Beatriz Schwantes Marimon

VEGETATION SUCCESSION IN THE CERRADO–AMAZONIAN FOREST TRANSITION ZONE OF MATO GROSSO STATE, BRAZIL

The occurrence of cerrado (as tree and shrub savanna is called in Brazil) and forest formations side by side is common at the southern margin of the Brazilian Amazonian Forest, and previous studies have demonstrated the advance of forests over cerrado areas. The aim of the present study is to provide an accurate documentation of the transition process between the two major biomes. Tree data (≥ 5 cm diameter at 0.3 m above soil level) from three plots of cerrado sensu stricto lying near three of cerradao (the taller, denser form of cerrado ) were inventoried starting in 2002 in an area of 1.5 ha made up of 150 subplots of 10 × 10 m (50 in each area). This showed that the most important species of the cerradao were invading areas previously occupied by smaller, lower forms of cerrado (although it is sometimes difficult to define which are ‘forest’ and which ‘ cerrado ’ species as many are flexible in size – for instance Emmotum nitens can often be intermediate, establishing in cerrado that develops into cerradao and on to forest). Some typical species such as Eriotheca gracilipes and Emmotum nitens , established since the first inventories, have increased their populations (between 27 and 210%). Tachigali vulgaris , a typical, weedy, adventive species of the Cerrado–Amazonian Forest transition, showed the largest increase in abundance in areas of cerrado sensu stricto (between 100 and 1200%), and is probably the most important pioneer species in the initial advance of the forest into cerrado at the Southern Amazonian border.

Height-diameter input data and R-code to fit and assess height-diameter models, from 'Field methods for sampling tree height for tropical forest biomass estimation' in Methods in Ecology and Evolution

1. Quantifying the relationship between tree diameter and height is a key component of efforts to estimate biomass and carbon stocks in tropical forests. Although substantial site-to-site variation in height-diameter allometries has been documented, the time consuming nature of measuring all tree heights in an inventory plot means that most studies do not include height, or else use generic pan-tropical or regional allometric equations to estimate height. 2. Using a pan-tropical dataset of 73 plots where at least 150 trees had in-field ground-based height measurements, we examined how the number of trees sampled affects the performance of locally-derived height-diameter allometries, and evaluated the performance of different methods for sampling trees for height measurement. 3. Using cross-validation, we found that allometries constructed with just 20 locally measured values could often predict tree height with lower error than regional or climate-based allometries (mean reduction in prediction error = 0.46 m). The predictive performance of locally-derived allometries improved with sample size, but with diminishing returns in performance gains when more than 40 trees were sampled. Estimates of stand-level biomass produced using local allometries to estimate tree height show no over- or under-estimation bias when compared with estimates using measured heights. We evaluated five strategies to sample trees for height measurement, and found that sampling strategies that included measuring the heights of the ten largest diameter trees in a plot outperformed (in terms of resulting in local height-diameter models with low height prediction error) entirely random or diameter size-class stratified approaches. 4. Our results indicate that even remarkably limited sampling of heights can be used to refine height-diameter allometries. We recommend aiming for a conservative threshold of sampling 50 trees per location for height measurement, and including the ten trees with the largest diameter in this sample.