Post-fire plant regeneration across a closed forest-savanna vegetation transition

Forest Ecology and Management 400 (2017) 77–84

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Post-fire plant regeneration across a closed forest-savanna vegetation transition Felipe D.C. Araújo a, David Y.P. Tng b,⇑, Deborah M.G. Apgaua a,b, Polyanne A. Coelho a, Diego G.S. Pereira a, Rubens M. Santos a a b

Department of Forest Science, Federal University of Lavras, Av. Doutor Sylvio Menicucci, Lavras, Minas Gerais 37200-000, Brazil College of Science and Engineering, James Cook University, McGregor Road, Smithfield, Queensland 4878, Australia

a r t i c l e

i n f o

Article history: Received 2 February 2017 Received in revised form 29 May 2017 Accepted 31 May 2017

Keywords: Alternative stable states Diversity Structural change Fire disturbance Forest-savanna ecotones Vegetation dynamics

a b s t r a c t Fire is a major environmental factor influencing vegetation heterogeneity, with closed forest and savanna ecosystems having different management needs due to their different responses to fire disturbance. However, the differences in post-fire vegetation dynamics between these ecosystems have seldom been compared using a uniform set of parameters. Additionally, post-fire dynamics of forest-savanna ecotones is poorly characterized. With the hypothesis that closed forest, savannas and ecotones will exhibit different post-fire responses, we studied the vegetation diversity, structure and dynamics in an upland forestsavanna vegetation mosaic in Minas Gerais, Brazil following a fire that occurred in September 2011. In January 2012, we identified, tagged, and measured the basal diameter of all regenerating juvenile tree stems within forty-six 4 m2 plots in closed forest, savanna and ecotone vegetation, and conducted recensuses in 2013 and 2014. We modelled the relationship between short-term dynamics parameters (recruitment, mortality, basal area loss and gain, and the turnover and net changes in the number of individual stems and basal areas) and vegetation type. Species diversity was higher in closed forests and ecotones than in savanna. Across all vegetation types, stem density decreased and basal area increased. Parameters such as recruitment, net changes in the number of individuals, and the gain, loss and turnover in basal area did not differ across vegetation types. However, stem mortality was higher in closed forest and ecotones combined than in savannas, and the net change in the number of individuals was the lowest in the savanna. Overall, our results support that within a climatically-similar vegetation mosaic, closed forests exhibit different post-fire regeneration dynamics from savanna as expected. Ecotones exhibited post-fire responses and dynamics more similar to closed forests than to savanna, but more studies will be needed to establish if this pattern is applicable to other areas. Understanding the longer-term vegetation dynamics and plant regeneration patterns is a potential next step that will help inform fire management strategies for forest-savanna mosaics. Ó 2017 Elsevier B.V. All rights reserved.

1. Introduction Fire is a key factor driving the distribution of many of the world’s vegetation communities (Bond and Keeley, 2005; Bond et al., 2005; Bowman et al., 2009), through interactions with vegetation composition and structure (Bond and Midgley, 1995; Brooks et al., 2004). Given trends in rising concentration of atmospheric CO2, severe weather events and land use, tropical ecosystems are under a regime of unprecedented change with respects to fire ecology (Dale et al., 2001; Bonan, 2008). Because this impacts on a mul-

⇑ Corresponding author at: College of Science and Engineering, James Cook University, 14-88 McGregor Rd, Smithfield, Queensland 4878, Australia. E-mail address: [email protected] (D.Y.P. Tng). http://dx.doi.org/10.1016/j.foreco.2017.05.058 0378-1127/Ó 2017 Elsevier B.V. All rights reserved.

titude of socioeconomic, management and ecological issues, understanding vegetation responses to fire is paramount (Cochrane, 2003; Hardy, 2005). From a macroecological perspective, terrestrial ecosystems are often polarized into fire-adapted or -sensitive systems. Because such systems or vegetation co-occur in landscape mosaics within the same climatic envelope, they can be interpreted as alternative stable states with self-reinforcing dominance, under the control of intrinsic environmental factors and biotic feedbacks (Warman and Moles, 2009; Hoffmann et al., 2009; Staver et al., 2011a; Dantas et al., 2016). Vegetation states will therefore be maintained provided that changes in underlying environmental drivers are not strong or consistent enough to result in a regime shift (Whitlock et al., 2010; Lindenmayer et al., 2011; Knox and Clarke, 2012).

