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1、基于景观连接度的斑块分级的尺度效应张景华1,2,3，吴志峰1*，吕志强1，刘晓南1，程兰11. 广东省生态环境与土壤研究所，广东 广州 510650；2. 中国科学院广州地球化学研究所，广东 广州 510640；3. 中国科学院研究生院，北京 100039摘要：认识到尺度对景观格局分析结果的影响，生态学家们越来越多地进行尺度效应的相关研究。已有的尺度效应研究多注重描述景观格局指数对尺度变化的响应，这只能对景观的状态进行描述，无法辨别那些对景观功能具有重要意义的关键景观元素。文章选取8个景观连接度指数，通过改变最小制图单元和物种的搜索范围，研究尺度对斑块分等定级的影响，并据此确定各连接度指数的尺
2、度敏感性。结果表明：景观中斑块的相对重要性随尺度变化而变化，其变化程度因指数而异。其中，AWF为尺度效应最不明显的指数，PC和IIC次之，其余指数（NL，NC，LCP，H和F）的尺度效应均十分显著；在衡量景观的连通性时，除IIC外的其他所有指数的尺度效应均十分显著。由此说明，根据连接度指数确定的斑块相对重要性的尺度敏感性与该指数本身的尺度敏感性无关。关键词：景观连接度；连接度指数；斑块分级；尺度效应；东莞市中图分类号：Q14 文献标识码：A 文章编号：1672-2175（2008）05-1926-05景观中存在某些关键性的局部、元素和空间位置及联系，它们对维护景观中某种过程（包括生态过程、社会
3、文化过程等）的健康和安全具有关键性的意义1，辨别、保护这些对景观功能具有重要意义的关键景观元素（如斑块、廊道等）2对建立景观安全格局具有重要作用。确定景观元素相对重要性的标准有很多，如斑块的面积、质量等。由于景观中物种的分布、物种多样性以及生态系统的稳定性和完整性在很大程度上依赖于景观的连接程度3-4，因此，本文尝试根据斑块在保持景观连通性中的重要程度对其进行分等定级。景观连接度是指景观空间结构单元之间的连续性程度5。景观连接度可以从结构连接度和功能连接度两个方面来考虑。前者指景观在空间上表现出来的表观连续性，可根据航片、卫片或各类地图来确定。后者是以所研究的生态学对象或过程的特征来确定的景观
4、连续性。例如，种子传播距离、动物取食和繁殖活动的范围等与景观结构连续性一起确定景观的功能连接度。不考虑生态学过程，单纯考虑景观的表观连接度是没有意义的，因此，本文选择景观的功能连接度对斑块进行分级。景观的功能连接度不仅依赖于观察尺度，而且与所研究对象的特征尺度有关。本文通过变换最小制图单元（minimum mapping unit, MMU）和物种的搜索范围，研究尺度变化对景观中各斑块相对重要性的影响，并据此确定所选各指数的尺度敏感性，以期为景观规划等实际工作提供依据。1 研究区域与数据来源1.1 研究区概况东莞市（1133111415E，22392309N）位于广东省中南部，珠江口东岸，北接
5、广州，南邻深圳，毗邻香港，是广州与香港之间水陆交通的必经之地。全市陆地面积2465 km2，海岸线长115.94 km，总人口数644.57万人。该市属亚热带季风气候，长夏无冬，日照充足，雨量充沛。年平均气温23.6 ，年均降水量1844.5 mm。地势自东向西倾斜，大部分为丘陵台地和冲积平原。东莞是广东省的中心城市之一，属于珠江三角洲经济发达区，经济的快速发展对原有景观形成强烈的改造作用6，致使景观破碎化程度加剧，连通性降低。景观连接度分析通常是关注某种濒危物种或关键物种及其生境的保护，因此往往只对应于某种特定的土地利用类型7。本文以东莞林地景观为例，根据各斑块对林地景观连通的贡献大小，对其
6、进行分等定级。1.2 数据来源与处理本文的基础数据来源于2000年1月2日拍摄的轨道为122-44的TM遥感影像，经人工解译得到1100000的研究区土地利用图。原图包括6个第一大类和27个子类，第一大类分别为耕地、林地、草地、水域、城乡工矿居民用地和未利用土地。本文根据研究内容的需要，只选择其林地景观，林地斑块分布图见图1。图1 东莞市林地景观斑块分布示意Fig.1 Distribution of forest patches in Dongguan2 研究方法本文选取了8个景观连接度指数，通过改变最小制图单元和物种的搜索范围，研究尺度变化对斑块分级的影响。2.1 指数的选择衡量景观连接度的
7、指数有很多，已有研究表明，基于图的连接度指数（graph-based connectivity metrics）在景观连接度分析及斑块分等定级时显示出巨大的优势8-10。本文选取了8个基于图的连接度指数来进行斑块分级的尺度效应研究。各指数含义如下11：斑块间的链接数。：组分数，组分是指一组互相连通的斑块，不同组分之间彼此孤立。，其中，为组分的面积（属于组分的所有斑块的面积和）；为景观的总面积（包括林地斑块和非林地斑块）。，其中，为景观中林地斑块总数；为斑块与斑块间最短路径上的链接数。，其中，为斑块的面积。和，其中，为斑块与斑块直接连通的概率。，其中，为斑块与斑块间所有路径概率乘积的最大值。上述
8、8个指数中，除外，其他所有指数均随着景观连接度的增加而增大。其中，和 的变化范围为01，其它指数最小值为0（，）或1（），无上限。根据某一连接度指数计算各斑块的重要性dXi：其中，X为景观的某一连接度指数值，X为将斑块从景观中剔除后，景观的该连接度指数值。通过计算dXi即可对景观中各斑块的重要性进行排序，从而确定那些对景观连通具有重要意义的斑块。研究中所选的连接度指数和各斑块相对重要性的计算均通过软件Conefor Sensinode 2.2实现。2.2 尺度变换方法本文通过不断扩大最小制图单元（MMU）的方法来变换观察尺度。最小制图单元是指景观中最小空间实体的面积12。扩大MMU的方法有很多
9、，如不断合并栅格单元等13。为比较斑块的相对重要性，需保证每个斑块的边界位置不变，因此本文采取将小于指定MMU的斑块剔除的方法来实现。将MMU依次指定为10，15，20，25，50和100 hm2，将原始图像中小于指定MMU的林地斑块剔除，从而得到一系列斑块数目不同的林地景观图。各景观图的共有斑块，即用于后续比较的斑块，为MMU等于100 hm2时仍存在的斑块。衡量景观连接度仅仅考虑景观的空间结构是不够的，因为同一景观对于具有不同运动能力的物种来说，其连通程度可能不同，每个斑块的重要程度也可能不同。因此，本文针对MMU不同的各幅图像，又分别设定了1、2、5、10和20 km 5个不同的物种搜索
