220 



Terrestrial Ecnsystems — Our Living Resinmes 



30- 



20 



Eastern region 

 (53) 



30 



20 

 10 

 0- 

 40- 

 30- 



Soultieastem region 



(64) 



Midwestern region 

 (70) 



20— i- 



10 

 0- 



30 



20 



I 



Western region 

 (208) 



ui "O "O T3 T3 "O TJ 



oi c cz c c cr c 



ii^ m eu m m m m 



iP T31 "O X3 -O J=» JD 



S s 



-t^ ^ -c: -o > aj 



Figure. Rare terrestrial communi- 

 ties by region and physiognomic 

 class. Numbers in parentheses 

 refer to number of community 

 types. 



these habitats for land conversion or due to 

 association with naturally rare habitats. 



Southeastern Region 



The rare communities occurring in the 

 southeastern region account for about \89c of 

 the nationally listed types (Patterson et al. 

 1994). This region is dominated by forest, and 

 numerous diverse and intact rare forest associa- 

 tions remain. Most of the rare types fall within 

 the forest class, followed by the herbaceous and 

 woodland classes (Figure). The communities 

 within the herbaceous class remain poorly 

 defmed throughout this region, but this class 

 still represents a large portion of the rare types. 

 We believe that the total number of types and 

 the number of rare types within the herbaceous 

 class will increase as additional information 

 becomes available. Fire suppression has threat- 

 ened many of the woodland types, and the actu- 

 al number of rare woodland types is also pre- 

 sumed higher than now reported. 



Midwestern Region 



About 19% of the communities in the list of 

 nationally rare communities occur in the mid- 

 western region (Ambrose el al. 1994). Although 

 the proportion of rare community types in this 

 region is relatively small because of the histori- 

 cally coarse level of classification for this 

 region, the magnitude of land conversion to 

 agricultural production is staggering. The 

 herbaceous class accounts for 40% of the rare 

 types in the midwestern region, and the wood- 

 land and sparse woodland types make up anoth- 

 er 38% (Figure). The rare herbaceous types 

 reflect the remnant patches of the once-exten- 

 sive prairie province. The woodland and sparse 

 woodland communities have been heavily 

 affected by the disruption of historical fire 

 regimes and agricultural development. 



Western Region 



Most rare and threatened types identified in 

 the national list of rare communities (about 

 56%) occur in the western region (Reid et al. 

 1994). This reflects the region's rich base of 

 ecological and biological data and the consis- 

 tent application of a detailed level of communi- 

 ty classification, as well as a high level of nat- 

 ural diversity in this large region. Most rare 

 types in the western region occur within the for- 

 est class, followed by the woodland, herba- 

 ceous, and shrubland clas.ses (Figure). Fire sup- 

 pression as a widespread forest-management 

 practice over many decades has pushed many 

 forest types to this status of rarity. Flood-control 

 and water-diversion projects have similarly 

 affected many of the forest and woodland ripar- 

 ian types. The rarity of the herbaceous commu- 

 nities across the western region is reported to be 



primarily the result of overgrazing and, to a 

 lesser degree, direct agricultural conversion. 



No regions reported rare communities in the 

 nonvascular class and few were documented 

 within the dwarf shrubland, sparse dwarf shrub- 

 land, and sparsely vegetated class. This result 

 may not reflect the actual status of rare commu- 

 nities in these classes throughout the United 

 States but rather the shortage of available infor- 

 mation. 



Knowledge Gaps 



The rare communities for several states are 

 not documented at this time. This does not mean 

 there are no rare communities in those states but 

 instead indicates the lack of available informa- 

 tion. These knowledge gaps were documented 

 during the listing of rare communities. 

 Information gaps at the state level included 

 incomplete or overiy coarse classifications, lack 

 of conservation ranks, and the lack of time and 

 support for field verification. Those states where 

 significant work remains are listed in Table 3. 



Many communities recognized as rare still 

 require additional work to complete their classi- 

 fication, ranking, and description process. The 

 number of communities in this group presently 

 totals 482. 



Limitations 



The number of rare communities varies 

 among regions, reflecting unevenness in the 

 quantity and quality of community information 

 among the regions, along with varying levels of 

 classification development and subtle differ- 

 ences in procedures for conservation ranking. 

 To some extent, the regional variation also 

 reflects the actual differences in ecological and 

 biological diversity, the results of landscape 

 fragmentation, and land-cover conversion. 



While rarity of ecological communities is 

 critical information for biodiversity conserva- 

 tion and management, appropriate protection 

 and management activities should be deter- 

 mined for each individual rare community. 

 Communities assigned a rank of Gl or G2 are 

 very rare and occur generally within a restricted 

 range of environmental conditions. The.se ranks 

 do not reflect why a particular community is 

 rare: such analysis, however, is fundamental to 

 setting guidelines for protection and long-term 

 management. 



Some communities are naturally rare 

 because of their association with an uncommon 

 habitat. For example, the rarity of the inland salt 

 marsh association (Scirpiis maritimus-Athplex 

 potula-Eleocharis parvuhi herbaceous vegeta- 

 tion) has been documented, but the community 

 is not noticeably rarer than it was 100 years ago. 



