Impact of increasing shade levels on the dry‐matter yield and botanical composition of multispecies forage stands

Abstract

Botanical diversity has been linked to increased biomass production of grasslands, but these relationships have not been explored as extensively in silvopasture systems where shade impacts on forage mass are variable due to the unique structure and environment of each system. The objective of this study was to evaluate the impact of multiple artificial shade levels on the DM yield and botanical composition of three cool‐season forage mixtures near Blackstone, Virginia, USA. Mixtures were as follows: simple = tall fescue [Schedonorus arundinaceus (Schreb.) Dumort., nom. cons.] and white clover (Trifulium repens L.); intermediate = simple + orchardgrass (Dactylis glomerate L.) and red clover (Trifolium pretense L.); and complex = intermediate + Kentucky bluegrass (Poa pratensis L.), birdsfoot trefoil (Lotus corniculatus L.) and alfalfa (Medicago sativa L.). Slatted structures created conditions of 30%, 50% and 70% shade relative to a full sun control. Forages were harvested mechanically (no grazers present). Annual yield (DM kg/ha) did not differ among mixtures. As compared to full sun, annual yield was no different at 30% shade, but was reduced by 22 and 36% at 50 and 70% shade respectively. In contrast to other species in the mixtures, orchardgrass increased in proportion when grown beneath all shade levels and is recommended for silvopasture use. Orchardgrass is not particularly well‐adapted to the transition zone between the northern temperate and southern subtropical United States; therefore, these results indicate that silvopastures may be an effective way to integrate marginally adapted, shade‐tolerant cool‐season forages into transition zone grazing systems.

Contrasting yield responses at varying levels of shade suggest different suitability of crops for dual land-use systems. A meta-analysis.

“…Also forages show adaptation mechanisms to RSR, which resulted in no effect on dry matter yield at 30% RSR (Mercier et al 2020) and 45% RSR or, depending on the crop species, even a slight increase of dry matter yield at 45% RSR . showed that alfalfa, a forage legume, can maintain an adequate photosynthetic activity even under dense shading conditions, suggesting that the light saturation point is reached, which is in general ranging between 25-60% of maximum sunlight for C3 plants ).…”

Hair Cortisol as a Measure of Chronic Stress in Ewes Grazing Either Hardwood Silvopastures or Open Pastures

“…This corresponded with reduced levels of PAR in that system but may also reflect changes in forage species that have been observed under BSP at this site [5,15,16,35]. Changes in forage biomass in response to increasing shade levels are not linear [36] but yield generally declines substantially when PAR is reduced to less than 50% of full sun. Similar yield reductions have been observed in pine-walnut silvopastures in Missouri when compared with OP systems [23].…”

“…The experimental systems (OP, BSP, and HSP) were replicated three times and arranged in a randomized complete block design. Thirty-six (36) open Katahdin ewes from Virginia Tech's Southwest Virginia Agricultural Research and Extension Center, Glade Spring, VA were used for the study each year. In 2020, ewes used for the study were 3 to 6 years old with a mean initial body weight of 53 kg ± 0.9 kg.…”

Persistence of winter forage grasses in Silvopastoral Systems: dynamics of appearance and mortality of tillers under Eucalyptus sp. trees and full sunlight

“…Despite exhibiting higher TS in full sunlight, FA showed lower TS and reduced tiller appearance during summer when cultivated under tree canopies, when compared to DG. As a shade-tolerant specie, DG exhibits the adaptive capacity to modulate its photosynthetic processes, ensuring optimal functionality under low-light conditions (Mercier et al 2020). This inherent trait underscores the species' pro ciency for sustained survival over an extended period within the canopy's shaded environment.…”

“…Some C3 species, which can tolerate moderate shade, maintain their productivity as they possess physiological characteristics that allow them to sustain high photosynthetic rates under shaded conditions (Sage and McKown 2006). Dactylis glomerata (orchardgrass; DG) and Festuca arudinacea (tall fescue; FA) are two of the main perennial species cultivated in agroforestry systems (Peri et al 2002;Mercier et al 2020), with DG reported to be more shade tolerant than FA (Peri et al 2002;Mercier et al 2020;Belesky et al 2011). Studies in New Zealand and Uruguay have also demonstrated the positive responses of the biannual grass Holcus lanatus (Yorkshire fog, HL) to shading (Devkota et al 2009;Olmos et al 2011), a specie largely present in oodplain wetlands, with relatively low persistence in dry conditions (Boigné et al 2017).…”