Biodiversity (1988) / Chapter Skim
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Part 4: Diversity at Risk: The Global Perspective
Part 4: Diversity at Risk: The Global Perspective
Pages 155-190
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From page 157... ...
and which have proviclecl to a large degree the timber and in part the fuel to support the growing human population. In the next chapter, Risser discusses the impact of humans on biological diversity in grasslands, the blame that has largely provided, either directly or indirectly, the food for the world's human population.
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From page 158... ...
reported that the number of plant species he encountered in 0.1hectare plots increased as he moved from dry tropical to wet tropical forests (Table 17-1~. In his most diverse sites in Panama he encountered more than 150 species of woody plants thicker than 1 inch in diameter at breast height.
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From page 159... ...
of Species Dry Tropical Foresta Costa Rica upland, Guanacaste Costa Rica riparian, Guanacaste Venezuelan Llanos, Calabozo Venezuelan coastal, Boca de Uchire Moist Tropical Foresta Panama Canal Zone, Curundu Brazil, Manaus Panama Canal Zone, Madden Forest Wet Tropical Foresta Panama Canal Zone, pipeline road Ecuador, Rio Palenque Costa Rica, near La Selvab Temperate Zonea Missouri, Babler State Park Temperate Zoner Australia, forests and woodlands Tennessee, Great Smoky Mountains Oregon, Siskiyou Mountains Arizona, Santa Catalina Mountains Colorado, Rocky Mountain National Park Mediterranean Zoned Israel, grazed woodlands Israel, open shrubland Israel, closed shrubland California, grazed woodlands California, closed shrubland Chile, open shrubland Australia, heath South Africa, fynbos 41 64 41 67 88 91 125 151 118 236 21 48 25 26 21 32 136 139 35 64 24 108 65 75 aData from Gentry, 1979. bData from Whitmore, 1986, for a 0.01-hectare plot.
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From page 160... ...
, the flora indigenous to the South African Cape, which is found in an area of 46,000 square kilometers, contains at least 6,000 higher plant speciesa species richness three times that found in tropical regions of similar areas. This subregion has been considered one of the world's six distinctive floristic regions.
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From page 161... ...
are included, these figures increase to 3,583 endemics and 1,968 rare or threatened plant species (Leon et al., 1985) In contrast to California and South Africa, where large areas of climax vegetation remain, much of the Mediterranean basin has been completely transformed from its native state.
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From page 162... ...
Very few of these species are known to be part of Mediterranean climax vegetation. Most of them correspond to successional stages affected by either natural or artificial exploitation, and they should be conserved under the prevailing conditions of relative instability." INCREASING BIOTIC DIVERSITY THE INVADERS As indicated above, plant diversity in Mediterranean-climate regions is among the worId's richest in terms of numbers of species, but there have been losses of species and continuing threats of extinction to many others.
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163 as TIC o E_ ._ - Cat :: ~ 4= al Z Cr)
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South African National Scientific Programmes Report No.
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From page 165... ...
1985. Conservation of plant species within their native ecosystems.
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From page 166... ...
These needs are to maintain, or, where absent, to create a complete array of forest successional stages, including old-growth forest conditions; to maintain structural and functional diversity throughout the forest landscape, e.g., by retaining standing dead trees and fallen logs; to protect aquatic diversity in the streams, lakes, and rivers associated with temperate forests and to develop effective stewardship programs that can maintain (and create, when 166
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From page 167... ...
MAINTAINING SUCCESSIONAL STATES Preserving biodiversity in temperate regions requires the maintenance of all successional stages. Since early successional stages are typically well represented, a major concern is preserving or recreating old-growth forests.
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From page 168... ...
011-growth forests may contrast with younger forests in their influence on some important hydrologic processes. Old-growth coniferous forests present a very large crown surface and occupy an extensive volume of space, because dominant trees are commonly taller than 75 meters.
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From page 169... ...
Although these examples are all drawn from the temperate coniferous forests of the Pacific Northwest, old-growth forests in other temperate regions probably exhibit similar distinctions of composition, structure, and function. Ecological investigations of olcl-growth forests in northeastern North America are just beginning, but differences between early and late successional stages in composition and structure are already apparent.
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From page 170... ...
Maintaining deadwood structures should be a regular objective of silvicultural activities within the forests of the temperate zone and other zones, quite apart from any program for maintaining oIcl-growth-forest conditions. Maintaining nitrogen-fixing organisms within our forest landscapes is an example of maintaining functional diversity.
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From page 171... ...
