Quantifying the effects of Eucalyptus plantations and management on water resources at plot and catchment scales

Abstract

Our aim was to quantify the effects of forest plantation and management (clear cut or 30% partial harvest) in relation to pasture, on catchment discharge in southeast Rio Grande do Sul state, Brazil. A paired‐catchment approach was implemented in two regions (Eldorado do Sul and São Gabriel municipalities) where discharge was measured for 4 years at three catchments in each region, two of which were predominantly eucalypt plantation (mainly Eucalyptus saligna, rotation of approximately 7–9 years) with native forest and grass in streamside zones. The third catchment was covered with grazed pasture. Weather, soils, canopy interception, groundwater level, tree growth, and leaf area index were also measured. The 3‐PG process‐based forest productivity model was adapted to predict spatial daily plantation and pasture water balance including precipitation interception, soil evaporation, transpiration, soil moisture, drainage, discharge, and monthly plantation growth. The TOPMODEL framework was used to simulate water pools and fluxes in the catchments. Discharge was higher under pasture than pre‐harvesting plantation and increased for 1–2 years after complete plantation harvest; this change was less pronounced in the catchments under partial harvest. The ratio of discharge to precipitation before harvesting varied from 7% to 13% in the eucalypt catchments and 28% to 29% under pasture. The ratio increases to 23–24% after total harvest, and to 17% after partial harvesting. The ratio under pasture also increases during this period (to 32–44%) owing to increased precipitation. The baseflow, in relation to total discharge, varied from 28% to 62% under Eucalyptus and from 38% to 43% in the pasture catchments. Hence, eucalypt plantations in these regions can be expected to influence discharge regimes when compared with pasture land use, and modelling suggests that partial harvesting would moderate the magnitude of discharge variation compared with a full catchment plantation harvesting. The model efficiency coefficient (Nash–Sutcliffe model efficiency coefficient) varied from 0.665 to 0.799 for the total period of the study. Simulation of alternative harvesting scenarios suggested that at least 20% of the catchment planted area must be harvested to increase discharge. This model could be a useful practical tool in various plantation forestry contexts around the world. Copyright © 2016 John Wiley & Sons, Ltd.

Forests and water in South America

“…Evapotranspiration in plantations varies with climate, season, forest type, and affected portion of the hydrograph (floods, low flows, groundwater; Almeida & Soares, ; Calder, ; Hervé‐Fernández et al, ; Lima, ; Lima et al, ). Evapotranspiration may exceed 90% of precipitation in plantations of Eucalpytus and Pinus spp., reducing water yield and depleting groundwater (Almeida, Smethurst, Sigins, Cavalcante, & Borges, ; Huber, Iroumé, & Bathurst, ; Jobbágy and Jackson 2004; Jobbágy et al, 2013; Silveira, Gamazo, Alonso, & Martinez, ; van Dijk & Keenan, ). Plantation forestry may not be cost‐effective when the value of evapotranspired water is taken into account (Chisholm, ; Núñez, Nahuelhual, & Oyarzún, ).…”

“…Long‐term, paired watershed studies, which have a before‐after, control‐impact design, provide appropriate spatial and temporal scales for integrated study of forest effects on water and may be complemented by before‐after or space‐for‐time studies and modeling. Although some paired watershed studies exist in South America (e.g., Almeida et al, ; Ferraz et al, ; Germer et al, ; Iroumé et al, ; Jobbágy et al, 2013; Little et al, ; Ochoa‐Tocachi et al, ), studies are needed to compare forest plantations with native forests in various management and disturbance regimes and to contrast with studies from other continents (e.g., Brown, Zhang, McMahon, Western, & Vertessy, ; Creed et al, ; Jones et al, ; Jones & Post, ; Scott, ; van Dijk & Keenan, ). Long‐term data on precipitation, temperature, soil moisture, streamflow, and groundwater (e.g., Figure ) allow researchers to test hypotheses about change in water yield and storage over time in watersheds with contrasting forest cover and management practices.…”

“…In these efforts, interdisciplinary teams can describe the response of forest structure and composition to disturbance and climate variability and develop consensus on appropriate protocols and indicators of the water balance and water partitioning. Hydrologists should partner with foresters to experiment with forest management practices including tree species, rotation lengths, and planting densities in order to optimize trade‐offs between wood production and water ecosystem services from forest plantations (e.g., Almeida et al, ; Bremer & Farley, ; Brockerhoff, Jactel, Parrotta, & Ferraz, ; Ferraz et al, ; Hartley, ; Lima, ; Lima et al, ; Lima et al, ; Little et al, ; Pawson et al, ; Thompson et al, ). Hydrologists and forest engineers should collaborate to quantify effects of forest practices and roads on erosion, flood occurrence, and water quality (e.g., sediment load, turbidity, and eutrophication).…”

Efeitos hidrológicos da composição da paisagem em microbacias com florestas plantadas de <i>Eucalyptus</i>

“…Enquanto, a microbacia 3 passou pela colheita de 80% de sua área no primeiro ano hídrico, a microbacia 1 passou pela colheita de 17% de sua área, no mesmo ano. Estudos indicam que a retirada ou o plantio de florestas em menos de 20% da área total da microbacia não são perceptíveis no deflúvio (BOSCH; HEWLETT, 1982;STEDNICK, 1996;BROWN et al, 2005;ALMEIDA et al, 2016). Portanto, a redução do deflúvio no segundo ano hídrico na microbacia 1 não deve estar relacionada à mudança na evapotranspiração, pois a cobertura florestal da microbacia 1 foi pouco alterada.…”

“…Deste modo, pode se dividir a área da microbacia em talhões com idades diferentes (manejo em mosaico), para que pelo menos uma parte contribua para a entrada de água nas camadas mais profundas do solo. A colheita de parte do eucalipto a cada dois anos, como proposto por Almeida et al (2016), pode ser realizada a partir da divisão da área de floresta plantada na microbacia em três talhões, o que poderia beneficiar os recursos hídricos.…”