湘南丘陵区林下间种作物生产量与泥沙流失量的关系研究

通过对湘南丘陵区林下间种农作物和泥沙量的定位测定研究，分别对林下间种的花生、油菜的覆盖度与输沙率和花生、油菜各组成部分的生产量与泥沙量的关系进行了探讨，并建立了林下间种花生、油菜覆盖度的动态变化与输沙率的关系式和花生，油菜各种组成部分生产量对泥沙流失量影响的关系式。     

湘南丘陵幼林林下植被覆盖对土壤侵蚀的影响

为削减缓坡梯土幼林地的水土流失,设立１０００ｍ＾２迳流小区,进行定位观测。探讨了植被覆盖对板栗幼林林地土壤侵蚀的影响。丘陵红壤区域开垦的缓坡梯地是绿化达标后泥沙的主要来源地,在无植被覆盖条件下,年土壤侵蚀蚀量可达６．４７７８ｔ／１０００ｍ＾２。植被覆盖能很好的削减土壤侵蚀量,种植面积为２４．２％－５８．４％时,年土壤侵蚀量可减少３５．４９％－５７．５５％,迳流系数平均减少２４．０９％,输沙率平均减少４０．０２％,覆盖度每增加０．１则输沙率减少０．００１９－０．００２７。加大幼林地地面植物覆盖面积和覆盖速度,是控制水土流失的有效途径,油－花生套种或连种是一保土功能很好的模式。     

红壤丘陵防护林幼林林分结构水土流失规律的研究

在红壤丘陵坡地上建立了16个迳流小区，在每个迳流场地设置不同林分结构类型，按随机区组设计。经过对各林分结构迳流场的前期定位观测，分析了各林分结构迳流与年降水的关系，从中得出的结论是：单纯以乔木树种、灌种或乔灌种的林分结构水土流失严重，以乔灌草配置的多层次林分结构保持水土较好，其次是乔草种林分结构类型。     

缓坡梯土幼林林下植被覆盖与水土流失

为了探讨南方丘陵缓坡梯土上经济林幼林林地的水土流失及植被覆盖的防蚀保土效果,采用设立1 000 m2径流小区定位观测和人工模拟测定相结合的方法,测定和研究了植被覆盖和生物地埂模式对板栗幼林林地土壤侵蚀的影响.结果表明(1)在无植被覆盖条件下,当年降水量为1 638.2 mm时,丘陵红壤区域开垦的缓坡梯地的年土壤侵蚀量可达6.48 kg/m2;(2)林下间种能很好的削减土壤侵蚀量,如当花生、油菜种植面积与林地面积的比分别为24.2%、31.5%至44.9%、58.4%时,年土壤侵蚀量可减少35.49%～57.55%,径流系数平均减少9.04%,输沙率平均减少40.02%,作物覆盖率每增加10%则输沙率减少0.001 9～0.002 7;(3)农林复合经营区的生物保土埂具有明显的拦截泥沙的作用,可减少径流含沙量17.07%,花生、油菜套种或连种模式及萱草、白茅生物地埂是南方丘陵缓坡梯土幼林地上的几种保土效果好的生物保土模式.     

植被恢复与重建过程中小流域降雨及水沙变化特征研究

以女儿寨小流域为研究对象，着重研究了植被恢复与重建过程中小流域系统的降雨和水沙变化特征，并对植被恢复过程中的总体减沙水平做了分析。结果表明：①受大气环流的影响，小流域年际降雨量差异较大；小流域降雨年内时间分布极为不均，集中性很大，主要集中在汛期（4-8月），但年内降雨量的月间分布趋势基本一致。②小流域迳流年际变化很大，迳流年内分配不均。迳流集中是该小流域迳流变化的一个显著特征：小流域的植被恢复与重建对洪峰的出现和洪峰流量具有明显的延缓和削减作用。③径流（Qi）主要来源于降水（Pi），二者呈明显的一元线型关系：Pi=115．7678＋2．7386Qi。④小流域的年输沙模数与年迳流量的变化规律基本一致，小流域年内产沙也高度集中，且与降水、迳流关系密切，小流域的土壤侵蚀主要由汛期的强降水引起。⑤随着小流域大面积、高标准的生态环境建设，1990年至2004年间小流域的输沙模数呈锐减之势，植被恢复与重建起到了显著的减沙效应。     

