Risk and uncertainties incorporated in the management of root and butt rot infected forest areas

By Cathrine Glosli

RotråtePhoto: Kennerth Kullman/Shutterstock

In her PhD thesis, Ana Claudia Ferreira Aza has examined the effect of root and butt rot uncertainty on forest management decisions. 

Root and Butt Rot (RBR) caused by the pathogenic fungi Heterobasidion spp. is a significant problem affecting Norway's main coniferous tree species, Norway spruce and Scots pine. RBR occurrence information is uncertain yet essential in forest management, as it can change decisions with long-term, often irreversible consequences. When facing uncertainty, the decision-maker may proceed based on currently available information or try to reduce the uncertainty by gathering new information. This thesis investigated the effect of considering RBR uncertainty, as well as acquiring detailed information on relevant parameters, on forest management decisions in RBR-infected areas in Norway.

The first study looked at how the uncertainty regarding the presence of RBR affects the economically optimal rotation age of even-aged spruce dominant stands. Although the results indicated the possibility of a slightly reduced rotation age in some stands, the expected gain from harvesting a rotten stand earlier than its rot-free optimal rotation age was modest. Advance harvesting seldom pays off in the absence of information on the extent and severity of RBR.

The second study investigated the effect of RBR on tree species selection in previously spruce dominated clear-cut sites. While it is optimal to continue planting Norway spruce in areas with low rot levels, shifting to Scots pine pays off when rot levels are high. The threshold rot level for switching from Norway spruce to Scots pine increases with the site index. Planting any species in low productivity areas results in negative net present values (NPVs), implying that natural regeneration is the best alternative in this condition. The use of pixel-level information on site index and rot level to decide on tree species selection in a case study increased the land expectation value (LEV) of almost all stands in the dataset compared to planting one single species.

Given the importance of site index and rot level information, the third study applied the Value of Information (VoI) concept to assess the benefit of having accurate pixel-level information on site index and rot level when deciding on tree species selection. Medium-to-low dominant site indexes stands had the highest VoIs. There, shifting from spruce to pine in some pixels rather than planting spruce across the whole stand, and adjusting the plant densities to the pixel site index, had the best-expected impact on the stand's NPV. Given that the stand's dominant site index is known, information on rot levels alone is more valuable than information on site index alone.

Even though the study's findings cannot be extrapolated to the entire country, the approaches discussed here can be applied in similar contexts with minor adjustments. Rather than ignoring uncertainties, approaching them and gathering new information for the decision-making process adds value to the decision and helps to avoid economic losses.

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