QUEEN'S BOG

Issaquah, Washington

Aerial Photo 1961

Aerial Photo 1978

Areial Photo 1991

 


Introduction

Bogs are unique wetland systems found typically in cool, northern environments. They are characterized by their accumulation of peat and growth of sphagnum moss. Cool temperatures, saturated soil conditions, and acidic conditions are all factors that depress the rate of organic decomposition, allowing peat to accumulate. The low acidity found in bogs can be attributed to the high CEC of organic materials, which increases the concentration of hydrogen ions in the water. Bogs are ombrotrophic and consequently, nutrient poor systems, with low primary productivity. The plants associated with bogs have special adaptations that allow them to live under acidic and nutrient poor conditions.

Historically, the peat within bogs was mined as a fuel source for ancient peoples. Presently, acid-loving crops such as blueberries and cranberries are farmed in bogs. In Finland, bogs have also been drained and used as buffers between logged areas and streams. They have be found to effectively retain suspended solids, and trap nutrients and suspended metals.
 
Our site of study was Queen’s bog, in Issaquah, located within the Klahanie housing development on the Sammamish Plateau. Historically, the site had little input of minerals from ground or surface water flow allowing a large mat of sphagnum moss to form with associated vegetative species. Currently, the bog is receiving hydrologic inputs from surface water in contact with mineral soils. Queen’s bog, therefore, is more accurately described as a fen. Around the perimeter of the bog is a lag, varying in width and depth according to the season. (The water level in the lag had increased about a foot between the time of the class fieldtrip and our field study.) The upland surrounding the bog is dominated by Psudotsuga menziesii, Tsuga heterophylla, Thuja plicata, and Alnus rubra, indicating that rich mineral soils surround the bog. The lag is dominated by the presence of Spirea douglasii, a species not typically associated with bogs. Along the edges of the bog, the Spirea douglasii is encroaching upon the sphagnum moss and competing with the shrubby vegetation within the bog.

Understanding the characteristics of the bog environment, we designed a study to determine whether or not a measurable difference could be observed from the center to the edge of the bog. We suspect that a change is occurring due to the presence of surface water introducing minerals and nutrients to the bog, and the presence of Spirea douglasii encroaching on the bog. We tested the water, soil, and assessed the relative amounts of vegetation along two transects to determine if a gradient exists. We expect to see more nutrients, higher productivity, and less acidic conditions towards the outside edge of the bog.

VEGETATION
 
Reindeer lichen hummock
Mushrooms on Sphagnum sp.
On the west side of the site, where a pond exists, we found typical marsh vegetation such as Iris pseudacorus, Carex obnupta and Typha latifolia. Also along that edge are several stunted red alder (Alnus rubra) and Salix sp. (most likely Piper willow due to its ability to tolerate standing water). The typical bog species of Sphagnum sp., Labrador tea (Ledum groenlandicum), bog cranberry (Vaccinium oxycoccos), bog laurel (Kalmia microphylla) and reindeer lichen began to dominate as we moved further east to the middle of the bog. The edges of the bog are dominated by dense monocultures of Spiraea douglasii. We believe that the Spiraea will continue to encroach on the site due to the increased nutrient run-off from the surrounding house developments and its ability to tolerate both fluctuating water tables and lengthy shallow inundation (Cooke, p. 53). In years past, roundleaf sundew (Drosera rotundifolia) was found in the bog, though none was found on either the class fieldtrip or during our fieldwork. Its absence may be attributed to an increased water level as it is usually found on drier Sphagnum hummocks (Cook, p. 110). Hemlocks (Tsuga heterophylla) grow on several of the hummocks in the middle of the bog. Hemlock is one of the few conifer species able to tolerate acidic and anaerobic conditions (Fitzgerald p. 2), though it does display stunted growth when found in a bog environment. 

