Linkages in the Landscape——part4

Migratory shorebirds and waterfowl, for example, use a limited number of ‘stopovers’ along migration paths for feeding and shelter before continuing their journey. At these times a large proportion of the population can be concentrated in a relatively restricted area. Consequently, degradation or destruction of stopover wetland habitats, or excessive hunting at these points, can have a severe impact on migration and on overall population numbers and conservation status. Thus, game managers in North America, for example, have extensively mapped the migratory flyways of waterfowl and protection of major stopover points is a high priority (Peek 1986).

例如，迁徙的滨鸟和水禽在继续迁徙之前，会在迁徙路线上使用一定数量的“中转停留站”进行觅食和栖息。在这些时候，大部分种群可能集中在一个相对有限的区域。因此中转停留湿地栖息地的退化或破坏，或在这些区域的过度狩猎，都可能对迁徙以及整个种群数量和保护状况产生严重影响。因此，北美的狩猎管理人员已经广泛绘制了水禽的迁徙路线，并将保护主要中途停留站列为重中之重。

Seasonal nomadic movements by species whose food resources vary in a relatively unpredictable manner may likewise be assisted by habitat corridors or stepping stone

linkages.

食物资源变化相对较难预测的物种，其季节性游牧活动同样也可以通过栖息地廊道或脚踏石的连接得到帮助。

Dispersal can be described as the one-way movement of an individual away from a home range or territory to a new area. For example, a young hopping-mouse, squirrel, or wallaby leaves its maternal home range and disperses to a new area where it establishes its own range. The use of linkages to assist dispersal of animals between otherwise-isolated patches of habitat is an important way in which they can enhance species’ conservation. Immigration of new individuals can supplement a declining population to prevent its disappearance, introduce new genes to an isolated population, or allow colonization of new habitats as they

become suitable.

扩散可以被描述为个体离开家园范围或领地到新区域的单向移动。例如，一只年轻的跳鼠、松鼠或小袋鼠离开母体的活动范围，扩散到一个新区域，在那里建立自己的活动范围。

利用连接区来帮助动物在孤立的栖息地之间扩散，是加强物种保护的一种重要方式。新个体的迁入可以补充减少的种群以防止其消失，也可以向孤立的种群引入新基因或允许在合适的新栖息地定居。

These observations show that high-quality stopover habitats are critical links along migratory corridors for some land birds. If natural variation in habitat quality has such an appreciable effect on the survival of migrating birds, then degradation or complete destruction of critical

stopover points must be a cause for great concern.

这些观察结果表明，高质量的中转停留栖息地是一些陆地鸟类迁徙廊道的关键环节。如果栖息地质量的自然变化对候鸟的生存有如此显著的影响，那么关键中转停留栖息地的退化或完全破坏就必须引起高度重视。

PART3

LINKAGES AND CONSERVATION STRATEGY

It is important to recognize that in the real world there is rarely an opportunity to design an‘ideal’ system of habitats to maintain landscape connectivity. The all-too-frequent reality is the challenge of how to:

• best manage remnant linkages that have survived in heavily disturbed landscapes;
• maximize landscape connectivity by using habitats retained primarily for other purposes;
• restore connectivity between the vestiges of natural habitats that remain after development.

重要的是认识到，在现实世界中，很少有机会设计一个“理想”的栖息地系统来保持景观的连通性。经常出现的现实挑战是：

• 如何最好地管理在受到严重干扰的景观中幸存下来的残存连通性。
• 利用主要为其他目的而保留的栖息地，最大限度地提高景观连通性
• 恢复开发后残存的自然栖息地之间的连通性

结构连通性

影响结构连通性的变量包括：间隙的数量和长度，合适栖息地之间是否存在替代路径或网络，以及系统中是否存在有利栖息地的“节点“。

For species able to move between stepping stone habitats, key elements of connectivity include the distance between ‘steps’, the number of alternative steps available, and the land use and quality of habitat in the surrounding matrix. The gaps between steps must

be within the range that animals will normally cross.

