(^iir Liviiii^ Resources — Plants 



207 



southern slates (Fig. 3), with greatest propor- 

 tions in Arizona. California. Florida. Georgia. 

 Hawaii. Nevada, New Mexico, Texas, and Utah. 

 In addition to these globally rare species, 

 about 4,500 other species of widespread or 

 more common vascular plants (ranked G4 or 

 G5) are being actively inventoried in at least 

 one state where they are rare. 



Loss of Species 



The patterns and causes of plant species" 

 losses are often important components of state- 

 level conservation studies. The loss, or suspect- 

 ed loss, of a species from a portion of the land- 

 scape is referred to as "extirpation." 



A recent study (Kutner and Morse, unpub- 

 lished report) of the losses of U.S. native vas- 

 cular plants revealed that about 1,772 (9.8%) of 

 these species have been lost from at least one 

 state. Of these species, 438 (25%) may be lost 

 from the floras of two or more states. The pro- 

 portion of species potentially extirpated from 

 each state varies dramatically across the nation 

 (Fig. 4), with the largest losses reported from 

 northeastern states and from Hawaii. Delaware 

 has experienced the proportionately highest 

 loss from its flora, with more than 15% of its 

 species potentially extirpated. Many of the 

 northeastern and mid-Atlantic states have lost 

 more than 5% of their native vascular plants. 

 This region of the United States has experi- 

 enced hinidreds of years of human development 

 and includes many of the most densely populat- 

 ed and intensely developed states. Many plants 

 that have been lost from these states may now 

 be similarly threatened in portions of their 

 remaining ranges. 



About 28% of the native flora is considered 

 globally rare (ranked Gl, G2, or G3) by the 

 Natural Heritage Network, but only 12% of the 

 potentially extirpated species are globally rare. 

 Most potentially extirpated species have been 

 lost from one or two states and are currently 

 globally common (ranked G4 or G5). In the 

 United States, 110 of these globally common 

 species have been lost from three or more 

 states, and more than 35 species have been lost 

 from four or more states. Of the most common 

 species (global rank G5). about 285 have been 

 lost from two or more states. Common species 

 that have been lost from many states may not be 

 as secure from imperilment as previously 

 believed. Additionally, the effect of species' 

 losses on other plants and animals in a commu- 

 nity is often unknown. Rangewide analyses 

 could indicate species that would benefit from 

 further research and a better understanding of 

 potential threats, thus helping prevent subse- 

 quent losses. 



Many species that are endangered, threat- 

 ened, or formal candidates for federal protec- 

 tion have also lost parts of their ranges. Nearly 

 6% of listed and proposed endangered species 

 and 20% of listed and proposed threatened 

 species are reported extirpated from at least one 

 state. About 16% of the category 1 candidate 

 species (top candidates for listing as endan- 

 gered or threatened) and almost 1 1% of the cat- 

 egory 2 candidate species (possibly qualifying 

 for threatened or endangered status, but more 

 information is needed) have been similarly 

 affected. 



Some currently rare species had widespread 

 historical distributions. For example, American 

 chaffseed {Scliwalhea americuna) is a federally 

 listed endangered species with a Natural 

 Heritage rank of G2. The historical range of this 

 species extended from Mississippi to 

 Massachusetts; the plant is cunently known 

 from about 20 populations in five states, mostly 

 in South Carolina. The most significant threat 

 to this species is fire suppression, which allows 

 plant succession to proceed to the point where 

 there is not enough light for the plant to com- 

 pete successfully. Habitat loss has also caused 

 the extirpation of several Schwalbea popula- 

 tions. For rare species such as S. amehvami, 

 further state-level extiipations could seriously 

 affect the species" survival. 



Wetland Species 



Although there are fewer than 7.000 native 

 wetland vascular plant species in the United 

 States, plants that occur mostly in wetlands are 

 more likely to be extirpated from at least one 

 state. Based on the USFWS National Wetlands 

 Inventory (Reed 1988), about half of the poten- 

 tially extirpated species are either obligate (see 

 glossary) or facultative (see glossary) wetland 

 species. 



Wetlands and aquatic ecosystems have been 

 severely affected in the United States; approxi- 

 mately 53%' of these ecosystems have been 

 destroyed in the 48 contiguous states (Dahl 

 1990). Aquatic species frequently have specific 

 habitat requirements and can be threatened by 

 both habitat loss and changes in local hydrolo- 

 gy. In the mid-Atlantic region, several intertidal 

 vascular plants have been extirpated from the 

 Delaware River system because of habitat alter- 

 ation (Ferren and Schuyler 1980). 



Possibly Extinct Species 



About 90 mainland U.S. and 1 10 Hawaiian 

 vascular plant species may be extinct, accord- 

 ing to records of the USFWS and The Nature 

 Conservancy (Russell and Morse 1992). For 



Proportion rare plants (%) 



■ >2g 



■ 12.0-17.0 



□ 8.0-11.9 



□ 5.0 — 7.9 



□ 2.6-4.9 



□ 0-2.5 



Fig. 3. Tlie proportion of globally 

 tare vascular plant species (ranked 

 Gl. rarest, to G3, more common) 

 in the native flora of each U.S. 

 state. 



Proportion of slate flora lost (%) 



■ >1 5 (Delaware) 



■ 5.0-14.9 

 (SI 3.0-4.9 

 □ 1.0-2.9 

 n <1.0 



Fig. 4. The proportion of species 

 reported potentially extirpated 

 from the native flora of each U.S. 

 .state. 



