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Island systems are generally more sensitive to the introduction of non-native species than comparable mainland systems and are particularly vulnerable to disturbances that create opportunities for invasion. We examined the impact of browsing by introduced deer on seedling establishment and physiology in three obligate seeding (i.e., non-resprouting) species on Santa Catalina Island for two years following a large fire in 2007: Arctostaphylos catalinae P. Wells (Ericaceae), Ceanothus arboreus E. Greene (Rhamnaceae), and Ceanothus megacarpus Nutt. var. megacarpus (Rhamnaceae). Four post-fire sites were established, with each site containing 12-20 plots exposed to browsing and 12-20 control plots protected from deer browsing. Browsing did not significantly affect seedling survival or physiology in C. arboreus, the only species to experience significant browsing; browsing did, however, significantly reduce seedling height. Predawn and midday water potentials, stomatal conductance, and growth differed among species during their first post-fire dry season. Arctostaphylos catalinae experienced the lowest dry season predawn water potentials (-3.3 MPa compared to -1.7 MPa for C. arboreus and -2.2 MPa for C. megacarpus). Ceanothus arboreus and C. megacarpus exhibited relatively high seedling survival (56% and 69%, respectively) and high resistance to xylem cavitation of stems (P50 = -6.0 and -6.7 MPa, respectively), compared to A. catalinae which had lower seedling survival (30%) and was less resistant to cavitation (P50 = -4.2 MPa). Browsing significantly impacted seedling height, which could impact stand structure. Differential browsing pressure and seedling resistance to water limitation may have important consequences for long-term distribution and abundance of these island endemics on Santa Catalina Island.

Del Mar manzanita (Arctostaphylos glandulosa Eastw. subsp. crassifolia (Jeps.) P.V. Wells) is a federally listed endangered shrub found in San Diego County, California and Baja California, Mexico. This manzanita forms part of the imperiled southern maritime chaparral of southwestern California and adjacent Baja California, Mexico. Del Mar manzanita is problematic to identify because of morphological intergradation with other subspecies of A. glandulosa. Such intergradation could result from biological phenomena, such as gene flow among subspecies. Alternatively, it could be that the current circumscription of the Del Mar manzanita is not correct, and that the morphological characters used to diagnose this subspecies are inaccurate indicators of underlying genetics. This situation leads to problems for conservation planning, where accurate identification of individual plants is essential. Here, we used high-throughput sequencing of restriction-site associated DNA markers (RADseq) to develop single nucleotide polymorphism (SNP) data for a large sample of putative Del Mar manzanita, and a small sample of closely related subspecies of A. glandulosa. We analyzed genetic relationships using a total of 65,964 SNPs, with the aim of testing whether morphological traits used to identify Del Mar manzanita are an accurate reflection of underlying genetic patterns. We conclude that vegetative morphology is a poor predictor of genetic patterns, and that the current morphology-based circumscription of Del Mar manzanita is probably in need of some change. However, due to the limited sampling of A. glandulosa subspecies in this study, it is not possible to determine the taxonomic limits of Del Mar manzanita using our SNP data.

Despite being one of the most extensive vegetation types in the North American Mediterranean Climate Zone, information on the amount of biomass and carbon stock associated with shrubland vegetation is still largely unknown. Efforts to quantify shrubland biomass through fieldwork consist of either direct measurement using destructive vegetation sampling or indirect measurement through the combined use of stem measurements and allometric equations. Both methods have their own benefits and shortcomings, resulting in substantial variation in how shrubland biomass is reported. Here we aim to provide a comprehensive review and synthesis of available shrubland biomass data from studies based in California to provide a concise and reliable source for natural resource managers. We conducted a literature review of 37 studies published over a span of 72 yrs to compile estimates of aboveground biomass (live, dead, and total), leaf biomass, stem biomass (live, dead, and total), litter biomass, and belowground biomass for three prominent shrubland communities and four shrubland species in the California Floristic Province. Overall aboveground biomass in shrub communities was greatest in mixed chaparral (3461 g/m2), followed by chamise chaparral (2114 g/m2), and coastal sage scrub (1583 g/m2). In each community total aboveground biomass increased with the age of the stand. Leaf, stem, and litter biomass estimates were also highest for mixed chaparral compared to the other communities. Of the four shrub species we summarized biomass data for, Ceanothus greggii A. Gray (Rhamnaceae) had the highest average aboveground biomass, followed by Adenostoma fasciculatum Hook. & Arn. (Rosaceae), Quercus berberidifolia Liebm. (Fagaceae), and C. cuneatus (Hook.) Nutt. By compiling these studies and summarizing the biomass data reported in them, we provide a single resource to characterize the amount of biomass of three different shrublands and four species over their life cycle. This is an essential resource for land managers and practitioners who need field-based biomass and carbon stock figures for monitoring and reporting purposes.

