Arctostaphylos Glandulosa Research Articles

Characteristics of Pyrolysis Products of California Chaparral and Their Potential Effect on Wildland Fires

The aim of this study was to investigate the pyrolysis of selected California foliage and estimate the energy content of the released volatiles to show the significance of the pyrolysis of foliage and its role during wildland fires. While the majority of the volatiles released during the pyrolysis of foliage later combust and promote fire propagation, studies on the energy released from combustion of these compounds are scarce. Samples of chamise (Adenostoma fasciculatum), Eastwood’s manzanita (Arctostaphylos glandulosa), scrub oak (Quercus berberidifolia), hoaryleaf ceanothus (Ceanothus crassifolius), all native to southern California, and sparkleberry (Vaccinium arboreum), native to the southern U.S., were pyrolyzed at 725 °C with a heating rate of approximately 180 °C/s to mimic the conditions of wildland fires. Tar and light gases were collected and analyzed. Tar from chamise, scrub oak, ceanothus and sparkleberry was abundant in aromatics, especially phenol, while tar from manzanita was mainly composed of cycloalkenes. The four major components of light gases were CO, CO2, CH4 and H2. Estimated values for the high heating values (HHVs) of volatiles ranged between 18.9 and 23.2 (MJ/kg of biomass) with tar contributing to over 80% of the HHVs of the volatiles. Therefore, fire studies should consider the heat released from volatiles present in both tar and light gases during pyrolysis.

Influence of Pyrolysis Gas Composition and Reaction Kinetics on Leaf-Scale Fires

ABSTRACT The impact of pyrolysis gas composition and the underlying reaction kinetics on the burning characteristics of a leaf was computationally investigated. The computational configuration resembled a previous experimental setup where vertically oriented manzanita (Arctostaphylos glandulosa) leaves were burned. Different compositions and reaction kinetics for the pyrolysis gas released during the leaf thermal decomposition were examined. The most detailed composition included , , , and , which was suggested by the previous experimental study of pyrolysis products of different plant species. The least involved compositions only included either or . In all considered compositions, in addition to pyrolysis gas, the release of the heavy gas, i.e. tar, was accounted for. Tar breakdown was represented by a single-step reaction with the light gases above and soot as the products where the stoichiometric coefficients were determined by an optimization technique for consistency with the measurements for the tar molecule. The burning simulation results agreed best with the previous experimental data when a mixture of , , was used. The least agreement was noted when pyrolysis gas was represented by only . Inclusion of tar breakdown reaction appreciably increased the overall heat release due to combustion of its products above the leaf.

Subspecies differentiation in an enigmatic chaparral shrub species.

Delimiting biodiversity units is difficult in organisms in which differentiation is obscured by hybridization, plasticity, and other factors that blur phenotypic boundaries. Such work is more complicated when the focal units are subspecies, the definition of which has not been broadly explored in the era of modern genetic methods. Eastwood manzanita (Arctostaphylos glandulosa Eastw.) is a widely distributed and morphologically complex chaparral shrub species with much subspecific variation, which has proven challenging to categorize. Currently 10 subspecies are recognized, however, many of them are not geographically segregated, and morphological intermediates are common. Subspecies delimitation is of particular importance in this species because two of the subspecies are rare. The goal of this study was to apply an evolutionary definition of "subspecies" to characterize structure within Eastwood manzanita. We used publicly available geospatial environmental data and reduced-representation genome sequencing to characterize environmental and genetic differentiation among subspecies. In addition, we tested whether subspecies could be differentiated by environmentally associated genetic variation. Our analyses do not show genetic differentiation among subspecies of Eastwood manzanita, with the exception of one of the two rare subspecies. In addition, our environmental analyses did not show ecological differentiation, though limitations of the analysis prevent strong conclusions. Genetic structure within Eastwood manzanita does not correspond to current subspecies circumscriptions, but rather reflects geographic distribution. Our study suggests that subspecies concepts need to be reconsidered in long-lived plant species, especially in the age of next-generation sequencing.

