Management of landscape biodiversity is facing the challenge of global change (climatic and land cover) that would modify their ecological functions. A particular attention should be paid to tree species diversity as they are a key component of landscape biodiversity influencing many other compartments in forest and in neighbouring agriculture. The patch area and the edge effect have been identified as key factors for species diversity of many taxonomic groups in fragmented landscapes, but similar studies are rare for woody species. To disentangle the effect of these two factors and to quantify their respective importance on woody species diversity, a woodlot scale study was designed in an agricultural landscape of south-western France. An exhaustively survey of woody species was undertaken in 43 woodlots by “walking transect”. A 20m wide edge zone was distinguished. Separate lists were held for the edge and the interior zone. Woodlot area varied from 0.32 ha to 167 ha. We used the Patton shape index to characterize each patch shape. This shape index ranges from 1.16 to 2.8 in our woodlot sample. Tree richness was significantly and positively correlated to woodlot area logarithm. About 70 to 100% of total woodlot richness came from the edge zone. Patch shape index also has a high and significant positive correlation with the total species richness, but it was very correlated with edge area. Some true forest species as Fagus sylvatica and Ilex aquifolium that showed a significantly higher frequency in the largest woodlots, showed a stronger link with the core area than with the edge area. These results suggest that in the studied area, the edge area of woodlots has the highest importance for the woody species’total richness, while the core area of the largest forests is of interest for some species well adapted to these true forest conditions. These results are in line with others works on patch area effect made with a different approach. To go further on the importance of edge effect in woodlots’diversity, a functional approach using a classification of species according to their successionnal stage and their habitat preference would be useful. Landscape management for biodiversity purposes should take these results into account and pay attention to the forest fragmentation process that would shrink core areas, containing low frequency species, in favour of new edge habitats, containing many but common species. Such species patterns could be integrated in forest management by planning practices according to this edge gradient. Our results also highlight the importance of planning forest and agriculture management at a landscape scale which is the relevant scale to deal with forest patch shape forming.