Effects of Fire Frequency on Plant Species Composition of Sandstone Communities in the Sydney Region: Inter-Fire Interval and Time-Since-Fire

Australian Joumal of Ecology (1995) 20, 239-247

Effects of fire frequency on plant species composition of sandstone communities in the Sydney region: Inter-fire interval and time-since-fire

DAVID A. MORRISON, GEOFFREY J. CARY,* STUART M. PENGELLY, DAVID G. ROSS, BRUCE J. MULLINS, COLLETTE R. THOMAS AND TIMOTHY S. ANDERSON Department of Applied Biology, University of Technology Sydney, PO Box 123, Broadway, NSW 2007, Australia

Abstract Eire frequency is the number of fires experienced by a particular community within a given time period. This concept can potentially be resolved into a number of interacting variables, including: time since the most recent fire, the length of the inter-fire intervals, and the variability of the length of the inter-fire intervals. We estimated the effects of these three variables on the floristic composition of 65 samples from dry sclerophyll vegetation with different fire histories in Brisbane Water, Ku-ring-gai Chase and Royal National Parks near Sydney. Our analyses suggest that fire frequency may account for about 60% of the floristic variation among our samples. They confirm the hypothesis that the recent (<30 years) fire frequency produces effects on floristic composition of fire-prone communities that can recognizably be attributed both to the time since the most recent fire and to the length of the intervals between fires. These effects are equal in magnitude but are different in the nature of the floristic variation they are associated with. Increasing time-since-fire is associated with a decline in the evenness of fire-tolerant species, indicating that fewer of these species come to dominate the community in the prolonged absence of fire. Herbs and small shrubs decrease in abundance, while larger shrubs increase in abundance. Inter-fire intervals of decreasing length are associated with a decrease in the evenness of the fire-sensitive species, particularly those large Proteaceae shrubs that often dominate the community biomass in dry sclerophyll shrublands of southeastern Australia. Furthermore, the variation associated with inter-fire intervals is not necessarily solely related to the shortest inter-fire interval, but is related to combinations of inter-fire intervals through time. Thus, increasing variability of the length of the inter-fire intervals is associated with an increase in the species richness of both fire-sensitive and fire-tolerant species, implying that it may be variation of the inter-fire intervals through time that is primarily responsible for maintaining the presence of a wide variety of plant species in a particular community. Our results also suggest that the floristic variation associated with different inter-fire intervals decreases with increasing time-since-fire.

Key words: fire, frequency, inter-fire interval, species composition.

INTRODUCTION Australia, and has been since the mid-Quaternary (Gill et al. 1981). Fire regimes are usually considered to have Fire is a common source of change in the plant species ^j^^^^ interrelated components that can affect plant composition of the dry sclerophyll communities of community composition: fire frequency, season of occurrence and fire intensity (Gill 1975). Effects of fire intensity .^ ,, _ _ . „ u c u 1 r on the floristic composition of dry sclerophyll com- *Present address: Ecosystetti Dynatnics, Research School of . • , , , • , n j- j • A I- Biological Sciences, Attstralian Natiotial University, ACT 2601, ^"1^'"^^ ^ave been relatively well Studied in Australia Australia. (c-g- Gill & Groves 1980; Christensen et al. 1981; Accepted for publication May 1994. Bradstock & Myerscough 1988; Auld & O'Connell 1991; 240 D. A. MORRISON ET AL.

