How can you use a belt transect to record changes in species distribution?

[Monster92]

I need to study the measurement of population size of density. However, I can't find information on this that is understandable. Has anyone got any ideas?

[FarmForest Research]

You can do a belt transect in a defined area. However to reduce the possibility of psuedoreplication you need to do an outlier. So you take an area and if you have not marked the species..I am not sure whether its trees or mammals..you need to mark them. Not wure what your working on..