RESEARCH ARTICLE ABSTRACT: The Darlingtonia fens, found on serpentine soils in southern Oregon, are distinct commu­ nities that demonstrate a balance among high water tables, shallow soils, the presence of heavy metals, and limited nutrients. While conservative efforts have been made to preserve them, soil patterning or the specific processes that appear to underlie soil variability are poorly understood. I investigated the relationship of fire-free period on soil gradients and succession in three Darlingtonia fens, each with a different amount of time since last fire. Changes in vegetation and belowground variables were distin­ • guished across fen, savanna, and shrub communities and across the three sites. I suggest that belowground gradients may be more important than time since fire at preserving these uniquely adapted systems, Soil Patterns in Three since vegetation undergoes post fire succession from fen to shrub to savanna after approximately 100 years since fire. Although restoration of ecosystem structure and processes was not the primary focus of this study, my data suggest that time since fire may drive ecosystem processes in a trajectory away Darlingtonia Fens from the normal succession cycle and that soil moisture decreases and nitrogen levels increase with an increase in fire-free period.

of Southwestern Index terms: Darlingtonia fen, Jeffrey pine savanna, soil ammonium, soil gradients Oregon INTRODUCTION of an intermediate stature such as shrubs (Whittaker 1960). Although a number of Deborah A. Tolman 1 Soil gradients in terrestrial ecosystems are rare plant species are common to these Portland State University often conceptualized as having discrete communities, the dominant understory P.O .Box 751 but mutually dependent above and below­ species includes the carnivorous plants Portland, Oregon, 97207-0751 ground components (Smith et al. 1986; Darlingtonia californica and the sedge Hook et al. 1991; Jackson and Caldwell Carex mendocinensis, while scattered 1993). While there is a rich history of soil Jeffrey pine (Pinus jejjreyi) constitute the • ecological research and a general recog­ upper canopy (Whittaker 1954; Franklin nition of the importance of soil chemical and Dyrness 1988). Few other ecosystems and physical properties (Huston 1979; demonstrate a comparable balance among Robertson et al. 1988; Tilman 1988; Keddy high water tables, shallow soils, the pres­ 1989), the extent to which belowground ence of heavy metals, and limited nutrients processes can affect aboveground com­ where fire is presumably the primary factor munity structure and patterns has been restricting the formation of a closed canopy largely understated. This is especially true forest in the succession cycle. for serpentine soil ecosystems. In the fen ecosystems of southwestern Darlingtonia fens are part of a complex Oregon, two important aboveground fac­ mosaic of fen and pine savanna commu­ tors are believed to influence the vegetative nities found on serpentine soils in south­ patterns and composition (Proctor and western Oregon. The fens display distinct Woodell 1975; Mellichamp 1983). The aboveground, savanna-fen ecotones, both most important is vegetative position rela­ floristically and physiognomically, and tive to soil moisture. Fens reside in peren­ can create high variability in the spatial nial streams and typically are characterized characteristics of local plant communities. by a rich floral community dominated by Perennial springs presumably maintain the Darlingtonia californica and Carex men­ savanna-fen ecotone in the southwestern dosinensis. The second factor is position Oregon ecosystems (H. Glasheen, unpubl. relative to fire intensity, which ultimately data; V. Stansell, unpubl. data; Lang 1999), depends on hydrology. Unburned vegeta­ while the maintenance of similar boundar­ tion growing on saturated soils can create ies for pine savannas in the southeastern distinct patterns of vegetation growth United States is attributed to fire (Wells and between fen and savanna. If this is the Skunk 1931; Christensen 1977; Christensen case, then soil nutrients should reflect cor­ 1 Corresponding author: 1985; Rome 1988). Plant carnivory is an responding transitions or discontinuities in [email protected]; 503-725-3918 important characteristic of these serpentine vegetative patterns. ecosystems and reflects the unique soil requirements of contrasting forms of plant While soil patterning is unclear on ser­ Natural Areas Journal 27:374-384 growth that also include a grass understory pentine soils, the specific processes that and a pine overstory, but disfavors plants appear to underlie soil variability are more

