STRINGS.CODEX.DECORSYSTEM.PARAGRAPH_2
Many things have an effect on the Decor value of a tile. A building's effect is expressed as a strength value and a radius. Often that effect is positive, but many buildings also lower the decor value of an area too. Plants, Critters, and Furniture often increase decor while industrial buildings, debris, and rot often decrease it. Duplicants experience the combined decor of all objects affecting a tile.
The Bluff Briar has a decor value of 25 and a radius of 4 tiles.
The Microbe Musher has a decor value of -15 and a radius of 3 tiles.
The result of placing a Microbe Musher next to a Bluff Briar would be a combined decor value of 10.