Hamilton et al. 1991), and fire intensity influences seed period; e.g. Bradstock & O'Connell 1988). Similarly, new release, breaking of seed dormancy and the suitability of individuals of fire-tolerant species will not be recruited the seed-bed for germination. On the other hand, the to the population if an inter-fire interval is shorter than effects of fire season are relatively poorly understood the time taken for the plants to reach first post-fire (e.g. Bradstock & O'Connell 1988; Enright & Lamont reproduction (the secondary juvenile period) and the 1989; Cowling et al. 1990; Lamont et al. 1991), but time taken by juvenile plants to reach fire-tolerant size appear to be important for the establishment of seedlings (e.g. Bradstock & Myerscough 1988). Furthermore, and the survival of resprouting individuals. species may disappear from the above-ground community However, most Australian work on plant-fire inter- during long fire-free periods, persisting as seeds or actions has concentrated on the effects of fire frequency. below-ground storage organs, but eventually becoming Fire frequency as originally described by Gill (1975) is a locally extinct if fire is withheld (e.g. Specht et al. 1958). function of the number of fires experienced by a particular It is thus apparent that time-since-fire and inter-fire community within a given time period. The effects of fire interval may have distinctly different effects on plant frequency on plant communities can therefore be resolved species composition (via effects on different demographic into at least two variables (Nieuwenhuis 1987): (i) the characteristics of the plants), and that these different shortest time interval between fires; and (ii) the time effects have not always been clearly distinguished in since the most recent fire. These variables are interrelated, previous studies of fire frequency. Consequently, the because as the number of fires per unit time changes so nature of the relationship between the components of fire does the average length of the inter-fire intervals in any frequency remain largely unknown, as is their relative one period as well as the time-since-fire. However, the importance. Therefore, we wished to investigate the majority of studies concerning fire frequency effects on interactive effects of the components of fire frequency in Australian plant communities have focused on the more detail. In this paper we report a study ofthe effects successional effects of time-since-fire (e.g. Jarrett & Petrie of fire frequency on the floristic composition of common 1929; Specht et al. 1958; Cochrane 1963; Purdie & plant communities of the Sydney region. In particular, Slatyer 1976; Siddiqi et al. 1976; Purdie 1977; Russell & we estimated the effects of: time since the most recent Parsons 1978; Bell & Koch 1980; Clemens & Franklin fire, the average length of the inter-fire intervals and the 1980; Posamentier et al. 1981; Brown & Podger 1982; variability of the length of the inter-fire intervals. Brown & Hopkins 1983; Bell et al. 1984; Clark 1988; Fox Our study was a purely descriptive (i.e. non-manipu- 1988; McFarland 1988) while the effects of inter-fire lative) one, relying entirely on the sampling of fortuitously interval have been less intensively studied (e.g. Fox & available areas in the field with different recent histories Fox 1986a; Bowman et al. 1988; Fensham 1990). Only of fire frequency. Such an experimental design is not Bradfield (1981) and Nieuwenhuis (1987) have explicitly ideal (e.g. see Gill 1977), but, given the practical compared the relative effects of these two variables on a difficulties of manipulating fire regimes over long time single plant community. periods (particularly near urban areas), large-scale manipu- The floristic composition of a community after a fire is lative field experiments for the study of fire frequencies dependent on the pre-bum composition, but it can vary may be logistically impossible. Furthermore, our study significantly away from it. In particular, species richness was only concerned with the above-ground component and diversity tend to increase immediately after the fire of plant species composition, as we did not quantify the and then to gradually decline (e.g. Specht 1981; Fox & soil-stored seed bank for any species (see Leek et al. Fox 1986b). Initial regrowth is usually by those species 1989). whose adult plants can survive fire (fire-tolerant species), while those species whose adult plants do not normally survive fire (fire-sensitive species) tend to contribute more to the above-ground community several years later. METHODS Furthermore, the abundance of fire-sensitive species Our work was carried out in dry sclerophyll communities tends to decrease as the number of fires increases, while in three of the coastal national parks of the Sydney fire-tolerant species show more variable responses (Fox region. Samples were collected from the area between & Fox 1986a; Nieuwenhuis 1987). Staples Lookout and Kariong in Brisbane Water National The demographic effects of fire frequency therefore Park in winter 1992 (33°27'S, 151°17'W: 22 samples), on appear to be primarily concerned with the time taken for the Lambert Peninsula in Ku-ring-gai Chase National the plants to reach a life-history stage that enables the Park in spring 1991 (33°37'S, 151°16'W: 24 samples), population to survive a subsequent fire. For example, the and between Loftus Heights and WattamoUa in Royal local extinction of fire-sensitive species will occur if an National Park in spring 1992 (34°07'S, 151°05'W: 19 inter-fire interval is shorter than the time taken for the samples; Table 1). All samples were taken from Hawkes- plants to reach first reproduction (the primary juvenile bury Sandstone plateaus and ridgetops {ca 150 m a.s.l.). FIRE FREQUENCY AND PLANT SPECIES COMPOSITION 241 in closed scrub and low to low-open woodland or forest all fires since 1964. Suitable replicate samphng areas (Benson & Fallding 1981; Thomas & Benson 1985). were then chosen with respect to vegetation type and These are the most widespread vegetation types of the ease of access. dominant sandstone areas in the Sydney region (Benson Our sampling design assumed that the fire history of & Howell 1990). each of the areas within each park was similar (or at least Sample areas were chosen to represent the range of fire randomized) before detailed records were started in the frequencies present in each national park in terms of early 1960s. This assumption is reasonable, given that combinations of inter-fire intervals and time-since-fire many of the fires in the Sydney region before that time (Table 1). Each sample was taken from a plant community were wildfires that consumed very large areas of bushland that met all of the following criteria: with a much lower frequency than occurs today (Kodela (1) It was part of an area burnt by a large wildfire & Dodson 1989), and that the Aborigines probably within the period 1964-68 (to provide a baseline with a employed a consistent fire management policy for each known 'first' fire). vegetation type (Clark & McLoughlin 1986). Our sam- (2) The most recent fire was at least 18 months before pling also assumed that the intensity, season and type sampling (to avoid problems identifying small seedlings, (i.e. wildfire versus prescribed fire) of fire were ran- and to avoid the potentially dramatic temporary floristic domized across areas. This assumption also appears to be changes during early successional stages, particularly quite reasonable, based on our sampling programme. those related to unsuccessful post-fire establishment). However, the sampling design was not a balanced one (3) Each fire was a wildfire or prescribed bum covering either within or between parks, as would be expected of a at least 5 ha (to avoid small spot fires). planned manipulative experiment, but relied entirely on (4) There were clearly defined boundaries between the availability of areas with different fire histories in the areas with different fire histories (to ensure accuracy of required vegetation types. In particular, areas with a sample placement). 'medium' time-since-fire were relatively rare in all three (5) The structure of the understorey was apparently of the national parks (Table 1). consistent with the recorded fire history, and the under- The abundance of each vascular plant species was storey was apparently completely burnt by at least the estimated for each sample using the nested quadrat most recent fires; for example, no old plants of fire- technique of Outhred (1984). Each sample consisted of a sensitive species in recently burnt areas (to ensure pair of nested quadrats separated by 100-200 m, with accuracy of recorded fire regime). importance scores assigned to each species in each quadrat The fire history of each area was determined from the using seven square sub-quadrats varying from 1 to 100 m^. detailed fire history records maintained by the National This technique produces abundance scores (on a scale of Parks and Wildlife Service for each of these national 1-14) that are functionally equivalent to frequencies parks. We constructed a fire-history map at 1:25000 or (Morrison et al, 1995), and which are directly related to 1:30 000 for each of the parks, showing the occurrence of plant density (Bonham 1989). All species nomenclature foUows Beadle et al, (1982). The effects of fire frequency on plant species com- Table 1. Number of samples taken from each of the three position for each national park were first analysed by sampling areas and their fire-frequency characteristics redundancy analysis (ter Braak 1988). This is a constrained ordination technique based on principal Shortest inter-fire interval* components analysis that, in a joint analysis of two data Time-since-fire* Short Medium Long sets (e.g. floristic and environmental), assesses the degree Brisbane Water National Park to which they show covariation (ter Braak & Prentice Short 5 3 4 1989). That is, it seeks patterns among the samples that Medium — 1 — occur in both data sets, while ignoring patterns that are Long 3 3 3 unique to either one of the data sets. This is thus a direct Ku-ring-gai Chase National Park gradient analysis technique analogous to canonical correl- 5 4 5 Short ation analysis but which avoids many of the mathematical Medium 1 1 1 Long — 2 5 constraints inherent in that technique (ter Braak & Royal National Park Prentice 1989), as these are unrealistic for most biological Short 4 3 3 data sets. Medium — — — The redundancy analysis produces two interrelated Long 5 2 2 ordination diagrams, one for each of the two data sets, which can be displayed simultaneously in a species- *Short: 1-5 years; medium: 6-10 years; long: >10 years (based on Conroy 1987). A dash indicates that no sample areas environment biplot. The degree to which the floristic were available with those fire-frequency characteristics. variation associated with the environmental variables is 242 D. A. MORRISON£7"/4L.

