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1. Introduction
Fire has been occurring in the Brazilian savannas (Cerrado) for 10 million years and is associated with physiognomies where grasses and herbs are present (Simon et al., 2009; Simon and Pennington, 2012). Cerrados usually border more closed vegetation types, as forests, and if a burning happens, fire will affect plants from both cerrado and forest. However, tree species of gallery forests are less tolerant to fire than savanna species (Hoffmann et al., 2012), and although little is known about what happens with the forest understory after a burning event, we could expect a fire-sensitive forest understory when compared to a fire-adapted cerrado ground-layer.
In the absence of fire, most herbs tend to grow and reproduce during the wet season (Sarmiento, 1984; Batalha and Martins, 2004). Thus, a fire that occurs in the dry season would remove the dry biomass (Ramos-Neto and Pivello, 2000) and stimulate a fast recovery of the non-woody species after the first rains (Gottsberger and Silberbauer-Gottsberger, 2006; Munhoz and Amaral, 2010). The effects of burning on reproduction may be more complex though. Some studies conducted in Cerrado areas have shown that herbaceous species are able to flower and fruit shortly after fires (Coutinho, 1976; César, 1980; Munhoz and Felfili, 2007); while in a grassland in the South of Brazil, Fidelis and Blanco (2014) showed some species only reproducing more than one year after fire.
In addition to the complexity of this issue, most researchers have conducted only a few months of observations after fire and almost none of them have evaluated the post-fire phenology patterns of a cerrado sensu stricto-gallery forest ecotone. So, we aimed to describe the reproductive activity (flowering + fruiting) of the ground layer vegetation after a fire event along a savanna-forest boundary during 16 months after an accidental fire.
2. Material and Methods
2.1. Site description
The study was performed at the IBGE (Instituto Brasileiro de Geografia e Estatística) Ecological Reserve, located 35 km south of Brasilia, in the Federal District of Brazil (15º55’-15º58’ S and 47º52’-47º55’ W), at an elevation of 1,100 m. The Reserve encloses different Cerrado vegetation physiognomies, such as grasslands, savanna (cerrado sensu stricto), woodlands and gallery forests (Ribeiro, 2011). The average annual rainfall recorded at IBGE meteorological station is 1,461 mm (1980-2008), with a well-defined dry season from May to September and a mean annual temperature of 22.5 °C (Paiva et al., 2015). At the time this study was performed (2011-2013) yearly rainfall was 1,418 mm; driest months were from June to August, when burnings can happen (RECOR, 2013). Soils at the reserve are deep well-drained oxisols (Ribeiro, 2011).
2.2. Sampling design
The research was carried out at the boundary between gallery forest and savanna. Six transects were positioned perpendicularly to the boundary; each transect was 10 m × 70 m and extended 30 m into the savanna, 10 m into the border and 30 m into the forest. An accidental fire occurred in September 2011 and burned savanna and forest environments, which had only burned once in the previous 35 years due to a policy of fire suppression in the reserve (Ribeiro, 2011). This accident gave us the chance to observe post-fire flowering and fruiting of herbs. We did not have data from non-burned areas, but we checked dates of collected fertile material of the studied species from SpeciesLink website to make comparison possible (SpeciesLink, 2016).
During the 16 month post-fire survey, we registered ground layer species with flowers and/or fruits in all transects, as the majority of herbs species had rapid flowering and fruiting, that overlapped in time. In the first four months, survey was fortnightly (seven surveys total) because of the quick post-fire response of herbs (Coutinho, 1976). After this period and until January 2013 the surveys were done seasonally (in the beginning, middle and end of each season), which added up to six surveys. Fertile material was herborized, identified and deposited at Herbário da Universidade de Brasília. For plant family classification, we used the Angiosperm Phylogeny Group III (APG III, 2009). Ground layer plants, e.g, grasses, herbs, vines and subshrubs shorter than 1.5 m were considered herb species (Rizzini, 1997).
To test whether cerrado, border and gallery-forest herbaceous species reproduced uniformly through the first year post-fire (from October 2011 to October 2012), we applied Rayleigh test (Zar, 1999). Statistical analyses were performed using the R version 3.2.1 (R Development Core Team, 2013).
