Long-term monitoring of Aloidendron dichotomum populations: Does tracking individuals make a difference to general demographic findings?

The findings of the first four Aloidendron dichotomum population surveys in 2015 that form part of a longterm monitoring initiative started by the South African Environmental Observation Network at Meerkat National Park were compared with the findings of a second survey in the same populations in 2021. Aloidendron dichotomum is a keystone species and was previously suggested as a climate change indicator species therefore understanding its population dynamics is important. A general population density and mortality survey, as well as a detailed demographic survey were repeated in August 2021 using the same methods that were used in 2015. The surveys were conducted in the same populations but not of exactly the same individuals. The aim of this study was to compare the findings of the 2021 surveys with the findings of the 2015 surveys in order to assess whether it is crucial to survey exactly the same individuals within a population or not. Live: dead ratios varied considerably across the populations between the surveys conducted in 2015 (range: 17 to 35 per ha) and in 2021 (range: 6 to 28 per ha). For each population the size class distribution (SCD) types did not differ significantly between 2015 and 2021. Populations had zero permutation indices for basal diameter for the two surveyed years suggesting that the populations are monotonically declining and therefore the populations are stable. However, two permutation indices for height were not zero. The presence of leaf fungi and scale during the two surveys was generally low while the presence of lichen remained similar between survey years. There was more damage to leaves and stems in 2021. Our conclusion is that the general demographic findings for the 2015 and 2021 surveys were similar so it is not necessary to survey exactly the same individuals within a population to determine the general demography of a population. However, marking and measuring exactly the same individuals could provide valuable insights onto the finer nuances of population demographics and dynamics in this species.(c) 2022 SAAB. Published by Elsevier B.V. All rights reserved.

Automated summary

This study compares the findings of population surveys conducted in 2015 and 2021 for the plant species Aloidendron dichotomum. The results suggest that it is not necessary to survey the exact same individuals within a population to determine the general population dynamics, but marking and measuring the same individuals can provide valuable insights into the finer nuances of population demographics and dynamics in this species.