Short-Term Ground Vegetation Responses to Fertilization in Latvian Forests: Effects on Species Richness and Diversity

This study investigated the impact of forest fertilization on ground vegetation in deciduous and conifer stands across different forest site types (forests with drained mineral soils, forests with drained organic soils, and dry upland forests), stand age groups (young, middle-aged, and pre-mature), and fertilizer types (ammonium nitrate (NH4NO3) and wood ash alone, and both together). Ground vegetation was surveyed one to three years after fertilizer application, with the projected ground cover of individual species in the moss and herb layers determined. Thus, results reflect short-term impact of fertilization. Species richness and diversity (Shannon diversity index, H′) were compared between fertilized and control (unfertilized) plots. The results show that species diversity in the moss layer of silver birch stands was significantly affected by fertilization, while species richness was significantly influenced by the interaction between fertilization and forest site type. Differences between control and fertilized plots in birch stands suggest a potentially negative response of the moss layer to fertilization. In contrast, no significant effect of fertilization was observed in Norway spruce stands, where site type and stand age emerged as significant factors. In Scots pine stands, where NH4NO3 was applied alone, fertilization had a significant impact on both species richness and diversity in the herb layer. In the moss layer, a marginally significant effect was found for the interaction between fertilization and stand age. NH4NO3 alone appeared to enhance herb layer richness, although its effect on species diversity was more variable. Our study highlights the context-dependent nature of fertilization effects on species richness and diversity in Latvian hemiboreal forest ecosystems.