Geology topics
Publications and source records attributed to C. J. Fotheringham.
The effects of fire on seed germination and plant regeneration are discussed. Among the topics considered are the triggering of opening of serotinous fruits or cones by fire, the breaking of dormancy in seeds in the soil seed bank, the effects of smoke on germination, and the role of fire in initiating seedling recruitment by opening gaps in closed vegetation.
Although many residents of southern California have long recognised that wildfires in the region are an ongoing, constant risk to lives and property, the enormity of the regional fire hazard caught the world’s attention during the southern California firestorms of 2003 (Figure 5.1). Beginning on 21 October, a series of fourteen wildfires broke out across the five-county region under severe Santa Ana winds, and within two weeks, more than 300,000 ha had burned (Keeley et al., 2004). The event was one of the costliest in the state’s history, with more than 3,600 homes damaged or destroyed and twenty-four fatalities. Suppression costs for the 12,000 firefighters have been estimated at US$120 million, and the total response and damage cost has been estimated at more than US$3 billion (COES, 2004). [Excerpt]
The 2007 wildfire season in southern California burned over 1,000,000 ac (∼400,000 ha) and included several megafires. We use the 2007 fires as a case study to draw three major lessons about wildfires and wildfire complexity in southern California. First, the great majority of large fires in southern California occur in the autumn under the influence of Santa Ana windstorms. These fires also cost the most to contain and cause the most damage to life and property, and the October 2007 fires were no exception because thousands of homes were lost and seven people were killed. Being pushed by wind gusts over 100 kph, young fuels presented little barrier to their spread as the 2007 fires reburned considerable portions of the area burned in the historic 2003 fire season. Adding to the size of these fires was the historic 2006‐2007 drought that contributed to high dead fuel loads and long distance spotting. As in 2003, young chaparral stands and fuel treatments were not reliable barriers to fire in October 2007. Second, the Zaca Fire in July and August 2007 showed that other factors besides high winds can sometimes combine to create conditions for large fires in southern California. Spring and summer fires in southern California chaparral are usually easily contained because of higher fuel moisture and the general lack of high winds. However, the Zaca Fire burned in a remote wilderness area of rugged terrain that made access difficult. In addition, because of its remoteness, anthropogenic ignitions have been low and stand age and fuel loads were high. Coupled with this was severe drought that year that generated fuel moisture levels considerably below normal for early summer. A third lesson comes from 2007 conifer forest fires in the southern California mountains. In contrast to lower elevation chaparral, fire suppression has led to major increases in conifer forest fuels that can lead to unnaturally severe fires when ignitions escape control. The Slide and Grass Valley Fires of October 2007 occurred in forests that had been subject to extensive fuel treatment, but fire control was complicated by a patchwork of untreated private properties and mountain homes built of highly flammable materials. In a fashion reminiscent of other recent destructive conifer fires in California, burning homes themselves were a major source of fire spread. These lessons suggest that the most important advances in fire safety in this region are to come from advances in fire prevention, fire preparedness, and land-use planning that includes fire hazard patterns.
In the paper 'NO News', Preston et al. (2004) make a number of erroneous assumptions regarding nitrogen oxide chemistry. These authors also present some very significant misinterpretations of previous research into the effects of various nitrogen oxides on germination of post-fire followers. Methodological differences between the study by Preston et al. (2004) and previous work are also problematic, such as using NO-donors in solution versus the use of direct application of various nitrogen oxides in the gaseous phase. A closer review of these studies, with the proper understanding of nitrogen oxide chemistry, and interpretations of the available literature, would lead to the conclusion that, contrary to the authors' assertions, the Preston et al. (2004) study supports, rather than refutes, earlier findings by Keeley and Fotheringham (1997, 1998a, b, 2000). ?? CAB International 2005.
Wildfires elicit a perceived need for emergency action to stabilize denuded landscapes. Aerial seeding of rapidly growing nonnative grasses is used routinely in an attempt to control postfire erosion, despite limited scientific basis for its effectiveness and with little consideration for its unintended ecological impacts. As fire size and magnitude have increased in recent decades, so has the prevalence and cost of postfire seeding and the potential footprint of its unintended impacts. We see a growing consensus in the research community on two important points: this management practice often is not cost-effective and it appears to create more problems than it solves.
