Efeitos de tratamentos silviculturais na dinâmica de Platonia insignis Martius "bacurizeiro" (CLUSIACEAE) em florestas secundárias no nordeste do Pará, Brasil.

Abstract

The fruit of the species Platonia insignis, in the Bragantina region, is essential as source of livelihood and income for small farmers. The management of secondary forests through application of silvicultural treatments can stimulate the growth of the species and allow a better understanding of the forest dynamics. In order to describing the dynamics of Platonia insignis in two secondary forests, in the municipal district of Bragança, the effect of silvicultural treatments was analyzed on diameter increment of individuais selected and the ingrowth and mortality for two years of monitoring. Each forest was denominated of Agrarian Unit (AU) and four plots were installed with embroidery of 10 m with 70 m x 105 m (AU1) and 35 m x 100 m (AU2). Two treatments were applied with two replication in 2005, TO - control and TI - plots with silvicultural treatment that consisted of liberation thinning and girdling the release of competitor individuais whose crown overlapped a radius of 20 m, crowning of 2,5 m (AU1) and 2 m (AU2) and ali lianas were cut. Ali individuais live tree were measured with diameter at breast height (DBH) > 10 cm in 2005. In 2007, it was remeasurement of trees in exixtence, evaluation of the mortality and marking and measurement of the recruitment (ingrowth). To study of the variation was used Student t test and Mann Whitiney for the comparison of means. In TO plots recorded in a total of 185 individuais distributed in 119 for AU1 and 66 for AU2. TI recorded in a total of 167 individuais, with 92 for AU1 and 75 for AU2. In 2007 that number decreased to 341 individuais due to mortality, with 176 individuais in TO plots, distributed in 111 for AU1 and 65 in AU2. In TI it was classified 165 trees, distributed in 91 (AU1) and 74 (AU2). The annual diameter increment average in TI was significantly higher in both secondary forests (p <0.0001), with two years of monitoring. TO presented overall average of 0,28 cm.year 1 and TI of 0,56 cm.ycar'1. AU1 presented 0,14 cm.year 1 for TO and 0,25 cm.year 1 for TI; In AU2 the average went of 0,53 cm.year1 to TO and 0,93 cm.year1 for TI. In AU1, 13 individuais at TI had no positive results, in other words, without increasing diameter. In the TO treatment, the number of individuais enhanced for 27; in AU2 TO presented 3 and none in TI. It was evidenced in AU1 a distribution decreasing in the J-inverted form. There were not individuais in the superior classes of the diameter in AU2. The treatment with higher number of ingrowth, in AU1, was TI with 1,33 trccs.ha'1 .ycar; while TO presented 1 trcc.ha'1 .ycar. The ingrowth rates was from 4,35% to TI and 2,52% for TO. The treatment that presented higher mortality was TO with 2,66 trcc.ha'1 .ycar, TI was with O.SSlrcc.ha'1 .ycar. The mortality rate was from 1,09% to TI and 6,72% for TO. The treatment with higher ingrowth, in AU2 was TI with 6,42 tree.ha" 1 .year, TO was with 5,71 tree.ha"1.ycar. The ingrowth rate for TO was from 12,12% and 12% to TI. For the mortality, both treatments had the same amounts of individuais in the period (0,71 tree.ha"1.ycar). The mortality rate was from 1,52% to TO and 1,33% for TI. AU1 presented higher mortality rate in TO. In the treatment TI in AU2 recorded higher rate than registered in AU1, and, that difference is due to the number of individuais found in the plots in 2005, because the Agrarian Units registered the same number of the death individuais in the period. Therefore, the positive effect of silvicultural treatments in the diameter increase can serve as subsidy for activities of management and application in secondary forests as growth inductor and it is advisable studies with other species of importance for use. The results found for the recruitment rates can help to understand the dynamics on secondary forests.