3. Results
We registered 170 herb species flowering or fruiting during the study time, distributed in 37 families. The most abundant families were Asteraceae, Fabaceae and Poaceae (each with 22, 22 and 21 species, respectively), followed by Cyperaceae, Euphorbiaceae, Malphigiaceae, Myrtaceae and Rubiaceae (with eight species each), which altogether represented 62% of the richness. Three species were exotic/invasive (Ageratum fastigiatum, Melinis minutiflora and Sida linifolia). We found 158 species in savanna (90 species were exclusive of this environment) and 17 species in the gallery forest (only four species exclusive to this vegetation). Five species were common among the gallery forest, cerrado and border (Bauhinia rufa, Cyperaceae sp.1, Croton antisyphiliticus, Melinis minutiflora, Psychotria cf. nemorosa; Table 1).
Table 1 Post-fire reproductive period of herbs through the study time in a savanna-forest boundary in IBGE Ecological Reserve, Brasília, DF, Brazil.
| Family | Species | Habitat | 2011 | 2012 | 2013 | Non fire | |||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Oct | Nov | Dec | Jan | Mar | May | Aug | Oct | Dec | Jan | ||||
| Acanthaceae | Justicia pycnophylla Lindau * | c | *** | Dec-Feb | |||||||||
| Ruellia dissitifolia (Nees) Hiern | c | *** | Sep-Nov | ||||||||||
| Ruellia sp. * | c, b | *** | *** | - | |||||||||
| Amaranthaceae | Gomphrena arborescens L.f. | c | *** | Nov-Feb | |||||||||
| Anacardiaceae | Anacardium humile A.St.-Hil. | c, b | *** | *** | Jun-Oct | ||||||||
| Apocynaceae | Barjonia cf. cymosa E.Fourn. *+ | c | *** | May-Jun | |||||||||
| B. cf. erecta (Vell.) K.Schum. + | c | *** | *** | *** | Feb-Jun | ||||||||
| Mandevilla cf. longiflora (Desf.) Pichon * | c, b | *** | Oct-Jan | ||||||||||
| M. illustris (Vell.) Woodson * | c | *** | *** | Oct-Dec | |||||||||
| Oxypetalum erectum Mart. * | c | *** | Nov-Feb | ||||||||||
| Asteraceae | Achyrocline satureioides (Lam.) DC. | m | *** | *** | Feb-Oct | ||||||||
| Ageratum fastigiatum (Gardner) R.M.King & H.Rob. | m, b | *** | *** | *** | *** | *** | *** | Mar-Jul | |||||
| Aspilia cf. foliacea (Spreng.) Baker | c, b | *** | *** | *** | *** | *** | Sep-Nov | ||||||
| Asteraceae sp.1 | c | *** | *** | *** | *** | - | |||||||
| Asteraceae sp.2 | c | *** | *** | - | |||||||||
| Asteraceae sp.3 | c, b | *** | *** | - | |||||||||
| Baccharis tridentata Vahl + | c | *** | Jan-Feb | ||||||||||
| Bidens graveolens Mart. | c | *** | *** | Jan-Apr | |||||||||
| Campuloclinium megacephalum (Mart. ex Baker) R.M.King & H.Rob. | c, b | *** | *** | *** | *** | Jan-Mar | |||||||
| Chaptalia integerrima (Vell.) Burkart | c, b | *** | *** | *** | Sep-Nov | ||||||||
| Chromolaena cf. maximiliani (Schrad. ex DC.) R.M.King & H.Rob. + | m | *** | Apr-Jun | ||||||||||
| C. chaseae (B.L. Rob.) R.M. King & H. Rob | c, b | *** | *** | *** | *** | Mar-May | |||||||
| C. stachyophylla (Spreng.) R.M.King & H.Rob. * | c, b | *** | *** | *** | *** | Sep-Nov | |||||||
| Elephantopus elongatus Gardner | c, b | *** | *** | Feb-Mar | |||||||||