374 Natural Areas Journal Volume 27 (4), 2007 poorly understood. Even less certain is the levels of exchangeable magnesium relative (Calocedrus de currens ) constitute the persistence of vegetative patterns: 0) are to other cations; (2) lower calcium levels upper canopy (Whittaker 1954; Franklin they_~ontrol~_4J:>:YJ>_Qil ~adient§_ an(U~2 ~th~ Jhose found on nons~rp~ntine_s_Qil!l; _ _and_Q)'rnessJ~R8}._Auhetime_thestudy: to what extent do gradients change with (3) lower levels of nitrogen, phosphorus, was initiated, time since last fire was: five regard to time since last fire? Several and potassium than are required for normal years at Cedar Log Creek, eight years at above and belowground variables in these plant growth; and (4) high concentrations Josephine Creek, and approximately 100 ecosystems are theoretically quantifiable, of heavy metals (chromium and nickel) years at Eight Dollar Mountain. Eight yet few studies have attempted to evaluate with molybdenum levels insufficient Dollar Mountain had the longest fire-free their relative importance to aboveground for normal plant growth (Walker 1954; period, a significant expanse of shrub com­ vegetative structure and composition. Kruckeberg 1984). munity, and a number of endemic species. The fens ranged from 3-12 m in width and This study addresses such questions as: 0) The fen soils belong to a laterite clay series 300-600 m in length, while the savannas do soil gradients exist in these serpentine rich in olivine and pyroxene minerals and surrounding the fens were expansive 0- soils? (2) do they mimic aboveground pat­ serpentinized to various extents, giving 300 km2). The sites had moderate slopes terns? and (3) what effects do fire-free pe­ them a dark, blue-green color (Becking (2-10 %). riod, serpentine soil, and soil moisture have 1997). Immediately sUlTounding the fens on vegetation patterns across boundaries in are shallow red soils with stony profiles that During the comparatively dry months these plant communities? To answer these vary in surface depth depending on age of of August and September, maximal fuel and similar questions, this study examines the laterite, amount of erosion or surface loads and sources of ignition (primarily the subterranean patterns. in serpentine movement to which it has been subjected, lightning) result in fires, the majority of soils at three Darlingtonia fen sites with degree of fracturing and alteration of the which were, until the summer of 20Q2; different fire-free periods to determine site parent rock, history of precipitation in the small in spatial extent due to fuel breaks variability in vegetation-soil relationships area, vegetative cover, and composition of of bare serpentine rock and topographic associated with Darlingtonia fens. My the parent rock (Ramp and Peterson 1979). discontinuities (Frost and Sweeney 2000). goals were to determine the presence of The upper surface (depth from 0-.3m) is The 1986 bum in the Josephine Creek site biogeochemical gradients in these sites typically dark, reddish-brown soil with mi­ was a prescribed ground fire that removed and to determine if length of time since nor organic residue and abundant to minor all flammable herbaceous biomass and fire influences biogeochemical gradients. amounts of iron oxide pellets and chromite most of the accumulated litter; the fire I hypothesized that soil moisture would grains (variable amounts of relatively un­ scorched only the lower needles of pines. decrease and that nutrient levels would weathered peridotitie boulders) (Ramp and The 1996 bum in the Cedar Log Creek site increase with increase in fire-free period. Peterson 1979), slightly acidic in pH (6.6 was also a prescribed fire that burned over Soil nutrient levels should be highest at to 6.8), and low in nutrients (Walker 1954; both communities. Both burns OCCUlTed the site with the longest fire-free period, Kruckeberg 1984). Beneath this (.3-1m), a during the late summer, cOlTesponding to especially following the establishment of yellow-brown soil with variable amounts the fire regime for the area (D. Borgias a shrub community. of partly weathered peridotite occurs. A and J. Beigel, unpubl. data). shrub community soil, surrounding the fen at Eight Dollar Mountain, is intermediate in METHODS Soil and Vegetation Sampling both hydropeliod and organic layer, slightly more than the savanna, and slightly less Replicate transects were established across Study Area than the fen, but still saturated for most each vegetation community within each of the year. . site and 1m2 quadrats were sampled for The research was conducted at three Dar­ soil and vegetation variables both continu­ lingtonia fens, each approximately .5-1 ha The sites used in this study were selected ously and adjacently across each transect. in extent and located within the Siskiyou for their distinct boundaries, unique vegeta­ Transects were oriented perpendicular to National Forest in southwestern Oregon tive requirements, and bum histories. 1\vo community boundaries and to the main (420 07' 30" N, 123 0 37' 30" W, elevation of the study sites, Cedar Log Creek and environmental gradients (perennial stream 700 m) (Figure 1). The study area is located Josephine Creek, include pine savanna and and topography) (Knapp 1984; Palmer and within the Josephine ultramafic sheet, a fen plant communities. The third site, Eight Dixon 1990). Each transect contained a geologic region of southwestern Oregon Dollar Mountain, is forested, adjacent to a minimum of nine and a maximum of 12 characterized by unweathered rock frag­ mesic shrub community and most closely soil and vegetation sample quadrats, with a ments underlain by Jurassic-aged marine resembles the southeastern United States' total of six transects in each site. Tnmsects ~ediments (White 1971; OlT et al. 1992). carnivorous plant communities. This shrub at the Eight Dollar Mountain site extended Surface sediments consist of weathered community (unique to Eight Dollar Moun­ an additional 5 m to ensure sampling of ultramafic rock (serpentinite and partly tain) is characterized by Rhamnus califor­ the shrub to savanna communities. Sample serpentinized peridotite), which contributes nica and Rhododendron occidentalis, while quadrat size was increased to 5 m x 5 m in to the serpentine soil chemistry: 0) high scattered Jeffrey pine and incense-cedar

Volume 27 (4), 2007 Natural Areas Journal 375 Josephine County

Grants Pass • Cedar Log Creek Illinois River

Eight Dollar Mountain

N

lcm= 5 Ian

Figure 1. Study sites, Cedar Log Creek, Josephine Creek, and Eight Dollar Mountain, located in Josephine County, Oregon.

376 Natural Areas Journal Volume 27 (4), 2007 both the shrub and savanna communities. ammonium and nitrate were extracted in a The environmental matrix of the CCA Sampling at the Eight Dollar Mountain site 1: 10 soil 2 N KCI solution using the Brem­ included 10 soil variables: (1) soil mois­ iI!~lu~~ an~dditionaln samQle guadrats mer method (Bremmer and KeeneY_12Ji5.t tur_e_(grav:imetric_water_determination),-C2) to include the shrub community. Two Extracts were analyzed colorimetrically bulk density, (3) pH, (4) N03, (5) NH4, (6) hundred and nineteen samples were col­ on a Technicon II auto analyzer. Organic organic matter, (7) sand, (8) silt, (9) clay, lected from the three sites that collectively matter content was determined by loss on and (10) CEC. Bulk density and pH are contained 2682 m2 of sampling area. Soil ignition (Shulte and Hopkins 1996) and continuous variables while soil moisture is samples were collected along transects at CEC by extraction with 1 N ammonium a proportionate variable (wet: dry wt./vol.) each site during June, July, August, and acetate solution (Rhoades 1986). Physical ranging from 22 to 573%. I log transformed