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For instance, closed forests (or rainforests) are characterized by a set of environmental and biotic features that render them fire retardant (Biddulph and Kellman, 1998; Hennenberg et al., 2006; Little et al., 2012). Given the correct environmental conditions however, closed forest can and does burn (Uhl et al., 1988), but can be expected to recover rapidly from a small fire disturbance (Marrinan et al., 2005; Williams et al., 2012). Still, frequently repeating fires or a very large fire may cause a regime shift leading to permanent changes in structure and floristics, or even a vegetation state shift (Kinnaird and O’Brien, 1998; Cochrane et al., 1999; Cochrane, 2003). Conversely, savannas are maintained by a regime of frequent fires (Staver et al., 2011b; Simon and Pennington, 2012), and are characterized by species that are typically resilient to, or even promotive of fire (Bowman, 2000; Hoffmann et al., 2003). Prolonged fire exclusion can therefore lead to an increased tree dominance and canopy closure (Bowman and Fensham, 1991; Durigan and Ratter, 2006; Pinheiro et al., 2010). Where closed forest and savanna interface, ecotones often arise, and it is much less clear how ecotones will respond to a fire disturbance. Ecotones often exhibit floristic and structural characteristics that are intermediate between their flanking vegetation types (Puyravaud et al., 1994; Durigan and Ratter, 2006; Kark and van Rensburg, 2006). However, some trait-based comparisons between closed forest, savanna and their ecotones suggest a greater ecological convergence between ecotones with their flanking closed forest compared to savanna (Tng et al., 2013). In other words, some closed forest-savanna ecotones may be better interpreted as belonging within the closed forest environmental regime (Tng et al., 2014), and at least some dynamic responses of ecotones to fire disturbance may be hypothesized to be similar to closed forests. Despite the ecological importance of ecotones, they have received little attention (Durigan and Ratter, 2006), and having baseline data on how ecotones respond to fire has important management implications for forest-savanna mosaics as a whole (Tng et al., 2014). An approach to testing if closed forests, savannas and their ecotones have differential dynamic responses would be to use a common set of parameters to characterize community changes during species regeneration after fire (Vesk and Westoby, 2004; RussellSmith, 2006; Russell-Smith et al., 1998). Plant species in both forest and savanna may survive and persist in an environment after fire through different means: (1) by resisting the direct effects of fire and (2) by tolerating the changed post-fire conditions (Whelan, 1995). Post-fire flushes of seedlings and sprouting are adaptative traits for recovery after fire that can produce community-level changes (Uhl et al., 1981; Hoffman, 1996; Guariguata and Ostertag, 2001; Matt Davies et al., 2010;). While the regenerative capacities of tree species after fire have been intensively researched in some places such as Australia and Africa (Okello et al., 2008; Prior et al., 2009; Ondei et al., 2016), such research is still lacking in some regions in South America (see Balch et al., 2013). The southeastern region in Brazil encompasses the Atlantic Forest Domain, a topographically and edaphically heterogeneous phytogeographic region comprised of various vegetation types (SOS Mata Atlântica, 2011). The broad geographical vegetation transition of tropical and subtropical closed forests (rainforests) in the Atlantic Forest domain to the open savanna west of the region gives rise to a complex mosaic of closed canopy vegetation grading into open canopy grass-dominated vegetation (Oliveira-Filho and Fontes, 2000). In addition to climatic and soil factors, natural and anthropogenic disturbance are considered the main determinants of vegetation heterogeneity in the region (Oliveira-Filho and Fontes, 2000; González-Pérez et al., 2004). Because the Atlantic Forest region has been subjected to massive land clearing, much of the work on forest regeneration in the region has focused on

