Day 1 – Sunday, Dec. 6th, 2020
2pm – 3pm
Trees increase the frequency of cool-season grasses in silvopastoral systems on temperate native grasses
Dante Pizarro, UW-Madison Department of Animal and Dairy Sciences
Silvopastoral systems may provide important production and environmental benefits. The loss of cool-season C3 grasses from temperate grazed native grasslands is associated with selective grazing and excessive solar radiation that limits their survival. Silvopastoral systems integrate trees with grasslands that provide shade to both cattle and herbaceous plants, potentially favoring C3 species. There is limited information on the effect of trees on the species and functional composition of native grasslands in the Campos biome in South America. The objective of this study was to detect gradients in the botanical composition of grasslands associated with isolated native trees under two common soils: Prosopis spp. on solonetz and Acacia caven on brunisoils. Frequency and soil cover of the herbaceous species under three trees in each situation was systematically recorded every 0.5 m in 15 m transects on the four cardinal directions taking each tree as the center. The pastures on brunisoils showed a greater species richness than those on solonetz, and a higher frequency of grasses and legumes. In both situations, there were differences in pasture composition in the different shade regions. Under the canopy (0-5m), the herbaceous layer was enriched with cool-season grasses such as Lolium multiflorum, Stipa setigera, S. hyalina, and Bromus catharticus. At a greater distance (10-15m), warm-season grasses increased in the coverage such as Paspalum notatum and P. dilatatum. The gradients detected allow us to conclude that trees in silvopastoral systems can increase the abundance of cool-season species and therefore the forage nutritive value of the native pasture.
Pablo Boggiano, [email protected], Facultad de Agronomía, Universidad de la Republica, Uruguay
Mónica Cadenazzi, [email protected], Facultad de Agronomía, Universidad de la Republica, Uruguay
Valentin Picasso, [email protected], Department of Agronomy, University of Wisconsin – Madison, Wisconsin, USA
Environmental impacts associated with converting woodland to silvopasture
Diane Mayerfeld, University of Wisconsin-Madison Extension and Center for Integrated Agricultural Systems
Many farmers are interested in converting woodland to silvopasture to provide shade for their animals and increase forage stocks. We found that converting a mixed hardwood woodland in southwestern Wisconsin to silvopasture provided these benefits but also had some adverse impacts on soil condition. We compared soil penetration resistance, water infiltration, understory density, and tree growth and health in three treatments: an ungrazed control, silvopasture with periodic livestock access and forages planted in the understory, and grazed woodland with periodic livestock access but no understory manipulation. Soil penetration resistance increased, and water infiltration capacity decreased in both grazed treatments relative to the ungrazed control. Tree growth as measured by plot basal area increment was slightly greater in the grazed woodland and ungrazed control than in the silvopasture treatment, but the difference was not statistically significant. Trunk and canopy health and the percentage of dead branches were not different among the three treatments, but the silvopasture treatment had a greater increase in epicormic branching than the other two treatments. The sensitivity of soil quality measures to grazing underscores the need for careful management of grazing intensity in silvopasture systems.
Eric Kruger (1), Mark Rickenbach (1), and Rhonda Gildersleeve (2)
1) University of Wisconsin-Madison; 2) Farmer and retired UW Extension Professor and Grazing Specialist
Abiotic and biotic drivers of soil C cycling change throughout the lifespan of riparian agroforests
Serra-Willow Buchanan, Department of Physical and Environmental Sciences, University of Toronto Scarborough, Canada
Agricultural landscapes play a major role in global carbon (C) emissions. Rehabilitation of agricultural riparian buffers with trees (agroforestry) provides a unique and elegant solution to enhance carbon storage while also augmenting local biodiversity. Yet the scope and role of riparian plant community diversity in key soil dynamics remains unresolved. Operationalizing riparian age [young (<10 years) and mature (>30 years) since establishment] and forest stand type [coniferous and deciduous dominant], we measure plant functional trait diversity, microbial diversity, abiotic soil conditions and rates of soil CO2 efflux (mg CO2-C m-2 h-1). We use structural equation modelling (SEM) to further refine the role of biotic and abiotic factors on soil C cycling processes in riparian systems. We found significantly lower rates of CO2 efflux (F = 8.47; p<0.01) and higher total soil C (F = 3.46; p=0.03) in mature buffers as compared with young buffers. These differences were not significant between forest stand types. Using SEMs, we describe influences on soil C content (marginal r2=61) and soil CO2 efflux (marginal r2=53). Within young buffers, soil C content was significantly predicted by fungal:bacterial ratio and root length density, whereas in mature buffers, soil C content was associated with higher tree leaf functional trait diversity. Soil CO2 efflux was predicted by soil moisture, soil carbon content, and root functional trait diversity. Evidently, leaf and root functional traits in combination with broad soil parameters significantly describe soil C dynamics in the field, with these pathways changing throughout the life cycling of riparian agroforest.
Tolulope Mafa-Attoye, [email protected], School of Environmental Sciences, University of Guelph, Guelph, Ontario, Canada
Kari Dunfield, [email protected], School of Environmental Sciences, University of Guelph, Guelph, Ontario, Canada
Naresh V. Thevathasan, [email protected], School of Environmental Sciences, University of Guelph, Guelph, Ontario, Canada
Marney E. Isaac, [email protected], Department of Physical and Environmental Sciences, University of Toronto Scarborough, Canada.
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