Pablo Ramírez de Arellano’s research while affiliated with Pontifical Catholic University of Chile and other places

This paper reviews the current knowledge of hydrological processes in Chilean temperate forests which extend along western South America from latitude 29° S to 56° S. This geographic region includes a diverse range of natural and planted forests and a broad sweep of vegetation, edaphic, topographic, geologic, and climatic settings which create a unique natural laboratory. Many local communities, endangered freshwater ecosystems, and downstream economic activities in Chile rely on water flows from forested catchments. This review aims to (i) provide a comprehensive overview of Chilean forest hydrology, to (ii) review prior research in forest hydrology in Chile, and to (iii) identify knowledge gaps and provide a vision for future research on forest hydrology in Chile. We reviewed the relation between native forests, commercial plantations, and other land uses on water yield and water quality from the plot to the catchment scale. Much of the global understanding of forests and their relationship with the water cycle is in line with the findings of the studies reviewed here. Streamflow from forested catchments increases after timber harvesting, native forests appear to use less water than plantations, and streams draining native forest yield less sediment than streams draining plantations or grassland/shrublands. We identified 20 key knowledge gaps such as forest groundwater systems, soil-plant-atmosphere interactions, native forest hydrology, and the effect of forest management and restoration on hydrology. Also, we found a paucity of research in the northern geographic areas and forest types (35-36°S); most forest hydrology studies in Chile (56%) have been conducted in the southern area (Los Rios Region around 39-40° S). There is limited knowledge of the geology and soils in many forested areas and how surface and groundwater are affected by changes in land cover. There is an opportunity to advance our understanding using process-based investigations linking field studies and modeling. Through the establishment of a forest hydrology science “society” to coordinate efforts, regional and national-scale land use planning might be supported. Our review ends with a vision to advance a cross-scale collaborative effort to use new nation-wide catchment-scale networks Long-term Ecosystem Research (LTER) sites, to promote common and complementary techniques in these studies, and to conduct transdisciplinary research to advance sound and integrated planning of forest lands in Chile.

This paper reviews the current knowledge of hydrological processes in Chilean temperate forests which extend along western South America from latitude 29° S to 56° S. This geographic region includes a diverse range of natural and planted forests and a broad sweep of vegetation, edaphic, topographic, geologic, and climatic settings which create a unique natural laboratory. Many local communities, endangered freshwater ecosystems, and downstream economic activities in Chile rely on water flows from forested catchments. This review aims to (i) provide a comprehensive overview of Chilean forest hydrology, to (ii) review prior research in forest hydrology in Chile, and to (iii) identify knowledge gaps and provide a vision for future research on forest hydrology in Chile. We reviewed the relation between native forests, commercial plantations, and other land uses on water yield and water quality from the plot to the catchment scale. Much of the global understanding of forests and their relationship with the water cycle is in line with the findings of the studies reviewed here. Streamflow from 2 forested catchments increases after timber harvesting, native forests appear to use less water than plantations, and streams draining native forest yield less sediment than streams draining plantations or grassland/shrublands. We identified 20 key knowledge gaps such as forest groundwater systems, soil-plant-atmosphere interactions, native forest hydrology, and the effect of forest management and restoration on hydrology. Also, we found a paucity of research in the northern geographic areas and forest types (35-36° S); most forest hydrology studies in Chile (56%) have been conducted in the southern area (Los Rios Region around 39-40° S). There is limited knowledge of the geology and soils in many forested areas and how surface and groundwater are affected by changes in land cover. There is an opportunity to advance our understanding using process-based investigations linking field studies and modeling. Through the establishment of a forest hydrology science "society" to coordinate efforts, regional and national-scale land use planning might be supported. Our review ends with a vision to advance a cross-scale collaborative effort to use new nationwide catchment-scale networks Long-term Ecosystem Research (LTER) sites, to promote common and complementary techniques in these studies, and to conduct transdisciplinary research to advance sound and integrated planning of forest lands in Chile.

