像元尺度上不确定性对空间景观直观模型模拟的影响

LANDIS模型是模拟自然和人为干扰下森林景观变化的空间直观景观模型。模型把景观概念化为由相同大小的像元或样地组成的格网。在每一个像元上,模型要求输入物种和年龄组信息。但是,由于研究区一般由成千上百万个像元构成,不可能通过实际调查获取每一个像元上的物种和年龄组信息。因此,采用了一种基于小班的随机赋值法从森林调查数据中获取每一个像元的物种和年龄组信息。该方法是一种基于概率的方法,会在LANDIS模型模拟的物种和年龄组信息的输入中引入不确定性。为了评价由基于小班的随机赋值法所引入像元尺度上的不确定性对模型模拟结果的影响,用蒙特卡罗模拟法进行不确定性分析。对LANDIS模型模拟的每一个物种,用众数年龄组发生频率来定量化单个像元上年龄组信息的不确定性,用所有像元上的众数年龄组平均发生频率来定量化年龄组信息在像元尺度上总的不确定性。平均发生频率越高,不确定性越低。为了评价基于小班的随机赋值法对景观尺度上模型模拟结果的影响,计算了每一个物种在整个研究区内的面积百分比和聚集度指数。变异系数越大,不确定性越高。对所有物种,年龄组信息不确定性在模型模拟的初期是比较低的(平均发生频率大于10)。种子传播、建群、死亡和火干扰使模型结果的不确定性随模拟时间增加而增加。最后,不确定性达到稳定状态,达到平衡状态的时间与物种寿命接近。此时,初始的物种和年龄组信息不再对模型结果有影响。在景观尺度上,物种分布面积百分比和由聚集度指数所定量化的空间格局并未受像元尺度上不确定性增加的影响。因为LANDIS模型模拟研究的目的在于预测总的景观格局变化,而不是单一的事件,所以,基于小班的随机赋值法可用于LANDIS模型的参数化。     

空间直观景观模型LANDIS在大兴安岭呼中林区的应用

应用空间直观景观模型(LANDIS),研究有采伐和无采伐预案下大兴安岭呼中林区的森林景观的长期变化。用APACK计算每一个物种及各年龄级的分布面积。为了研究物种分布格局的变化,计算了物种分布的聚集度指数。研究结果如下：(1)在无采伐预案下。火干扰模式为低频率大面积高强度火烧;在有采伐预下,火干扰模式为高频率小面积低强度火烧;(2)在无采伐预案下,火会造成各种群分布面积的强烈波动,但是对种群的年龄结构没有很大影响;在有采伐预案下,火对种群分布面积和年龄结构都没有很大的影响;(3)采伐能完全改变各种群的年龄结构。降低种群分布的聚集度,但是对各种群的分布面积并没有很大影响;(4)在有采伐预案下,各种群为增长型种群,增长量通过采伐取走,群落处于演替的干扰顶极状态;在无采伐预案下,各种群为稳定型种群(樟子松和偃松除外),大面积高强度火烧使群落产生较大的波动。结果表明,在呼中林业局,在没有人为干扰情况下,火干扰是森林景观变化的主导因素。自从有了人为干扰,采伐开始逐渐取代火干扰成为影响森林景观变化的主导因素。空间直观景观模型的一个挑战是模型的验证。由于缺乏详细的空间数据及模型模拟中的随机性,很难通过模型模拟结果与实地调查或遥感数据的比较进行验证。通过对火模拟、物种分布和物种组成的生态或生物学实现对模型进行验证。     

森林采伐对森林景观的长期影响模拟

应用空间直观景观模型(LANDIS),模拟了小兴安岭友好林业局在有无采伐方案下400年内森林景观的动态变化,并利用统计软件APACK计算代表性树种的分布面积、年龄级和反映物种分布格局的聚集度指数.结果表明:与无采伐相反,采伐下的火干扰模式为高频率小面积低强度火烧;采伐对各种群的分布面积影响不大,但显著改变了种群的年龄结构,主要表现为降低了过熟林的分布面积,而增加了其他年龄级森林的分布面积;采伐降低了各树种的聚集度,导致森林景观一定程度上的破碎化.     

