Dynamics of a Mixed Ombrophilous Forest Fragment Located in the Irati National Forest, Parana

Abstract

The present study aimed to evaluate the processes governing forest dynamics in a fragment of Mixed Ombrophilous Forest located in the Irati National Forest, Paraná. For this purpose, growth, recruitment, and mortality were described at the botanical family, species, and ecological group levels, based on data from a Continuous Forest Inventory conducted over nine years. Data from 25 permanent one-hectare plots (100 m × 100 m) were used. All individuals with a diameter at breast height greater than or equal to 10 cm (DBH ≥ 10 cm) were properly identified and measured in the years 2002, 2005, 2008, and 2011. Growth was assessed based on the increase in diameter and basal area of trees measured on the four occasions. Recruitment was defined as all trees that reached a DBH of 10 cm or more in a given remeasurement. Mortality was obtained by counting trees that died during the evaluated periods. The forest exhibited an average diameter increment of 0.23 cm.year⁻¹, with the highest increments observed for the species Araucaria angustifolia (0.42 cm.year⁻¹), Ocotea porosa (0.38 cm.year⁻¹), and Cedrela fissilis (0.35 cm.year⁻¹). The forest's basal area increment was 0.21 m².ha.year⁻¹. In percentage terms, the basal area increase over the study period was 6.62%, corresponding to an annual growth rate of 0.74%. In this regard, A. angustifolia stood out, with an increment of 0.12 m².ha.year⁻¹. The average mortality rate of the forest was higher than the recruitment rate (1.69% and 1.31%, respectively), with the species Coussarea contracta and Ilex paraguariensis accounting for the highest number of recruited and dead individuals, respectively. The family Myrtaceae was the most representative in terms of recruited individuals (22.3% of the total), while Aquifoliaceae was the most representative in terms of mortality (18.9% of the total). Individuals belonging to the early secondary group showed the highest recruitment and mortality rates during the period, with annual rates of 1.04% and 1.98%, respectively. The higher mortality compared to recruitment did not affect the net growth of the average basal area per hectare, characterizing the successional advancement of the forest, which increasingly assumes the characteristics of its primary configuration and evolves toward reaching its full stock.