This study uses detailed demographic data to determine the extent to which functional groupings, based on seedling recruitment and resprouting response to fire, capture the dynamics of postfire responses and early successional change in fire-prone ecosystems. Following massive wildfires in southern California, USA, we sampled chaparral and sage scrub vegetation in nested 0.1-ha plots from 90 sites for five postfire years. Prefire density of woody skeletons and cover and density of all postfire species were recorded. Functional types of postfire obligate seeder, facultative seeder, and obligate resprouter are broadly useful but fail to capture much of the dynamics of postfire succession in these shrublands. For the woody flora, stratifying these three regeneration modes by life-form captures important differences. Postfire obligate-seeding shrubs exhibit a single postfire seedling cohort whereas the faster growing suffrutescent species reach reproductive maturity by the second year and produce multiple seedling cohorts. Postfire obligate-resprouting shrubs reach reproductive maturity early but have very limited seedling recruitment in the early postfire years, whereas obligate-resprouting subshrubs flower the first year from resprouts and have seedling recruitment pulses in the second and subsequent postfire years. For the rich herbaceous flora, further subdivisions are needed to capture the range of variation. Herbaceous perennials are nearly all postfire obligate resprouters, and there are important demographic differences during early succession in different growth forms such as geophytes and rhizomatous grasses. Annuals lack resprouting ability and are postfire obligate seeders. Some exhibit extreme life-history specialization and are present only in the immediate postfire year(s). Others are highly specialized on fire but persist during early succession, and still others are opportunistic species widely distributed on open sites but can expand their populations during early succession. ?? 2006 by the Ecological Society of America.
No abstract available.
Plant community diversity, measured as species richness, is typically highest in the early post-fire years in California shrublands. However, this generalization is overly simplistic and the present study demonstrates that diversity is determined by a complex of temporal and spatial effects. Ninety sites distributed across southern California were studied for 5 years after a series of fires. Characteristics of the disturbance event, in this case fire severity, can alter post-fire diversity, both decreasing and increasing diversity, depending on life form. Spatial variability in resource availability is an important factor explaining patterns of diversity, and there is a complex interaction between landscape features and life form. Temporal variability in resource availability affects diversity, and the diversity peak in the immediate post-fire year (or two) appears to be driven by factors different from subsequent diversity peaks. Early post-fire diversity is influenced by life-history specialization, illustrated by species that spend the bulk of their life cycle as a dormant seed bank, which is then triggered to germinate by fire. Resource fluctuations, precipitation in particular, may be associated with subsequent post-fire diversity peaks. These later peaks in diversity comprise a flora that is compositionally different from the immediate post-fire flora, and their presence may be due to mass effects from population expansion of local populations in adjacent burned areas. ?? 2005 Blackwell Publishing Ltd.
Abstract. Question: Do rectangular sample plots record more plant species than square plots as suggested by both empirical and theoretical studies? Location: Grasslands, shrublands and forests in the Mediterranean-climate region of California, USA. Methods: We compared three 0.1-ha sampling designs that differed in the shape and dispersion of 1-m 2 and 100-m 2 nested subplots. We duplicated an earlier study that compared the Whittaker sample design, which had square clustered subplots, with the modified Whittaker design, which had dispersed rectangular subplots. To sort out effects of dispersion from shape we used a third design that overlaid square subplots on the modified Whittaker design. Also, using data from published studies we extracted species richness values for 400-m 2 subplots that were either square or 1:4 rectangles partially overlaid on each other from desert scrub in high and low rainfall years, chaparral, sage scrub, oak savanna and coniferous forests with and without fire. Results: We found that earlier empirical reports of more than 30% greater richness with rectangles were due to the confusion of shape effects with spatial effects, coupled with the use of cumulative number of species as the metric for comparison. Average species richness was not significantly different between square and 1:4 rectangular sample plots at either 1- or 100-m 2 . Pairwise comparisons showed no significant difference between square and rectangular samples in all but one vegetation type, and that one exhibited significantly greater richness with squares. Our three intensive study sites appear to exhibit some level of self-similarity at the scale of 400 m 2 , but, contrary to theoretical expectations, we could not detect plot shape effects on species richness at this scale. Conclusions: At the 0.1-ha scale or lower there is no evidence that plot shape has predictable effects on number of species recorded from sample plots. We hypothesize that for the mediterranean-climate vegetation types studied here, the primary reason that 1:4 rectangles do not sample greater species richness than squares is because species turnover varies along complex environmental gradients that are both parallel and perpendicular to the long axis of rectangular plots. Reports in the literature of much greater species richness recorded for highly elongated rectangular strips than for squares of the same area are not likely to be fair comparisons because of the dramatically different periphery/area ratio, which includes a much greater proportion of species that are using both above and below-ground niche space outside the sample area.
