Maximization of Aboveground Grassland Production: The Role of Defoliation Frequency, Intensity, and History

Abstract

Production of tallgrass prairie vegetation was measured on experimental plots in which defoliation intensity and frequency were manipulated by mowing and using movable exclosures on areas chronically grazed by cattle. Defoliation history largely controlled whether or not defoliated plants overcompensated (exhibited enhanced production compared to undefoliated controls) for tissue removal. Plants on chronically grazed sites only compensated for foliage removed by grazers. Production on plots mowed prior to the year of measurement was similar to that on chronically grazed sites, while previously unmowed plots exhibited substantial aboveground overcompensation. Aboveground production was maximized by the most frequent mowing treatment and by intermediate mowing heights. Nitrogen and phosphorus concentrations and amounts in aboveground tissues were increased by mowing and grazing. Current mowing regime was more important than mowing history in determining nitrogen concentrations except very early in the growing season. Effects of grazing and mowing on belowground biomass were inconsistent, but frequent mowing appeared to limit accumulation of belowground N reserves and biomass. In North American grasslands, overcompensation is a nonequilibrium plant response to grazing. Photosynthate that would be stored as reserves and used for root growth and flower and seed production instead is used to replace lost leaf area, thereby resulting in higher foliage productivity. However, under chronic grazing or mowing, vegetation is prevented from maintaining high nutrient and water uptake capacity (large root biomass) and accumulating reserves that allow overcompensation responses.

Effects of mowing regimes and climate variability on hay production of Leymus chinensis (Trin.) Tzvelev grassland in northern China

“…3a), and it also increases the operation cost of haymaking. This result is different from that obtained in temperate grasslands under more humid environments, where more herbage production is normally expected under multiple than single harvests in each year (Turner et al 1993). The result in the present experiment probably means that the rate of growth of the herbage after mowing in mid June is similar to that of the plots that had not been harvested at this time.…”

Effects of Root-trimming and Cutting-heights on Growth Performance of Potted Native Warm-season Grasses

“…In fact, immediately following defoliation, grasses usually experience a stoppage in root growth that reflects the percentage of foliage removed and continues until recovery of the top growth is advanced (Crider, 1955). For example, in most C 3 and C 4 grasses, root growth ceases immediately following a ≥ 50% leaf area removal (Richards, 1993;Turner et al, 1993). For shorter cutting-heights and/or harvest frequencies, therefore, reduction in respective root and crown biomass is expected, an observation also made in the current study.…”

“…For shorter cutting-heights and/or harvest frequencies, therefore, reduction in respective root and crown biomass is expected, an observation also made in the current study. This is so because of preferential resource allocation to aboveground growth at the expense of roots, a scenario usually exhibited by plants recovering from defoliation (Richards, 1984;Turner et al, 1993;Turner et al, 2007).…”

More than a century of Grain for Green Program is expected to restore soil carbon stock on alpine grassland revealed by field 13 C pulse labeling

“…Other studies have reported that moderate grazing could cause an increase in ANPP by overcompensation (Turner et al, 1993;Zou et al, 2014), and the photoassimilate partitioned to the root and soil (Hafner et al, 2012;Zou et al, 2014). In the future, when implementing and managing GfGP grassland, factors that could improve ANPP and belowground C allocation, including the selection of suitable grass with higher ANPP and belowground C allocation (Zhao et al, 2015), and the reasonable intensity of grazing, should be considered.…”