福建长汀河田水土流失地区的迳流试验及类芦的绿化效果分析

在福建长汀河田水土流失地区建立迳流小区，进行迳流试验研究，并以优良乡土草种——类芦为主栽草种进行快速绿化，以迳流试验分析其水土流失治理效果。经过两年的试验，获得了可靠的数据，收到了明显效果，类芦生长旺盛，植被覆盖率达90％以上，使治理区地表年迳流量减少31．2％，土壤年侵蚀量减少52％，严重的水土流失现象基本得到控制，生物多样性明显增加，绿化效果显著。类芦在水土流失地区的推广应用前景广阔。     

森林保持水土作用的定量观测（Ⅱ）

2 对地表径流的抑制作用林地内的地表迳流,是在降雨量超过渗透能力的情况下产生的,一般林地的渗透能力较大,很少发生地表径流,但在降暴雨时也可能发生.测定地表迳流是在迳流试验区里进行的,如上述对设置在枥木县下矢板营林署(采尺)迦丘国有林的山毛榉天然林及其采伐迹地和邻近的高原山县有林的扁柏人工林的迳流试验区.进行了迳流测定的试验.在宽为5.3米.坡面长为10米(坡度各为28°、32°、31°)的迳流区.连续两个夏季(5—11月)对地表迳流量的测定结果是,两个夏季合计降雨量为2900mm,其地表迳流     

不同间作模式对油茶幼林树体生长的影响

为寻求油茶幼林林下经济作物高效间作模式,对花生、大豆、黄菊这3种经济作物进行油茶幼林林下间种试验,并对油茶幼树树体生长指标进行测定分析。结果表明:采用油茶幼林林下间种均能有效促进油茶幼树树体的生长,其影响顺序分别为间种花生间种黄菊间种大豆,建议推广油茶幼林间种花生模式。     

间种对油茶幼林生长的影响及效益分析

选用黄豆、花生、红薯和烟叶4种农作物于油茶幼林内进行间作,研究不同间种模式对油茶幼树树体生长的影响,并对间种不同经济作物的油茶幼林林地经济效益进行分析。结果表明:间种可促进油茶幼林的生长,其中间种黄豆效果最好,树高增加了0.11 m,地径增加了0.04 cm,冠幅增加了0.21 m~2,花芽数增加了20个/枝。间种可增加油茶幼林的经济效益,其中间种烟叶效益最高,经济产出为48 960元/hm~2。综合来看,油茶幼林间种的经济作物宜选择较矮小、具根瘤固氮菌的花生、黄豆。     

不同间作模式对油茶幼林生长的影响

对不同间种模式(间种黄豆、西瓜、花生、松苗和不间种)油茶幼林的生长量情况进行分析比较得出,油茶新造林以间作花生和松苗较好,但是有间作植物的油茶林的成活率及生长量均低于未间作的油茶纯林。     

Impact of vegetation restoration on hydrological processes in the middle reaches of the Yellow River, China