Proposed causes of the latitudinal-propagule size gradient invoke differences among biome structures or seed dispersal syndromes. Latitudinal seed-size gradients so far have been predominantly investigated using entire floras, prompting the question of whether such trends exist at smaller scales. Here we consider effects of latitude and elevation on fruit size between and within species in Arctostaphylos L. (Ericaceae), a zoochorous, primarily Californian chaparral shrub genus. We measured fruit size, strongly correlated with seed size in Arctostaphylos, in three species of this genus from multiple localities in the Sierra Nevada foothills, and conducted a character analysis of fruit size across the genus using the standard California flora plant manual (Baldwin et al. 2012). Across the genus we found a weak negative correlation between fruit size and latitude (0.0026 mm diameter/km) and a weak positive correlation between fruit size and elevation (1.3 mm diameter/km). AIC indicates that these trends are not explained by autocorrelation between fruit size and other variables such as maximum plant size. By contrast, intraspecific field data revealed a positive relationship between fruit size and both elevation and latitude. Propagule size gradients within Arctostaphylos oppose those reported for angiosperms globally. This contrast may result from uniformity of fruit structure and animal dispersal, disturbance ecology of chaparral, or local precipitation gradients characteristic of Mediterranean-type climates. Studies of propagule size gradients within taxa can uncover ecological mechanisms behind this trend that remain obscure at global scales.

This paper presents the digitized edition of the Wieslander Vegetation Type Maps (VTMs). The VTMs were part of the first statewide systematic survey of California's vegetation, conducted 1928–1939. Under the direction of Albert Wieslander, crews recorded the patterns of vegetation that they observed from vantage points across the state. The survey covers 176,901 km2 including border and lake polygons and 165,652 km2 of landscapes that we describe in more detail. There are 251,541 polygons in the full extent of the maps, with 249,630 in the analysis extent. These polygons are annotated with codes indicating the dominant plant species, for which voucher specimens were collected. The maps contain 655 species codes, representing 535 species or sub-species in 229 genera, including 34 Arctostaphylos Adans. and 16 Quercus L. species. The 249,630 polygons contain 26,013 unique combinations of species and levels of disturbance. These can be classified into 525 vegetation alliances or provisional alliances...

Vegetation structure, composition, and community patterns on the landscape of southwest Oregon have changed since Euro-American settlement began in the mid-1800s. Much of this change has been attributed to the transition of land management strategies from those dominated by Native American practices, through the early Euro-American settlement period, and on to the post World War II era of industrial scale timber harvest and fire suppression. Using homestead patent applications and associated land classification maps generated under the Forest Reserve Homestead Act of June 11, 1906, we add to the understanding of historic vegetation conditions and evaluate vegetation change over time for land applied for by homesteaders in the Applegate River watershed of southwest Oregon. These homesteads were predominately located on areas now supporting chaparral, Pinus and/or Quercus woodlands, mixed conifer forests, pastures, and agricultural land. Our study presents primary source documentation that describe...

Ceanothus decornutus V. T. Parker is a newly described species found on serpentine outcrops in western Marin County. This taxon has been considered as part of C. jepsonii Greene in recent treatments. Ceanothus decornutus differs in a number of ways from C. jepsonii and suggests relationships to other northern San Francisco Bay species. Beyond the species description and a key to similar taxa north of San Francisco Bay, an analysis of leaf characters is used to indicate possible relationships.

