Abstract
A regional decline in the Korean fir (Abies koreana) has been observed since the 1980s in the subalpine region. To explain this decline, it is important to investigate the degree to which environmental factors have contributed to plant distributions on diverse spatial scales. We applied a hierarchical regression model to determine quantitatively the relationship between the abundance of Korean fir (seedlings) and diverse environmental factors across two different ecological scales. We measured Korean fir density and the occurrence of its seedlings in 102 (84) plots nested at five sites and collected a range of environmental factors at the same plots. Our model included hierarchical explanatory variables at both site-level (weather conditions) and plot-level (micro-topographic factors, soil properties, and competing species). The occurrence of Korean fir seedlings was positively associated with moss cover and rock cover but negatively related to dwarf bamboo cover. At the site level, winter precipitation was significantly and positively related to the occurrence of seedlings. A hierarchical Poisson regression model revealed that Korean fir density was negatively associated with slope aspect, topographic position index, Quercus mongolica cover, and mean summer temperature. Our results suggest that rising temperature, drought, and competition with other species are factors that impede the survival of the Korean fir. We can predict that the population of Korean fir will continue to decline in the subalpine, and only a few Korean fir will survive on northern slopes or valleys due to climate change.
Highlights
Environmental differences play a critical role in species establishment and growth [1,2]. in mountain areas, the heterogeneity of topographic factors can exert strong effects on a wide variety of micro-habitats [3,4,5]
We predict that drought conditions can increase Korean fir seedlings’ mortality
The distribution area of dwarf bamboo and Q. mongolica will be expanded in subalpine regions
Summary
Environmental differences play a critical role in species establishment and growth [1,2]. in mountain areas, the heterogeneity of topographic factors can exert strong effects on a wide variety of micro-habitats [3,4,5]. Environmental differences play a critical role in species establishment and growth [1,2]. Different elevations, topographic position, and slope aspects can create a mosaic of diverse microclimates, and these factors can affect the distribution and diversity of species. Ecological data are often hierarchically structured, and environmental variables act in a hierarchical manner on different ecological scales [6,7]. With regard to experimental designs, ecological field data often involve random effects [8]. Common random effects in field ecology data are blocks that are replicated across sites or times [9,10]. When a hierarchical relationship (or random effects) within explanatory variables is ignored, the actual results can be distorted or obscured because the assumption of independent errors is violated [8].
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