The most expensive tree species in the United States are typically those with rare, exotic, or highly sought-after characteristics. Among these, the following species often command premium prices:

1. Giant Sequoia (Sequoiadendron giganteum): Known for their immense size and majestic beauty, Giant Sequoias are highly valued for their timber and as ornamental trees. They are particularly expensive due to their rarity and the difficulty in transporting them.

2. California Redwood (Sequoia sempervirens): Similar to Giant Sequoias, California Redwoods are prized for their large size and longevity. Their lumber is highly sought after for its durability and aesthetic appeal.

3. Bald Cypress (Taxodium distichum): These trees are valued for their unique appearance and the high quality of their wood, which is used in furniture making and other high-end applications.

4. Japanese Zelkova (Zelkova serrata): This species is favored for its ornamental value and is often used in landscaping. Its rarity and the difficulty in propagating it contribute to its higher cost.

The reasons for the high prices of these tree species are multifaceted. Firstly, the rarity of certain species makes them more valuable. For instance, Giant Sequoias and California Redwoods are native to specific regions and are not easily propagated, which limits their availability. Secondly, the unique characteristics of these trees, such as their size, wood quality, and aesthetic appeal, make them highly desirable for both commercial and ornamental purposes. Additionally, the cost of transportation and handling these large trees can be significant, further contributing to their higher prices.

According to a report by the American Forest & Paper Association, the average price per board foot of high-quality Giant Sequoia lumber can range from $50 to $100, while California Redwood lumber can cost between $30 and $70 per board foot. The rarity and demand for Japanese Zelkova logs have also driven their prices up, with some logs selling for over $100 per cubic foot. These figures highlight the premium placed on these tree species due to their unique qualities and limited availability.