Chaparral Sites Research Articles

Epiphytic macrolichen communities take decades to recover after high‐severity wildfire in chaparral shrublands

AbstractAimFire regimes are shifting globally due to climate change, land management practices and population growth, putting species at risk if they are unable to adapt to more frequent or severe wildfires. While many fire‐adapted species may be able to accommodate some amount of change in fire regimes, fire‐sensitive or late‐successional species that colonize fire‐prone ecosystems between wildfires may be especially vulnerable to more frequent or severe fires. Here, we seek to understand the rate of lichen recolonization after high‐severity fires in an ecosystem that is experiencing increasing fire frequency.LocationThe Inner North Coast Range of California, USA.MethodsUsing a chronosequence of wildfires in a Northern California chaparral shrubland, we compare lichen communities among sites that burned 3, 13, 22, 30 and 65 years previously, as well as old‐growth chaparral sites without a recorded fire over the past century.ResultsWe find that lichen richness increases consistently with time since fire but begins to level off 20–30 years following fire, roughly corresponding to the closure of the shrub canopy. Some taxa and guilds were found only in old‐growth chaparral.ConclusionsOur findings highlight that fire‐intolerant organisms may be relatively slow to recolonize landscapes after high‐severity fire and that the majority of chaparral lichen taxa may be lost where fire intervals shorten to <20 years, which has already occurred in some parts of California.

Mapping plant growth forms using structure-from-motion data combined with spectral image derivatives

ABSTRACTMapping plant growth forms are useful to classify and monitor chaparral shrubland community types in southern California. This study evaluates the utility of plant height information, derived from high spatial resolution aerial images and structure-from-motion photogrammetry, for the purpose of distinguishing tree, shrub and sub-shrub growth forms from herbs and bare ground. Canopy height models (CHMs) were derived for two chaparral sites on Santa Rosa Plateau which contain intermixed growth forms. A multi-criterion, knowledge-based thresholding approach was used to classify growth forms based on spectral data (Normalized Difference Vegetation Index, hue, intensity, and focal texture) alone, CHM data alone, and hybrid combinations of spectral and CHM data. Overall accuracies were 66.0–69.0% from spectral data, 72.0–75.5% from CHM data, and 80.5–82.5% from the hybrid data sets. This study highlights the utility in combining multi-spectral and canopy height data for characterizing Mediterranean-type plant communities and changes therein.

Evaluating uncertainty in Landsat-derived postfire recovery metrics due to terrain, soil, and shrub type variations in southern California

ABSTRACT Temporal trajectories of apparent vegetation abundance based on the multi-decadal Landsat image series provide valuable information on the postfire recovery of chaparral shrublands, which tend to mature within one decade. Signals of change in fractional shrub cover (FSC) extracted from time-sequential Normalized Difference Vegetation Index (NDVI) data can be systematically biased due to spatial variation in shrub type, soil substrate, or illumination differences associated with topography. We evaluate the effects of these variables in Landsat-derived metrics of FSC and postfire recovery, based upon three chaparral sites in southern California which contain shrub community ecotones, complex terrain, and soil variations. Detailed validations of prefire and postfire FSC are based on high spatial resolution ortho-imagery; cross-stratified random sampling is used for variable control. We find that differences in the composition and structure of shrubs (inferred from ortho-imagery) can substantially influence FSC-NDVI relations and impact recovery metrics. Differences in soil type have a moderate effect on the FSC-NDVI relation in one of the study sites, while no substantial effects were observed due to variation of terrain illumination among the study sites. Arithmetic difference recovery metrics – based on NDVI values that were not normalized with unburned control plots – correlate in a moderate but significant manner with a change in FSC (R 2 values range 0.47–0.59 at two sites). Similar regression coefficients resulted from using Landsat visible reflectance data alone. The lowest correlations to FSC resulted from Soil-Adjusted Vegetation Index (SAVI) and are attributed to the effects of the soil-adjustment factor in sparsely vegetated areas. The Normalized Burn Ratio and Normalized Burn Ratio 2 showed a moderate correlation to FSC. This study confirms the utility of Landsat NDVI data for postfire recovery evaluation and implies a need for stratified analysis of postfire recovery in some chaparral landscapes.