空间直观景观模型在呼中林区土壤侵蚀预测研究中的初步应用

土壤通用流失方程(USLE)已被广泛应用于大尺度的土壤侵蚀预测．在以往的土壤侵蚀研究中,由于只能获得静态的植被图,土壤通用流失方程只能用于土壤侵蚀的静态估算．空间直观景观模型能在大尺度上模拟植被动态,为土壤通用流失方程提供动态的植被因子,从而使土壤侵蚀的动态模拟成为可能．本研究结合空间直观景观模型LANDIS和土壤通用流失修正方程,以大兴安岭呼中林区为研究区。动态地模拟未来650年内有采伐和无采伐预案下的土壤侵蚀量;同时以无火无采伐预案下的土壤侵蚀为对比值．结果表明,土壤侵蚀量随时间变化呈周期性的波动,其波动程度在无火无采伐预案下最小,而在有火无采伐预案下最大;采伐对土壤侵蚀的影响没有火对土壤侵蚀的影响在空间上表现得明显,但是其累积效果则比火的影响强;降低采伐所产生的裸露土能有效降低年平均土壤侵蚀量,但是对土壤侵蚀动态变化的影响不明显;虽然采伐增加使平均土壤侵蚀量增加,但是也同时使土壤侵蚀的年际变化更趋于平稳．     

浙江天童国家森林公园植被自然演替动态模拟

应用空间明晰景观模型LANDIS 6.0 PRO,以浙江天童国家森林公园常绿阔叶林为研究对象,根据天童国家野外观测站的长期研究和观测数据对LANDIS模型进行参数化,模拟无干扰情况下常绿阔叶林在未来500年间的演替动态,分析优势种和主要景观类型的空间分布以及年龄结构组成,揭示了常绿阔叶林演替的规律.结果表明： 研究区物种的交替多发生在常绿阔叶林阶段之前,马尾松、白栎和枫香等先锋物种在演替初期占有较大比例,但随着时间的推移逐渐退出,木荷和栲树等物种在演替后期占有较大优势,并逐渐发展成木荷 栲树顶极群落;无干扰的情况下,在演替前期,群落多由幼龄林构成,后期则多以成熟林或过熟林为主,群落更新能力不足.LANDIS模型可应用于我国东部常绿阔叶林的景观动态模拟,今后的研究应结合亚热带常绿阔叶林的复杂性和多样性,对模型结构和模型参数进行完善和
改进.     

FARSITE火行为模型的原理、结构及其应用

应用空间直观火行为模型模拟大的时空尺度上的林火蔓延过程成为林火管理、规划和科学分析的有效工具。FARSITE(Fire Area Simulator)是一个基于热物理、燃烧学和试验理论为一体的空间直观火行为模型,它集成了现有的地表火、树冠火、飞火和火加速等子模型。FARSITE能够利用GIS和RS提供的空间数据,模拟大时空尺度的林火蔓延,模拟结果能够以地图形式输出,反映林火行为的瞬时状态。本文介绍了FARSITE模型的基本原理、结构和运行机制,并将其应用到丰林自然保护区林火蔓延模拟,以期为国内林火管理和火行为模型的开发提供参考。     

太白山锐齿栎林物种-多度分布格局

以太白山1.5 hm²的锐齿栎原始林和次生林样地中环境因子和胸径≥1 cm的木本植物调查数据为基础,采用统计模型(对数正态模型)、生态位模型(Zipf模型、断棍模型、生态位优先模型)和中性模型,拟合了锐齿栎群落的物种多度分布。结果表明: 太白山锐齿栎林物种多度分布格局受到生境异质性的影响。其中,地形因子对原始林物种分布影响较大,在凹凸度较大的生境中,物种分布同时受到中性过程和生态位过程的影响,但中性过程发挥的作用较小;而在凹凸度较小的生境中,中性模型被拒绝,物种的多度分布符合生态位理论的假设。在群落坡度大的区域,群落中生态位过程和中性过程同等重要;而在坡度较小的平缓区域,生态位分化对群落物种分布的影响较大。在次生林中,影响物种分布的因素主要是土壤养分。在次生林土壤速效磷含量高的生境中,生态位过程是影响群落物种分布的主要生态学过程;而在土壤速效磷含量低的生境中,中性过程和生态位过程在群落物种分布中同时存在。太白山锐齿栎林物种多度分布格局存在明显的尺度效应。原始林在20 m×20 m尺度上,生态位模型和中性模型都能预测物种多度分布,而在40 m×40 m和70 m×70 m尺度上,生态位过程可解释物种多度分布格局。在次生林样地20 m×20 m、40 m×40 m、70 m×70 m尺度上,生态位过程和中性过程共同作用于物种的分布,但是生态位过程更为重要。可见,除了尺度和生境异质性外,原始林与受干扰的次生林中的物种多度分布也存在明显的差异。     

生态多样性模型的理论分析及应用：以新疆维吾尔自治区阜康地区为例

生态多样性是诸如物种、景观元和HLZ生态系统等研究对象丰富性和空间分布均一性的综合.理论分析表明,Shannon模型存在诸多理论的缺陷和应用的局限性.例如,Shannon模型具有大样本需求,不能反映空间尺度信息,也不能表达丰富性方面的多样性信息.本文引进Scaling生态多样性模型,以新疆维吾尔族自治区阜康市为案例区进行模拟研究.结果表明,随着空间分辨率逐渐粗化,Shannon模型模拟结果缺乏规律性,而Scaling生态多样性模型模拟得到的景观元多样性在30 m×30 m～150 m×150 m的空间尺度范围内不受空间分辨率的影响;在150 m×150 m～480 m×480 m的空间尺度范围内,随着空间分辨率的逐渐粗化,景观元多样性的模拟结果严格递减.     

