Wildfire induced changes in aquatic invertebrate communities and mercury bioaccumulation in the Okefenokee Swamp

Fire is an important natural disturbance in the Okefenokee Swamp. From April–June 2007, wildfire burned 75% of the wetland area. With the existence of extensive pre-fire data sets on community structure and total mercury of invertebrates, the fire presented an opportunity to assess impacts of wildfire on invertebrates. Post-fire collection of samples occurred in September, December, and May, 2007–2009. Sample sites included 13 burned and 8 non-burned (reference) sites. Comparisons of data among pre-fire, post-fire reference, and post-fire burned sites revealed that the major difference between pre-fire communities and post-fire communities was a decrease in the number of water mites. We also found a decrease in mercury concentrations in amphipods, odonates, and crayfish post-fire. The differences between pre-fire and post-fire samples may be confounded by drought conditions during the baseline study. NMDS ordinations and ANOSIM tests suggested that habitat was an important factor; communities in burned cypress differed from reference cypress. Unexpectedly, burned sites had lower mercury concentrations in odonates and crayfish, with variation again being greatest in cypress stands. These findings and others suggest mercury levels do not follow a predictable pattern but can vary with pre-fire concentrations, variation in water levels, and burn intensity. We found that wildfire in the Okefenokee had little impact on invertebrates in prairies and scrub-shrub thickets, but can affect indicator organisms (Oecetis, Ischnura, and Sigara) in cypress stands. Our study suggests that vegetation type and burn intensity may have impacts on the invertebrate communities and mercury concentrations of organisms.     

Fire intensity and herbivory effects on postfire resprouting of Adenostoma fasciculatum in southern California chaparral

Summary Resprouting is the main regeneration mechanism after fire in Mediterranean-type ecosystems. Herbivores play an important role in controlling postfire seedling establishment, but their influence on regeneration by resprouting is less well known. To study the effects of fire intensity on resprouting of Adenostoma fasciculatum in southern California chaparral, and its interaction with herbivory, we conducted an experimental burn at three levels of fire intensity. We found that increasing fire intensity increased plant mortality, reduced the number of resprouts per plant, and delayed the time of resprouting. Herbivory increased with fire intensity, and was related to the time of resprouting. Plants resprouting later in the season and out of synchrony with the main flush were attacked more readily by herbivores. Post-resprouting mortality also increased with fire intensity and was significantly associated with herbivory in the higher fire intensity plots. Fire intensity effects on chaparral regeneration by resprouting may be farreaching through effects on the population structure, resprout production, and growth of Adenostoma fasciculatum.     

Effects of heterogeneity of pre-fire forests and vegetation burn severity on short-term post-fire vegetation density and regeneration in Samcheok,Korea

This study investigated the combined effects of heterogeneity of pre-fire forest cover and vegetation burn severity on post-fire vegetation density and regeneration at an early stage in Samcheok, Korea. To measure the spatial heterogeneity of pre-fire forests, spatial pattern metrics at a landscape level and class level were adopted, and a regression tree analysis for post-fire vegetation density and regeneration was used to avoid spatial autocorrelation. Two regression tree models were estimated for post-fire vegetation density and post-fire vegetation regeneration with the same independent variable sets, including heterogeneity of pre-fire forest cover and vegetation burn severity. The estimated model suggested that the percentage of Japanese red pine and burn severity were the most significant variables for post-fire vegetation density and regeneration, respectively. The compositional and spatial heterogeneity of pre-fire forest and burn severity, as well as the degree of burn severity, was found to have significant impacts on post-fire vegetation density and regeneration. Overall, more rapid vegetation regeneration can be expected in more severely burned areas. However, this rapid vegetation regeneration at an early stage is due mostly to perennials and shrubs, not to the sprouting or regrowth of trees. The study results strongly indicated that a susceptible forest cover type and its spatial patterns directly influence the heterogeneity of burn severity and early vegetation density and regeneration. Hence, the management of susceptible forest cover types is particularly critical for establishing more fire-resilient forests and for post-fire forest restoration.     

