近30年来小兴安岭地区生物量变化及地统计分析

以20世纪80年代、90年代、2000年以后三个时期的遥感数据和同期的森林资源清查样地数据为基础,应用遥感信息模型的方法,估算了小兴安岭地区森林生物量,并应用GIS和地统计相结合的方法,研究了小兴安岭地区20世纪80年代、90年代、2000年以后三个时期的森林生物量时空变化、空间自相关性和异质性.结果表明:研究区的生物...     

资源环境保护下天津市用地空间增长模拟

从资源承载和生态保护的角度预测城镇土地利用变化,是实现国土空间用途管制的客观需求。以典型缺水城市天津市为研究区,采用系统动力学模型预测土地利用规模、最小成本路径法构建生态廊道和FLUS模型模拟土地利用变化等方法,分别模拟自然扩张和资源环境保护情景下天津市2035年土地利用情况。结果表明：① 资源约束条件显著制约城镇人口和建设用地的超量发展,随着资源约束增强、科技发展增速,人口和建设用地增长量随之降低,城镇GDP保持稳定增长。② 天津市重要生态廊道以南北向联系为主,东部和北部生态廊道重要性较高,部分生态廊道由于路径较长或距离建设用地较近而面临被蚕食挤压的风险。③ 水体湿地在资源环境保护情境下面积略有增长,在自然扩张情境下则延续以往不可持续的发展模式,出现向草地退化的情况,部分生态源地和廊道受到耕地侵占和建设用地扩张的影响。④ 受交通发展和京津职住分离的影响,天津市城镇建设用地增长主要发生在蓟州、武清和宝坻区。此外,在资源环境保护情景下,中心城区和滨海新区增长率较低,津南区表现出较大发展潜力。以资源环境承载约束城镇扩张,能够为国土空间规划实践提供科学引导。     

结合小波包变换和随机森林的ASTER蚀变信息提取

为了更准确地提取蚀变信息,本文选择新疆、甘肃和内蒙古三省交界部位为研究区,结合小波包变换和随机森林提取ASTER蚀变信息.首先,选择主要蚀变类型的诊断性波段进行特征向量主成分分析,得到主分量影像;接着,对主分量影像进行小波包变换,使用代价函数选择最优小波包树,并提取高低频信息构造分类向量;然后,经过特征筛选构造随机森林...     

Snow disappearance timing is dominated by forest effects on snow accumulation in warm winter climates of the Pacific Northwest,United States

Forests modify snow processes and affect snow water storage as well as snow disappearance timing. However, forest influences on snow accumulation and ablation vary with climate and topography and are therefore subject to temporal and spatial variability. We utilize multiple years of snow observations from across the Pacific Northwest, United States, to assess forest–snow interactions in the relatively warm winter conditions characteristic of maritime and transitional maritime–continental climates. We (a) quantify the difference in snow magnitude and disappearance timing between forests and open areas and (b) assess how forest modifications of snow accumulation and ablation combine to determine whether snow disappears later in the forest or in the open. We find that snow disappearance timing at 12 (out of 14) sites ranges from synchronous in the forest and open to snow persisting up to 13 weeks longer in the open relative to a forested area. By analyzing accumulation and ablation rates up to the day when snow first disappears from the forest, we find that the difference between accumulation rates in the open and forest is larger than the difference between ablation rates. Thus, canopy snow interception and subsequent loss, rather than ablation, set up longer snow duration in the open. However, at two relatively windy sites (hourly average wind speeds up to 8 and 17 m/s), differential snow disappearance timing is reversed: Snow persists 2–5 weeks longer in the forest. At the windiest sites, accumulation rates in the forest and open are similar. Ablation rates are higher in the open, but the difference between ablation rates in the forest and open at these sites is approximately equivalent to the difference at less windy sites. Thus, longer snow retention in the forest at the windiest sites is controlled by depositional differences rather than by reduced ablation rates. These findings suggest that improved quantification of forest effects on snow accumulation processes is needed to accurately predict the effect of forest management or natural disturbance on snow water resources.     

