Mapping forest growth and decline in a temperate mixed forest using temporal trend analysis of Landsat imagery, 1987-2010

- 1986-2010 temperate forest dynamics modeled and mapped using vegetation indices.
- Tasseled Cap Wetness was the most robust indicator of vegetation quantity.
- Contextual Mann-Kendall and Thiel-Sen analyses used to map growth and deterioration.
- Significance of temporal trends determined in relation to the data 'noise floor'.
- Change results were found to be reliable using intervals up to 3 to 5 years.

Forest management seeks sustainability for a diverse set of goals, including economic objectives, provision of ecosystem services, and provision of a variety of possible land uses. It is important to quantify, map and monitor forest dynamics resulting from natural and anthropogenic processes over time periods appropriate to the temporal scale of change as well as to land management goals and decision making. This paper presents temporal trend analyses of temperate mixed forest dynamics in Gatineau Park, Québec, Canada, using a time series of Landsat 5 TM scenes. Several vegetation indices were first evaluated as indicators of field measured vegetation abundance parameters such as leaf area index, canopy openness, DBH, and basal area. Of these, Tasseled Cap Wetness (TCW) provided the best relationships (e.g., r = 0.81 against LAI) and it differentiated between coniferous, mixed and deciduous forests. Thirteen clear sky 5 TM scenes from the growing seasons of 1987 to 2010 were relatively calibrated and assembled into an image time-series. TCW applied to the image time-series followed by Theil-Sen and Contextual Mann-Kendall trend analysis detected subtle and gradual field-verified forest change. Gradual and abrupt forest decline or regrowth periods were identified; over the full period, 641 ha (1.8% of the park) exhibited statistically significant growth, and 689 ha (1.9%) exhibited decline. Mapping the timing, location, magnitude, and duration of forest change will help inform land management policy and actions within Gatineau Park and such methods may be applied in other similar forests.