Retention of Nitrogen Following Wildfire in a Chaparral Ecosystem

Wildfires alter nitrogen (N) cycling in Mediterranean-type ecosystems, resetting plant and soil microbial growth, combusting plant biomass to ash, and enhancing N availability in the upper soil layer. This ash and soil N pool (that is, wildfire N) is susceptible to loss from watersheds via runoff and leaching during post-fire rains. Plant and soil microbial recovery may mitigate these losses by sequestering N compounds in new biomass, thereby promoting landscape N retention in N-limited chaparral ecosystems. We investigated the relative balance between wildfire N loss, and plant and soil microbial N uptake and stream N export for an upland chaparral watershed in southern California that burned (61%) in a high-intensity wildfire in 2009 by using a combination of stream, vegetation, soil microbial, and remote sensing analyses. Soil N in the burn scar was 440% higher than unburned soil N in the beginning of the first post-fire wet season and returned within 66 days to pre-fire levels. Stream N export was 1480% higher than pre-fire export during the first post-fire rain and returned within 106 days over the course of the following three rainstorms to pre-fire levels. A watershed-scale N mass balance revealed that 52% of wildfire N could be accounted for in plant and soil microbial growth, whereas 1% could be accounted for in stream export of dissolved nitrogen.     

Post-fire seedling establishment in Florida sand pine scrub

Abstract. This study deals with a quantification of pre- and post-fire seedling establishment and microsite characteristics in two Florida sand pine scrub sites burned in May 1993. In addition, life history characteristics related to seedling establishment are described for five perennial species –Calamintha ashei, Chapmannia floridana, Eriogonum floridanum, Garberia heterophylla and Palafoxia feayi. Post-fire seedling establishment in sand pine scrub was sparse (median = 1, 12 seedling/m²), with 17 of 35 species establishing seedlings. Chapmannia, Eriogonum, Garberia and Palafoxia resprouted and flowered after fire; Eriogonum and Garberia had strong post-fire seedling establishment responses within 19 months post-fire. Calamintha individuals were killed by fire, but this species had a strong post-fire seedling establishment response, presumably from seeds in a soil seed bank. Eriogonum and Calamintha seedlings established preferentially in plots centered on conspecific adults. For these species with poor seed dispersal, spatial patterns of seedling establishment may be influenced more by pre-fire adult plant location than by post-fire microsite conditions. Post-fire seedling density in sand pine scrub was much lower than in California chaparral and South African sand plain lowland fynbos.     

Establishment of microscale vegetation pattern in maritime chaparral after fire

We quantified microscale pattern in vegetation and seed assemblages along a 24 m transect before and for two years following a controlled burn in chamise (Adenostoma fasciculatum) chaparral in central coastal California. Our objective was to document scale-dependent correlation between pre-burn seed assemblages, pre-burn canopy cover, microtopography, soil temperatures during burning, post-burn seed assemblages and post-burn vegetation. Scale-dependent correlations among pre- and post-burn seed densities, maximum soil temperatures during burning, microtopography and post-burn vegetation were measured based on two-term local covariance analysis.Seed distribution varied among species prior to fire, with seeds of some annual species concentrated in gap areas. Maximum soil temperatures during burning ranged from less than 50 °C to 225 °C, and were generally lowest in gaps in the pre-burn canopy. These gaps were associated with local topographic depressions. After burning, readily germinable seeds were concentrated in or near gaps in the pre-burn canopy. Germination of different species was variously enhanced, diminished or unchanged by the passage of fire. Post-burn vegetation was very patchy, with some areas nearly devoid of seedlings and other areas, especially pre-burn canopy gaps, supporting numerous seedlings. Seedling recruitment patterns in the second year were generally highly correlated with patterns in pre-burn seed banks and first year vegetation. Although many species exhibited similar recruitment patterns, several different mechanisms may have been responsible for the origin of those patterns.     

黑龙江省大兴安岭林区火烧迹地森林更新及其影响因子

林火干扰是大兴安岭森林更新的影响因子之一,研究火烧迹地森林更新的影响因子(立地条件、火前植被、火干扰特征)对理解生态系统的结构、功能和火后演替轨迹具有重要意义。选取呼中及新林林业局55个代表性火烧样地,利用增强回归树分析法分析了火烧迹地森林更新的影响因素。结果表明:(1)立地条件是影响针、阔叶树更新苗密度的主要因素;海拔对针叶树更新苗密度的影响最大;坡度对阔叶树更新苗密度影响最大;(2)距上次火烧时间对针叶树更新苗比重影响最大,其次是林型;(3)中度林火干扰后森林更新状况好于轻度和重度火烧迹地。根据火烧迹地森林更新调查分析可知:林型影响火后演替模式,火前为针叶树或阔叶树纯林,火后易发生自我更新(火后树种更新组成与火前林型相同),而针阔混交林在火干扰影响下易于发生序列演替(火后初期以早期演替树种更新为主)。     

