Managing forests for increased structural complexity as well as acknowledging them as ‘complex adaptive systems’ has become a paradigm in modern silviculture. Primary forests usually show greater structural complexity than managed forests since forest management often aims for several reasons at less complex but specific structures, e.g. for the production of desired wood assortments. Therefore, the question why natural forests seem to gravitate towards maximum structural complexity, at least aboveground, remains. Here we argue that the consideration of thermodynamic theory in forest ecosystem research holds great potential for a deeper understanding as to why structural complexity is beneficial to forests when it comes to evolutionary adaptation. We bring together several existing theories and highlight how structural complexity relates to thermodynamic principles and correspondingly forest productivity, potentially also providing us a means to quantify forests’ adaptive capacity.