Estimates of Habitat Use by Rabbits (Sylvilagus spp.) from Fecal Pellet Counts Varies by Plot Design in Southern California

Studies of rabbits and hares often use fecal pellet counts to estimate population density, create indices of abundance, and monitor habitat use, because fecal pellet counts are more easily deployed and less labor intensive than visual surveys and live trapping. In some habitats, plot size and shape can affect the measured pellet density and the resulting estimates of habitat use by rabbits. We compared rabbit (Sylvilagus spp.) fecal pellet density estimates derived from 0.155-m2 rectangular, 0.155-m2 circular, 1-m2 square, and 1-m2 circular plots in southern California chaparral and coastal sage scrub communities to evaluate habitat use by rabbits. Pellet plots were not an effective sampling design in our chaparral site where rabbit pellet density was low. Our coastal sage scrub site had an abundance of fecal pellets, and pellet density estimates varied by plot design. The 0.155-m2 plots were more easily deployed and counted, however they produced higher estimates of fecal pellet density, exhibited greater variance, and were unable to detect habitat differences in fecal pellet density. The 1-m2 plots required more effort but produced lower pellet density estimates, exhibited less variation, and were both able to detect habitat differences in fecal pellet density. We recommend that researchers conducting rabbit fecal pellet counts in Californian Mediterranean scrub habitats use 1-m2 circular plots for their ease of deployment, counting, and clearing and for their greater detection and precision in estimates of pellet densities.

Biochronological data inferred from the early Pleistocene Arvicolinae (Mammalia, Rodentia) of the El Chaparral site (Sierra del Chaparral, Cádiz, southwestern Spain)

ABSTRACT In this paper are described the arvicolines from El Chaparral site (Villaluenga del Rosario, Cádiz, Southwestern Spain). Due to their wide geographical distributions and rapid evolutionary rates, arvicolines are especially useful for biostratigraphical purposes. The stratigraphic layers of El Chaparral have yielded arvicolines remains of the genera Allophaiomys, Iberomys, Pliomys, and Terricola. The presence of these rodents together the other vertebrates recovered allows to determinate the age of the El Chaparral site and compare our data with other Iberian Pleistocene sites, such as of the Sierra de Atapuerca. El Chaparral site ranges between the Jaramillo Subchron (1.07-0.99 Ma) and shortly after the Brunhes-Matuyama transition at 0.78 Ma covering a important time span for the knowledge of the earliest humans occupations in western Europe.

Post-Fire Soil Water Repellency, Hydrologic Response, and Sediment Yield Compared between Grass-Converted and Chaparral Watersheds

In 2002, the Williams Fire burned >90 % of the San Dimas Experimental Forest, providing an opportunity to investigate differences in soil water repellency, peak discharge, and sediment yield between grass-converted and chaparral watersheds. Post-fire water repellency and moisture content were measured in the winter and summer for four years. Peak discharge was determined using trapezoidal flumes with automated stage-height recorders. Sediment yields were measured by making repeated sag-tape surveys of small debris basins. Other than the high summer 2005 increase in repellency on the grass watersheds, only small differences in repellency were observed between the grass and chaparral sites. In general, soil water repellency increased with depth, decreased with time following the fire, and was inversely related to soil moisture content (i.e., least repellent during the winter and most repellent during the summer). Reduction in repellency occurred at moisture contents ranging between 8 % to 16 %. Approximately 85 % of the sediment delivered to the debris basins occurred during the first year, with first year sediment yields being greatest in the chaparral watersheds. Peak discharge was similar for both the grass and chaparral watersheds and was highest following the record rainfall of the 2005 hydrologic year. However, only minor sedimentation followed the record rain events and was similar in both watershed types, suggesting that percent plant cover was sufficient and that the supply of easily mobilized sediment and ravel was depleted after the first post-fire winter.

The Early Pleistocene paleontological site in the Sierra del Chaparral (Villaluenga del Rosario, Cádiz, Southwestern Spain)

This article outlines the results obtained during the first study of the Chaparral site (Villaluenga del Rosario, Cádiz, Spain) situated in the karst area of the Sierra de Grazalema. The varied macro- and micro-vertebrate fauna include carnivores, herbivores and rodents, as well as reptiles and amphibians, suggesting an Early Pleistocene age. The taphonomic study of the fauna discovered on the site is underway.