The influence of dominant shrubs,fire, and time since fire on soil seed banks in mixed chaparral

The composition and density of soil seed banks beneath co-occurring Adenostoma fasciculatum and Ceanothus greggii shrubs from three chaparral stands last burned 9, 35 and 85 years before 1986 were investigated. The overall density of seeds in the soil, as estimated by germinations under greenhouse conditions, increased with time since fire (ca. 8000 to 25000/m²). However, this increase was due entirely to the accumulation of A. fasciculatum seed in the soil (ca. 2000 to 21000/m²). In contrast, the density of C. greggii seed was different in each of the three stands, but was not correlated with time since fire: maximum densities were recorded from the 35 year old stand (ca. 2000/m²).A total of 31 taxa germinated and 17 occurred in sufficient numbers to be analyzed statistically. Germinable seed densities of three herb species were not influenced by soil source (beneath A. fasciculatum or C. greggii), time since fire, or the direct effects of a controlled fire treatment. Germinable seed densities of a further nine species were significantly influenced by the elapsed time since stands last burned. The densities of four decreased and five increased. Four of the species that increased in seed density over the three stands were annuals, suggesting that the chaparral sub-canopy habitat is not as unfavorable for annuals as is often assumed. The fire treatment decreased germinable seed densities of four annual species by 40–70%, but increased the germinable seed densities of the shrubs A. fasciculatum and C. greggii, and the annual Phacelia brachyloba. Our results indicate that seeds of A. fasciculatum will increase in the soil bank for at least 85 years after fire in chaparral where it is dominant. In contrast, seed reserves of C. greggii appear to be influenced primarily by site-specific patterns of seed production and by the intensity of post-dispersal seed predation.     

Remote Sensing Analysis of Vegetation Recovery following Short-Interval Fires in Southern California Shrublands

Increased fire frequency has been shown to promote alien plant invasions in the western United States, resulting in persistent vegetation type change. Short interval fires are widely considered to be detrimental to reestablishment of shrub species in southern California chaparral, facilitating the invasion of exotic annuals and producing “type conversion”. However, supporting evidence for type conversion has largely been at local, site scales and over short post-fire time scales. Type conversion has not been shown to be persistent or widespread in chaparral, and past range improvement studies present evidence that chaparral type conversion may be difficult and a relatively rare phenomenon across the landscape. With the aid of remote sensing data covering coastal southern California and a historical wildfire dataset, the effects of short interval fires (<8 years) on chaparral recovery were evaluated by comparing areas that burned twice to adjacent areas burned only once. Twelve pairs of once- and twice-burned areas were compared using normalized burn ratio (NBR) distributions. Correlations between measures of recovery and explanatory factors (fire history, climate and elevation) were analyzed by linear regression. Reduced vegetation cover was found in some lower elevation areas that were burned twice in short interval fires, where non-sprouting species are more common. However, extensive type conversion of chaparral to grassland was not evident in this study. Most variables, with the exception of elevation, were moderately or poorly correlated with differences in vegetation recovery.     

云南松混交林火烧迹地更新早期草本层物种多样性的空间格局

云南松(Pinus yunnanensis)林是我国西南地区最为广布的针叶林。火烧是云南松林常见的一种自然(或人为)干扰, 但对云南松林火后更新群落的物种多样性特征很少研究。该研究以云南禄丰县勤丰镇2013年“4.13”火灾后云南松混交林火烧迹地更新早期群落草本层为研究对象, 设置了47条1000 m²样带进行群落和环境因子调查, 探讨火烧后更新早期群落草本层的物种构成与丰富度的空间格局及其影响因素。结果表明: 火后更新草本层按物种构成可分为4个群落类型; 草本层物种丰富度受地形和火前群落冠层的影响显著, 与立木生物量和地形坡度正相关, 而与坡位和海拔负相关, 但与火烧强度没有显著的相关性。样带内草本群落β多样性与火前立木胸面积及火烧强度显著正相关, 而与海拔和坡位负相关。总体上, 生境地形特征、火前冠层和火烧强度构成了火烧后早期群落草本层物种构成与丰富度变化的主要控制因子。此外, 一年生和多年生草本物种的更新格局及其对环境的响应存在显著差异。     