Invading Spirea douglasii


 
 
Transect 1 Plot 1

This sample characterized the vegetation of a Sphagnum hummock in the middle of the bog. The surface stratum was 100% Sphagnum moss with a mixed cover of Labrador tea (Ledum groenlandicum), bog cranberry (Vaccinium oxycoccos), bog laurel (Kalmia microphylla) and reindeer lichen. The stems of the Labrador tea and bog laurel averaged 25 cm while the bog cranberry, having a more creeping, vine-like habit, averaged 10 cm. The leaves of the three species showed a distinct reddish color.

 
L. groenlandium stems & leaves and V. oxycoccos berries
Reindeer lichen and L. groenlandium
Transect 2 Plot 1

This sample was similar to Transect 1 Plot 1 in that it was taken from a Sphagnum hummock in the middle of the bog. The surface again was 100% Sphagnum moss with a much denser cover of Labrador tea (Ledum groenlandicum) and bog laurel (Kalmia microphylla) and a considerable decrease in bog cranberry (Vaccinium oxycoccos). Reindeer lichen was absent from this sample. The stems of the Labrador tea and bog laurel were considerably longer than those taken from Transect 1 Plot 1, averaging 40 cm. The few bog cranberry plants present in the sample appeared stunted and were only a few centimeters in length.

Transect 1 Plot 2

This sample characterized the vegetation of the bog edge. The increase in standing water made it more difficult to visually assess the amount of Sphagnum cover, though we found it was abundant when we reached down below the water surface. Ledum groenlandicum was the dominant vegetation, growing densely to nearly a 1.5 meters in height. Ledum is more tolerant of changed conditions than Kalmia and can actually be grown outside of a strict bog environment (Riggs, pg. 264). This explains its dominance over Kalmia at the edge of the bog.

Transect 2 Plot 2

 


This sample was similar to Transect 1 Plot 2 in that it characterized the edge of the bog, but as it was on the opposite side, it received a considerable amount more sunlight. Ledum groenlandicum again was the dominant vegetation, though it grew less densely and averaged just less than a meter in height. The water level appeared lower here than Transect 1 Plot 2 as it was easier to visually assess the full blanket of sphagnum moss at the surface.

Transect 1 Plot 3

 


This transect was shaded by the conifers on the ridge behind the bog. The vegetation of the edge changed abruptly to a monoculture of Spireae douglasii that averaged 2 meters in height. Below the water surface the soil? was sphagnum moss. 

Transect 2 Plot 3

 


Outside the edge of the bog, the vegetation was a mix of Spiraea dougalsii and Ledum groenlandicum. The Spiraea averaged 2.5 meters in height while the Ledum averaged 1.5 meters. Below the water surface, Sphagnum dominated the surface stratum. 


 

SOILS
 
Collection 

We sampled at three points along each of two transects, taking organic soil matter from a 3 inch wide ten inch deep pit. This size was selected to get organic matter from the area of the soil most affected by and effecting plant growth and rooting (as observed at this site). Samples were taken from both a hummock (if available) and hollow at each sampling point to account for the differences between these two types of microsites. We were able to obtain both hummock and hollow samples for both transects at bog-center and spirea/sphagnum edge. The spirea-dominated areas did not have clear hummocks and were uniformly flooded at the time of collection.

All samples (ten total) were bagged and labeled individually, and returned to the lab on November 21st, the day of collection. They were placed in a forced air drying furnace and kept at 75 degrees C from November 21st until November 28th when they were removed and fine-ground using a Whiley mill. These samples were then sub-sampled and turned over to the lab technician for C-total and N-total analysis using a LECO CN 2000 analyzer. 

What we expect

With what we have learned in class, and from new materials gathered for the literature search for this project we have found some soil variables which we can forecast for our evaluation of Queen’s bog. 

