Light distribution in scattered-trees open woodlands in Western Spain

We have studied the percentage of radiation transmitted through the tree canopy to the underlying pasture and crops in dehesas of Southwest Spain by means of fish-eye photographs taken at different distances from the tree. Thirty-six trees were studied covering all the diametric classes (0.1–14 m canopy width) of two stands, with mean density of 19 mature trees ha⁻¹. Intercepted light decreased with distance following an logistic curve, indicating a rapid increase in the light availability with distance from the tree. For mature trees, radiation was constant beyond 20 m. Applying a multivariable regression light equation, distance, stem diameter and canopy width explained more than 88% of the light variability for each orientation studied. A simple model was built up from light equations, tree growth curves and allometric relationships. From this model, we have estimated that radiation available for crops and pasture decreased up to 21% due to the presence of trees in a standard dehesa with 24 mature trees ha⁻¹ and 13% of canopy cover. In addition, we have generated different radiation maps of virtual dehesas differing in tree age, density and arrangement, which could be useful to determine optimal tree planting schemes and consequent pruning and thinning regimes.     

Effect of management on the spatial spread of mountain pine beetle (Dendroctonus ponderosae) in Banff National Park

To evaluate control measures, the spread of mountain pine beetles, Dendroctonus ponderosae, in management and monitoring regions in Banff National Park was analyzed for years 1997 to 2004. The Park allowed mountain pine beetles to follow their natural course in a monitoring zone (74,041 ha), whereas in a management zone (45,997 ha) an extensive eradication program was established in 2001 which included baiting mountain pine beetles and cutting and burning all colonized trees. We used data collected from an annual aerial survey and the geo-referenced location of trees that were cut and removed to assess if the area colonized and the spatial extent of mountain pine beetles differed between the two zones. After 4 years, the control measures did not significantly affect the area colonized by mountain pine beetles, and in 2004 mountain pine beetles were still expanding in both zones, although at a slow rate (1.23 ha per year). The spatial extent and the rate at which 500 m × 500 m cells (25 ha) were colonized were much reduced in the management zone. Thus, the management program appeared to have reduced the success of long distance movement as measured by colonizing new 25 ha cells, but short distance dispersal remained successful as indicated by the continued increase in area colonized. The effectiveness of control measures was probably limited by the number of colonized trees that were missed and by survival rates determined by other untested factors.     

美国白蛾直升飞机防治中的雾滴分析及其对防治效果的影响

飞机防治是美国白蛾防控的最主要措施之一。为进一步明确飞行参数对林间雾滴密度分布和对美国白蛾幼虫防控效果的影响,该文通过检测、比较不同飞行方案下林间雾滴密度及雾滴穿透力等数据,发现航速和高度对林间喷幅、雾滴穿透力、雾滴密度、雾滴均匀度均产生显著影响。方案2(航速150 km/h,飞行高度40—45 m),地面喷幅宽度为59.35 m,高于方案1(航速120 km/h,飞行高度30—35 m)的地面喷幅宽度。飞行方案2的雾滴穿透性也相对较好,顶层、中层、下层雾滴密度相对均匀;而方案1不同高度雾滴密度差异相对较为显著,树冠顶层(高度11—12 m)雾滴密度较多,最高雾滴密度可达9.8/cm2,随高度降低,雾滴密度下降明显,到底层叶片位置(高度3 m)时,雾滴密度仅为2.07/cm2,下降了78.9%。观测试验表明,林间雾滴密度应高于5.093/cm2,防控效果才能确保达到90%。     

飞播马尾松林抚育间伐试验研究

对11年生飞播马尾松林进行综合抚育间伐试验的结果表明,不同的间伐强度和次数均产生不同的效果。胸径生长以间伐强度大和2次间伐为好;树干形质以间伐强度小为好;间伐对树高、冠幅、林木分化等均有影响。     

Determination of number of stems in coniferous forest stands by means of aerial photo‐interpretation

Two models for determination of the number of stems per hectare in forest stands (N) from attributes derived by aerial photo‐interpretation were developed. The models relied on the assumption that N could be determined by dividing the total stand volume per hectare with the volume of the “average tree”; defined by stand mean height and the diameter corresponding to mean basal area of a stand. Input variables of the models were stand mean height, crown closure and site quality. Additionally, model II required input of average stand volume per hectare and average mean diameter derived from stratified field sample plot inventories. Material for 143 coniferous stands was used for the testing of the models. The stands were recorded by intensive field measurements. Aerial photographs at the approximate scale of 1:15 000 were used for photo‐interpretation. The N value was underestimated in model I by 5.4–47.0%. The standard deviation for the differences was 15.2–26.2% for mature stands and 41.4–44.2% for young thinning phase stands. For model II, the mean difference between the predicted and observed N value was in the range ‐16.1% to 12.2%.     

