Canadian Forest Service Publications
Resource heterogeneity relationship with understory vegetation in post-fire xeric jack pine forests. 2018. Das Gupta, S.; Pinno, B.D.; Errington, R.C. Ecosystems 22(2):401-415.
Issued by: Northern Forestry Centre
Catalog ID: 39794
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Xeric jack pine forests in northern boreal ecosystems are becoming more vulnerable with the increasing fire frequencies in this region. Understory vegetation is the most diverse aboveground component of this seemingly homogeneous system consisting of only jack pine in the overstory. Understanding the relationship between understory vegetation, fire severity, and resource availability is therefore necessary for managing these forests. In this study, we used spatial statistics to examine the relationship between understory vegetation and resource conditions as affected by two different pre-fire ages (< 30 and > 60 years) and two fire severities (non-stand replacing fire, NRF, and stand replacing fire, SRF) in xeric jack pine forests in northern Alberta, Canada, four growing seasons post-fire. Using the same framework, we also tested the relationship between resource heterogeneity and species richness commonly known as the resource heterogeneity hypothesis. Spatial heterogeneity, that is, variability, scale of spatial dependency, and patchiness in plant functional groups (cover and richness), microsite conditions (forest floor and soil properties), and light availability were characterized using semivariograms, and their interrelationships were analyzed using spatial autoregressive models. Our findings indicated a stronger fire severity effect on the spatial properties of vegetation composition and microsite conditions than the pre-fire stand age effect. The spatial variability of microsite properties was greater in the NRF sites compared to the SRF sites, but varied in between pre-fire stand ages. Positive relationships were detected between species richness and variability of microsite properties in the NRF sites, whereas such relationships were negative in the SRF sites. Partial Mantel tests indicated a possible dependency of species richness on forest floor variability in the NRF and older sites, and on soil variability in the SRF and younger sites. Overall, findings from this study suggest that spatial heterogeneity in post-fire resource conditions influences the spatial assemblages of understory vegetation in xeric jack pine forests, and a change in fire severity might significantly alter the microsite variability and therefore the mechanisms that drive spatial patterns in understory vegetation.
Plain Language Summary
Vegetation in the understory (underneath the canopy) of northern boreal jack pine forests is the most diverse component of these rather simple ecosystems. Recent climate change prediction models indicate that high-severity fires (i.e., fires that have a greater affect on the forest ecosystem components) will probably occur more frequently as a result of climate change. It is important to understand the mechanisms that maintain the understory of boreal forests in the face of such disturbances so that these forests can be successfully managed in the future. In this study, we examined the relationship between understory vegetation, fire severity, and resources (i.e., soil properties and light availability). Fire severity had a stronger effect on vegetation composition and forest floor conditions, such as the percentage of exposed soil and unburnt and charred debris, than did the age of a stand before it experienced a fire. We found more variation in understory vegetation and forest floor conditions in stands that underwent less severe fires than in stands that underwent more severe fires. A change in fire severity might significantly alter the variability in growing conditions within a stand and therefore the mechanisms that drive spatial patterns in understory vegetation.