I have done something very similar on my server recently to try to control the tree pulp being left around. Keep in mind these laws are new on not well tested so I am not sure how this in going to work for new players that join the server. Also we are doing it with a global currency that we created called the EOG Dollar.
First we charge a deposit for harvesting the two tree types of 1 EOG. This then gets put into the treasury.
Then we refund .25 for each pulp picked up. This then gets taken back out of the treasury. I have found that this amount is going to be too high for the average amount of pulp created per tree. I wish I could modify the law but all it looks like you can do is delete the law and create a new one.
Under the server interface click the user tab and there is an option for private server, make it true. I am not sure but you probably need to add all the names of the players you only want to have access to the whitelist which can be access from the same tab.