Seasonal forests are found among tropical evergreen wet forests and savannas or deserts and show peculiar floristic composition, structure, diversity, height, net production and other functional aspects. This study was carried out at the Pico do Jabre Montane Seasonal Forest (06° 02’12’’ a 08° 19’18’’ S and 34° 45’12’’ a 38° 45’45’’W), the highest regional elevation (1.197 m), at 360 km from the sea at Maturéia and Mãe D’água municipalities in Paraiba state, Brazil. The main target was to assess the floristic composition and phytosociology of the trees and regeneration strata in order to correlate species abundance and local environment factors. Classification (UPGMA and TWINSPAN) and ordination (CCA) techniques were used as the main tools. A comparison including 17 other forest communities, of Pernambuco and Paraíba states, placed our studied forest within the regional floristic context. All trees, DBH ≥ 4,8 cm, were sampled in 36 (10x50m) plots, 1,8 ha, placed in transects along a 225 m altitudinal range. During six years trees botanical samples were monthly collected outside plots to enrich the local floristic list. Altitude, geographical position, soils physical and chemical properties were taken for each plot. In the total there were 87 species, of 65 genera and 34 families. Within plots it was found 2050 trees of 64 species of 51 genera and 31 families which resulted in 1.148 ind.ha-1 and 22.45 m2.ha-1. Diversity was established as H’ = 3.17 nats.ind-1 and J = 0.76 as a result of Byrsonima nitidifolia ecological dominance. The local flora included species from Ombrophylous Montane and Seasonal Forest as well as from the neighboring Caatinga. Natural regeneration showed 21 species of 16 genera and 14 families which resulted in H’ = 1.57 nats.indiv-1 and J = 0.52. In this strata B. nitidifolia ecological dominance was also registered. Similarity among regeneration and tree community was calculated as 40%. The UPGMA and TWINSPAN classification indicated two floristic communities which included PP, well preserved, and PAR, less preserved and rocky plots. Indicators and preferential species were also established. A CCA analysis pointed out a altitudinal gradient along which the PP community was found colonizing acid, humid and less fertile soils in the highest positions of mountain, while PAR community was found associated to the less acid and humid and more fertile soils in the lowest positions. Environmental variables were responsible for 38,83% and, together with space they accounted for 49,61% of the total variance. The Pico do Jabre Montane Seasonal Forest showed low floristic similarity, average 0,22, to other regional Forest communities. The highest floristic similarity was associated to geographical proximity. As a consequence of the high floristic and structural heterogeneity it was not found indicator species associated to the regional Montane Seasonal Forest communities.