the effects of forest disturbance by human activity (Oliveira-Filho et al., 1997; Gomes et al., 2003; Guimarães et al., 2008; Carvalho and Felfili, 2011; Fontes and Walter, 2011). Comparatively, the role of fire in shaping vegetation communities in the region has received little attention. Some studies have examined post-fire regeneration of forest vegetation or savanna individually (Hoffman, 1996, 1999; Rodrigues et al., 2005) or focused on responses of target species (Hoffmann et al., 2009) but to the best of our knowledge, there have been no studies comparing the differences in post-fire plant regeneration and vegetation dynamics between vegetation types. With an aim to answer the question of how post-fire community structure and dynamics will differ across different vegetation types in a forest-savanna mosaic, we made use of an opportunity to study plant regeneration in an upland area in southeast Brazil, after a fire in late 2011. Using the ASS framework as a context for this study, we hypothesize that after a fire, plant communities of closed forests, savannas, and their ecotones will differ in species diversity, community structure, and short-term temporal dynamics. Because closed forests are characterized as species-rich communities with massive regeneration after disturbance (Richards, 1996; Hiratsuka et al., 2006), we predict that this vegetation type will exhibit the highest tree species diversity, density, basal area and abundance of regenerating tree seedlings throughout the census period, followed by ecotones and savanna. Additionally, because ecotones are considered to be zones of rapid change in response to environmental change (Allen and Breshears, 1998; Kark and van Rensburg, 2006), we predict that regenerating ecotones will have the most rapid growth, highest mortality and turnover, followed by closed forests and then savanna.

2. Materials and methods 2.1. Study site and vegetation sampling Our study site was located in a privately-managed park, the Bonito River Ecological Cascades Park (Parque Ecológico Quedas do Rio Bonito; 21°200 0900 S and 44°580 4900 W, 1100–1300 m a.s.l.), near the city of Lavras, Minas Gerais, Brazil (Fig. 1). The park covers an area of 235 ha, and experiences a subtropical climate with mild summers and winter drought and an average temperature of 19.3 °C (Oliveira-Filho and Fluminhan-Filho, 1999). The average annual precipitation at the site is 1490 mm, with 67% of the rainfall concentrated between the months of November to February and peaking in December (Dalanesi et al., 2004). Geographically, the park is situated in Serra do Carrapato, a part of the Serra da Bocaina complex. The underlying geology of the region consists of granitic gneisses, quartzites and micaschists, giving rise to predominantly Cambisols in the valley areas and Litholic Neosols in plateau areas (Curi et al., 1990). Our study site falls broadly within a biome transition area between closed forest (Atlantic Domain) and savanna (Cerrado Domain) and the vegetation of the park is well-documented and mapped (Oliveira-Filho and Fluminhan-Filho, 1999; Dalanesi et al., 2004). The vegetation consists of a mosaic of closed forests (locally classified as semideciduous Atlantic forests; Oliveira-Filho and Fontes, 2000) and savannas dominated by short trees and grasses (Table 1). The closed forests occupy over deep poorly to moderately drained soils in within valleys and on slopes while the savannas occur over shallow, strongly-drained soils on plateaus and gentler sloping topography. Bands of ecotonal vegetation up to 200 m wide occur inbetween the closed forest and savanna vegetation on moderately drained soils of intermediate depth, and these ecotones are characterized by the presence and dominance of Eremanthus erythropap-

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pus (Asteraceae) in the canopy (Table 1; Oliveira-Filho and Fluminhan-Filho, 1999). On the 8th-23th September 2011, a fire burnt 170 ha (72% of the area) of the park (Jornal de Lavras, 2011), affecting all the three main vegetation types. A preliminary inspection after the fire revealed that the closed forests did not suffer from canopy fire (scorch height 5–7 m) but the understorey stratum under this scorch height was entirely burnt and/or killed. In the savanna and ecotones where trees were shorter (<4 m and up to 7 m respectively), crown scorch was noted, and smaller trees and shrubs in the understorey stratum of the ecotone were entirely burnt and/or killed. The fire in September was followed immediately by the onset of rains in October (total rainfall: 132 mm) peaking in January 2012 (total rainfall of 530 mm; Fig. A.1; INMET, 2012) by which time plant regeneration was conspicuous. 2.2. Plot sampling

