Tree dynamics of a fire-protected cerrado sensu stricto surrounded by forest plantations, over a 13-year period (1991–2004) in Bahia, Brazil

Abstract

Structural and floristic changes of a fireprotected cerrado sensu stricto are described over a 13-year period. The study site is located in a biological reserve (2,800 ha) surrounded by large Pinus spp. and Eucalyptus spp. plantations (36,000 ha), in southwestern Bahia, Brazil. The region occurs in the outer-core of the Cerrado domain, near the Cerrado-Caatinga ecotone, and is mainly occupied by pasture and cropland. Surveys were carried out in 1991 and 2004 in 13 permanent plots (20 9 50 m). Stems with diameter C5 cm at 0.30 m above ground level were identified and measured. Floristic changes were significant (Søren-seńs index = 0.45). Species number rose from 62 to 84 (35.48%). Alpha diversity increased significantly (P [ 0.001). New species migrated to the area, and there was an expansion of many fire-sensitive species. Woody layer expanded, increasing 19.09% in density and 14.93% in basal area. Diameter distributions followed a ''reversed-j'' pattern on both occasions, but differed (P [ 0.05) due to a significant increase in the first two size-classes, indicating a high recruitment. Community dynamics was high and had a positive balance between recruitment (3.72% yr -1 ) and mortality (1.93% yr -1 ). Conversely, mean annual increment was very small, 0.096 cm yr -1 (SD = 0.14; N = 808). Most species, including many dominant ones, had a positive balance in favor of recruitment and low turnover, indicating that although species immigration rate is high (1.42 spp ha -1 ), structural changes in species composition happens at a much slower pace. The surrounding forest plantations are permeable and do not limit species immigration; and may be connecting the reserve with the larger neighboring natural fragments, providing an abundant source for diaspores, and possibly neutralizing any fragmentation effects. Succession is also influenced by the ecotonal condition. The structure and floristics of the cerrado sensu stricto at this site (under present climatic conditions) is fire-dependent.

Woody encroachment and its consequences on hydrological processes in the savannah

“…[30,33]). Fire suppression or decreasing fire frequency have been reported as the main explanation for woody encroachment in Cerrado vegetation across Brazil [29][30][31][32][33]64], with frequent fires, regardless of season, been shown to reduce woody biomass [65].…”

“…[30,33]). Fire suppression or decreasing fire frequency have been reported as the main explanation for woody encroachment in Cerrado vegetation across Brazil [29][30][31][32][33]64], with frequent fires, regardless of season, been shown to reduce woody biomass [65]. Changes over time in density and TBA in our study differed: TBA increased in the cerradão plots at similar rates as those of the cerrado stricto sensu, but density stabilized around 2000 ind ha 21 , corresponding to a basal area around 23 m 2 ha 21 , and after that, mortality equalled recruitment, resulting in no significant changes in density over 5 years.…”

“…The larger trees kept growing, accumulating carbon and probably increasing the roughness of the canopy surface, which leads to increase in rain interception [58]. Eventually, the community structure instead resembles a tropical [30,33,54]. In the long term, due to competition, the community will probably be composed of even larger trees at lower densities.…”

Variações temporais na comunidade arbórea de uma floresta decidual sobre afloramentos calcários no Brasil Central: composição, estrutura e diversidade florística

“…O conhecimento da dinâmica da vegetação é importante para detectar padrões de mudanças fl orísticas e estruturais e inferir sobre as tendências futuras no funcionamento da fl oresta (Hubbell & Foster 1992). Análises de dinâmica ainda são escassas em relação à vasta extensão do bioma Cerrado, e foram realizadas em algumas áreas de cerrado sensu stricto (Felfi li et al 2000;Libano & Felfi li, 2006;Aquino et al 2007;Roitman et al 2008), matas de galeria (Felfi li 1995a,b;Felfi li 1997 a,b;Schiavini et al 2001;Lopes & Schiavini 2007;Oliveira & Felfi li 2008), e em alguns tipos de fl orestas estacionais, como nas fl orestas semideciduais (Schiavini et al 2001;Pinto & Hay 2005;Paiva et al 2007;Silva & Araújo 2009) e deciduais (Werneck et al 2000;Werneck & Franceschinelli 2004). Estes estudos vêm conferindo às fl orestas do bioma Cerrado o caráter de altamente dinâmicas, pois o condicionamento ao défi cit hídrico sazonal leva a processos de mortalidade e recrutamento mais intensos do que nas fl orestas úmidas tropicais.…”

Measuring Woody Encroachment along a Forest–Savanna Boundary in Central Africa

“…There are fewer studies finding such an increase in tropical savannas, but some do exist: for example in northern Australia (Hopkins et al 1996;Bowman et al 2001;Russell-Smith et al 2004;Brook and Bowman 2006), the Western Ghats of India (Puyravaud et al 2003), and South America Durigan and Ratter 2006;Marimon et al 2006;Roitman et al 2008). In Africa just four studies showing increasing tree cover in tropical rain forestsavanna boundary regions have been reported.…”