Effects of Changes in Forest Use on Biodiversity 3
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Chapter 3 EFFECTS OF CHANGES IN FOREST USE ON BIODIVERSITY 3. Introduction Chapter 3 Chapter 3 Introduction Satoshi Yamashita Research Institute for Humanity and Nature In Chapter 2, the changes in forest utilization during the past 50 to 100 years were revealed for each study site. Based on this understanding, we will discuss the effects of forest utilization on the biological community at each study site in section 3.1 and the effects of human activities on ecosystem functions in section 3.2. In section 3.1, we discuss the effects of forest utilization on communities or populations of living organisms at each study site. At Lambir, species diversity and the species composition of plants (Momose et al.), insects (i.e. butterflies (Itioka et al.), beetles (Kishimoto-Yamada et al.), ants (Matsumoto et al.) ), mammals (i.e. bats (Fukuda et al.), small mammals (Nakagawa et al.)), and macrofungi (Yamashita et al.) were compared among several forest types (i.e. rubber plantation, secondary forest after swidden agriculture, isolated natural forest, and primary forest). In every biological community except for the beetle community, species diversity was highest in the primary forest and generally decreased with increasing disturbance of the forest. At Sabah, species diversity and the species composition of plants (Aiba et al.), insects (i.e. flies (Akutsu et al.)), soil animals (Ito et al.) and mammals (Onoguchi & Matsubayashi) were compared between forest managed under reduced-impact logging, forest managed under conventional logging, and primary forest. Species diversity of plants and mammals was higher in forest managed under reduced-impact logging than in forest managed under conventional logging methods. On Yaku Island, the species diversity and biomass of plants (Aiba et al., Tsujino et al.) and insects (e.g., beetles, horseflies, wasps (Yamauchi et al.)) and the density of the Japanese macaque (Hanya et al.), were surveyed in primary forest, plantations of Japanese cedar, and secondary forest. Species diversity of plants and insects was lower in the plantation forest than in the primary forest. At Abukuma, the community structure of the forest-floor vegetation (Tanaka et al., Nagaike et al.) and of arthropods (e.g., butterflies, moths, wasps, beetles, springtails, mites (Makino et al.)) was surveyed in several different forest types (e.g., plantations of Japanese cedar and secondary and old growth broadleaved deciduous forest) for a range of forest ages. Species diversity of the forest-floor vegetation was higher in young stands than in intermediate-aged and old stands in both the secondary forest and the plantation forest. Species composition differed among the forest types. Arthropods could be divided into three groups based on the response of their species diversity to the age of the forest: in one group, species diversity decreased with increasing forest age (e.g., butterflies, longhorn beetles); in the second group, species diversity increased with increasing forest age (e.g., mycophagous mites); and in the third group, species diversity did not change with increasing forest age (e.g., moths, ground beetles). In section 3.2, we discuss the effects of human activities on ecosystem functions. Here, we define ecosystem functions as the functions that are necessary for the growth or sustenance of the ecosystem, such as pollination, the food chain, and matter and energy flows. Recently, the area of forest has decreased rapidly, accompanied by fragmentation of large stands into smaller stands, as was seen in Chapter 2. We hypothesized that fragmentation of forests would reduce the size of plant populations, leading to reductions in visitation by pollinators, reductions in the number of individuals capable of reproduction, and inbreeding depression. In section 3.2.1., we discuss the results of some basic studies of plant ecology at Lambir (Aiba & 65 3. Introduction Chapter 3 Nakashizuka, Kenzo et al., Ichie et al.) and Yaku island (Tanabe et al.). In section 3.2.2., we introduce studies on plant reproductive ecology (Momose et al.) and plant–pollinator interactions (Kumano & Yamaoka, Ushimaru et al.), and then we discuss the effects of forest fragmentation caused by human activities on plant community. Studies of one tree species at Lambir (Takeuchi et al.) and two tree species at Abukuma (Matsuki & Isagi, Tateno et al., Kikuchi et al., Shibata et al.) revealed that forest fragmentation does not always have a negative influence on tree reproduction. In section 3.2.3., we discuss the results of studies of changes in seed-dispersal systems in response to changing human utilization of the forest. At Lambir, the pattern of fruit utilization by bird communities is