In assessing a present possessory estate, what is ameliorative waste?

A life estate is only temporary ownership, even if it lasts a lifetime. The law wants to make sure that the people who have dibs on the land after the life estate is over get the land back in a condition that is nearly identical to that which the life estate owner had.

Ameliorative waste is the weirdest of wastes. Where other wastes involve some sort of harm or damage to the property, ameliorative waste is the unauthorized improvement to property.

For example, imagine a place called Meadowacre. Meadowacre is a 10 acre meadow with a small cottage on it that has been in Oz's family for generations. It is a peaceful, tranquil area that allows its owners a unique place to relax and meditate. Imagine if someone decided to build a 300 room hotel on Meadowacre, which generates millions of dollars per year in revenue. This wouldn't be affirmative waste, because no natural resources are being exploited or harmed. Neither would it be permissive waste to invest money in creating a new hotel on the land. That's where ameliorative waste fits in. Yes, its nice that the property is now economically worth more, but the cost was destroying the original purpose, which was to be a lovely, empty plot of land.

With that in mind, modern courts are more forgiving of such changes so long as the market value isn't harmed for future interests in the land, and either (a) the people with future interests are cool with it, or (b) the ameliorative waste was necessary to counteract an outside change which stripped the land of its original economic value (for example, if land was originally a farm surrounded by other farms, but the other farms converted to hotels, making it harder to maintain a farm supply chain alone — then it may be permissible to also become a hotel).