Ch. 3— Status of Biological Diversity • 73 



Table 3-2.— Summary of Data From Endangered Plant Species Lists 



Rare and 

 Country/region Species threatened species Extinct taxa Endangered taxa 



Australia SsioOO 1J16 iT? 215 



Europe^ 11,300 1,927 20 117 



New Zealand 2,000 186 4 42 



South Africa 23,000 2,122 39 107 



USSR 21,100 653 =20 =160 



United States" 20,000 2^050 90 ? 



^Excludes European U S.S.R,. Azores, Canary Islands, and Madeira. 



''Excludes Hawaii, Alaska, and Puerto Rico. 



SOURCE: S. Davis, et al.. Plants in Danger: What Do We Know? (forthcoming), as cited in H Synge, "Status and Trends of Wild Plants," OTA commissioned paper, 1985. 



Table 3-3.— Data on Threatened Plant Species 

 of Selected Oceanic Islands 



Number of endemic Number listed as 

 Island species^ rare or threatened 



Azores 55 30 (55%) 



Canary Islands 569 383 (67%) 



Galapagos 229 150 (66%) 



Juan Fernandez ... . 118 95(81%) 



Lord Howe Island ... 75 73 (97%) 



Madeira 131 86 (66%) 



Mauritius 280 172 (61%) 



Seychelles 90 73 (81%) 



Socotra 215 132 (61%) 



^Endemic means tfie species occurs only on tfie island. 



SOURCE; 8. Davis, el al.. Plants in Danger: What Do We Know? (forthcoming), 

 as cited in H, Synge, "Status and Trends of Wild Plants," OTA com- 

 missioned paper, 1985. 



nal that its prey and other species associated 

 with the habitat are also in decline (3). 



Diversity losses due to pollution may be in- 

 dicated by animals' food chains, such as the 

 bald eagle and other fish-eating birds. Plants 

 susceptible to air pollution, such as lichens, may 

 also be useful indicators. Extensive records of 

 observations on smaller animals of long-stand- 

 ing interest to professional and amateur biolo- 

 gists can also gauge diversity change. The 

 decline of Bay Checkerspot butterflies, for ex- 

 ample, is taken as an indication of decline of 

 many associated organisms in the San Fran- 

 cisco Peninsula area (13). 



Models off Species-Area Relationships 



The scale of diversity reduction can be esti- 

 mated for most tropical countries only by in- 

 ferences from the reduction of habitat. Nearly 

 all attempts to estimate global extinction rates 

 focus on the tropical moist forests. These eco- 



systems are exceedingly species-rich, contain 

 areas of narrow endemism, and are undergo- 

 ing extensive and rapid conversion to other 

 uses. Because they typically have erosion-prone 

 soils incapable of holding many plant nutrients 

 and occur where rain and heat are especially 

 intense, these forest ecosystems are highly sus- 

 ceptible to degradation. In fact, the undevel- 

 oped forests are so diverse, and the deforested, 

 degraded landscapes to which they are often 

 converted support so few species, that the 

 models used to estimate extinction rates gen- 

 erally treat the diversity of deforested land- 

 scapes in the moist tropics as negligible (43). 



A recent projection of bird and flowering- 

 plant extinctions that could be caused by con- 

 tinued deforestation in tropical America is 

 based on a mathematical model of the species- 

 area relationship (see box 3-A). About 92,000 

 flowering plant species have been described for 

 regions where the forested area for recent 

 human-caused deforestation was about 6.9 mil- 

 lion square kilometers (43). Over the next 15 

 to 20 years, the forested area will be reduced 

 to about 3.6 million square kilometers if the rate 

 of deforestation remains at the level of the 

 1970s. The mathematical relationship between 

 area and species numbers, derived by analysis 

 of some 100 empirical data sets (5), indicates 

 that this reduced forest could be expected to 

 support about 79,000 species. Thus, a 15-per- 

 cent reduction in numbers of species is pro- 

 jected for the near future. 



Deforestation is expected to continue for 

 more than 20 years, however, and it seems likely 

 that it will accelerate as the rapidly growing 

 human populations of tropical American coun- 



