Here's how it works: If the land is nursing seedlings or pre-merchantable timber, it is generally valued at the price of the bare land, plus the discounted future value of the young trees. If the timber is merchantable-that is, big enough to sell as timber or pulpwood-the price can also include an amount anywhere between 10% and 70% of the timber's value. In recent years, those prices have become extremely volatile. They are affected by the variable costs of logging and hauling. 

As trees grow, their value grows. Harvests yield cash flow. Forest economics also differ substantially by species, and prices for the same species can vary by as much as 25% to 30% between mills in the same micro-market.

For example, Southern yellow pines harvested from the ages of 15 to 20 (for pulpwood and paper) currently sell for $8 or $9 a ton. From the ages of 18 to 24, some of it is used for pulpwood and the rest for construction lumber and 2-by-4's, and sells for $15 to $18 per ton. And from ages 27 to 35, when it's mostly used as structural lumber, it fetches $24 to $27 per ton. (These prices are the lowest in decades, no doubt because of the financial crisis and the slowdown in construction.)

Note the "S" curve: A tree grows fastest physically-and reaps its largest economic gains-during its teenage years. After it reaches maturity, both its physical growth and its financial value grow at a slower rate.

While the principles are the same, timber economics differ by species. Douglas fir and hemlock, which grow in the Northwest, are not merchantable until they reach middle age, during the ages of 30 to 45. (They are harvested for saw logs; pulpwood and paper are residuals.) But at maturity (between the ages of 55 and 70) they are four times as voluminous as a Southern yellow pine. That renders their quality, and pricing, superior.

In addition to trees, forests provide a host of "ecosystem services"-clean water, flood control, habitats for fish and wildlife, soil building, carbon storage, etc. According to the United Nations-backed Millennium Ecosystem Assessment (2005), there are 24 main ecosystem services-most of them found in forests. Another United Nations-backed project, the Economics of Ecosystems and Biodiversity (TEEB), has estimated the negative externalities from forest loss and degradation at $2 trillion to $4.5 trillion per year-an amount equivalent to nearly half the U.S. GDP.

As a result, there is a growing interest in investing in bona fide forests with their ecosystem services intact-not just timberland and the wood it produces.

Vineyards are a similar story. In this case, the rule of thumb is that it takes three years to get a crop (and some cash flow), five to six years for the crop to mature, and seven years for it to earn a return. While vineyards are generally 30-year investments (meaning they generate an income for roughly 23 of those years), even 60- to 70-year-old vines can be prized.

As with timber, the bare land can be worth substantially less without the vines. According to Jay Silverstein, a partner at Moss Adams LLP in Santa Rosa, Calif., for example, the value of the land part of a recent deal in Sonoma was roughly $60,000 while the vines were valued at $20,000.

But the value of acreage varies substantially with geography. According to Mario Zepponi, a winery and vineyard investment broker with Zepponi Group, in Santa Rosa, Calif., the current values for non-trophy properties in Napa range from $200,000 to $225,000 per acre-whereas the value of land and vines together is $80,000 in Sonoma, $35,000 to $60,000 in the Central Coast region, and $10,000 to $15,000 in Mendocino and Lake counties.