Which tool is used to check the growth rate of trees?

The tool used to check the growth rate of trees is the increment borer. This specialized instrument allows users to extract a small core sample from the trunk of a tree without causing significant harm to the tree itself. By analyzing the growth rings in the core sample, one can determine the age of the tree and assess its growth rate over time. This helps in understanding environmental changes and the health of the forest ecosystem.

The other options serve different purposes: a lag screw is used for fastening purposes, a junction block is related to electrical connections, and a hose bib is a plumbing fixture. None of these tools would be utilized for measuring tree growth, highlighting the specific function of the increment borer in forestry and tree management.