Trees have been around for more than 370 million years, and today there are about 80 thousand
spe... more Trees have been around for more than 370 million years, and today there are about 80 thousand species of them, occupying 3.5 billion hectares worldwide, including 250 million ha of commercial plantations. While forests can provide tremendous environmental, social, and economic benefits to nations, they also affect the hydrologic cycle in different ways. As the demand for water grows and local precipitation patterns change due to global warming, plantation forestry has encountered an increasing number of water-related conflicts worldwide. This document provides a country-by-country summary of the current state of knowledge on the relationship between forest management and water resources. Based on available research publications, the Editor-in-Chief of this document contacted local scientists from countries where the impact of forest management on water resources is an issue, inviting them to submit a chapter.
Resumo O manejo sustentável dos recursos hídricos e da terra é atualmente uma das principais prio... more Resumo O manejo sustentável dos recursos hídricos e da terra é atualmente uma das principais prioridades na agenda de muitos países ao redor do mundo, o que exige informações sobre as mudanças na cobertura da terra em bacias hidrográficas. Neste estudo, mapas de 1984, 1996, 2005 e 2016 foram desenvolvidos utilizando-se composições falsa-cor e o Índice de Vegetação por Diferença Normalizada (NDVI) para identificar as principais mudanças ocorridas na bacia do Córrego Guariroba. Essa bacia hidrográfica é uma Área de Proteção Ambiental desde 1995, quando se tornou a fonte de abastecimento urbana da capital do estado de Mato Grosso do Sul, Brasil. Para tanto, o software livre QGIS e imagens Landsat foram usados para determinar as mudanças no uso e ocupação da terra. Essas informações permitiram a discussão das possíveis pressões e consequências ambientais das mudanças nesses períodos. A bacia hidrográfica tem estado sob intensa atividade agropecuária, com a maior parte de sua superfície sendo ocupada por pastagens para a pecuária e silvicultura de eucalipto. Os resultados indicam que a influência direta das atividades humanas reduziu drasticamente a cobertura natural na área, com implicações para o cumprimento da legislação do Código Florestal. Os usos antrópicos da terra representam mais de 57% da cobertura total do solo em todos os anos, atingindo 79,70% em 2005. Em 2016, houve um aumento na recuperação da vegetação nativa, mas apesar desse incremento o uso humano da terra continua alto (74,09%). Parte do pequeno ganho de vegetação nativa deve-se aos planos de reflorestamento realizados a partir de 2010. A sedimentação do reservatório de água é visível em 2016, formando bancos de areia que se estendem por cerca de 700 m na porção distal do Córrego Guariroba. Os resultados deste estudo podem ser aplicados para uma possível revisão do plano de manejo da bacia, considerando-se a gestão de seus recursos hídricos integrados ao planejamento ambiental e ao desenvolvimento econômico. Esse tipo de análise pode auxiliar no processo de tomada de decisão de órgãos governamentais, de forma que as bacias utilizadas para o abastecimento de água apresentem restrições de uso da terra, devido ao risco de redução na quantidade e a qualidade da água.
Streamflow and its storm-flow elements in four catchments were analyzed by the paired catchment m... more Streamflow and its storm-flow elements in four catchments were analyzed by the paired catchment method for a response to fire. Prior to burning two of the catchments were vegetated with over-mature fynbos (the indigenous scrub vegetation of the southwestern Cape, South Africa), one was afforested with Pinus radiata and the fourth with Eucalyptus fastigata. One of the fynbos catchments was burned in a prescribed fire in the late dry season. The other catchments burned in wildfires. Neither of the fynbos catchments showed a change in storm-flow. Annual total flow increases of around 16% were in agreement with model predictions, being related to the reductions in transpiration and interception. The manner of streamflow generation appeared to have remained unaltered despite the presence of some water repellency in the soils and consequent overland flow on some steep midslope sites. The two timber plantation catchments experienced large and significant increases in storm-flows and soil losses, while total flow increased by 12% in the pine catchment and decreased marginally in the eucalypt catchment. The pattern of the storm-flow increases was similar in both cases. After fire, storm hydrographs were higher and steeper though their duration was little changed. The respective first year increases in the pine and eucalypt catchments were 290% and 1110% for peak discharge, 201% and 92% for quick-flow volume, and 242% and 319% for storm response ratio. These fire effects are considered to be due to changes in storm-flow generation consistent with an increased delivery of overland flow (surface runoff) to the stream channel. This was caused, in part, by reduced infiltration resulting from water repellency in the soils of the burned catchments. Overall the hydrological effects of fire are related to numerous interactive factors, including the degree of soil heating, the vegetation type and soil properties.
