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Aboveground carbon (AGC) maps will assist with the monitoring and verification of carbon stored through restoration of subtropical thicket. Field methods are required to capture AGC ground truth data at the plot scale, but they are highly impractical for large area mapping of carbon stocks. Against this background, a remote sensing method to estimate AGC from very high spatial resolution multi-spectral imagery was developed. AGC ground truth was acquired for 85 plots in a small study area in the Baviaanskloof, South Africa. Using the ground truth, univariate and multivariate snapshot models were developed to predict AGC from features in a 2017 WorldView-3 (0.34-m resolution 8-band) satellite image. Informative features were selected from a large set of spectral, textural, and vegetation index features using stepwise forward selection. Using this approach, the multivariate model produced a coefficient of determination (R2) of 0.886 and root mean square error of 2.862 t C ha − 1. This study demonstrates the efficacy of regression approaches for estimating AGC from multi-spectral imagery and provides a foundation for the spatial and temporal extension of AGC remote sensing in the thicket biome.

Aloe pillansii is a large succulent tree confined to the hyper arid region of the Richtersveld and southern Namibia. Because of its narrow distribution, its small population size and decline in adult plant numbers it is considered an endangered species, susceptible to the impacts of climate change. Using two databases compiled for the 1 202 known South African individuals of the species we identified 10 sub-populations, defined as clusters of individuals within 2 km of their nearest con-specific neighbour. Seven sub-populations were located relatively close to each other in the northern part of their range while three were located together 60 km further south than this. Using correlation and multivariate ordination analyses of the environmental variables associated with each sub-population, we show that the sites of the southern populations are higher, cooler and wetter than their more northern counterparts, which were themselves divided into warm, low-lying sites in the west, with a predominance of winter rain, and moderately high elevation sites with more summer rain in the east. An examination of the height class frequency distribution of all South African individuals shows a bi-modal distribution with more than 25 % of the recorded individuals being less than 1 m in height. There is a significant decline in the 2- 4 m height class, but an increase to 5 m and a steady decline thereafter to the largest height class of 12 m. The best explanation for this pattern suggests that there has been poor recruitment in the species prior to the last 20 years, although theft and herbivory of small individuals might also explain the absence of 2-4 m high individuals in the population. The height class frequency distributions of the various sub-populations differ significantly. The three southern sub-populations exhibit a uni-modal distribution with a low proportion of seedlings and juveniles (individuals