Spatial patterns of species diversity in the herb layer of early post-fire regeneration in mixed Pinus yunnanensis forests

Herb layer plays an important role in maintaining ecosystem functioning of forests. The aims of this study were to determine the pattern of species diversity in early post-fire regeneration of the herb layer in mixed Yunnan pine forests and to identify the effects of topography, fire severity, pre-fire vegetation and herb species life-history feature on post-fire regeneration.     

Effect of fire on soil nutrients and under storey vegetation in Chir pine forest in Garhwal Himalaya,India

The study was carried out in the Pinus roxburghii Sargent (Chir pine) forest in the sub-tropical region of Garhwal Himalaya to assess the effect of fire on soil nutrient status at different altitudes (700 m, 800 m and 1000 m), soil depths (0–20 cm, 20–40 cm and 40–60 cm) and on under storey vegetation. The soil nutrients and under storey vegetation were assessed before fire (pre-fire) and after fire (post-fire). The results of the study indicate that fire plays an important role in soil nutrient status and under storey vegetation. The nutrients (soil organic carbon, nitrogen, phosphorus and potassium), decreased in post-fire assessment and with increasing altitudes, and soil depths, compared to pre-fire assessment. The under storey vegetation diminished after fire in all forest sites. The study concludes that in Chir pine forest, fire plays a role in reducing soil nutrients along the altitudinal gradient, soil depths and under storey vegetation. Thus, these nutrients can be saved through some management practices e.g. by early controlled burning and by educating local villagers about the negative impacts of severe wild fires on soil and vegetation.     

气候、植被和地形对大兴安岭林火烈度空间格局的影响

在北方森林中火干扰是森林景观变化的主导因素。林火烈度作为衡量林火动态的重要指标,较为直观地反映了火干扰对森林生态系统的破坏程度,其空间格局深刻地影响着森林景观中的多种生态过程(如树种组成、种子扩散以及植被的恢复)。解释林火烈度空间格局有助于揭示林火干扰后森林景观格局的形成机制,对预测未来林火烈度空间格局以及制定科学合理林火管理策略均有重要意义。基于LandsatTM/ETM遥感影像,将2000—2016年大兴安岭呼中林区的36场火的林火烈度划分为未过火、轻度、中度、重度4个等级。采用FRAGSTAT景观格局分析软件从类型水平上计算了斑块所占景观面积比、面积加权平均斑块面积、面积加权平均斑块分维数、面积加权边缘面积比、斑块密度5个景观指数,以对林火烈度空间格局进行了定量化描述。并且采用随机森林模型,分析了气候、地形、植被对林火烈度空间格局的影响及其边际效应。通过研究得出以下结果:(1)相对于未过火、轻度、以及中度火烧斑块,重度火烧斑块的面积更大、形状更简单;(2)海拔对重度火烧斑块的空间格局起着至关重要的作用,其次是坡向、坡度、植被覆盖度、相对湿度、温度等;(3)随着海拔的升高,面积加权平均斑块面积和面积加权平均斑块分维数的边际效应曲线呈上升趋势,而面积加权边缘面积比和斑块密度呈下降趋势;除了面积加权平均斑块面积外,都受到火前植被覆盖度的影响,且植被覆盖度为0.2—0.3范围内,重度火烧斑块在景观中所占比例最大。总的来看,2000—2016年大兴安岭呼中森林景观中重度火烧斑块与未过火、轻度以及中度火烧斑块存在显著差异性。相对于气候,地形和植被对于塑造重度火烧斑块空间格局具有重要作用。因此,应针对重度火烧区域进行可燃物处理,从景观层面上合理配置森林斑块,从而降低高烈度森林大火发生的风险。     

Human intervened post-fire forest restoration in the Northern Great Hing’an Mountains: a review