Resistance of stem xylem to water stress-induced cavitation and embolism among chaparral shrub species in California has been extensively studied, providing the opportunity to examine broad patterns in cavitation resistance. We used previously published as well as unpublished vulnerability to cavitation curve data from 16 chaparral shrub species of southern California to examine the variability of cavitation resistance across sites, regions, and seasons. Additionally, these data provided a unique opportunity to address a recent methodological debate within the field of plant hydraulics. We found that different methods, specifically a centrifuge method and a dehydration method, produced similar results (P = 0.184). Vulnerability to cavitation varied seasonally, with species exhibiting greater susceptibility to water-stress induced cavitation during the wet season (P = 0.003). Cavitation resistance did not differ among sites that were less than 10 km apart even though these sites differed in th...

Devils Postpile National Monument is 319 ha in size, located in Madera County, California, on the western slope of the Sierra Nevada at an average elevation of 2280 m. Though small in size, the monument supports diverse habitats, including forests, chaparral, riparian corridors, meadows, seeps, and ponds. In 2001, the National Park Service conducted a survey to 1) inventory the vascular flora and document with vouchered specimens; and 2) describe the distribution and abundance of species of special management concern (rare and/or non-native). Methods coupled a species-level inventory with vegetation mapping, covered an estimated 70 percent of the monument's surface area, and combined broad and targeted search strategies. Survey results yielded a 121 percent increase (from 169 to 373) in the number of documented plant taxa, representing 60 families and 199 distinct genera. Forty-five percent of species were clustered within six families: Asteraceae, Poaceae, Cyperaceae, Brassicaceae, Onagraceae, a...

Carex xerophila Janeway & Zika is described from gabbro and serpentine soils on the west slope of the northern Sierra Nevada in California. It is documented from four populations in or on the margins of chaparral and open forest. The new species is assigned to Carex section Acrocystis Dumort., and a key is provided for all California representatives of the section. Carex xerophila differs from C. globosa Boott in its uniformly short, erect basal peduncles and Sierra foothills habitats. Carex xerophila differs from C. brainerdii Mack. by its green leaves that are not densely papillose below, its relatively shorter perigynium beaks, and its lower elevation montane habitats. Carex xerophila has more strongly nerved scales and perigynium faces than C. rossii Boott.

In the Oakland Hills there may be found two manzanitas that are species of Arctostaphylos growing in localized areas. Arctostaphylos andersonii Gray grows on the main ridge a mile south of the summit of the Snake Road which leads into the headwater basin of San Leandro Creek. Arctostaphylos glandulosa Eastw. grows on the same ridge on yellow shale, and also abundantly on Moraga Ridge on the same formation. A number of years ago while making field studies of these shrubs, my attention was directed to the rather striking fact that individuals of Arctostaphylos andersonii had been killed outright by fire, and that Arctostaphylos glandulosa was stump-sprouting abundantly from heavy root-crowns. No root-crown or tabular development at base of the stem could be found in the former species, nor even any attempts at root sprouting at all, while in the case of the latter species the root-crowns became very heavy, globose, or turnip-shaped, or even eventually forming broad tabular areas of irregular shape at the surface of the ground. Since then many further observations have been made upon the species of this genus in various parts of the state to determine if reaction to fire ran parallel with the specific limitations. Arctostaphylos andersonii is a larger shrub, eight to twelve feet high. One individual within a few feet of the bridle-path along the eastern brow of the Oakland Hills, and about half-mile south of Snake Road summit, is sixteen feet high, with a trunk circumference of three feet nine inches, at six inches above the ground. As said above, this species is killed by fire. Trunks decapitated four feet high failed to regenerate. This species may be recognized by its densely set leaves, which are heart-shaped at base, and by its very close flower-clusters. (PI. I.) Arctostaphylos glandulosa. This is a rather low-growing species of the immediate coast region, occurring in formations of considerable extent on slopes of yellow shale. It is perhaps the most remarkable species in California in the matter of its behavior under repeated fire devastation. After the stems are fire-killed, young plants begin to form a root-crown which becomes turnip-shaped or globose (Fig. 1) and lies immediately at or below the surface of the ground. As the plants increase in age and fires continue to run, as characteristically in chaparral, the root-crowns increase in size (Pl. II, A) and give rise to many stems. While at first small, root-crowns often become two to five, or indeed ten to thirteen, feet broad. The very large ones form irregular circles or crescent-shaped areas, and are truly remarkable structures. (Fig. 2) Such crowns can be studied to advantage upon the southeastern slopes of Mt. Tamalpais or in the Oakland Hills just south of the low wagon pass

