Effects of forest vegetation on runoff and sediment transport of watershed in Loess area, west China

This paper aims to study the effects of vegetation on runoff and sediment transport at the watershed scale, and to provide a theoretical basis for afforestation in the Loess area, in the nested Caijiachuan watershed, Jixian County, Shanxi Province of west China. Forest watersheds and farmland watersheds with similar terrain features were selected through cluster analysis to study their runoff and sediment transport characteristics. Results showed that compared with farmland watersheds, runoff generation time in forest watersheds was delayed remarkably, and peak flow was reduced greatly, which indicates that vegetation played an important role in holding and absorbing rainfall. Besides, with the increase of forest coverage, the runoff amount, runoff depth and runoff coefficient decreased during the rainy seasons. The runoff depth and runoff coefficient of farmland watersheds in the rainy season were 5–20-fold as much as that of forest watersheds, and runoff and sediment yield of watersheds with low forest coverage were 2.7–2.9-fold and 3–6-fold as great as those with high coverage during rainstorms, and low forest coverage had larger variation in sediment hydrograph. For the complexity and scale dependence of the influence of forest vegetation on runoff, forest hydrological functions based on regional scale or watershed scale were worthy of further studies. __________ Translated from Science of Soil and Water Conservation, 2006, 4(3): 48–53 [译自: 中国水土保持科学]     

The value of the flood control service of tropical forests: A case study for Trinidad

To date there have been only few case studies that specify how hydrological processes regulated by forests convey into benefits for society. The objective of this paper is to analyse the relation between forest cover and the reduction of flood risks on Trinidad. Our hypothesis is that the relation between forest cover and flood control is non-linear, in other words that deforestation of a watershed will increase flood risks in a non-linear way. This implies that the per hectare value of the hydrological service is determined in part by the remaining forest cover of the catchment. We find that this varies strongly between watersheds, between 16 and 268 US $ per hectare per year. Our results demonstrate a non-linear relationship between catchment's forest cover and the generation of the flood control service, and indicate that even small levels of deforestation can lead to a significant increase in flood risks in Trinidad.     

Long-term influence of stream water chemistry in Japanese cedar plantation after clear-cutting using the forest rotation in central Japan

Because both natural and anthropogenic disturbances affect biogeochemical cycles in forest ecosystems, monitoring is needed to separate their influences. Chronosequence is very useful for such studies. In our study area, plantation through forest rotation on a watershed basis resulted in more than 40 adjacent watersheds of between 0 and 87 years of stand age, kind of chronosequence. Here, we examined the biological similarity of the watersheds and the long-term effects of clear-cutting on stream water chemistry. The stream water NO₃⁻–stand age relationship was similar between the two observation years; stream water NO₃⁻ concentrations increased dramatically in the watersheds after clear-cutting and decreased in 7–10-year-old replanted watersheds. The slope of stream water NO₃⁻ concentrations between the different watersheds covered by same age stand was significant, at 1:1. Additionally, stream water NO₃⁻ concentrations were more strongly correlated between the different watersheds covered by same aged stand than between the observations at 4 years intervals within a watershed. These findings indicate that stream water NO₃⁻ concentration is mainly regulated by stand age, i.e., by vegetation regrowth, rather than watershed-specific characteristics. Hence, adjacent watersheds are biologically similar apart from stand age and can be regarded as a chronosequence. While there was a clear relationship between stream water NO₃⁻ concentration and stand age, there was significant correlation with stream water SO₄²⁻, Ca²⁺, Mg²⁺, Cl⁻ or Na⁺ between two observations in the same watershed. This indicates that watershed-specific characteristics, rather than vegetation regrowth, control stream SO₄²⁻, Ca²⁺, Mg²⁺, Cl⁻, and Na⁺ concentrations. After 25 years of clear-cutting Ca²⁺, Mg²⁺ and Na⁺ concentrations significantly increased. It is likely the contribution of forest floor accumulation with stand development. Based on these results, clear-cutting influences stream chemistry, not only NO₃⁻, but also the major cation and the influence of clear-cutting continues for several decades at this study site.     

