biological diversity and tropical forests in tunisia - PART

Fight major islacd archipelagos are distributed alocg the coast of
'hicisia (figcre 5). There are also ma~y smaller islacds, same of which
are mere rocks jutticg from the water acd some laree ecosgh to sapport a
bit of vegetatioc, bst cot large enough to be co~sidered inportant in
terms of natjonal biological diversity. The two largest islacds,
Kerkeccah and Jerba, are both ic the south. The islands are separated by
distacces of 26 to 135 km, biit cone are more than 50 kn from the mai~lacd.
Species composition ic vegetation associatiom or jslacds are affected
by a factor known as icsularity. Cece pools are restricted primarily to
placts present oc the islands with a micimm of icvasion by vied borce acd
floaticg seeds. Vi thoct the frequert di spersi oe of seeds betueec areas,
as is commoc OR the naiclacd, species are more easSlp elimicated from ar
islacd. Therefore, there are ssually feuer total species or jslards acd
rare species merit special attectjoc.
The combicatioc of the icsularity factor, thic soils acd oc southerr
islacds the relatively low acciial precipitatioc nakes isfacd flnrh acd
fa,ca q~jte secsitive to icflaecces oc the ecosystem. Crazlcg is already
so i.ctecse oe most islands that it is ~rdoubtedly drasti call? af fecticg
species conpostioc. Ac increase ic livestock cumbers, c.sltivated lard or
wban areas cc~ld resiilt ic fewer native species of flora zble to occ,py
the lin:ted space.
Developmeet projects oftec iipset the soil stability of islacds,
resslticg ic sard dixe formatioc or the loss of lard by erosior.
Pollctioc is also a serious concerc that sho-sld be assessed ir regard to
developmeet plars for the islands. The water nroacd Kzriate, Kerkeccah
acd Jerba are already affected by the large amozcts of icd.~strlal acd
urbac poll>.itio~ isssi r~ from coastal cities (~ectioc 3.: ). Iccreased
pollctioc ic the shallow waters woiild cot ocly be detrinectal to marice
facra acd flora and shorebirds, biit the local harvest of fish and other
seafood wo..ild have higher levels of coctarnir-ar-ts, thiis affectice h~nac
health acd welfare.
Popclation erowth acd iccreasicg tourism will also iccrease demacds or
the islacds' resocrces. Fresh water is an especially valuable resosrce,
acd as cse iccreases the groundwater may be overexploited. If groucdwater
use is cot properly regulated it may be pcmped faster thar. it is
replecished by freshwater, thus lowering the wa t~r table acd allouic~
seawater to ir-filtrate, causirg ac irreversible i.rcrease ir. salirity (acd
in pollstacts from the sea). A lowered water table wncld also affect
vegetatioc connucities that exist in areas where the groiicduater Is
currertl:; cear the s.srface.