Fire-prone Habitats Research Articles

Delayed post-fire seedling emergence linked to season: a case study with Leucopogon species (Epacridaceae)

In many fire-prone habitats around the world, natural fire regimes have shaped the evolution of the associated flora. Critical life history stages are often linked to fire in species that occur in these fire-prone habitats but many species are unstudied. We investigated seedling emergence patterns over time, after several fires in south-eastern Australia, for three obligate seeders in the Genus Leucopogon (Family Epacridaceae): L. setiger, L. esquamatus and L. exolasius. Fixed quadrats were monitored for 12 to 30 months for newly emerged seedlings, both after fire and in unburnt L. exolasius and L. esquamatus habitats. There was a flush of seedling emergence in the first year after fire for all three Leucopogon species, with smaller pulses recorded in subsequent years. Time elapsed between fire and the onset of emergence differed between fires, but not between Leucopogon species. Whatever the timing of the fire, seedling emergence was restricted to the late autumn and winter periods, coinciding with emergence in unburnt habitat. This contrasts with patterns of emergence previously reported for other taxa, and also in this study, where emergence of the Leucopogon species after fire was delayed compared with co-occurring species in other genera. Our results suggest that seasonal factors are important to the germination ecology of these species and that combinations of fire-related and seasonal factors are necessary to maximise germination. Rainfall has a non-seasonal pattern in the study region and seasonal emergence post-fire has not previously been recorded. The magnitude of delay to emergence of species with seasonal emergence patterns will be determined by the season of fire but not by a seasonal pattern of rainfall in the post-fire year. A shift of the peak fire season could increase this delay, possibly affecting plant population recovery.

Towards an understanding of population change for the long-lived resprouting tree Angophora inopina (Myrtaceae)

In fire-prone habitats some long-lived tree species appear resilient to fire. However, fire frequency may affect recruitment patterns. This study investigates the reproductive features of the long-lived tree species Angophora inopina Hill in recognised priority conservation areas with a high fire frequency. Plants exhibit high survival rates when burnt and respond to fire events with high rates of growth, flowering and seed set. Aged capsules on plants contain few seeds but released seeds germinate readily, suggesting high viability, low dormancy and limited seed storage in aerial or soil seed banks. Population modelling indicates that the species will be resilient to low recruitment levels in the short term. However, over the long term, population structure is significant in determining the ability of the population to respond to recruitment cues. Thus, understanding and monitoring population structural change is a priority for this species.

WHY DON'T CARNIVOROUS PITCHER PLANTS COMPETE WITH NON-CARNIVOROUS PLANTS FOR NUTRIENTS?

Most field studies suggest that competition for nutrients is important in nutrient-limited systems. Nevertheless, the mechanisms by which species avoid competition for nutrients in nutrient-poor but species-rich communities remain poorly understood. I used a model system, the carnivorous pitcher plant Sarracenia alata, to measure competition for nutrients. In a field competition experiment, I increased the potential for nutrient-niche overlap between established juvenile pitcher plants and their non-carnivorous neighbors by denying a unique source of nutrients (prey) to pitcher plants. Contrary to predictions based on nutrient-niche complementarity, prey exclusion did not reduce the performance of pitcher plants competing with non-carnivorous neighbors. Hence, differences in nutrient-source specialization did not explain the coexistence of Sarracenia alata and its non-carnivorous neighbors in the field. Instead, prey exclusion reduced the positive growth response to increased light following the removal of neighbors. By reducing allocation to pitchers in the presence of neighbors, pitcher plants appeared to reduce their demand for nutrients when shaded. I hypothesize that carnivorous plants avoid competition with non-carnivorous plants by using changes in the light environment to cue adjustments in their demand for nutrients. I suggest that such plasticity is adaptive in any long-lived perennial plant that periodically experiences simultaneous pulses of light and nutrients during its lifetime (e.g., as might occur in fire-prone habitats). Corresponding Editor: E. S. Menges

Aseasonal reproduction and high fecundity in the Cape grass lizard, Cordylus anguinus, in a fire-prone habitat

AbstractWe investigated life history characters of the Cape grass lizard, Cordylus anguinus, and relate them to survival in the fire-prone habitat in which it occurs. Unlike in other cordylids, reproductive activity was found to be asynchronous among females, with vitellogenic and gravid females encountered virtually throughout the year. Aseasonal breeding will circumvent reduction or complete loss of reproductive effort for any given year due to fire. Female grass-lizards attain significantly larger body sizes than males. Clutch size ranged from three to seventeen and was positively correlated with snout-vent length. Maximum clutch size is more than three times that recorded for any other cordylid. We suggest that high fecundity will allow quick recruitment after a fire. To determine the reproductive cycle exhibited by males, testicular volume and seminiferous tubule diameter were measured, and spermatogenic activity assessed qualitatively, using Licht's classification system. Our data indicate that C. anguinus has a post-nuptial spermatogenic cycle. The species differs from other cordylids having a post-nuptial cycle, in that spermatogenesis already commences in spring.

