Evaluation of the impact of resin tapping on the spectral index response of Pinus pinaster stands in the NW of the Iberian Peninsula

Pine resin represents one of the most relevant non-wood forest products on a global scale. This type of harvesting has historically provided a source of goods and services for many people, forming an important fount of revenue and economic activity. The exact impact of this activity on the condition of the trees is yet to be determined. Nevertheless, satellites provide information to monitor and detect changes in forest stands. Thus, we conducted an analysis of a series of satellite-based vegetation indices, including CIG, RDI, DSWI, NDVI and NDWI at three sites, each of which includes stands of resin tapped and non-tapped trees (control). The objective was to identify statistically significant monotonic trends or breakpoints in the data series of differences between control and resin tapped pixels. This was achieved through the utilisation of the Mann-Kendall test and the Pettitt test. The results indicate that, for the locations considered, there is mostly no evidence of monotonic increasing or decreasing trends for any of the indices. Our analysis of the data series to identify potential breakpoints and point effects of resin extraction did not yield any significant results. This suggests that resin tapping does not influence the spectral response of resin tapped trees compared to non-tapped trees in the same locations.