Kella Sadler

Ph.D candidate (2000 - present)

Thesis Title:

Vegetation of rock outcrops in the Coastal Douglas-fir Zone of British Columbia: taxonomy, ecology, and influence of scale

Funded in part by: NSERC, UBC Graduate Fellowship, Islands Trust Fund, Vancouver Foundation Bryology & Lichenology Fund, Weyerhaeuser Ltd.

Outline of Ph.D. Research: The ability to detect changes in pattern and make predictions at more than one scale (population, community, landscape) are topics of fundamental importance in ecology.  Considerations of scale provide a reconciliation of Clements’ (1916) continental picture of plant communities constrained by climate and Gleason’s (1926) analysis of individual plant communities, where competition is the critical process (Peterson & Parker 1998).  Dominant processes change when the focus of analysis changes from one scale to another.  Unstable systems may appear stable, bottom-up control turns into top-down control, and competitive interactions become less important than climatic effects.  Ultimately, patterns observed at a given focal level are a function of constraints and processes operating at higher and lower organizational levels (Bedward 1995).  The study of patterns and processes relating to scale is, therefore, vital to the progress of practical and theoretical aspects of ecological science.  Studies endeavoring to detect scale-dependent phenomena and predict ecosystem dynamics across scales have begun to appear in significant numbers only in recent years, demonstrating the need for more research on this topic. 

Identifying and understanding scale-dependent changes in pattern and process is a pre-requisite for biodiversity conservation.  The cataloguing of the elements of diversity that may be at risk (e.g.  rare species or habitats), followed by studies of their ecological requirements, and/or composition, structure, and function are the first steps toward generating credible conservation actions (Crins 1997).  As such, successful conservation strategies may require knowledge at several scales of ecological organization. 

The Coastal Douglas-fir (CDF) biogeoclimatic zone is confined to a small fraction (ca 0.3% of the provincial land base) of south-western British Columbia.  Although small in total area, the CDF zone contains some of the rarest ecosystems and associated plant species in BC and Canada.  Intense development pressure in the CDF landscape has resulted in the fragmentation and loss of much of the original habitat.  Garry Oak savannas and associated rock outcrop ecosystems in the CDF zone provide an example of a community type that is both rare in its own right, and contains numerous provincially (and nationally) rare species.  With so few of these rare and fragile ecosystems remaining, there is an urgent need to understand the impact of disturbance on species diversity and composition in this region, and the relevant scale of conservation for species and habitats at risk.  A critical information gap exists for non-vascular plants (e.g. mosses and liverworts) which are sensitive indicators of habitat change but are underrepresented in provincial and national floristic surveys.

 In the CDF zone, rock outcrops are locally frequent throughout the landscape.  Previous studies (Harpel 1997, Vitt & Belland 1997) have demonstrated that rocky substrates support high taxonomic diversity, particularly for non-vascular plants.  In this research project, rock outcrop ecosystems will be examined at different scales (smaller nested within larger): site-level (≥1000m²), plot-level (100m²) and two microplot-levels (1m², 0.0625m²).  This strategy will allow the primary objectives of this research project to be achieved: (1) to increase the inventorial and distributional information for vegetation in CDF ecosystems, particularly for bryophytes, and (2) to describe the patterns of rock outcrop plant species and species assemblages (both rare and dominant taxa) in relation to measured environmental variables at different levels of analysis, identifying scale-dependent patterns of organization.  These data will subsequently be used to investigate vegetation dynamics operating at different scales (e.g. primary succession, disturbance effects) and suggest strategies for future researchers and/or conservationists.

Kella Sadler

M.Sc. 1999

Thesis Title:   

Multivariate analysis of terrestrial bryophyte-habitat relationships in a subalpine forest of coastal British Columbia

Funded in part by Forest Renewal British Columbia

Abstract: This thesis had two general objectives: to describe the patterns of distribution and abundance of terrestrial bryophytes in old growth subalpine forests at two study areas (Cypress and Mt. Seymour Provincial Parks) in southern coastal British Columbia, and to determine the scale at which environmental factors influence these patterns.  Using principal components analyses, it was demonstrated that regional scale (“biogeographical”) plant associations correspond only weakly to the patterns of distribution and abundance of terrestrial bryophytes.  Thus, bryophytes may “sense” the environment differently than is the case with vascular plants, i.e. their distribution may be more related to microclimate characteristics.

Patterns of bryophyte diversity and abundance were examined at the scale of 20m x 20m study plots using canonical correlation analysis and Pearson correlation coefficients.  At this scale, bryophyte diversity and coverage were found to be positively correlated with variables relating to increased light availability.  Plots with a northern aspect, reduced canopy coverage, more abundant vascular vegetation, lower abundance of woody debris, and lower LFH depth and organic matter content were associated with higher bryophyte diversity and abundance.  The microscale (i.e. 0.1m2 microplots) environmental preferences of individual bryophyte species were examined using Pearson correlation coefficients, and by examining the range of microhabitat conditions in which species were noted to occur.  Species in open habitats exhibited narrower ranges of soil surface layer (LFH) characteristics (pH, C:N ratios) than those in closed habitats, possibly because of greater flux in soil surface conditions (e.g. litterfall) in closed sites.

The substratum affinities of bryophytes were examined using their microscale frequencies on available substrata.  To investigate the combined influence of substratum and microhabitat, the species associations on different substratum types were investigated using principal components analysis.  Microscale features (environment and/or substratum) were found to be closely related to the distributions of some bryophyte species.  Assemblages on fine litter and woody debris in open, “stable” habitats with abundant bryophytes and vascular plants differed from those in closed-canopy, steeper, “unstable” habitats with lower bryophyte and vegetation cover.  Bryophyte assemblages occurring on exposed humus and creeping stems were most closely related to the availability of the substratum types.

The relationship of bryophyte species to stable and dynamic types of microenvironments was investigated using logistic regression.  Bryophytes associated with unstable environments (i.e. dynamic surface layer) had a more random distribution than species that were associated with open, stable habitats, or that displayed strong substratum affinities.  The physiological tolerance of species for microhabitat features (environment and/or substratum), and the degree of microhabitat stability seem to play important roles in determining the structure and dynamics of  terrestrial bryophyte vegetation.

Bedward, M. (1995) Simple models of pattern and process. Proc. Linn. Soc. New South Wales, 115: 17-23.  Clements F.E. (1916) Plant Succession. Carnegie Institute Publication 242. Washington, D.C.  Crins, W. (1997) Rare and endangered plants and their habitats in Canada. Can. Field-Nat., 111(3): 506-509.  Gleason, H.A. (1926) The individualistic concept of the plant association. Bull. Torr. Bot. Club, 53:7-26.  Harpel, J. (1997) The phytogeography and ecology of mosses within the San Juan Islands, WA. Ph.D. Thesis, UBC.  Peterson, D.L. & Parker, V.T., Eds. (1998) Ecological Scale: Theory and Applications. Columbia University Press, NY.  Vitt, D. & Belland, R. (1997) Attributes of rarity among Alberta mosses: patterns and predictions of diversity. The Bryologist, 100(1):1-12.