The effect of Eucalyptus plantations on water balance is thought to be more severe than for commercial alternatives such as Pinus species. Although this perception is firmly entrenched, even in the scientific community, only four direct comparisons of the effect on the water balance of a Eucalyptus species and a commercial alternative have been published. One of these, from South Africa, showed that Eucalyptus grandis caused a larger and more rapid reduction in streamflow than Pinus patula. The other three, one in South Australia and two in Chile, did not find any significant difference between the annual evapotranspiration of E. globulus and P. radiata after canopy closure. While direct comparisons are few, there are at least 57 published estimates of annual evapotranspiration of either the Eucalyptus or Pinus species. This paper presents a meta-analysis of these published data. Zhang et al. (2004) fitted a relationship between the vegetation evaporation efficiency and the climate wetness index to published data from catchment studies and proposed this approach for comparing land uses. We fitted this model to the published data for Eucalyptus and Pinus and found that the single parameter of this model did not differ significantly between the two genera (p=0.48). This was also the case for all parameters of an exponential relationship between evapotranspiration and rainfall (p=0.589) and a linear relationship between the vegetation evaporation index and rainfall (p=0.155). These results provide strong evidence that, for a given climate wetness index, the two genera have similar annual water use. The residuals compared to the model of Zhang et al. (2004) were significantly correlated with soil depth for Eucalyptus, but this was not the case for Pinus. For Eucalyptus, the model overestimates the vegetation evaporation efficiency on deep soils and underestimates the vegetation evaporation efficiency on shallow soils.

The effect of Eucalyptus plantations on water balance is thought to be more severe than for commercial alternatives such as Pinus species. Although this perception is firmly entrenched, even in the scientific community, only four direct comparisons of the effect on the water balance of a Eucalyptus species and a commercial alternative have been published. One of these, from South Africa, showed that Eucalyptus grandis caused a larger and more rapid reduction in streamflow than Pinus patula. The other three, one in South Australia and two in Chile, did not find any significant difference between the annual evapotranspiration of E. globulus and P. radiata after canopy closure. While direct comparisons are few, there are at least 57 published estimates of annual evapotranspiration of either a Eucalyptus or Pinus species. This paper presents a meta-analysis of these published data. Zhang et al. (2004) fitted a relationship between the crop factor and the climate wetness index to published data from catchment studies and proposed this approach for comparing land uses. We fitted the same model to the published data for Eucalyptus and Pinus and found that the single parameter of this model did not differ significantly between the two genera (p=0.48). This implies that for a given climate wetness index the two genera have similar annual water use. The residuals compared to this model were significantly correlated with soil depth for Eucalyptus, but this was not the case for Pinus. For Eucalyptus the model overestimates the crop factor on deep soils and underestimates the crop factor on shallow soils.

Wildfires are an important disturbance affecting catchments’ soil and hydrological processes within. Wildfires are predicted to increase in both frequency and severity under climate change. Here, we present measurements of tritium (³H) in surface water of three streams before and after the ‘las Máquinas’ megafire of January 2017 in central Chile and streamflow metrics. Mean transit times (MTTs) of water were calculated in three coastal catchments with the Mediterranean climate type, covered by native forest, a mixture of native forest and Pinus radiata D. Don, and P. radiata. Lumped parameter models (LPMs) were used to obtain MTTs. Tritium activities from 2012 to 2018 ranged from 0.597 to 0.927 Tritium Units (TU), with the lowest TU activity in 2018. These ³H concentrations indicated water ages from 5 to 30 years. Following the fire, peak flows and baseflow have increased in two catchments but decreased in the third. Even though we have seen changes in the hydrological responses within the three catchments, pre- and post-fire MTT values were not significantly different. Therefore, there is no conclusive evidence of hydrological changes at the groundwater level due to wildfire at this early stage. However, since the MTT ranges from 5 to 30 years, it is likely that more time is required for the changes in the hydrograph to be clearly reflected in the tritium signal even though there are noticeable changes in streamflow metrics such as runoff and baseflow. Within the following years from this study, a sampling schedule to continue to investigate both the long-term drought and the effect of wildfire on these catchments will be maintained.

