We are exploring different approaches to model qualitatively the vegetation, dynamics of Brazilian cerrado, in order to assess their suitability to provide the domain-specific knowledge in tutoring systems. Two formalisms, the System of Interpretation of Measurements, Analysis and Observations (SIMAO) and the Qualitative Process Theory (QPT), are compared here in two aspects: capacity for making predictions about the behaviour of a plant population, and the generation of explanations from encoded knowledge. Both SIMAO and QPT-based models can produce similar predictions to those obtained with a numerical model of the same problem. S1MAO provides a useful qualitative algebra to make calculations with heterogeneous variables. However it is not possible to incorporate descriptions of the ecological components nor do dynamic simulations with the SIMAO-based model. On the other hand, QPT allows the encoding of qualitative knowledge and building more detailed models, but does not provide a qualitative algebra for combining empirical values of variables. Both SIMAO and QPT permit the generation of system-based explanations, whereas QPT might be more recommended to generate domain-based explanations. We also discuss the role of different organisational levels and scales of space and time in explaining the behaviour of ecological systems. A combined approach could be advantageous in building tutoring systems.