森林水文研究方法

森林水文研究方法，是以研究大气降水在森林流域中的水分循环为核心，提出系统的观测研究方法。包括：森林小流域的选择与布设，水量平衡场修建与观测，降水，下渗与渗透，蒸散发，土壤水分，森林流域径流，流域水文模型的模拟，水质测定等。本方法参考当代国内外现行的先进和实用的方法撰写而成，可供水文站，森林生态定位站应用和参考。     

Response of vegetation, shade and stream temperature to debris torrents in two western Oregon watersheds

This study examines watershed patterns of riparian vegetation, shade, and stream temperature eight years after extreme storm events triggered numerous debris torrents throughout the Pacific Northwest. We examined twelve impacted streams in two western Oregon watersheds: the Calapooia River in the western Cascades and the Williams River in the Coast Range. Red alder (Alnus rubra) and willow (Salix spp.) were the dominant species on debris torrented areas in both watersheds. Post-disturbance vegetation recovery was significant in both watersheds, impacting shade and stream temperatures. However, red alder density, basal area, and height were significantly greater along streams in the Williams River watershed than along streams in the Calapooia River watershed. Willow density, basal area and height were similar between the watersheds. Stream shading levels mirrored red alder growth, with greater average shading in the Williams River watershed. The greater shade translated into lower summer maximum stream temperatures and maximum diurnal stream temperature fluctuations in the Williams River as compared to the Calapooia River watershed. Minimum stream temperatures were not different between the two watersheds. The rapid re-growth of red alder along the Williams River watershed ultimately lead to a rapid decline in maximum summer stream temperatures for that watershed compared to the Calapooia River watershed. The location where the disturbance occurred had an important role in determining the rate and pathway of stream recovery.     

Effects of reforestation on the hydrological function of a small watershed in the Three Gorges Reservoir Area

For vegetation communities with hydrological function in the Three Gorges Reservoir Area, the storm event distributed hydrological model Precipitation-Runoff Modeling System (PRMS)-Storm was built based on modular modeling system developed by the US Geological Survey, and was employed to study the effects of forests on peak flows in the Xiangshuixi forest watershed in the Three Gorges Reservoir Area. The results showed that: 1) this simulation study suggested that PRMS-Storm can meet the second level national flood prediction standards of China for simulating storm events of small forest watersheds, and can issue flood forecasting; 2) hydrological functions of different vegetation communities were evaluated, and three simulation scenarios were arranged: mixed conifer-broadleaf forests (scenario 1), broad-leaved forests (scenario 2), and general forests arrangement (scenario 3); 3) the well-arranged forest scenarios can reduce over 20% of surface runoff, result in an increase of over 16% in subsurface flow, and decrease peak flow by 20.8%, 9.6%, and 18.9%, respectively. The reduction of peak flow rates was significant when rainfall peak was higher than 0.8 mm/min, especially for short-term rainfall events. In general, we found that scenarios 1 and 3 were preferable for reducing peak flow rates and volumes in the reforestation practices in the study region, and scenario 1 was better than scenario 3, so the mixed conifer-broadleaf forests had the best hydrological function. __________ Translated from Journal of Beijing Forestry University, 2006, 28(5): 42–51 [译自: 北京林业大学学报]     

分布式水文模型在森林水文学中的应用

在探讨森林水文模型发展历史的基础上,着重分析了分布式水文模型的理论基础,类型和特点,与传统的集总式模型相比,分布式水文模型考虑了流域内部各地理要素的空间异质性,可以反映流域内部水文过程的时空变化,从而更加准确地预测自然和人为因素对流域水资源和水环境的影响,为流域的科学管理提供可的决策依据,景观生态学可以作为分布式模型进一步发展的理论基础,地理信息系统（ＧＩＳ）技术可分为分布式模型的实现技术支持,在     

Native forest (Caatinga) watershed management for runoff inducement for irrigation

The results of hydrological investigations for two years on eight levels of native forest (Caatinga) watershed management, principally for runoff inducement for water harvesting for irrigation, are reported. The first four watershed treatments consisted of one or a combination of intensified surface drainage treatments within native forest watershed, clearing alternate contour strips of native forest at 25-cm vertical intervals while alternate strips are maintained in native cover, constructing narrow-based channel terraces below cleared strips and application of common salt in cleared strips for impermeabilization of the soil. The next three watershed treatments are without native forest and the eight (the last) watershed is maintained undisturbed under native forest cover as a control treatment.In the arid zones of the Northeast of Brazil, the combination of (i) clearing alternate strips of Caatinga with alternate virgin strips about 30 m wide at 25-cm vertical interval on gently sloped watersheds and (ii) the construction of narrow based channel terraces, can make available for irrigation about 5–11% of the incident rainfall. At the same time this combination helps conserve soil and natural forest ecosystems.     