对于能够在脚踏石栖息地之间移动的物种，连通性的关键要素包括脚踏石之间的距离，可用的替代脚踏石的数量，周围基质的土地利用和栖息地质量。脚踏石之间的间距必须在动物通常会跨越的范围内。

Incorporation of nodes of favoured habitat as part of a link can increase its effectiveness by providing additional habitat in which animals may take refuge or forage during lengthy movements. Habitat nodes may also maintain larger breeding populations within the linkage, thus introducing more dispersers into the system. Examples of nodes include (Fig. 7–3):

• nature reserves associated with a major landscape link (Noss and Harris 1986).
• floodplain expansions along riparian corridors (Dobbyns and Ryan 1983; Recher et al.1987);
• additional vegetation at T and cross (+) junctions along hedgerow and fencerow networks (Forman and Godron 1986; Lack 1988);
• small forest patches adjacent to roadside corridors.

Intuitively, it is evident that landscape connectivity will be greatest when there is a high level of structural connectivity created by a combination of alternative and network pathways, nodes along linkages, and few gaps or breaks (Fig. 7–1).

将有利栖息地的节点作为连接区的一部分，可以提供额外的栖息地，使动物在漫长的运动中可以避难或觅食，从而提高其有效性。栖息地节点也可在连接区中维持较大的繁殖种群，从而将更多的扩散者引入系统。节点的例子包括：

• 与主要景观连接区相关的自然保护区
• 沿着河岸廊道扩展的洪泛区
• 沿树篱和篱笆网络的T形和交叉路口连接处的额外植被
• 道路两边廊道附近的小片森林

直观地看，当替代路径和网络路径、沿连接的节点和很少的间隙或断裂都同时满足，形成高水平的结构连通性时，景观连通性将最大。

the availability and reliability of resources such as food, shelter, refuge from predators and nest sites are critical if animals are to be able to live in linkages and use them as pathways for movement. A variety of studies have shown relationships between the occurrence and abundance of animals in connecting habitats and the availability of certain habitat components (Pollard et al. 1974; Yahner 1983a, b; Arnold 1983; Osborne 1984; Recher et al. 1987; Lindenmayer et al. 1993, 1994b; Bennett et al. 1994). The provision of high quality habitat raises several important issues in the design and management of linkages.

要使动物能够在连接栖息地中生活并将其作为移动路径，食物、栖息地、避难所和巢穴等资源的可用性和可靠性至关重要。多项研究表明，在连接栖息地中动物的出现和数量与某些栖息地成分的可用性之间存在关系。提供高质量的栖息地在设计和管理连通性方面提出了几个重要问题。

First, habitat quality is a critical issue for landscape linkages that form part of an integrated conservation network at the regional scale (Harrison 1992). Landscape links that maintain resident populations and communities must provide year-round resources for feeding, shelter and breeding. Similarly, stepping stone links, such as those that provide short-term ‘stopover’ points for migratory birds, must provide rich food resources at critical times of the year. Habitat quality is also important at the scale of local networks. Typically, linkages in which animals are resident must provide a greater range and specificity of resources (food, shelter, breeding sites) than those used only for brief movement (Bennett et al. 1994; Lindenmayer et al. 1994a, b; Lynch et al. 1995). Animals undertaking direct movement may simply need adequate cover or refuge for the brief duration of the movement, and may use linkages not otherwise suitable to live in (see Box 4–2).

首先，栖息地质量是构成区域尺度综合保护网络一部分的景观联系的关键问题。维持种群和群落的景观联系必须提供全年的觅食、栖息和繁殖资源。同时，为候鸟提供短期“中途停留”站的脚踏石等也必须在一年中的关键时刻提供丰富的食物资源。在地方网络的规模上栖息地质量也很重要。通常，动物常驻的网络必须比那些只用于短暂移动的网络提供更大范围和更更特殊的资源（食物、栖息地、繁殖地）。直接移动的动物可能只需要在短暂的移动期间内有足够的遮蔽或避难所，并可能使用不适宜生活的联系。

Second, to provide effective continuity between large reserves that encompass several contrasting habitats (such as ridges and gullies in mountainous forest, dunes and swales in arid environments), landscape links must be sufficiently diverse to provide for species that occur in each habitat. This can be achieved by a broad connecting tract that itself encompasses the range of topography and habitats, or by duplication to provide links of different vegetation types (Bennett 1990a; Claridge and Lindenmayer 1994).