A computational study of burning of vertically oriented leaves with various fuel moisture contents by upward convective heating

Pyrolysis and combustion of a solid fuel representing a vertically oriented leaf of manzanita (Arctostaphylos glandulosa) were computationally investigated. Various fuel moisture content (FMC) values corresponding to four manzanita leaf treatments studied experimentally by others, were considered. The fuel was exposed to an upward stream of hot gases in a computational configuration resembling the experimental setup where leaves were burned. Time evolution of the normalized mass of the leaves was used to validate the simulations against the experimental data. Examining the time history of heat release rate confirmed that increasing FMC delays ignition time. The ignition times in simulations were in good agreement with those determined by empirical correlations for all FMCs. The burnout times were somewhat shorter in simulations than the empirically-determined ones. Simulations showed that thermal, momentum and concentration boundary layers are formed on the leaf faces. The boundary layers played a significant role in heating, and subsequent moisture evaporation and pyrolysis of the leaves. Within the leaves, an evaporation front propagating inward from the edges, was detected. A considerable amount of liquid moisture remained in the leaf after ignition. Accumulation of water and fuel vapor around the leaf, as a consequence of the leaf moisture evaporation and pyrolysis, displaced oxygen, decreasing the oxygen concentration therein. A post ignition time was characterized by a high temperature zone around the leaf. At such times, oxygen consumption by gas phase combustion resulted in a noticeable decrease in oxygen concentration around the leaf. The flaming pattern after ignition was qualitatively in agreement with previously reported experimental observations.

Conservation Genetics of the Endangered Del Mar Manzanita (Arctostaphylos glandulosasubsp.Crassifolia) Based On Rad Sequencing Data

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.

An investigation of pyrolysis and ignition of moist leaf-like fuel subject to convective heating

The burning of a thin rectangular-shape moist fuel element, representing a living leaf subject to convective heating, was investigated computationally. The setup resembled a previous bench-scale experimental setup (Pickett et al., Int. J. Wildland Fire19, 2010, 153-162), where a freshly harvested horizontally oriented manzanita (Arctostaphylos glandulosa) leaf was held over a flat flame burner and burned by its convective heating. Computations were performed by FDS coupled with an improved version of Gpyro3D. This improvement was concerned with the calculation of the mean porosities in the computational cells to account for the net volume reduction that the condense phase experiences within the computational cells during moisture evaporation and pyrolysis. The dry mass was assumed to consist of cellulose, hemicellulose and lignin undergoing the pyrolysis reactions proposed by Miller and Bellan (Combust. Sci. Technol.126, 1997, 97-137) for biomass. The reaction scheme was initially validated against published experimental and computational TGA results. Then, the burning of leaf-like fuels with three initial fuel moisture contents (40%, 76%, 120%), selected as per the range of experimentally measured values, was modeled. The time evolutions of the normalized mass were good for the modeled fuels with 76% and 120% FMCs and fair for the one with a 40% FMC, as compared to the experimental burning results of four manzanita leaves with unspecified FMCs. The computed ignition time was also in good agreement with the measurement. The computed burnout time was somewhat shorter than the measurement. Modeling revealed the formation of unsteady flow structures, including vortices and regions with high strain rates, near the fuel that acted as a bluff body against the stream of the burner exit. These structures played a significant role in the spatial distribution of gas phase temperature and species around the fuel, which in turn, had an impact on the ignition location. Fuel moisture content primarily affected the temperature response of the fuel and solid phase decomposition.

A numerical investigation of the influence of radiation and moisture content on pyrolysis and ignition of a leaf-like fuel element

The effects of thermal radiation and moisture content on the pyrolysis and gas-phase ignition of a solid fuel element containing high moisture content were investigated using the coupled Gpyro3D/FDS models. The solid fuel has dimensions of a typical Arctostaphylos glandulosa leaf which is modeled as thin cellulose subjected to radiative heating on one side. We incorporated a five-step extended Broido-Shafizadeh reaction model for thermal degradation, moisture evaporation, and pyrolysis of cellulose in Gpyro3D. The solid-phase model was successfully validated against published data. Ignition of the modeled leaf-like fuel element at three initial moisture contents (5%, 40%, or 80%) exposed to a 1500 K radiant source was simulated. Lower moisture content resulted in earlier onset of pyrolysis and ignition resulting in higher solid and gas phase temperatures. Local moisture evaporation and temperature rise were observed in all three cases and a significant amount of moisture remained in the sample during ignition. The numerical results suggested that moisture content not only affected the process of pyrolysis, but also influenced the ignition and gas phase combustion of the solid fuel.

