The major environmental changes that bryophytes are facing (Chapter 10) have increasingly brought about concerns for their conservation. Conservation biology is a fairly new, multidisciplinary science that has developed to deal with the crisis confronting biological diversity (Primack 1993). As a crisis discipline, conservation biology appeared in response to a rising political demand to face the dramatic loss of biodiversity and the need to take steps to anticipate, prevent and reverse the trend (Heywood & Iriondo 2003). Subsequent ratification of the ‘Convention on Biological Diversity’ at the United Nations conference held in Rio in 1992 by most of the world's governments has placed the subject of biodiversity firmly on the political agenda.

The development of the concept of conservation biology is closely interrelated with that of biodiversity. Biodiversity is defined in the Convention on Biological Diversity as ‘the variability among living organisms, from all sources … and the ecological complexes of which they are part’.

In this broad conservation picture, bryophytes were initially completely overlooked. Cryptogams in general were, for example, the focus of only about 4% of published papers between 2000 and 2005 in leading conservation journals (Hylander & Jonsson 2007). The situation has, however, been changing recently and there has been an increasing awareness of the necessity to include cryptogams in general, and bryophytes in particular, in conservation programmes (Hylander & Jonsson 2007).

Bryophytes are familiar and attractive components of many natural landscapes such as peatlands, tundra environments and moist forests, where their shaggy coverings on branches, crags and boulders, add distinction to the landscape (Figs. 2.1,2.2). In particular, epiphytic bryophytes make up a conspicuous portion of many rain forest canopies, hanging from branches (Fig. 8.6) and densely festooning tree trunks (Wolf 1993, Kürschner & Parolly 2004).

Less appealingly, they also occasionally grow on unexpected substrates, like the leather of a discarded boot, or a rusty iron pipe. Even in modern cities where air pollution and the man-made environment may seem unrelenting, bryophytes are able to colonize crevices in masonry (Bates 2000). The occurrence of bryophytes in a wide range of terrestrial and freshwater habitats suggests intriguing questions on how they manage to colonize, adapt and develop in such environments. The occurrence of bryophytes in nearly every ecosystem on earth (all but salt water and permanently frozen ecosystems) also raises questions about their ecological significance in those ecosystems. This is the focus of the present chapter, where we will explore the contribution of bryophytes to ecosystem functioning and, more precisely, how they may influence vegetation dynamics, soil formation and characteristics, global geochemical cycles and hence, climate regulation.

Water and biogeochemical cycles

Bryophytes contribute to a substantial proportion of the global biomass in a range of ecosystems (Fig. 2.3) and hence play a major role in the cycling of carbon and nutrients through growth and decomposition.

The common ancestor to the Marchantiophyta arose immediately after the conquest of land, some 450 mya. Their evolutionary history is, however, also characterized by a more recent diversification during the early Tertiary Period. This diversification may coincide with the establishment of modern rainforests and resulted in species rich crown groups such as the Lejeuneaceae (Heinrichs et al. 2007). With approximately 5000 extant species currently recognized, liverworts compose a diverse lineage of land plants, represented on every continent and in nearly all ecosystems. Some species are virtually invisible to the naked eye, whereas others rival mosses in their stature. Although the experienced eye may easily distinguish liverworts from other bryophytes in the wild, not a single conspicuous unifying morphological vegetative character defines them. The architecture of the gametophyte varies from thallose, with or without internal differentiation, to leafy, with leaves divided in some lineages into two or more lobes. It is only after sexual reproduction is completed that liverworts reveal their shared ancestry: the sporangium is enclosed by an epidermis lacking stomata and elevated above the maternal protective tissue on a translucent seta that elongates after sporogenesis. Furthermore, the capsule lacks a columella and the sterile cells within the sporangium develop into elaters. Except for the Blasiales, liverworts lack endophytic cyanobacteria, but most species establish symbiotic associations with mycorrhizal fungi. Although inconspicuous at the landscape level, liverworts form diverse assemblages in moist habitats such as temperate and tropical rainforests, where they thrive on trunks and leaves.