## 1 Introduction  
Wildfire is an important process in regulating vegetation succession, plant regeneration, and species composition in boreal forest ecosystems [1, 2, 3]. Large areas of the boreal forest zone, which natural fire have shaped over several millennia, are burned annually. Industrial and recreational use of boreal forests and forest fire suppression capabilities have dramatically increased over the past century [4]. Northeast China maintains abundant forest resources, with a forest area of \(\sim\)47.0 \(\times\) 10\({}^{4}\) km\({}^{2}\), occupying 31% of China's total forest area [5]. This region stores 1.0-1.5 Pg C and contributes to approximately 24%-31% of the total carbon storage in China [6]. Most carbon is stored in living trees. For thousands of years, wildfires have been the predominant disturbances in this region, which have been strongly modified by humans during the recent half century. Historically, fire regimes in these systems were characterized by frequent, low intensity surface fires mixed with sparse stand-replacing fires over relatively small areas. From 1950 to 1995, the annual average burned area in the northeast region accounted for 55% of the national total [7]. Wildfires play a dominant role in boreal ecosystems, altering the forest succession, biogeochemical cycling and carbon sequestration [8]. During pre-fire periods, forests are believed to be a net carbon sink--a place where carbon is stored (or sequestered). When wood is burned, carbon is emitted in decomposition, and wildfires are believed to represent a globally significant source of terrestrial carbon in the atmosphere. Following a wildfire, more carbon is absorbed in younger trees during the faster regrowth phases and it is transformed to a carbon sink again after fire. Therefore, a better observational base for understanding post-fire vegetation dynamics in the boreal forests will contribute to predicting the effects of the increasing number of wildfires caused by climate change in these ecosystems and subsequently forecasting the future role of boreal forests as a carbon sink or source [9]. Wildfires create profound changes in ecosystems, causing variations in vegetation reflectance, moisture and temperature, which can be detected by means of satellite imagery [10, 11]. Fire disturbance causes substantial spectral changes by consuming vegetation, destroying the leaf chlorophyll, exposing soil, charring stems and altering vegetation moisture. These effects of a fire on vegetative ecosystem properties are often defined as burn severity, which is restricted to the loss of organic matter in or on the soil surface, and in this respect represents what BAER assessments term \"soil burn severity\" [12]. The post-fire re-growth process is of great importance because while fire releases carbon into the atmosphere, carbon sequestration through post-fire regeneration of plants and woody vegetation may help to reduce the amount of carbon in the atmosphere [13]. Numerous studies have focused on the use of the Normalized Difference Vegetation Index (NDVI) to analyze seasonal and inter-annual vegetation dynamics and trends following wildfire disturbances [14,15]. The NDVI data capture the contrast between red and near-infrared reflectance of vegetation, which signals the abundance and energy absorption of leaf pigments, e.g., chlorophyll. NDVI can be used as a proxy for the vegetation response to wildfire disturbances because it is well correlated with vegetation regrowth and the fraction of photosynthetically active radiation absorbed by plant canopies and, thus, leaf area and biomass [16]. In the present paper, NDVI derived from and the Advanced Very High-Resolution Radiometer (AVHRR) satellite measurements is exploited to investigate post-fire regeneration and temporal dynamics in the boreal forest. Because of an unusually prolonged drought and high winds in northeastern China, the Great Xing'an Mountains exploded in a catastrophic wildfire in May 1987.