影响大蒜试管鳞茎形成的因素分析

用大蒜幼嫩气生鳞茎作试材，系统研究了影响大蒜试管鳞茎形成的因素。结果表明：植物激素配比、pH值、糖源、温度、光周期和基因型都对试管鳞茎的发生有一定程度的影响。其中，无激素的MS培养基、pH值为7．5，5％的糖浓度、低温预处理、较长日照和适宜高温（25℃）有利于鳞茎的发生。     

利用未纠正航片确定汇水面积的方法

为了在小桥涵勘测中更好地利用未经纠正的航片量测汇水面积，必须提高量测的精度。本文分析了航片上的倾斜误差和投影差，并推导出在倾斜航片上量测汇水面积时倾斜误差和投影差的改正系数，给出了改正方法。实践证明，其量测精度不低于１／７０，这对精度要求不高的农林资源调查，具有普遍的实用价值。     

航空摄影测量技术在高标准基本农田建设项目中的应用研究

高标准基本农田建设是我国“十二五”土地整治的重要目标,是提高耕地质量的重要措施.高标准基本农田建设项目要求质量高,时间紧,如何在短时间内完成规划设计工作是困扰设计单位的重要难题,尤其是项目区现状图的测绘和踏勘工作往往会消耗大量的时间.该研究介绍了高标准基本农田建设项目的地形图测绘要求,并详细探讨了航空摄影测量方法在重大土地整治项目中的应用.     

Estimation of yield zones using aerial images and yield data from a few tracks of a combine harvester

Yield maps derived from yield mapping systems are often erroneous not only due to limitations in measuring the yield precisely but due to insufficient consideration of the requirements of yield mapping systems in practice as well. Aerial images of cultivated crop fields at an advanced growth stage frequently provide a spatial pattern similar to that of yield maps. Therefore, the possibility of generating a yield map using aerial images and measured yield data of a few tracks was examined for a period of 2 years in two fields grown with cereals. Yield zones based on Visible Atmospherically Resistant Index (VARI) values were compared with yield zones based on measured yield data of the whole field. About half of the grid cells of a field were allocated to the same yield zones irrespective of the mode of yield determination. Using the Kruskal–Wallis test, the data sub-sets of measured yield within the yield zones based on the VARI values differed significantly for all tested yield zones. As a result, the approach was successful in the case of these experimental sites.     

Detecting subsurface drainage systems and estimating drain spacing in intensively managed agricultural landscapes

Detailed location maps of tile drains in the Midwestern United States are generally not available, as the tile lines in these areas were laid more than 75 years ago. The objective of this study is to map individual tile drains and estimate drain spacing using a combination of GIS-based analysis of land cover, soil and topography data, and analysis of high resolution aerial photographs to within the Hoagland watershed in west-central Indiana. A decision tree classifier model was used to classify the watershed into potentially drained and undrained areas using land cover, soil drainage class, and surface slope data sets. After masking out the potential undrained areas from the aerial image, image processing techniques such as the first-difference horizontal and vertical edge enhance filters, and density slice classification were used to create a detailed tile location map of the watershed. Drain spacings in different parts of the watershed were estimated from the watershed tile line map. The decision tree identified 79% of the watershed as potential tile drained area while the image processing techniques predicted artificial subsurface drainage in approximately 50% of the Hoagland watershed. Drain spacing inferred from classified aerial image vary between 17 and 80 m. Comparison of estimated tile drained areas from aerial image analysis shows a close agreement with estimated tile drained areas from previous studies (50% versus 46% drained area) which were based on GIS analysis and National Resource Inventory survey. Due to lack of sufficient field data, the results from this analysis could not be validated with observed tile line locations. In general, the techniques used for mapping tile lines gave reasonable results and are useful to detect drainage extent from aerial image in large areas. These techniques, however, do not yield precise maps of the systems for individual fields and may not accurately estimate the extent of tile drainage in the presence of crop residue in agricultural fields and/or existence of other spatial features with similar spectral response as tile drains.