Differences in Burning Behavior of Live and Dead Leaves, Part 1: Measurements

Burning behaviors of individual live and dead leaves were measured in a well-instrumented, well-controlled flat-flame burner. Manzanita (Arctostaphylos glandulosa) branches were harvested from the Chaparral near Riverside, California. Leaves were conditioned to several moisture contents. Two “live” (i.e., not fully dried) groups remained above the fiber saturation point at 34% moisture content (MC; dry basis) and 63% MC. Two “dead” groups were dried to about 4% MC, and one was rehydrated back up to 26% MC. Distinct plateaus in surface temperatures at 175°C were observed while burning live leaves, but dead leaves showed weaker plateaus, if any. Evidence of high internal leaf pressures during burning of live leaves was seen in flame patterns. Moisture was retained in live and dead leaves with local surface temperatures in the 160°C to 220°C range. This article describes the measured results, while a second article describes mass release modeling for the same data set.

Regeneration in Manzanita

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

Seasonal dynamics of nutritional quality of California chaparral species

This study determined the seasonal dynamics in the chemical composition and in vitro digestion properties in leaf and stem of 11 chaparral species collected monthly during fall, spring, and summer at two sites in California, USA: (i) Hopland ( Adenostoma fasciculatum, Arctostaphylos canescens, Arctostaphylos glandulosa, Arctostaphylos stanfordiana, Quercus durata, Ceanothus cuneatus, Eriodyction californicum, and Baccharis pilularis) and (ii) Sierra ( Quercus wislizenii, Quercus douglasii, Ceanothus cuneatus, and Heteromeles arbutifolia). Among the browse species studied, stems of A. canescens collected in fall showed the lowest concentration of crude protein (CP), while C. cuneatus (in both sites) and B. pilularis leaves in spring showed the highest. Neutral detergent fibre (aNDF) and acid detergent fibre (ADF) contents were lowest in spring for leaves of E. californicum and C. cuneatus, respectively and highest for fall stems of C. cuneatus (Sierra). All species contained condensed tannins (CT) except B. pilularis and E. californicum. Soluble CT concentration was lowest in fall leaves of A. fasciculatum and highest in leaves and stems of A. canescens throughout the seasons. Condensed tannins from C. cuneatus (Sierra and Hopland) had the lowest ability to precipitate protein (avg = 0.02 mg BSA/mg SCT), whereas Quercus spp. had the greatest (avg = 0.16 mg BSA/mg SCT). In vitro fermentation study using bovine rumen fluid revealed that leaves of E. californicum in spring and stems of A. fasciculatum in fall had the highest and lowest values of in vitro organic matter digestibility (IVOMD), metabolizable energy (ME), and gas production, respectively. Fermentation rate ( γ) varied from 0.03 to 0.096 ml/h in leaves and from 0.03 to 0.09 ml/h in stems. Compared to the leaves, stems of all species had the lowest concentration of CP, IVOMD, ME and the highest concentration of fibre aNDF and ADF. Among all chemical compounds and fermentation parameters examined, only CP content from most species showed a clear tendency to decline from spring to fall. Linear regression showed that aNDF and ADF contents, as well as CT reactivity are the main constraints for the gas production of chaparral browse plants by ruminants. All these data suggest that predominant California chaparral species do not represent a high quality feeding source for ruminants used to reduce fuel load in chaparral. However, plant's nutrient content and digestibility attributes serve as a guide to the feeding value of forage species, but they are not sufficient to determine its degree of utilization by ruminants. Accurate assessment of the feeding value of these browse species requires measurement of animal response to free choice selection studies.

Species-mediated soil moisture availability and patchy establishment of Pseudotsuga menziesii in chaparral.