Streamflow and its storm-flow elements in four catchments were analyzed by the paired catchment m... more Streamflow and its storm-flow elements in four catchments were analyzed by the paired catchment method for a response to fire. Prior to burning two of the catchments were vegetated with over-mature fynbos (the indigenous scrub vegetation of the southwestern Cape, South Africa), one was afforested with Pinus radiata and the fourth with Eucalyptus fastigata. One of the fynbos catchments was
The longer-term effects of afforestation with Pinus radiata and Eucalyptus grandis on streamflows... more The longer-term effects of afforestation with Pinus radiata and Eucalyptus grandis on streamflows were analyzed using data from two paired-catchment experiments in South Africa. The experiments are rare in that they have been maintained over longer periods than the typical rotation period for industrial timber plantations in the tropics or subtropics. In both experiments the planting treatments led to large reductions in streamflow, which increased with the age of the trees and were positively related to water availability. The pine plantation caused peak reductions in yield over a 5-year period of 44 mm a À1 or 7.7% a À1 for each 10% of catchment planted when the trees were between 10 and 20 years old. The eucalypt plantation caused peak reductions over a 3-year period of 48 mm a À1 and 10% a À1 for each 10% of catchment planted. However, as the plantations matured (over 30 years of age in the case of pines and over 15 years of age in the case of eucalypts) the flow reduction trend was reversed, and streamflow effects appear to be tending toward preafforestation levels. The longer-term effects of planted forests need not be as harmful on the water yield of catchments as has been predicted from shorter-term studies. The implication of these results is that if trees are grown on very long rotations, they may be used for restoring degraded catchments or as a means of storing carbon without completely denuding available water resources.
Changes in vegetation cover can significantly affect streamflow. Two common methods for estimatin... more Changes in vegetation cover can significantly affect streamflow. Two common methods for estimating vegetation effects on streamflow are the paired catchment method and the time trend analysis technique. In this study, the performance of these methods is evaluated using data from paired catchments in Australia, New Zealand, and South Africa. Results show that these methods generally yield consistent estimates of the vegetation effect, and most of the observed streamflow changes are attributable to vegetation change. These estimates are realistic and are supported by the vegetation history. The accuracy of the estimates, however, largely depends on the length of calibration periods or pretreatment periods. For catchments with short or no pretreatment periods, we find that statistically identified prechange periods can be used as calibration periods. Because streamflow also responds to climate variability, in assessing streamflow changes it is necessary to consider the effect of climate in addition to the effect of vegetation. Here, the climate effect on streamflow was estimated using a sensitivity-based method that calculates changes in rainfall and potential evaporation. A unifying conceptual framework, based on the assumption that climate and vegetation are the only drivers for streamflow changes, enables comparison of all three methods. It is shown that these methods provide consistent estimates of vegetation and climate effects on streamflow for the catchments considered. An advantage of the time trend analysis and sensitivity-based methods is that they are applicable to nonpaired catchments, making them potentially useful in large catchments undergoing vegetation change.
Research results on the effects of land cover change on water resources vary greatly and the topi... more Research results on the effects of land cover change on water resources vary greatly and the topic remains controversial. Here we use published data worldwide to examine the validity of Fuh's equation, which relates annual water yield (R) to a wetness index (precipitation/potential evapotranspiration; P/PET) and watershed characteristics (m). We identify two critical values at P/PET=1 and m=2. m plays a more important role than P/PET when m<2, and a lesser role when…
... South-western Cape Forestry Areas? AJArmstrong1 , HJ van Hensbergen&amp;#x27;, DF Scott&a... more ... South-western Cape Forestry Areas? AJArmstrong1 , HJ van Hensbergen&amp;#x27;, DF Scott&amp;quot; and SJ Milton3 ... The forest is also an &amp;quot;inhospitable sea&amp;quot; for the rodent species, but not to all the ant species, recorded in the fynbos &amp;quot;islands&amp;quot; (Midgley and Bond, 1990). ...