displayed by the biplot can be assessed by calculating the analysis (ter Braak & Prentice 1989). The effect of what percentage is shown of the variation shared in time-since-fire was the covariable, thus allowing us to common between the two data sets. The degree to which investigate the effects of inter-fire interval on plant the variability associated with the environmental variables species composition in more detail. in the direct gradient analysis accounts for the overall variation in species composition among the samples can (a) be assessed by comparing the constrained ordination 800 with the equivalent unconstrained ordination of the species data alone; in this case this involves comparing SD IFI the results of the redundancy analysis with the results from a species-centred principal components analysis. The two data sets analysed by redundancy analysis for each park were the species abundance (floristic) data and the fire frequency (environmental) data. For the fire frequency data, each of the inter-fire interval times and TSF the time since the most recent fire were log transformed (see Specht 1981), and the following characteristics were Mean IFI\ then determined for each sample: time since the most Shortest IFI recent fire, the shortest inter-fire interval, the mean inter-fire interval and the standard deviation of the inter- fire intervals. For those samples from communities that -800 had experienced only a single fire since 1964, the inter- -800 800 fire interval and time-since-fire were treated as synon- (b) ymous (this will underestimate the true inter-fire interval 900 for these samples). The floristic data for the three national parks were then pooled and re-analysed by redundancy analysis, thus revealing general trends for the Sydney region. SD IFI For the combined data set, each plant species was also recorded as fire-sensitive (> 50% of the plants usually TSF killed by fire) or fire-tolerant (<50% of the plants usually killed by fire). For each sample, the floristic Mean IFI richness and evenness were calculated for each of these t Shortest IFI two species groups, with richness calculated as the total number of species present and evenness as the modified Hill's ratio (Ludwig & Reynolds 1988). This richness/ evenness data set was then passively plotted on to the redundancy analysis, thus investigating the relationship -900 of fire frequency to the relative abundance of species in 900 samples with each of these fire characteristics. 800 The combined data set was then analysed by partial redundancy analysis (ter Braak 1988), which is a modified form of the same analysis that allows the effect of one or more variables (called covariables) to be partialled out of

Fig. 1. Projection of the sample sites on to axes representing the first two components of the species-environment biplot from the redundancy analyses of the floristic composition and fire frequency data for (a) Brisbane Water, (b) Ku-ring-gai Chase and (c) Royal National Parks. The floristic similarities of the sites are indicated by the spatial relationship of the symbols, while the influence of the fire frequency characteristics are indicated by the direction and length of the arrows. TSF, time since most recent fire; Mean IFI, mean of inter-fire intervals; SD IFI, standard deviation of inter-fire -800 -800 intervals; Shortest IFI, shortest inter-fire interval. Axis 1 800 FIRE FREQUENCY AND PLANT SPECIES COMPOSITION 243

