This work is the result of a search for general (or nearly general) regularities at ecosystem level, and an exploration of their practical relevance in our relations with the environment.
I began by adding some new contributions to the thermodynamic approach to systemic ecology, but concluded that there is little scope for further progress of strictly ecological interest with this orientation. Instead, the key for a systemic ecology seems to lie in the "large number" effects that arise at the limit of many organisms and/or species, just like the whole scientific body of statistical physics stands on the general features that emerge at the limit of many particles. The concept of criticality seems to have a special importance within this context (criticality is the quality of lying at the critical point in which there is a second order phase transition).

Some specific issues that I analyze in depth, taking advantage of the concept of criticality and other concepts related to statistical physics, are:

·Wildland fire dynamics. Practical tools to predict and manage fire in boreal forests and in the Mediterranean. Limits to anthropogenic impacts on tropical rainforests before a major fire catastrophe unfolds. The possible generalization of the findings on wildland fires to other kinds of catastrophes, with emphasis on agricultural pests and epidemics.

· Diversity patterns. The origin of species abundance distributions and species-area relations. Their interpretation (and misinterpretation). The case of marine phytoplankton. The quantification of diversity for conservation purposes.

· The effects of diversity on stability. The sources of the apparent inconsistencies between theoretical models, both historical and current, and between theoretical expectations and some experimental results.

I conclude with a discussion on the interest of my and other related findings from the point of view of ecological economics.