Breeding success at the range margin of a desert species: implications for a climate‐induced elevational shift

If the breeding range of a species is limited by biotic or abiotic environmental factors that depress breeding success at the range margin, then range expansion is expected when those limiting factors are alleviated. Over a three‐year period, we measured breeding success of a desert species, black‐throated sparrowAmphispiza bilineata, along a steep elevation gradient between the Peninsular Mountains and Colorado Desert (San Diego County, California) that is undergoing a warming trend. We compared breeding success at geographically marginal locations (higher‐elevation chaparral sites) to more central locations (lower‐elevation desert scrub sites) only a short distance apart. Breeding success was measured at the nest level, territory level, and population level. At each level measured, breeding success tended to be greater at higher‐elevation chaparral sites at the distribution margin compared to lower‐elevation sites where the bird was more common. Black‐throated sparrows had 100% reproductive failure at lower‐elevation sites during the two driest years of our study (2006–2007), but did relatively well at higher‐elevation sites. Only in a wetter year (2008) was breeding success improved at lower‐elevation sites. Surprisingly, there was no evidence of an upward elevational shift in distribution over a 26‐year period despite a clear warming trend and drier conditions. Greater territory density at lower‐elevation sites with reproductive failure during dry years suggests the possibility of an ecological trap in this system, which could prevent or delay climate‐induced range shifts. A common presumption has been that desert species will undergo relatively mild negative impacts due to a warming climate, but it is possible that some desert species are already at or near their temperature and aridity tolerance limits within their current range and shifts may not always be possible.

Plant Community Water Use and Invasibility of Semi-Arid Shrublands by Woody Species in Southern California

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 characteristics. Of the three communities, the coastal sage community may be particularly susceptible to invasion by woody shrub species because its soil moisture content would allow for germination and persistence of a wider range of potential invaders. Current differences among sites in numbers of non-native woody species are consistent with predicted differences in susceptibility to non-native species based on community water use and dry seasonal soil moisture.

Post-Fire Burn Severity and Vegetation Response Following Eight Large Wildfires Across the Western United States

Vegetation response and burn severity were examined following eight large wildfires that burned in 2003 and 2004: two wildfires in California chaparral, two each in dry and moist mixed-conifer forests in Montana, and two in boreal forests in interior Alaska. Our research objectives were: 1) to characterize one year post-fire vegetation recovery relative to initial fire effects on the soil surface that could potentially serve as indicators of vegetation response (and thus, ultimately longer-term post-fire ecosystem recovery), and 2) to use a remotely-sensed indicator of burn severity to describe landscape patterns in fire effects. We correlated one-year post-fire plant species richness and percent canopy cover to burn severity and to soil surface cover immediately after the fires. For all eight wildfires, plant canopy cover and species richness were low and highly variable one year post-fire. We found a greater number of forbs when compared to other plant life forms, independent of burn severity. Plant cover was dominated by grasses in chaparral systems, by forbs in mixed-conifer forests, and by shrubs in boreal forests, similar to the unburned vegetation. Fine-scale variability in post-fire effects on soils, the diversity of pre-fire vegetation, and the resilience of plants to fire likely explain the high variation observed in post-fire vegetation responses across sites and burn severities. On most low and moderate burn severity sites, >30% of the soil surface was covered with organic material immediately post-fire, and one year later, the canopy cover of understory vegetation averaged 10% or more, suggesting low risk to post-fire erosion. In California chaparral and the two Montana mixed conifer sites, 5% or less of the area within the fire perimeter burned with high severity, while in Alaska, 58% was mapped as high burn severity; we think this is characteristic in Alaska, but uncharacteristic of chaparral fires, especially given the high proportion of non-native species post-fire in our chaparral sites. All fires had a mosaic of different burn severities (as indicated by delta Normalized Burn Ratio, dNBR) with highly variable patch size (mean 1.3 ha to 14.4 ha, range from <1 ha to over 100,000 ha).

Reproduction and growth of the chaparral geophyte, Zigadenus fremontii (Liliaceae), in relation to fire

Zigadenusfremontii is often a striking component of the flora following firein the chaparral. Like other geophytes, it produces large numbers of flowers inthe first spring after a burn. Although these plants are most conspicuous intheearly postfire environment, the question that remains is, how do they persistinthe interval between fires? To address this we investigated differences in thegrowth and reproduction of Z. fremontii in burned andunburned chaparral. We monitored marked individuals for nine years at threesites: two that were burned in 1990 and one in the same area that was inunburned mature chaparral. We measured leaf area, and production of flowers andfruits. We also conducted seed experiments in the field to determine the ratesand timing of germination. We found that reproduction occurs only in theimmediate postfireperiod: flowering and production of fruits and seeds in the first yearfollowingfire, and seedling establishment by year 3. There was a cost of reproduction;plants that flowered (in the burn area) had negative growth rates the followingyear. In contrast, plants in unburned chaparral, which did not flower, hadpositive growth rates over the same period. Moreover, plants that produced themost flowers had the lowest growth rates. In the unburned chaparral site,plantswere not dormant as predicted from previous literature; instead they producedleaves nearly every year. In most years the average leaf area per plant wasgreater than that in the burned sites. Our results indicate that postfirereproduction depends on growth and carbohydrate storage in the inter-fireperiod. We also suggest that this species is relatively long-lived for aherbaceous perennial.