Following disturbance, seed pre-treatment is essential for re-establishing many species with low germination rates. However, some seeds, such as those from chaparral plants, do not respond to common horticultural treatments. Instead, methods that mimic chaparral's natural succession cues (e.g., fire) should be used to improve seed germination and restoration success. Fire effects, such as heat, charate, leachate, smoke, and/or liquid smoke, are effective in breaking long-term seed dormancy in many chaparral plants. The challenge is to break seed dormancy in a cost- and time-efficient manner that can be used in large-scale restoration projects. Results of our study show that short-term exposure (10 minutes to one hour) to liquid smoke and/or heat enhances seed germination of Adenostoma fasciculatum Hook. & Arn. (chamise), Ceanothus cuneatus (Hook.) Nutt. (buckbrush), and Salvia mellifera Greene (black sage). Chamise seeds treated with liquid smoke have the greatest percent increase of seed germination odds: 394%, from the control (P < 0.000). Buckbrush seeds treated with liquid smoke and heat have the greatest percent increase of seed germination odds: 953%, from the control (P < 0.000). Black sage seeds treated with heat have the greatest percent increase of seed germination odds: 354%, from the control (P < 0.000). Implementing these procedures in restoration may reduce the seed costs of certain species by nearly 90%.

Native plants in most California ecosystems are adapted to fire, but altered fire regimes and disturbance from firefighting activity, such as the construction of firebreaks or firelines, can change plant community composition and the ratio of native to nonnative species. In October 2007, a wildfire burned 710 acres through a chaparral/grassland mosaic on an ecological reserve, providing an opportunity to quantify fire and fireline disturbance impacts on native and nonnative species under differing disturbance conditions. In the spring of 2012 we sampled the plant community in three adjacent sites, focusing on Centaurea melitensis, which is a common nonnative invader after fire in California chaparral. The first site was burned and bulldozed, the second site was burned but not bulldozed, and the third site was not burned or bulldozed. The first site had also been sampled in the spring of 2008. After four years within the burned fireline site, the mean relative cover of C. melitensis decreased from...

This study compares postfire regeneration and diversity patterns in fire-prone chaparral shrublands from mediterranean (California) and non-mediterranean-type climates (Arizona). Vegetation sampling was conducted in tenth hectare plots with nested subplots for the first two years after fire. Floras in the two regions were compared with Jaccard's Index and importance of families and genera compared with dominance-diversity curves. Although there were 44 families in common between the two regions, the dominant families differed; Poaceae and Fabaceae in Arizona and Hydrophyllaceae and Rosaceae in California. Dominance diversity curves indicated in the first year a more equable distribution of families in Arizona than in California. Woody plants were much more dominant in the mediterranean climate and herbaceous plants more dominant in the bimodal rainfall climate. Species diversity was comparable in both regions at the lowest spatial scales but not at the tenth hectare scale. Due to the double growi...

Knowledge gaps regarding the greenhouse propagation of rare, fire-adapted plant species can impede community level conservation efforts that require fire and active revegetation as management tools. Ericameria fasciculata is a rare shrub endemic to the maritime chaparral community of the central California coast and a listed species of concern. Prescribed burning is actively used in maritime chaparral to maintain community composition and conserve several species of concern with known affinities for fire-related conditions. No study has investigated the seed viability and germination requirements for E. fasciculata. The goal of this study was to ascertain the (1) greenhouse propagation potential of E. fasciculata for planned restoration efforts and (2) to determine if fire-related conditions inhibit or promote E. fasciculata germination. Seed dissection and viability testing indicated that a large percentage of seed were empty or inviable. A greenhouse study examined the potential for fire-relate...

