I guess it really depends on the type of plant. if is it a ground cover, flower, shurb or bush, I would say using the quadrat method.

https://www.csus.edu/indiv/b/baxterj/bio%20221b/vegetation%20sampling%20quadrat.pdf

If the species you are look for is taller or woodier then I would use a transect tape method, where you can sample species along a specific distance.

Below are a few more ideas, hope they help Abdenour Kheloufi

https://www.ntc.blm.gov/krc/uploads/285/Field-Techniques-handouts.pdf

Thank you dear David fir your help

You can conduct a survey of the whole area using aerial photography or ground based search

Line transect, random sampling of plots especially in forest plantation of similar size and age on a relatively uniform site or stratified sampling together with random sampling in the natural forest.

Thank you dear James and Andrew

Abdenour,

What type of plant are you interested in (size, habitat, any known or suspected

occurences) and how large of an area do you think you will be sampling (1 hectare, or thousands of hectares)?

A systematic sampling is most common in traditional forest inventory despite having statistical critics. Depending on the geography and distribution of species transect line plots and cluster samplings are also in practices and that can increase efficiency. Adaptive cluster sampling speciallly for surface and understory vegetation and variable plot sampling for commerical tree species would also be very useful in terms of economizing time and money.

Dear Lloyd,

Thank you for your consideration. I am looking to estimate espetially Trees for 1 hectare.

I know that there is a difference between humid and arid or saharian region.

Best regards

Abdenour

Dear Abdenour,

The type of sampling method that you will use, should consider the type of plant you are dealing with and the objective of your survey. For instance, you said that you want to estimate trees for one hectare. You can use either the simple random sampling or systematic sampling (preferably) to locate your quadrats (either 35 x 35 m or 20 x 20 m depending on your region of study) in your study area. Depending on the number of quadrats that you sampled, you can later extrapolate to hectare. However, if your study area has more than one vegetation type, there may be need for you to divide the area into different strata to capture the representative vegetation types, and then use the stratified random sampling method in allocating the quadrats to the different strata. In this case, allocation of quadrats may be proportional to the sizes of the strata or equal for the various strata.

If the environment is different one can go for stratified random sampling method.

But simply I can suggest you that if plant to plant distance is 10m. and row to row distance is 10m. too then in 1 hact.(10000 sq.m.)there will be 100 trees. So,this way you can draw your sampling frame.

Abdenour,

Since you are only looking at 1 hectare a 100% sample is not unreasonable. If it is dense foilage and difficult to navigate then a gridded sample with fixed plots is best. If the plant of interest is rare on the landscape then you'll need more plots to sample a rare occurence. If it is more common then you can use less samples. It would help, of course if you knew the CV (coefficient of variation) of your population then you could design a statistical sample. One other method we use in vegetation sampling is the line transect method. This might be appropriate for a pre-sample to get a round idea of the population and their distribution.

Dear Lloyd Fuller Jayanta Kumar Das Uzoma Darlington Chima,

Thank you very much for your clarification and your time.

Best regards

Abdenour

Estimate of species diversity and density is a good place to start. For tree estimates BDH and basal measurements are key. Next would be grade and health. Pay close attention to the tree crowns as these are a very good indicator of tree health.

Thanks Abdenour for your questions.

Your first question was on the usual sampling methods used in forests. Chima and Lloyd hinted on the species of interest and the type of forest (Plantation or natural forest) you are interested in collecting information on. In addition to this, you also need to first consider the type of information/parameters to be collected from the forest and for what duration, one time or over a period of time. However, if the area for sampling is large where you believe there variations in the environment, do stratified random sampling, if a small area where you believe there is uniformity, conduct systematic sampling of smaller plots alternating along an established transect. otherwise, establish random research plots along different strata for a long term study.

In case it is a rare species, to avoid wasting a lot of time and resources, first study inventory reports of your study area whether the species have ever been spotted in the area or not as this will help you narrow your sampling area to specific location with higher chances of spotting the species of interest.

In your second question for the essential parameters studied to evaluate the presence of a plant species in a given environment, this is linked to association studies where some species most often times grow together in a community of trees, insects and animals. You need to understand the ecology of the species of interest. If the specie is located, also identify and record the closest neighbors, soil characteristics, drainage, common insects, birds and animals found co-existing with the species of interest. You may need information on the DBH, height, crown width, phenology, health among others.

For plantation forest of uniform sizes, line transect and random sampling are preferable.

For even aged or natural forest of similar large site stratified along with random sampling is suitable.

Thanks

Thank you all of you for your consideration and answers