wise use of mires and peatlands - Peatland Ecology Research Group

MIRES AND PEATLANDS37formed peat and a consequent scarcity ofnutrients. Nutrients may further fail becauseof limited supply (as in ombrogenous mires)or inaccessibility (as in calcareous mires,where all phosphates are bound to calcium 133 ).Mire plants therefore generally show variousadaptations to nutrient shortage:■ Moss species have cation exchangemechanisms, that enable them to exchangethe rare cations in the water for selfproducedhydrogen ions. This mechanismis particularly well developed inSphagnum 134 ;■ Trees often show stunted growth, e.g.conifers and Nothofagus species 135 ;■ Many species have large rhizome and rootsystems that function for several years 136 ;■ Dwarf shrubs are slow-growing and oftenhave perennial or “xeromorphic” (small andthick) leaves, which reduce their need fornutrients, e.g. Ericaceae, Empetraceae,Betulaceae, Salicaceae, Rosaceae,Myrtaceae;■ Monocotyledon 137 herbs often haveperennial or thin, blade-like leaves, e.g.Cyperaceae, Poaceae, Juncaceae,Juncaginaceae, Scheuchzeriaceae,Iridaceae, Restionaceae 138 ;■ Various dicotyledon vascular plants onmires are parasitic and have developedspecialized organs to “steal” nutrients fromother plants, e.g. Scrophulariaceae,Santalaceae;■ Other herbs are carnivorous 139 and catchinsects for food, e.g. Droseraceae,Lentibulariceae, Sarraceniaceae,Cephalotaceae, Nepenthaceae;■ Many higher plants live in symbiosis withfungi or bacteria that help them to retrieverare nutrients 140 (e.g. Orchidaceae,Ericaceae 141 ) or that fix atmosphericnitrogen (e.g. in Alnus, Myrica, andFabaceae 142 ).A third complicating factor for plant growthis the continuous cover by accumulating peatand the constantly rising water levels 143 .Perennial plants must be capable ofcontinuous upward growth and must be ableto develop new roots every year on a higherlevel 144 . Few tree species are able to makenew roots on the stem 145 leading to a generalscarcity or stunted growth of trees intemperate and boreal bogs.The growth of tall and heavy trees is alsohampered because the surface-rooting treeseasily fall over or, in mires with a spongy peatstructure such as percolation andschwingmoor mires, drown under their ownweight.Peats generally conduct heat poorly, causinga relatively short growing season for vascularplants in boreal areas. The prevalence ofwater and the limitations to tree growthprovide mires with a climate that is generallycooler and more extreme than that of itssurroundings 146 , which leads to ecosystemfeatures which are not typical of the climatezone. In forested boreal and temperate areas,open mires represent tundra-like conditionsand often harbour “ice-age relicts” anddisjunct 147 species and communities 148 .The acidity caused by cation exchange andorganic acids, especially in the case ofSphagnum-dominated mires 149 and theproduction of toxic organic substances 150 formadditional handicaps to organisms.As a result of these extreme conditions, miresin general are relatively poor in species ascompared with mineral soils in the samebiographic region. This is true for temperate,boreal and tropical mires 151 . Many peatlandspecies are, however, strongly specialised andnot found in other habitat types.The fauna of mires is also generallyinfluenced by the scarcity of water nutrientsand ions, the acidity of the water, the relativecoolness, and (in the case of non-forestedmires) the strong temperature fluctuations.Sphagnum-dominated mires in particular arecharacterised by poor nutrient availabilitybecause “almost nothing eats Sphagnum” 152 .