ABSTRACT Backgrounds: Urban and peri-urban fragments are vital for biodiversity conservation, requiring genetic assessment of tree species in fragmented forests. The aim of this study was to analyze the genetic variability and diversity for adult individuals of J. micrantha along an urban-rural gradient in the Araucaria Forest. Fifteen individuals were sampled, with five from each remaining forest type. Initially, 10 ISRR primers were tested. Five mother trees were chosen from each site (urban, peri-urban, and rural) with a minimum distance of 100 m. The experimental design was a RCBD with 15 progenies, three provenances, three blocks, and 20 plants per plot, totaling 900 seedlings. Results: The average percentage of polymorphic loci was 93.33%. The urban population showed a greater loss of genetic diversity (H=0.1806). 79% of the genetic diversity was found within populations. The observed gene flow value (Nm) was 1.8790, indicating that there were no random losses of alleles within populations. The fragments did not exhibit significant differences, but there were significant differences among the progenies. The stem diameter (SD) and the height-diameter relationship (H/SD) emerged as the key traits for selecting new individuals due to their higher heritability (< 0.50), accuracy (< 0.70), and relative coefficient of variation (< 7%). Conclusion: The urban fragment is the most affected, but gene flow between fragments prevents the random loss of alleles. The analysis suggests that these fragments form a unique population, despite geographic barriers. Thus, the three fragments can be considered when choosing superior individuals for future progeny tests in genetic improvement programs for the species. Backgrounds periurban peri conservation forests J urbanrural rural Forest sampled type Initially 1 tested urban, (urban periurban, m progenies provenances blocks 2 plot 90 seedlings Results 9333 93 33 93.33% H=0.1806. H01806 H H=0.1806 . 0 1806 (H=0.1806) 79 populations Nm (Nm 18790 8790 1.8790 SD (SD heightdiameter height H/SD HSD (H/SD < ( 0.50, 050 0.50 , 50 0.50) 0.70, 070 0.70 70 0.70) 7%. 7 7% 7%) Conclusion affected barriers Thus 9 933 3 93.33 H0180 H=0.180 180 (H=0.1806 1879 879 1.879 05 0.5 5 07 0.7 93.3 H018 H=0.18 18 (H=0.180 187 87 1.87 0. 93. H01 H=0.1 (H=0.18 8 1.8 H0 H=0. (H=0.1 1. H=0 (H=0. H= (H=0 (H= (H