Hazardia orcuttii (A. Gray) Greene is a 5–10 dm tall perennial shrub that is native to coastal sage scrub communities of southern California and northern Baja California. This species was listed as threatened by the California Department of Fish and Game in 2002 and is a federal candidate species, and the only known population in the U.S. is on a 1.6 ha mesa located in Encinitas, California. Very little is known about the general ecology of this species, thus, the goal of this research was to characterize the basic soil physical and chemical properties and plant community characteristics associated with this species. Research was conducted between January 2004 and July 2005 in 12.56 m2 randomly-located plots that either contained or lacked H. orcuttii. Soil in plots containing H. orcuttii had significantly higher clay, soil organic matter, total N, and soil moisture content than plots lacking H. orcuttii, while plots lacking H. orcuttii had significantly more surface litter content. Significant differences were also observed in plant species abundance between plots containing and lacking H. orcuttii, indicating fundamental differences in plant community composition associated with patches of H. orcuttii. Our data support the notion that H. orcuttii is a soil endemic; however, it is unclear whether H. orcuttii prefers soil richer in clay or is restricted to these soils because of other factors. Given the restricted nature of H. orcuttii, and the proximity of the extant population to residential areas, habitat protection from human degradation and fire should be a high priority.

Pine Hill lies near the center of a gabbrodiorite intrusion in the foothills of the Sierra Nevada mountain range in El Dorado County, CA, USA. We assembled an extensive flora, examined the distribution and associations of vascular plant taxa, and specifically focused on associations of six rare plant taxa. The influence of environmental variables on plant distribution was investigated using a stratified random plot sampling technique and applying canonical correspondence analyses. The site contained over 10% (741 plants) of the flora of the entire state of California including seven rare species. Species segregated into chaparral, oak woodland, and grassland communities. In chaparral and woodland, and on serpentine sites, over 75% of the flora was comprised of native species. The non-serpentine grassland community was dominated by exotic species (64% exotic) and contained no rare species. Shrub and tree cover were the most important biotic factors associated with plant species distribution; serpe...

Soil moisture is a key limiting resource in arid and semi-arid environments for woody shrub species. We assessed if three arid communities differed in their level of dry season soil moisture content and if the dominant species in these communities differed in their ability to use soil moisture. Water potential of all of the dominant woody plant species occurring in chaparral, coastal sage, and Mojave Desert communities and soil moisture content of these sites were measured seasonally. Species occurring in the Mojave Desert exhibited the most negative water potentials while the coastal sage community displayed the least negative water potentials. Dry season volumetric soil moisture content of the Mojave Desert site was lowest (7%), the chaparral site was intermediate (10%), and the coastal sage scrub site had the moistest dry season soil (20%). These moisture differences developed even though the coastal sage and chaparral communities both received the same annual rainfall and had similar soil cha...

Fuel treatments to reduce fire danger are being applied to public lands throughout the western United States, affecting significant acreage at considerable expense. This study compares the short term effects of two fuel treatment methods, shrub mastication and “hand cut, pile, and burn” (HPB), on chaparral communities in southwestern Oregon. Ceanothus cuneatus dominated the study sites where permanent paired plots were established on either side of treatment-control boundaries. Over a two year period, we recorded all vascular plant species within each treatment or control plot, along with an abundance class for each species. The effects of treatment on species composition and abundance of forbs and graminoids, overall as well as by plant trait group, were surprisingly small. Time since treatment, 1 yr or 2 yr, had a stronger effect on species composition than did treatment method. Species abundance and richness were greater in the first year after treatments than in the second year or in controls...

Experimental burns involving rare plants can provide important information for managers of those species. This study examined the response to prescribed fire of Ceanothus roderickii, a federally endangered chaparral species endemic to gabbro soils of the Pine Hill Formation in western El Dorado County, California. I conducted a laboratory study of germination cues, a field comparison of germination and survival on burned and unburned plots, and a comparison of seedling survival in burned plot subplots that were protected from vertebrate herbivores by wire exclosures. Seed germination was stimulated by heat (70° or 100° C) followed by a cold treatment. Burned plots contained 22-fold more seedlings than unburned plots, and seedling survival was significantly greater on burned plots. Exclosures significantly increased seedling survival on burned plots by 2 yr postfire. Plants on burned plots began to bloom and to branch layer (root at the nodes) by the sixth year postfire, with larger plants produci...