September over four consecutive years soil characteristics (sand, silt, and clay) the variables CEC, soil pH, N03, NH4, (1999-2002). were determined by pipette according and bulk density. Soil moisture, organic to MacKeague (1978). Soils were also matter, sand, silt, and clay and variables analyzed gravimetrically for soil moisture of vegetation abundance required square Vegetation Analyses according to Western States Laboratory root and arcsine transformations prior to Proficiency Testing Standards (Gavlak et analysis to more closely approximate the Vegetation data were recorded throughout al. 1997). assumptions of normality (Jongman et al. the growing season from June to October. 1995). The final analysis incorporated both Plants were identified to species where pos­ soil and species variables; 14 vegetation sible, after Hickman (1993). Some plants Statistical Analyses variables and 11 soil variables comprised remained in a vegetative state throughout the matrices. the season and were identified only to To ordinate vegetation of the study sites, genus, resulting in the grouping of several I used canonical correspondence analysis Multivariate analyses used the program species. Percent cover for each species was (CCA) (ter Braak 1986) by means of CANOCO v. 3.1 (ter Braak 1987). Species estimated using one of six cover classes the CANOCO program v.3.1 (ter Braak variables were ordimited with respect to «1 %, 1-4%,5-25%,26-50%,51-75%, and 1987). Vegetation data for the analysis soil variables using CCA (ter Braak 1986). 76-100%) (Braun-Blanquet 1965). were based on percent cover estimates for Significance levels for the first and second each quadrat along the transects and were axes were set at p :s; 0.05. A forward-se­ recorded during the peak of the growing Soils Analyses lected CCA ordination was then used to season (June). Since a primary objective determine which soil variables accounted was to gain information on biogeochemical Variation in soil chemistry across com­ for the greatest amount of variance in the gradients relative to community structure munity boundaries was assessed using soil distribution of the plants. This process and composition, the species matrix in­ samples collected along transects during chooses variables that explain significant cluded percent cover of observable spe­ June through September at each site over (p :s; 0.05) and independent directions of cies from each community. These species four consecutive years (1999-2002). One total variation in the spatial distribution were: Ceanothus pumila (CEPU), Festuca core (12 cm deep and 3 cm in diameter; of plant vegetation. The significance of idahoensis (FEID) , Arctostaphylos viscida 340 cm3) was taken from each 1m2 quadrat each variable added in this fashion was (ARVI), Tojietdia glutinosa (TOGL), Hast­ for chemical and physical characteristics: tested using a Monte Carlo permutation ingsia bracteosa (HABR), Darlingtonia N0 , NH , soil moisture, bulk density, test with 999 unrestricted permutations. 3 4 californica (DACA), Sanguisorba micro­ pH, cation exchange capacity (CEC), soil Following the CCA, a non-parametric cephala (SAMI), Rudbeckid californica texture, and organic matter. In shrub areas median test between sites was used to (RUCA), Carex mendocinensis (CAME) (the Eight Dollar Mountain site) where confirm that the communities represented and Agrostis spp. (AG) which character­ sample area was larger, three cores were statistically different populations (Sokal ized large communities of heliophytes taken randomly within a quadrat and com­ and Rolf 1982). (plants tolerating full sun). Rhododendron posited. All soil cores were taken between (RHOC) and Rhamnus (RHCA) character­ shrub root zones. Soil pits were dug within Among multivariate methods, the eigenvec­ ized the shrubs while Jeffrey pine (PIJE) each community at each site and described tor method (CCA) preserves the chi-square and incense-cedar (CADE) constituted the using Soil Conservation Service soil survey distance among points, and is appropriate upper canopy community. Site scores from guidelines (Bcnine 1983). when the responses of the dependent vari­ species scores were screened for outliers ables are expected to be unimodal along (> 2 standard deviations from site score) Soil samples collected for nutrient analysis environmental gradients. Unimodality prior to analysis; three samples were found were air dried at 70° C for 48 hours and for this analysis was confirmed using an outside of distinctive clusters of vegetation passed through a 2 mm sieve to remove unconstrained analysis, detrended corre­ by running a principal components analysis stones and coarse roots. All subsequent spondence analysis (DCA), on the species (PCA) and removing them from the total analyses were performed on this sieved data; all gradient lengths were greater than (n = 216). material. Soil pH was determined in a 3.5 and indicated high spatial variability 1:1 soil-water paste (McLean 1982). Soil among species.