Fig. 1. The study site (a) at the River Bonito Ecological Cascades Park (Parque Ecológico Quedas do Rio Bonito) in the Municipality of Lavras, Minas Gerais, Brazil. Inset shows the broader location of the study site within Minas Gerais (grey shading). Points on the map denote 2 m  2 m vegetation sampling plots allocated across a closed forest, ecotone and savanna vegetation mosaic and are enlarged for emphasis. A non-metric multidimensional scaling ordination (b) of juvenile tree stem abundance data of the plots demonstrate the floristic segregation of the three vegetation types. In addition to other characteristics like canopy closure and height (see Table 1), permutated multivariate analysis of variance (PERMANOVA) testing for differences in floristic composition across plot types showed a significant difference (F2,43 = 6.377, P = 0.0049), and plot type pair-wise comparisons were all significant (Bonferroni-corrected a of 0.1/3 tests = 0.033).

In January 2012, we carried out an experiment to study tree regeneration in three putative different vegetation types in the landscape four months after the September 2011 fire. Forty-six 2  2 m (4 m2) plots were randomly allocated within burnt areas, resulting in 18 closed forest, 17 ecotone and 11 savanna plots (Fig. 1a), based on a pre-established vegetation classification for the area and a number of structural criteria and the abundance of certain indicator species that were observable in the field (Table 1). Because of the sloping terrain, we had to allocate our plots taking into account safety of access and also the pattern of burning across the landscape, resulting in some closed forest and ecotone plots being more clumped (Fig. 1a). Within each plot, we tagged, identified and measured all juvenile stems of trees species (5 cm stem diameter at soil level). Necessarily, our plots encompassed a range of fire severities described previously across the three vegetation types, but within each vegetation type we situated plots at spots where it was observable that all living vegetation had been burnt. Also, we positioned our plots away from the bases of established trees to ensure that the stem basal area was not dominated by pre-established individuals, and to avoid biasing our data with basal resprouts from these trees. To track temporal patterns of plant regeneration within our plots, we carried out two subsequent recensuses in January 2013 and 2014 respectively, where we re-measured all previously tagged individuals, noted mortality, and identified and measured new individuals. 2.3. Data analysis

Table 1 Characteristics of the studied vegetation types within the Bonito River Ecological Cascades Park, Minas Gerais, southeast Brazil. Vegetation type

Number of plots

Characteristics

Closed forest

18

Ecotone

17

Savanna

11

Canopy 15–22 m high, consisting of a mix of evergreen and deciduous tree species. Locally known as semideciduous forests, a subtype of the Atlantic forest domain. Scorch marks up to 7 m observed after the 2011 fire A marginal forest community to 7 m high (maximum 12 m) with a broken canopy and containing an element of both semideciduous forest and savanna woody species. Conspicuously, this community has a high occurrence of Eremanthus erythropappus (DC.) Macleish), ‘‘candeal” (Oliveira-Filho and Fluminhan-Filho, 1999; Dalanesi et al., 2004) Open-canopied savanna (‘‘Cerrado”) dominated by short trees 4 m, shrubs and grass (‘‘campo cerrado”; Goodland 1971). Formed over shallow soils on rocky substrates