Analysis of soil moisture variation by forest cover structure in lower western Himalayas, India

Soil moisture affects various hydrological processes, including evapotranspiration, infiltration, and runoff. Forested areas in the lower western Himalaya in India constitute the headwater catchments for many hill streams and have experienced degradation in forest cover due to grazing, deforestation and other human activities. This change in forest cover is likely to alter the soil moisture regime and, consequently, flow regimes in streams. The effect of change in forest cover on soil moisture regimes of this dry region has not been studied through long term field observations. We monitored soil matric potentials in two small watersheds in the lower western Himalaya of India. The watersheds consisted of homogeneous land covers of moderately dense oak forest and moderately degraded mixed oak forest. Observations were recorded at three sites at three depths in each watershed at fortnightly intervals for a period of three years. The soil moisture contents derived from soil potential measurements were analyzed to understand the spatial, temporal and profile variations under the two structures of forest cover. The analysis revealed large variations in soil moisture storage at different sites and depths and also during different seasons in each watershed. Mean soil moisture storage during monsoon, winter and summer seasons was higher under dense forest than under degraded forest. Highest soil moisture content occurred at shallow soil profiles, decreasing with depth in both watersheds. A high positive correlation was found between tree density and soil moisture content. Mean soil moisture content over the entire study period was higher under dense forest than under degraded forest. This indicated a potential for soil water storage under well managed oak forest. Because soil water storage is vital for sustenance of low flows, attention is needed on the management of oak forests in the Himalayan region.     

黄土高原和六盘山区森林面积增加对产水量的影响

[目的]定量评价黄土高原地区造林对流域产水量的影响,指导林水协调的林业发展和森林管理。[方法]综合分析多年在黄土高原、泾河流域、六盘山区开展的森林产流影响的多尺度研究结果。[结果]在黄土高原区域尺度,林地平均年径流(16 mm)比非林地(39 mm)减少59%;在典型流域尺度(泾河干流上游流域),森林年均产水量(76 mm)比自然草地减少51%,其中,半湿润土石山区的森林年均产水量(88.8 mm)比自然草地减少58%;在典型小流域尺度(半湿润的香水河小流域),完全覆盖森林后的年均产流比无森林覆盖情景减少59%。森林增加导致的年产流减幅在干旱地区和干旱年份会更大,并可能超过100%,如年降水量低于450 mm的黄土流域、半干旱的泾河上游黄土区的林地及半干旱的叠叠沟小流域的坡面乔木林分样地,其年产水量常为零或负值,即需消耗土壤水分和坡上汇入径流等维持生存。低度间伐不能显著减少森林蒸散耗水。[结论]在黄土高原研究的小流域、流域和区域空间尺度内,造林减少年产流量的平均幅度都在50%~60%以上,且随干旱程度的增加可达到100%,并因消耗降水外的其他水源而出现负产流。需依据水分承载力合理选择待恢复植被类型和确定森林覆盖率,这是保障区域供水安全和实现林水协调管理的基本途径。     

Concentrated flow paths in riparian buffer zones of southern Illinois

Riparian buffers in agricultural landscapes should be designed to trap pollutants in overland flow by slowing, filtering, and infiltrating surface runoff entering the buffer via sheet flow. However, observational evidence suggests that concentrated flow is prevalent from agricultural fields. Over time sediment can accumulate in riparian buffers forming berms that restrict sheet flow; these berms ultimately back up surface runoff, resulting in an eventual breakthrough that concentrates overland flow. This study examines the occurrence of concentrated flow paths (CFPs) in riparian buffers at both the field and watershed scale. At the field scale, intensive topographic surveys were conducted at ten field sites in southern Illinois. To assess the prevalence of CFPs at the watershed scale, three watersheds in southern Illinois were selected for walking stream surveys along randomly selected 1,000 m reaches. CFPs were identified in all topographic surveys and all walking stream surveys. Among field sites, concentrated flow accounted for 82.5–100% of the drainage leaving the agricultural fields. Sediment berm accumulation was identified at all field sites and was positively correlated with CFP size. At the watershed scale, CFPs were more abundant in agricultural areas compared to forested land. Results from this study indicate that concentrated flow was prevalent across all study sites at both the field and watershed scale. Thus, surface water quality may suffer in areas with poorly functioning buffers, and managers must consider the occurrence of CFPs when designing and maintaining riparian buffers to protect stream water quality.     