Along the transects which run from bog center (sphagnum) through edge (spirea/sphagnum mix) to the spirea dominated plots we expect to see some differences in the soil values which we are testing. We hypothesize that the in-growth of spirea is changing the low nutrient and low pH environment of the sphagnum dominated bog, creating a more condusive environment for more general (less specialized) plant species. .

Overall we expect to find some significant differences from what we see commonly in mineral soils

We expect to see along the transects Organic content

Soils on both transects appeared visually very similar. Both bog-center plots were almost entirely sphagnum, to the sampled depth of 10 inches. Sphagnum/Spirea edge plots appeared identical to bog-center soils. The most unique soils were found in the Spirea dominated edge. These plots had soils, which were noticeably darker and more decomposed than other plots. Soils had similar organic content between 90-100%. With values being slightly lower in the Spirea dominated plots.

Pore space

As noted in the above section the bog-center and edge plots had visually indistinguishable soils in the area sampled. The pore spaces of these areas were judged to be visually identical. These soils can limit plant species in-growth by the unique characteristics of the soil substrate. Factors such as pore space, instability, nutrient holding capacity, temperature insulation and moisture holding capacity are limiting factors for species composition in these soils. Soils found in the Spirea dominated plots showed less pore space than bog-center or edge. These soils were darker in color, composed of more decomposed, less recognizable organic matter. This difference in soil structure changes the growing environment and removes some of the factors limiting growth listed above.
 


Soil pH

Soil pH was determined by drying and fine grinding plot samples, suspending in a 1:1 mixture with DI water and sampling pH. The values listed on the chart above represent the averages of hummock and hollow samples taken at bog and edge plots. Spirea pH values represent a single sample. As seen above both transects show an increase of soil pH at spirea plots as compared to bog center. Transect two shows a gradient of pH increasing as species composition shifts to spirea domination. This trend is not supported by the edge plot in transect one, but may be a product of sub-sampling error. The pH change seen in this data shows that the outside edge of the bog has an environment which is less limiting to in-growth of non-bog specific species. This change in pH may also reflect increased in nutrient availability, important in changing the nutrient-limiting environment of an ombrotrophic bog.

 


Carbon-Nitrogen Ratio

The C/N ratio of a soil represents an important plant growth parameter. When the C/N ratio is high, much of the nitrogen in the soil is utilized by the microbial population to build ‘bug bodies’, when the ratio is lower, more nitrogen becomes available for plant uptake. Pritchett states that forest soils may have an average C/N ratio around 20:1.
 



 


The values listed on the chart above represent averaged values of hummock and hollow samples taken at bog-center and edge plots. Spirea plot carbon/nitrogen values represent a single sample. This chart shows a decrease in the C/N ratio between bog-center and Spirea center plot. Our data shows that the C/N ratio is an average of 44% lower in the Spirea dominated plots. This means that there may be increased nitrogen availability in these areas. The transect two data shows a sharp increase from bog-center to Spirea/sphagnum mix, decreasing again in the Spirea dominated plot. This sample contained a large amount of woody material and may have been taken from the location of a decomposing tree, which would significantly increase the C/N ration over what would be expected. Re-sampling this plot may give data, which more closely approximates what was seen in transect one.

Summary

Both transects showed similar data supporting theorized differences between bog-center and Spirea-center plots. The Spirea-center plots showed increased pH (7.5% increase average), and lower C/N ratio (44% decrease average). These changes in microsite effectively create a more hospitable environment and allow for less specialized plant in-growth. These patterns were not strongly mirrored by the Spirea/Sphagnum edge plots, which we felt would show slightly increased pH and slightly lower C/N ratios than bog-center plots. Our theorized values were seen in pH in the T2 transect, and C/N ratio in the T1 transect but not in both. This may be a product of limited samples and sampling error, we would hope to find values as we hypothesized with more sub-samples of each plot.