RESULTS associated with the time since the most recent fire. The richness of both species types is positively associated A total of 234 plant species were recorded in this study, with the variability of the inter-fire intervals. 80 (34%) of them occurring in all three national parks The partial redundancy analysis of the three measures and 100 (43%) of them unique to one of the parks. of inter-fire interval (with the effect of time-since-fire Individual samples contained from 39 to 81 species per removed as a covariable) shows a different pattem than is 200 m^, with Brisbane Water and Royal National Parks having more species per sample (54-73 and 55-81, respectively) than did Ku-ring-gai Chase National Park (a) 800 (39-59 species per sample). TSF The first two axes of the species-environment biplot from the redundancy analyses of the floristic data and fire frequency characteristics for each of the national parks are shown in Fig. 1. The similarities among the samples are indicated by the spatial relationship of the points; points near each other show more similarity among themselves (based on the floristic characteristics) than they do to points further away. The influence of each of the fire frequency characteristics is indicated by the direction and length of the arrows; longer arrows indicate a more influential factor, and orthogonal arrows SD IFI indicate unrelated factors. These analyses thus show a clear distinction between the effects of time-since-fire -800 and inter-fire interval on floristic composition, as these -600 1000 two characteristics each have a relationship with floristic composition that is about equal in magnitude but different (b) 800 in effect (equal length but orthogonal arrows). This TSF means that variation in these two characteristics is associated with changes in abundance of different plant species, and that the floristic composition of any one area Shortest IFI will thus be a reflection of the combined influence of E fs these two variables. In these analyses there is very little Mean IFI distinction between the effects of variation in the three measures of inter-fire interval. As a result of the consistency of the analyses from each of the national parks, the combined data set reveals the same general pattem (Fig. 2a). The two axes shown account for 67% of the total variation of the constrained ordination (i.e. the variation shared in common between the floristic and environmental data sets) and they account -800 for 59% of the total sum of squares of the first two axes of -600 1000 the equivalent unconstrained ordination analysis (i.e. the Axis 1 variation in the floristic data set alone). There are 10 Fig. 2. Projection of the sample sites on to axes representing the first species that show a notable negative relationship with two components of the species-environment biplot from the time-since-fire (Fig. 2a, Table 2), these being the ones redundancy analysis of the floristic composition and fire interval data for the combined data set from all three national parks, (a) that show the largest decrease in abundance as the length showing the relationship of time-since-fire with 10 individual plant of the time since the most recent fire increases. species, and (b) showing the relationship of frequency with species Of the 234 species, 182 (78%) could be classified as richness and evenness. The Ooristic similarities of the sites are either fire-sensitive (82 species) or fire-tolerant (100 indicated by the spatial relationship of the symbols, while the species), the remainder either exhibiting variable be- influence of the fire interval and species abundances are indicated haviour in different areas or being unknown. The relative by the direction and length of the arrows. TSF, time since most recent fire; Mean IFI, mean of inter-fire intervals; SD IFI, standard distribution of the fire-sensitive and fire-tolerant species deviation of inter-fire intervals; Shortest IFI, shortest inter-fire relates to the various fire frequency characteristics (Fig. interval; R fs, richness of fire sensitive species; R ft, richness of fire 2b). The evetiness of the fire-sensitive species is positively tolerant species; E fs, evenness of fire sensitive species; E ft, associated with the length of the inter-fire intervals, evenness of fire tolerant species. The 10 plant species are hsted in while the evetiness of the fire-tolerant species is negatively Table 2. 244 D. A. MORRISON FT AL.

Table 2. Species showing the strongest relationships with the fire frequency characteristics

Regeneration Length of inter-fire Variability of Species strategy Time-since-fire interval inter-fire interval

Dillwynia retorta Fs Grevillea sericea Fs Hemigenia purpurea Fs — Hibbertia bracteata Fs Lomandra glauca Ft — — Lomandra gracilis Ft — Mitrasacme polymorpha Fs — Pimelea linifolia Fs Platysace linearifolia Ft — Puhenaea elliptica Fs — Banksia ericifolia Fs -t- Bossiaea scolopendria Fs -1- Casuarina distyla Fs + Hakea sericea Fs -1- Hakea teretifolia Fs + Petrophile pukhella Fs + Caustis flexuosa Ft — Epacris microphylla Fs -1- Grevillea sphacelata Ft —

Fs: fire sensitive; Ft: fire tolerant (see text for definitions); (+) strong positive relationship; (—) strong negative relationship; blank entry: no strong relationship. Only the strongest relationship(s) for each species is shown.