To provide a context for the study and to summarize initial species composition data in 2012, we performed an ordination of our species abundance data using non-metric dimensional scaling in R. We performed non-metric multidimensional scaling ordinations using the ‘metaMDS’ function of the package ‘vegan’ (v 1.13–8) in R statistical software (R Foundation for Statistical Computing, Vienna, AT) and transformed (Wisconsin standardization and square root transformation) abundance data for all tree species (Oksanen et al., 2013) (Fig. 1b). To detect trends in species diversity and vegetation structure, we compared species richness of total live stems (surviving and new stems) in a given year by constructing stem-based rarefaction curves using the iNEXT package (Hsieh et al., 2015) for plots within each of the three vegetation types, based on the formulation by Hurlbert (1971). These rarefaction curves plot the number of species sampled with the addition of each stem, and this stem-based (rather than plot-based) analysis was employed to allow for different densities between the three vegetation types (Gotelli and Colwell, 2001). Species diversity was expressed in terms of

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Shannon-Wiener indices (H’) and Pielou evenness (J) (Brower and Zar, 1984). Vegetation structural characteristics were expressed in terms of stem density and basal area (Mueller-Dombois and Ellenberg, 1974). To parameterize temporal vegetation dynamics, we calculated the following for each plot between the first (2012) and final census (2014): mortality (M) and recruitment (R) for the total number of individual stems (N); Gain (G) and Loss (L) for basal area (BA) (Sheil and May, 1996). From these rates we calculated the turnover (T) and net change for the number of individuals (TNN and DN respectively) and basal area (TNBA and DBA respectively) as follows: M = (1  ((N0  m)/N0)1/t)  100; R = (1  (1  r/Nt)1/t)  100 TNN = (M + R)/2; DN = [(Nt/N0)1/t  1]  100; G = (1  [1  (BAr + BAg)/BAt)1/t)  100; L = (1  [(BA0  (BAm + BAl))/BA0)1/t)  100; TNBA = (L + G)/2; DBA = [(BAt/BA0)1/t  1]  100 In the above equations, N0 and BA0 refer respectively to the initial number of individuals and their collective basal area; t is the time interval between surveys; m and BAm to the number of dead individuals and their basal area; r and BAr to the number of recruits and their basal areas; Nt and BAt to the number of individuals and their basal area at the final census; BAg to the basal area gained, and; BAl to the basal area lost (Korning and Balslev, 1994). All vegetation dynamics parameters are expressed in% year1. To test for differences in vegetation parameters across vegetation types, we fitted a set of linear mixed effects models using M, R, TNN, DN, Gain, Loss, and TNBA and DBA as response variables, and vegetation type as a fixed effect. We included plot coordinates as a random factor using the corStruct function in the ‘‘nlme” package in R to address spatial autocorrelation issues in our lme models. This function calculates the semi-variogram for the withingroup residuals and adds the semi-variogram of the corStruct element into the model, thus adjusting the model results to account for the spatial distances between plots. Because the ecotones represent a tree-dominated forest vegetation, we also ran another set of models fitting vegetation dynamics parameters using both forest vegetation types (closed forest and ecotone) as a combined category for comparison with savanna. For a multiple comparison between vegetation types, we used the ‘glht’ function in the ‘multcomp’ package (Hothorn et al., 2008). 3. Results Within our 46 plots, we sampled in 2012 a total of 2923 individual juvenile stems comprising 158 tree species from 95 genera and 49 botanical families. Among the individuals sampled, 45 species (28.5%) were only represented by a single individual. The Myrtaceae was the most species-rich family (30 species), followed by the Fabaceae (16 species) and the Melastomataceae (14 species), the Lauraceae (12 species), and the Euphorbiaceae (9 species). Subsequently in 2013 and 2014, we re-measured 1829 and 1489 individuals respectively in the plots. 3.1. Diversity and structural patterns Over the three censuses, the pattern of stem-based species accumulation was similar within vegetation types. Consistently, closed forests exhibited the highest species richness, and their species accumulation curves overlapped in their 95% confidence inter-

