AN ABSTRACT OF THE THESIS OF Barbara L. Toth for the degree ofMaster of Sciencein General Science (Biological Sciences) presented on October 10. 1991 . Title: Factors Affecting Conifer Regeneration and Community Structure After a Wildfire in Western Montana Redacted for Privacy Abstract approved: A severe wildfire burned 454 hectares of a second-growth Douglas-fir forest in 1977 on a north-facing slope in Pattee Canyon, near Missoula, Montana. The slope was aerially seeded with a grass mixture, from which Dactylis glomerata established best. Community structure, conifer regeneration, and the impact of the seeded grass on the plant community were evaluated with two data sets. One set tracked postfire vegetation development from 1979 to 1987 on permanent transects established on upland sites in areas of varying fire severity. The second data set was collected in 1989 on upland sites nearest to the burn edge where conifer regeneration was expected to be greatest. Most stands converged to a similar ordination space by 1987, showing that several key species which established in the initial postfire year determined community structure. These species were largely on-site survivors (including Calamagrostis rubescens, Physocarpus malvaceus, and Spiraea betulifolia) and the seeded grass, D. glomerata. The spread of this species by 1987 to stands that apparently escaped seeding in 1977 suggested that this species may persist at this site. Patterns of species abundance and distribution in 1989 were primarily controlled by factors summarized by a topographic-moisture index and by pre-burn disturbance history. Three general site types were described by an ordination. Areas that appeared as open woodlands in 1937 occurred on ridges and had more xerophytic vegetation in 1989, including native grasses.Conifer regeneration in this region was limited primarily to Pseudotsuga menziesii (Douglas-fir). Areas that appeared as an even, young forest in 1937 were on open slopes and were associated with Pinus contorta (lodgepole pine), Larix occidentalis (western larch), Vaccinum globulare, and Amelanchier alnifolia.Areas that appeared as an older, uneven-aged forest in 1937 were on open slopes near the upper burn edge and were characterized by Douglas-fir and Spiraea betulifolia in 1989. D. glomerata was more successful on the drier ridges and was negatively associated with Calamagrostis rubescens. Competition with C. rubescens, rather than differences in environmental tolerances, most likely restricted D. glomerata to the more xeric sites. An adverse effect of D. glomerata on conifer regeneration was most likely for western larch on xeric sites. Site factors and historical factors were most important in determining patterns of conifer regeneration. Regeneration was moderate on mesic slopes and sparse on xeric ridges. The extreme density of lodgepole pine regeneration (13,000 stems/hectare) in one mesic area reflected the importance of serotiny for post-fire regeneration of this species.Douglas-fir regeneration ranged from 370 stems/ha in a mesic area where no mature survivors were noted to 4045 stems/ha on a mesic slope near survivors. On mesic slopes near survivors, western larch regeneration was 857 stems/ha and was minimal elsewhere. A regression model confirmed the importance of site factors, site history, and availability of seed source for Douglas-fir and lodgepole pine. The model for western larch was only able to explain 14% of regeneration pattern, suggesting that microsite variation as well as other variables would be needed to predict regeneration for this species. Factors Affecting Conifer Regeneration and Community Structure After a Wildfire in Western Montana by Barbara L. Toth A THESIS submitted to Oregon State University in partial fulfillment of the requirements for the degree of Master of Science Completed October 10, 1991 Commencement June 1992 APPROVED: Redacted for Privacy Professor of General Science in charge of major Redacted for Privacy Head of Department of General Science Redacted for Privacy Dean of Graduate Skhoo1 o Date thesis is presented October 10, 1991 Barbara L. Toth ACKNOWLEDGEMENTS The author wishes to thank Bruce McCune, for his guidance, endless patience, and good humor; Pat Muir for her support and conversation; Bill Emmingham for his willingness to jump aboard at the last moment; Dale Pillsbury for his interest; Paul Farber for his laughter and insights; Karla, Jane, and Trudy for their help; the entire General Science Department, including faculty, fellow graduate students, and students, for a wonderfully supportive atmosphere. Thanks to Jeff Kooris for mailing the "cookies" from Pattee Canyon and to Sue Tangeman for field assistance and tick removal.I am grateful for the General Science teaching assistantship that sustained me these three years. This work was also partly funded by a Grant-in-Aid of Research from Sigma Xi, The Scientific Research Society. Thanks especially to my husband, Mark Boudreau, for his encouragement and love, and to Sadie, for walks in the woods. TABLE OF CONTENTS CH. I.Introduction 1 CH. II. Ten Years of Vegetation Change After Wildfire in a Pseudotsuga menziesii Forest in Montana 9 Introduction 9 Methods 12 Results and Discussion 16 Conclusions 25 References 39 CH. III.Vegetation After a Forest Fire in Relation to Site, Preburn History, and Aerially Seeded Grasses 41 Introduction 41 Methods 43 Results and Discussion 49 Conclusions 55 References 66 CH. IV. Factors Controlling Conifer Regeneration After a Wildfire in Western Montana 68 Introduction 68 Methods 73 Results and Discussion 79 Conclusions 90 References 97 CH. V. Conclusions 100 Bibliography 103 Appendices 109 Appendix I.Data used in Chapter 2.Plot averages for cover estimates for eight transects followed from 1979-1987 at Pattee Canyon. 