Patterns of Early Conifer Succession on Montane River Flood Plains in Olympic National Park, Washington
Scott Stolnack
Aquatic and Fishery Sciences
In the Pacific Coastal Ecoregion (an area extending from northern California
to Alaska), coniferous trees growing on river flood plains can have far-reaching
influences on river processes and biocomplexity. With their ability to
grow to extraordinarily large sizes and to resist decay, coniferous trees
often form the basis of channel-spanning log jams that change the course
of rivers. Pacific salmon (Oncorhynchus spp.) and other animal and plant
species have evolved to capitalize on these large- and small-scale disturbances.
Despite the clear importance of flood plain conifers to the ecology of
the region’s rivers, the pathways of early conifer succession on
river flood plains have received little study to date; as a consequence,
we are limited in the ecological knowledge we can bring to bear on the
restoration, conservation and management of the region’s rivers
and flood plain forests. This project is investigating patterns of early
conifer succession on river flood plains across a variety of spatial
scales, and will describe commonalities and differences crucial to targeting
effective management strategies in river ecosystems.
Objectives. The central goal of this project is to discover where the
most common riparian conifer trees (Picea sitchensis, Pseudotsuga menziesii,
and Abies grandis) establish on flood plains of a variety of rivers Olympic
National Park, Washington, and to quantify patterns of environmental
conditions associated with their presence at patch and reach scales.
Using aerial photographs and field surveys, sites will be located along
a flood plain reach of up to six rivers (North Fork Skokomish, Elwha,
Hoh, Quinault, Sol Duc and Queets Rivers) inside the Park.
Specific objectives will 1) quantify conifer distribution on young flood
plain surfaces (age ~3-40 yr) along study reaches on each river; 2) describe
the relationship between conifer abundance and common biological and
environmental variables such as overstory, shrub cover, substrate size
class, depth to cobble, elevation above low water, soil moisture, soil
nutrient status, and conifer growth rates; 3) compare growth rates and
relative vigor of young conifers among species and sites. Specific hypotheses
will test whether sites with conifers differ significantly from sites
without conifers in any of a number of biophysical factors; where conifers
are present, conifer growth rates will be compared between sites with
and without a competing hardwood cohort.
Methods and Interpretation. Field approaches include surveying and mapping
flood plain reaches, vegetation survey transects and quadrat sampling.
Growth rates will be quantified through height/age regressions or dendrochronological
analysis. Chemical analyses include standard foliar and soil C:H:N analysis.
Statistical tests will include goodness-of-fit tests and multivariate
methods. Analyses will establish the conditions under which conifers
establish on river flood plains, the relative proportions of those conditions
in the target reaches, and the relative differences between conifer patches
growing with and without hardwood competitors.