Demographic structure across all known populations of the rheophyte Dyckia brevifolia Baker (Bromeliaceae) in the Itajaí-Açú River, Southern Brazil

Understanding the distribution and demographic structure of populations is essential for species conservation. In Brazil, the rheophyte group has been greatly affected by the construction of hydroelectric dams. All know populations of Dyckia brevifolia along Itajaí-Açu River were studied. The plants were classified as seedlings, immature or repoductive rosettes. In addition, the number of dead rosettes, except for seedlings, was determined in five populations of D. brevifolia. The total number of rosettes per population ranged from 273 to 7,185, totaling 30,443 rosettes, and 1,789 seedlings (5.9%). Only 2.4% of rosettes occurred isolated and 97.6% occurred clumped into 2,254 clumps. The number of rosettes per clump ranged from two to 339 rosettes. The percentage of reproductive rosettes per population ranged from 7.8 to 26.7%. The correlation between the number of clumps or between the total number of rosettes and the area of occupation was significant and positive (r = 0.82; P < 0.05). The production of offshoots (1-4) occurred on immature and reproductive rosettes. D. brevifolia has herbivory by Hydrochaeris hydrochaeris. These rosettes die or often resprout, emitting from 1 to 20 offshoots. The populations did not present a pattern of distribution of rosettes in the diametric classes, but in all populations a decrease in the number of rosettes can be observed in the classes with the largest diameter. The small area of occupation (9,185 m2) showed environmental specificit and vulnerable to habitat loss and environmental changes. Therefore, the maintenance these sites is essential for the long-term conservation of D. brevifolia.