Wood strategies in a lowland rainforest of eastern Amazonia
Facultad: medicina

 This thesis consists of six chapters: the general introduction (this chapter), four research chapters (chapters 2-5), and a synthesis chapter (chapter 6). I first focused on WSG and wood anatomical traits (chapter 2), then looked at wood chemical traits (chapter 3), and then combined data on wood traits and species demography to assess the links between traits and demographic rates (chapter 4). Finally, I examined the implications of within-stem variations in WSG on biomass estimations at both the species and stand level (chapter 5). It is well established that wood specific gravity (WSG) can vary substantially from pith to bark (Williamson & Wiemann, 2010), which can reflect ontogenetic shifts in hydraulic, mechanical and storage demands during tree development (Hietz et al., 2013). However, the wood anatomical traits underlying these radial variations in WSG are not well understood, particularly for angiosperm tree species from humid tropical forests. In chapter 2, I used a set of wood functional traits, measured along the stem radial profile, to explain the anatomical drivers of radial shifts in WSG. Wood nutrients are expected to play a central role in tree functioning and life-history variations among woody species (Martin et al., 2014; Heinemann et al., 2016). Yet, very few studies have investigated how wood nutrients are related to other wood functional traits, or how they vary radially within stems, or across species and ecological guilds. In chapter 3, I related wood nutrients (i.e., phosphorous, calcium, potassium and magnesium) to WSG and xylem parenchyma fractions ininner and outer wood, and evaluated nutrient resorption rates at the species and ecological guilds level. One central assumption in trait-based ecology is that traits can predict species demography (Shipley et al., 2016). However, the predictive power of most traits on tree demographic rates is in general low. This pattern may be explained by two reasons: the use of “soft traits”, which might not fully capture some plant functions (Yang et al., 2018), and the lack of consideration of size-related changes in both traits and demographic rates (Iida & Swenson, 2019). In chapter 4, I combined demographic rates (i.e., diameter growth and mortality rates) of trees of different sizes and “hard traits” (i.e., chemical and anatomical traits) measured at different radial positions to explain the associations between wood traits and species demography during tree development. Besides its functional significance, wood specific gravity is also an important predictor of above-ground biomass (AGB) and, consequently, of biomass growth rates (BGR) estimations. Although radial shifts in WSG may have considerable effects on AGB and BGR estimations, at both the species and stand level, most regional and local studies do not consider these possible effects. In chapter 5, I quantified species percentage errors in AGB and BGR estimations that resulted from not taking into account radial trends in WSG, and extrapolated these species percentage errors to the stand level. Finally, in the last chapter (chapter 6), I synthesized the results of this thesis, and discussed how they complement existing knowledge on trait-based ecology. Furthermore, I outlined the limitations of this study and proposed future research directions.