Water
 
 
 
Water Quality

Hydrologically, bogs can be characterized as precipitation-dominated systems having poor drainage and stable water levels, often with an associated moat or "lagg" surrounding the perimeter (Kulzer et al.1999). Bog surface water is acidic with pH around 4.0, the result of low alkalinity (CaCO3) combined with humic and fulvic acid production from sphagnum peat decomposition, redox reactions with sulfur species, and cation exchange by the moss. Bogs are low nutrient/low mineral systems typified by low dissolved oxygen (DO). Those in marine-influenced regions such as western Washington tend to have elevated concentrations of sodium (Na) and chloride (Cl) ions. Examples of values from the Puget Sound area are: hardness (as CaCO3), just above 1.0 mg/L; total phosphorus (TP), ~0.05 mg/L or less; nitrate-N (NO3-N), </= 0.01 mg/L; DO, 0.75 mg/L at four inches depth. Other values can be found in Kulzer et al. 1999.

We measured several water quality parameters at bog center, species edge, and Spirea center (moat) along two transects in Queen’s Bog to discern any environmental gradients. Vitt and Bayley (1983) found significant differences in pH, Ca++, and Mg++ between the interior and edge of an oligotrophic bog in Ontario. Nutrient samples were also collected from a runoff stream entering the bog at the southwestern corner. pH, DO, and temperature data were all collected in the field using Beckman and YSI-brand probes. Surface water samples were collected in acid-washed polyethylene bottles and glass BOD bottles, to be laboratory-analyzed for TP, ammonium nitrogen (NH4-N), total suspended solids (TSS), and five-day biochemical oxygen demand (BOD). Soluble reactive phosphorus (SRP) and NO3-N were not examined, as most researchers reported levels to be below detection limits (eg. Damman 1986, Gerdol 1990), both in surface water and in soil extracts in the case of NO3-N (Waughman and Bellamy 1980, Verhoeven et al. 1990). All nutrient samples were analyzed colorimetrically, in duplicate. Samples to be assayed for NH4-N were filtered immediately upon return to the lab and frozen for a period of one week. After two days of thawing, samples were analyzed using the phenate method. TP samples were stored at 4C for about two weeks, then analyzed using the persulfate digestion/molybdenum-antimony method. BOD samples were filtered through 100um mesh before analysis to remove large pieces of plant matter, and were analyzed in triplicate. Results can be seen in Table 1 and in Figures 1-3.

 
 
  

Plot
pH
temp (C)
DO (mg/L)
BOD (mg/L)
TSS (mg/L)
NH4 (mg/L)
TP (mg/L)
Runoff stream
         
0.28
0.04
T1 Bog center
4.12
7.0
5.6
11.0
66.2
0.02
0.33
T1 Species edge
3.86
7.3
1.8
4.1
23.0
0.01
0.27
T1 Spirea center
 
7.0
2.0
2.4
8.0
0.02
0.17
T2 Bog center
3.53
8.0
2.3
0.2
0.6
0.01
0.02
T2 Species edge
3.72
8.0
5.3
7.9
124.9
0.01
0.24
T2 Spirea center
4.51
8.0
1.0
2.3
7.9
0.03
0.06
Table 1: Water quality results from Queen’s Bog, King County. Values not reported = not sampled or missing data.

 


Values shown here are within the ranges found in the literature. Gerdol (1990) reported pH values ranging from <4.0 - ~5.8 in both "mire expanse vegetation" and "mire margin vegetation," the latter including woody species, in an ombrotrophic bog in the southern Alps. Heinselman (1970) examined peatlands in Minnesota and found pH values between 3.1 and 3.8 in an ombrotrophic raised bog (moat: 3.7- 4.0), semi-ombrotrophic bog, and transitional bog, while the range was greatter (3.9 – 6.1) in a weakly minerotrophic swamp. Kulzer et al. (1999) reported pH values of 4.2 in the mat and 6.9 in the lagg of a Puget Sound area bog. DO values ranged from 0.2 mg/L – 9.4 mg/L, and BOD-5 from <1.0 mg/L (4/10 stations) – 5.6 mg/L (one station) in a Florida peatland sampled in the spring (Roddy and Tomlinson 1989). In this same study, TSS values ranged from <5.0 mg/L (3/10 stations) – 66.0 mg/L (one station).