Volume 27 (4), 2007 Natural Areas Journal 377 To display and interpret relationships Table 1. Mean and standard error of the mean (±) of cover values (%) for the species matrix data between plant communities and envi­ for Eight Dollar Mountain, Josephine Creek, and Cedar Log Creek sites. Variable codes presented ronmental variables biplots of species in the results appear in parentheses. ordination, scores and the centroids of the environmental variables scores were used. Directional arrows from the environmental Genera (Variable names) Eight Dollar Josephine Cedar Log variable centroids represent the weighted Mountain Creek Creek averages of each of the species with respect Darlingtonia (DACA) 13.0±1.8 31.2±4.2 11.4±2.5 to each of the environmental variables. Tofieldia (TOGL) 0(0) 0.9±0.1 4.3±1.2 Proximal distances from the centroids indicate relatively weaker relationships to Arctostaphylos (ARVI) 5.6±1.4 0.2±0.1 1.2±0.5 the environmental gradients than the more Agrostis (AG) 33.0±1.0 1.1 ±O A 604±1.3 distant locations. Carex (CAME) 23.5±2.7 22.0±3.l 504±2.0 Rudbeckia (RUCA) 23.0±2.5 0.2±0.01 9.9±1.5 RESULTS Rhododendron (RHOC) 25±3.3 0(0) 2.6±1.0 Fourteen species were used in the analysis Ceanothus (CEPU) 0.30±0.01 0.7±0.6 2.3±0.8 (Table 1). Two tree, four shrub, and eight Hastingsia (HABR) llo4±1.8 11.0±2.0 0.5±0.3 herbaceous species were inventoried from Sanguisorba (SAMI) 9 o4±1.3 3.0±0.6 6.8±1.7 all quadrats at the three sites. One tree 12±2.l 5.9±2.0 species, Jeffrey pine (PlJE) , along with PinusjeJrereyi (PlJE) 1.5±0.8 nine herbaceous genera, Darlingtonia Festuca (FEID) l8.2±3.0 2.9±0.9 8.6±2.1 (DACA), Hastingia (HABR), Festuca Calocedrus (CAD E) 0.9±0.5 0(0) 0.6±Oo4 (FEID), Rudbeckia (RUCA), Sanguisorba Rhamnus (RHCA) 6.1±lo4 0(0) 3.8±1.5 (SAMI), Tofieldia (TOGL), Agrostis (AG), Arctostaphylos (ARVI) and Carex (CAME) (stellulatae group), were recorded at each conditions in the fen community. There fen to savanna with NH levels superseding of the three sites. Incense-cedar (CADE) 4 are no clear bulk density, soil texture, N0 1evels in some cases by a factor of 200 and two of the four shrub species, Rhamnus 3 or CEC gradients at Cedar Log Creek; (Table 2). This range of values coincides (RHCA) and Rhododendron (RHOC), were however, bulk density levels were similar with changes in organic matter that were present at Eight Dollar Mountain. These to both the Josephine site and the savanna highest in the fen, lowest in the savanna, two shrub species dominated a shrub com­ community at the Eight Dollar Mountain and intermediate in the shrub community. munity of the Eight Dollar Mountain site site. Organic matter levels were relatively Additional gradients at this site were soil while the remaining two shrub species, consistent across communities with a texture with a sand gradient decreasing (Ceanothus (CEPU) and Arctostaphylos median pH of 6.7. from fen to savanna, a clay gradient that (ARVI», were represented in the savanna increased from fen to savanna, and a bulk communities at all three sites (Table 1). Josephine Creek showed a slight soil N03 density gradient that increased from fen to gradient across communities from the fen savanna and from source offen to the outlet. From the 10 soil variables used in the to the savanna (Table 2). However, there The median pH of this site was 6.6. analysis, several biogeochemical gradients were evident (Table 2). The Cedar Log was a stronger soil NH4 gradient from the fen to the savanna, with the levels of NH4 Creek site had the lowest concentrations Canonical Correspondence Analysis dropping slightly from 40 ppm in the fen to of soil N0 compared to the other sites. 3 29 ppm in the savanna (a 70% decrease). Within the Cedar Log Creek site, soil The canonical coefficients represent the As with the Cedar Log Creek site, levels N0 was lowest in the fen and highest in weight that each soil variable contributed 3 of NH4 were considerably higher than the the savanna communities (Table 2). Soil to the ordination axes, and the inter-set N0 levels (30- to 40-fold greater). Organic ammonium levels at this site were also 3 correlations (site scores from species matter levels decreased from fen to savanna lowest but were considerably higher than scores) reflect the correlation between the but there were no apparent gradients for N0 levels (14 to 33 times higher), with environmental variables and the ordina­ 3 soil texture, bulk density, or CEC. The decreasing values from center of fen to tion axes (Table 3). Both axes 1 and 2 of median pH was 6.8 at this site. savanna across all transects. A strong soil the CCA ordination were significant (p moisture gradient was present at Cedar ::;; 0.05), with high eigenvalues (11,1=0046, In general, two strong gradients occurred at Log Creek from the fen to the savanna 11,2=0.29). Species-soil correlations (0.790 the Eight Dollar Mountain site - a soil N0 with gravimetric moisture as low as 21 % in 3 for axis 1,0.795 for axis 2) accounted for gradient that increased from fen to savanna the savanna community and supersaturated 15 % of the variance explained by the soil and an NH4 gradient that decreased from

378 Natural Areas Journal Volume 27 (4), 2007 Table 2. Mean and standard error of the mean for soil variables at all communities, fen, shrub (s), and savanna (sav) at each site. Shrub vegetation is restricted to the Eight Dollar Mountain site. Soil texture at all three sites is sandy clay loam. Significant median comparisons (Kruskal-Wallis) are indi-

----.~~.------~--~ -~ - I .._cated.by_anasterisk_(>j<)._ ------~-----.- .---.--~------

Eight Dollar Mountain Josephine Creek Cedar Log Creek (100 years since fire) (8 years since fire) (5 years since fire) Soil N03 (ppm) Fen 1.0 ± 0.05 Fen 0.8 ± 0.08 Fen 0.6 ± 0.05 S 1.0 ± 0.12 Say 2.5 ± 0.2 Say 1.2 ± 0.2 Say 0.9 ± 0.1

Soil NH4 (ppm) Fen 147.5 ± 14.3* Fen 36.7 ± 3.2* Fen 20.5 ± 1.8 * S 62.4 ± 7.9 Say 8.2 ± 0.46* Say 32 ± 3.4* Say 15.4 ± 4.2*

Ayg.pH 6.4 6.8 6.7

Bulk density (g/cc) Fen 1.0 ± 0.Q1 * Fen 1.5 ± 0.03* Fen 1.3 ± 0.03 * S 0.9 ± 0.03 Say 1.4 ± 0.009* Say 1.6 ± 0.04* Say 1.4 ± 0.04 *

Soil moisture (%) Fen 318.0 ± 23.3 Fen 98.0 ± 7.7 Fen 71.0 ± 5.7 S 90.0 ± 10.3 Say 10.7 ± 0.8 Say 69.0 ± 6.3 Say 20.5 ± 3.2