Changes in vegetation cover can significantly affect streamflow. Two common methods for estimatin... more Changes in vegetation cover can significantly affect streamflow. Two common methods for estimating vegetation effects on streamflow are the paired catchment method and the time trend analysis technique. In this study, the performance of these methods is evaluated using data from paired catchments in Australia, New Zealand, and South Africa. Results show that these methods generally yield consistent estimates of the vegetation effect, and most of the observed streamflow changes are attributable to vegetation change. These estimates are realistic and are supported by the vegetation history. The accuracy of the estimates, however, largely depends on the length of calibration periods or pretreatment periods. For catchments with short or no pretreatment periods, we find that statistically identified prechange periods can be used as calibration periods. Because streamflow also responds to climate variability, in assessing streamflow changes it is necessary to consider the effect of climate in addition to the effect of vegetation. Here, the climate effect on streamflow was estimated using a sensitivity-based method that calculates changes in rainfall and potential evaporation. A unifying conceptual framework, based on the assumption that climate and vegetation are the only drivers for streamflow changes, enables comparison of all three methods. It is shown that these methods provide consistent estimates of vegetation and climate effects on streamflow for the catchments considered. An advantage of the time trend analysis and sensitivity-based methods is that they are applicable to nonpaired catchments, making them potentially useful in large catchments undergoing vegetation change.
This article may be used for research, teaching, and private study purposes. Any substantial or s... more This article may be used for research, teaching, and private study purposes. Any substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to anyone is expressly forbidden. The publisher does not give any warranty express or implied or make any representation that the contents will be complete or accurate or up to date. The accuracy of any instructions, formulae, and drug doses should be independently verified with primary sources. The publisher shall not be liable for any loss, actions, claims, proceedings, demand, or costs or damages whatsoever or howsoever caused arising directly or indirectly in connection with or arising out of the use of this material.
The reductions in streamiIow following the afforestation of grassland with Eucalyptus grands and ... more The reductions in streamiIow following the afforestation of grassland with Eucalyptus grands and Pinus pun& in the Mokobulaan research catchments on the Mpumalanga escarpment, and the subsequent response in streamflow to cleat-felling of the eucalypts are presented. Afforestation with eucalypts of an entire catchment with a virgin annual runoff of 236 mm, caused a statistically significant decrease in streamflow in the third year after planting and the stream dried up completely in the ninth year after planting. The eucalypts were clearfelled when 16 years old but full perennial streamflow did not return until five years later. Afforestation with pines of an entire catchment with a virgin annual runoff of 217 mm, produced a significant decrease in streamflow in the fourth year after planting and caused the stream to dry up completely in the twelfth year after planting. The drying up of the streams was not altogether surprising as the annual runoff was lower than the expected reductions owing to complete afforestation. The delayed return of streamflow in the clearfelled catchment is surprising though, and is attributed to the desiccation of deep, soil-water stores by the eucalypts. These stores had to be replenished before the streams could return to normal behaviour. Q 1997 Elsevier Science B.V.
A wild®re in an aorested research catchment presented the rare opportunity to compare the hydrolo... more A wild®re in an aorested research catchment presented the rare opportunity to compare the hydrological eects of wild®re with the eects of clearfelling in the same catchment in the Jonkershoek Valley, in the southwestern Western Cape Province of South Africa. The timber plantation, which occupies 57% of the 2 km 2 catchment, had been clearfelled and replanted to Pinus radiata roughly ®ve years before the ®re. The eects of the two treatments on total¯ow, stormow and quick-¯ow volumes, peak discharge and storm response ratio were determined by means of multiple regression analysis, employing the dummy variable method to test for the signi®cance of treatments. Both clearfelling and wild®re caused signi®cant increases in all the stream-¯ow variables analysed. But the clearfelling eect was dominated by large increases in total¯ow (96% over three years), of which storm-¯ow and quick-¯ow volumes formed only minor parts. After the wild®re, by contrast, increases in total¯ow were small (12%) but the storm¯ow increases were three-to fourfold in the ®rst year and roughly double in the second year. The wild®re caused ®re-induced water repellency in the soils which led to overland¯ow on mid-slope sites, where soil in®ltrability normally far exceeds local rainfall intensities. It is argued that these results support the hypothesis that stream-¯ow generation processes were changed by the wild®re in that overland¯ow made a direct contribution to storm¯ows, but that clearfelling had no such eect.