The occurrence of mature individuals of Pseudotsuga menziesii in stands of Arctostaphylos species mark the initial stages of mixed evergreen forest invasion into chaparral in central coastal California. We planted two cohorts of P. menziesii seeds at three sites under stands of two Arctostaphylos species and Adenostoma fasciculatum in order to determine whether first-year seedling emergence and survival, particularly during the regular summer drought, underlie the spatial distribution of mature trees observed in chaparral. Regardless of the chaparral species they were planted under, P. menziesii seeds that were not protected from vertebrate predation displayed very little emergence and no survival. In contrast, emergence of P. menziesii that were protected from vertebrate predators was much higher but still did not significantly differ among the three chaparral species. However, survival of protected seedlings under Arctostaphylos glandulosa was much greater than under A. fasciculatum, with intermediate survival under Arctostaphylos montana. While mortality of protected seedlings due to insect herbivory, fungal infection, and disturbance displayed no consistent patterns, summer drought mortality appeared to drive the patterns of survival of P. menziesii under the different chaparral species. These emergence, mortality, and survival data suggest that spatial patterns of P. menziesii recruitment in chaparral are driven by first-year summer drought seedling mortality, but only in years when seeds and seedlings are released from vertebrate predation pressure. Because the first-year drought mortality and survival patterns of P. menziesii seedlings differed strongly depending on the chaparral species, we examined the additional hypothesis that these patterns are associated with differences in the availability of soil moisture under different chaparral species. Both higher survival and lower drought mortality of P. menziesii seedlings were associated with higher soil water potential under Arctostaphylos stands during the summer drought, especially in the subsurface soil. The data suggest that Arctostaphylos stands, particularly stands of A. glandulosa, ameliorate xeric summer conditions to a degree that facilitates first-year establishment of P. menziesii and strongly influences spatial distribution of mature trees.

Root distribution and seasonal water status in weathered granitic bedrock under chaparral

Soils in mountainous terrain are often thin and unable to store sufficient water to support existing vegetation through dry seasons. This observation has led to speculation about the role of bedrock in supporting plant growth in natural ecosystems, since weathered bedrocks often have appreciable porosity and, like soil, can store and transmit water. This study, within a chaparral ecosystem in southern California, was designed to determine the extent of rooting within weathered granitic bedrock and to measure the relative contributions of soil and weathered bedrock to water-use by chaparral shrubs ( Adenostorna fasciculatum Hook and Am., Arctostaphylos glandulosa Eastw., and Ceanothus greggii A. Gray). The rooting pattern was mapped from the wall of a trench excavated into the weathered bedrock. Water contents of soil-weathered bedrock profiles were measured at one to four week intervals for two years using a neutron probe. Chaparral roots penetrate deeply (≥ 4 m) into the weathered bedrock and are largely confined to joint traces. During summer dry seasons, the shrubs extracted 39.4 cm of water from a 2.9-m-thick zone of weathered bedrock — accessing nearly ten times as much water as from the 0.35-m-thick soil (Typic Xerorthents). Although it is commonly neglected in ecological inventories and analyses, weathered bedrock can be an essential ecosystem component, particularly where soils are thin and seasonal drought occurs.

Burning California Chaparral - an Exploratory Study of Some Common Shrubs and Their Combustion Characteristics.

Prescribed fire is a tool used to manage vegetation in southern California. The nature and quan tity of gaseous and particulate emissions have not been described for California chaparral. A study examining carbon monoxide (CO), carbon dioxide (CO2), and par ticulate matter emissions from fuel beds constructed from common chaparral shrubs was initiated. Chamise (Adenostoma fasciculatum), ceanothus (Ceanothus crassifolius), manzanita (Arctostaphylos glandulosa), and scrub oak (Quercus dumosa) fuel beds were burned in December 1989, and March, May, and August, 1990. Gas and particulate matter samples were collected from 45 fires. Emission factors for CO2 and particulate matter were affected by species and month individually; month and species interacted and affected CO emission factors. Pearson's correlation coefficient and Kendall's tau indi cated that emission factors for CO and particulate matter were inversely related to combustion efficiency.

Seasonal changes in tissue elasticity in chaparral shrubs

An important physiological feature of chaparral shrubs is the development of low water potentials during periods of drought characteristic of southern Californian summers. Changes in tissue elasticity may be an important characteristic allowing these low water potentials to be reached and maintained without the development of detrimental water deficits. To examine this possibility, seasonal changes in tissue elasticity were measured in 3 species of chaparral shrubs, Arctostaphylos glandulosa Eastw., Quercus dumosa Nutt. and Ceanothus greggii Gray., by the pressure‐volume method. Tissue elasticity was characterized using graphs of the modulus of elasticity plotted as a function of turgor pressure, and maximum values of the elastic modulus. The moduli of elasticity of the shrubs increased following leaf emergence in the spring, were highest during periods of low soil water potential, and tended to decrease following the summer‐fall drought period. Increases in tissue elasticity facilitate water uptake from drying soils, but result in greater turgor loss during tissue dehydration.

