Brazilian pine diameter at breast height and growth in mixed Ombrophilous forest in Southern Brazil

摘要

Information on the diameter at the breast height (DBH) growth of trees can be useful to understand their productivity and temporal dynamics in natural forests. This study presents the first results of increments in DBH of Araucaria angustifolia trees since their logging prohibition in southern Brazil, in late 1970s. We used dendrochronology techniques in 210 individuals in three different sites, which allowed a retrospective analysis of the DBH increment from 60 to 150 years. We adjusted temporal dimensional models whose results may help to support a sustainable forest management of A. angustifolia in southern Brazil. The results showed that the width of annual growth rings varied from 0.04 to 4.8 cm year -1 along the last 60 to 150 years, and the mean annual increment ranged from 0.3 to 0.9 cm year -1 . The DBH increment accumulated in the last ten years showed a decreasing pattern, indicating that most of the sampled trees had already reached maturity. This result denotes a proportional loss in DBH increment with increasing DBH and age. Decreasing DBH growth rates became even more evident in the last ten years (i.e. ~0.15 cm year -1 ), indicating a need of silvicultural intervention in some sites to reduce competition among trees for soil nutrients and light. Regarding the average DBH increment growth, the time the trees need to reach the optimal DBH harvesting diameter of 40 cm ranged from 25 to 112 years, according to the local site index characteristics. The curve inflection point that represents the DBH increment occurred between 35 and 45 years for this specific DBH. These results confirm the viability and need of forest management practices of A. angustifolia trees due to the saturation of the trees DBH growth and increment capacity that reached its inflection. Therefore, since their logging prohibition, most A. angustifolia trees reached their optimal DBH harvesting size. Forest management is necessary for conservation of the forest structure. It would favor the growth of young A. angustifolia, seedling productions, the natural regeneration of this species and genetic diversity; and stimulate the increase of timber production.