Effects of prefire stand age, fire intensity, and hillslope position on postfire vegetation recovery during the first two postfire seasons were studied in two contrasting stands of mixed chaparral at San Diego State University's Sky Oaks Field Station (San Diego County, CA). One stand was approximately 60-years old and the other 12-years old when both burned in the July 2003 Coyote Fire. The two stands showed contrasting patterns of postfire community composition among different plant groups based on their modes of postfire regeneration. Fire intensity was significantly higher in the older stand. Increased fire intensity was positively correlated with establishment of seedlings of Ceanothus greggii var. perplexans (an obligate seeder), and negatively correlated with seedling abundance of Adenostoma fasciculatum (a facultative seeder). Hillslope position was also important in determining patterns of abundance, suggesting that soil erosion and deposition following fire may have a significant effect...

Fremontias, or flannel bushes (Fremontodendron), are a distinctive element of California's chaparral communities. Fremontodendron decumbens is only known from a few populations in gabbro soil plant communities of the Sierra Nevada foothills in El Dorado County. Although a recovery plan for these communities has been drafted, the long-term management of F. decumbens is complicated by its treatment as a subspecies of the more widespread F. californicum, and by the recent discovery of additional populations of decumbent plants in Yuba and Nevada Counties that are not easily assigned to either F. californicum or F. decumbens. Genetic relationships among 5 populations, including F. californicum, F. decumbens, and the decumbent plants in Yuba County, were ascertained using AFLP markers. Principal coordinates and population structure analyses of the AFLP data showed that F. decumbens is genetically distinguishable from the populations of F. californicum that we sampled. This distinction, coupled with it...

Postfire resprouting by woody plants confers a marked advantage in rate of recovery over species that regenerate entirely from seed. However, the predictability of this advantage varies markedly between species, with some showing nearly 100% rootcrown survival and others often much lower. This study examined patterns of fire-caused mortality and tested the relative importance of fire severity and plant age between various shrubs and subshrubs characteristic of chaparral and sage scrub associations. Resprouting success varied from about 10% for Eriogonum fasciculatum to a high of 98% for Quercus berberidifolia. For most of the shrub species, skeletons of resprouting plants were significantly taller than those of dead individuals of the same species, indicating less biomass consumption, and thus lower severity fires were associated with higher resprouting success. This pattern was less strongly the case with sage scrub species. Shrubs and subshrubs, however, differed in the effect of aboveground pl...

Although widespread throughout the interior foothills of central and northern California, Pinus sabiniana Dougl. has a disjunct distribution in the southern Sierra Nevada, where it is abundant in the Kern River and Tule River watersheds, but is absent from the Kaweah River watershed between 36° and 37°N. This gap in the pine's distribution has long intrigued botanists and ecologists and has elicited a number of hypotheses for this anomalous biogeographical pattern. Here we propose a new hypothesis that couples unique features of the southern Sierra Nevada topography with unique features of P. sabiniana's response to fire. This low elevation pine is widely distributed in grassland and chaparral, and where it occurs with the latter vegetation, it is extremely vulnerable to high intensity wildfires. Under these conditions, meta-populations persist over time in refugia in riparian areas and during fire-free intervals expand outwards re-colonizing shrubland dominated slopes. The lack of such refugia i...

Lepechinia rossii (Lamiaceae) is described as a new species narrowly endemic to the western Transverse Ranges of southern California. It is a member of section Calycinae, which includes four additional species endemic to California and adjacent Baja California, Mexico—L. calycina, L. cardiophylla, L. fragrans, L. ganderi—and L. mexicana, an anomalous, and probably unrelated, species from central Mexico. Lepechinia rossii is most readily distinguished from other members of section Calycinae by geniculate inflorescence axes, bent at 60–90° angles relative to the subtending stems, and by large, foliaceous inflorescence bracts which are generally equaling or exceeding their adjacent flowers in length, and little reduced distally. At present, two populations are documented, one in the Liebre Mountains (Los Angeles County) and one in the Topatopa Mountains (Ventura County), both occurring in chaparral, on public lands administered by the U.S. Forest Service. Conservation concerns include habitat degrad...