Sediment discharge from the Yellow River originates mainly from the drainage area between Hekouzhen and Longmen, i.e., the Helong area. Spatial-temporal variations of the vegetation cover in this area during the 1981–2007 period have been investigated using GIMMS and SPOT VGT NDVI data. We have also analyzed the interannual variations in vegetation cover and changes in annual runoff and sediment discharge, the consequences from precipitation change and the Grain for Green Project (GGP). The results show that vegetation cover of the Helong area has increased during the 1981–2007 period. The northwestern part the Helong area, where the flat sandy lands are covered by grass, has experienced the largest increase. The region where the vegetation cover has declined is largely found in the southern and southeastern Helong area, which is a gullied hilly area or forested. Although precipita-tion was relatively low during the 1999–2007 period, the vegetation cover showed a significant increase in the Helong area, due to the implementation of the GGP. During this period, the most significant improvement in the vegetation cover occurred mainly in the gullied hilly areas of the Loess Plateau, such as the drainage basins of the Kuyehe and Tuweihe rivers and the middle and lower reaches of the Wudinghe and Yanhe rivers. A comparison of the average annual maximum NDVI between the earlier (1998–2002) stage and the next five years (2003–2007) of the GGP indicates that the areas with increases of 10% and 20% in NDVI account for 72.5% and 36.4% of the total area, respectively. Interannual variation of annual runoff and sediment discharge shows a declining trend, especially since the 1980s, when the decrease became very obvious. Compared with the 1950–1969 period, the average runoff during the 1980–2007 period was reduced by 34.8×108 m3 and the sediment discharge by 6.4×108 t, accounting for 49.4% and 64.9% of that in the 1950–1969 period, respectively. There is a positive correlation between the annual maximum NDVI and annual runoff and sediment discharge. This correlation was reversed since the implementation of the GGP in 1999 and vegetation cover in the He-long area has increased, associated with the decrease in runoff and sediment discharge. Less precipitation has been an important fac-tor driving the decrease in runoff and sediment discharge during 1999–2007. However, restoration and improvement of the vegetation cover may also have played a significant role in accelerating the decrease in annual runoff and sediment discharge by enhancing evapotranspiration and alleviating soil erosion.     

Characteristics of runoff and sediment generation of forest vegetation on a hill slope by use of artificial rainfall apparatus

We studied the impact of forest vegetation on soil erosion,surface runoff, and sediment generation by using field simulated rainfall apparatus. We measured runoff and sediment generation of five 4.5 × 2.1m runoff plots (a bare soil as a control; two Pinus tabulaeformis forestplots and two Platycladus orientalis forest with row spacing of 1 m × 1m and 1.5 m × 1.5 m, respectively) in Beijing Jiu Feng National ForestPark under three rainfall intensities (0.42, 0.83, 1.26 mm per minute).Forest vegetation significantly reduced soil erosion and sediment yield.Mean total runoff volume in the four tree stand plots was 93% of that inthe control plot, demonstrating the limited effectiveness of forest vegetation in runoff control. With increasing rainfall intensity, runoff reductionin forest plots declined from 28.32% to 2.1%. Similar trends in runoff coefficient and the relationship between runoff volume and rainfall duration was observed. Mean total sediment yield and mean sediment yield reduction rate under different treatments was 55.05% and 43.17% of those in the bare soil control plot, respectively. Rainfall intensity playedan important role in runoff and sediment generation processes, and had agreater impact on runoff than on soil erosion and sediment generation.When considering several factors in runoff and sediment transport processes, the P. tabulae form plot with row spacing at 1 × 1 m had a greater effect on soil and water conservation than did other forested plots.     

Prescribed burning of Pinus oocarpa in Honduras I. Effects on surface runoff and sediment loss

The effects of low-intensity prescribed burning on surface runoff and sediment loss were studied in a stand of oocarpa pine (Pinus oocarpa Schiede) in central Honduras. The effects of burning in two seasons were compared on small paired plots on 10°, 25° and 40° slopes. Over a period of almost 2 years, mean percent runoff was 1.73% on the control plots and 5.03% on the burned plots. Mean sediment loss during the same period was 80 kg ha^?1 on the control plots and 1732 kg ha^?1 on the burned plots. The relationship between slope and surface runoff and sediment loss was negative; the effect of slope being masked by variation of other site factors. Recovery from burning was rapid and is attributed to the rapid rate of recovery of the ground vegetation of grasses and forbs which are adapted to frequent burning. Surface runoff and sediment loss on control plots were very low and the increases caused by burning are considered an acceptable alternative to the exposure of the overstory and site to the high risk of wildfires in accumulated fuels. Greater runoff and sediment loss were recorded on the plots burned in February than on those burned in June. As the period November to mid-February offers the greatest number of days with weather conditions suitable for low-intensity prescribed burning, it is concluded that burning for hazard reduction should be conducted as early as possible in this period, in November and December, to permit greater recovery of the ground vegetation before the heavy rains of May and early June.     