森林采伐方式对森林景观的影响模拟——以大兴安岭呼中林区为例

干扰对森林景观变化的影响是一个长期的过程,传统的定位观测很难探究大空间尺度上干扰对森林景观的长期影响,模型模拟是目前常用的研究方法.本研究采用空间直观景观模型(LANDIS),模拟大兴安岭呼中林区在无采伐、皆伐、渐伐和择伐共4种预案下300年内森林景观的长期动态变化.选取落叶松和白桦为典型代表,以平均斑块面积、物种面积比例、聚集度以及年龄结构为指标,探讨不同采伐方式对森林景观的长期影响.结果表明:采伐降低了落叶松的面积比例,提高了白桦的面积比例,不同采伐方式之间差异不明显;采伐降低了落叶松的聚集度,提高了白桦的聚集度,皆伐预案高于其他预案;采伐在模拟前期降低了落叶松的平均斑块面积,提高了白桦的平均斑块面积;采伐提高了落叶松和白桦的中幼龄林比例,皆伐预案下白桦中幼龄林面积增加最明显.采伐使森林生态景观破碎化,皆伐预案下森林景观破碎化最为严重.建议,在采伐强度相同的条件下,尽量采用择伐方式,降低森林采伐对森林生态系统的影响,进而促进森林生态系统健康稳定的发展.     

空间直观景观模型的验证方法

空间直观景观模型已是当前景观生态学研究的一大热点。空间景观模型模拟空间格局变化。其模拟结果包含非空间数据和空间数据。空间直观景观模型的验证除进行非空间数据的验证外,还需要进行空间数据的验证。本文回顾了空间直观模型发展历程,总结现有的空间直观模型验证方法。包括主观评价、图形比较、偏差分析、回归分析、假设检验、多尺度拟合度分析和景观指数分析,同时提出今后空间直观景观模型验证方法研究的重点方向。     

The Effects of Seed Dispersal on the Simulation of Long-Term Forest Landscape Change

The study of forest landscape change requires an understanding of the complex interactions of both spatial and temporal factors. Traditionally, forest gap models have been used to simulate change on small and independent plots. While gap models are useful in examining forest ecological dynamics across temporal scales, large, spatial processes, such as seed dispersal, cannot be realistically simulated across large landscapes. To simulate seed dispersal, spatially explicit landscape models that track individual species distribution are needed. We used such a model, LANDIS, to illustrate the implications of seed dispersal for simulating forest landscape change. On an artificial open landscape with a uniform environment, circular-shaped tree species establishment patterns resulted from the simulations, with areas near seed sources more densely covered than areas further from seed sources. Because LANDIS simulates at 10-y time steps, this pattern reflects an integration of various possible dispersal shapes and establishment that are caused by the annual variations in climate and other environmental variables. On real landscapes, these patterns driven only by species dispersal radii are obscured by other factors, such as species competition, disturbance, and landscape structure. To further demonstrate the effects of seed dispersal, we chose a fairly disturbed and fragmented forest landscape (approximately 500,000 ha) in northern Wisconsin. We compared the simulation results of a map with tree species (seed source locations) realistically parameterized (the real scenario) against a randomly parameterized species map (the random scenario). Differences in the initial seed source distribution lead to different simulation results of species abundance with species abundance starting at identical levels under the two scenarios. This is particularly true for the first half of the model run (0–250 y). Under the random scenario, infrequently occurring and shade tolerant species tend to be overestimated, while midabundant and midshade tolerant species tend to be underestimated. The over- and underestimation of species abundance diminish when examining long-term (500 y) landscape dynamics, because stochastic factors, such as fire, tend to make the landscapes under both scenarios converge. However, differences in spatial patterns, and especially species age-cohort distributions, can persist under the two scenarios for several hundred years. Received 24 November 1998; accepted 17 March 1999.     

大兴安岭呼中林区虫害与火干扰交互作用的长期模拟

虫害和林火是森林生态系统的两种主要干扰类型,各种干扰在大时空尺度上存在一定的交互作用.本文采用空间直观景观模型LANDIS模拟虫害和林火在300年内的交互作用.结果表明:虫害干扰降低了细可燃物载量,提高了模拟前期(0～100 a)和中期(100～200 a)的粗可燃物载量,降低了模拟前期和中期的林火频率,不同干扰预案模拟后期(200～300 a)火烧频率的结果比较接近;虫害干扰降低了模拟前期和后期的火烧强度,增加了模拟中期的火烧强度,提高了模拟中期的森林火险等级,降低了模拟前期和后期的火险等级.人类灭火可增加虫害的发生面积,因此建议森林管理部门采取适当的防虫措施,不可只注重灭火,可以采取可燃物去除和计划火烧等方式管理林火,促进森林生态系统的可持续发展.     