In fire-prone vegetation, non-sprouting, obligate-seeding species depend on a persistent seed bank to reestablish post-fire populations. Thus, for such seeds, seed development and survival in the soil are critical life history stages. The objectives of our study were to examine the structure and composition of Ceanothus seed banks, analyze the viability of seeds in the soil, and determine rates of predation before and after seed dispersal. This study focused on populations of Ceanothus jepsonii var. albiflorus (J. Howell), which is restricted to serpentine soils. We also included data on Ceanothus cuneatus (Hook.) Nutt., a widespread, non-restricted species, for comparison. We found that the seed bank of C. jepsonii loses seeds due to destruction or removal at several stages of development. Pre-dispersal seed predators attacked 37% of inflorescences included in experimentation and up to 50% of shrubs from which fruits were collected, post-dispersal predators removed over 70% of seeds in the litte...

Fire represents an important recruitment phase for many chaparral species. Prescribed burns are often scheduled during winter or spring when soil moisture is high in order to minimize risks of uncontrolled fire. However, chaparral wildfires typically occur in the summer or fall when soil moisture is low. Changing the seasonality of burn affects pre-burn soil moisture, burn temperature and timing of germination. High soil moisture during winter or spring burns is hypothesized to lower germination rates of chaparral plants compared to fall burns. The purpose of this study was to evaluate the effects of prescribed spring burns on the germination of chaparral species in the Mendocino National Forest, California. We conducted two experiments to test for effects of moisture on seed germination. In the soil heating experiment, soil collected under chaparral was heated at several temperatures and soil moistures, and germinating seeds were counted. In the seed heat treatment experiment, seeds of 13 species were heated moist and dry to determine the moisture effect on heated seeds. Results indicate a differential response of seeds to heat and soil moisture. Lotus humistratus, Daucus pusillus and Penstemon heterophyllus were negatively affected by temperature in both moist and dry treatments. Ceanothus cuneatus and Genista monspesullana germination increased with temperature in both dry and moist treatments. Germination of six species (Adenostoma fasciculatum, Camissonia contorta, Emmenanthe pendiflora, Epilobium ciliatum, Galium aparine and Malacothrix clevelandii) decreased under moist heat treatments. These results suggest that spring burns may lead to decreased diversity of chaparral due to reduced seed survival and germination of certain species.

The California chaparral community has a rich flora of species with different mechanisms for cuing germination to postfire conditions. Here we report further germination experiments that elucidate the response of several widespread shrub species whose germination response was not clear and include other species from the Sierra Nevada, which have not previously been included in germination studies. The shrubs Adenostoma fasciculatum and Eriodictyon crassifolium and the postfire annual Mentzelia dispersa exhibited highly significant germination in response to smoke treatments, with some enhanced germination in response to heating as well. The shrubs Fremontodendron californicum and Malacothamnus fremontii were stimulated only by heat-shock treatments. Seeds buried in the soil for one year exhibited substantially higher germination for controls and most treatments. In the case of two postfire annuals, Mimulus bolanderi and M. gracilipes, germination of fresh seed was significantly greater with smoke...

In a 1922 monograph on the California chaparral, William S. Cooper called attention to some patches of chamise (Adenostoma fasciculatum) growing robustly on deep alluvial soils on the west side of the lower Sacramento Valley. He submitted that these patches were relicts of “the true regional climax,” suggesting that centuries of Indian burning accounted for the prevalence of grass instead of brush when the Sacramento Valley was first seen by Europeans. We examined available historical evidence and found that Cooper was right in concluding that the chamise patches he saw were vestiges of a much more extensive (ca. 4000 ha) aboriginal stand. Whether the controlling local influence was edaphic or anthropogenic, and whether the local pattern had any wider regional implications, are questions that remain open to speculation.