800 evident when the effects of time-since-fire are included (Fig. 3). The estimate of the variability of the inter-fire intervals (the standard deviation) shows a different trend from that of the two estimates of the length of the inter- fire intervals (shortest interval and mean interval), im- cf^. • •-• .•: SD IFI plying that the effects of inter-fire interval are more complex than has hitherto been suggested. Once again, this means that variation in these characteristics is associated with changes in abundance of different plant species, and that the floristic composition of any one area will thus be influenced in two different ways by these variables. There are six species that show a notable Mean IFI positive relationship with length of the inter-fire interval (Fig. 3, Table 2), these being the ones that show the -1000 largest increase in abundance as the length of the time -800 1000 between fires increases. Only three species showed a Axis 1 notable relationship with variability of the inter-fire Fig. 3. Projection ofthe sample sites on to axes representing the first interval (Fig. 3, Table 2). two components ofthe species-environment biplot from the partial redundancy analysis of the floristic composition and fire interval The interaction between time-since-fire and inter-fire data for the combined data set from all three national parks, interval is also evident from the partial redundancy showing the relationship of inter-fire interval with 10 individual analysis. Those samples from areas with a time-since-fire plant species. The floristic similarities of the sites are indicated by of 9 years or less show a greater variability aroimd the the spatial relationship of the symbols, while the influence of the origin (estimated as the variance of the biplot distances fire interval characteristics are indicated by the direction and length of each sample from the origin ofthe partial redundancy of the arrows. Mean IFI, mean of inter-fire intervals; SD IFI, analysis) than do those samples from areas with a time- ndard deviation of inter-fire intervals; Shortest IFI, shortest |ter-fire interval; Be, Banksia ericifolia; Bs, Bossiaea scolopendria; since-fire of 12 years or more (F = 2.267, d.f. — 1,63, d, Casuarina distyla; Cf, Caustis flexuosa; Em, Epacris microphylla; P<0.05). This means that the floristic variation associated «, Grevillea sphacelata; Hs, Hakea sericea; Ht, Hakea teretifolia; with inter-fire intervals decreases with increasing time K, Lomandra glauca; Pp, Petrophile pukhella. since the most recent fire. FIRE FREQUENCY AND PLANT SPECIES COMPOSITION 245

