Reflectance factor dynamics of boreal forest clear-cut communities during early secondary succession

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Abstract
Spectral reflectance factors in the visible and near-infrared spectral bands were measured over five years on permanent sample plots in forest clear-cut communities in Estonia. The spectral-temporal profiles of vegetation indices Greenness and Brightness were calculated from discrete measurements of reflectance factors. The following hypotheses concerning successional reflectance dynamics in boreal forest communities following clear-cutting and understory destruction were tested. 1. Changes in the Greenness seasonal profile peak value (PV) during secondary succession are mainly directional and related to time after clear-cutting rather than to environmental fluctuations. 2, The rate of succession, i.e., difference between seasonal PVs of consecutive years, declines over time. 3. The seasonal PVs of forest communities from different site types become more similar (converge) during secondary succession. The results show that the secondary succession of forests in reflectance terms is directed towards the enhancement of contrast between visible to near-infrared reflectance, towards obtaining maximum spectral vegetation index Greenness value at a given Brightness level. The PV changes during secondary succession were explained by the age of the communities. The seasonal PVs of different site type clear-cuts converge during early secondary succession, resulting from different speed of clear-cut recolonization on fertile and poor sites.