Podocarpus lambertii (Podocarpaceae) is an endangered conifer, endemic to Brazil and occurring in continuous forest and forest-grassland landscapes from the Araucaria Forest. Aiming to support conservation efforts for P. lambertii populations and gain insights into the preservation of forest-grassland mosaics in southern Brazil, we assessed the spatial pattern, genetic diversity, and fine-scale genetic structure (FSGS) within a population situated in a forest-grassland mosaic. The study was conducted in a 9-ha plot in forest-grassland mosaic. All P. lambertii individuals with height ≥ 0.1 m were sampled and the population was stratified into four demographic categories (Seedling, Juvenile, Immature, and Reproductive). For each of these categories, we used 13 allozyme markers to evaluate the spatial pattern, genetic diversity and FSGS. All individuals occurred inside the forest-patches, presenting an aggregated pattern of distribution. Low genetic diversity was recorded for all categories and for the population (
{\mathord{\buildrel{\lower3pt\hbox{$\scriptscriptstyle\frown$}}\over H} _E} = \,0.046
), as well as a high number of rare alleles (20). Positive and significant FSGS was estimated only for the Juveniles (
{\mathord{\buildrel{\lower3pt\hbox{$\scriptscriptstyle\frown$}}\over \theta } _{xy}} = \,0.012
) up to maximum distance of 7.1 m, and the minimum viable area for the long-term conservation of Reproductive genetic diversity was approximately 68 ha. The set of our findings suggests that conservation actions need to enhance connectivity among forest-patches to prevent the loss of rare alleles due to genetic drift. Additionally, we highlight the significance of preserving forest-patches as repositories of species diversity and as crucial connectors between populations.