10、范围，以研究物种的特征尺度对斑块分级的影响。2.3 尺度效应分析为了确定斑块的相对重要性是否随观察尺度的变化而变化，针对每个连接度指数，以MMU为10 hm2时各斑块的值为基础，运用Spearman秩相关分析，分别计算其他尺度下斑块值与该尺度下斑块值之间的相关系数rs（rs的取值范围为01）。若rs=1，表明各斑块的相对重要程度未随尺度发生变化；若rs1，表明各斑块的相对重要程度随尺度发生变化。因此，rs也可以作为衡量连接度指数尺度敏感性的指标。较小的rs值表明该指数的尺度效应显著，基于该指数在某尺度下的进行的分析、规划不适用于其他尺度。最小制图单元/hm2最小制图单元/hm2最小制图单元/h
11、m2相关系数相关系数相关系数 相关系数最小制图单元/hm2最小制图单元/hm2最小制图单元/hm2相关系数相关系数 相关系数相关系数 最小制图单元/hm2最小制图单元/hm2图2 斑块值相关系数尺度效应Fig. 2 Scale effect curves of Spearman rank correlations3 结果与分析3.1 斑块分级的尺度效应3.1.1 MMU对斑块分级的影响从图2可以看出，随着MMU增大，各指数的rs值均逐渐减小，表明尺度改变，各斑块的重要程度发生变化，其变化程度因指数而异。其中，对于，据其计算的值在不同尺度间的相关系数基本保持为1不变，表明根据计算的各斑块的相对重
12、要性，在不同尺度间基本保持不变，说明为尺度效应最不敏感的指数。同样，根据和计算的值，在不同尺度间的相关系数均大于0.8，表明斑块的相对重要性随尺度变化不大，其尺度效应不明显，和也是稳定的指数。其他指数均有较强的尺度效应（rs0.8）。其中，和由于未考虑斑块的面积，使得其对尺度的变化非常敏感（rs0.6）。因为考虑斑块面积的指数在计算景观的连接度时，会给面积较大的斑块赋以较大的权重，这样在MMU增大过程中，该类指数对破碎小斑块的剔除就相对不敏感，从而使得其尺度效应不显著。当然，是否考虑斑块面积并不是影响指数稳定性的唯一因素，例如，也未考虑斑块的面积，但其对尺度变化的响应较和稳定的多。3.1.2
13、物种运动能力对斑块分级的影响从图2可以看出，物种的运动能力越强，搜索范围越大，斑块分级的尺度效应越不明显。这是因为物种运动能力强，使得景观中任意两个斑块间都可以直接建立链接，这样对于考虑斑块面积的指数来说，每个斑块的相对重要性与其在景观中的位置无关，完全由其面积大小决定，而面积作为斑块自身的属性，与尺度无关，也不受其他斑块的影响。从图2还可看出，当搜索范围大于2 km时，无法根据值判断斑块的相对重要性（均为0，rs缺失）。这同样是因为物种搜索范围过大，使得景观中所有的斑块能够互相连接，从属于同一个组分，删除任何一个斑块都不会使景观变成孤立的两部分，从而使得景观中所有斑块的地位相同。3.2 景观
14、连接度指数的尺度效应尺度除对各斑块的相对重要性（）产生影响外，对整个景观的连接度指数（）也有影响。由表1可以看出，景观连接度随MMU增大而减小，造成这种现象的原因有很多，如斑块间链接丢失，由于关键斑块丢失造成的组分破碎，剩余斑块间距离增大等。在所有的指数中，除比较稳定外，其他指数对尺度变化都很敏感。表1 物种搜索范围为2 km时的景观连接度指数Table 1 Landscape connectivity indices with 2km dispersal distance指数最小制图单元10 hm2100 hm2NLNCHLCPIICFAWFPC2634528,085.060.07190.0
15、15110,156.333.82E+160.0420299181,460.260.02430.0080975.462.87E+160.0227从本研究中，我们应当注意到，根据连接度指数确定的斑块相对重要性的尺度敏感性与该指数本身的尺度敏感性无关，用于确定斑块相对重要性时稳定的指数，在描述整个景观的连接度时未必稳定（如），反之亦然。4 结论研究表明，斑块的相对重要性具有尺度效应。其粒度敏感性与所选指数有关，为尺度效应最不敏感的指数，和次之，其他指数均有较强的尺度依赖性。物种运动能力越强，斑块分级的尺度效应越不明显。此外，景观连接度指数也随尺度变化而变化，但基于连接度指数确定的斑块等级的尺度敏感性
16、与该指数本身的尺度敏感性无关。参考文献：1 俞孔坚，李迪华，韩西丽, 等. 新农村建设规划与城市扩张的景观安全格局途径: 以马岗村为例J. 城市规划学刊, 2006, 5: 38-45.Yu Kongjian, Li Dihua, Han Xili, et al. Rescuing a Village: The Approach of Landscape Security PatternsWith the Case of Magang, Shunde, Guangdong provinceJ. Urban Planning Forum, 2006, 5: 38-45.2 LUCIA P H,
17、SANTIAGO S. Comparison and development of new graph-based landscape connectivity indices: towards the prioritization of habitat patches and corridors for conservationJ. Landscape Ecology, 2006, 21: 959-967.3 SCHIPPERS P, VERBOOM J, KNAAPEN J P, et al. Dispersal and habitat connectivity in complex he
18、terogeneous landscapes: an analysis with a GIS-based random walk modelJ. Ecography, 1996, 19: 97-106.4 SCHUMAKER N H. Using landscape indices to predict habitat connectivityJ. Ecology, 1996, 77: 1210-1225.5 邬建国. 景观生态学: 格局、过程、尺度与等级M. 北京：高等教育出版社, 2000: 55-56.Wu Jianguo. Landscape Ecology: Pattern, Pro
