response to landscape context
Pine sites were not bryophyte ‘deserts’. However, they lacked 40% of the total number of species found in the native vegetation, lacked unique species, and had a depressed average richness compared with native vegetation. In contrast, eucalypt remnants were valuable habitat for bryophytes, being species-rich and with little difference in composition to the large areas of continuous forest. All but six of the 58 species found in this study were present in the remnants and 17 were only found in the remnants. Both strip- and patch-shaped remnants had a higher total number of species than the continuous eucalypt forest, although mean numbers of species were not significantly different. Analyses of both landscape context and forest type showed that the main contrast was between native eucalypt forest and the exotic radiata pine plantation.
There are no comparable studies of bryophyte response to landscape context and few studies have examined vascular plant response to landscape context. A study of eucalypt-dominated remnants in the dry forests of Tasmania showed that landscape context was important for vascular plants (Gilfedder & Kirkpatrick 1998). Remnants in an urban matrix had higher vascular plant richness compared with remnants in an agricultural matrix. North American studies of vascular plant communities have also found that the landscape matrix can provide important habitat for many species (Jules et al. 1999; Cook et al. 2002).
importance of substrate
This study showed substrate type to be a better predictor of species richness than landscape context. In other words, in terms of both species richness and composition at the substrate level, it mattered more what substrate was sampled than which landscape context class it was sampled from. Ojala, Monkkonen & Inkeroinen (2000) also concluded that epiphytic bryophyte species richness on Populus tremula trees was independent of landscape structure across heavily fragmented Norwegian forests and more continuous Russian forests, but positively related to Populus tremula abundance and the size of the trunk. Others have argued that microhabitat availability might be a crucial factor in determining bryophyte presence (Herben, Rydin & Söderström 1991; Humphrey et al. 2002).
Radiata pine sites often failed to provide a full suite of substrate types for epiphytic bryoflora, with four of the eight pine sites supporting no epiphytes while all native vegetation sites had epiphytes. At the other four sites, bryophytes were found on pine tree roots, at the base of pine trees, or on native tree species established within the otherwise pine-dominated sites. Even in areas where pines are native, bryophytes can be restricted to the stable areas at the base of Pinus spp. (Palmer 1986).
Windrows of burned eucalypt logs left from clearing the original native forest to establish the pine plantation at Tumut were important substrates for bryophytes. Windrows are piles of woody debris bulldozed into long, parallel rows that clear the area for replanting. Approximately 90% of bryophyte samples collected in the radiata pine sites were from these remnant eucalypt logs. This suggests that, when the eucalypt logs have broken down completely, some of these pine-invading bryophyte species will disappear. Logs are particularly important habitat in forests where there is a dense layer of litter and the dominant trees are poor hosts (Jarman & Kantvilas 1994). Both the dry sclerophyll forests and pine plantations of this study fall into that category.
response to remnant variables
Remnant responses were complex and may be a function of within-group life-history differences. Significant relationships were identified between the attributes of eucalypt remnants and both overall bryophyte richness and species composition. Strip-shaped remnants supported a bryoflora more similar to the continuous eucalypt forest than did the patch-shaped remnants. Substrate differences did not explain this pattern, with only rocks showing a significant difference when each substrate was analysed separately for the effect of landscape context class. Sites were chosen so that there was a variety of forest types, ages and sizes for both patch- and strip-shaped remnants. The main difference between patch- and strip-shaped remnants was that all three remnants surrounded by pine plantation of heterogeneous age (more than 20 years) were patch-shaped. A larger number of species on uprooted trees was found in patch-shaped remnants, so there may also be an effect of ongoing disturbance in some of the patches, either directly through changes in microclimate or indirectly through changes in habitat provision.
Mosses were most species rich in the intermediate size remnants in this investigation. In contrast, there was a clear response to remnant size in a study of tropical leaf-inhabiting bryophytes in central Amazonia, with smaller remnants being less species-rich (Zartman 2003). In both Zartman's (2003) study and this one, the fragments have been isolated for at least 15 years, which should be long enough for the bryoflora to have adjusted to new conditions. In our study there may be more complex spatial effects influencing numbers of moss species in remnants, such as the distance to other areas of native vegetation. Alternatively, remnant disturbance history may influence moss richness.
Bryophyte response to remnant age was less complex than the results for remnant size. Liverworts were species poor in the relatively recently isolated remnants compared with the continuous forest. Overall species composition of bryophytes was different. Some bryophytes, and liverworts in particular, may be slow to become established in new habitats. The only liverwort studied for spore production, Ptilidium pulcherrimum, has a considerably lower output of spores than mosses (Söderström & Herben 1997). However, most of the mosses studied were ‘weedy’ species and perhaps not representative (Söderström & Herben 1997). The other variable implicated in long distance dispersal is wind (Muñoz et al. 2004). Spores launched from a long seta and in open fields, rather than forests, appear to have the best chance of being carried long distances by winds (Söderström & Herben 1997). Seta length and other variables that may be related to dispersal distance, such as spore size, asexual propagule size and spore longevity, all vary greatly between species of both liverworts and mosses. Therefore, bryophyte response to fragmentation in the more open habitat of agricultural landscapes may differ from the patterns in this study.
Eucalypt remnants had lower mean liverwort richness than both continuous forest and pines. Liverworts also showed no significant difference in species composition between remnants, continuous forest and pines, which appears largely to be because of the similar composition of the patches and continuous forest. Liverwort richness was low across all sites, which was not surprising given that these are relatively dry forests and liverworts are most species rich in moist areas (Gradstein, Van Reenen & Griffin 1989; Kantvilas & Jarman 1993). The results for liverworts largely reflect the substrate preferences of three common species and the location of the 10 uncommon species. Cephaloziella exiliflora prefers burned logs and both Frullania probosciphora and Chiloscyphus semiteres tolerate dry conditions and are flexible in their substrate requirements (Scott 1985). All three are widely distributed (Scott 1985), therefore it is not surprising that landscape context class effects were less pronounced for liverworts than for mosses.
Our study sites had been examined previously for the response of mammals and birds to landscape context (Lindenmayer et al. 1999; Lindenmayer, Cunningham & Pope 1999; Lindenmayer et al. 2000; Lindenmayer, Cunningham & Donnelly 2002). Four main points emerge from comparing responses of both the taxa from the same study sites at Tumut and results of other studies. First, exotic pine plantations suppressed richness compared with native forest. Secondly, the main contrast was between the pine plantations and the native eucalypt forest, with remnants providing valuable habitat, often regardless of size. Thirdly, responses of individual species were variable. Although we did not examine the response of individual taxa in this study, the variability of responses within taxa such as mammals and birds, invertebrates (Margules 1996) and liverworts and lichens (Moen & Jonsson 2003) is a common theme in fragmentation studies (Debinski & Holt 2000). Finally, an understanding of the biology of the taxa in question is vital in predicting the response to fragmentation. In the case of bryophytes, it appears that mobility and small size resulted in a stronger response to substrate than forest type, although the two are not independent. Substrate effects were critical in understanding patterns, with soil and burned eucalypt logs supporting much of the diversity in radiata pine sites. Plantations that maintain remnant vegetation and maintain key substrates such as decayed eucalypt logs will be vital for regional bryophyte diversity.