Habitat fragmentation and low patch connectivity threaten the genus Abies Mill. (Pinaceae) in southern North America

Abstract Fir forests ( Abies , Pinaceae) are patchily distributed in the montane ecoregions of the United States Southwest, Mexico, and northern Guatemala. We assessed habitat fragmentation for nine Abies species native to southern North America. We estimated the number of patches (NumP), mean patch size (MPS), median patch size (MedPS), mean shape index (MSI), patch density (PD), total edge (TE), mean patch edge (MPE), class area (CA), total landscape area (TLA), and percentage of class area within an ecoregion (ZLAND) based on Abies species distribution maps. Then, we calculated NumP, MPS, and ZLAND for land covers in each ecoregion between 2010 and 2020. We estimated the Integral Index of Connectivity of patches covered by Abies species according to two dispersal scenarios (0–500 m and 0–1000 m) and classified them as low, medium, or high connectivity. We also assessed the extent to which protected areas are intersected with patch connectivity levels. Most Abies species occupied small patches with low patch densities in restricted areas of each ecoregion. NumP increased significantly in conifer forests (76%) and croplands (72%), MPS decreased in mixed forests (39%), conifer forests (37.4%), and croplands (34.8%), whereas ZLAND increased in urban areas (2.7%). Most patches exhibited low connectivity in both dispersal scenarios; only two species hosted large medium and high connectivity patches. Moreover, at least 30% of the distribution of two species was protected, and most of the protected extent was intersected with low connectivity patches. Our findings suggest habitat fragmentation and low patch connectivity could threaten Abies species long term.