Out of steady state: Tracking canopy gap dynamics across Brazilian Amazon

Abstract

Canopy gaps are evidence of disturbances on forest landscapes. A forest stand is in constant flux, with long stretches of biomass accumulation punctuated by episodic disturbances. We used multitemporal airborne laser scanning data to compare the gap dynamics of four Amazon forest sites. We assessed gap dynamics over 1.9–3.8 years between 2017 and 2020 at sites in the central, central eastern, southeastern, and northeastern regions of the Brazilian Amazon, over areas ranging from 590 to 1205 ha at each site. Gap size ranged from a minimum of 10 m2 to a maximum of about 10,000 m2. We analyzed four stages of gap dynamics: formation, expansion, persistence, and recovery based on two consecutive airborne laser scanning surveys. The gap fraction at our study sites varied between 1.26% and 7.84%. All the sites have similar proportion of gaps among gap size classes. What notably differed among sites was not the gap size‐distribution, but the relative importance of stages of gap dynamics. Expansion and persistence rates ranged from 12 to 118 m2 ha−1. The gap formation rate (formation + expansion) was lower than the recovery rate for three of the four study sites. In contrast, the southeastern site has 1.44 times more area in formation and expansion compared to gap recovery. Over the 2–4 years interval of our study, no site was close to steady state. Multitemporal analyses of large areas over many years are needed to improve our understanding of tropical forest dynamics.

Gap expansion is the dominant driver of canopy openings in a temperate mountain forest landscape

“…Specifically, we did not detect a signal towards more open forests, such as expected for many ecosystems under global change (McDowell et al, 2020), but rather found indications of a densification of forests in our study system. This is well in line with terrestrial observations from earlier studies both in BGNP , in the Alps more broadly (Kulakowski et al, 2017), and was also reported for other systems (Gorgens et al, 2023;Rodes-Blanco et al, 2023). Nonetheless, emerging novel disturbance regimes and ecological responses will likely continue to alter ecosystem dynamics (Seidl, & Turner, 2022).…”

“…Once a gap is created, the course for the surrounding forests is set for the coming years, as new gaps are more likely to emerge next to existing gaps, and as gaps keep growing over multiple years. This pattern of spatial dependence was found also in other studies in temperate (Blackburn et al, 2014;Senf, Campbell, et al, 2017), tropical (Gorgens et al, 2023) and boreal forests (Hytteborn & Verwijst, 2014;Vepakomma et al, 2012). Potential processes contributing to the contagious nature of canopy gaps are edge effects (Hunter et al, 2015;Pöpperl & Seidl, 2021), as edge trees are more susceptible to drought and wind (Buras et al, 2018;Seidl et al, 2014); but also dispersal mechanisms, such as the flight of bark beetles, which can contribute to spatially clustered canopy openings (Kautz et al, 2011;Seidl et al, 2016;Senf, Campbell, et al, 2017).…”

“…Moreover, repeated lidar acquisitions enable researchers to track gap development over time, allowing for a fine-grained analysis of gap formation and closure (Jucker, 2022;Maltamo et al, 2014). The increasing availability of repeated lidar acquisitions and a rapidly developing processing infrastructure (Roussel et al, 2020;Silva et al, 2019) make multi-temporal lidar a powerful tool for understanding forest canopy dynamics (Blackburn et al, 2014;Dalagnol et al, 2019;Gorgens et al, 2023;Leitold et al, 2022;Rodes-Blanco et al, 2023;Vepakomma et al, 2012).…”

Sensitivity of Optical Satellites to Estimate Windthrow Tree-Mortality in a Central Amazon Forest

“…As previously reported, these severities accounted for decadal changes in floristic composition [1,62,103], biomass stock and balance [2,4], organic soil carbon stocks [104], and insect diversity [105,106] in other Central and Northwestern Amazon forests affected by windthrows. Future investigations are needed to improve the remote detection of smaller canopy disturbances across local-to-regional variations in topography, climate, soils, and forest attributes [42][43][44]107].…”

“…In addition to optical satellites, other approaches such as SAR (Synthetic-Aperture Radar [39,40]), LiDAR [41][42][43] and aerial photos [44] have been tested to estimate treemortality associated with windthrows. SAR offers data that are less dependent on weather effects and with spatial resolutions comparable to high-and medium-resolution satellites [45,46].…”