Contents lists available at ScienceDirect Forest Ecology and Management journal homepage: www.elsevier.com/locate/foreco How do soil and fire control aboveground biomass in natural forest patches? Mateus C. Silva a, ⁎ , Grazielle S. Teodoro b , Evelyn F.A. Bragion a , Eduardo van den Berg a a Federal University of Lavras, Department of Biology, Mailbox: 3037, 37200-000 Lavras, Minas Gerais, Brazil b Federal University of Pará, Biological Sciences Institute, 66075-110 Belém, Pará, Brazil 1. Introduction The aboveground biomass (AGB) of world’s forests plays an essen- tial role in the global carbon cycling (Pan et al., 2011; Saatchi et al., 2011). Forests provide important interconnected ecosystem services, through the mitigation of CO 2 -induced climate changes due to the re- tention of C in their massive organic matter pool (Houghton et al., 2015, 2009). Tropical forest occupies a special position in this context as they store one fourth of terrestrial carbon and are responsible for one-third of gross primary productivity of land systems (Beer et al., 2010; Bonan, 2008). However, the AGB stock of tropical forests is spatially heterogeneous, getting more than 100 Mg ha -1 of AGB var- iation within the same region (Malhi et al., 2006; Saatchi et al., 2011). Therefore, identifying the factors that control tropical AGB hetero- geneity in space and time is a priority to fully understand the carbon cycle and its dynamics. The main environmental driver of AGB stocks varies according to the spatial scale. In the global scale, the cumulative precipitation and rainfall seasonality shape the patterns of AGB, with minor importance of temperature (Baraloto et al., 2011; Malhi et al., 2004; Poorter et al., 2015; Raich et al., 2006; Slik et al., 2013; Toledo et al., 2011). On the other hand, in the local scale (e.g., within watersheds) there is little to no climatic variation. Thus, the topography, soil fertility and texture, and historical disturbances play a major role in determining the AGB stock. The generality of the effects of soil and fire on AGB is still in debate due to their contingency. In fact, previous studies have found that soil plays a key role in influencing the AGB stock (Davidson et al., 2004; Giardina et al., 2003; Quesada et al., 2012). However, the effect of soil fertility, acidity, and texture on AGB is ambiguous, ranging from positive to negative effects, even within the same region. For example, studies in the Amazon rainforest found positive, negative and even neutral effects of soil phosphorus on AGB (Baraloto et al., 2011; Laurance et al., 1999; Quesada et al., 2012). Similarly, Slik et al. (2013) reported the same ambiguity between the Pantropical continents, as AGB in America and Asia increases with soil fertility, an opposite pat- tern for the African forests. Fire disturbance also leads to differences in AGB at the local scale, since a great amount of AGB is quickly lost in the form of atmospheric CO 2 after burning (De Castro and Kauffman, 1998). Unlike soil, fire effects are clearly negative to AGB. Thus, the fundamental question is not the effect itself, but whether and how the AGB of natural flammable ecosystems remains stable regardless of fire impact. In a tropical forest landscape, fire events can be a consequence of fragmentation, because anthropic edges are dryer and consequently have higher flammability than forest interiors (Laurance, 2004). In this case, fire can easily spread kilometers deep within the forest. (Broadbent et al., 2008; Cochrane, 2001; Laurance, 2004). On the other hand, fire occurrence can be decoupled from anthropic fragmentation and be associated to drought events (Aragão et al., 2018). In fact, studies in forest patches inserted in savanna matrix found them to be highly resistant and resi- lience to fire (Hoffmann et al., 2012b). Therefore, in natural forests patches, fire possibly does not have a drastic impact on AGB as in human-induced forest fragments (Hoffmann et al., 2012a). The gallery forests are narrow strips of forest associated with small streams, present in the Cerrado savanna biome (Ribeiro and Walter, 1998), one of two biodiversity hotspots in Brazil (Myers et al., 2000). These forests are surrounded by a dry fire-prone matrix of grassland savanna, forming natural forest patches (Fig. 1). The edge-interior gradient encompasses fundamental environmental variations associated with light penetrance, soil moisture, and fertility. The fire pressure and light penetrance tend to increase toward edges, while soil moisture, acidity, and fertility increase toward interiors (Hoffmann et al., 2012a, 2009; van den Berg and Santos, 2003). Therefore, natural patches of gallery forests offer an amazing opportunity to explore how soil prop- erties and fire disturbance control AGB, and how these factors explain AGB heterogeneity between forest edges and interiors. In order to understand how the environmental factors controlling the AGB of forests at local-scale, we used natural patches of old-growth gallery forests as a model ecosystem and we addressed the following question and hypothesis. How do soil acidity, fertility, and historical fires control AGB in gallery forests’ edges and interiors? We expected that: (i) once the nutrient content is a key driver of gallery forest structure, diversity, and functioning (Silva et al., 2013; van den Berg and Oliveira-Filho, 1999), soil fertility enhances AGB both among the forests and in the interiors when compared to the edges; (ii) Soil acidity limits AGB especially in interiors since pH decreases toward interiors (van den Berg and Santos, 2003) and the impact of this stressful con- dition should be higher in this habitat than in forest edge; (iii) Fire https://doi.org/10.1016/j.foreco.2019.117518 Received 25 January 2019; Received in revised form 30 July 2019; Accepted 30 July 2019 ⁎ Corresponding author at: Câmpus Universitário, Caixa Postal 3037, CEP 37200-000 Lavras, MG, Brazil. E-mail address: mateuscardosobio@gmail.com (M.C. Silva). Forest Ecology and Management 451 (2019) 117518 0378-1127/ © 2019 Elsevier B.V. All rights reserved. T