Vegetation plays a fundamental role in the biosphere–atmosphere system, while vegetation is extremely influenced by water availability in the atmosphere and soil. Therefore, this paper aims to evaluate the response time of vegetation to the availability of water in the soil in the Jaru Biological Reserve. The variables used to determine the response time were soil moisture and leaf area index. The response time was obtained for a time interval every four days and was investigated using the cross-correlation method to obtain the maximum correlation coefficient between the variables. From the tests carried out, it was observed that precipitation is an important environmental factor and is highly correlated with other hydrological and vegetational parameters. The response time between vegetation and soil moisture was 56 days. However, it showed a weak but significant correlation. Because of that, it was found that the availability of water in the soil is not the most relevant parameter in the development of vegetation, showing that this issue is complex and requires further studies to determine which variables influence the dynamics of vegetation in Rebio Jaru.