The devastating fire in May 1987 in the northern Great Hing’an Mountains created a mosaic of burned severity. Subsequent log harvesting and tree planting complicated the restoration process. Based on intensive field work and GIS analysis for the burned area, we studied the landscape pattern change in relation with its influencing factors, the restoration of some ecosystem functions and the long-term effect of human planting on vegetation restoration. A post-fire vegetation restoration process was also established using spatial series instead of temporal series. The results indicated that coniferous forest, broad-leaved forest and mixed forest increased obviously in the burned area. Factors influencing the restoration process are ranked as the burned severity, way of restoration (planting, promoted restoration or natural restoration) and topographical factors. The latter was further ranked as the slope, elevation, slope position and aspect. Primary productivity, hydrological functions, habitats for wild animals and permanent frozen soil of the area have all largely been restored to the pre-fire level after more than 15 years. Parameters demonstrated a transitional character of the forest from the early succession stage to middle stage. LANDIS simulation for the long-term forest succession under pure natural restoration and human-intervened restoration indicated that post-fire tree planting largely influenced the age structure, spatial pattern and timber stock of dominant species such as Larix gmelini, Betula platyphylla and Pinus sylvestris var. mongolica. In general, the influence of post-fire human planting can remain for more than 200 years.     

Spatiotemporal dynamics of recruitment in Aleppo pine (Pinus halepensis Miller)

Spatial and temporal aspects of recruitment play a central role in plant population and community dynamics and have important basic and applied implications. Here we summarize and discuss the results from studies of spatiotemporal dynamics of recruitment stages (seeds-seedlings-saplings) in Aleppo pine (Pinus halepensis) throughout the species' native range. Seed release is induced either by fire (pyriscence) or by drying atmospheric conditions (xeriscence), each generating a distinct temporal pattern. In both cases most seeds travel relatively short distances (<30 m). Pyriscence is not expected to promote long-distance seed dispersal, but xeriscence is associated with relatively strong winds that can transport seeds over 1 km and more, as predicted by a new mechanistic dispersal model. In the absence of fire, seed survival increases with distance from adults because of higher competition with adults and sibs and higher seed predation near the seed sources. New data provide further evidence for such distance-dependent seed predation and also show that predation rates vary among habitats and are lowest in times of high seed abundance. The resulting recruitment patterns in the absence of fire are characterized by rapid spread and complex spatiotemporal dynamics that are fairly unpredictable and give rise to variable age structure. In contrast, the spatial pattern of the first post-fire generation is highly predictable because it explicitly replicates the spatial pattern of the pre-fire population. Unlike fire-free regeneration in which multiple factors operating at various stages are likely to be important, post-fire regeneration is governed by a fairly specific set of factors (the chemical properties of ash) operating during a specific stage (saplings) and at a specific location (the canopy projection of large burned pines). Post-fire forests are therefore even-aged and have predictable spatiotemporal dynamics. Most studies of Aleppo pine recruitment have focused on the seedling and sapling stages and on post-fire regeneration; we call for greater attention to the seed stage and to more extensive sampling of all recruitment stages in both space and time.     

Remote sensing approach to detect post-fire vegetation regrowth in Siberian boreal larch forest

Remote sensing with time series data offers considerable potential in the trajectory of post forest fire dynamics beyond the current monitoring of structural attributes that are displayed in the post-fire area. Many studies have addressed this topic by using time series remote sensing indices; however, this approach has sometimes been demonstrated as an unrealistic and biased representation of the post-fire forest patterns due to the saturation issues of vegetation indices. These saturation issues then lead to an underestimation of the forest successional stages and an overestimation of the forest recovery rate. This paper aims to develop a framework for trajectory of the post-fire forest patterns in the Siberian boreal larch forest (Larix sibirica) with the synergistic use of different remote sensing based vegetation-cover indicators derived from the Landsat time series and the WorldView-2 images. A time-series of the forest recovery index (FRI) and fractional vegetation cover (FVC) has been analyzed to estimate the rates of forest regeneration and vegetation recovery across different burn severity levels in the Siberian larch forest. The results showed that the FRI method can be used to observe the regrowth of the larch forest from the tenth year after the fire overlapping with the period of significant increase in the sapling stem volume. The post-fire larch forest canopy can fully recover to the pre-fire condition with respect to the magnitude of the FRI values after 30–47 years where the highest regeneration rate was observed in the moderate burn severity areas followed by the low and high burn severity. On the other hand, the FVC method was positively correlated with burn severity and more sensitive for evaluating the early stages of the forest succession in which the FVC dramatically increases after 5–6 years after the fire. The significant growth of FVC was accentuated by the maximum emergence of the sapling density as well as the rapid growth of herbaceous plants, grasses, shrubs, and shade-intolerant trees immediately after the fire, which could not be evaluated using the FRI. Both time series of the FRI and the FVC are valuable tools for determining the dominant stages of the post-fire larch forest succession in order to understand the relationships between fire disturbance and natural cycles of the boreal larch forest.     