Effects of discharge level on the load of dissolved and particulate components of stream nitrogen and phosphorus from a small afforested watershed of Japanese cypress (<Emphasis Type="Italic">Chamaecyparis obtusa</Emphasis>)

The behavior of dissolved and particulate components of stream nitrogen (N) and phosphorus (P) were measured for 2 years in a small mountainous watershed covered primarily with a plantation forest of Japanese cypress (Chamaecyparis obtusa). The load of dissolved N and P bore a consistent relationship to discharge while the load of particulate N and P varied by up to two orders of magnitude at a given discharge level. Most N was exported in a dissolved form (DN) while most P was exported in a particulate form (PP), which bears similarity to loads from agricultural watersheds. Owing to the different behaviors of DN and PP, changes in the total nitrogen (TN) load were primarily attributed to variations in discharge unlike changes in the total phosphorus (TP) load. High flow conditions, resulting from heavy rainfall, displayed PP release significantly larger than expected. The TP load in high flow conditions was severely underestimated using a regression equation expressed as a function of discharge, which was based on the weekly sampling data biased toward low flow conditions. In addition, the TN load during peak discharges in heavy rain events was underestimated by the regression equation because of unpredictable increases in the particulate component. Our study shows that the particulate component ratio determines whether discharge can explain changes in load regardless of chemical species. The results suggest that plantation forests in rainy regions can be a diffuse source of particulate nutrients depending on soil surface conditions.     

森林流域水文过程研究进展

指出了森林水文循环是森林联系气候对森林生态系统产生时空变化影响的重要因子。森林水文过程的研究以流域尺度为大多学者研究所接受,但如何正确地描述或者评价森林生态水文过程对于准确理解流域生态系统水循环及其对全球气候变化响应机制是其基础性关键。基于此,总结归纳了前人成果,以流域尺度森林水文过程的几个关键过程(林冠截留、蒸散、土壤蓄渗及径流)为基点,梳理了4个过程的衡量理论及方法,并提出了建立模型、水文过程的参数修正、结合GIS等技术进行流域尺度的模拟以及结合氢氧同位素技术对森林水文过程的溯源刻画将是正确理解森林流域水文过程机制的发展趋势,但现今仍存在如何将流域尺度外推于区域尺度乃至全球尺度这一科学问题。     

Assessment of ecosystem services as an opportunity for the conservation and management of native forests in Chile

This paper quantifies two important native forest ecosystem services in southern Chile: water supply and recreational fishing opportunities. We analyzed streamflow in relation to forest cover in six watersheds located in the Valdivian Coastal Range (39°50′–40°05′S), the effect of forest management on streamflow in two watersheds in the Valdivian Andes (600–650 m of elevation; 39°37′S), and fish abundance as a function of forest cover in 17 watersheds located in the Coastal Range and the Central Depression (39°50′–42°30′S). We found that the annual direct runoff coefficient (quickflow/precipitation) and total streamflow/precipitation in the dry summer season were positively correlated with native forest cover in the watershed (R² = 0.67 and 0.76; ^*P = 0.045 and 0.027, respectively) during four years of observations. Conversely, a negative correlation was found between summer runoff coefficients (total streamflow/precipitation) and cover of Eucalyptus spp. and Pinusradiata plantations (R² = 0.84; ^*P = 0.010). We estimated a mean increase of 14.1% in total summer streamflow for every 10% increase in native forest cover in the watershed. The analysis of streamflow changes between two paired watersheds dominated by native secondary Nothofagus stands, one thinned with 35% of basal area removal and a control, showed that the former had a 40% increase during summer (four years of observations). The best correlation between fish abundance and forest cover was found between trout abundance (%) and secondary native forest area in 1000 m × 60 m stream buffers (R² = 0.65, ^***P < 0.0001). We estimated a 14.6% increase in trout abundance for every 10% increase of native forest cover in these buffers. Similar approaches to quantify forest ecosystem services could be used elsewhere and provide useful information for policy and decision-making regarding forest conservation and management.     

Managing watershed services of tropical forests and plantations: Can meta-analyses help?

The watershed services provided by tropical natural and planted forests are critical to human well-being. An increasing number of valuation studies and experiences with payment for ecosystem services have dealt with the role of ecosystems in regulating the flow of water. However, several studies and experiences have been based on misconceptions about the role of forests and plantations in the hydrological cycle, despite the publication of many reviews by hydrologists. The objective of this paper is to evaluate whether meta-analyses applied to studies comparing water flows in tropical watersheds under natural or planted forests and non-forest lands can provide useful results for valuing watershed ecosystem services and making decisions. The meta-analyses show significantly lower total flows or base flows under planted forests than non-forest land uses. Meta-analyses conducted with subsamples of the data also show lower total flow and higher base flow under natural forests than non-forest land uses. However, the available studies were restricted to humid climates and particular forest types (Pinus and Eucalyptus planted forests and lowland natural forests). The small number of available studies with sufficient original data is a major constraint in the application of meta-analyses. This represents a major technical challenge for valuation studies or payment for ecosystem services, especially in countries where financial resources for implementing field research are scarce.     