Evergreen chaparral and semideciduous sage scrub shrublands were studied for five years after fires in order to evaluate hypothesized determinants of postfire recovery and succession. Residual species present in the immediate postfire environment dominated early succession. By the fifth year postfire, roughly half of the species were colonizers not present in the first year, but they comprised only 7–14% cover. Successional changes were evaluated in the context of four hypotheses: (1) event-dependent, (2) fire interval, (3) self-regulatory, and (4) environmental filter hypotheses. Characteristics specific to the fire event, for example, fire severity and annual fluctuations in precipitation, were important determinants of patterns of change in cover and density, supporting the “event-dependent” hypothesis. The “fire interval” hypothesis is also supported, primarily through the impact of short intervals on reproductive failure in obligate seeding shrubs and the impact of long intervals on fuel accumulation and resultant fire severity. Successional changes in woody cover were correlated with decreases in herb cover, indicating support for “self-regulatory” effects. Across this landscape there were strong “environmental filter” effects that resulted in complex patterns of postfire recovery and succession between coastal and interior associations of both vegetation types. Of relevance to fire managers is the finding that postfire recovery patterns are substantially slower in the interior sage scrub formations, and thus require different management strategies than coastal formations. Also, in sage scrub (but not chaparral), prefire stand age is positively correlated with fire severity, and negatively correlated with postfire cover. Differential responses to fire severity suggest that landscapes with combinations of high and low severity may lead to enhanced biodiversity. Predicting postfire management needs is complicated by the fact that vegetation recovery is significantly controlled by patterns of precipitation.
Over 75 species of alien plants were recorded during the first five years after fire in southern California shrublands, most of which were European annuals. Both cover and richness of aliens varied between years and plant association. Alien cover was lowest in the first postfire year in all plant associations and remained low during succession in chaparral but increased in sage scrub. Alien cover and richness were significantly correlated with year (time since disturbance) and with precipitation in both coastal and interior sage scrub associations. Hypothesized factors determining alien dominance were tested with structural equation modeling. Models that included nitrogen deposition and distance from the coast were not significant, but with those variables removed we obtained a significant model that gave an R 2 = 0.60 for the response variable of fifth year alien dominance. Factors directly affecting alien dominance were (1) woody canopy closure and (2) alien seed banks. Significant indirect effects were (3) fire intensity, (4) fire history, (5) prefire stand structure, (6) aridity, and (7) community type. According to this model the most critical factor influencing aliens is the rapid return of the shrub and subshrub canopy. Thus, in these communities a single functional type (woody plants) appears to the most critical element controlling alien invasion and persistence. Fire history is an important indirect factor because it affects both prefire stand structure and postfire alien seed banks. Despite being fire-prone ecosystems, these shrublands are not adapted to fire per se, but rather to a particular fire regime. Alterations in the fire regime produce a very different selective environment, and high fire frequency changes the selective regime to favor aliens. This study does not support the widely held belief that prescription burning is a viable management practice for controlling alien species on semiarid landscapes.
The Southern California fires of late Oct. 2003 burned 742,000 ac and destroyed 3,361 homes and 26 lives. Factors leading up to this event were very different between forests, which comprised about 5% of the area burned, and shrublands. Three lessons are (1) although these fires were massive, they were not unprecedented, and future fires of this magnitude are to be expected; (2) the current fire management policy is not effective at preventing these massive fires; and (3) future developments need to plan for these natural fire events much the same way we currently incorporate engineering solutions to earthquakes and other natural catastrophes.