Influence of forest and shrub canopies on precipitation partitioning and isotopic signatures

Over a 4‐month summer period, we monitored how forest (Pinus sylvestris ) and heather moorland (Calluna spp. and Erica spp.) vegetation canopies altered the volume and isotopic composition of net precipitation (NP) in a southern boreal landscape in northern Scotland. During that summer period, interception losses were relatively high and higher under forests compared to moorland (46% of gross rainfall [GR] compared with 35%, respectively). Throughfall (TF) volumes exhibited marked spatial variability in forests, depending upon local canopy density, but were more evenly distributed under heather moorland. In the forest stands, stemflow was a relatively small canopy flow path accounting for only 0.9–1.6% of NP and only substantial in larger events. Overall, the isotopic composition of NP was not markedly affected by canopy interactions; temporal variation of stable water isotopes in TF closely corresponded to that of GR with differences of TF‐GR being ?0.52‰ for δ²H and ?0.14‰ for δ¹⁸O for forests and 0.29‰ for δ²H and ?0.04‰ for δ¹⁸O for heather moorland. These differences were close to, or within, analytical precision of isotope determination, though the greater differences under forest were statistically significant. Evidence for evaporative fractionation was generally restricted to low rainfall volumes in low intensity events, though at times, subtle effects of liquid–vapour moisture exchange and/or selective transmission though canopies were evident. Fractionation and other effects were more evident in stemflow but only marked in smaller events. The study confirmed earlier work that increased forest cover in the Scottish Highlands will likely cause an increase in interception and green water fluxes at the expenses of blue water fluxes to streams. However, the low‐energy, humid environment means that isotopic changes during such interactions will only have a minor overall effect on the isotopic composition of NP.     

The effects of forest litter on snow energy budget in the Tianshan Mountains,China

Forest litter exerts an impact on the energy budget of snow surfaces, which lie beneath forest canopies. In this study, we measured shortwave and longwave radiation levels, as well as quantities of Asian spruce (Picea schrenkinan ) forest litter, over 3 snow study plots that representing an open environment, 20% forest canopy openness (20% FCO), and 80% forest canopy openness (80% FCO). The fractional litter coverage (lc ) was obtained through the binarization of digital photographs of forest litter. The effects of forest litter on snow surface albedo (α ), snow surface temperature (T _s ), upward shortwave and longwave radiation (K _↑ and L _↑), and sensible heat flux (H ) were then analyzed. According to our results, the energy budget over snow surface influenced by forest litter principally due to forest litter forcing α decrease and T _s increase. The effects of forest litter on the energy budget increased with time and lc . We found that forest litter exerted the most significant impact on K _↑ and L _↑ at daytime during the latter stages of the snowmelt period. The influence of forest litter on H was more apparent on windy days. The presence of forest litter increased gains in shortwave radiation and losses in longwave radiation and decreased gains in H . Compared to the simulated energy (K _↑ + L _↑ + H ) over a snow surface without litter, the calculated energy decreased by ?13.4 W/m² and increased by 9.0 W/m², respectively, at the 20% FCO and 80% FCO sites during the latter stages of the snowmelt period. Overall, forest litter facilitated snow surface energy gains at the 80% FCO site and impeded them at the 20% FCO site during the latter stages of the snowmelt period.     

Landslide detection using probability regression,a case study of Wenchuan,northwest of Chengdu

Landslides have become one of the dominant disasters all around the world. Reliable and efficient landslide mapping is playing a significant role in landslide studies. However, to the best of our knowledge, there is little research on detecting multiple landslides simultaneously from images to stimulate practical cases. In this work, we propose a regression model to detect landslides and investigate its applicability in practical cases. It synthesizes contextual, spectral and geometric features. Among the test images, F-measure of landslide detection has a range between 0.771 and 0.998, validating its robustness and high efficiency.     

