Quantifying the effect of surrounding forest cover on the recovery rate of secondary forests using Landsat timeseries

By Louise Prins

Abstract
A substantial part of forest worldwide is secondary forest, i.e. woody vegetation that regrows after disturbance. For forest management and regeneration strategies, it is important to know how fast the biomass and biodiversity of secondary forests recover, and what factors influence this. The recovery rate of biomass and biodiversity depends on biotic and abiotic factors such as stand age, climate, prior land use, soil type and fertility and seeds dispersed from surrounding forests. The effect of the surrounding forest cover on the recovery rate is expected to be strongest just after disturbance. However, earlier studies often used the surrounding forest cover of years after disturbance, which may not be representative for the forest cover just after disturbance. In this thesis we assess the effect of the surrounding forest cover of the first 7 years after disturbance within different neighbourhood sizes, together with stand age (6-14) and soil fertility, on the recovery rate of biomass and biodiversity of secondary forests. To quantify the surrounding forest cover in the years after disturbance of 76 sample plots in Yucatan, Mexico, a novel classification approach was developed, using Landsat timeseries and a Random Forest classifier. This resulted in 15 annual forest/non-forest maps. Here we show that the surrounding forest cover just after disturbance has an overall positive effect on the recovery rate of biomass and biodiversity. The effect on both biomass and biodiversity is dependent on the neighbourhood size of the surrounding forest. The surrounding forest cover in the first year after disturbance affects the recovery of biodiversity more than later years. Biodiversity is only affected by the surrounding forest in the first successional stages, while the surrounding forest cover seems to affect the recovery of biomass in the long term. These results show that the recovery of secondary forests is affected by the higher seed dispersal related to more forest in the surroundings. For future research, we recommend taking a longer timeseries to be able to assess the effect of forest cover in later years after disturbance and with a longer timeseries the effect on forests in later stages in succession can be analysed.