19、cess, Scale and HierarchyM. Beijing: Higher Education Press, 2000: 55-56.6 曾辉，郭庆华，喻红. 东莞市风岗镇景观人工改造活动的空间分析J. 生态学报, 1999, 19(3):298-303.Zeng Hui, Guo Qinghua, Yu Hong. Spatial analysis of artificial landscape transform in Fenggang Town, Dongguan CityJ. Acta Ecologica Sinica, 1999, 19(3): 298-303.7 SAN
20、TIAGO S, LUCIA P H. A new habitat availability index to integrate connectivity in landscape conservation planning: Comparison with existing indices and application to a case studyJ. Landscape and Urban Planning, 2007.8 URBAN D, KEITT T. Landscape connectivity: a graph-theoretic perspectiveJ. Ecology
21、, 2001, 82: 1205-1218.9 JORDAN F, BALDI A, ORCI K M, et al. Characterizing the importance of habitat patches and corridors in maintaining the landscape connectivity of a Pholidoptera transsylvanica (Orthoptera) metapopulationJ. Landscape Ecology, 2003, 18: 83-92.10 CALABRESE J M, FAGAN W F. A compar
22、ison-shoppers guide to connectivity metricsJ. Frontiers in Ecology and the Environment, 2004, 2(10): 529-536.11 LUCIA P H, SANTIAGO S. Impact of spatial scale on the identification of critical habitat patches for the maintenance of landscape connectivityJ. Landscape and Urban Planning, 2007.12 LILLE
23、SAND T M, KIEFER R W. Remote Sensing and Image InterpretationM. Third Edition. New York: John Wiley and Sons, 1994.13 申卫军，邬建国，林永标，等. 空间粒度变化对景观格局分析的影响J. 生态学报, 2003, 23(12): 2506-2519.Shen Weijun, Wu Jianguo, Lin Yongbiao, et al. Effects of changing grain size on landscape pattern analysisJ. Acta Ecol
24、ogica Sinica, 2003, 23(12): 2506-2519.The scale effects of patches prioritization based on the landscape connectivityZhang Jinghua1,2,3, Wu Zhifeng1*, Lv Zhiqiang1, Liu Xiaonan1, Cheng Lan11. Guangdong Institute of Eco-environment and Soil Sciences, Guangzhou 510650, China;2. Guangzhou Institute of
25、Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China;3. Graduate University of Chinese Academy of Sciences, Beijing 100039, ChinaAbstract: Recognizing the effects of the spatial scale on landscape pattern analysis, the ecologists have conducted more and more researches related to scale
26、 effect. Nevertheless, previous studies have just focused on describing the reactions of different landscape metrics to the scale variation, which could only describe the state of the landscape and not be able to identify those critical landscape elements for eco-function. In this paper, 8 connectiv
27、ity indices were selected to examine the effects of scale on the identification of patches prioritization by changing the minimum mapping unit and dispersal distance of the animals, and then the scale sensitivity of all the connectivity metrics were determined. The results showed that the relative i