The paired catchment method was used to test for the effects of thinning on the water yield in th... more The paired catchment method was used to test for the effects of thinning on the water yield in three afforested catchments in South Africa, namely, Biesievlei, Jonkershoek, 98% afforested with Pinus rudiutu (three thinnings); Westfalia catchment D, 100% afforested with EucuEyptlrs grandis (two thinning& and Cathedral Peak CII that was 74% afforested with Pinus purulu (one thinning). During and after two separate thinning& each of which removed roughly one third of the stems in a maturing P. rudiutu plantation in the Biesievlei catchment, annual streamflow increased by between 10 and 71% (19-99 mm). These increases persisted for three and two years after the thinning, respectively. A final thinning in the same catchment removed only 22% of stems at an age of 28 yr. The following years (1977 and 1978) were wetter than average, and reductions in annual streamflow of 26 and 55% were recorded in these two years. At Westfalia catchment D and Cathedral Peak CII, the hydrological trends were entirely dominated by the rapidly declining streamflow caused by the developing E. grandis and P. putt&z plantations respectively. Any savings in water use that may have resulted from the thinning of these plantations were insufficient to affect the downward trend in annual streamflow. Thinnings may have had a minor effect of delaying or reducing the desiccation of these catchments but such effects could not be assessed due to natural variability and the limited resolution of the paired catchment method. The trends in total water yield from the catchments were generally mirrored in the dry season streamflow, and there were no strong indications that thinning effects are linked to a particular season.
Trees have been around for more than 370 million years, and today there are about 80 thousand
spe... more Trees have been around for more than 370 million years, and today there are about 80 thousand species of them, occupying 3.5 billion hectares worldwide, including 250 million ha of commercial plantations. While forests can provide tremendous environmental, social, and economic benefits to nations, they also affect the hydrologic cycle in different ways. As the demand for water grows and local precipitation patterns change due to global warming, plantation forestry has encountered an increasing number of water-related conflicts worldwide. This document provides a country-by-country summary of the current state of knowledge on the relationship between forest management and water resources. Based on available research publications, the Editor-in-Chief of this document contacted local scientists from countries where the impact of forest management on water resources is an issue, inviting them to submit a chapter.
Resumo O manejo sustentável dos recursos hídricos e da terra é atualmente uma das principais prio... more Resumo O manejo sustentável dos recursos hídricos e da terra é atualmente uma das principais prioridades na agenda de muitos países ao redor do mundo, o que exige informações sobre as mudanças na cobertura da terra em bacias hidrográficas. Neste estudo, mapas de 1984, 1996, 2005 e 2016 foram desenvolvidos utilizando-se composições falsa-cor e o Índice de Vegetação por Diferença Normalizada (NDVI) para identificar as principais mudanças ocorridas na bacia do Córrego Guariroba. Essa bacia hidrográfica é uma Área de Proteção Ambiental desde 1995, quando se tornou a fonte de abastecimento urbana da capital do estado de Mato Grosso do Sul, Brasil. Para tanto, o software livre QGIS e imagens Landsat foram usados para determinar as mudanças no uso e ocupação da terra. Essas informações permitiram a discussão das possíveis pressões e consequências ambientais das mudanças nesses períodos. A bacia hidrográfica tem estado sob intensa atividade agropecuária, com a maior parte de sua superfície sendo ocupada por pastagens para a pecuária e silvicultura de eucalipto. Os resultados indicam que a influência direta das atividades humanas reduziu drasticamente a cobertura natural na área, com implicações para o cumprimento da legislação do Código Florestal. Os usos antrópicos da terra representam mais de 57% da cobertura total do solo em todos os anos, atingindo 79,70% em 2005. Em 2016, houve um aumento na recuperação da vegetação nativa, mas apesar desse incremento o uso humano da terra continua alto (74,09%). Parte do pequeno ganho de vegetação nativa deve-se aos planos de reflorestamento realizados a partir de 2010. A sedimentação do reservatório de água é visível em 2016, formando bancos de areia que se estendem por cerca de 700 m na porção distal do Córrego Guariroba. Os resultados deste estudo podem ser aplicados para uma possível revisão do plano de manejo da bacia, considerando-se a gestão de seus recursos hídricos integrados ao planejamento ambiental e ao desenvolvimento econômico. Esse tipo de análise pode auxiliar no processo de tomada de decisão de órgãos governamentais, de forma que as bacias utilizadas para o abastecimento de água apresentem restrições de uso da terra, devido ao risco de redução na quantidade e a qualidade da água.
