Post-Fire Changes in Forest Biomass Retrieved by Airborne LiDAR in Amazonia

Abstract

Abstract:Fire is one of the main factors directly impacting Amazonian forest biomass and dynamics. Because of Amazonia's large geographical extent, remote sensing techniques are required for comprehensively assessing forest fire impacts at the landscape level. In this context, Light Detection and Ranging (LiDAR) stands out as a technology capable of retrieving direct measurements of vegetation vertical arrangement, which can be directly associated with aboveground biomass. This work aims, for the first time, to quantify post-fire changes in forest canopy height and biomass using airborne LiDAR in western Amazonia. For this, the present study evaluated four areas located in the state of Acre, called Rio Branco, Humaitá, Bonal and Talismã. Rio Branco and Humaitá burned in 2005 and Bonal and Talismã burned in 2010. In these areas, we inventoried a total of 25 plots (0.25 ha each) in 2014. Humaitá and Talismã are located in an open forest with bamboo and Bonal and Rio Branco are located in a dense forest. Our results showed that even ten years after the fire event, there was no complete recovery of the height and biomass of the burned areas (p < 0.05). The percentage difference in height between control and burned sites was 2.23% for Rio Branco, 9.26% for Humaitá, 10.03% for Talismã and 20.25% for Bonal. All burned sites had significantly lower biomass values than control sites. In Rio Branco (ten years after fire), Humaitá (nine years after fire), Bonal (four years after fire) and Talismã (five years after fire) biomass was 6.71%, 13.66%, 17.89% and 22.69% lower than control sites, respectively. The total amount of biomass lost for the studied sites was 16,706.3 Mg, with an average loss of 4176.6 Mg for sites burned in 2005 and 2890 Mg for sites burned in 2010, with an average loss of 3615 Mg. Fire impact associated with tree mortality was clearly detected using LiDAR data up to ten years after the fire event. This study indicates that fire disturbance in the Amazon region can cause persistent above-ground biomass loss and subsequent reduction of forest carbon stocks. Continuous monitoring of burned forests is required for depicting the long-term recovery trajectory of fire-affected Amazonian forests.

Dynamics of Above-Ground Biomass in the Brazilian Amazon Using LiDAR Data

“…The pattern found for CH is similar to the inverted-J, typical of natural forests where a large number of trees that populate the smallest diameter classes is found, following an exponential decrease in the number of large diameter trees (Odum, 2001). This pattern was also found by Sato et al, (2016) when quantifying fire impacts on forest height and biomass in southwestern Brazilian Amazonia using LiDAR technology. Regarding the positive structural changes in crown areas, they may be related to the increase in the availability of resources, which increases the NPP (Net Primary Productivity), and, increases the growth rates of individuals, as a consequence.…”

“…Even as results that did not differ significantly, we cannot disregard the fact that negative changes are occurring in forest AGB stocks, requiring a longer period of time for an assessment of changes in a forest with no evidence of large events, such as observed by Sato et al (2016) who detected changes in forest biomass and height for a period equivalent to 10 years, at least, after the occurrence of a sub--forest fire event. These authors also point out that this type of disturbance may cause a persistent loss in AGB and subsequent reduction in forest carbon stocks, and that LiDAR is a powerful technology to exploit these impacts.…”

Post-fire recovery of a dense ombrophylous forest in Amazon

“…However, in this study, before and after the occurrence of fire, the highest mortality occurred among trees with smaller diameters (DBH < 30 cm) (Xaud et al 2013) and the fire in the study area did not impact the survival of large trees (Sato et al 2016), explaining why the reduction in the density of living trees (Barlow et al 2003) did not strongly affect the decrease of the basal area in the burned forest.…”

“…Thus, forest fires may be increasingly recurrent (Barlow et al 2016), considering that the leakage fire agricultural areas surrounding forests is threatening synergy between deforestation and climate change (Aragão et al 2008), while little knowledge is available on the resilience of these forests to fire. The monitoring of burned forests is the best way to know the mechanisms of resilience after fire (Betts et al 2016) and to describe the recovery path (Sato et al 2016). The impact of forest fire is directly associated with tree mortality (Sato et al 2016).…”

“…The monitoring of burned forests is the best way to know the mechanisms of resilience after fire (Betts et al 2016) and to describe the recovery path (Sato et al 2016). The impact of forest fire is directly associated with tree mortality (Sato et al 2016). The existing knowledge infers that, in fire-affected forests, mortality is directly proportional to the severity of the fire and after initial light burning, is higher in trees with smaller stems (Xaud et al 2013).…”