其次，为了在包含多种不同栖息地（如山地森林中的山脊和沟壑，干旱环境中的沙丘和沼泽）的大型保护区之间提供有效的连续性，景观联系必须足够多样化，以便服务于出现在每个栖息地的物种。这可以通过一个本身包含各种地形和栖息地的广阔连接带，或通过重复提供不同植被类型的联系来实现。

Third, wherever possible, linkages should be based on existing natural vegetation rather than on degraded or reconstructed vegetation. A high-quality habitat for wildlife requires the full diversity of natural vegetation, maintained by natural ecological processes. Resources in forests and woodlands, such as leaf litter, tree hollows, large dead trees, hypogeal fungi and diverse invertebrate communities, cannot be created simply by planting trees and shrubs in rows. An urgent task, therefore, is to identify, retain and protect natural links that are still present in the landscape before they are lost. Where it is necessary to re-establish vegetated links, priority should be given to restoration that mimics the natural environment. Restoration of existing semi-natural vegetation or revegetation directly adjacent to natural vegetation is likely to enhance the re-establishment of natural processes in new habitats (Hobbs 1993b).

第三，在可能的情况下，连接区应基于现有的自然植被而不是退化或重建的植被。一个高质量的野生动物栖息地需要自然植被的多样性，并通过自然生态过程维持。森林和林地中的资源，如落叶、树洞、枯树、地下真菌和各种无脊椎动物群落，不能简单地通过成行种植树木和灌木来创造。因此，当务之急是在景观中仍存在的自然联系消失之前识别、保留和保护它们。在需要重建植被联系的区域应优先考虑模仿自然环境的修复。恢复现有的半自然或直接在自然植被附近进行植被修复可能会促进新栖息地中自然过程的重建。

Fourth, wildlife habitats are not static but change with time. Some resources, such as large trees, natural tree hollows and large decaying logs, only develop after long periods of time; whereas other resources may occur only in early successional stages. Animal species show different patterns of occurrence in relation to vegetation age and so the seral stage of the habitat can be a determining influence on its value as a link.

Consequently, although potential habitat corridors were present and were used by other species, the nature of the habitat apparently precluded this species from using the links. In the longer term it will be necessary to actively manage vegetation in many conservation networks to ensure that key habitat resources are maintained.

第四，野生动物栖息地不是一成不变的，而是随着时间的推移而变化。有些资源，如大树、天然树洞和大型腐木（只有经过很长时间才会形成）；而其他资源可能只出现在早期演替阶段。动物物种的出现模式与植被年龄相关，因而栖息地的演替阶段可对其作为联系的价值产生决定性影响。

因此，尽管存在潜在的栖息地廊道，并被其他物种使用，但栖息地的性质显然使该物种无法使用这些廊道。从长远来看，有必要积极管理许多保护网络中的植被，以确保维持关键的栖息地资源。

Last, linear habitats are particularly vulnerable to edge effects (see below), and consequently a greater level of management is required to maintain the integrity of vegetation in linkages than for comparable areas within extensive natural environments.

最后，线性栖息地特别容易受到边缘效应的影响。因此，与广泛自然环境中的类似区域相比，需要更高的管理水平来维持连接区植被的完整性。

How far do edge effects extend? How wide is an edge? How wide must landscape links, local habitat corridors or stepping stones be to minimize the impact of edge disturbance and include high quality habitat? These are difficult questions of direct relevance to wildlife conservation. The solutions must be considered in relation to a particular process or parameter (Box 7–2).