Post-fire response of shrubs in the tablelands of eastern Australia: do existing models explain habitat differences?

Fire is an important ecological factor that influences the distribution and abundance of plant populations of shrub species in fire-prone habitats. Comprehensive information about the fire-response syndromes and post-fire recruitment of seedlings in tableland habitats of eastern Australia is poorly known. In particular, data on shrubs occurring in grassy habitats are lacking for temperate regions of Australia. The post-fire response and recruitment patterns of shrub taxa were recorded from research burns and wildfires on the New England Tablelands over 4 years in the following four habitats: grassy woodlands and open forests, shrubby open forests, wet heaths and rocky outcrops. The ratio of obligate seeder to resprouter species differed among habitats, with the highest ratio occurring on rocky outcrops (90 : 10) and the lowest in grassy forests (19 : 81). Post-fire recruitment of seedlings was also highest on rocky outcrops whereas seedlings were rarely observed in the wet heaths and grassy forests. The following six models that explain these patterns were reviewed: fire and grazing frequency, soil nutrients and texture, habitat openness and environmental variability. No one model could uniformly explain differences in fire response across all habitats but a combination of disturbance-frequency and regeneration-niche models may provide a mechanism for the patterns observed. Field and laboratory experiments are needed to examine allocation to persistence (resprouting) and reproduction in species with different fire-response syndromes. These experiments also need to examine both disturbance-frequency and regeneration-niche factors in manipulative experiments.

Post‐fire recovery of acorn production by four oak species in southern ridge sandhill association in south‐central Florida

We examined post-fire recovery of two components of acorn production (percentage of bearing ramets [stems] and number of acorns per bearing ramet) for four species of oaks in southern ridge sandhill vegetation in south-central peninsular Florida. Annual counts of acorns on two white oaks (Quercus chapmanii and Q. geminata) and two red oaks (Q. laevis and Q. myrtifolia) were conducted annually (except in 1991) on two 2.7-ha grids from 1969 to 1998. A prescribed burn was conducted on one of the grids in May 1993. Newly sprouted ramets of both white oaks produced acorns during the first year following the fire, whereas red oaks required 3 yr (Q. myrtifolia) or 4 yr (Q. laevis) to produce acorns. The difference in the timing of post-fire acorn production between the white and red oak species reflected the difference in the number of years from flower bud initiation to mature acorns in the two groups, with the additional year-long lag in Q. laevis probably attributable to the fact that it is typically a tree rather than a shrub species. The data suggested that percentage of bearing ramets in the smallest size class of the two white oak species was markedly lower in the burned than unburned grid in the first year of post-fire acorn production and higher in the fifth year, but these trends were not evident for the red oaks. Among all four species, differences between mean number of acorns in burned and unburned grids were significant in only two cases (the largest size class of both white oak species in the fifth year). There was no evidence of recruitment from acorns on the burned grid, possibly due to the rapid redevelopment of the shrub layer because of low mortality of the extensive clonal root systems. Rapid post-fire recovery of acorn production in xeric fire-prone habitats is presumably the result of selection to increase the probability of recovery and persistence following sufficiently intense fires that result in high oak mortality. The timing and magnitude of post-fire acorn production in sandhill and other xeric Florida associations has a potential impact on a wide variety of insects, birds, and mammals that feed on acorns, as well as on the species with which they interact.

A Revision of Gomphocarpus R. Br. (Apocynaceae: Asclepiadeae)

Gomphocarpus is a genus of mostly shrubby herbs with non-tuberous rootstocks native to Africa, Arabia and adjacent territories south of the Dead Sea. The genus is here restricted to a putatively monophyletic assemblage of20 species in several complexes. The corona lobe is remarkably constant in form within a species and is the most useful organ for species determination. The concept of G. fruticosus proposed by Bullock (1952) has been rejected, and 5 regional subspecies are recognised. Several other species sunk into G. fruticosus by Bullock have been reinstated. The G. glaucophyllus complex consists of 5 species native to fire-prone habitats in the Brachystegia belt of south-central Africa and grasslands further south. The conservation status of all taxa has been assessed - the majority being in the Lower Risk: Least Concern category, but information is lacking for G. tomentosus subsp. frederici, and G. munonquensis must be considered Vulnerable as it is known only from four collections. An epitype is designated for Asclepias fruticosa L., and a further 15 names are lectotypified. An index to the almost 200 names published in Gomphocarpus is included to indicate their currently accepted names.