DISCUSSION Our results also indicate that the effects of inter-fire interval are more complex than hitherto has been sug- Our analyses suggest that fire frequency may account for gested (e.g. Gill 1975; Nieuwenhuis 1987), as the about 60% of the floristic variation among our samples. variability of the inter-fire intervals shows effects that are If this conclusion is a general one for the fire-prone equal in magnitude to those of the length of the inter-fire sandstone communities of the Sydney region, then clearly intervals but are associated with floristic variation of a fire frequency is a major source of within-community different nature. Increasing variability of the inter-fire variability in the relative abundances of the component intervals is associated with an increase in the species plant species. richness of both fire-sensitive and fire-tolerant species. Our results confirm the hypothesis (Bradfield 1981; This implies that it may be variation of the inter-fire Nieuwenhuis 1987) that the recent (<30 years) fire intervals through time that is primarily responsible for frequency produces effects on floristic composition of maintaining the presence of a wide variety of plant dry sclerophyll communities that can be attributed both species in a particular community, rather than time- to the time since the most recent fire and to the length of since-fire as has been suggested by most previous studies the intervals between fires. These effects are equal in (e.g. Specht et al, 1958; Russell & Parsons 1978; Bell & magnitude but are different in the nature of the floristic Koch 1980; Clemens & Franklin 1980; Specht 1981; Fox variation that they are associated with. 1988). Increasing time-since-fire is associated with a decline As maintaining species richness is one of the objectives in the evenness of fire-tolerant species, indicating that of vegetation management for conservation (Conroy fewer of these species come to dominate the community 1987), it follows that bushfire management should be in the prolonged absence of fire. Herbs and small shrubs aimed at maintaining a diversity of inter-fire intervals in such as Lomandra glauca, Lomandra gracilis and Platysace any one community, in addition to the current practice of linearifolia decline in abundance with increasing time- maintaining a range of times-since-fire. The maintenance since-fire, while larger shrubs such as Banksia serrata, of a mixture of areas with various times-since-fire within Banksia spinulosa, Isopogon anemonifolius and Leucopogon any one vegetation type appears to be part of a manage- juniperinus increase in abundance. Furthermore, the ment strategy based on the reduction of hazard from the abundance of several fire-sensitive species (notably small accumulation of fire fuel loads (Conroy 1987), rather shrubs such as Dillwynia retorta, Grevillea sericea, than a strategy directed at plant species conservation. Hemigenia purpurea, Hibbertia bracteata, Pimelea linifolia Consequently, the variation associated with inter-fire and Pultenaea elliptica) declines with increasing time- intervals is not necessarily solely related to the shortest since-fire, indicating the reliance of these species on fire inter-fire interval, as was suggested by Nieuwenhuis for the continuation of their contribution to the above- (1987), but is related to combinations of inter-fire intervals ground biomass. Presumably these species are still through time. Thus, both the length of the inter-fire represented in the community by a soil-stored seed-bank. intervals and the variability of these lengths during any Inter-fire intervals of decreasing length are associated one time period have effects on the floristic composition with a decrease in the evenness of the fire-sensitive of the community. Repetitions of any particular length of species, indicating that fewer of these species come to inter-fire interval will have different consequences for dominate the community under frequent fires. The most community composition than will a mixture of fire notable of the species that are reduced in abundance by regimes. short inter-fire intervals are those large shrubs that often Furthermore, there is evidence for the effects of the dominate the community biomass in dry sclerophyll interaction between time-since-fire and inter-fire inter- shrublands of southeastern Australia, including Banksia vals. Our results suggest that the floristic variation ericifolia, Casuarina distyla, Hakea sericea, Hakea tereti- associated with different inter-fire intervals decreases folia and Petrophile pulchella. These species are apparently with increasing time-since-fire. This may be a con- reduced in abundance as a result of their relatively long sequence of the disappearance of short-lived species primary juvenile periods (e.g. Benson 1985; Nieuwenhuis from the above-ground community through time, as any 1987; Bradstock & O'Connell 1988), so that inter-fire floristic differences associated with their relative abun- intervals that are shorter thari the time taken for these dance will thus be reduced, or it may result from plants to build up adequate seed reserves effectively competitive effects (Gill & Groves 1980). restrict or prevent establishment of their seedlings after These conclusions indicate that the design of our the fire. Each of these species also has a canopy-stored study cannot reveal the full complexity of the effects of seed-bank, which is effectively exhausted after each fire variability of inter-fire intervals, even though it considers (unlike soil-stored seed-banks, part of which may be more of the components of fire frequency than do previous unaffected by any one fire); see also Siddiqi et al, (1976), studies. First, only one of our sample areas (in Brisbane Bradfield (1981), Fox and Fox (1986a), and Nieuwenhuis Water National Park) had more than four fires in the past (1987). 