A comparison of ant assemblages (Hymenoptera, Formicidae) on serpentine and non-serpentine soils in northern California

Summary In northern California, ant assemblages in 8 sites in serpentine chaparral habitat were compared with those occurring in 8 chaparral sites on adjacent non-serpentine soils. A total of 27 species of ants was found: 22 species were collected in non-serpentine chaparral and 20 species in serpentine chaparral. Seven species were collected exclusively in non-serpentine, and 5 species were found only in serpentine habitats. A Formica species, conspecific with or closely related to F. xerophila, was found only in serpentine chaparral. Subsequent collections suggest that in northern California, this species is confined to serpentine outcrops. Two other species significantly differed in frequency of occurrence in each habit: Camponotus hyatti, C. cf. vicinus. Five species showed marginal significant differences in their relative abundance between habitats: Camponotus hyatti, C. cf. vicinus, Formica moki, Prenolepis imparis, Leptothorax nevadensis, Stenamma diecki.

Soil properties and nutrient relations in burned and unburned Mediterranean-climate shrublands of Baja California, Mexico

We compared soil chemical properties and total N and P in ecosystem compartments (soil, litter, root, stem, and leaf) of adjacent burned and unburned shrublands in northwestern Baja California during the first annual cycle after burning. We sampled one stand of coastal sage scrub growing on soil derived from basalt, and two stands of mixed chaparral growing on soils developed from granitic rocks. In the coastal sage scrub site, total soil N (1350–2140 mg/kg) and P (360–540 mg/kg) were similar to concentrations reported for Mediterranean-climate shrublands growing in fertile soils of Alta California (USA), Chile and the Mediterranean Basin. But at the chaparral sites, total soil N (750–1180 mg/kg) and P (90–150 mg/kg) were as low as those of the relatively infertile Australian heath. There was no significant reduction in organic C, nor increase in pH or salinity, in the burned areas. Only inorganic N was slightly, but significantly, higher in the soil of all three burned areas. No significant differences were found in total N or P between burned and unburned ecosystem compartments across the three sites when the entire annual cycle was considered. But N was significantly higher in leaves and stems of burned areas, although only briefly during the middle of the first growing season after fire. Nutrient enrichment following wildland fire was thus less pronounced and more transitory than is typically reported for burned shrublands in Alta California. Fire suppression has not been effective in Baja California, and fuel loads and fire intensities tend to be lower than in Alta California. Lower fuel loads and fire intensities, and consequently lower ash deposition, may partly explain the lack of marked differences in soil properties found between burned and unburned areas.

Flowers and their insect visitors in the arid winter rainfall region of southern Africa: Observations on permanent plots. Composition of the anthophilous insect fauna

The composition of the anthophilous insect fauna of a plant community in the north-western Cape, South Africa, has been investigated. During a 3-year survey more than 300 species belonging to four orders and 41 families have been identified as day-active floral visitors. The vast majority are solitary bees (136 spp.), but masarine wasps (14 spp.), bombyliid flies (53 spp.), and monkey beetles (20 spp.) are also well represented. The anthophilous insect fauna of Goegab appears to be far more diverse than those of desert scrub communities in California and Chile, but equally diverse as that of a Californian Chaparral site. Compared to the latter, Goegab seems to be particularly rich in bee flies, Masarinae and possibly Eumenidae, but poorer in bees and butterflies.