Prescribed burning of Pinus oocarpa in Honduras II. Effects on nutrient cycling

The effects of prescribed burning on nutrient cycling were studied in a stand of oocarpa pine (Pinus oocarpa Schiede) in central Honduras. Small paired runoff plots were subjected to a low-intensity prescribed burn in one of two seasons and nutrient losses in runoff water and sediment were monitored together with nutrient inputs in bulk precipitation.Burning increased the loss of nutrients and net losses of calcium, potassium and magnesium were recorded during the first $\text{16}\text{1}\text{2}$ months after burning. Increased rates of sediment loss rather than increased losses in surface runoff were responsible for the greater part of the increase in total nutrient losses from the burned plots. Greater quantities of nutrients were lost from the plots burned just prior to the dry season than from those burned after the start of the wet season because of slow recovery of the ground vegetation during the dry season and exposure to the intense rains of May and early June. Recovery from burning was rapid and runoff and sediment loss from the burned plots approached the levels of controls 2 years after burning. As nutrient losses are a reflection of total runoff and sediment losses, it is probable that no net nutrient losses would have been detected during the 2nd year after burning had sampling been continued. The net nutrient losses recorded were small and this is attributed to the low initial fuel loadings, low fire intensities and the rapid rate of recovery of the ground vegetation. The significance of other potential sources of losses and gains of nutrients is discussed and it is concluded that low-intensity prescribed burning for hazard reduction, with burning cycles ranging from three to seven or more years, will reduce the rate of nutrient accumulation on the site rather than deplete the nutrient capital.     

Effects of foliage and traffic intensity on runoff and sediment in skid trails after trafficking in a deciduous forest

After ground-based skidding operations, soil particles are rearranged closer together resulting in increased bulk density, reduced total porosity, and decreased infiltration capacity. The aim of the present study was to assess and quantify runoff and sediment in both leafed and leafless periods (foliage) over a 1-year duration following three levels of skidder traffic intensity (low, medium, high) performed in the Hyrcanian forests, Iran. By increasing traffic frequency, soil bulk density increased significantly, whereas total porosity decreased as compared to undisturbed (control) plots. After trafficking, runoff and sediment yield were significantly affected by foliage and traffic frequency. Regardless of foliage, mean total runoff and sediment increased with increasing traffic frequency performed on the skid trail. Mean runoff in the low, medium, and high traffic plots in the leafless period were 95.5, 54.2, and 21.7% higher than the values of runoff in the leafed period, respectively. Mean sediment yield in the low, medium, and high traffic plots in the leafless period was 7.1, 5.1, and 3.3 times higher than the values of sediment in the leafed period, respectively. Based on regression analysis, the runoff and sediment response to rainfall for the control plots and three traffic intensity classes were linear and statistically significant for both leafless and leafed periods. The total runoff in the high traffic intensity plot was 239.8 mm (62%) during the leafless period, and 38% of total runoff (148 mm) occurred during the leafed period. The sediment response to runoff over both leafless and leafed periods at all the traffic intensity classes and control plots were significantly linear. Restricting ground-based skidding operations to trail segments where the machine traffic is less than 4 (low)—9 (medium) traffic cycles can be effective to reduce runoff and sediment over compacted soil after machine-induced traffic.     