The water-use of plantations compared to alternative land uses is an important natural resource management issue in central Chile. The need for local data is heightened by a drying trend in the local climate, the potential for planted forests to store carbon and local plans to replace plantations of Pinus radiata D. Don with Eucalyptus globulus Labill. This paper compares the growth and water balance of P. radiata and native forest (Hualo – Nothofagus glauca (Phil.) Krasser) at a low rainfall site (1016 mm) and of P. radiata, E. globulus and native forest (Roble – N. obliqua Mirb.) at a medium rainfall (1395 mm) site. Evapotranspiration of plantations of P. radiata in the north and of P. radiata and E. globulus further south was greater than in the local native forest by about 100 mm per year. This difference in total water use was due to greater transpiration by the plantation species; the sum of interception and soil evaporation was very similar for all forest types. Pinus radiata used more water than native forest throughout the year, owing to a more than two-fold greater stand sapwood area in the P. radiata. The difference between E. globulus and native forest was due to much higher sap flux density in the E. globulus during spring and early summer. Although there was no annual difference between the water use of E. globulus and P. radiata, the much greater transpiration of E. globulus in spring may result in earlier drying of soils and catchments planted with E. globulus than P. radiata species. The annual growth rate of all forest types increased in the years after the end of Chilean mega drought. During the first year of this period, E. globulus produced significantly more wood per unit of water used (3.5 g wood kg−1) than P. radiata (2.1 g kg−1) which was, in turn, more than five times more efficient then the native forest (0.4 g kg−1).

In central Chile, many communities rely on water obtained from small catchments in the coastal mountains. Water security for these communities is most vulnerable during the summer dry season and, from 2010 to 2017, rainfall during the dry season was between 20% and 40% below the long‐term average. The rate of decrease in stream flow after a rainfall event is a good measure of the risk of flow decreasing below a critical threshold. This risk of low flow can be quantified using a recession coefficient ( α ) that is the slope of an exponential decay function relating flow to time since rainfall. A mathematical model was used to estimate the recession coefficient ( α ) for 142 rainstorm events (64 in summer; 78 in winter) in eight monitored catchments between 2008 and 2017. These catchments all have a similar geology and extend from 35 to 39 degrees of latitude south in the coastal range of south‐central Chile. A hierarchical cluster analysis was used to test for differences between the mean value of α for different regions and forest types in winter and summer. The value of α did not differ ( p < 0.05) between catchments in winter. Some differences were observed during summer and these were attributed to morphological differences between catchments and, in the northernmost catchments, the effect of land cover (native forest and plantation). Moreover, α for catchments with native forest was similar to those with pine plantations, although there was no difference ( p < 0.05) between these and Eucalyptus plantations. The recession constant is a well‐established method for understanding the effect of climate and disturbance on low flows and baseflows and can enhance local and regional analyses of hydrological processes. Understanding the recession of flow after rainfall in small headwater catchments, especially during summer, is vital for water resources management in areas where the establishment of plantations has occurred in a drying climate.

Forestal Arauco (FA), a global manufacturer of forest products, manages more than one million hectares of forest plantations and oversees the conservation of more than half a million hectares of native forest and vegetation in Brazil, Argentina and Chile. In 2008, FA responded to local concerns about the effect of plantations on water resources and commenced streamflow monitoring in catchments in the coastal range of central‐southern Chile between 35° and 39° of latitude south. This data note presents an overview of daily streamflow and rainfall records for 10 small catchments (18 to 112 hectares) from 2008 to 2018. The catchments are covered by three different forest types, namely native forest (2), pine plantations of different ages (6) and eucalypt plantations (2). All of these catchments share similar metamorphic geology. A 90° V notch weir was built at each catchment outlet and data collected at 5 min interval using a pressure transducer that was calibrated monthly. The dataset is part of a research program aiming to improve our understanding about the role of forest plantations on water balance at a stand and catchment level. It also includes the rainfall data from these catchments estimated using a combination of local rain gauges and data from the longer‐term records of the Chilean Directorate of Water (DGA). This dataset can be used in hydrological modelling and in a wide range of research questions and water management issues regarding forest plantations in a Mediterranean climate. This article is protected by copyright. All rights reserved.

The large wildfires of January 2017 burned more than 500,000 ha, including areas of high conservation value native forest, in central Chile. Runoff, streamflow and water balance were measured in a native forest catchment for 7 years before and 2 years after the fires. The annual peak flows and runoff coefficients decreased after the fire as did summer flows and total streamflow. These reductions in flow were despite rainfall being higher in the two years after the fire than in the two years before the fire. The forest re-sprouted vigorously after the fire and evapotranspiration in the second year after the fire was approximately two thirds of the rate before the fire. While the forest water use is recovering rapidly, streamflow in the two years after the fire was reduced relative to the seven years before the fire. In the two years after the fires, more than 50% of rainfall is not accounted for by either evapotranspiration or by streamflow. Potential explanations for this gap in the water balance include recovery in storage after the fire and increased bypass flow below the measuring weirs.