Structural Dynamics of Tropical Moist Forest Gaps

Area of Science:

• Tropical ecology
• Forestry
• Remote sensing

Background:

• Gap phase dynamics are the primary driver of forest turnover in tropical ecosystems.
• Studying these fine-scale gap processes across large landscapes has been challenging.
• Airborne lidar provides detailed 3D forest structure data for landscape-scale analysis.

Purpose of the Study:

• To develop and apply a lidar-consistent definition of forest gaps for tropical forests.
• To analyze and compare gap dynamics at two distinct sites in the Brazilian Amazon using multi-temporal lidar data.
• To investigate the influence of gap size, mortality, and ingrowth on gap closure rates.

Main Methods:

• Utilized multi-temporal airborne lidar data (2008, 2012) covering 1000 ha at Tapajos National Forest and Ducke Reserve.
• Defined dynamic forest gaps as contiguous areas > 10 m² with height < 10 m.
• Quantified gap area, closure rates (height gain), height loss (mortality), and horizontal ingrowth.

Main Results:

• Tapajos National Forest exhibited over twice the gap area (4.8%) compared to Ducke Reserve (2.0%).
• Gaps at Ducke Reserve were smaller and closed faster (1.2 m/yr) than at Tapajos (1.1 m/yr).
• Height loss (mortality) was a more significant factor in gap dynamics at Tapajos (23%) than at Ducke Reserve (13%).

Conclusions:

• Airborne lidar enables landscape-scale characterization of tropical forest gap dynamics.
• Significant spatial variation exists in gap dynamics between the two studied Amazonian forest sites.
• Gap contagiousness was limited at both sites, with mortality risk only slightly elevated near existing gaps.