A spatially interactive simulation of climate change, harvesting, wind, and tree species migration and projected changes to forest composition and biomass in northern Wisconsin, USA

In the coming century, forecast climate changes caused by increasing greenhouse gases may produce dramatic shifts in tree species distributions and the rates at which individual tree species sequester carbon or release carbon back to the atmosphere. The species composition and carbon storage capacity of northern Wisconsin (USA) forests are expected to change significantly as a result. Projected temperature changes are relatively large (up to a 5.8°C increase in mean annual temperature) and these forests encompass a broad ecotone that may be particularly sensitive to climate change. Our objective was to estimate the combined effects of climate change, common disturbances, and species migrations on regional forests using spatially interactive simulations. Multiple scenarios were simulated for 200 years to estimate aboveground live biomass and tree species composition. We used a spatially interactive forest landscape model (LANDIS‐II) that includes individual tree species, biomass accumulation and decomposition, windthrow, harvesting, and seed dispersal. We used data from two global circulation models, the Hadley Climate Centre (version 2) and the Canadian Climate Center (version 1) to generate transient growth and decomposition parameters for 23 species. The two climate change scenarios were compared with a control scenario of continuing current climate conditions. The results demonstrate how important spatially interactive processes will affect the aboveground live biomass and species composition of northern Wisconsin forests. Forest composition, including species richness, is strongly affected by harvesting, windthrow, and climate change, although five northern species (Abies balsamea, Betula papyrifera, Picea glauca, Pinus banksiana, P. resinosa) are lost in both climate scenarios regardless of disturbance scenario. Changes in aboveground live biomass over time are nonlinear and vary among ecoregions. Aboveground live biomass will be significantly reduced because of species dispersal and migration limitations. The expected shift towards southern oaks and hickory is delayed because of seed dispersal limitations.     

LANDIS PRO: a landscape model that predicts forest composition and structure changes at regional scales

LANDIS PRO predicts forest composition and structure changes incorporating species‐, stand‐, and landscape‐scales processes at regional scales. Species‐scale processes include tree growth, establishment, and mortality. Stand‐scale processes contain density‐ and size‐related resource competition that regulates self‐thinning and seedling establishment. Landscape‐scale processes include seed dispersal and disturbances. LANDIS PRO is designed to be compatible with forest inventory data, thus extensive inventory data can be directly utilized to initialize and calibrate model parameters before predicting future forest changes. LANDIS PRO allows for exploring the effects of disturbances, management, climate change, and modeling the spread of invasive species. We demonstrate that LANDIS PRO successfully predicts forest successional trajectories and stand development patterns in the Central Hardwood Forest region in U.S.     

Simulating the Effects of Fire Reintroduction Versus Continued Fire Absence on Forest Composition and Landscape Structure in the Boundary Waters Canoe Area, Northern Minnesota, USA

The Boundary Waters Canoe Area (BWCA) Wilderness of northern Minnesota, USA, ememplifies how fire management and natural disturbance determine forest composition and landscape structure at a broad scale. Historically, the BWCA (>400,000 ha) was subject to crown fires with a mean rotation period of 50–100 y. Fires often overlapped, creating a mosaic of differently aged stands with many stands burning frequently or, alternatively, escaping fire for several centuries. The BWCA may never have reached a steady-state (defined as a stable landscape age-class structure). In the early 1900s, a diminished fire regime began creating a more demographically diverse forest, characterized by increasingly uneven-aged stands. Shade-tolerant species typical of the region began replacing the shade-intolerant species that composed the fire-generated even-aged stands. Red pine (Pinus resinosa) stands are relatively uncommon in the BWCA today and are of special concern. The replacement of early-to-midsuccessional species is occurring at the scale of individual gaps, producing mixed-species multiaged forests. We used LANDIS, a spatially explicit forest landscape model, to investigate the long-term consequences of fire reintroduction or continuing fire absence on forest composition and landscape structure. Fire reintroduction was evaluated at three potential mean fire rotation periods (FRP): 50,100, and 300 y. Our model scenarios predict that if fire reintroduction mimics the natural fire regime (bracketed by FRP = 50 and 100 y), it will be most successful at preserving the original species composition and landscape structure, although jack pine (Pinus banksiana) may require special management. With limited fire reintroduction, all of the extant species are retained although species dominance and landscape structure will be substantially altered. If fire remains absent, many fire-dependent species will be lost as local dominants, including red pine. The landscape appears to be in a state of rapid change and a shift in management to promote fire may need to be implemented soon to prevent further deviation from historic, presettlement conditions.