Nutrient data is widely reported in the literature, though more so for major cations (ex. K+, Ca+) than for N- and P- species. Below is a summary of values found for NH4-N and TP: 

 
Type of Peatland
NH4-N
TP (mg/L)
Gerdol 1990
ombrotrophic bog
10 – 25 ueq/L
 
Damman 1986
ombrogenous bog
0.02 mg/L
 
Vitt and Bayley 1983
2 oligotrophic basin mires
0.009 mg/L

0.002 mg/L

 
Vitt and Chee 1990
poor fen
0.02 mg/L
0.01 (summer) – 0.02 (fall)
Roddy and Tomlinson 1989
   
0.41 – 1.10
Kulzer et al. 1999
bog
 
~0.05 
Table 2: Summary of nutrient values reported in the literature. Missing values = parameter not analyzed.

 


Gerdol also reported that NH4 was one of the main ions in surface waters. Vitt and Chee found that while organic-N was the most common form of nitrogen, NH4 was the most common labile species.
 
  Figures 1 – 3 demonstrate the observed patterns in water quality parameters along the two transects. Surprisingly, there were no consistent patterns between the two transects, only within each transect. While there appears to be no definable gradient for pH, DO, or NH4-N, a separate pattern for each transect does emerge for BOD, TSS, and TP. Along the first transect (T1), from bog center south to Spirea center (lagg), these values all decreased. Along T2, running from bog center northwards, there was a sharp increase in values between bog center and species edge, and then a decline (to values higher than those from bog center) in the Spirea center. It appears as though BOD and TSS are meausuring the same phenomena, i.e. all TSS is created by organic suspended solids. This is not surprising, given that sphagnum bogs are by definition isolated from sedimentary influences. The fact that TP follows the pattern makes it likely that the bulk of phosphorous was confered by vegetative particlulate matter rather than the labile form of SRP.

It should be noted that our grab samples were collected on one day in the fall, after the onset of vegetative senescence, and are not reflective of year-round conditions or of whole-bog conditions. It is probable that nutrient values are somewhat elevated at this time of year as N and P can be leaked from plants as they senesce and the plasmalemma increases in permeability. Although leaching accounts for <1% of N-loss in leaves of taiga trees, simpler species such as sphagnum moss that have no storage organs may be more susceptible (Gerdol 1990).
 
It is interesting to note that while the inlet stream did contain elevated levels of NH4-N, the receiving moat showed lower concentrations than the interior portions of the bog. It appears as though the Spirea is actively taking up most of this nutrient, effectively cleansing the incoming water and maintaing the system as one that receives its nutrients from rainfall. Indeed, Gerdol (1990) reported elevated rainwater concentrations with respect to bog water concentrations due to active uptake by both mosses and vascular plants. Damman (1986) found N and P removal in a bog to be greatter than 95 and 80% respectively, when he measured rainwater concentrations (corrected for evaporation) and compared them to outlet stream concentrations. 

TP levels were depressed in the stream relative to those found in all plots of the bog with the exception of the T2 bog center, which is not surprising given that there was little vegetative matter in the inlet. Values in other Puget Sound area runoff streams range from 0.02 mg/L to 5.0 mg/L (Kulzer et al. 1999), so this stream is at the low end. It would be interesting for future researchers of Queen’s Bog to attempt to measure SRP of both the stream and the moat, to better ascertain whether the Spirea is also acting in this capacity for P. It would also be interesting to analyze the surface waters for cation content, as the importance of increased nutrient supply from streams is greatter with respect to metallic cations than to N and P (Malmer 1986).
 



