Water budget fluxes in catchments under grassland and Eucalyptus plantations of different ages

Abstract

The area with planted forests increased in the last decades and they have an important role in programs to sequester carbon. However, the effects of eucalyptus plantations on water resources in the Southern Grasslands biome are largely unknown, and we herein address water budget fluxes including green and blue flows. We evaluated green (canopy interception and evapotranspiration) and blue (discharge) water flows in three watersheds; two predominantly covered with Eucalyptus, either in the first years after planting or at the end of the rotation, and one with livestock-grazing grassland. We used field measurements of rainfall, streamflow and throughfall, and estimated canopy interception and evapotranspiration by water balance. Water flows in the monitored watersheds with eucalyptus plantations were influenced by forest development stage. Annual canopy interception and transpiration were always higher in the watersheds with eucalyptus than in the one with grassland, except for the transpiration in the first year after plantation in watershed with young eucalyptus. Increase in evapotranspiration (green water flow) and the consequent decrease in streamflow (blue water flow) should be considered in local water resources management. Studies on catchment hydrology and forest management for improved water use efficiency and streamflow regulation are required, particularly in understudied regions.

Afforestation of degraded grasslands reduces sediment transport and may contribute to streamflow regulation in small catchments in the short-run

“…Soil and forest/grassland management should be oriented towards protecting or restoring soil moisture and manage the green water flux for increased water productivity. An improved soil structure allows for increased infiltration and retention in the soil (Cavalli et al, 2020;Ferreto et al, 2020).…”

“…Under extensive livestock production, the farming system has low productivity per animal and per area because of low forage availability where livestock is obliged to walk long distances in search of forage and water. The natural soil fragility combined with overgrazing has led to intense soil degradation by soil erosion (Roesch et al, 2009;Reichert et al, 2016;Ebling et al, 2020;Ferreto et al, 2020;Valente et al, 2020), and loss of soil carbon and grassland species diversity (Overbeck et al, 2007). Intense grazing and trampling by cattle cause soil compaction (Collares et al, 2011;Cecagno et al, 2016;Ambus et al, 2018), through an increase in the soil bulk density and a decrease in porosity.…”

“…This expansion is a response to the increased demand for forest-based raw-materials, low prices of land in this region, and currently encouraged by carbon offset projects. This change in land use and management of natural resources consequently raised concerns on environmental sustainability associated with the introduction of exotic, fast-growing forest species (Andriollo et al, 2017;Mateus and Padilha, 2017;Reichert et al, 2017), requiring conservation methods to reduce soil erosion and sedimentation (Ebling et al, 2020;Valente et al, 2020), runoff (Ferreto et al, 2020), soil compaction (Holthusen et al, 2018;França et al, 2021), and water consumption (Ferreto et al, 2021). Similar concerns had been raised in Uruguay, where the conversion of native grasslands into croplands and exotic forest plantations (Eucalyptus and Pinus) has fast-tracked during the last two decades (Brazeiro et al, 2020).…”

Experimental catchments in the Pampa biome: Database on hydrology in grasslands and eucalyptus plantations in subtropical Brazil

“…In the wetter-than-normal year, streamflow was 66% lower in the eucalyptus than in the grassland, while evapotranspiration was 27% greater in E. saligna than in grassland catchment and groundwater recharge was 46% greater. From 2014to 2018, Ferreto et al (2021a observed that specific discharge was lower in E. saligna by 44-58% and in E. benthamii by 16-78% compared with grassland.…”

Best tillage practices for eucalyptus growth and productivity: A review on the Brazilian experience

“…Furthermore, study approaches used for agricultural crops can be adapted or improved for eucalyptus. In particular, opportunities are related to tillage in compacted areas by forest harvesting, by previously defining different soil compaction states in the field, such as performed for agricultural crops (Secco et al, 2009), considering spatial variability in soil physical properties (Silva et al, 2003;Marins et al, 2018); short-and long-term tillage (Veiga et al, 2008(Veiga et al, , 2009(Veiga et al, , 2010Reichert et al, 2016c) and cropping systems effects (Awe et al, 2015;Cecagno et al, 2016;Ambus et al, 2018;Reichert et al, 2022); refinement of plant available water as affected by soils and tillage, using existing pedotranfer functions (Vaz et al, 2005;Reichert et al, 2009Reichert et al, , 2020b or by developing improved ones, as well as via soil water balance (Reichert et al, 2021d), forest hydrology (Ferreto et al, 2021a) or catchment water-budget fluxes (Reichert et al, 2017bEbling et al, 2021;Ferreto et al, 2021b;Valente et al, 2021).…”