CO-REGISTERED AERIAL STEREOPAIRS FROM LOW-FLYING AIRCRAFT FOR THE ANALYSIS OF LONG-TERM TROPICAL RAIN-FOREST CANOPY DYNAMICS

Ground-based censusing of tagged trees in permanent plots has been the standard research method for monitoring the long-term dynamics of tro pical rainforest tree populations. This paper describes a method for q uantifying the turnover and crown growth rates of tropical rainforest canopy trees over an 18-year period using a temporal sequence of large -scale aerial stereopairs. The stereopairs were co-registered using an array of control points that consisted of surveyed aerial targets and primary branch bifurcation points (BIPs) having the same persisent ge ometry and spatial coordinates in the crowns of selected canopy trees. Six crown size classes were distinguished, and critical late stages i n the life history of mature canopy trees were identified. The smalles t crown size classes (<20 and 20 to 40 m(2)) experienced, more than 75 percent of the canopy tree mortality over the 18-year period; Of the canopy trees that survived, the mid-range 60- to 80-m(2) crown size cl ass was identified as a critical late stage, having both the highest m ean crown growth rate (2.42 m(2) yr(-1) among those trees that exhibit ed positive growth as well as the highest proportion of trees (47 perc ent) experiencing a reduction in crown size. The results demonstrate t hat high resolution, aerial stereophotography from low-flying aircraft can serve as a valuable tool for demographic research in tropical rai nforest ecosystems.