Response of selected water chemical quality parameters to slight thinning in a mature oak–beech forest ecosystem under sub-humid climate conditions

The objective of this study was to determine the effect of 18% thinning on streamflow nutrient flux from a mature oak–beech forest ecosystem by paired watershed approach. Two experimental watersheds including control (W-I) and treatment (W-IV) watersheds were used in the study. The experimental watersheds were monitored about 6 years from 2006 to 2011 for the calibration period and 4 years from 2012 to 2015 for the treatment period. The forest in the treatment watershed was thinned between October and December in 2011, and the forest in the control watershed was left untreated. Water grab samples were collected from the streams in the watersheds on weekly basis during both the calibration and treatment periods and analyzed for calcium (Ca²⁺), magnesium (Mg²⁺), Kjeldahl nitrogen (KN), sodium (Na⁺), potassium (K⁺), iron (Fe³⁺), aluminum (Al³⁺), ammonium nitrogen (NH₄ ⁺-N), and sulfate (SO₄ ²⁻). The simple linear regression equations were developed between mean monthly nutrient fluxes of two watersheds in the calibration period with significantly high correlation coefficients, and they were used to estimate nutrient fluxes from the treatment watershed during the treatment period as if thinning had not been applied. The changes in the monthly nutrient fluxes were estimated as the differences between measured and values calculated with the linear regression equations. Results showed that removal of 18% standing timber volume did not significantly change nutrient exports except for KN and Na⁺ from the treatment watershed.

     

Calcium addition at the Hubbard Brook Experimental Forest increases sugar storage, antioxidant activity and cold tolerance in native red spruce (Picea rubens)

In fall (November 2005) and winter (February 2006), we collected current-year foliage of native red spruce (Picea rubens Sarg.) growing in a reference watershed and in a watershed treated in 1999 with wollastonite (CaSiO(3), a slow-release calcium source) to simulate preindustrial soil calcium concentrations (Ca-addition watershed) at the Hubbard Brook Experimental Forest (Thornton, NH). We analyzed nutrition, soluble sugar concentrations, ascorbate peroxidase (APX) activity and cold tolerance, to evaluate the basis of recent (2003) differences between watersheds in red spruce foliar winter injury. Foliar Ca and total sugar concentrations were significantly higher in trees in the Ca-addition watershed than in trees in the reference watershed during both fall (P=0.037 and 0.035, respectively) and winter (P=0.055 and 0.036, respectively). The Ca-addition treatment significantly increased foliar fructose and glucose concentrations in November (P=0.013 and 0.007, respectively) and foliar sucrose concentrations in winter (P=0.040). Foliar APX activity was similar in trees in both watersheds during fall (P=0.28), but higher in trees in the Ca-addition watershed during winter (P=0.063). Cold tolerance of foliage was significantly greater in trees in the Ca-addition watershed than in trees in the reference watershed (P<0.001). Our results suggest that low foliar sugar concentrations and APX activity, and reduced cold tolerance in trees in the reference watershed contributed to their high vulnerability to winter injury in 2003. Because the reference watershed reflects forest conditions in the region, the consequences of impaired physiological function caused by soil Ca depletion may have widespread implications for forest health.     

五雷山生态公益林对小流域洪水过程的影响

以五雷山生态公益林区女儿寨小流域为研究对象,采用长期定位监测的方法,研究了生态公益林对小流域洪水过程的影响.结果表明:小流域洪水年的森林覆盖率Fi(％)与洪水滞后时间差Hi始(min)、洪峰滞后时间差Hi峰(min)、洪峰流量Wi峰(m3/s)均以一元线性关系藕合最为密切,Fi=a+bHi(始、峰)(Wi峰),a、b为...     

长江上游低山丘陵区小流域森林植被变化对径流影响分析

森林植被的变化可以调节森林水文过程。本文以广元市碗厂沟的5个小流域为研究对象,根据实测水位资料,分析了在植被恢复过程中流域径流的变化情况。结果表明:随着森林植被的不断恢复,(1)流域降水转化为径流的数量(即径流系数)降低;(2)在相同的雨量级与相似的雨强情况洪峰得到削弱,洪峰时间延长;(3)在相似的降雨历时的条件下洪水过程线历时增长。     

板桥河小流域防护林体系的水文效应研究

对乌江板桥河小流域防护林体系的水文效应进行 10年的定位监测 ,初步掌握了小流域的气候、水量分配情况 ,以及防护林体系建成对流域水文功能的影响。 10年来 ,小流域防护林体系对径流产生了明显的调节作用 ,洪峰径流量有所减少 ;林地的水量分配发生了一定的变化 ,林冠截留量和树干流有所增加 ,地表径流量减少 ;林地的地表径流系数仅为农地的5 3 3 % ;封山育林对改善次生植被的水文功能是非常有效的