CEC (meq/100g) Fen 31.5 ± 1.6 Fen 31.8 ± 1.16 Fen 40.7 ± 0.3 S 36.0 ± 0.3 Say 28.0 ± 0.9 Say 28.1 ± 1.5 Say 47.0 ± 0.8

Organic matter (%) Fen 21.0 ± 1.4 Fen 7.9 ± 0.4 Fen 12.1 ± 0.7 S 19.4 ± 0.6 Say 9.1 ± 0.8 Say 6.5 ± 0.59 Say 13.2 ± 0.6

SloEe (%) 2-5 2-5 10

variables. Six out of 10 soil variables (soil tonia (DACA), Sanguisorba (SAMI), and density (p < 0.001) between sites. Other moisture, N03, NH4, CEC, bulk density, Hastingsia (HABR) clumping tightly in a variables were suggested to be significantly and clay) were significant at p ~ O.OOL wetter habitat while Ceanothus (CEPU), different between sites (Table 3), and while Inter-set correlations (Table 3) show soil Arctostaphylos (ARVI) and Festuca (FEID) knowing this provides insight, it.does not chemical factors, such as NH4 make sig­ clump more tightly in the drier habitats. provide the firm conclusion that could nificant contributions to axis 'I, whereas In these sites, the savanna separated from be provided by replication of sites and a axis 2 likely represents a gradient that is the fen communities (Figure 2). Along the broader statistical rigor (Hurlbert 1984). related to the physical properties of the second axis, bulk density occurred as a soil affected by either time since fire or slight gradient from Jeffrey pine savanna to In summary, the findings from the CCA on soil moisture. All results indicated that Darlingtonia fen communities, increasing soil gradients yield information concern­ plant species separate widely. from low to high, respectively. Separa­ ing the relative importance of spatial and tion within sites across communities and environmental processes operating at stand The first CCA axis ordered sites along between all three sites was clear with the and landscape scales in the Darlingtonia an NH4 gradient (-.66) and soil moisture exception of the savanna community in the systems. Three main soil relationships exist (-.58) ranging from recently burned sites Eight Dollar Mountain site (Figure 3). The with these serpentine sites: (1) soil NH4 (5 and 8 years) to long-time since fire (100 non-parametric median comparison (Sokal increases, (2) organic matter increases,and years) (Figure 2). Species occurred across a and Rolf 1982) indicated significant dif­ (3) bulk density decreases with increasing range of moisture conditions with Darling- ferences in soil NH4 (p <0.001) and bulk fire-free period.

Volume 27 (4), 2007 Natural Areas Journal 379 Cedar Log Creek sites. This suggests that Table 3. Summary of canonical coefficients and inter-set correlations of environmental variables. either eight years is insufficient time to Significance (0:50.05) is indicated by * (between sites) and ** (within sites). build higher soil NH4 levels than those found at Cedar Log Creek or that the Environmental Variable Canonical coefficients Inter-set correlations slightly higher sand content at this site (label) Axis 1 Axis 2 Axis 1 Axis 2 creates effectively drier (higher matric potential) soil conditions. In addition, a Soil moisture (smoist)** -0.24 0.43 -0.58 -0.14 range of other site-specific variables may pH (PH)* -0.06 0.09 0.15 0.21 account for these relationships (Lu et al. Soil N03-N (sN03)** 0.44 -0.05 0.44 -0.20 2006; Tolman 2006). Soil NH4-N (sNH4)** -0.64 0.08 -0.66 -0.27 Both soil texture and bulk density are im­ Organic matter (orgmat)* -0.14 0.01 -0.35 -0.53 portant in shaping post-fire communities. Cation exchange capacity 0.05 -0.40 0.15 -0.27 The ordination values show that bulk den­ (cec)** sity (strongly correlated with sand content) accounts for some spatial distribution of Soil bulk density (bdens)** -0.23 0.60 0.26 0.66 communities. Specifically, savanna plants Soil texture (sand)* 0.49 -0.15 -0.45 -0.37 increase in dominance with increasing (silt)* 0.30 -0.19 0.45 0.05 bulk density. Fine-textured soils, on the (clay)** 0.35 0.63 0.39 0.46 other hand, with high total pore space (such as silt loams, clays, and clay loams) generally have lower bulk densities than sandy soils, especially if organic matter DISCUSSION (1996) in their study of soil ammonium is present (Brady and Weil 1996). This changes following burning. Rhododendron, relationship is most evident at the Eight The results of this ordination analysis Rudbeckia, and Carex (Figure 2) occupy Dollar Mountain site, where organic matter show observable differences in the types sites having high NH4 relative to Ceano­ content is highest in the fen community, of plants grouped between and within sites thus, Festuca, and Arctostaphylos, whereas lowest in the savanna, and intermediate in three southern Oregon serpentine soil shrub community plants incense-cedar in the shrub community (Table 2). Plant communities. Specifically, the analysis and Rhamnus occur somewhere between species, and thus communities, separated indicates that soil-related variables offer the wettest sites for Darlingtonia and the widely, thereby demonstrating that soil partial explanation about patterns and driest sites for Ceanothus and Festuca. variables (such as soil moisture, pH, bulk distributions of plant species in combi­ Along with community separation by soil density, CEC, and soil texture) may con­ nation with fire-free period. Four main NH , the ordination separates the three 4 tribute to site differentiation as strongly as trends suggest that some pattern of plant sites based on fire-free period. However, fire-free period. distribution within a site can be attributed understanding of the influence of ecosys­ to soil ammonium and soil moisture; at a tems over time is not possible without Flammable litter and branch dieback, both landscape scale, soil ammonium may be a replicated sites within each fire-free age produced by savanna species, encourage larger factor determining the presence of class. These findings cannot suggest stand frequent fire. In the event of a fire, lit­ communities within a site. In short, this age effects between sites or conclude site ter is reduced and invading vegetation is study suggests that succession without fire comparisons but instead fire-free, time­ eliminated, thus temporarily inhibiting soil on these serpentine sites proceeds toward related soil characteristics, particularly at development. By contrast, this research increasing soil ammonium levels. Eight Dollar Mountain, where NH , N0 , 4 3 suggests another possibility; the absence and organic matter levels are highest. These of fire at the Eight Dollar Mountain site Use of Kruskal and Wallis (Sokal and findings should be attributed to individual may promote the development of the Rolf 1982) median comparisons shows site differences due to the inherent limita­ current vegetation over successionally statistically significant differences in soil tions of pseudoreplication (Hurlbert 1984; relevant time periods (i.e., approximately NH4 and bulk density between sites. Soil Stewart-Oaten et al. 1986). 100 years), causing litter decay and the ammonium accounts for a major portion development of a relatively nutrient-rich of the variance in the gradient analysis: .79 Examination of these sites (Figure 3) shows humus. This is commensurate with find­ of the species-soil correlation and 15% of that Josephine and Cedar Log Creek are ings from studies on serpentine soils in the variation in spatial distribution of plants juxtaposed with regard to bulk density. the northeastern United States (Knox within each site. These results are consis­ The Josephine Creek site values do not 1984; Latham 1993; Arabas 1997) where tent with Bedford et al.'s (1999) review of correspond with fire-free period where they fire suppression and adequate moisture nutrient-poor fens and bogs in temperate would hypothetically exist - intermediate conditions promote litter accumulation and North America and with Andreu et al. between the Eight Dollar Mountain and decomposition that raise soil organic matter