How much water do Chilean forests use? A review of interception losses in forest plot studies

After several years of decreased annual rainfall and water shortages, the Chilean society is demanding that forest plantations take accountability of their role in consuming scarce water resources. Evidence has shown that interception losses are considerable when determining water production in watersheds. The aim of this study was to determine if site and stand variables explain interception losses by Chilean forests for the development of an empirical model that could predict the potential impacts of forest management practices and land‐use change. A total of 127 data from annual water balance plot studies in Chile were compiled to derive relationships between interception and precipitation, species composition, plantation age and other stand and site variables. The reviewed data indicated that annual interception losses are mainly explained by annual rainfall and basal area of the forest stands, with a clear difference between the northern (dryer) and southern (wetter) regions of Chile. For a wide latitudinal gradient, forest composition and age, annual interception accounted for approximately 21% of incoming precipitations. Broadleaved forest stands (including native broadleaved and eucalypt forests) generally presented higher interception losses than conifers. Interception was higher in northern zones, indicating that forests have greater impacts on water resources in dryer regions. Our results were compiled in empirical models, which can be used to estimate forest interception in a latitudinal gradient in Chile and to support policy making. These results are also proposed as an approximate analogue of the changes in forest interception losses, which may occur as vegetation belts shift latitudinally as a result of the impact of climate change. Copyright © 2016 John Wiley & Sons, Ltd.     

A weighing lysimeter in a regenerating eucalypt forest: Design,construction, and performance

A 36 tonne monolithic weighing lysimeter (3.7 m diameter and 1.5 m deep) was installed in Kioloa State Forest near Batemans Bay, New South Wales, Australia, to provide a continuous record of water use from a regenerating natural eucaplyt community, five years old at installation. The resolution is equivalent to 0.05 mm of evaporation and provides hourly information for diurnal variation of forest evaporation. The sensitivity of 14 ppm compares favourably with those reported for other lysimeters, similar in magnitude, in the U.S.A. Design criteria for selecting, isolating and suspending a sample community ‘in situ’ with an electro-mechanical balance are outlined. Procedures adopted during installation are described with emphasis placed on precautions taken to minimize disturbance and to avert possible changes in character of the isolated natural community. Lysimeter performance was assessed both in terms of its accuracy and its operation as a remote facility with infrequent attention.     

Fog precipitation in the Sierra de las Minas Biosphere Reserve,Guatemala

Fog precipitation occurs when fog droplets are filtered by the forest canopy and coalesce on the vegetative surfaces to form larger water droplets that drip to the forest floor. This study examines the quantity of throughfall compared with incident precipitation produced by the canopy of a lower montane rain forest (2100 m) and an upper montane cloud forest (2550 m) in the Sierra de las Minas Biosphere Reserve, Guatemala. Fog precipitation was measured with throughfall and precipitation gauges from 23 July 1995 to 7 June 1996. Fog precipitation occurred during sampling periods when throughfall exceeded incident precipitation. Fog precipitation contributed <1% of total water inputs in the cloud forest at 2100 m during the 44‐week period, whereas fog precipitation contributed 7·4% at 2550 m during the same period. The depth equivalent of fog precipitation was greater at 2550 m (203·4 mm) than at 2100 m (23·4 mm). The calculation of fog precipitation in this study is underestimated. The degree of underestimation may be evident in the difference in apparent rainfall interception between 2100 m (35%) and 2550 m (4%). Because the apparent interception rate at 2550 m is significantly lower than 2100 m, the canopy probably is saturated for longer periods as a result of cloud water contributions. Data show a seasonal pattern of fog precipitation most evident at the 2550 m site. Fog precipitation represented a larger proportion of total water inputs during the dry season (November to May). Because cloud forests generate greater than 1 mm day^?1 of fog precipitation in higher elevations of the Sierra de las Minas, the conservation of the cloud forest may be important to meet the water demands of a growing population in the surrounding arid lowlands. Copyright © 2003 John Wiley & Sons, Ltd.