Seasonal and Diurnal Water Relations Adjustments in Three Evergreen Chaparral Shrubs

Pressure—volume curves were measured in three co—occurring chaparral shrubs, Arctostaphylos glandulosa, Quercus dumosa, and Ceanothus greggii, during a seasonal drought cycle. The pressure—volume approach was used to quantify diurnal and seasonal changes in plant water relations. Field measurements of plant water potentials and microclimate were also made to relate the pressure—volume results to the field setting. The seasonal trend was toward increasingly negative osmotic potentials with little (Q. dumosa) or no (A. glandulosa and C. greggii) recovery following the end of the drought. Shifts in the turgor loss point occurred both seasonally and diurnally. The largest diurnal shifts occurred during periods of maximum air temperature and minimum soil water potential. Concurrent field measurements of water potential indicate that these shifts were necessary for preventing turgor loss during periods of midday water stress in Q. dumosa and C,. greggii. The shrubs differed in their mode of seasonal osmotic adjustment. Ceanothus greggii accomplished changes in osmotic potential by variation in the osmotic water volume; the other two shrubs appeared to accomplish such changes largely by solute variation while maintaining relatively constant osmotic water volumes.

Seasonal changes in composition and intake of chaparral by Spanish goats

Seasonal changes in utilization of one-year regrowth of chaparral vegetation by Spanish goats were investigated. The dominant shrub species were: oak ( Quercus dumosa and Q. wislizenii), chamise ( Adenostoma fasciculatum), manzanita ( Arctostaphylos glandulosa) and ceanothus ( Ceanothus cuneatus, and C. foliosus). Oesophageal and faecal samples were obtained during the spring, summer and autumn seasons of 1979. Mean daily temperatures for the three seasons were 19, 18 and 12° C, respectively. Winter sampling was restricted by cold weather at the 985-m elevation site. Cover was measured from ten permanent transects. Preference of Spanish goats was highly directed towards oak (> 50%) and chamise (> 30%) in all seasons. Correlation of selectivity (percentage botanical composition in the diet) and availability data indicated that goats may be generalist in their feeding strategies, but display some sort of specialized behaviour in selecting between the most dominant species. The observation that selection of herbaceous vegetation was restricted by availability conforms with the recent classification of goats as adaptive mixed feeders rather than browsers. Daily feed intake (g DM/kg BW 0.75) was calculated by dividing faecal residue by (100—digestibility in vitro). Intake values were equivalent to maintenance requirements during spring (60 g) and summer (57 g). However, autumn chaparral provided sub-maintenance intake levels (36 g). Condensed tannins (ADF—NAD), estimated as the difference between acid detergent fibre (ADF) and sequential acid detergent residue of neutral detergent residue (NAD), were variable in the clipped shrub samples but low in all dietary samples (2.1 ± 1.8%). The low levels of tannins did not appear to be affecting utilization of this browse. Predictive equations for intake (DMI) and digestibility in vitro (IVOMD) were derived from step-wise regression analysis using the following independent variables: cell wall content (CWC), NAD, cellulose (NADC), NAD sulphuric acid insoluble lignin (NADL s), hemicellulose (NADHC), lignin: ADF—NAD tannins, ash and nitrogen (N) The equation for intake was: DMI (g DM/kg BW 0.75) = −25.67 + 1.80 OMD ( n = 56, Syx = 17.72, r = 0.59, P < 0.005), while digestibility (%) was predicted as OMD = 56.98 − 0.46 CWC − 0.45 NADL s + 0.65 N + 0.09 DMI ( n = 56, Syx = 2.77, r = 0.88, P < 0.005). It is concluded that recently-burnt chaparral vegetation would provide a maintenance browse for Spanish goats during the spring and summer seasons only.