380 Natural Areas Journal Volume 27 (4), 2007 o

bdens

clay

Fen species

sNH

Shrub species:

o

rl I -1.0 +1. 0

Figure 2. CCA ordination of species scores for environmental variables. Dots correspond to plant species (Table 1); large circles indicate plant communities. Species identifiers and abbreviations for environmental variables follow variable codes used in Tables 1 and 3, respectively.

and soil ammonium levels. Speculatively, essential to the understanding of uniquely shrub species at the Eight Dollar Moun­ Soil gradients likely playa role in main­ adapted systems - well worth considering tain site may draw down moisture levels taining the carnivorous fens of these ser­ for future research. adjacent to the fen and facilitate faster pentine sites. At the point of decreasing decomposition, contributing to higher water-saturated soils, along the gradients Management Implications and soil ammonium levels at this site. Ear­ from savanna to fen, soil nul:J.ients increase, Further Research lier research has shown that surface plant notably NH4. This is particularly evident distributions can influence below ground in these systems, given increases in silicate The key to long-term understanding and variables and" nitrogen cycling through clay content and subsequently higher lev­ management of fire-dependent ecosystems differences in'litter quality and quantity els of CEC. In a biogeochemical context, lies in answering important ecological (Hobbie 1992); and in nitrogen-poor sys­ increases in clay contribute to the soil questions concerning belowground vari­ tems, small changes in the soil organic nutrient levels by subsequently elevating ables. Management of the Siskiyou matter fraction can have large effects on the NH levels in the direction of the shrub 4 Darlingtonia fens has recently emerged ecosystem N dynamics (Wedin and Tilman community (Table 3). These soil-related as a conservation priority in the Pacific 1990; Wedin and Pastor 1993). variables and their subsequent levels are Northwest with little research to substanti-

Volume 27 (4), 2007 Natural Areas Journal 381 o l=Eight Dollar Mountain (100 years since fire) n Josephine Creek + fen and savanna quadrats 2=Cedar Log Creek (5 years since fire) 3=Josephine Creek (8 years since fire)

Cedar Log Creek fen quadrats Eight Dollar Mountain savanna quadrats

Cedar Log Creek savanna quadrats Eight Dollar Mountain shrub quadrats:

-1.0 LowNH +1.0 HighNH4 4

Figure 3. CCA ordination of a subset of sample scores and sites showing inter- and intra-site distinction. Prefixes of either 1, 2, or 3 indicate the separate sites. ate management strategies. Thus, selection details with increased appreciation of their by fire suppression. Furthermore, water of appropriate management strategies in consequent ecological processes in terms management efforts, such as maintaining ecosystems adapted to high water tables, of the overall ecosystem. From this study, water levels, should not be understated shallow soils, the presence of heavy metals, conservation efforts aimed at preserving the as anthropomorphically lowering these and limited nutrients in the context of fire biologically diverse flora and fauna of the levels may alter microhabitat processes and the succession cycle should recognize Darlingtonia fen ecosystems must consider and artificially hasten the demise of the that fen vegetation patterns are strong re­ a more regional landscape perspective. Darlingtonia fens (Tolman 2004). flections of soil gradients, soil moisture, Prescribed burns, in particular, need to time since last burning, and natural suc­ include belowground inventory and associ­ Lacking appropriate definition of temporal cession. Management decisions should ated communities, particularly in the shrub scale or sufficient replication poses serious more fully account for these subterranean community, which is likely maintained challenges for extrapolation and predic-