Demographic structure of California chaparral in the long‐term absence of fire

Abstract. Demographic structure of 12 chaparral sites unburned for 56 to 120 years was investigated. All sites were dominated by vigorous shrub populations and, although there was colonization by seedlings of woodland tree species in several stands, successional replacement of chaparral was not imminent. Although successional changes in community composition were evident, there was no indication of a decline in species diversity. Non‐sprouting species of Ceanothus suffered the greatest mortality at most, but not all, sites. Sprouting shrubs, such as Quercus and Heteromeles had very little mortality, even in stands more than a century old. All postfire resprouting species had multiple stems of different ages indicating these shrubs were capable of continuously regenerating their canopy from basal sprouts. Ceanothus populations were highly clumped and there was a significant correlation across all sites between variance/mean ratio and percentage mortality. As Ceanothus populations thinned, they became less clumped. In mixed chaparral stands, Quercus and Heteromeles were significantly taller than associated Ceanothus shrubs and overtopped the Ceanothus; at two sites, the density of live Quercus per plot was correlated with the density of dead Ceanothus. Thus, mortality of Ceanothus stems is likely related to both intra and interspecific interations.Seedling recruitment was observed for most shrub species that regenerate after fire by resprouting; seedling and sapling densities ranging from 1000–36 500 ha‐1 were recorded for Quercus dumosa, Rhamnus crocea, Prunus ilicifolia, Heteromeles arbutifolia and Cercocarpus betuloides. For all but the last species, seedlings and saplings were most abundant beneath the canopy cover and not in gaps. Across all sites, recruitment was significantly correlated with depth and bio‐mass of the litter layer. Cercocarpus betuloides was present in several stands, but seedling establishment was found only in one very open, disturbed stand. Regardless of stand age, taxa such as Adenostoma, Arctostaphylos and Ceanothus, which recruit seedlings after fire, had no significant seedling production.

Role of Allelopathy, Heat and Charred Wood in the Germination of Chaparral Herbs and Suffrutescents

(1) Herbaceous and suffrutescent species are uncommon in mature chaparral but dominate after fire. Colonization is largely from dormant seeds in the soil. This study examined the role of allelopathic inhibitors and fire-related cues in the control of germination of species in the major life-history groups. (2) Herbaceous perennials are often dormant under the chaparral canopy and their presence in burnt areas is due to sprouts from bulbs or rhizomes. Their seeds germinated readily without any treatment and they were not inhibited by leachate from living Adenostoma fasciculatum foliage, but high temperatures were lethal to seeds of many species. (3) Suffrutescents are not present under the chaparral canopy and their presence in burnt areas is due entirely to seed. Their germination was stimulated by heat, or powdered charred wood, or both, although a portion of the seeds of some species germinated without treatment. (4) Opportunistic annuals have polymorphic seeds; a portion germinated readily whereas others germinated only after heat or charred wood treatment. The non-refractory seeds account for colonization into gaps in the canopy and the refractory portion accounts for their abundance immediately after a fire. Whether or not the non-refractory seeds are inhibited by allelopathic leachate from the A denostomafasciculatum canopy is equivocal; leachate did inhibit the germination of two of the twenty-two annual species investigated, but the germination of one-third of the species was stimulated by leachate. (5) Fire-annual species are largely restricted to recently burnt chaparral sites and the seeds of these species remain dormant in the soil between fires. There is little germination without cues relating to fire. Some species responded to heat but the highest germination was with the charred wood or heat plus charred wood treatments.

Leaf conductance and transpiration, and water relations of evergreen and deciduous perennials co-occurring in a moist chaparral site

Leaf conductance and transpiration, and water relations of evergreen and deciduous perennials co-occurring in a moist chaparral site

Leaf conductance and transpiration, and water relations of evergreen and deciduous perennials co‐occurring in a moist chaparral site

Abstract. Diurnal courses of leaf conductance, water potential and environmental parameters were measured through the year. The seasonal decreases in plant water potentials were greatest in evergreen H. arbutifolia, intermediate in winter deciduous C. occidentalis and least in drought deciduous A. californica. The seasonal patterns of water use were very similar. Estimates of soil root‐stem conductances to liquid water flux indicate that during the spring, conductances are high, that during the early summer there is a daily shift from high morning conductances to lower afternoon conductances, and that late summer conductances are low.

Nutrient gain from wet and dry atmospheric deposition and rainfall acidity in southern California chaparral.

Ionic concentration and annual deposition of NO -3 -N, NH +4 -N, Ca2+, and Mg2+ from bulk precipitation and dry atmospheric deposition were studied for one year in southern California. Data were collected from an inland chaparral site at 1,300 m elevation, 75 km from the coast. The annual depositions of NO -3 -N and NH +4 -N amounted to 96.3 and 56.0 mg m-2 ground area yr-1, respectively. The corresponding values for calcium and magnesium ions were 207.4 and 57.4 mg m-2 yr-1. The average pH of rainwater was 3.74 (range 3.37 to 4.75), thus documenting acid rain for an inland site in California, distant from urban sources of air contamination. An estimate of nitrogen gains and losses indicated that the time between recurrent chaparral fires should be about 60 years in order to maintain a balanced nitrogen budget.

Effects of Grazing on Lizard Abundance and Diversity in Western Arizona

Effects of Grazing on Lizard Abundance and Diversity in Western Arizona