This paper investigates the joint production of timber and biodiversity by non-industrial private forest owners using a micro-econometric household production model. The objective of the paper is to explain the relationships between harvest strategies, timber price and the observed diversity of trees. To do so, we analyze (1) forest owners' demand of species diversity and their timber supplies, (2) the jointness in timber and nontimber products. We use a database of uneven-aged forests in France for which several economic and ecological variables are regularly collected. We use cluster-sample methods to simulate the forest owner in a multi-product framework where the di_erent products and the timber prices depend on species, tree diameter and timber quality. We estimate a two-step model by reporting the predicted value of demand in tree diversity in the timber supply equation. Our results show that timber and tree diversity are substitutes but that timber price positively a_ects tree diversity.