382 Natural Areas Journal Volume 27 (4), 2007 tion of research results. Generalizations ACKNOWLEDGMENTS Oecologia 31:27-44. regarding ecosystem change require data Christensen, N.L. 1985. Shrubland fire regimes collection over annual to decadal time An NSF Doctoral Dissertation Research and their evolutionary_~onseCJ.ue~es._:pp. scales. Thus, the greatest opportunities for Improvement grant, the Mountaineers 85-100 in The Ecology of Natural Dis­ further research in the Darlingtonia fens Foundation, and the Departments of Ge­ turbance and Patch Dynamics. Academic involve long-term monitoring or short­ ography and Environmental Sciences and Press, New York. term controlled burns. Monitoring should Resources at Portland State University Franklin, J.F., and C.T. Dyrness. 1988. Natural include seedling and sapling surveys to generously supported this research. Vegetation of Oregon and Washington. Or­ egon State University Press, Corvallis. establish long term regeneration patterns Frost, EJ., and R Sweeney. 2000. Fire re­ following either natural or prescribed gimes, fire history and forest conditions in burning. Prescribed burns must include Deborah Tolman has a Ph.D. from the the Klamath-Siskiyou Region: an overview expanded research on fire behavior in Department ofEnvironmental Sciences and and synthesis of knowledge. World Wildlife these ecosystems (e.g., individual species' Resources with an emphasis in Geography Fund, Klamath Siskiyou Ecoregion Program, responses to burns, ecotone responses to at Portland State University. She currently Ashland, Ore. burns, community responses to burns) teaches courses in Environmental Studies Gavlak, RG., D.A. Homeck, and R.O. Miller. as well as N tracer research in nutrient and Geography. 1997. Plant, soil, and water reference meth­ cycling. Geomorphology, location of the ods for the western region. Western Regional fens relative to seeps and bare serpentine Extension Publication #125, Oregon State rock, topographic discontinuities, and University, Corvallis. LITERATURE CITED genetic research regarding age of fens is . Hickman,IC. (ed.).1993. The Jepson Manual: also crucial to predict potential fire effects Higher Plants of California. University of Andreau, v., J.L. Rubio, I Forteza, and R Cerni. California Press, Berkeley. on succession. Since complex interactions 1996. Post-fire effects on soil properties between soil moisture, vegetation structure, Hobbie, S.B. 1992. Effects of plant species on and nutrient losses. International Journal nutrient cycling. TREE 7:336-339. litterfall and decomposition rates, and of Wildland Fire 6:53-58. soil nutrient stocks are difficult to sort, Hook, P.B., I.C. Burke, and W.K. Lauenroth. Arabas, K. 1997. Fire and vegetation dynamics 1991. Heterogeneity of soil and plant Nand more research on the litter component in in the Eastern Serpentine Barrens. Ph.D. C associated with individual plants and open­ these systems is required before its role diss., Pennsylvania State University, State ings in North American shortgrass steppe. in successional relationships can be fully College. Plant and Soil 138:247-256. understood. For example, do the commu­ Becking, RW. 1997. The Darlingtonia bog Hurlbert, S.H. 1984. Pseudoreplication and nity types differ in their N requirements? communities of the Klamath Mountains: the design of ecological field experiments. This in tUrn will influence litter chemistry NW California - SW Oregon. Pp. 1-7 in IK. Ecological Monographs 54:187-211. Beigel, B.S. Jules, and B. Snitkin, eds., Pro­ and potentially the rate of decomposition. ceedings of the First Conference on Siskiyou Huston, M.A. 1979. A general hypothesis Second, information regarding post burn Ecology, 1997 May 30-Jun 1, Kerby and of species diversity. American Naturalist effects on gradients would be useful for a Cave Junction, Ore. The Siskiyou Regional 113:81-101. more comprehensive investigation. Education Project, Portland, Ore. Jackson, R.B., and M.M. Caldwell. 1993. Bedford, B L, M.R. Walbridge, andA. Allison. Geostatistical patterns of soil heterogeneity As uniquely adapted plant ecosystems 1999. Patterns in nutrient availability and around individual perennial plants. Journal decline in the Northwest and more in­ plant diversity of temperate North American of Ecology 81:682-692. tensive management is required, detailed wetlands. Ecology 80:2151-2169. Jongman, R.RG., C.J.F. ter Braak, and O.F.R. information of plant interactions with Borine, R. 1983. Soil Survey of Josephine Van Tongeren. 1995. Data Analysis in Com­ County, Oregon. U.S. Department of Agri­ munity and Landscape Ecology. Cambridge driving variables, such as hydrology or University Press Cambridge, U.K. fire, can guide management actions and culture, Grants Pass, Ore. Brady, N.C., and RR Weill. 1996. The Nature Keddy, P.A. 1989. Competition. Chapman and decisions. For example, an understanding Hall, London. of the extent of habitat specificity can and Properties of Soils. Prentice Hall, Upper Saddle River, N.I Knapp, R 1984~ Sampling Methods and Taxon contribute to the identification of the range Analysis in Vegetation Science. W. Junk, of habitat variation necessary to mruntain Braun-Blanquet, J. 1965. Plant Sociology: the Study of Plant Communities. Hafner, The Hague. rare plants of restricted habitats. Under­ London, U.K. Knox, RG. 1984. Age structure of forests on standing the extent to which subterranean Bremmer, J.M, and D.R. Keeney. 1965. Deter­ Soldiers Delight, a Maryland serpentine variables contribute to plant distribution mination and isotopic ratio analysis of differ­ area. Bulletin of the Torrey Botanical Club can influence decisions about habitat ent forms of nitrogen in soils: 1. Apparatus 111:498-501. conservation. Ultimately, informed man­ and procedure for distillation and determina­ Kruckeberg, A.R. 1984. California Serpentines: agement decisions can help conserve the tion of ammonium. Soil Science Society of Flora, Vegetation, Geology, Soils, and Man­ uniquely adapted and rare plant ecosystems America Proceedings 29:504-507. agement Problems. University of California of southwestern Oregon. Christensen, N.L. 1977. Fire and soil-plant Press, Berkeley. nutrient relations in a pine-wiregrass savanna Lang, F.A. 1999. Klamath-Siskiyou natural on the coastal plain of North Carolina. history. Natural Areas Journal 19:298-299.