 


Conclusion

The vegetation of Queen’s bog changes dramatically in both size and composition from the center out toward the Spiraea dominated edge. The center is composed of plants typical of Sphagnum bogs such as bog laurel (Kalmia microphylla), Labrador tea (Ledum groenlandicum), and bog cranberry (Vaccinium oxycoccus). Environmental conditions at the bog edges appear to be quite different as Ledum groenlandicum is significantly taller and both Kalmia microphylla and Vaccinium oxycoccus are either dwarfed or absent. Beyond the bog edge, Spiraea douglasii successfully outcompetes all other vegetation.

The correlation between sphagnum bog vegetation and elemental content in bog waters has been well-studied (Vitt and Chee, 1990). For example, these authors found that variation in vascular plant species in three types of Canadian fens was more closely associated with N and P levels, whereas bryophytes were more closely associated with changes in acidity and in mineral concentrations. Over all, the vegetation gradient correlated significantly (DECORANA and Spearman's rank order correlation techniques) with organic N, NH4-N, Na, NO3, P, Fe (last three in spring only), and sulfur (fall only) concentrations in the water. Additionally, they cite Malmer (1986) who found that bog sites with similar water chemistry may support different vegetation gradients due to the availability of multiple nutrients (including N, P, and cations), which in turn is determined by the hydrotopographic gradient and flow rate. Heinselman (1970) also found chemical controls on vegetation patterns, citing "sharp boundaries related to changes in water properties, peat surface configuration, and paths of water flow." Bridgham et al. (1998) give a comprehensive and detailed list of the major literature and the results of many limiting nutrient studies.

Our results were mostly inconclusive in this respect, simply due to the fact that we were time-limited and were only able to examine two transects on one day. For any given water quality parameter, only one transect showed a distinct gradient. Essentially, this means that we have no replication of data. We suggest that future studies be designed such that multiple transects over a long time period (at minimum, all four seasons) can be examined. It would also be helpful to conduct a more thorough investigation on the elemental content of the soil. Finally, it was concluded that the Spirea stand may actually be helping the bog to survive in an area that is increasingly encroached upon by development.

The soils portion of our project did show some noteworthy results. The pH was seen to have a gradient from bog-center (pH low) to Spiraea-center (pH higher). This was seen in only one of two transects studied. Similar results for Carbon/Nitrogen ratio were seen, one transect having a strong gradient from high to low C/N ratio when traveling from bog-center to Spiraea-center. Our results may indicate a problem of limited replications of samples. We are confident that with an increased number of sub-samples at each plot strong gradients for both pH and C/N ratio would be observed. Additional sampling outside the Spiraea could be included to assess the levels of nutrients entering the bog and whether Spiraea might actually act as a buffer for the sensitive vegetation of Queen's bog.
 
 

Slide Show
 



 




Literature Cited

Damman, A. W. H. 1986. Hydrology, development, and biogeochemistry of ombrogenous peat bogs with special reference to nutrient relocation in a western Newfoundland bog. Can. J. Bot. 30:490-520.

Gerdol, R. 1990. Seasonal variations in the element concentrations in mire water and in Sphagnum mosses on an ombrotrophic bog in the southern Alps. Lindbergia. 16:44-50.

Heinselman, M. L. 1970. Landscape evolution, peatland types, and the environment in the Lake Agassiz Peatlands Natural Area, Minnesota. Ecol. Monogr 40:235-261.

Kulzer, L.; Luchwessa, S.; Weinmann, F.; Cooke, S. 1999. Sphagnum bogs…would they be as acid by any other name? Powerpoint presentation available online at http://faculty.washington.edu/kern/uhf475/sws99cla.ppt

Malmer, N. 1986. Vegetational gradients in relation to environmental conditions in northwestern European mires. Can. J. Bot. 64:375-383.

Roddy, M.; Tomlinson, M. 1989. Peat deposit water quality in Lake Istokpoga, Florida, USA. Environ. Geol. Water Sci. 13(1):45-50.

