Carbon sinks...
A growing tree is called a "sink" because it absorbs carbon dioxide from the atmosphere. Much of the carbon absorbed through the leaves of the tree is converted into wood. Young trees absorb more than older trees, but all retain the carbon within their wood until they are burned or otherwise disposed of. That means old wooden antiques still contain the carbon from hundreds of years ago. This also means that recycled wood products maintain the carbon stored in the timber used.
350 billion tonnes of carbon are locked within forests above ground, with another 800 billion below ground (in roots and humus layers) worldwide.
The "pool" of stored carbon in existing buildings in New Zealand is substantial. But when these existing buildings are demolished and the wood burnt or left to decay, this carbon returns to the atmosphere. If new wood is used in the construction that replaces these structures then the next result is a continuation of the status quo.
If a different building material is chosen then the loss of the stored carbon can negatively impact upon the atmosphere. What's more, additional fossil fuels will have been used in the production of that other building material which cumulatively adds to the concern of global climate change.