Volume 27 (4), 2007 Natural Areas Journal 383 Latham, RE. 1993. The serpentine barrens of D.R Keeney, eds., Methods of Soil Analy­ ordination by [partial] [detrended] [canoni­ temperate eastern North America: critical sis, pt. 2. Chemical and Microbiological cal] correspondence analysis, principal com­ issues in the management of rare species Properties. American Society of Agronomy, ponents analysis and redundancy analysis and communities. Proceedings of the sym­ Soil Science Society of America, Madison, (version 3.1) Agricultural Mathematics posium on rare plants of Pennsylvania and Wis. Group, Wageningen, NL. adjacent states, 1991 Mar 28. Philadelphia, Robertson, G.P., M.A. Huston, EC. Evans, Tilman, D. 1988. Plant Strategies and the Penn. Bartonia 57, Suppl. 61-74. and J.M. Tiedje. 1988. Spatial variability Dynamics and Structure of Plant Communi­ Lu, T., K.M. Ma, W.H. Zhang, and B.J. Fu. 2006. in a successional plant community: pat­ ties. Princeton University Press, Princeton, Differential responses of shrubs and herbs terns of nitrogen availability. Ecology N.J. present at the Upper Minjiang River basin 69:1517-1524. Tolman, D.A. 2004. Environmental gradients, (Tibetan Plateau) to several soil variables. Rome, A. 1988. Vegetation variation in a pine­ community boundaries, and disturbance: Journal of Arid Environments 67:373-390. wiregrass savanna in the Green Swamp, the Darlingtonia fens of southwestern Or­ MacKeague, LA. 1978. Manual of Soil North Carolina. Castanea 53: 122-131. egon. Ph.D. diss., Portland State University, Sampling and Methods of Analysis. Soil Shulte, E.E., and B.G. Hopkins. 1996. Estima­ Portland, Ore. Research Institute, Research Branch, Agri­ tion of soil organic matter by weight Loss­ Tolman, D.A. 2006. Ecotone characterization culture Canada, Ottawa. On-Ignition. Pp. 21-32 in M.A. Magdoff, of Jeffrey pine savanna and Darlingtonia McLean, E.O. 1982. Soil pH and lime require­ M.A. Tabatabvai, and E.A. Hanlon, Jr., eds., fens of southwestern Oregon. Madrono ments. Pp. 199-223 in A.L. Page, R.H. Soil organic matter: analysis and interpreta­ 53:199-210. Miller, and D.R. Keeney, eds., Methods of tion. Special Publication (46), Soil Science Walker, RB. 1954. The ecology of serpentine soil analysis, pt.2. Agronomy Monographs Society of America, Madison, Wis. soils: II. Factors affecting plant growth on 9, American Society of Agronomists, Smith, G.A., J.S. Nickels, B.D. Kerger, serpentine soils. Ecology 35:259-266. Madison, Wis. J.D. Davis, S.P. Collins, IT. Wilson, lE Wedin, D.A., andl Pastor. 1993. Nitrogen min­ Mellichamp, T.L. 1983. Cobras of the Pacific McNabb, and D.C. White. 1986. Quantita­ eralization dynamics in grass monocultures. Northwest. Natural History 94:46-51. tive characterization of microbial biomass Oecologia 96: 186-192. and community structure in subsurface mate­ Orr, E.L., W.N. Orr, and E.M. Baldwin. Wedin, D.A., and D. Tilman. 1990. Species rial: a prokaryotic consortium responsive to 1992. Geology of Oregon. KendalllHunt, effects on nutrient cycling: a test with peren­ organic contamination. Canadian Journal of Dubuque, Iowa. nial grasses. Oecologia 84:433-441. Microbiology 32: 104-111. Palmer, M.W., and P.M. Dixon. 1990. Small­ Wells, B.W., and LV. Skunk. 1931. The vegeta­ Sokal, RR, and EJ. Rolf. 1982. Biometry: scale environmental heterogeneity and tion and habitat factors of the coarser sands the Principles and Practice of Statistics in the analysis of species distributions along of the North Carolina Coastal Plain: an Biological Research, 3rd ed. W.H. Freeman gradients. Journal of Vegetation Science ecological study. Ecological Monographs and Co., New York. 1:57-65. 1:465-521. Stewart-Oaten, A., w.w. Murdoch, and K.R. Proctor, J., and J. Woodell. 1975. The ecology White, C.D. 1971. Vegetation--soil chemistry Parker. 1986. Environmental impact assess­ of serpentine soil. Advanced Ecological correlations in serpentine ecosystems. Ph.D. ment: "pseudoreplication" in time? Ecology Research 9:255-366. diss., University of Oregon, Eugene. 67:929-940. Ramp, L. and N.V. Peterson. 1979. Geology Whittaker, RH. 1954. The ecology of serpen­ ter Braak, C.lE 1986. Canonical correspon­ and mineral resources of Josephine County, tine soils: IV. The vegetational response to dence analysis: a new eigenvector technique Oregon. Oregon Department of Geology and serpentine soils. Ecology 35:275-288. Mineral Industries Bulletin 100: 1-45. for multivariate direct gradient analysis. Ecology 67: 1167 -1179. Whittaker, RH. 1960. Vegetation of the Sis­ Rhoades, J.D. 1986. Cation exchange capacity. kiyou Mountains, Oregon and California. ter Braak, C.J.E 1987. CANOCO - a FOR­ Pp. 167-179 in A.L. Page, RH. Miller, and Ecological Monographs 30:279-338. TRAN program for canonical community

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