make a sound investment and save the planet ?

ok, excuse the sensationalist title, I refer to the following, which is, of course, more relative :

In the northern Paraguay Chaco region undeveloped, clear title properties, consisting entirely of natural impenetrable forest, cost roughly US$300/hectare. The good ones do, prices can go below US$100/hectare, when soils are poor and rainfall low, but those are not buys I can recommend.
(properties are usually no smaller then 4000 hectare, so in absolute terms those are million dollar investments)

These lands are different from what might come to your mind, like the tropical rainforests of the amazon, or similar.
They usually consist of very deep sedimentary soils, rather rich in nutrients, and receive less (though not too little) rainfall then the rainforests further north. Forests of this climate belt (transition semi arid to semi humid tropics) are of lesser height and drop their leaves during dry season.

Unlike the land the amazon rainforest grows on, those soils make good farmland, not just for cattle grazing, but real farmland to grow grains etc.
It is so cheap because it is so remote. Paraguay is a low development country and road network in the Chaco is very poor. That makes it arduous to develop those properties now before roads improve, which they do.

But the point might be, humanity might be better served not to cut those forests but leave them and let them do their job of storing carbon, wildlife, evaporating moisture etc, or, say, leave 80% and convert only the rest into farmland.
So, where is the return for a land buyer refraining from deforestation, apart from being a good guy -
Now it gets hypothetical.
If you own an asset and can either do something that generates personal income or do something that benefits society and essentially so, in many cases (not all, admittedly) sooner or later there will be a mechanism that reembourses you to do the beneficial thing, a mechanism that possibly develops out of the existing global carbon offset trade, the UN-REDD (http://en.wikipedia.org/wiki/Reducing_Emissions_from_Deforestation_and_Forest_Degradation) points in that direction.

So far for being a good guy, now for cold-hearten asset allocation.

Lands with soil/topography/climate characteristics similar to the above mentioned at US$300/hectare cost US$9000 in some first world countries where location, infrastructure and legal/institutional framework is first rate, like Australia.
Now, 1:30 is quite a valuation gap if there ever was any.
That means there is a huge margin for appreciation. And it means, if once carbon credit type of rents set in, related to that moment's property value, your return on purchase price value could be very nice.

Like that it may develop.

Or - it simply gets prohibited to cut any forest, no compensations paid, then your asset value drops severely.
Or - they prohibit, after you bought, the sale of large tracts of land to foreigners, that would harm the market value of your land somewhat, though not its intrinsic value.
Or - you once get governed by a business unfriendly, Hugo Chavez type of government, who harasses land owners in a hundred different ways, raising property taxes, invent stupid regulations, whatever.

Judge by yourself, if you like the chance-risk-profile.
I like it.
I buy land over there with my own money.