边缘效应能延伸多远？边缘有多宽？景观连接区、当地栖息地廊道或脚踏石的宽度必须多宽才能最大限度地减少边缘干扰的影响，并能包括高质量的栖息地？这些都是与野生动物保护直接相关的难题。必须结合特定的过程或参数来考虑解决方案。

The impact of edge disturbance processes is greatest where there is a sharp contrast between two types of habitat, such as forest and farmland. They are less marked at interfaces between two forest types, or different age classes within continuous forest (Rudnicky and Hunter 1993).

当两种类型的栖息地（如森林和农田）对比明显时，边缘干扰过程的影响最大。它们在两种森林类型或连续森林中不同年龄等级的的交界处，边缘干扰过程就不太明显。

There are at least three main benefits of increased width of connecting habitats.

First, reduction of edge effects can be most effectively countered by increasing the width or size of the habitat. Wider linkages are more likely to maintain some habitat little disturbed by edge effects. For this reason, it is imperative that linkages between nature reserves or large natural areas that aim to preserve continuity for whole communities of animals are as large as possible. Continuity of populations depends on the quality and integrity of the habitat being maintained so that communities are able to live throughout the length of the linkage.

Second, for a linkage of given length, increased width incorporates a larger area and the potential for a greater diversity of habitats and a greater abundance and diversity of wildlife. This is simply an application of the well known species-area relationship: larger areas tend to support more species than smaller areas.

Last, greater width increases the likelihood that a linkage will provide for species with requirements for large amounts of space or specialized feeding and habitat requirements. Thus, the relative composition of faunal assemblages in wide habitat corridors differs from that in narrow strips.

增加连接栖息地的宽度至少有三个主要好处。

首先，增加栖息地的宽度或面积可最有效地抵消边缘效应。更宽的连接区更有可能维持一些很少受到边缘效应干扰的栖息地。因此，自然保护区或大型自然区域的连接区必须尽可能大以保持整个动物群落的连续性。种群的连续性取决于栖息地的质量和完整性，以便动物群落在整个连接区内生存。

其次，对于给定长度的连接区，增加宽度意味着更大的面积，更有可能增加的栖息地多样性以及野生动物的丰富性和多样性。这只是众所周知的物种与面积关系的一个应用：面积较大的区域往往比面积较小的区域拥有更多的物种。

最后，宽度越大，就越有可能为需要大量空间或特殊觅食和栖息地需求的物种提供食物。因此，宽阔栖息地廊道中动物群落的相对组成与狭窄栖息地廊道不同。

In the absence of empirical information on the requirements of particular species or communities, the most useful measure for determining an optimum width appears to be the distance over which edge disturbances are likely to affect the function of the linkage. To ensure that the link maintains some portion relatively free of disturbance, the width must be more than twice that over which edge disturbances influence ecological processes. This measurement must be based on the circumstances of a particular link and the disturbance to which it is subject.

在缺乏关于特定物种或群落要求的经验资料的情况下，确保最佳宽度的最有用的衡量标准似乎是边缘干扰可能影响连接区功能的距离。为了确保连接区保持相对不受干扰的部分，宽度必须大于边缘干扰对生态过程的影响距离的两倍以上。这一衡量标准必须基于特定连接区的具体情况以及受到的干扰。

The challenge is to implement the best management practices to maintain connectivity of existing linkages, or to maximize connectivity based around existing vegetation patterns. In other situations, such as extensive forested regions, options still remain as to where linkages can be most effectively placed to maintain natural connectivity. Location is also an important issue in landscapes where plans are underway to regenerate or establish new linkages.

面临的挑战是如何实施最佳管理措施，以保持现有连接区的连通性，或在现有植被模式的基础上最大限度地提高连通性。在其他情况下，如大面积的森林地区，仍然可以在何处最有效地建立连接区以保持自然的连通性。在规划重建或建立新的连接区的景观中，位置也是一个重要问题。

The primary function of linkages is to maintain connectivity for populations and habitats that were naturally continuous. Habitat corridors should not be established to link populations or habitats separated by some form of natural environmental barrier: for instance, it is inappropriate to establish wooded linkages across a natural grassland plain. Care should also be taken when re-establishing habitat continuity to ensure that it does not facilitate the spread of diseases that may have established in isolated populations. Although these concerns have been raised as criticisms of habitat corridors, they are of limited relevance because they apply primarily to situations where linkages are being deliberately re-established. The protection of existing tracts of natural vegetation is simply maintaining natural ecological connections.