Patterns of abundance of a narrow endemic species in a tropical and infertile montane habitat

We examined the entire spatial distribution of a narrow endemic shrub (Coccoloba cereifera, Polygonaceae) in Serra do Cipo, Brazil. We tested the hypothesis that a narrow endemic species would show a gradual decline in either size and density towards the edges of its distribution. The contribution of soil specificity and post-fire growth to C. cereifera abundance and distribution were also investigated. C. cereifera showed multimodal and highly aggregated distribution pattern at several scales, from 25 m2 to 3000 m2 (blocked quadrat variance analyses). This pattern seems to be strongly related to the predominance of clonal recruitment and to the close association of the species to sandfields, which have discrete distribution between gallery forests and rocky outcrops. Population density did not decline towards the edge of the species distribution. Plants near the distribution boundaries had slightly more leaves and more inflorescences per plant (p<0.005), but there was no significant change in the mean number of ramets per clone. The absence of large plants in some populations at the center of the species distribution may be related to the higher frequency of fire in this region, killing aerial plant parts. Nearly all aggregations had inverse-J shaped size-distribution, suggesting effective recruitment of ramets, most frequently via asexual reproduction. Similar patterns of plant abundance may be common in fire-prone habitats characterized by infertile, and well-drained soils since these areas generally have high numbers of endemic plants, with strong soil specificity. Possible mechanisms for the observed pattern are discussed considering current models concerning distribution of abundance of species.

Low genetic diversity in Persoonia mollis (Proteaceae), a fire-sensitive shrub occurring in a fire-prone habitat

Allozyme frequency data were used to estimate hierarchical levels of genetic diversity within and among the nine subspecies of the morphologically variable shrub Persoonia mollis R. Br. (Proteaceae). This species is a fire-sensitive component of the fire-prone sclerophyllous vegetation of south-eastern Australia. The total gene diversity (HT = 0.139) within P. mollis was less than half that typically found within angiosperm species. However, P. mollis was typical of angiosperms in the way its gene diversity was distributed, with 78.3 per cent of the total gene diversity found within populations. Of the 21.7 per cent found among populations, 17.9 per cent was attributed to differences among subspecies and only 3.8 per cent attributed to differences among populations within subspecies. Heterozygosity (HE) within populations varied 10-fold from 0.023–0.206, with a comparatively low mean over all populations of 0.109. A significant deficit of heterozygotes for the outbreeding P. mollis is consistent with the ‘heterozygosity paradox’, is caused by a Wahlund effect, and suggests an average genetic neighbourhood size of between 3 and 60 plants. Explanations for these patterns and the weak correlation of these data with morphological variation are discussed. It is suggested that the high frequency and haphazard occurrence of fire plays a major role in affecting the levels and distribution of genetic diversity within P. mollis, and probably within other fire-sensitive plant species also occurring in fire-prone habitats, through relatively frequent localized extinction and subsequent recolonization.

Low genetic diversity in Persoonia mollis (Proteaceae), a fire-sensitive shrub occurring in a fire-prone habitat

Allozyme frequency data were used to estimate hierarchical levels of genetic diversity within and among the nine subspecies of the morphologically variable shrub Persoonia mollis R. Br. (Proteaceae). This species is a fire-sensitive component of the fire-prone sclerophyllous vegetation of south- eastern Australia. The total gene diversity (H(T)=0.139) within P. mollis was less than half that typically found within angiosperm species. However, P. mollis was typical of angiosperms in the way its gene diversity was distributed, with 78.3 per cent of the total gene diversity found within populations. Of the 21.7 per cent found among populations, 17.9 per cent was attributed to differences among subspecies and only 3.8 per cent attributed to differences among populations within subspecies. Heterozygosity (H(E)) within populations varied 10-fold from 0.023-0.206, with a comparatively low mean over all populations of 0.109. A significant deficit of heterozygotes for the outbreeding P. mollis is consistent with the 'heterozygosity paradox', is caused by a Wahlund effect, and suggests an average genetic neighbourhood size of between 3 and 60 plants. Explanations for these patterns and the weak correlation of these data with morphological variation are discussed. It is suggested that the high frequency and haphazard occurrence of fire plays a major role in affecting the levels and distribution of genetic diversity within P. mollis, and probably within other fire-sensitive plant species also occurring in fire-prone habitats, through relatively frequent localized extinction and subsequent recolonization.