Streamflow and its storm-flow elements in four catchments were analyzed by the paired catchment m... more Streamflow and its storm-flow elements in four catchments were analyzed by the paired catchment method for a response to fire. Prior to burning two of the catchments were vegetated with over-mature fynbos (the indigenous scrub vegetation of the southwestern Cape, South Africa), one was afforested with Pinus radiata and the fourth with Eucalyptus fastigata. One of the fynbos catchments was burned in a prescribed fire in the late dry season. The other catchments burned in wildfires. Neither of the fynbos catchments showed a change in storm-flow. Annual total flow increases of around 16% were in agreement with model predictions, being related to the reductions in transpiration and interception. The manner of streamflow generation appeared to have remained unaltered despite the presence of some water repellency in the soils and consequent overland flow on some steep midslope sites. The two timber plantation catchments experienced large and significant increases in storm-flows and soil losses, while total flow increased by 12% in the pine catchment and decreased marginally in the eucalypt catchment. The pattern of the storm-flow increases was similar in both cases. After fire, storm hydrographs were higher and steeper though their duration was little changed. The respective first year increases in the pine and eucalypt catchments were 290% and 1110% for peak discharge, 201% and 92% for quick-flow volume, and 242% and 319% for storm response ratio. These fire effects are considered to be due to changes in storm-flow generation consistent with an increased delivery of overland flow (surface runoff) to the stream channel. This was caused, in part, by reduced infiltration resulting from water repellency in the soils of the burned catchments. Overall the hydrological effects of fire are related to numerous interactive factors, including the degree of soil heating, the vegetation type and soil properties.
Streamflow and its storm-flow elements in four catchments were analyzed by the paired catchment m... more Streamflow and its storm-flow elements in four catchments were analyzed by the paired catchment method for a response to fire. Prior to burning two of the catchments were vegetated with over-mature fynbos (the indigenous scrub vegetation of the southwestern Cape, South Africa), one was afforested with Pinus radiata and the fourth with Eucalyptus fastigata. One of the fynbos catchments was
The longer-term effects of afforestation with Pinus radiata and Eucalyptus grandis on streamflows... more The longer-term effects of afforestation with Pinus radiata and Eucalyptus grandis on streamflows were analyzed using data from two paired-catchment experiments in South Africa. The experiments are rare in that they have been maintained over longer periods than the typical rotation period for industrial timber plantations in the tropics or subtropics. In both experiments the planting treatments led to large reductions in streamflow, which increased with the age of the trees and were positively related to water availability. The pine plantation caused peak reductions in yield over a 5-year period of 44 mm a À1 or 7.7% a À1 for each 10% of catchment planted when the trees were between 10 and 20 years old. The eucalypt plantation caused peak reductions over a 3-year period of 48 mm a À1 and 10% a À1 for each 10% of catchment planted. However, as the plantations matured (over 30 years of age in the case of pines and over 15 years of age in the case of eucalypts) the flow reduction trend was reversed, and streamflow effects appear to be tending toward preafforestation levels. The longer-term effects of planted forests need not be as harmful on the water yield of catchments as has been predicted from shorter-term studies. The implication of these results is that if trees are grown on very long rotations, they may be used for restoring degraded catchments or as a means of storing carbon without completely denuding available water resources.
Changes in vegetation cover can significantly affect streamflow. Two common methods for estimatin... more Changes in vegetation cover can significantly affect streamflow. Two common methods for estimating vegetation effects on streamflow are the paired catchment method and the time trend analysis technique. In this study, the performance of these methods is evaluated using data from paired catchments in Australia, New Zealand, and South Africa. Results show that these methods generally yield consistent estimates of the vegetation effect, and most of the observed streamflow changes are attributable to vegetation change. These estimates are realistic and are supported by the vegetation history. The accuracy of the estimates, however, largely depends on the length of calibration periods or pretreatment periods. For catchments with short or no pretreatment periods, we find that statistically identified prechange periods can be used as calibration periods. Because streamflow also responds to climate variability, in assessing streamflow changes it is necessary to consider the effect of climate in addition to the effect of vegetation. Here, the climate effect on streamflow was estimated using a sensitivity-based method that calculates changes in rainfall and potential evaporation. A unifying conceptual framework, based on the assumption that climate and vegetation are the only drivers for streamflow changes, enables comparison of all three methods. It is shown that these methods provide consistent estimates of vegetation and climate effects on streamflow for the catchments considered. An advantage of the time trend analysis and sensitivity-based methods is that they are applicable to nonpaired catchments, making them potentially useful in large catchments undergoing vegetation change.