连接区的主要功能是维持自然连续的种群和栖息地的连通性。不应建立栖息地廊道来连接被某种形式的自然环境阻碍隔开的种群或栖息地。例如，不宜在天然草原平原上建立林木连接区。在重建栖息地连续性时，还应注意确保不会助长可能已在孤立种群中形成的疾病的传播。尽管这些问题被作为对栖息地廊道的批评而提出，但它们的意义有限，因为它们主要适用于有意重建连接区的情况。保护现有的自然植被只是为了保持自然生态联系。

Linkages will be most effective when they protect known pathways taken by animals, such as seasonal migratory routes of large mammals, stopover points of migratory waterfowl, daily foraging or movement routes of large animals, or habitats typically used by individuals dispersing between populations (Harrison 1992). Clearly, preliminary observations of actual movements, or information from ecologists or knowledgeable local people will be particularly useful.

在保护动物的已知路径，如大型哺乳动物的季节性迁徙路线、迁徙水禽的中途停留站、大型动物的日常觅食或移动路线，或个体在种群扩散时经常使用的栖息地时，这种连接区将最为有效。显然，对实际运动的初步观察、生态学家或当地知情人提供的信息将特别有用。Whenever possible, linkages should be located away from known sources of human disturbance, or the disturbance should be moved from the designated linkage. Where disturbance is unavoidable, its impact will be reduced if it is located to one side, rather than centrally within a link. Disturbance to natural environments from two key sources – encroaching human settlements and road systems – are a major challenge to the management of landscape linkages.

只要可能，连接区应远离已知的人类干扰源，或应将干扰从指定的连接区移动。在干扰不可避免的情况下，如果把干扰放在一侧，而不是连接区的中心，就会减小干扰的影响。对自然环境的干扰主要来自两个方面：不断侵占的人类居住区和道路系统，这是对景观连接区管理的主要挑战。

The designation of buffer zones or the deliberate establishment of buffer vegetation may help to protect sensitive habitats within linkages (Noss and Harris 1986; Noss 1992). This may take several forms. To protect broad landscape links, a system of land zoning can be used to permit limited use of natural resources or limited recreational use in an outer buffer zone, while excluding such activities from the core of the linkage. The use of buffer zones in this way has been widely advocated to protect tropical reserves (Sayer 1991) and is a key element in the planning strategy for Biosphere Reserves under the Man and the Biosphere Programme of UNESCO (see also Box 8–3). Another form of buffering is to use strips of natural or planted vegetation adjacent to linkages to protect them from environmental change and other disturbance. Such narrow buffers can also serve as a clear marker of the boundary of the linkage, to limit incremental encroachment or clearing. Obviously, if buffer strips are established adjacent to habitat corridors care must be taken to ensure that they are of indigenous vegetation, not of species that will invade and degrade the linkage.

指定缓冲区或有意建立缓冲植被可能有助于保护连接区内的敏感生境。可能的形式主要有以下几种。为保护广阔的景观连接区，可使用土地分区系统，允许在外围缓冲区内有限地使用自然资源或有限的娱乐活动，同时将这些活动排除在连接区的核心区之外。以这种方式利用缓冲区保护热带保护区已经得到广泛提倡，也是教科文组织人与生物圈计划下生物圈保护区规划战略的一个关键要素。另一种缓冲形式是在连接区附近使用天然或人工植被带，以保护连接区不受环境的变化和其他干扰。这种狭窄的缓冲区也可可作为连接区边界的明确标志，以限制不断侵占或清除。显然，如果是在栖息地廊道附近建立缓冲带，必须注意确保缓冲带是本地植被，而不是入侵或破坏连通性的物种。