No abstract available at this time
Aim To determine the best-fit model of species–area relationships for Mediterranean-type plant communities and evaluate how community structure affects these species–area models. Location Data were collected from California shrublands and woodlands and compared with literature reports for other Mediterranean-climate regions. Methods The number of species was recorded from 1, 100 and 1000 m 2 nested plots. Best fit to the power model or exponential model was determined by comparing adjusted r 2 values from the least squares regression, pattern of residuals, homoscedasticity across scales, and semi-log slopes at 1–100 m 2 and 100–1000 m 2 . Dominance–diversity curves were tested for fit to the lognormal model, MacArthur's broken stick model, and the geometric and harmonic series. Results Early successional Western Australia and California shrublands represented the extremes and provide an interesting contrast as the exponential model was the best fit for the former, and the power model for the latter, despite similar total species richness. We hypothesize that structural differences in these communities account for the different species–area curves and are tied to patterns of dominance, equitability and life form distribution. Dominance–diversity relationships for Western Australian heathlands exhibited a close fit to MacArthur's broken stick model, indicating more equitable distribution of species. In contrast, Californian shrublands, both postfire and mature stands, were best fit by the geometric model indicating strong dominance and many minor subordinate species. These regions differ in life form distribution, with annuals being a major component of diversity in early successional Californian shrublands although they are largely lacking in mature stands. Both young and old Australian heathlands are dominated by perennials, and annuals are largely absent. Inherent in all of these ecosystems is cyclical disequilibrium caused by periodic fires. The potential for community reassembly is greater in Californian shrublands where only a quarter of the flora resprout, whereas three quarters resprout in Australian heathlands. Other Californian vegetation types sampled include coniferous forests, oak savannas and desert scrub, and demonstrate that different community structures may lead to a similar species–area relationship. Dominance–diversity relationships for coniferous forests closely follow a geometric model whereas associated oak savannas show a close fit to the lognormal model. However, for both communities, species–area curves fit a power model. The primary driver appears to be the presence of annuals. Desert scrub communities illustrate dramatic changes in both species diversity and dominance–diversity relationships in high and low rainfall years, because of the disappearance of annuals in drought years. Main conclusions Species–area curves for immature shrublands in California and the majority of Mediterranean plant communities fit a power function model. Exceptions that fit the exponential model are not because of sampling error or scaling effects, rather structural differences in these communities provide plausible explanations. The exponential species–area model may arise in more than one way. In the highly diverse Australian heathlands it results from a rapid increase in species richness at small scales. In mature California shrublands it results from very depauperate richness at the community scale. In both instances the exponential model is tied to a preponderance of perennials and paucity of annuals. For communities fit by a power model, coefficients z and log c exhibit a number of significant correlations with other diversity parameters, suggesting that they have some predictive value in ecological communities.
Patterns of native and alien plant diversity in response to disturbance were examined along an elevational gradient in blue oak savanna, chaparral, and coniferous forests. Total species richness, alien species richness, and alien cover declined with elevation, at scales from 1 to 1000 m 2 . We found no support for the hypothesis that community diversity inhibits alien invasion. At the 1-m 2 point scale, where we would expect competitive interactions between the largely herbaceous flora to be most intense, alien species richness as well as alien cover increased with increasing native species richness in all communities. This suggests that aliens are limited not by the number of native competitors, but by resources that affect establishment of both natives and aliens. Blue oak savannas were heavily dominated by alien species and consistently had more alien than native species at the 1-m 2 scale. All of these aliens are annuals, and it is widely thought that they have displaced native bunchgrasses. If true, this means that aliens have greatly increased species richness. Alternatively, there is a rich regional flora of native annual forbs that could have dominated these grasslands prior to displacement by alien grasses. On our sites, livestock grazing increased the number of alien species and alien cover only slightly over that of sites free of livestock grazing for more than a century, indicating some level of permanency to this invasion. In chaparral, both diversity and aliens increased markedly several years after fire. Invasive species are rare in undisturbed shrublands, and alien propagules fail to survive the natural crown fires in these ecosystems. Thus, aliens necessarily must colonize after fire and, as a consequence, time since fire is an important determinant of invasive presence. Blue oak savannas are an important propagule source for alien species because they maintain permanent populations of all alien species encountered in postfire chaparral, and because the vegetation mosaic in this region places them in proximity to chaparral. The speed at which alien propagules reach a burned site and the speed at which the shrublands return to their former closed-canopy condition determine alien invasion. Frequent burning of this vegetation alters the balance in favor of alien invasion. In the higher-elevation coniferous forests, species diversity was a function of fire severity and time since fire. High-intensity fires create gaps that decrease canopy coverage and increase light levels and nutrients for an ephemeral successional flora. Few species have persistent seed banks, so the time since fire is an important determinant of colonization success. There was a highly significant interaction between fire severity and time since fire for understory cover, species richness, and alien richness and cover. Understory was sparse in the first year after fire, particularly in low-severity burns, and increased substantially several years after fire, particularly on high-severity burns. Both fire severity and time since fire affected alien species richness and dominance. Coniferous forests had about one-third as many alien species as the foothill oak savannas, and fewer than half of the species were shared between these communities. Unburned coniferous forests were largely free of alien species, whereas some burned sites had a significant alien presence, which presents a challenge for fire restoration of these forests.
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No abstract available at this time