Towards testing the "honeycomb rippling model" in cerrado

Abstract

Savannas are tropical formations in which trees and grasses coexist. According to the "honeycomb rippling model", inter-tree competition leads to an effect of trees growing and dying due to competition, which, at fine spatial scale, would resemble honeycomb rippling. The model predicts that the taller the trees, the higher the inter-tree distances and the evenness of inter-tree distances. The model had been corroborated in arid savannas, in what appears to be caused by uneven distribution of rains, but had not yet been tested in seasonal savannas, such as the cerrado, which could be caused by the irregular occurrence of fire.A basic assumption of the model is that strong inter-tree competition affects growth (estimated by height) and mortality (estimated by inter-tree distances). As a first step towards testing this model in the cerrado, we tested this assumption in a single cerrado patch in southeastern Brazil. We placed 80 quadrats, each one with 25 m², in which we sampled all shrubs and trees. For each individual, we measured its height and the distance to its nearest neighbour--the inter-tree distance. We did not find correlations between tree height and both inter-tree distances and evenness of inter-tree distances, refuting the honeycomb rippling model. Inter-tree distances were spatially autocorrelated, but height was not. According to our results, the basic assumption of the model does not apply to seasonal savannas. If, in arid savannas, rainfall events are rare and unpredictable, in seasonal savannas, the rainy season is well-defined and rainfall is considerable. We found horizontal structuring in the community, which may be due to soil nutrient heterogeneity. The absence of vertical structuring suggests that competition for light among adult trees is not as important as competition for nutrients in the soil. We tested the basic assumption of the model in a single patch and at a single moment. To test the model effectively, we suggest this assumption to be tested in many patches over time.

Understorey vegetation gradient in a Eucalyptus grandis plantation between a savanna and a semideciduous forest

“…This variation may be at least partially due to differences in methodology as these earlier studies only included individuals with at least 3 cm diameter at soil level. The density of individuals of native species (1700 ind.ha −1 ) in the current study was between two and five times smaller than observed in two nearby cerrado areas, where density ranged between 4000 and 8250 ind.ha −1 (Dantas andBatalha 2011, Gonçalves and. This difference in density is even more pronounced given that the sampling criterion used in the current study included individuals with less than 3 cm diameter.…”

Edge and land use effects on dung beetles (Coleoptera: Scarabaeidae: Scarabaeinae) in Brazilian cerrado vegetation

“…This pattern may be partially due to the patchy and ephemeral nature of their resources (manure and carcasses), making these insects mobile and eicient in tracking those resources throughout the landscape (Roslin 2000). In addition, similar to other savannas, the cerrado is a naturally patchy environment with alternating patches of greater or smaller woody plant cover (Wiegand et al 2006;Gonçalves and Batalha 2011). Furthermore, small-sized cerrado mammals may not be afected by edges at the scale of this study (Di Napoli and Caceres 2012).…”

The role of edge contrast and forest structure in edge influence: vegetation and microclimate at edges in the Brazilian cerrado

“…The variability in factors such as edge orientation and age also plays an important role, as well as regional heterogeneity in vegetation structure and composition. Vegetation structure in the cerrado is structurally complex at multiple scales (Gonçalves and Batalha 2011). Therefore, a larger sample size and a wider range of values of edge contrast may be needed to detect clearer effects on EI.…”