| Emilia sonchifolia (L.) DC. ex Wight | c | *** | *** | *** | *** | Whole year | |||||||
| Lessingianthus compactiflorus Mart. ex Baker) H.Rob. | c, b | *** | *** | *** | Feb-Mar | ||||||||
| L. erythrophilus (DC.) H.Rob. * | c | *** | *** | *** | Nov-Dec | ||||||||
| L. ligulifolius (Mart. ex DC.) H.Rob. | c | *** | *** | *** | Feb-Mar | ||||||||
| Riencourtia oblongifolia Gardner | c, b | *** | *** | *** | *** | *** | *** | Dec-Mar | |||||
| Vernonia aurea Mart. ex DC. + | c | *** | *** | Apr-May | |||||||||
| 2011 | 2012 | 2013 | |||||||||||
| Family | Species | Habitat | Oct | Nov | Dec | Jan | Mar | May | Aug | Oct | Dec | Jan | Non fire |
| Viguiera grandiflora (Gardner) Gardner | c, b | *** | *** | *** | Aug-Nov | ||||||||
| Wedelia bishopii H.Rob | c, b | *** | *** | *** | Dec-Mar | ||||||||
| Bignoniaceae | Anemopaegma arvense (Vell.) Stellfeld ex de Souza * | c | *** | *** | Sep-Nov | ||||||||
| Bignoniaceae sp.1 | c | *** | - | ||||||||||
| Fridericia sp. | c | *** | *** | - | |||||||||
| Bromeliaceae | Dyckia sp. | m | *** | - | |||||||||
| Clusiaceae | Kielmeyera abdita Saddi + | m, b | *** | *** | *** | *** | Oct-Apr | ||||||
| K. variabilis Mart. | c | *** | *** | *** | *** | Oct-Dec | |||||||
| Convolvulaceae | Ipomoea procurrens Meisn. | c | *** | *** | Dec-Mar | ||||||||
| Merremia contorquens (Choisy) Hallier f. | c | *** | *** | Jan-May | |||||||||
| Cyperaceae | Bulbostylis sp. | c | *** | - | |||||||||
| Bulbostylis cf. emmerichiae T.Koyama + | c | *** | *** | Sep | |||||||||
| B. pachypoda Kral & M.T.Strong *+ | c | *** | *** | Oct | |||||||||
| B. sphaerocephala (Boeckeler) C.B. Clarke | c | *** | *** | *** | *** | *** | Nov-Feb | ||||||
| Cyperaceae sp.1 | m, c, b | *** | *** | *** | *** | - | |||||||
| Rhynchospora albiceps Kunth | c, b | *** | *** | *** | *** | *** | *** | *** | Sep-Apr | ||||
| R. patuligluma C.B.Clarke ex Lindm. | c, b | *** | *** | Nov-Dec | |||||||||
| Scleria leptostachya Kunth | c | *** | *** | Jan-Mar | |||||||||
| Erythroxylaceae | Erythroxylum campestre A.St.-Hil. | c | *** | Aug-Nov | |||||||||
| E. cf. deciduum A.St.-Hil. | c, b | *** | *** | Sep-Jan | |||||||||
| E. cf. nanum A.St.-Hil. | c, b | *** | *** | Sep-Oct | |||||||||
| Euphorbiaceae | Croton antisyphiliticus Mart. * | m, c, b | *** | *** | *** | Sep-Nov | |||||||
| C. campestris A.St.-Hil. | c | *** | *** | *** | *** | Oct-Mar | |||||||
| C. cf. longinervius Müll.Arg. * | c, b | *** | *** | - | |||||||||
| C. goyazensis Mull.Arg. | c, b | *** | *** | *** | *** | *** | *** | *** | Jul-Sep | ||||
| Dalechampia caperonioides Baill. | c, b | *** | *** | *** | *** | *** | *** | *** | *** | Sep-Feb | |||
| Euphorbia sp. | m, b | *** | *** | *** | *** | *** | *** | *** | - | ||||
| Manihot gracilis Pohl * | c, b | *** | *** | Oct-Jan | |||||||||
| Sebastiania ditassoides (Didr.) Müll.Arg. * | c, b | *** | *** | *** | Sep-Nov | ||||||||
| Fabaceae | Fabaceae sp.1 | c | *** | *** | - | ||||||||
| Fabaceae sp.2 * | c | *** | - | ||||||||||
| Fabaceae sp.3 | c | *** | *** | - | |||||||||
| Fabaceae sp.4 | c, b | *** | - | ||||||||||
