Navegando por Autor "Luedemann, Gustavo"
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Item Analysis of competition effects in Mono- and mixed cultures of juvenile beech and spruce by means of the plant growth simulation model PLATHO.(2006) Gayler, Sebastian; Grams, Thorsten E. E.; Kozovits, Alessandra Rodrigues; Winkler, J. B.; Luedemann, Gustavo; Priesack, E.Inter- and intra-specific competition between plants for external resources is a critical process for plant growth in natural and managed ecosystems. We present a new approach to simulate competition for the resources light, water, and nitrogen between individual plants within a canopy. This approach was incorporated in a process-oriented plant growth simulation model. The concept of modelling competition is based on competition coefficients calculated from the overlap of occupied crown and soil volumes of each plant individual with the occupied volumes of its four nearest neighbours. The model was parameterised with data from a two-year phytotron experiment with juvenile beech and spruce trees growing in mono- and mixed cultures. For testing the model, an independent data set from this experiment and data from a second phytotron experiment with mixed cultures were used. The model was applied to analyse the consequences of start conditions and plant density on plant-plant competition. In both experiments, spruce dominated beech in mixed cultures. Based on model simulations, we postulate a large influence of start conditions and stand density on the outcome of the competition between the species. When both species have similar heights at the time of canopy closure, the model suggests a greater morphological plasticity of beech compared with spruce to be the crucial mechanism for competitiveness in mixed canopies. Similar to the experiment, in the model greater plasticity was a disadvantage for beech leading to it being outcompeted by the more persistent spruce.Item Effects of nutrient additions on plant biomass and diversity of the herbaceous-subshrub layer of a Brazilian savanna (Cerrado).(2012) Bustamante, Mercedes Maria da Cunha; Brito, Darlan Quinta de; Kozovits, Alessandra Rodrigues; Luedemann, Gustavo; Mello, Thiago de Roure Bandeira de; Pinto, Alexandre de Siqueira; Munhoz, Cássia Beatriz Rodrigues; Takahashi, Frederico Scherr CaldeiraThe Brazilian Cerrado is a diversity hotspot due to its high level of endemism and rapid loss of habitats. It is estimated that the number of herbaceous species is four times higher than that of woody species. Increasing levels of nitrogen additions to natural ecosystems have been indicated as a determinant of biodiversity loss. We investigated the effects of nutrient additions on the productivity (aboveground and belowground) and on diversity of the herbaceoussubshrub layer of a Brazilian savanna (cerrado stricto sensu). The experiment was carried out in the IBGE Ecological Reserve, near Brası´lia, Brazil. Between 1998 and 2006, N, P, N plus P, or Ca were applied to sixteen 225 m2 plots, arranged in a completely randomized design. Aboveground biomass was compared 1 year after the first fertilization and 10 years later. Floristic diversity was significantly different (P\0.01) between the treatments. The highest and lowest species richness were presented in control and NP, respectively. The addition of P alone or in combination with N induced invasion by Melinis minutiflora (exotic C4 grass). The aboveground biomass of this species was higher in NP and P plots. In the N treatment, Echinolaena inflexa (native C3 grass) presented elevated cover and biomass but M. minutiflora was absent. The invasion by alien species resulted in negative impacts on native grass species. Besides changes in aboveground biomass, addition of N and P also led, although to a lesser extent, to changes in the root morphology and biomass, but these responses were modulated by seasonal variation in soil moisture. The results suggest that environmental changes in nutrient availability can lead to important consequences for diversity and functioning of this savanna where the numerous rare species have more chance to persist under dystrophic conditions as some species that tend to be dominant would be less competitive.