How quickly do pine trees break down
Date: 18th May 2025
I have been asked a couple of times in the last few months about the above. People are interested as they consider whether to poison trees standing or fell them. Most of the time poisoning them with herbicide by various ground or air methods is the most practical solution particularly for big areas with lots of trees. Sometimes though we have to consider risk to people and/or property especially where trees may be near property or along walking tracks, roads etc. that people can access.
Arborists and foresters know how to assess this risk when they fell trees and often fell them or piece them down, so they fall away from any areas of risk but trees that are poisoned can be unpredictable and how quickly they break down is dependent on several factor including where they are, what species, age, condition, soil type, aspect and exposure to prevailing winds.
I asked Thomas Paul from Scion about this. Stem poisoning and its effect on stem decay has so far not been studied well for wilding conifers (more observational than actual measurements).
Loretta Garrett studied however the decay rates of felled radiata pine which can help to understand the timeframes involved (paper attached). Important to note is that standing trees have probably a different decay pattern as they are less exposed to moisture and lack soil contact. Also decay rate is dependent on the wood density (and this various a bit between different species /pines).
Loretta’s paper is here: https://www.sciencedirect.com/science/article/abs/pii/S0378112708002776
She found that Radiata pine stems take around 22 years till nearly complete mass loss – nearly fully decayed, (also temperature dependent). For standing stems this might be extended (might take longer) – of course we can expect that the stem falls over at one point – but we have not studied this in detail. Some observers comment that standing trees “collapse” standing after the branches break off as the surface area might not be enough to create wind pressure to topple them – this is again not been studied well.
One thing I know from killing standing old man Radiata at Tawharanui Regional Park, north of Auckland when doing a revegetation programme is that kereru LOVED the dead trees. They made great perches where they could see for miles but even better undertake some natural revegetation by pooping out endless seeds of many native tree species – we didn’t need to extend our revegetation programme right under poisoned trees because the kereru did the job for us.
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