30 years and so the combinations of inter-fire intervals 246 D. A. MORRISON ET AL. that we sampled were relatively limited. Second, we (<30 years) within which the various fire regimes must sampled a wide range of times-since-fire, and thus have occurred. This covariation occurs most obviously relatively few of our samples would show the maximum between the shortest inter-fire interval and the mean effect of inter-fire intervals. Clearly, any study of the inter-fire interval, but will also be apparent between the effects of fire frequency must take account of both the other characteristics. Clearly, a manipulative experiment independent effects of time-since-fire and inter-fire should be designed to replicate all possible combinations interval as well as their interaction. Therefore, a more of the fire frequency characteristics, rather than relying detailed study of the effects of patterns of inter-fire on the fortuitous presence in the field of appropriate intervals independently of time-since-fire is necessary combinations. This problem is compounded by the for a more complete understanding of the floristic unbalanced nature of the fire regimes that currently exist variation associated with fire frequency. in the three national parks that we sampled, in particular For example, Cary and Morrison (1995) concluded the absence of 'medium' (5-10 year) intervals. This is that there are at least two general and unrelated effects of partly a product of the sporadic nature of wildfires, but is the recent history of inter-fire intervals on the floristic also due to the current fire management practices, which composition of dry sclerophyll communities. First, shorter have left some areas unbumt for relatively long periods inter-fire intervals are associated with a reduction in the while burning others frequently. It is possible that these number of species present, and an inter-fire interval of design limitations may have caused some distortions of 1-6 years is associated with an additional, reversible the pattems that we have observed in our analyses. reduction in the number of fire-sensitive species. Second, repetition of inter-fire intervals of 1-5 years long is associated with variation in the abundance of herbaceous ACKNOWLEDGEMENTS fire-tolerant species. Unfortunately, our data are not necessarily directly Thanks to the National Parks and Wildlife Service of comparable with those from previous studies of fire New South Wales for permission to carry out this work frequency in dry sclerophyll communities. In particular, on land under their care; to the National Parks and we estimated floristic composition using the frequency of Wildlife Service staff of Ku-ring-gai Chase, Brisbane each species, rather than their percentage cover as has Water and Royal National Parks for access to their been done by most previous workers (e.g. Specht et al. records; to Ross Bradstock and David Keith for helpful 1958; Siddiqi et al. 1976; RusseU & Parsons 1978; Clemens discussions; and to Tony Auld, Ross Bradstock and & Franklin 1980; Posamentier et at. 1981; Fox & Fox Marilyn Fox for commenting on an earlier draft of the 1986a; Nieuwenhuis 1987; Fox 1988; Fensham 1990). manuscript. Frequencies are directly related solely to the number of plants present (Bonham 1989), unlike percentage cover which is a function of both plant number and plant size. REFERENCES Consequently, there can be large changes in per cent Auld T. D. & O'Connell M. A. (1991) Prediaing pattems of post- cover with time-since-fire, for example, without any fire germination in 35 eastem Australian Fabaceae. Aust. J. concomitant change in the relative number of plants Ecol. 16, 53-70. present. Such changes are not, strictly speaking, part of a Beadle N. C. W., Carolin R. C. & Evans O. D. (1982) Flora of the pyric succession and may confound the underlying Sydney Region, 2nd edn. A. H. & A. W. Reed, Sydney. demographic pattems that are responsible for the ob- Bell D. T., Hopkins A. J. M. & Pate J. S. (1984) Fire in the served changes in floristic composition. Our samphng kwongan. In: Kwongan: Plant Life of the Sandplain (eds J. S. method, based on frequencies, should have avoided such Pate & J. S. Beard) pp. 178-204. University of Westem Australia Press, Nedlands. problems. Bell D. T. & Koch J. M. (1980) Post-fire succession in the northem Furthermore, we avoided sampling the very early jarrah forest of Westem Australia. Aust. J. Ecol. 5, 9-14. stages of regeneration after fire, which may have sig- Benson D. H. (1985) Maturation periods for fire-sensitive shrub nificantly reduced the observed floristic variation associ- species in Hawkesbury sandstone vegetation. Cunninghamia 1, ated with time-since-fire (e.g. Purdie 1977; Clark 1988). 339-49. This decision was a deliberate attempt to focus attention Benson D. H. & Ho well J. (1990) Taken for Granted: The Bushland of Sydney and Its Suburbs. Kangaroo Press, Kenthurst. on the successful re-establishment of populations after Benson J. S. & Fallding H. (1981) Vegetation survey of Brisbane fire. However, our underestimates should not change any Water National Park and environs. Cunninghamia 1, 79-113. of the conclusions that we have reached. Bonham C. D. (1989) Measurements for Terrestrial Vegetation. J. Finally, there are a number of difficulties associated Wiley & Sons, New York. with the fact that ours was a 'natural' experiment (sensu Bowman D. M. J. S., Wilson B. A. & Hooper R. J. (1988) Response Diamond 1986) rather than a controlled manipulative of Eucalyptus forest and woodland to four fire regimes at Munmarlary, Northern Territory, Australia. J. Ecol. 76, one. Most notable among these problems is the co- 215-32. variation among the various fire frequency characteristics Bradficld G. E. (1981) Component analysis of fire panems in open due to the constraint imposed by the limited time period eucalypt forest. Aust. J. Ecol. 6, 99-109. FIRE FREQUENCY AND PLANT SPECIES COMPOSITION 247

