2020), also reported that only mulch and legume cover crop (LCC) shading pressure were effective in suppressing the population and growth of these four noxious and invasive weed species. Several gumla species are reported to be tolerant to various post-emergence herbicides (Dylan et al, 2023).…”

“…Bean plants generally have a shrub growth form (habitus) with a dense leaf canopy, are relatively more shade tolerant, require less light and have a shallow root system so the potential for competition with corn plants is low (Chieppa et al, 2020). Beans also have a large number of leaves so they have the potential to capture sunlight that is not captured by the canopy of corn leaves, thereby reducing the evaporation of soil moisture and being able to suppress the growth and population of weeds (Scott, 2020).…”

Impacts of two years of autumn cover crops in northwestern Washington on winter annual weed populations

“…However, in comparing means separation using cover crop biomass to cover crop cover among the various cover crop treatments, there were no changes (Figures 2 and 3). Although there are no studies comparing the correlation of cover crop biomass to cover crop cover on weed suppression, there are studies that indicate cover measurements can be used to estimate biomass (Abella 2020; Axmanova et al 2012; Chieppa et al 2020; Prabhakara et al 2015). These correlations are especially useful with the increase of remote sensing technologies (Prabhakara et al 2015) and the need to reduce the cost of vegetation sampling in remote rangeland areas (Abella 2020).…”

“…Although there are no studies comparing the correlation of cover crop biomass to cover crop cover on weed suppression, there are studies that indicate cover measurements can be used to estimate biomass (Abella 2020;Axmanova et al 2012;Chieppa et al 2020;Prabhakara et al 2015). These correlations are especially useful with the increase of remote sensing technologies (Prabhakara et al 2015) and the need to reduce the cost of vegetation sampling in remote rangeland areas (Abella 2020). Generally, when comparing the biomass of grass species to herbaceous plants, grass species often have more dry weight than herbaceous species if both have the same fresh weight, which may result in a bias in dry weight data indicating that a grass species might not be as suppressive to weeds as a herbaceous plant (Axmanova et al 2012).…”