Research results on the effects of land cover change on water resources vary greatly and the topi... more Research results on the effects of land cover change on water resources vary greatly and the topic remains controversial. Here we use published data worldwide to examine the validity of Fuh's equation, which relates annual water yield (R) to a wetness index (precipitation/potential evapotranspiration; P/PET) and watershed characteristics (m). We identify two critical values at P/PET=1 and m=2. m plays a more important role than P/PET when m<2, and a lesser role when…
... South-western Cape Forestry Areas? AJArmstrong1 , HJ van Hensbergen&amp;#x27;, DF Scott&a... more ... South-western Cape Forestry Areas? AJArmstrong1 , HJ van Hensbergen&amp;#x27;, DF Scott&amp;quot; and SJ Milton3 ... The forest is also an &amp;quot;inhospitable sea&amp;quot; for the rodent species, but not to all the ant species, recorded in the fynbos &amp;quot;islands&amp;quot; (Midgley and Bond, 1990). ...
Changes in vegetation cover can significantly affect streamflow. Two common methods for estimatin... more Changes in vegetation cover can significantly affect streamflow. Two common methods for estimating vegetation effects on streamflow are the paired catchment method and the time trend analysis technique. In this study, the performance of these methods is evaluated using data from paired catchments in Australia, New Zealand, and South Africa. Results show that these methods generally yield consistent estimates of the vegetation effect, and most of the observed streamflow changes are attributable to vegetation change. These estimates are realistic and are supported by the vegetation history. The accuracy of the estimates, however, largely depends on the length of calibration periods or pretreatment periods. For catchments with short or no pretreatment periods, we find that statistically identified prechange periods can be used as calibration periods. Because streamflow also responds to climate variability, in assessing streamflow changes it is necessary to consider the effect of climate in addition to the effect of vegetation. Here, the climate effect on streamflow was estimated using a sensitivity-based method that calculates changes in rainfall and potential evaporation. A unifying conceptual framework, based on the assumption that climate and vegetation are the only drivers for streamflow changes, enables comparison of all three methods. It is shown that these methods provide consistent estimates of vegetation and climate effects on streamflow for the catchments considered. An advantage of the time trend analysis and sensitivity-based methods is that they are applicable to nonpaired catchments, making them potentially useful in large catchments undergoing vegetation change.
This article may be used for research, teaching, and private study purposes. Any substantial or s... more This article may be used for research, teaching, and private study purposes. Any substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to anyone is expressly forbidden. The publisher does not give any warranty express or implied or make any representation that the contents will be complete or accurate or up to date. The accuracy of any instructions, formulae, and drug doses should be independently verified with primary sources. The publisher shall not be liable for any loss, actions, claims, proceedings, demand, or costs or damages whatsoever or howsoever caused arising directly or indirectly in connection with or arising out of the use of this material.
The reductions in streamiIow following the afforestation of grassland with Eucalyptus grands and ... more The reductions in streamiIow following the afforestation of grassland with Eucalyptus grands and Pinus pun& in the Mokobulaan research catchments on the Mpumalanga escarpment, and the subsequent response in streamflow to cleat-felling of the eucalypts are presented. Afforestation with eucalypts of an entire catchment with a virgin annual runoff of 236 mm, caused a statistically significant decrease in streamflow in the third year after planting and the stream dried up completely in the ninth year after planting. The eucalypts were clearfelled when 16 years old but full perennial streamflow did not return until five years later. Afforestation with pines of an entire catchment with a virgin annual runoff of 217 mm, produced a significant decrease in streamflow in the fourth year after planting and caused the stream to dry up completely in the twelfth year after planting. The drying up of the streams was not altogether surprising as the annual runoff was lower than the expected reductions owing to complete afforestation. The delayed return of streamflow in the clearfelled catchment is surprising though, and is attributed to the desiccation of deep, soil-water stores by the eucalypts. These stores had to be replenished before the streams could return to normal behaviour. Q 1997 Elsevier Science B.V.
