How to calculate plants number in a given population?
More details:
small annual species (less than 10 cm) often forming small but dense mats with many individuals growing close together but also growing as scattered individuals in the same population.
population ca. 0,2 hectares
vegetation covering pattern very heterogeneous with some large bushes and some small trees surrounded by more or less bare ground where annuals, herbaceous perennials and suffrutices can grow.
soil: more or less stony with some rocks emerging.
Quick reply
1 sq metre (or (1 metre radius round) plots for counting every individual small plant
5 metre radius round plots for shrubs
10 metre radius round plots for larger plants
Square is easier for the smaller plot as you can make a 1 x 1 frame
round is easier for larger plots as you can use a rope to measure the circle.
Then to randomly select plots for the area you would need to / want to cover
In this context, extrapolate. Set up some 1 x 1 m plots with varying densities of the plant, probably in 10 or 20% increments. Count the number of plants in these plots. Then once you have your control plots and the counts, go to bigger areas and say “this area is 10m2, and about 40% cover it must have about X plants” multiply 10 by the number of plants in your 40% cover control plot. Repeat.
I’m not sure how precise your estimate has to be, but this can give a good estimate over large areas.
This is the reference I found most useful when designing plant monitoring systems and protocols. It’s a weighty tome, and somewhat technical, but it’s excellent and can be downloaded free at the link below:
This technical reference describes the role of effective monitoring and provides a step-by-step overview of the entire monitoring process for single plant species. The challenges of successful monitoring involve efficient and specific design and a commitment to implementation of the monitoring project, from data collection to reporting and using results. The material in this reference is presented in a logical progression from planning and objective setting, designing the methodology, and taking the measurements in the field to analyzing and presenting the data and making the necessary management responses. However, many of the steps occur simultaneously or provide feedback for the others. Decisions made at each step of the monitoring process can affect the whole project and may sometime lead to reassessment of previous decisions.