described (Kamoi et al.). At Sabah, the loss of large mammal seed-dispersers after conventional logging appeared to have detrimental effects on the regeneration of two Durio species (Nakashima & Matsubayashi). On Yaku Island, the restoration of a Ficus species population after logging conducted 60 years ago is not yet complete (Otani & Sei-ichi). The behavior of the Japanese macaque determines the spatial distribution of the tree Myrica rubra (Terakawa et al.), and seeds of M. rubra was attacked by lepidopteran insects before dispersal (Fujita et al.). At Abukuma, forest fragmentation positively affected the growth of seedlings of plant species that are dispersed by birds (Naoe et al.). The second and third sections of this chapter show that the effects of human activities on plant regeneration are highly variable. The effects on species interactions might affect plant–seed disperser systems, plant–pollinator systems, or some other combination of these systems described in section 3.2.4. (Tanaka et al., Handa et al., Tzuchiya & Itioka, Okubo & Itioka). At Lambir, swidden cultivation reduced the species diversity of ants and plants, which means that simplification of the species composition also simplified the interspecific interactions, and the effects were still detectable at least 20 years after the initial disturbance (Tanaka et al.). Some studies of the effects of human activities on interspecific interactions have pointed out that human activities sometimes affects these interactions and that the response of the system differs depending on a range of factors. Such changes in community structure might affect matter and energy flows through the forest ecosystem. In section 3.2.5., we focus on matter flows, especially through the decomposition system (Wagai et al.). At Sabah, the decomposition rate of leaf litter was highest in the forest managed under conventional logging (Hasegawa et al.). In this report, we will present an assessment method for evaluating the level of sustainable forest use. The results permit an assessment of the ecological situation at the study sites. The results clearly demonstrate the different responses of species diversity of various organisms and of ecological functions to human activities, and suggest that understanding the traits of individual organisms is needed before evaluation can occur. 66 3.1. Effects of Forest Use on Biological Community Chapter 3 Effect of Forest Use on Microhabitat Environment and Vegetation Structure in Sarawak, Malaysia Kuniyasu Momose1, Michi Kaga2, Miyako Koizumi2, Keiko Kishimoto-Yamada3, Hiroshi O Tanaka3, Takashi Matsumoto3, Takao Itioka3, Michiko Nakagawa4, Masahiro Ichikawa5, Mitsunori Yoshimura5, Tohru Nakashizuka6, Lucy Chong7 1 Faculty of Agriculture, Ehime University 2 Graduate School of Asian and African Area Studies, Kyoto University 3 Graduate School of Human and Environmental Studies, Kyoto University 4 Graduate School of Bioagricultural Sciences, Nagoya University 5Research Institute for Humanity and Nature 6 Graduate School of Life Sciences, Tohoku University 7 Sarawak Forestry Corporation, Malaysia Introduction Tropical rain forests in Southeast Asia have been exposed to drastic and rapid deforestation because of an increasing human population and a rapidly developing economy. The annual deforestation rate in this region is 1.9%, whereas the average global rate is only 0.2 to 0.3% (Matthews 2001). Elucidation of the effects of forest use on plant biodiversity and on the microhabitat environment is an urgent subject for species conservation and proper forest management. Many studies have been performed on the effects of forest fragmentation on changes in tree species composition or abundance (e.g., Laurance et al. 2000). These studies have revealed that the structure of a forest remnant might be affected by its area, its distance from primary forest, and the elapsed time since fragmentation began (Laurance et al. 2002). In Southeast Asia, forests are used for various purposes, including traditional ones. Slash-and-burn agriculture remains a widespread method of cultivation; local people (the Iban) abandon a field and shift to a new site after harvesting. As a result, secondary forests (fallows) at various developmental stages form a mosaic of landscape. Because rubber trees have been planted in abandoned fallows, particularly since the 1950s to produce crude rubber as a cash crop in Sarawak, Malaysia, rubber plantations operated by small holders are another widespread vegetation type (Ichikawa 2003). To understand the effect of forest use on a region’s vegetation structure, research must be conducted on the diverse vegetation types that form the forest mosaic. The alternation of vegetation structures may also be accompanied by changes in the microhabitat environment, such as canopy openness