I used systematic sampling for this technique. I go to the same locations to collect the data each time as well as take account of the same things. Some difficulties I have faced is mostly with the weather. In Manitoba our fall/winter has not been normal with snow falling in bundles and then melting for a few days and then it snowing again. This haphazard weather has also caused the trees to lose their leaves at a different rate than seen in previous years. This has also been surprising to me when collecting the data for the study because i did not expect the pond to lose the leaves as fast as they had. With the weather I may have to change my sampling approach because of the leaves falling at a faster rate than I anticipated. I would do this likely haphazardly by finding any trees with leaves left and using those as guide to determine the length of time it takes for leaves to fall and if humans have any impact on that. This will allow my research to be able to continue and not be cut short because of the premature leaves falling.
I am interested in how you are sampling leaves. I haven’t seen the first or second small assignment from you yet.