109 Appendix II.Data for chapters 3 and 4. Cover class estimates for all species noted in Pattee Canyon in 1989. 114 LIST OF FIGURES Figure Page Location of study area on north slope (section 10) of Pattee Canyon, southest of Missoula, Montana (basemap: USGS 71/2' series, Missoula SE). 27 II.2a. NMS output, arranging 8 stands in species space. Each stand is represented by 2 vectors defined by 3 points (lines may be curved for clarity). The vectors for each stand show changes in species composition for the years 1979, 1982, and 1987. ... 28 II.2b. NMS output, arranging 8 stands in species space. Each stand is represented by three years of data 29 11.3. Overlays of species abundance of individual species from a Bray-Curtis ordination of 23 species in 8 stands sampled 3 times in 10 years. 30 11.4. Percent cover of Calamagrostis rubescens and Dactylis glomerata for the years 1979 (0) and 1987 () 32 III. la. Bray-Curtis ordination of 192 plots in species space by ranking of topographic-moisture gradient 57 MA b. Bray-Curtis ordination of 192 plots in species space by S1937, the vegetation type as it appeared in aerial photographs taken in 1937. 58 111.2. Overlays of abundance of individual species from a Bray- Curtis ordination (B-C ORD) of 192 samples in species space... 59 IV.1. Conifer density (stems/ha) as a function of distance to seed source for three conifer species at Pattee Canyon. 92 LIST OF TABLES Table Page Pearson (r) and Kendall (tau) correlations with NMS ordination axes for the 23 vascular plant species occurring in three or more sampling units. 33 11.2. Shrub cover, averaged by stand, for all shrub species.Percent cover for 1979 and 1982; midpoints of (percent) cover class estimates for 1987. 34 11.3. Stand average cover values for four conifer species, Douglas- fir, western larch, lodgepole pine, and ponderosa pine. 35 11.4. Percent cover of D. glomerata, C. rubescens, and other native grasses in Pattee Canyon. 36 11.5. Species presence list for 3 years in Pattee Canyon. 37 Pearson (r) and Kendall (tau) correlations for the Bray-Curtis ordination of 192 plots by 23 species. 63 111.2. Chi-square analysis to compare expected abundances of D. glomerata and C. rubescens. 64 111.3. Frequency distribution of cover class estimates for Calamagrostis rubescens and Dactylis glomerata in 1989. 65 IV.1. Density (saplings and seedlings/ha) by species in Pattee Canyon, for 1989 and 1980 93 IV.2. Density (stems/hectare) for 11 moderate-to-old-age Pseudotsuga menziesii communities in Pattee Canyon, 1965. ... 94 IV.3. Rotated factor matrix from principal components analysis of 193 plots in a space defined by combinations of environmental and historical factors. 95 IV.4. Results of regression of 2 principal component scores and distance to seed source on the density of conifer regeneration. .. 96 Factors Affecting Conifer Regeneration and Community Structure After a Wildfire in Western Montana CH.I Introduction Natural disturbances are now regarded as a normal part of ecosystem processes (Sousa 1984), rather than an external event from which an ecosystem recovers. Disturbances include abiotic events such as windthrow, avalanches, and fire, and biolotic agents such as herbivory and insects. These episodes initiate change, which can be measured as a change in biomass, nutrients, dead organic matter, species composition, and physical structure of an ecosystem. A disturbance can range in scale from that caused by a single tree limb falling to the forest floor to a wildfire encompassing thousands of hectares. The predominant disturbance in forest ecosystems of the western United States has been fire (Peet 1988). For a particular area, the pattern of fire occurrence is its fire regime, which is site-specific, and described by fire type, fire severity, size of fire, and fire periodicity (Heinselman 1978; Kilgore 1981). Differences in the disturbance itself, as well as site characteristicsvary the path of secondary succession (Agee and Huff 1987). Climate and vegetation affecta fire regime and, in the case of vegetation, is in turn affected by the fire regime (Agee 1981). Prior to settlement by Europeans, fire regimes in Douglas-fir forests of western Montana ranged from frequent, low-intensity surface fires with a 3- to 25- 2 year return interval to infrequent burns of varying intensities (Arno 1980, Barrett 1980, Kilgore 1981, McCune 1983).