Abstract
Wildfire, a primary natural disturbance in many forests, affects soil nutrient availability and spatial distributions of forest plants. However, post-fire changes in soil nutrients and spatial patterns of understory environments at fine scales are poorly understood. Here, we characterized spatial patterns of soil nitrogen availability and site characteristics at a 3-year-post-fire and an unburned site in a valley boreal larch forest. We also examined the relationship between soil nitrogen availability and site characteristics. The results showed that the burned site had higher NO3− and lower NH4+ than the control. The herb, litter and coarse wood debris cover was greater at the burned site than at the control site with higher soil pH, depth of the organic horizon (DOH) and shrub cover. Relative variability (coefficient of variation) in soil nitrogen and site characteristic variables at the control site was greater than at the burned site except for shrub and regeneration tree seedling cover. Spatial structure (quantified by semi-variograms) was lacking for soil nitrogen and site characteristic variables except for DOH, herb and shrub cover at the control site, but wildfire created a strong spatial structure for all variables. Shorter spatial autocorrelation ranges of soil nitrogen (1.6–3.5 m) and site characteristic variables (2.6–6.0 m) were detected at the burned site, indicating higher heterogeneity. The spatial scale of soil NH4+ was congruent with those of herb, shrub and regeneration tree seedling cover, indicating local coupling, while that of soil NO3− was not. The number of correlations between soil nitrogen and site characteristic variables in the burned site was greater than in the control. These results indicate that fire could not only create higher heterogeneity patches of soil resources, but also strengthen the local coupling between soil resources and understory vegetation, which may impact the establishment and growth of new individual plants.
Highlights
The heterogeneity of soil resources plays an important role in sustaining the structure and functioning of forest ecosystems [1,2,3], as such heterogeneity can impact the survival of colonizing individual vegetation species and the biodiversity of vegetation communities [4,5]
This study suggests higher fine-scale spatial heterogeneity in soil N availability and site characteristics after fire relative to the control
Significant correlations at the individual sampling point level indicated that soil resources influenced soil N and that available soil N
Summary
The heterogeneity of soil resources plays an important role in sustaining the structure and functioning of forest ecosystems [1,2,3], as such heterogeneity can impact the survival of colonizing individual vegetation species and the biodiversity of vegetation communities [4,5]. Plants can impact the spatial pattern of soil resources by altering physical, chemical and biological soil properties [6,7,8]. Wildfire is one of the most important natural ecological disturbance agents in forest ecosystems, is characterized by variations in fire severity and frequency [12,13], and produces spatial and temporal variations in ecological systems. Forests 2019, 10, 95 understanding changes in patterns of post-fire soil resources and plants across space is necessary to better understand the ecological effects of fires in fire-prone ecosystems. Fires decrease soil N pools, but increase N availability, and further influence N transformations [20,21,22,23,24]
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