  Forests are complex systems, and it is necessary to include this
characteristic in every forest definition, in order to consider the restriction
that this imposes in terms of prediction and control. This lost of
predictability and controllability should be incorporated in every
Environmental Impact Assessment or management program. We present two
case-studies located in Mexico and one in the US to illustrate three relevant
indicators of complexity. First, we introduce an informational framework to
measure the Zoquiapan forest systemic complexity. Then, we analyze complexity
changes among different types of forest and management systems, related with
spatial distributions, using data from a floristic study in the Montes Azules
National Park. Finally, we analyze time series of $CO_{2}$ fluctuations taken
from AMERIFLUX data bases. Our results show firstly that it is possible to
measure the systemic complexity of different forests, characteized by a
criticality state (1/f noise) which has been proposed as a finger print of
complexity. And secondly, that this characteristic can be used as a proxy of
their state of conservation, where the lowest complexity values are found in
perturbed areas showing the relevance of the concept and its measurement for
forest conservation and management.