Stability of pre- and post-fire spatial structure of pine trees in Aleppo pine forest

The study reported here describes for the first time the similarity between pre- and post-fire spatial patterns of the trees in a Mediterranean pine forest demonstrating that the pre-fire ancestor microsite is occupied also by the next generation. Although Aleppo pine Pinus halepensis Mill, is an obligatory post-fire seeder, it is adapted to regenerate in its pre-fire growing microsite. thus keeping suitable growing sites from generation to generation. We studied the effect of the dead burned adult pines on the density and size of their recruited saplings 2, 5, 11 and 20 yr after fire. A comparison of pine sapling density and size was made between the "near" zone (under the former effect of the burned canopy) and the'far'zone (beyond the former effect of the burned canopy).
In the site 2 yr after fire, seedling density was 56% higher in the "far" zone than in the'near'zone, but seedling .size was similar. However in the site 20 yr after fire, densities were similar in both zones, but the size was bigger by 89% in the "near" zone. Thus, population recruitment after fire seems to peak near the burned pine trees rather than at u distance from them, in contrast to Janzen's original'distance hypothesis' model suggested for undisturbed rainforest. Mere we present a new hypothetical model for the spatial pattern of post-fire regeneration of obligate seeder tree species forming open forests. It is proposed that in such trees the microsites which were kept by the burned adult trees, which are killed by the fire, are also the favorable regeneration microsite for the post-fire generation.     

Population structure of Adenostoma fasciculatum in mature stands of chamise chaparral in the southern Sierra Nevada,California

Summary In the low elevation chaparral areas of Sequoia National Park, California, pure stands of chamise (Adenostoma fasciculatum) are periodically rejuvenated by fire. Mature stands showed considerable variability in density and total biomass even though a positive correlation exists between the two. Mature stands showed a preponderance of individuals in the smaller size classes (inverse-J shape distribution). Dead shrubs found in mature stands also tended to be in the smaller size classes. This relatively high mortality of small individuals is important to post-fire stand development. In addition, resprout and seedling biomass one year after fire both showed inverse-J shaped size-class structures. A positive correlation existed between the preburn basal area of a shrub and its first year resprout biomass. Shrub biomass and distance to nearest neighbor were poorly correlated. A significant correlation existed between stand density and a stand's variance-to-mean ratio, indicating a trend toward more regular spacing as density increases. Pre-burn and fire-induced mortality tended to move the stand towards a more clumped distribution. Seedlings replaced dead individuals after a fire and thus restored regular spacing.     

Tree Mortality Following Boreal Forest Fires Reveals Scale-Dependant Interactions Between Community Structure and Fire Intensity

Fire disturbance patterns influence forest communities at a range of spatial scales. Forest community structure may also influence fire disturbance patterns, because tree species vary in their fuel value and in their tolerance to fire damage. However, the influence of community structure on fire disturbance likely depends on latent ecological differences between fires and on the spatial scale at which patterns are observed. Using data on fire intensity, community structure, and post-fire tree survival in four systematically sampled boreal forest fires, we tested the hypotheses that: (1) patterns in post-fire tree survival reflect interactions between fire intensity and community structure; (2) these relationships change with the spatial scale of observation. To test the first hypothesis, we used information theoretic methods to compare eight generalized linear mixed effects models describing the influence of community structure and fire intensity on tree survival in a 500 m² sample plot, accounting for latent fire-to-fire differences in response. To test the scaling hypothesis, we reaveraged the data at nine successively larger spatial resolutions up to approximately 2 km², at each resolution tracking the parameter values of the best model. When fit to the plot-level data, the dominant feature of the best model was a strong intensity–survival correlation which varied from fire to fire, and depended on plot-level community structure. In some fires, community structure and survival became more tightly coupled at larger scales, whereas fire intensity became less important. These results support the view that fire disturbance patterns are influenced by cross-scale interactions between community structure and fire intensity.     

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.