val with the ecotone across all the three censuses. In contrast, savanna plots had the least number of species, and their 95% confidence interval did not overlap with either ecotone or closed forest in any of the censuses (Fig. 2). Closed forests and ecotones exhibited an increase in terms of Shannon’s (H0 ) index, and was consistently higher than in savanna (Fig. 3a; Table A.1). Likewise, Evenness (J0 ) exhibited the same increasing trend, but the differences between the three vegetation types were slight (Fig. 3b; Table A.1). Stem density exhibited an overall decrease across the census years (Fig. 3c; Table A.2), whereas basal area showed an increase (Fig. 3d). In general across all years, closed forest had the highest stem densities and savanna the lowest. For basal area, closed forest had the highest mean basal areas in 2012 and this increased almost threefold in 2013, but dropped again in 2014 (Fig. 3d). Both ecotone and savanna exhibited the same trend, and had very similar starting basal area values throughout (Fig. 3d). 3.2. Vegetation dynamics patterns Among the vegetation dynamics responses tested, only mortality and turnover in the number of individuals were significantly predicted by vegetation type (Table 2; Tables A.3, A.4). Mortality was significantly different between the combined forests (closed forest and ecotone plots) and savanna (Fig. 4a; Table 2), but support for the relationship was lacking in the model with the three vegetation types (Fig. 4b; Table 2). Likewise for the turnover in the number of individuals, we found significant differences between the combined forests and savanna plots. Additionally, our multiple comparisons between vegetation types show that the net change in number of individuals was significantly lower in the savanna than closed forest and ecotone (Table 2; Fig. 4a). 4. Discussion Ecological theory predicts that post-fire dynamics of closed forest and savannas will differ, but little data is available for ecotones. Ecotones in particular, are in need of a more robust ecological basis to underpin management and conservation, and to guide fire management policies. After a fire in late 2011 burnt a vegetation mosaic consisting of closed forests, savannas and their ecotones, we monitored the post-fire dynamics of regenerating individuals from plots of these vegetation types for three successive years. We found overall differences in post-fire vegetation parameters between forest and savanna plots, particularly relating to the changes in stem basal area, mortality and turnover in the number of individuals. In addition, the balance of our results indicates that ecotones are more akin to closed forest in terms of post-fire responses. 4.1. Diversity and structural patterns Significant changes in vegetation structure may be expected during secondary succession in forest communities (Chazdon, 2008), and indeed, we found that the regeneration of burnt closed forest, ecotones and savanna vegetation was marked by high stem densities two month after fire in 2012, consistent with other studies on post-disturbance plant regeneration (Capers et al., 2005; Duah-Gyamfi et al., 2014; Dupuy and Chazdon, 2008; Balch et al., 2013). As expected, species diversity and vegetation structure differed between closed forest and savanna (Hoffmann et al., 2003; Banfai and Bowman, 2005). Additionally, species richness and diversity in the ecotones were more similar to closed forests than to savanna, in corroboration with the floristic similarities between the two vegetation types (Fig. 1). Moreover, despite the passage of

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Fig. 2. Stem-based rarefaction curves with 95% confidence intervals of estimated species richness in 46 closed forest, ecotone, and savanna plots (n = 18, 17, and 11 plots respectively) in 2012, 2013, and 2014.

Fig. 3. The annual change in Shannon’s diversity index (a), evenness (b), stem density (c), and basal area (d) of juvenile tree stems per hectare at each annual census across 46 closed forest, ecotone, and savanna plots (n = 18, 17, and 11 plots respectively) in the Bonito River Ecological Cascades Park, Minas Gerais, southeast Brazil. Standard error bars (±1 SE) are shown.

