Demanda hídrica em plantio de Pinus e em uma floresta nativa, na região de Telêmaco Borba

Abstract

This research aimed to study the demand for water in a soil under Pinus taeda plantation subjected to four different densities, a clear cut, and a native forest by monitoring the water balance variables. The work was conducted in the Klabin Forest Farm, located in the Telêmaco Borba County, Parana State, southern Brazil, during the year 2009. A split plot design in randomized blocks was used in order to study the relationships between the pine plantation densities, five soil depths, and the four seasons of the year. The DBH and the trees height were measured in order to determine the basal area and the wood volume in each plot. The average crown diameter was also measured to estimate the intercepted precipitation. In the forest only the DBH was measured, to calculate the basal area. The pine plantation treatments (densities) were: T1 - clear-cut; T2 - no trees removed (1666 trees.ha-1); T3 – 25% of the trees removed; T4 – 50% of the trees removed; and T5 – 75% of the trees removed. Three pluviometers were installed in each plot to measure the amount of precipitation. The water flow through the tree trunks were measured in two trees in each treatment, except the clear cut. The precipitation and stem flow, as well as the soil moisture at the depths 0 to 0.10 m, 0.10 to 0.20 m, 0.20 to 0.40 m, 0.40 to 0.60m, and 0.60 to 1.0m, were weekly monitored. Undisturbed soil samples were collected in trenches, both in the pine plantation and in the forest, in order to determine the soil density and porosity. Pressures of 0.06; 0.1; 1.0 and 15 atm were applied to the soil samples to determine the micro porosity, field capacity, wilting point, macro porosity, aeration porosity, and available water. The statistics used included the Bartlett’s test, the analysis of variance and co-variance, and the Student-Neuman–Keuls’ (SNK) test, through the MSTAT software. It should be emphasized that the year 2009 presented a total precipitation well above the historical average for the region, due to the occurrence of the El Niño episode. Results showed that in the pine plantation soil interactions between treatments, depths and seasons were no statistically significant at 5% level. However, soil depths and seasons of the year presented statistical differences. Treatment 1 (clear cut) presented the highest water storage during the year, followed by T3 and T2. Treatments T4 and T5 presented increases in the canopies diameter from 2008 to 2009, in the order of 72.62% and 103.70%, respectively, what may have interfered in the precipitation interception and affected the consumption of water in these treatments. Regarding the forest, the results showed that, except in the first depth, the water storage did not differ statistically at the 5% level of significance. The summer and autumn were statistically similar regarding the water storage. The precipitation interception in the forest was smaller when compared to the pine plantation, and the water stem flow was less important regarding the water input to the soil.