| 2011 | 2012 | 2013 | |||||||||||
| Family | Species | Habitat | Oct | Nov | Dec | Jan | Mar | May | Aug | Oct | Dec | Jan | Non fire |
| Fabaceae sp.5* | c | *** | - | ||||||||||
| -Caesalpinoideae | Bauhinia dumosa Benth. * | c | *** | Jul-Feb | |||||||||
| B. rufa (Bong.) Steud | m, c, b | *** | *** | *** | *** | *** | *** | Jan-May | |||||
| Chamaecrista cf. desvauxii (Collad.) Killip | c | *** | Jan-May | ||||||||||
| C. decrescens (Benth.) H.S.Irwin & Barneby | c | *** | *** | *** | *** | *** | Oct-Nov | ||||||
| C. orbiculata (Benth.) H.S.Irwin & Barneby | c, b | *** | *** | May-Aug | |||||||||
| -Faboidea | Centrosema bracteosum Benth. | c, b | *** | *** | *** | *** | *** | Oct-Dec | |||||
| Eriosema crinitum (Kunth) G.Don | c | *** | Oct-Mar | ||||||||||
| E. defoliatum Benth. | c | *** | *** | *** | *** | Jul-Sep | |||||||
| Galactia grewiaefolia (Benth.) Taub. * | c, b | *** | *** | *** | Sep-Nov | ||||||||
| Periandra mediterranea (Vell.) Taub. | c | *** | *** | Whole year | |||||||||
| Stylosanthes guianensis (Aubl.) Sw. | c | *** | *** | *** | Mar-Aug | ||||||||
| Papilionoideae sp.1 | c | *** | *** | - | |||||||||
| -Mimosoideae | Calliandra dysantha Benth. | c, b | *** | *** | May-Sep | ||||||||
| Mimosa cf. nuda Benth. | c, b | *** | *** | *** | Jan-Feb | ||||||||
| M. gracilis var. brevissima Barneby | c, b | *** | *** | *** | Feb-Mar | ||||||||
| M. lanuginosa Glaz. ex Burkart | c, b | *** | *** | Apr-Sep | |||||||||
| M. setosa Benth. | c | *** | *** | *** | Whole year | ||||||||
| Gentianaceae | Calolisianthus speciosus (Cham. & Schltdl.) Gilg + | c | *** | Apr-Jul | |||||||||
| Irlbachia speciosa (Cham. & Schltdl.) Maas + | c | *** | Mar-Jul | ||||||||||
| Iridaceae | Sisyrinchium restioides Spreng. * | c | *** | *** | Nov-Mar | ||||||||
| S. vaginatum Spreng. * | c | *** | *** | Oct-Apr | |||||||||
| Lamiaceae | Eriope crassipes Benth. | c, b | *** | *** | *** | *** | *** | Sep-Nov | |||||
| Hypenia macrantha (A.St.-Hil. ex Benth.) Harley | c, b | *** | *** | Apr-Oct | |||||||||
| Hyptis cf. peduncularis Benth. | c, b | *** | Jul-Aug | ||||||||||
| H. nudicaulis Benth. * | c | *** | Jan-Apr | ||||||||||
| H. villosa Pohl ex Benth. | c | *** | *** | *** | *** | Jan-Mar | |||||||
| Lamiaceae sp.1 * | c, b | *** | - | ||||||||||
| Marsypianthes cf. montana Benth. | c, b | *** | *** | *** | Sep-Oct | ||||||||
| Lythraceae | Cuphea linarioides Cham. & Schltdl. | m, b | *** | *** | *** | *** | *** | Oct-Dec | |||||
| C. spermacoce A.St.-Hil. | m, b | *** | *** | *** | *** | *** | *** | *** | *** | *** | Sep-Nov | ||
| Diplusodon oblongus Pohl + | c, b | *** | Jan-Mar | ||||||||||
| D. villosus Pohl | c, b | *** | *** | *** | *** | Jan-Apr | |||||||
| 2011 | 2012 | 2013 | |||||||||||
| Family | Species | Habitat | Oct | Nov | Dec | Jan | Mar | May | Aug | Oct | Dec | Jan | Non fire |
| Malphigiaceae | Banisteriopsis anisandra (A.Juss.) B.Gates | c, b | *** | *** | *** | Aug-Sep | |||||||
| B. campestris (A.Juss.) Little | c, b | *** | *** | *** | *** | Nov-Mar | |||||||
