PS 30-170 - Stand structure, not site or species diversity, drives variation in maximum stand density in old-growth kauri (Agathis australis) dominated forests

Abstract: Kauri (Agathis australis) dominated forests are highly diverse and species-rich, making their survival critical to maintaining global biodiversity. The ability to accurately quantify stand density in such complex forests is difficult, but imperative to their effective management and protection. However, studying mature versions of these forests today is unlikely due to extensive historic logging efforts and the recent onset of the prolific kauri dieback. Fortunately, an opportunity presented itself in the uncovering and reconfiguring of historic data collected across 25 old-growth kauri-dominated stands by Ahmed & Ogden (1991). We applied the Ducey-Knapp (2010) relative density technique to calculate maximum stand density, with results showing considerable variation across the stands. Surprisingly, differences in stand structure, not site or species diversity, appeared to be driving this. Of all the variables tested, only a measure of stand structural diversity was significant. This suggests that the horizontal and vertical distribution of stands may be important attributes to consider in accurately predicting stand density in similarly complex forests.