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Predicting canopy macrolichen diversity and abundance within old-growth inland temperate rainforests
Windward slopes of the inland mountain ranges in British Columbia support a unique inland temperate rainforest (ITR) ecosystem. Increasing fragmentation and the loss of old ITR stands have highlighted the need for determining conservation biology priorities among remaining old forest stands. We have addressed this issue by surveying foliose macrolichens within 53 old ITR stands in British Columbia's 135,000 ha very wet-cool interior-cedar hemlock (ICHvk2) biogeoclimatic subzone in the upper Fraser River watershed. Study plots were stratified by leading tree species and by “wet” versus “dry” relative soil moisture conditions. Other plot variables included: temperature, precipitation, incident solar loading, and canopy openness. Ordination plots showed a distinct assemblage of foliose cyanolichens, including Lobaria pulmonaria, Lobaria retigera, Sticta fuliginosa, Nephroma isidiosum, Nephroma occultum, and Pseudocyphellaria anomala, whose abundance was correlated with increasing relative soil moisture, temperature, canopy openness, precipitation, and basal area of spruce. Logistic regression models similarly identified relative soil moisture and temperature in all parsimonious models. Leading tree species, in combination with “wet” relative soil moisture and/or temperature, were important factors explaining the presence or absence of five (Cavernularia hultenii, L. retigera, N. occultum, Platismatia norvegica, and Sticta oroborealis) of the eight modeled old-growth associate lichen species. This combination of conditions favouring the development of canopy lichen communities in old forests was best expressed in low elevation water receiving sites. We hypothesize that groundwater availability in these sites promotes species richness and abundance of canopy lichens by creating more favourable conditions for growth, and by reducing fire return intervals which allows for the accumulation of rare species over time. Historically, forests in these wet “toe-slope” positions were disproportionately targeted for logging. Their conservation should now be a high priority, given their disproportionate significance to maintaining canopy lichen diversity in the present-day landscapes. 相似文献
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Small-scale spatial patterns in N2-fixation and nutrient availability in an arctic hummock-hollow ecosystem 总被引：1，自引：0，他引：1
Atmospheric nitrogen that is fixed by associative cyanobacteria can be released into the surrounding soil environment providing a key source of N for arctic ecosystems. Yet, little is known about nitrogen fixation by Biological Soil Crusts (BSCs) within hummock-hollow complexes that are typical of many arctic environments. In this study, we examined spatial and temporal patterns in N2-fixation, dinitrogenase reductase (nifH) gene abundance and release of N in a low arctic hummock-hollow ecosystem. The impacts of cyanobacteria on N status in soil were evaluated by assessing soil nitrogen in relation to the cyanobacterial associations found on Hummock and Hollow BSCs. In addition, potential P limitation of N2-fixation by cyanobacteria was assessed for Hummock and Hollow BSCs. The tops of hummocks and the bottoms of hollows were areas of high N2-fixation, whereas minimal N2-fixation occurred on the sides of hummock-hollow complexes. Compared with Hummock BSCs, Hollow BSCs had a higher mean growing season N2-fixation rate, a higher mean growing season nifH abundance, a higher mean total %N and δ15N values closer to that of atmospheric N2. Soil N status was linked to rates of N2-fixation by BSCs indicating that these N2-fixing associations act as important point sources of soil N in this low arctic ecosystem. Over the course of a growing season temporal variation in N2-fixation and nifH abundance were weakly linked suggesting that N2-fixation was carried out by complex communities of diazotrophic microorganisms and that factors such as nutrient availability may limit N2-fixation to a greater extent than nifH abundance. 相似文献
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The foliose cyanolichen Lobaria retigera is a sensitive old-growth forest indicator in British Columbia's inland rainforest. These forests are increasingly being fragmented by harvesting, raising concerns about edge effects and the maintenance of canopy lichen communities in remaining forest patches. We have examined the response of L. retigera to edge effects, using transplant experiments to compare growth responses between abrupt (hard) edges created by clearcut harvesting and more buffered (soft) edges created by variable-retention harvesting. L. retigera thalli placed along hard edges showed high mortality rates, with most thalli (from 64 to 100%) losing biomass at the end of each of the 3-year's measurement periods. Biomass loss along soft edges was much lower, occurring in fewer than 7% of thalli in the best year, up to 42% in the worst year. When growth rates were expressed against light availability at each branch location, thalli along variable-retention transects showed a positive response to increasing light availability. In contrast, thalli along the hard edge transects showed an abrupt decline in growth rates at equivalent levels of high light availability (canopy openness values >30%), where presumably the benefits of greater light availability were offset by heat or dessication stress. These results show a much greater sensitivity to edge effects in L. retigera, compared to earlier measurements at this site with the more common lichen Lobaria pulmonaria, a species that has a dominant green-algal photobiont partner. We suggest that increased use of variable-retention harvesting systems in which a substantial number of residual trees are left along cutblock edges has the potential to reduce the impacts of forest harvesting on canopy lichen biodiversity. 相似文献
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