Ecology of Indonesian Papua Part Two. Andrew J. Marshall
Читать онлайн книгу.
‘‘ecosystem’’ is used frequently and in a wide variety of contexts without formal definition. In this volume we use the term to classify specifically delineated parts of the environment and all biological organisms that inhabit them. For example, lower montane forest is a particular ecosystem type that encompasses the physical structure of a mountain (e.g., bedrock, soil) found between roughly 650 and 1,500 meters elevation and all of the flora and fauna living within this structure (Chapter 5.10). It is distinct from the alpine ecosystem type typically found at higher elevations and the lowland forest ecosystem type found below. We do not use the term ‘‘ecosystem’’ to refer to the habitat occupied by a particular species, as this term is highly-species specific: the habitat of one species may include many ecosystem types (e.g., many bird species), while another species might only be found in one particular subset of an ecosystem type (e.g., a tree species limited to a particular soil type).
Ecosystem Classification
One of the complications that has long plagued ecosystem ecologists is the difficulty in identifying the boundaries of an ecosystem. Sharp lines can rarely be drawn that delineate the extent of a particular ecosystem type or contain all relevant ecological processes and interactions (Whittaker 1970). Even boundaries that initially appear to be clearly delineated are revealed upon careful examination to be porous and dynamic. For example, at first glance few ecosystems would seem to be more clearly distinct than the abutting marine and terrestrial ecosystems found along coastlines around the world. However, closer investigation reveals that energy and nutrients flow between these ecosystems, organisms move back and forth between them, and that the health and stability of one can profoundly effect the other. These interactions make categorization of ecosystems as discrete entities somewhat artificial. For the purposes of description, we have classified Papua’s ecosystems into twelve broad categories. Nevertheless, it is important to remember that these classifications are simplifications made to facilitate discussion, and that in reality ecosystems are highly interconnected and interdependent.
The principle division of aquatic ecosystem types is based on water salinity, and two major categories are typically considered: saltwater (or marine) and freshwater ecosystems. Various ecosystem types are defined in each of these broad categories based on physical features such as substrate, temperature, water depth, and dominant vegetation type (Smith and Smith 2003). In this chapter we consider four major categories of aquatic ecosystems in Papua: coral reefs, seagrass ecosystems, mangroves, and inland water ecosystems.
The world’s major terrestrial ecosystem types (often referred to as biomes) are classified by vegetation type, which is largely dependent on rainfall and temperature (Whittaker 1970). Within these biomes, separate ecosystems can also be defined according to the composition and structure of the plant community. We follow this convention by considering six distinct vegetative formations (i.e., ecosystems) within the tropical forest biome, following a roughly altitudinal gradient from coastal ecosystems to alpine vegetation. We also consider the extensive monsoon grassland and savanna ecosystems found in plains and deltas of the great rivers in southern New Guinea. Finally, we discuss the unique and little-known cave ecosystems of Papua.
Ecosystem Diversity in Papua
Many of the terrestrial ecosystem types discussed in this section are further subdivided based on dominant vegetation, altitude, soil type, and degree of human disturbance. The wide array of ecosystem types found in Papua helps to explain why this is an area of such high biodiversity and a major center of endemism in many distinct taxonomic groups. From the reefs that contain the most coral species in the world to the cryovegetation communities growing in the ice and snow atop its highest mountains, Papua’s ecosystem diversity creates a wide range of ecological conditions, each of which supports a highly specialized community of flora and fauna. Some ecosystems are fairly well characterized and understood (e.g., seagrass ecosystems, coastal vegetation), while others are scarcely known and the diversity and ecological interactions contained therein have yet to be discovered (e.g., cave ecosystems). Yet the uniqueness, complexity, and diversity of each of these ecosystem types is abundantly clear, and helps to make Papua one of the most biologically important regions on earth (Supriatna 1999).
Papua’s high diversity of terrestrial ecosystems is largely due to its wide altitudinal range (Figure 5.1.1). Accurate measures of the extent of different ecosystem types in Papua are difficult to calculate, both because of difficulties in classifying ecosystems and complications in recognizing these ecosystem types on images obtained through remote sensing. However, based on general land cover classifications (Hansen et al. 1998) and recent Landsat 7 ETM imagery of Papua (1999–2000), the extent of broad land classes can be mapped (Figure 5.1.2). Analysis of the resulting map provides estimates of the extent of each major land class in Papua. When forests are broadly defined to include all land cover classes with greater than 10% tree or shrub canopy cover, roughly 85% of Papua was forested in 2000 (Table 5.1.1). Over 60% of these forests were lowland evergreen forests (51% of Papua’s total area), making Papua home to the largest remaining tracts of lowland tropical evergreen forest in Indonesia. Large areas of mangrove forest (15,124 km2, 4.3% of forested land), swamp ecosystems (68,312 km2, 19.5% of forested land), and montane forest (36,032 km2, 10.3% of forested land) are also found, in addition to several other ecosystem types, each of which comprise more than 1% of forested area in Papua (Table 5.1.1).
Figure 5.1.1. Surface elevation and ocean depth in Papua. The wide range of altitudes leads to a diversity of ecosystem types.
Figure 5.1.2. Forest cover in Papua. The picture is an interpretation of Landsat 7 ETM imagery of Papua, using a combination of images acquired in 1999 and 2000.
Source: Forest Watch Indonesia–Conservation International–Ministry of Forestry.
The distribution and diversity of ecosystem types across the island of New Guinea are similar to those found in Papua (Figure 5.1.3). Due to differences in data quality and forest classification, figures for New Guinea are not directly comparable to those from Papua. However, analyses show that in 2000 the island of New Guinea was overwhelmingly forested, containing almost 657,000 km2 (82% of the land area) of broadleaf forest and woodland (Table 5.1.2). For this reason New Guinea is considered one of the world’s three great lowland tropical rainforest Wilderness Areas (Mittermeier et al. 2003).
THE IMPORTANCE OF ECOSYSTEM DIVERSITY FOR PAPUAN FAUNA
Landscapes containing several ecosystem types have higher species richness than equivalent areas containing only a single ecosystem type (Figure 5.1.4). Thus Papua’s high ecosystem diversity helps to explain the high diversity found in a number of taxonomic groups of flora (Section 3) and fauna (Section 4). In addition, many vertebrate species rely on more than one ecosystem type, often utilizing different ecosystem types for breeding, nesting, and foraging. For example, several species of sea turtles feed in open oceans and seagrass ecosystems, but rely on coastal beaches to lay their eggs (Chapter 4.6). Similarly, many species of mammals, insects, and birds breed in mangrove forests but live and forage mainly in adjacent terrestrial or marine habitats (Chapter 5.4). Greater Melampittas nest in cave ecosystems but forage daily in nearby forest ecosystems (Chapter 5.13), and many other bird species utilize several forest types at a variety of altitudes during their normal life cycles (Chapter 4.9). Therefore, preservation of the full complement of ecosystem types in Papua is necessary both to preserve its high biodiversity and to provide the habitat requirements for a number of threatened vertebrate species.
Figure 5.1.3. Forest cover in New Guinea. The picture is an interpretation of Landsat 7 ETM imagery of Papua, using a combination of images acquired in 1999 and 2000.
Source: Forest Watch Indonesia–Conservation International–Ministry of Forestry.