Fire ecology of red pine (Pinusresinosa) in northern Vermont, U.S.A.

Red pines (Pinusresinosa Ait.) in northern New England exist within small islands of fire-prone habitat surrounded by relatively nonflammable, deciduous forest. We studied the fire history and age structure of six red pine stands at an upland site in northwestern Vermont. Red pine is dominant in the canopy but rare in seedling and sapling size classes. Red pine is usually dependent on fires for regeneration. Fire scars record at least 17 different fires in the study area between the early 1800s and 1922. No fires are recorded between 1922 and 1987. The survival of numerous saplings in burned stands indicates that most of the fires were light surface fires. At least eight fires preceded periods of red pine recruitment recorded by the ages of living trees. These fires were probably locally intense, tree-killing fires. A similar regime of frequent, nonlethal fires and infrequent, lethal fires occurs in other parts of red pine's range.

Response of Succulents to Fire: A review

Many succulents live in fire-prone habitats with fire frequencies ranging from 1-3 years (Canadian Prairies) to &gt;250 years (Sonoran Desert). Mortality after a fire is often &gt;50% but rarely total. A few plants are left unbumt in refugia but most cacti and leaf succulents persist by survival of the apical meristem, an adaptation to the normal climate of such habitats. Similarly, reproduction is governed by weather patterns, not fire. Apex survival is critical because growth from other meristems (above or below ground) is rare except in the leaf succ ulents Agave and Aloe. Survival is consequently dependent upon the frequency and intensity of fire.

Fire Temperature Heterogeneity in Contrasting Fire Prone Habitats: Kansas Tallgrass Prairie and Florida Sandhill

GIBSON, D. J. (Department of Biology, University of West Florida, Pensacola, FL 32514), D. C. HARTNETT AND G. L. S. MERRILL (Division of Biology, Ackert Hall, Kansas State University, Manhattan, KS 66506). Fire temperature heterogeneity in contrasting fire prone habitats: Kansas tallgrass prairie and Florida sandhill. Bull. Torrey Bot. Club 117: 349-356. 1990.Spatial patterns of fire temperatures from a tallgrass prairie and adjacent Gallery forest in northeast Kansas and a sandhill community in central Florida were recorded using temperaturesensitive pyrometers. The objectives of the study were to determine, in both habitats, the range of temperatures reached during prescribed burning under a range of different conditions. Both habitats are characterized by frequent, low-intensity fires confined to the herbaceous vegetation and low shrubs. In tallgrass prairie, fire temperature maxima ranged from 19 to 399?C (n = 243). The highest temperatures were associated with fires in isolated tree and shrub canopies (399?C). Fires were hotter in headfires compared with backfires (47?C difference), on lowlands compared with uplands (1 2?C difference), and in areas that had not been burned for many years compared with areas burned annually (34?C difference). In the Florida sandhill, fire temperature maxima ranged from 35 to 538?C (n = 240), with the highest temperatures recorded at ground level in sites which had not been burned for at least 5 years. Compared with frequently burned areas, areas that have not burned for many years build up high fuel loads that support a more homogeneous, hotter fire. In the tallgrass prairie, homogeneity of fire temperatures was greatest in areas of intermediate fire frequencies. The greater spatial heterogeneity in fire characteristics of prairie with very high fire frequency (annual fire) and very low frequency (> 15 years between fires) is likely a result of low fuel loads and more patchy vegetation structure, respectively. In sandhill, low fuel loads and patchy distribution of fuel contribute to high spatial variability in fire temperatures in annually burned sites.

Dead leaves and fire survival in Southern African tree aloes.

Many aloe species in southern Africa have stems clothed with a layer of persistent dead leaves. The degree of stem coverage is species-specific. The suggestion that persistent dead leaves have an insulatory function and are adaptive in fire-prone habitat was tested on Aloe ferox. Field surveys demonstrated a significant negative relationship between mortality and degree of stem coverage and laboratory studies confirmed the insulating properties of dead leaves. The distribution of southern African tree aloes supprts the prediction that bare-stemmed species would be confined to fire-free habitat whilst fully clothed species would occur in both fire-prone and fire-free habitat. The study suggests that harvesting of Aloe ferox leaves for medicinal purposes could result in significant mortality in fires.