| Diplopterys cf. lutea (Griseb.) W.R.Anderson & C.C.Davis | c | *** | *** | Aug-Nov | |||||||||
| Heteropterys byrsonimifolia A.Juss. | c | *** | Sep-Oct | ||||||||||
| Malphigiaceae sp.1 | c, b | *** | *** | - | |||||||||
| Malphigiaceae sp.2 * | c | *** | - | ||||||||||
| Peixotoa goiana C.E.Anderson + | c, b | *** | *** | *** | *** | Apr-Jul | |||||||
| Pterandra pyroidea A.Juss. | c, b | *** | Sep-Oct | ||||||||||
| Malvaceae | Byttneria scalpellata Pohl | c, b | *** | *** | *** | *** | Oct-Jan | ||||||
| Malvaceae sp.1 | c | *** | *** | - | |||||||||
| Pavonia rosa-campestris A.St.-Hil. | c, b | *** | *** | *** | *** | *** | *** | *** | Jun-Oct | ||||
| Sida linifolia Cav. * | c | *** | *** | *** | Mar-May | ||||||||
| Melastomataceae | Leandra cf. lacunosa Cogn. | c, b | *** | *** | *** | *** | *** | *** | *** | Aug-Nov | |||
| Ossaea congestiflora (Naudin) Cogn. | c | *** | Dec-Feb | ||||||||||
| Menispermaceae | Cissampelos ovalifolia DC. * | c | *** | *** | Oct-Dec | ||||||||
| Myrtaceae | Campomanesia adamantium (Cambess.) O.Berg | c | *** | Sep-Nov | |||||||||
| C. pubescens (Mart. ex DC.) O.Berg | c, b | *** | *** | Sep-Nov | |||||||||
| Myrcia decrescens (O.Berg) Mattos | c | *** | Aug-Nov | ||||||||||
| M. linearifolia Cambess. | c, b | *** | *** | *** | *** | Jul-Oct | |||||||
| M. torta DC. | c, b | *** | *** | *** | *** | *** | *** | *** | Sep-Nov | ||||
| Myrtaceae sp.1 | c | *** | - | ||||||||||
| Myrtaceae sp.2 | c | *** | - | ||||||||||
| Myrtaceae sp.3 | c, b | *** | - | ||||||||||
| Ochnaceae | Ouratea floribunda (A.St.-Hil.) Engl. | c | *** | *** | *** | Aug-Nov | |||||||
| Orchidaceae | Habenaria petalodes Lindl. | m, b | *** | *** | *** | Mar-Apr | |||||||
| Oxalidaceae | Oxalis cordata A.St.-Hil. | c | *** | *** | Oct-Jan | ||||||||
| O. densifolia Mart. & Zucc. ex Zucc. | c | *** | Jul-Oct | ||||||||||
| O. suborbiculata Lourteig | m, b | *** | *** | *** | *** | *** | *** | Oct-Nov | |||||
| Phytolaccaceae | Phytolacca thyrsiflora Fenzl. ex J.A.Schmidt | m | *** | *** | *** | *** | Oct-Mar | ||||||
| Poaceae | Andropogon leucostachyus Kunth * | c | *** | *** | Nov-Jan | ||||||||
| Andropogon sp. * | c | *** | - | ||||||||||
| Axonopus cf. marginatus (Trin.) Chase | c, b | *** | *** | *** | Nov-Dec | ||||||||
| 2011 | 2012 | 2013 | |||||||||||
| Family | Species | Habitat | Oct | Nov | Dec | Jan | Mar | May | Aug | Oct | Dec | Jan | Non fire |
| A. siccus (Nees) Kuhlm. | c | *** | *** | Jan-Mar | |||||||||
| Echinolaena inflexa (Poir.) Chase | c, b | *** | *** | *** | *** | *** | *** | *** | Dec-May | ||||
| Elionurus muticus (Spreng.) Kuntze * | c, b | *** | *** | *** | Sep-Nov | ||||||||
| Ichnanthus cf. camporum Swallen | c | *** | *** | *** | Jan | ||||||||
| I. procurrens (Nees ex Trin.) Swallen | c | *** | Oct-Mar | ||||||||||
| Imperata brasiliensis Trin. * | c, b | *** | *** | *** | Sep-Nov | ||||||||
| Leptocoryphium lanatum (Kunth) Nees * | c | *** | Oct-Dec | ||||||||||
| Melinis minutiflora P.Beauv. | m, c, b | *** | *** | *** | *** | *** | May-Jul | ||||||
| M. repens (Willd.) Zizka + | c | *** | Apr-Jun | ||||||||||
