This is not referring to the commercial scale of replacement since the rate at commercial scale exploitation cannot be estimated to any accuracy.
Ideally each man or woman plants a tree on his / her birthday!
1. The use as timber products for roofing and housing
This amount is to keep the balance of nature. If one has a house with 4 adults in it this estimate makes it 40 trees around their neighbourhood and the way the houses are built in a city next to each other there is is no room for to grow enough trees.
Colombo city can never regain its splendor what ever we do now for it.
The Kandy city has almost 3 three times population density of Palestine Refugee Camps and we are going to be no different to Israel in another 10 or 20 years.
Regarding the commercial exploitation the re-plantation has to be according to the tree’s cycle. If the tree grows to maturity in 4 years for every tree harvested 4 should be planted and only a few trees fall into this category.
For some trees, if it is lost it is lost for ever.
They take may be 400 to 500 years for it to grow to maturity and often not reproducing fast enough due to their longevity and this simple equation cannot be applied in recreating it natural habitat.
This is only a rough estimate and we have lost about 60% of our forest cover in 50 years of unsustainable use.
I do not think these people with mega-development ideas have understood the problem or have insight into the matters of concern we are facing now.
The have no futuristic goals but presence of mind for exploitation.
Very soon we will be like Dubai, the work we have to do now is enormous if we are to arrest these trends.