Elm wood is generally more prone to cracking than oak. Elm trees are known for their rapid growth, which can lead to a higher moisture content in the wood. This high moisture content makes elm more susceptible to cracking as it dries and seasons. Oak, on the other hand, is a slower-growing tree with a lower moisture content, which contributes to its greater stability and resistance to cracking.

According to the American Hardwood Export Council (AHEC), elm wood has a moisture content of around 25-30% when it is harvested, compared to oak's moisture content of about 15-20%. This significant difference in moisture content is a primary factor in the cracking propensity of the two woods. As the wood dries, the moisture content decreases, causing the wood fibers to contract. Elm's higher moisture content means that the fibers contract more, leading to a greater risk of cracking.

Additionally, the grain structure of elm wood also plays a role in its cracking tendency. Elm has a more open grain pattern, which allows for more movement and expansion as the wood dries. This movement can lead to cracks forming along the grain lines. Oak, with its denser and more closed grain, is less likely to crack due to its reduced movement and expansion.

Research conducted by the Forest Products Laboratory at the University of Wisconsin-Madison has shown that oak is more dimensionally stable than elm. Dimensional stability refers to the wood's ability to maintain its shape and size over time. The study found that oak had a lower coefficient of expansion and contraction than elm, further supporting the notion that oak is less prone to cracking.

In conclusion, elm wood is more prone to cracking than oak due to its higher moisture content and more open grain structure. These factors contribute to greater movement and expansion as the wood dries, leading to a higher likelihood of cracks forming. Oak's lower moisture content and denser grain make it a more stable and durable choice for applications where cracking is a concern.