| Panicum olyroides Kunth | c | *** | Jan-Mar | ||||||||||
| Panicum sp. | c | *** | *** | - | |||||||||
| Paspalum ammodes Trin. * | c | *** | *** | Oct-Dec | |||||||||
| P. cf. geminiflorum Steud. | c, b | *** | *** | *** | *** | *** | Mar-May | ||||||
| P. cf. pectinatum Nees ex Trin. * | c, b | *** | *** | Oct-Dec | |||||||||
| P. erianthum Nees ex Trin. | c, b | *** | *** | *** | *** | *** | Sep-Dec | ||||||
| P. eucomum Nees ex Trin. | c | *** | *** | Mar-May | |||||||||
| Paspalum sp. | c | *** | *** | *** | *** | - | |||||||
| Trachypogon spicatus (L.f.) Kuntze + | c | *** | *** | Jan-Apr | |||||||||
| Rhamnaceae | Crumenaria erecta Reissek * | c | *** | *** | Sep-Oct | ||||||||
| Rubiaceae | Palicourea coriacea (Cham.) K.Schum. | c | *** | Oct-Dec | |||||||||
| P. officinalis Mart. | c, b | *** | *** | Nov-Dec | |||||||||
| Psychotria cf. nemorosa Gardner | m, c, b | *** | *** | Jan-Apr | |||||||||
| Richardia grandiflora (Cham. & Schltdl.) Steud. | c | *** | *** | Jan-May | |||||||||
| Sabicea brasiliensis Wernham | c, b | *** | *** | Jan-Apr | |||||||||
| Spermacoce capitata Ruiz & Pav. | c | *** | *** | Feb-Jun | |||||||||
| S. cf. latifolia Aubl. | m, b | *** | *** | *** | *** | *** | *** | *** | Feb-Jun | ||||
| Tocoyena cf. formosa (Cham. & Schltdl.) K.Schum. | c | *** | Oct-Apr | ||||||||||
| Rutaceae | Esenbeckia grandiflora Mart. | c, b | *** | *** | *** | *** | Dec-May | ||||||
| Sapindaceae | Serjania erecta Radlk. + | c | *** | *** | *** | *** | Nov-Mar | ||||||
| Smilacaceae | Smilax goyazana A.DC. * | c | *** | *** | *** | Sep-Nov | |||||||
| Turneraceae | Piriqueta cf. sidifolia (Cambess.) Urb. * | c, b | *** | *** | Nov-Apr | ||||||||
| Turnera oblongifolia Cambess. * | c | *** | Oct-May | ||||||||||
| Umbelliferae | Eryngium juncifolium (Urb.) Mathias & Constance + | c | *** | Oct-Jan | |||||||||
| 2011 | 2012 | 2013 | |||||||||||
| Family | Species | Habitat | Oct | Nov | Dec | Jan | Mar | May | Aug | Oct | Dec | Jan | Non fire |
| Verbenaceae | Amasonia hirta Benth. | c | *** | *** | Jan-Mar | ||||||||
| Lippia lupulina Cham. | c | *** | *** | *** | *** | Sep-Nov | |||||||
| L. cf. rotundifolia Cham. | c | *** | *** | May-Sep | |||||||||
| L. martiana Schauer | c | *** | *** | *** | Jan-May | ||||||||
| Stachytarpheta chamissonis Walp. | c | *** | *** | Dec-Apr | |||||||||
| Violaceae | Hybanthus lanatus (A.St.-Hil.) Baill. * | c, b | *** | *** | Sep-Oct | ||||||||
| Vitaceae | Cissus erosa Rich. | c, b | *** | *** | *** | *** | *** | Nov-Apr | |||||
| - | Indeterminada 1 | c | *** | *** | *** | - | |||||||
| - | Indeterminada 2 * | c | *** | - | |||||||||
b=border; c=cerrado (savanna); and m=gallery-forest; jan = january, ...nov = november and dec = december. Species that reproduced only in the first four months after fire are marked with an asterisk. Species that had a different post-fire reproductive period when compared with commonly registered phenological data are marked with a plus sign. The fire event took place on 9 September 2011. Non-fire data was collected at SpeciesLink website (SpeciesLink, 2016).