PROTECTING AQUATIC DIVERSITY Protecting aquatic diversity, inclucling that of the riparian zones, is one of the most difficult tasks within the temperate zone. Streams and rivers have been clammed, diverted, and polluted.
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From page 172... ...
It cannot be permanently accomplished by a single action, such as establishing a national park or biological preserve. Indeed, we often forget that establishing a preserve is only the first step in the infinite responsibility that we have assumed for keeping many organisms and ecosystems afloat (Figure 184~.
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long-term commitment can ultimately come only from society at large. Resolving the risks to biodiversity in the temperate zones and developing the philosophy and technology of stewardship can provide an essential example for tropical regions.
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From page 174... ...
In forestry practices, we can see this emphasis on simplification from the level of the tree, where great efforts are being expended to create genetically uniform material, through the geometrically arranged stand to the landscape, where multiple age classes of conifer monocultures are sometimes cited as evidence of commitment to biological diversity. We must modify our treatments of forest stands and arrangements of forest landscapes to incorporate the objective of protecting biodiversity (Figure 18-5~.
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From page 175... ...
1986. Ecology of coarse woody debris in temperate ecosystems.
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Given this wide range of variations, it is not surprising that the grasslands of the world contain a large amount of native biodiversity. GRAZING AND AGRICULTURE CONVERSIONS All grasslands support an array of native herbivores.
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From page 177... ...
In fact, in the tall-grass prairie, periodic burning increases the species diversity above that found on an unbumed prairie, especially one that is not grazed. Buming is routinely used intentionally in grassland management to reduce invasion by woody shrub species and to encourage native perennial species.
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From page 178... ...
In the eastern tall-grass prairie, where remaining grasslands are relegated primarily to small patches in an otherwise agricultural landscape, there are several threats to biodiversity. One is the intrusion of several aggressive alien plant species, which are invading and replacing native species.
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From page 179... ...
in a given geographic region but that the species composition of these assemblages varied geographically. Patch size and structure of the host veg' elation stancis were of considerable importance, and the rarity of these leafhoppers was clirectly attributable to the rarity of the host plant species.
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From page 180... ...
1986. Preservation status of true prairie grasslands and ecological concepts relevant to management of prairie preserves.
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From page 181... ...
Extinction rates are also higher on islands because island species generally have small populations, restricted genetic diversity, and narrow ranges prior to human colonization, and because human alterations of land through use destroy an aIready-limited critical habitat. The plant and animal hitchhikers and fellow travelers who accompany humans to isolated islands interact with these other causes of extinction, however, and biological invaders endanger native species in reserves and other protected lands.
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From page 182... ...
Moreover, in most continental parks alien species are largely confined to roadsides and areas occupied by humans before the park was established. In contrast, Channel Islands National Park in California, Everglades National Park (an island of tropical vegetation at the tip of the Florida peninsula)
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From page 183... ...
National Parksa National Park Alien Species (% of total) Sequoia-Kings Canyon Rocky Mountain Yellowstone Mount Ranier Acadia Great Smoky Mountain Shenandoah Channel Islands Everglades Haleakala Hawaii Volcanoes 6-9 7-8 1 1-12 12-14 21-27 17-21 19-24 16-19 15-20 47 64 aFrom Loope, in press a.
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From page 184... ...
. At the other extreme, it has been argued that alien species are merely temporary components of island ecosystems, certain to be replaced by natives in the course of ecological succession (AlIan, 1936; Egler, 1942~.
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From page 185... ...
sense. There are nevertheless several steps that can be taken to reduce the effects of biological invasions and protect some of the native biological diversity on isolated oceanic islands: ~ identification of the aliens most likely to threaten native ecosystems and concentration of control efforts on those species; · selection of critical habitat areas from which most or all species of aliens are excluclecI; ~ protection of areas from further habitat destruction; and · study of biological invasion and species extinction on islands to team how these same processes may affect continents.
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From page 186... ...
able to invade intact native ecosystems, but plants species that can do so are not common. Most often, alien plants invade undisturbed native ecosystems in association with alien animals.
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From page 187... ...
occur in the Galapagos (Bram' well, 1979~. These interactions between alien plants and animals further illustrate why control of alien animals is fundamental to protecting the native ecosystems of islands.
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From page 188... ...
Alien Plant Invasions in Hawaii: Management and Research in Near-Native Ecosystems. Cooperative National Park Resources Studies Unit, University of Hawaii, Honolulu.
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From page 189... ...
Alien Plant Invasions in Hawaii: Management and Research in Near-Native Ecosystems. Cooperative National Park Resources Studies Unit, University of Hawaii, Honolulu.
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