Seaside bone (Hypogymnia heterophylla) COSEWIC assessment and status report: chapter 8

The primary factors limiting the dispersal and spread of Hypogymnia heterophylla are the necessity of early seral shore pine located on rocky windswept ledges with southwest to western aspects. Much of the coastline along the southwest coast of Vancouver Island is rocky undulating hills or sandy/gravelly beaches; rocky windswept ledges are less commonly found and thus could be a limiting factor.

Also, the frequency and severity of storms and high tides where the sea spray can be swept inland appear to be of importance as seen in destruction caused by the severe winter storms of 2006/2007 where many of the coastal trees were damaged. On the other hand, these storms, although damaging many trees, at the same time may be creating new shore pine habitat and thus increasing suitable substrate for Hypogymnia heterophylla.

Climate change will cause greater fluctuation in temperature and precipitation, higher storm intensities and more coastal flooding for the Pacific Northwest. Climate models predict an increase in temperature in this area of up to 3.2 ºC by the 2040s (Mote et al. 2003). In a study of rare epiphytic lichen habitats of the Pacific Northwest, Hypogymnia heterophylla was an associate lichen with the rare coastal lichens, Bryoria pseudocapillaris, B. spiralifera and H. leucomela in ≥ 67 % of plots where they were found. Logistic regression indicated that for all three species, the environmental variable of mean minimum December (winter) temperature above freezing identified the most suitable habitat  Generally, small changes in climate and forest type strongly affected the probability of occurrence for many species in this study (Glavich et al. 2005).

Thus climate change may be a positive force for northward expansion of Hypogymnia heterophylla into Canada if sufficient early seral shore pine habitat is available in exposed coastal areas. In Oregon and California, it appears that H. heterophylla persists into late seral aged forests (Glavich et al. 2005).

Damage from winter storms appears to be the major threat for Hypogymnia heterophylla and lack of suitable habitat is the main limiting factor.

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