Post-Fire Regeneration of Southern California Chaparral

Succession of chaparral shrubs was studied for the first 4 years after fire on the four major slope faces at three elevations in southern California. Although total cover fluctuated from year to year, shrub cover increased annually through the third year. There was little or no increase in shrub cover between the third and fourth years. Four years after fire the shrubs covered 55% ground surface at the highest elevation site but only 28% at the lowest elevation site. Shrub cover was similar between slope faces with one exception; at the lowest elevation site shrub cover was twice as great on the north and east-facing slopes as on the south and west-facing slopes. Post-fire recovery of shrubs was by seedlings and/or resprouts. Yucca whipplei was an exception in that it did not resprout once the aboveground parts were killed nor did seedlings establish after fire, however the aboveground parts of many Y. whipplei survived the fire. Species which reproduced entirely by seed did so in the first post-fire year from soil-stored seed with the exception of Ceanothus greggii at the highest elevation site. This species was entirely absent the first year after fire but abundant in the second year. Species producing both resprouts and seedlings varied from site to site in the proportion of resprouts:seedlings. Between 83–100% of the post-fire populations of Cercocarpus betuloides, Arctostaphylos glandulosa, and Xylococcus bicolor were resprouts whereas 12–13% of Ceanothus tomentosus were resprouts. For Adenostoma fasciculatum, resprouts constituted 27–54% of the population at the lowest elevation and 65–94% at the highest elevation; whereas, the Quercus dumosa population was 100% resprouts at the lowest elevation and 31–67% resprouts at the highest elevation. Data are presented on the height of resprouts and seedlings for all species at the end of the first post-fire year.

POST‐FIRE REGENERATION OF SOUTHERN CALIFORNIA CHAPARRAL

Succession of chaparral shrubs was studied for the first 4 years after fire on the four major slope faces at three elevations in southern California. Although total cover fluctuated from year to year, shrub cover increased annually through the third year. There was little or no increase in shrub cover between the third and fourth years. Four years after fire the shrubs covered 55% ground surface at the highest elevation site but only 28% at the lowest elevation site. Shrub cover was similar between slope faces with one exception; at the lowest elevation site shrub cover was twice as great on the north and east‐facing slopes as on the south and west‐facing slopes. Post‐fire recovery of shrubs was by seedlings and/or resprouts. Yucca whipplei was an exception in that it did not resprout once the aboveground parts were killed nor did seedlings establish after fire, however the aboveground parts of many Y. whipplei survived the fire. Species which reproduced entirely by seed did so in the first post‐fire year from soil‐stored seed with the exception of Ceanothus greggii at the highest elevation site. This species was entirely absent the first year after fire but abundant in the second year. Species producing both resprouts and seedlings varied from site to site in the proportion of resprouts:seedlings. Between 83–100% of the post‐fire populations of Cercocarpus betuloides, Arctostaphylos glandulosa, and Xylococcus bicolor were resprouts whereas 12–13% of Ceanothus tomentosus were resprouts. For Adenostoma fasciculatum, resprouts constituted 27–54% of the population at the lowest elevation and 65–94% at the highest elevation; whereas, the Quercus dumosa population was 100% resprouts at the lowest elevation and 31–67% resprouts at the highest elevation. Data are presented on the height of resprouts and seedlings for all species at the end of the first post‐fire year.

Summer Diet of Spanish Goats Grazing Chaparral

Summer Diet of Spanish Goats Grazing Chaparral

Fire and Manzanita Chaparral in the San Jacinto Mountains, California

Arctostaphylos glandulosa chaparral at 1,019 m (4,000 ft) elevation retained the same vegetational dominants after burning by producing root crown sprouts and/or seedlings. The floristic composition was changed by the appearance of annual species not found in the unburned chaparral. Most, if not all, of these herbs are considered to have arisen from seeds stored in the litter and or/soils. Post—fire succession is similar to that established for the lower elevational chamise (Adenostoma fasciculatum) chaparral, but is more rapid since the temporary herbaceous cover reaches a peak the first year following fire. Post—fire seedling mortality was most evident in Ceanothus spp. Although manzanita and chamise produced prodigious numbers seedlings with burning, these seedlings are suspected of seldom contributing to mature chaparral cover. Shrub distribution patterns and post—fire succession, particularly the appearance of shrub and herbaceous seedlings, may be determined more by the presence or absence of ash and related pH changes than by other factors. Arctostaphylos and Ceanothus seedlings were most numerous on gentle slopes and level sites where a deep ash layer persisted, while Adenostoma seedlings grew on steeper sites where little ash was deposited. Natural fire occurrences are considered to be less frequent than in the lower elevational chamise chaparral and the higher conifer communities, perhaps occurring only once or twice a century.