Bradstock R. A. & Myerscough P. J. (1988) The survival and Gill A. M., Groves R. H. & Noble I. R. (1981) Eire and the population response to frequent fires of two woody resprouters Australian Biota. Australian Academy of Science, Canberra. Banksia serrata and Isopogon anemonifolius. Aust. J. Bot. 36, Hamilton S. D., Lawrie A. C, Hopmans P. & Leonard B. V. (1991) 415-31. Effects of fuel-reduction burning on a Eucalyptus obliqua forest Bradstock R. A. & O'Connell M. A. (1988) Demography of woody ecosystem in Victoria. Aust. J. Bot. 39, 203-17. plants in relation to fire: Banksia ericifolia Lf. and Petrophile Jarrett P. H. & Petrie A. H. K. (1929) The vegetation ofthe Black's pulchella (Schrad.) R.Br. Aust. J. Ecol. 13, 505-18. Spur region: A study of the ecology of some Australian Brown M. J. & Hopkins A. J. M. (1983) The kwongan (sclero- mountain Eucalyptus forests IL Pyric succession. J. Ecol. 17, phyllous shrublands) of Tutanning Nature Reserve, Westem 249-81. Australia. Aust. J. Ecol. 8, 63-73. Kodela P. G. & Dodson J. R. (1989) A late Holocene vegetation and Brown M. J. & Podger F. D. (1982) Floristics and fire regimes of fire record from Ku-ring-gai Chase National Park, New South vegetation sequence from sedgeland heath to rain forest at Wales. Proc. Linn. Soc. NSW 110, 317-26. Bathurst Harbour, Tasmania, Australia. Aust. J. Bot. 30, Lamont B. B., Connell S. W. & Bergl S. M. (1991) Seedbank and 659-76. population dynamics oi Banksia cuneata: the role of time, fire, Cary G. J. & Morrison D. A. (1995) Effects of fire frequency on and moisture. Bot. Gaz. 152, 114-22. plant species composition of sandstone communities in the Leek M. A., Parker V. T & Simpson R. L. (1989) Ecology of Soil Sydney region: Combinations of inter-fire intervals. Aust. J. Seed Banks. Academic Press, San Diego. Ecol. 20 (in press). Ludwig J. A. & Reynolds J. F. (1988) Statistical Ecology: A Primer Christensen P., Recher H. & Hoare J. (1981) Responses of open on Methods and Computing. Wiley & Sons, New York. forest (dry sclerophyll forest) to fire regimes. In: Fire and the McFarland D. C. (1988) Fire and vegetation composition and Australian Biota (eds A. M. Gill, R. H. Groves & I. R. Noble) structure of subtropical heathlands in south-eastern Queens- pp. 367-93. Australian Academy of Science, Canberra. land. Aust. J. Bot. 36, 533-46. Clark S. S. (1988) Effects of hazard-reduction burning on popu- Morrison D. A., Le Brocque A. F. & Clarke P. J. (1995) An lations of understorey plant species on Hawkesbury sandstone. assessment of some improved techniques for estimating the Aust. J. Ecol. 13, 473-84. abundance (frequency) of sedentary organisms. Vegetatio (in Clark S. S. & McLoughlin L. C. (1986) Historical and biological press). evidence for fire regimes in the Sydney region prior to the Nieuwenhuis A. (1987) The effect of fire frequency on the arrival of Europeans: implications for future bushland manage- sclerophyll vegetation of the West Head, New South Wales. ment./iust. Geog. 17, 101-12. Aust. J. Ecol. 12, 373-85. Clemens J. & Franklin M. H. (1980) A description of coastal heath Outhred R. K. (1984) Semi-quantitative sampling in vegetation at North Head, Sydney Harbour National Park: Impact of survey. In: Survey Methods for Nature Conservation (eds K. recreation and other disturbance since 1951. Aust. J. Bot. 28, Myers, C. R. Margules & I. Musto) pp. 87-100. CSIRO, 463-78. Canberra. Cochrane G. R. (1963) Vegetation studies in forest-fire areas of the Posamentier H. G., Clark S. S., Hain D. L. & Recher H. F. (1981) Mount Lofty Ranges, South Australia. Ecology 44, 41-52. Succession following wildfire in coastal heathland (Nadgee Conroy B. (1987) Bushfire management planning in natural areas. Nature Reserve NSW). Ausl. J. Ecol. 6, 165-75. In: Bushfire Management in Natural Areas (ed. B. Conroy) pp. Purdie R. W. (1977) Early stages of regeneration after burning in 1-10. National Parks and Wildlife Service of NSW, Sydney. dry sclerophyll vegetation. II. Regeneration by seed germin- Cowling R. M., Lamont B. B. & Enright N. J. (1990) Fire and ation. Aust. J. Bot. 25, 35-46. management of south-western Australian banksias. Proc. Ecol. Purdie R. W. & Slatyer R. O. (1976) Vegetation succession after fire Soc. Aust. 16, 177-83. in dry sclerophyll woodland communities of southeastern Diamond J. (1986) Overview: laboratory experiments, field experi- Australia. Aust. J. Ecol. 1, 223-36. ments, and natural experiments. In: Community Ecology (eds J. Russell R. P. & Parsons R. F. (1978) Effects of time since fireo n Diamond & T J. Case) pp. 3-22. Harper & Row, New York. heath floristics at Wilsons Promontory, southern Australia. Enright N. J. & Lamont B. B. (1989) Seed banks, fire season, safe Aust. y. Bot. 26,53-61. sites and seedling recruitment in five co-occurring Banksia Siddiqi M. Y, Carolin R. C. & Myerscough P. J. (1976) Studies in species, y. Ecol. 77, 1111-22. the ecology of coastal heath in New South Wales. III. Regrowth Fensham R. J. (1990) Interactive effects of fire frequency and site of vegetation after fire. Proc. Linn. Soc. NSW 101, 51-63. factors in tropical Eucalyptus forests. Aust. J. Ecol. 15,255-66. Specht R. L. (1981) Responses to fire of heathlands and related Fox B. J. & Fox M. D. (1986b) Resilience of animal and plant shrublands. In: Ejre and the Australian Biota (eds A. M. Gill, communities to human disturbance. In: Resilience in Mediter- R. H. Groves & I. R. Noble) pp. 395-415. Australian Academy ranean-type Ecosystems (eds B. Dell, A. J. M. Hopkins & B. B. of Science, Canberra. Lamont) pp. 39-64. W. Junk, Dordrecht. Specht R. L., Rayson P. & Jackman M. E. (1958) Dark Island Fox M. D. (1988) Understorey changes following fire at Myall Heath (Ninety-Mile Plain, South Australia). VI. Pyric Lakes, New South Wales. Cunninghamia 2, 85-95. succession: changes in composition, coverage, dry weight and Fox M. D. & Fox B. J. (1986a) The effect of firefrequenc y on the mineral nutrient status. Aust. y. Bot. 6, 59-88. structure and floristic composition of a woodland understorey. ter Braak C. J. F. (1988) CANOCO—an extension of DECORANA to Aust. J. Ecol. 11,77-85. analyze species-environment relationships. Vegetatio 75, Gill A. M. (1975) Fire and the Australian flora: a review. Aust. Eor. 159-60. ter Braak C. J. F. & Prentice I. C. (1989) A theory of gradient 38, 4-25. Gill A. M. (1977) Management of fire-prone vegetation for plant analysis. Adv. Ecol. Res. 18, 272-317. species conservation in Australia. Search 8, 20-6. Thomas J. & Benson D. H. (1985) Vegetation Survey of Ku-ring-gai Gill A. M. & Groves R. H. (1980) Fire regimes in heathlands and Chase National Park. National Herbarium of NSW, Sydney. their plant ecological effects. In: Ecosystems of the World, Volume 9B, Heathlands and Related Shrublands (ed. R. L. Specht) pp. 61-84. Elsevier, Amsterdam.