Verhoeven, J. T. A.; Maltby, E.; Schmitz, M. B. 1990. Nitrogen and phosphorus mineralization in fens and bogs. J. Ecol. 78:713-726.

Vitt, D. H.; Bayley, S. 1983. The vegetation and water chemistry of four oligotrophic basin mires in northwestern Ontario. Can. J. Bot. 62:1485-1500.

Vitt, D. H.; Chee, W. 1990. The relationships of vegetation to surface water chemistry and peat chemistry in fens of Alberta, Canada. Vegetatio 89:87-106.

Waughman, G. J.; Bellamy, D. J. 1980. Nitrogen fixation and the nitrogen balance in peatland ecosystems. Ecology 61(5): 1185-1198.
 
 

Refrences

Stevens, Michelle L. and Ron Vanbianchi, Restoring Wetlands in Washington, Washington State Department of Ecology Publication #93-17 April 1993

Fitzgerald, Betty Jo, The Microenvironment in a Pacific Northwest Bog and its Implications for Establishment of Conifer Seedlings, Master of Science Thesis, University of Washington 1966

Project MAR, The Conservation and Management of Temperate Marshes, Bogs and other Wetlands, Volume I, IUCN Publications, Compiled by staff of IWRB/MAR Bureau.

Riggs, George B. Some Sphagnum Bogs of the North Pacific Coast of America

Ecology, Volume 6, Issue 3 (July, 1925) p. 260-278.
 
 

References

Damman, A.W.H. (1978) Distribution and movement of elements in ombrotrophic peat bogs. Oikos 30:480-495.

Damman, A.W.H. (1990) Nutrient status of ombrotrophic peat bogs. Aquilo Ser Bot. 28:5-14.

Franklin and Dyrness, (1973) Natural Vegetation of Oregon and Washington.

Gore, A.J.P. (ed) (1983). Ecosystems of the World 4B: Mires: Swamp, Bog, Fen, and Moor. New York: Elsevier Scientific Publishing Company.

Grzimek et.al., (1984) Grzimek's Animal Life Encyclopedia Series.

Hitchcock, C. Leo & Cronquist, Arthur (1973). Flora of the Pacific Northwest. Seattle and London: University of Washington Press.

Ingles, Lloyd G. (1973) Mammals of the Pacific States.

Mathews, Daniel. (1988) Cascade and Olympic Natural History. Portland, Oregon: Raven Editions.

Moore, T.R. (1988) Growth and net production of Sphagnum at five fen sites, subarctic eastern Canada. Can. J. Bot. 67:1203-1207.

Osvald, H. (1970). Vegetation and Stratigraphy of Peatlands in North America. Uppsala: Acta Universitatis Upsaliensis.

Osvald, H. (1933). Vegetation of the Pacific Coast Bogs of North America. Uppsala: Almqvist & Wiksell Boktryckeri.

Pojar, Jim and MacKinnon, Andy (1994). Plants of the Pacific Northwest Coast. Redmond and Vancouver:

Lone Pine Publishing.

Pritchard, K. (1992). A Field Guide to Wetland Characterization and Wetland Plant Guide. Seattle: Washington State University Cooperative Extension.

Sutherland, W.J. & Hill, D.H.(ed) (1995). Managing Habitats for Conservation. Cambridge: Cambridge University Press.

Maps

1992 Land Cover: Central Puget Sound Region: King, Kitsap, Pierce, and Snohomish Counties

obtained for the Puget Sound Regional Council contracted with Economic and Engineering Services of Olympia, WA and Environmental Research Institute of Michigan

August 10, 1992

Monitor urbanization of valuable resource lands such as agriculture and open space

Interim Regional Land Use Plan

Puget Sound Governmental Conference

Printed August 1971

Historical Pattern of Urbanization in the Puget Sound Region

1920, 1940, 1960 (data)