Post-Fire Vegetation Succession and Surface Energy Fluxes Derived from Remote Sensing

Abstract

The increasing frequency of fires inhibits the estimation of carbon reserves in boreal forest ecosystems because fires release significant amounts of carbon into the atmosphere through combustion. However, less is known regarding the effects of vegetation succession processes on ecosystem C-flux that follow fires. This paper describes intra-and inter-annual vegetation restoration trajectories via MODIS time-series and Landsat data. The temporal and spatial characteristics of the natural succession were analyzed from 2000 to 2016. Finally, we regressed post-fire MODIS EVI, LST and LSWI values onto GPP and NPP values to identify the main limiting factors during post-fire carbon exchange. The results show immediate variations after the fire event, with EVI and LSWI decreasing by 0.21 and 0.31, respectively, and the LST increasing to 6.89 • C. After this initial variation, subsequent fire-induced variations were significantly smaller; instead, seasonality began governing the change characteristics. The greatest differences in EVI, LST and LSWI were observed in August and September compared to those in other months (0.29, 6.9 and 0.35, respectively), including July, which was the second month after the fire. We estimated the mean EVI recovery periods under different fire intensities (approximately 10, 12 and 16 years): the LST recovery time is one year earlier than that of the EVI. GPP and NPP decreased after the fire by 22-45 g C·m −2 ·month −1 (30-80%) and 0.13-0.35 kg C·m −2 ·year −1 (20-60%), respectively. Excluding the winter period, when no photosynthesis occurred, the correlation between the EVI and GPP was the strongest, and the correlation coefficient varied with the burn intensity. When changes in EVI, LST and LSWI after the fire in the boreal forest were more significant, the severity of the fire determined the magnitude of the changes, and the seasonality aggravated these changes. On the other hand, the seasonality is another important factor that affects vegetation restoration and land-surface energy fluxes in boreal forests. The strong correlations between EVI and GPP/NPP reveal that the C-flux can be simply and directly estimated on a per-pixel basis from EVI data, which can be used to accurately estimate land-surface energy fluxes during vegetation restoration and reduce uncertainties in the estimation of forests' carbon reserves.that the area of boreal forest fires occupies approximately 35% of the national burn area; thus, the forest-fire frequency in Chinese boreal forests will increase by 100-200% over the next 100 years [5,6]. Currently, it has been confirmed that fires release significant amounts of carbon into the atmosphere through combustion; however, less is known regarding the effects of vegetation succession following fires on the ecosystem carbon flux (C-flux), which has potential feedback effects that may lengthen adjustments to regional and global ecosystem carbon cycles and further influence climate change.Boreal forests landscape is shaped by fire disturbances and the site's environmen...

Can Landsat-Derived Variables Related to Energy Balance Improve Understanding of Burn Severity From Current Operational Techniques?

“…Our results agree with previous studies showing that ET decreases after a fire event (e.g. [9,89] in semi-arid; [15,90] in boreal forests; and [13,35,91] in temperate conifer forests). In Mediterranean ecosystem, Sánchez et al [17] studied the temporal evolution of changes insurface energy balance over an eleven-year period following fire in a maritime pine-shrub mixed forest (Spain).…”

“…In contrast, variance in unburned areas in 2018 exceeded the variability of burned areas. The 2018 decrease in LST variance in burned areas suggests a reduction in the number of burn severity levels that may be differentiated between, as burn severity determines the magnitude of post-fire changes in LST [90].…”

“…Most previous studies on the impact of fire on energy balance have been based on field-measured surface fluxes, and are only valid at very local scales [13,15,91,92,124]. Others rely on variables derived from coarse spatial resolution satellites (e.g., MODIS), and are only valid at global scales [90,125,126]. There are very few studies (e.g., [17,37]) that use satellite-data-derived variables at a fine spatial resolution.…”

Fire dynamics in Mato Grosso State, Brazil: the relative roles of gross primary productivity

“…The impact of burning on GPP is basically due to the loss of plant biomass since after fire the affected plants decrease or even lose their ability to assimilate carbon through photosynthesis (Biswas et al, 2015;Rap et al, 2015). According to Li, Zhang, Yang, Ding, and Zhao (2018) burns significantly affect canopy structure and leaf area index, which ultimately causes changes in energy balance and forest evapotranspiration.…”

Neural-Network Time-Series Analysis of MODIS EVI for Post-Fire Vegetation Regrowth

“…Different approaches are also used for time-series analysis of remote-sensing data. Some methods use temporal trajectory diagrams and compare ground-truth sampling data or estimates of burn severity with unburnt control sites [16]. These comparisons are either visual or statistical between burnt and unburnt sites using the average differences [17].…”