In savanna, herb reproduction peaked seven months after the fire event (57 species flowering and or fruiting at the end of the rainy season (r=0.1135, p=0.004; Figure 1). In the border, peak was in January, two months earlier than in cerrado (r=0.2567, p<0.0001; Figure 1). Gallery forest had no seasonality in understory post-fire flowering and fruiting (r=-0.1997, p=0.9065; Figure 1).
Figure 1 Number of herbs that reproduced through the first year after fire, in a savanna-forest boundary (☐ represents species that occurred in cerrado vegetation; ○, in the border; and ×, in forest), in IBGE Ecological Reserve, Brasília, DF, Brazil. The fire event took place on 9 September 2011 and thus, October is the first post-fire inventory.
We registered 38 species that reproduced only in the first four months after fire and that did not present reproductive structures during the rest of the survey (marked with a star sign in Table 1, these species occurred mainly in savanna). We also registered 16 species that had a different post-fire reproductive period when compared with commonly registered phenological data (marked with a plus sign in Table 1). Two species (Barjonia cymosa and Busbostylis pachypoda) had a single reproduction episode in the first four months after fire and at a different time from the normal pattern registered for both species.
4. Discussion
Among the species that flowered or fruited in the 16-month study, the most abundant families sampled were Asteraceae, Fabaceae and Poaceae. The same result was found in flora surveys realized in post-fire grassland areas in Distrito Federal (Munhoz and Amaral, 2010) and Mato Grosso do Sul (Neves and Damasceno-Júnior, 2011). In fact, such families are dominant in the non-woody flora of Cerrado (Mendonça et al., 1998; Filgueiras, 2002) and locally, in savanna and grassland areas in the IBGE Reserve protected from fire (Pereira and Silva, 2011).
Reproduction of cerrado species peaked about seven months after fire, at the end of the rainy season, which is expected in a seasonal vegetation, such as Cerrado (Batalha and Martins, 2004). The change in the observation interval of the reproductive events (from fortnightly to bimonthly) might have subsampled the community phenological patterns, but our results agree with Munhoz and Felfili (2007) and Tannus et al. (2006), which indicated a peak of flowering for the herbaceous community at the end of rainy season. In the border, the number of species with flowers and/or fruits was greater in the middle of the rainy season, therefore earlier than in savanna, that had its reproductive peak in the end of the rainy season. Although 63 species were common to both environments, species that started reproducing from March were exclusive of cerrado (Table 1).
It is well known that shading of ground-layer in riparian forests limits plant richness (Felfili et al., 2001), as we observed for the studied area (where only 17 species were registered in the forest when compared to the 158 species of cerrado). Fires in gallery forest generally cause extensive topkill to small trees (Hoffmann et al., 2009) and leaf-fall to larger diameter trees (personal observation), allowing increased light to the forest floor. Thus, we might expect that this higher light availability would stimulate understory species to reproduce. On the contrary, we noticed a fire-sensitive reproduction of the gallery-forest understory.
We registered 52 species (31%) that may have been influenced by fire changing their times of reproduction. Several factors can trigger flowering after fire, such as increase in light (Brewer, 1995), temperature and soil nutrients (Elzinga et al., 2007). However, Coutinho (1982) argues that the induction of cerrado plant species flowering by fire is not a result of thermal effects during burning or of mineral nutrients supplied by the ashes, but what seems important is the removal of old branches and possible flowering inhibitors. The same has been shown by Fidelis and Blanco (2014), for subtropical grasslands. Therefore, the occurrence of a reproductive cycle soon after fire could result in a more efficient reproductive strategy for this plant guild, because the elimination of the herbaceous/grass layer provides greater visibility of the flowers to pollinators and because flowering synchrony between individuals favors crossings, especially for smaller species (Trabaud and Chanterac, 1985).
In summary, we have found a peak in reproduction seven months after fire for the cerrado and a small number of ground-layer species in the forest. We verified some cerrado species that may have been favored by the late dry season fire, but the majority of herbs had their reproduction events spread throughout the study time. The fire timing is able to change the flowering phenology of a grassland community (Rissi, 2016) and this changing may be related to the plant physiological status when burning happens (Frost and Robertson, 1987). In Cerrado, fire is an integral component of the biodiversity (Simon et al., 2009) and a fire management policy with prescribed and well-controlled fires at the correct frequency and season (Durigan and Ratter, 2016) would benefit the reproductive activity of some herbaceous species.