Factors affecting runoff and soil erosion: plot-level soil loss monitoring for assessing sustainability of forest management

The assessment on key ecological factors affecting runoff and soil erosion and the usefulness of plot-level monitoring of soil erosion was conducted by collecting runoff and soil loss records from 14 runoff plots. The runoff plots were set up in two catchments in Central Kalimantan, Indonesia, where conventional logging and Reduced Impact Logging (RIL) took place. Runoff plots were set up in forest areas with different levels of logging disturbances, i.e. harvesting areas (four plots), skid trails (six plots), and undisturbed/control areas (four plots). The magnitude of runoff and soil loss from skid trail plots were found to be the highest, followed by control plots and harvest plots. Canopy cover, sapling density, litter depth and woody debris appeared to be important ecological factors that determine the magnitude of soil loss. Tree canopy determines the size and erosive power of the raindrops. Sapling, litter layer, and woody debris protected soil surface, thus preventing soil detachment, and provided surface roughness that minimised soil particle movement down the slope. The roles of these ecological factors were less significant compared to rainfall in determining the magnitude of runoff.

Canopy cover, sapling density, litter depth and woody debris can be measured quantitatively or qualitatively without complicated equipment and methods. Furthermore, they are sensitive to logging disturbance which make them suitable verifiers of soil erosion. Forest managers need to limit disturbance to these factors in order to minimise soil erosion in their logging operation areas. Monitoring of soil loss using runoff plots was cost-effective and provided valuable information about soil erosion risks caused by logging operations. Runoff plots clearly demonstrated site disturbances where the plots are located. Monitoring allowed more direct linkages to be made between management practices and their impacts on runoff and soil erosion, thereby enabling forest managers to identify problems and take appropriate preventive measures to improve their management practices.     

Effects of forest harvesting on runoff and sediment characteristics in the Hyrcanian forests,northern Iran

Loss of canopy cover by forest harvesting generally increases the average surface runoff volume and sediment. Selective cutting (single and group selection method) is the most usual forest harvesting method in the Hyrcanian forests in the north of Iran. The purpose of this study is to find the effect of selective logging technique on the hydrological behavior of runoff and sediment in the Kheyrud forests located in northern Iran over 1 year. Four treatments were implemented: natural forest without harvesting (C), forest with selective harvesting (H) and area without canopy cover (WC) and skid trail (S). Three types of data were measured in each plot including soil chemical and physical properties, runoff and sediment load after each rainfall. The results indicate significant differences (P ≤ 0.05) in runoff generation and sediment production with respect to the treatments cover. The runoff in all treatments showed relatively similar response to rainfall, while the highest runoff and sediment were observed in skid trails, and the area without canopy cover (1.13 and 0.62 mm, and 1.2 and 0.51 g m^?2), averagely. In contrast, the natural forest without harvesting and the forest with selective harvesting treatments exhibited the lowest amounts of runoff (0.2 and 0.44 mm) and sediment (0.1 and 0.17 g m^?2), averagely. Implementation of low logging technique was useful to control the effects of logging on the runoff and sediment yield.     

紫色土丘陵区不同耕作模式土壤抗冲性对比分析

基于径流小区定位观测研究,分别研究紫色土丘陵区坡耕地不同耕作模式(横垄、顺垄、混合耕作)和不同土层(0～15 cm、15～30 cm)对土壤径流冲刷过程中径流含沙量及抗冲指数的变化特征的影响,以及影响因素的内在关系。研究结果表明:(1)在整个冲刷过程中,不同土层土壤表面径流泥沙流失量呈递减趋势,最后基本趋于稳定;(2)在整个冲刷过程中,径流泥沙流失量总体表现为0～15 cm土层>15～30 cm土层,这主要与土壤剖面特性有关,而农业耕作和根系的影响占次要地位;(3)在各种耕作模式中,抗冲指数的大小均表现为0～15 cm土层<15～30 cm土层,且后者分别是前者的2～3倍。