The Ozette Prairies of Olympic National Park - Natural Resources ...

(Kulzer et al. 2001). Bogs dominated by Sphagnum, along with fen plants such as sedges (Carex spp.) and
white beakrush (Rhynchospora alba) would be capable of keeping these wetlands open for millennia (Richard
Hebda pers. comm. 2009). Thus, the recent encroachment of the area with conifers could be due to
changes in groundwater levels and alteration of surface water hydrology with the construction of structures,
fences, trails, and plowing the land under the tenure of Lars Ahlstrom and Peter Roose. According
to Hebda (pers. comm. 2009), “We suspect that a water table decline of 10-20 cm over several decades
would be more than enough to cause succession in wetlands.” Further soil studies are needed to evaluate
this hypothesis. According to David Imper (pers. comm. 2009), “Unless drainage channels were built,
these developments are very unlikely to change the hydrology.”
David Peter (pers. comm. 2009) points out that, “Encroachment of trees onto the Ozette Prairies
also might cause a drop in the water table as trees increasingly transpire soil water.” Imper (pers. comm.
2009) explains: “As encroachment begins from islands in the wetland and around the edges, the increase
in transpiration, accumulation of litter and root mass increase radially, exponentially. Even at a low stocking
rate initially at say six inch radial growth per year, can fully close a site in not many years (twenty to
fifty years).”
The Ozette Prairies include wetland areas that might not forest over (Kunze 1989), but they also
contain wetland and non-wetland areas that almost certainly will grow up into forest and they are (R.
Pyle and T. Pyle 2000; observation of the author). The non-wetland open areas at Ozette are probably old
and would have been expected to be forested. So why aren’t they? One explanation might be that Roosevelt
elk grazed and browsed the open wetlands and ecotones, favoring this vegetation, and this disturbance
was frequent and extensive enough to keep the Ozette Prairies and other wetlands open, restricting
or slowing the invasion of woody species (Moral 1985; Skinner 1934). Exclosure studies in the Olympic
rain forest show that cervid herbivory is significant in structuring forest understories. Herbivory decreases
tree, shrub, and fern cover and increases grass cover (Woodward et al. 1994; Schreiner et al. 1996.) Additionally,
the grazing of large flocks of geese and other waterfowl, may have had a lesser role in keeping
the Ozette Prairies open. David Peter (pers. comm. 2009) argues that “Perhaps this would work if there
was already an opening--but then how did that opening form? If there was not already an opening, ungulate
browse might alter the understory, but leave the overstory more or less intact.” Furthermore, when
the natural predators were in place on the Olympic Peninsula, particularly gray wolves (Canis lupus), the
elk probably frequented openings for shorter periods of time, moving more often because their natural
predators would keep them moving.
This earlier grazing regime may have been altered with overharvest by non-Indians visiting and/
or settling on the Olympic Peninsula, reducing herd size, and thus leading to a respite--enabling conifers
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