28、mportance of patches in landscape was scale-dependent, and the responses to scale change were different for various metrics. AWF was the most robust metric, closely followed by PC and IIC, and the others (NL, NC, LCP, H and F) were strongly scale-dependent. For the measure of the whole landscape con
29、nectivity, all of the indices, except IIC, were strongly scale-dependent. So it could be concluded that the scale sensitivity of patches prioritization which was decided by connectivity indices had nothing to do with the scale sensitivity of these indices themselves.Key words: landscape connectivity
30、; connectivity indices; patches prioritization; scale effect; Dongguan cityEditors note: Judson Jones is a meteorologist, journalist and photographer. He has freelanced with CNN for four years, covering severe weather from tornadoes to typhoons. Follow him on Twitter: jnjonesjr (CNN) - I will always
31、 wonder what it was like to huddle around a shortwave radio and through the crackling static from space hear the faint beeps of the worlds first satellite - Sputnik. I also missed watching Neil Armstrong step foot on the moon and the first space shuttle take off for the stars. Those events were way
32、before my time.As a kid, I was fascinated with what goes on in the sky, and when NASA pulled the plug on the shuttle program I was heartbroken. Yet the privatized space race has renewed my childhood dreams to reach for the stars.As a meteorologist, Ive still seen many important weather and space eve
33、nts, but right now, if you were sitting next to me, youd hear my foot tapping rapidly under my desk. Im anxious for the next one: a space capsule hanging from a crane in the New Mexico desert.Its like the set for a George Lucas movie floating to the edge of space.You and I will have the chance to wa
34、tch a man take a leap into an unimaginable free fall from the edge of space - live.The (lack of) air up there Watch man jump from 96,000 feet Tuesday, I sat at work glued to the live stream of the Red Bull Stratos Mission. I watched the balloons positioned at different altitudes in the sky to test t
35、he winds, knowing that if they would just line up in a vertical straight line we would be go for launch.I feel this mission was created for me because I am also a journalist and a photographer, but above all I live for taking a leap of faith - the feeling of pushing the envelope into uncharted terri
36、tory.The guy who is going to do this, Felix Baumgartner, must have that same feeling, at a level I will never reach. However, it did not stop me from feeling his pain when a gust of swirling wind kicked up and twisted the partially filled balloon that would take him to the upper end of our atmospher
37、e. As soon as the 40-acre balloon, with skin no thicker than a dry cleaning bag, scraped the ground I knew it was over.How claustrophobia almost grounded supersonic skydiverWith each twist, you could see the wrinkles of disappointment on the face of the current record holder and capcom (capsule comm