A wild®re in an aorested research catchment presented the rare opportunity to compare the hydrolo... more A wild®re in an aorested research catchment presented the rare opportunity to compare the hydrological eects of wild®re with the eects of clearfelling in the same catchment in the Jonkershoek Valley, in the southwestern Western Cape Province of South Africa. The timber plantation, which occupies 57% of the 2 km 2 catchment, had been clearfelled and replanted to Pinus radiata roughly ®ve years before the ®re. The eects of the two treatments on total¯ow, stormow and quick-¯ow volumes, peak discharge and storm response ratio were determined by means of multiple regression analysis, employing the dummy variable method to test for the signi®cance of treatments. Both clearfelling and wild®re caused signi®cant increases in all the stream-¯ow variables analysed. But the clearfelling eect was dominated by large increases in total¯ow (96% over three years), of which storm-¯ow and quick-¯ow volumes formed only minor parts. After the wild®re, by contrast, increases in total¯ow were small (12%) but the storm¯ow increases were three-to fourfold in the ®rst year and roughly double in the second year. The wild®re caused ®re-induced water repellency in the soils which led to overland¯ow on mid-slope sites, where soil in®ltrability normally far exceeds local rainfall intensities. It is argued that these results support the hypothesis that stream-¯ow generation processes were changed by the wild®re in that overland¯ow made a direct contribution to storm¯ows, but that clearfelling had no such eect.
The paired catchment method was used to test for the effects of thinning on the water yield in th... more The paired catchment method was used to test for the effects of thinning on the water yield in three afforested catchments in South Africa, namely, Biesievlei, Jonkershoek, 98% afforested with Pinus rudiutu (three thinnings); Westfalia catchment D, 100% afforested with EucuEyptlrs grandis (two thinning& and Cathedral Peak CII that was 74% afforested with Pinus purulu (one thinning). During and after two separate thinning& each of which removed roughly one third of the stems in a maturing P. rudiutu plantation in the Biesievlei catchment, annual streamflow increased by between 10 and 71% (19-99 mm). These increases persisted for three and two years after the thinning, respectively. A final thinning in the same catchment removed only 22% of stems at an age of 28 yr. The following years (1977 and 1978) were wetter than average, and reductions in annual streamflow of 26 and 55% were recorded in these two years. At Westfalia catchment D and Cathedral Peak CII, the hydrological trends were entirely dominated by the rapidly declining streamflow caused by the developing E. grandis and P. putt&z plantations respectively. Any savings in water use that may have resulted from the thinning of these plantations were insufficient to affect the downward trend in annual streamflow. Thinnings may have had a minor effect of delaying or reducing the desiccation of these catchments but such effects could not be assessed due to natural variability and the limited resolution of the paired catchment method. The trends in total water yield from the catchments were generally mirrored in the dry season streamflow, and there were no strong indications that thinning effects are linked to a particular season.
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Books by David F Scott
species of them, occupying 3.5 billion hectares worldwide, including 250 million ha of commercial
plantations. While forests can provide tremendous environmental, social, and economic benefits to
nations, they also affect the hydrologic cycle in different ways. As the demand for water grows and
local precipitation patterns change due to global warming, plantation forestry has encountered an
increasing number of water-related conflicts worldwide.
This document provides a country-by-country summary of the current state of knowledge on the
relationship between forest management and water resources. Based on available research
publications, the Editor-in-Chief of this document contacted local scientists from countries where
the impact of forest management on water resources is an issue, inviting them to submit a chapter.
Papers by David F Scott
species of them, occupying 3.5 billion hectares worldwide, including 250 million ha of commercial
plantations. While forests can provide tremendous environmental, social, and economic benefits to
nations, they also affect the hydrologic cycle in different ways. As the demand for water grows and
local precipitation patterns change due to global warming, plantation forestry has encountered an
increasing number of water-related conflicts worldwide.
This document provides a country-by-country summary of the current state of knowledge on the
relationship between forest management and water resources. Based on available research
publications, the Editor-in-Chief of this document contacted local scientists from countries where
the impact of forest management on water resources is an issue, inviting them to submit a chapter.