Early decomposition rate and stabilization factors are influenced by precipitation, but not by the individual tree selection method in western deciduous Patagonian forests

Abstract

Litter decomposition is a key process in forest ecosystems because it influences the balance of primary production and respiration. However, the interaction between sites and forest management still needs empirical quantification and understanding. Here, I aimed to study the effects of distinct precipitation sites and low-severity management conducted 5 years ago within pure Nothofagus pumilio (Lenga) old-growth forests in western Patagonia. The well-established and standardized Tea Bag Index (TBI) was used to obtain the decomposition rate (k_TBI) and stabilization factor (S_TBI) among sites and management treatments. Three randomized blocks were displayed in three precipitation sites (dry, mesic, and wet), where each block contained three plots with different management intensity (heavy: 35m²/ha of residual basal area, light: 45m²/ha of residual basal area, and control: without intervention ~ 60m²/ha of basal area) conducted through the individual-tree selection method. At each plot, six incubation spots with pairs of green (labile) and rooibos (recalcitrant) tea bags were buried in the center of the plot following the TBI protocol. In the center of each plot a microclimate data logger was installed, and on each incubation spot a hemispherical photograph was taken to estimate total transmitted radiation. Two-way ANOVA was used to evaluate the effects of precipitation sites, management treatments, and their interaction on decomposition rate k_TBI and stabilization factor S_TBI (TBI proxies). Moreover, the generalized linear model (GLM) was used to establish the causal relationship for the TBI proxies using the mean transmitted radiation, mean soil temperature, mean soil water content, and their interaction mediated by precipitation sites as an indicator variable. The results highlight that the precipitation site was the significant variable to predict both TBI proxies. Management treatments, and their interaction with precipitation sites were not significant. Moreover, I found that the precipitation site was the best supported model for each TBI proxy, and non-effects of microclimate variables were revealed by the selection model approach. I discuss that precipitation acts as a main driver of the decomposition process in these cold temperate forests, and the low-severity management approach did not affect the microclimate, thereby the k_TBI and S_TBI. Therefore, these results show that this management alternative mimics the natural process and could be seen as a plausible and sustainable management option for the western Patagonian deciduous forest ecosystems.