In the coastal temperate rainforests of British Columbia, forest fragmentation from
logging has created three different landscape elements that vary in habitat quality for bryophytes:
unlogged old-growth remnant forest patches, edge habitats and younger-aged forest stands.
Bryophytes are an important component of these forest ecosystems, yet little is known about the
impact of habitat fragmentation on bryophyte patterns of richness and abundance. In this thesis I
examined the effects of three separate components of fragmentation on patterns of bryophyte
species richness, abundance and community composition: (1) effects of proximity to the edge
within remaining forest patches, (2) effects of stand age in younger-aged forests adjacent to oldgrowth
patches and (3) effects of remnant patch size. To achieve greater generality in my
conclusions, I examine each of these issues through comparative analysis using different
sampling scales and both taxonomic and ecological functional groupings of bryophytes.
Edge effects: Edge habitats (sampled from 0-45 m from the patch edge) showed an
increase in the richness of clearing-affiliated bryophytes without a loss of old-growth associated
bryophytes. In contrast, interior habitats (sampled primarily >100 m from the forest edge) had a
greater abundance of old-growth associated bryophyte functional groups (as measured by finescale
sampling and percent cover estimates). Old-growth associated species exhibited no
consistent changes with increasing distance up to 45 m from the edge, implying that the
influence of the forest edge on these species extends at least this far into unlogged remnants.
Effect of stand age: Bryophyte species richness peaked in regeneration stands (stand ages
5-30 years), declined to its lowest levels in immature stands (stand ages 25-49 years) and
increased in old-growth stands (stand ages >300 years). In comparison with old-growth, both
regenerating clear-cuts and immature forests had a greater richness of clearing affiliated
bryophytes. There was no loss of old-growth associated species in regeneration plots; however,
old-growth associated species in immature plots showed significant declines in richness which
suggests that immature forests represent a propagation bottleneck for bryophytes in harvested
landscapes. The pattern of bryophyte species occurrence in younger-aged stands supports an
initial floristics model of succession.
Effects of patch size: The richness and abundance of dispersal-limited and microclimate
sensistive groups showed significant declines as patch size decreased. In contrast, groups
expected to increase in richness or abundance as patch size decreased (colonist and open canopy
species) showed little association with patch size indicating that center of small remnant patches
had no greater richness of clearing affiliated species than large remnant patches. The absence of
clearing affiliated species in the center of small remnant patches may well reflect the lack of
available microhabitats.
The results of this thesis imply that the bryophyte community in the study area has been
impacted by human disturbance caused by large-scale forest fragmentation. The bryophyte
community in disturbed habitats (i.e., edge and younger-aged stands) showed an increase in the
number of clearing affiliated species and a decreased abundance of old-growth associated
species. This has important management implications. Although variable retention will
introduce greater structural heterogeneity into regenerating forests, it will do little to alleviate the
effects of fragmentation on bryophytes. The maintenance of bryophyte diversity in coastal
temperate rainforests will depend not only on adequate old-growth reserves but also on longer
forestry rotations that will help mitigate the adverse environmental effects associated with
introduced edges, younger-aged forests and decreasing patch size. / Science, Faculty of / Botany, Department of / Graduate
| Identifer | oai:union.ndltd.org:UBC/oai:circle.library.ubc.ca:2429/16196 |
| Date | 05 1900 |
| Creators | Baldwin, Lyn Kelly |
| Source Sets | University of British Columbia |
| Language | English |
| Detected Language | English |
| Type | Text, Thesis/Dissertation |
| Format | 7371074 bytes, application/pdf |
| Rights | For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https://open.library.ubc.ca/terms_of_use. |
Page generated in 0.0018 seconds