38、unications), Col. Joe Kittinger. He hung his head low in mission control as he told Baumgartner the disappointing news: Mission aborted.The supersonic descent could happen as early as Sunday.The weather plays an important role in this mission. Starting at the ground, conditions have to be very calm
39、- winds less than 2 mph, with no precipitation or humidity and limited cloud cover. The balloon, with capsule attached, will move through the lower level of the atmosphere (the troposphere) where our day-to-day weather lives. It will climb higher than the tip of Mount Everest (5.5 miles/8.85 kilomet
40、ers), drifting even higher than the cruising altitude of commercial airliners (5.6 miles/9.17 kilometers) and into the stratosphere. As he crosses the boundary layer (called the tropopause), he can expect a lot of turbulence.The balloon will slowly drift to the edge of space at 120,000 feet (22.7 mi
41、les/36.53 kilometers). Here, Fearless Felix will unclip. He will roll back the door.Then, I would assume, he will slowly step out onto something resembling an Olympic diving platform.Below, the Earth becomes the concrete bottom of a swimming pool that he wants to land on, but not too hard. Still, he
42、ll be traveling fast, so despite the distance, it will not be like diving into the deep end of a pool. It will be like he is diving into the shallow end.Skydiver preps for the big jumpWhen he jumps, he is expected to reach the speed of sound - 690 mph (1,110 kph) - in less than 40 seconds. Like hitt
43、ing the top of the water, he will begin to slow as he approaches the more dense air closer to Earth. But this will not be enough to stop him completely.If he goes too fast or spins out of control, he has a stabilization parachute that can be deployed to slow him down. His team hopes its not needed.
44、Instead, he plans to deploy his 270-square-foot (25-square-meter) main chute at an altitude of around 5,000 feet (1,524 meters).In order to deploy this chute successfully, he will have to slow to 172 mph (277 kph). He will have a reserve parachute that will open automatically if he loses consciousne
45、ss at mach speeds.Even if everything goes as planned, it wont. Baumgartner still will free fall at a speed that would cause you and me to pass out, and no parachute is guaranteed to work higher than 25,000 feet (7,620 meters).It might not be the moon, but Kittinger free fell from 102,800 feet in 1960 - at the dawn of an infamous space race that captured the hearts of many. Baumgartner will attempt to break that record, a feat that boggles the mind. This is one of those monumental moments I will always remember, because there is no way Id miss this.