Table 2 Results of generalized linear mixed effects models of vegetation dynamics rates (2012–2014) fitted to vegetation type as a fixed effect and plot coordinates as a random effect to account for spatial autocorrelation in the Bonito River Ecological Cascades Park, Minas Gerais, southeast Brazil. The All forests-savanna models consider both Closed forest and Ecotone as forest vegetation while the Closed forest-ecotone-savanna models considers all vegetation types separate. Only models with significant effects (P < 0.05) are shown (see Appendix Table A.1 for results of all models). Mortality Estimate

Turnover in number of individuals SE

t-value

p-value

Random residual

AIC

Estimate

SE

t-value

p-value

Random residual

AIC

0.091 0.073

5.952 2.086

>0.001*** 0.043*

0.21

3.093

0.538 0.091

0.051 0.042

10.456 2.191

>0.001*** 0.034*

0.118

49.422

Closed forest-ecotone-savanna Intercept 0.542 0.098 Ecotone 0.006 0.075 Savanna 0.156 0.083

5.505 0.079 1.894

>0.001*** 0.938 0.065

0.212

8.442

0.541 0.008 0.095

0.056 0.044 0.047

9.655 0.188 2.018

>0.001*** 0.852 0.049*

0.12

43.035

All forests-savanna Intercept 0.539 Savanna 0.153

a wildfire, these diversity patterns were maintained, suggesting resilience of species inhabiting these vegetation types (Figs. 2 and 3). In terms of structure however, we found that regenerating stem densities in the ecotone appeared to be intermediate between closed forest and savanna, while the stem basal areas were more

similar to savanna. (Fig. 3), which suggests that the environment in the ecotone may have been less suitable for post-fire plant regeneration than closed forest. Propagule pressure can influence post-fire regeneration (Colautti et al., 2006; Gómez-González et al., 2011) and also appears to play a strong role in the patterns we observed. Not sur-

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Fig. 4. Boxplots showing the percentage mortality and the turnover in the number of individuals between 2012 and 2014 in Forests (combined Closed forest and ecotone; n = 35) vs. savannas (n = 17) plots (a, c), and in closed forest (n = 18), ecotone (n = 17) and savanna (n = 11) plots (b, d) in the Bonito River Ecological Cascades Park, Minas Gerais, southeast Brazil. Each box encompasses the 25th to 75th percentiles; the median is indicated by the horizontal line within the box and the other horizontal lines outside the box indicate the 10th and 90th percentiles. Dots indicate outliers. Significant differences between vegetation types are indicated by different letters based on post hoc multiple comparisons following model fitting (see Table 2).

prisingly, the regenerating species in each plot was relatively filial to the vegetation type in which the plot was situated (OliveiraFilho and Fluminhan-Filho, 1999; Dalanesi et al., 2004), and there are a number of species worthy of mention which may have influenced these differences in post-fire vegetation dynamics patterns. For instance, Croton urucurana (Euphorbiaceae) and Eremanthus erythropappus (Asteraceae) were the two most abundant species of juvenile stems we encountered in the study. Croton urucurana regeneration was abundant in the closed forest and ecotone plots (41% and 40% of the total individuals in these plots respectively), suggesting massive regeneration from a seed bank. Interestingly, the regeneration of the species Eremanthus erythropappus (Asteraceae) was proportionally greater in savanna plots (55% of the individuals) than in ecotones (13% of individuals), even though adult trees were the dominant species in the latter vegetation type. This species has light wind-dispersed seeds and is a characteristic component of closed forest-savanna ecotones in the region, but is also known to be able to colonize open environments (OliveiraFilho and Fluminhan-Filho, 1999).

4.2. Vegetation dynamics We had expected ecotones to exhibit the fastest dynamics among the three vegetation types, but this expectation was not supported by our findings. It is possible that recruitment, mortality and some density-related parameters may not show large differences in the short term, or in a fire that is not stand-replacing. However, we found that when closed forest and ecotones plots were combined, their overall mortality was significantly higher than in the savanna. This possibly reflects overall differences in the regeneration niches between forest and savanna vegetation, since species regenerating in forest typically exhibit high mortality

