Risk of misinterpreting the Tea Bag Index: Field observations and a random simulation

Abstract

AbstractTo understand the global impact of anthropogenic activities on litter decomposition, it is necessary to obtain large decomposition datasets using a standardized method. The Tea Bag Index (TBI) approach determines the decomposition constant (k) of an asymptote model of litter decomposition and a stabilized ratio of the hydrolyzable fraction (stabilization factor S) using a single measurement of the mass loss ratios of green and rooibos teas. This approach requires the assumption that S is equal for rooibos and green tea. Here, we performed a field experiment in four temperate forest stands that demonstrated that this assumption is not always true. In a forest on limestone soils, more than half of the mass loss ratios of rooibos tea exceeded the decomposable fraction predicted by the assumption and the green tea data, which implies that the S was higher for green tea than rooibos tea. This indicated that the main assumption is not always true. We also performed a random simulation study that demonstrated that the derivation of k based on this assumption leads to a biased positive relationship between k and S, regardless of whether the assumption is correct. Thus, we suggest that the use of k and S in an identical analysis causes biased results because these variables are not independent of each other under the assumption. These risks should be considered depending on the purpose of studies that use the TBI approach.