due to self-thinning, while species in savanna species often regenerate strongly by resprouting (Ondei et al., 2016). The turnover in the number of individuals was significantly higher in closed forest than in savanna plots as we predicted. Contrary to our expectations, ecotone plots were not significantly different from closed forest in this parameter. One explanation why savanna exhibited low turnover in the number of individuals relative to forests could be due to resource limitations. For instance, low phosphorus is a well-known feature of savanna soils (Goedert, 1983; Lilienfein et al., 2000) and may be a limiting factor for turnover of individuals in savanna plots. Also, the savanna soils at our study site and elsewhere in southeastern Brazil exhibit high concentrations of aluminum (Oliveira-Filho and Fluminhan-Filho, 1999; Ruggiero et al., 2002; Dalanesi et al., 2004), which may be inhibitive for the regeneration of some species (Ma et al., 2001). Additionally, rocky substrates such as granitic gneiss, and the accompanying shallow soils typical of higher altitude savannas may be an environmentally harsh place for plant establishment (Porembski, 2007; Vasconcelos, 2011). Such substrates may inhibit plant growth and basal area increment through limitations on root growth (Botkin et al., 1972; Kozlowski, 1999). However, we did not detect significant difference in this parameter between vegetation types, possibly due to the short time period of monitoring.

4.3. Synthesizing patterns in an alternative stable states framework The differences between closed forest and savanna are in line with these two vegetation types being alternative stable states (Warman and Moles, 2009; Murphy and Bowman, 2012). This framework posits that forest and savanna are controlled by different environmental drivers such as water availability, fire frequency, and vegetation feedbacks respectively, which play important roles in enabling these vegetation types to co-exist in

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an area under the same climatic envelope. Collectively these environmental drivers create a ‘‘basin of attraction” in which the ecosystem state is maintained (Warman and Moles, 2009; Tng et al., 2014). For instance, the massive regeneration of almost exclusively forest species within our closed forest plots reflect the maintenance of the forest stable state, and likewise, plant regeneration in the savanna was characterized by many species filial to savanna. The post-fire vegetation dynamics and also the species composition of the ecotone resembled more strongly that of closed forests than savanna, and thus we may speculate that ecotones lie within the closed forest ‘‘basin of attraction”, albeit within a shallow trench. However, it would be premature to assume that these patterns are universally-applicable on forest-savanna ecotones, and longer term vegetation dynamics data and perhaps communityweighted plant trait comparisons (Tng et al., 2013) may be helpful in providing more insights. 5. Conclusions Monitoring natural regeneration after fire enables us to compare the differences in vegetation dynamics between closed forests, ecotones and savannas and to synthesize a better understanding of mosaic vegetation responses to fire. Responses in diversity patterns were conspicuously different between closed forest/ecotone and savanna but temporal regeneration patterns were less explicit in the two years following a fire. Overall, ecotones are more ecologically similar to closed forests than savanna in their diversity and dynamics responses, and may therefore have similar management needs. This conclusion has implications for management on the local and regional level, and requires further investigation. Experimental burns (Balch et al., 2013) are a potential next step to fine-tune our understanding of how much fire disturbance is need to shift or maintain closed forest – savanna boundaries, and also to understand species-level feedbacks. Conflicts of interest The authors declare that they have no conflicts of interest. Acknowledgements We thank the Coordination for the Improvement of Higher Education Personnel (CAPES) and Fundação de Amparo à Pesquisa de Minas Gerais (FAPEMIG) for financial support during the study, and the management at the Parque Ecológico Quedas do Rio Bonito for site access. DYPT was supported by an Australian Endeavour Fellowship, and DMGA by a Schlumberger Foundation Faculty of the Future Fellowship. FDCA, DYPT, DMGA and RMS conceived and designed the experiments. Our funding sources played no role in the study design; data collection, analysis, interpretation and write-up; and in the decision to submit the article for publication. FDCA, DMGA, PAC, DGSP and RMS conducted fieldwork. FDCA, DYPT and DMGA, analyzed the data. FDCA, DYPT, DMGA and PAC wrote the manuscript; other authors provided editorial advice. We also thank David Bowman for valuable discussions on the study, Vinicius Dantas for critically pre-reviewing an earlier draft of the manuscript, and two anonymous reviewers for their suggestions which greatly improved the manuscript. Appendix A. Supplementary material Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.foreco.2017.05. 058.

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