Abstract
Fire is a powerful natural disturbance influencing vegetation patterns across landscapes. Recent transitions from mixed-species forests to post-fire shrublands after severe wildfire is an increasingly prevalent phenomenon in pine-oak and conifer forest ecosystems in southwestern North America. However, we know little about how variation in fire severity influences other common forest types in the region. In this study, we evaluated fire-induced changes in woody plant community composition and forest structure in Chiricahua Mountains in southeastern Arizona in the United States that hosts a diverse set of vegetation types. Cluster analysis of the pre-fire vegetation data identified three dominant pre-fire vegetation types including juniper woodland, piñon forest, and pine-oak forest. All vegetation types experienced significant tree mortality across a wide range of size classes and species, from forests to shrublands. The magnitude of change within sample plots varied with fire severity, which was mediated by topography. Significant shifts in dominance away from coniferous obligate seeder trees to resprouting hardwoods and other shrubs occurred across all vegetation types in response to the fire. Regeneration from seed can be episodic, but projected increases in aridity and fire frequency may promote continued dominance by hardwoods and fire- and drought-resistant shrub communities, which is a regional forest management concern as wildfire size and severity continue to increase throughout the southwestern USA.
Highlights
We examined the contribution of fire severity, topographic relative moisture index (TRMI), and elevation in explaining spatial and temporal differences in the woody plant community using Pearson correlation analyses and by plotting the plots in species space with 95th percentile confidence ellipses for the pre- vs
This pattern can be explained by the death of many obligate seeder conifers (e.g., P. discolor, P. leiophylla), few post-fire seedlings for most of these species, widespread resprouting (e.g., Quercus spp., Mimosa aculeaticarpa), and abundant shrub seedlings (e.g., Arctostaphylos pungens)
Tree regeneration after fire can occur over long timespans; the lack of post-fire obligate seeder taxa in Chiricahua National Monument (CHIR) with increasing fire severity over the short-term suggests that continued monitoring is important for understanding Sky Island post-fire successional trajectories
Summary
Received: 19 August 2021Accepted: 12 October 2021Published: 20 October 2021Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations.Licensee MDPI, Basel, Switzerland.Attribution (CC BY) license (https://creativecommons.org/licenses/by/ 4.0/).Fire is a powerful ecological disturbance that regulates plant species composition and vegetation structure in fire-adapted ecosystems worldwide [1,2,3,4]. Topography, climate, fire weather, and vegetation are major drivers of spatio-temporal variation in fire behavior within fire-prone systems, which interact to generate landscape mosaics of burn severity and fire effects on vegetation [5,6,7,8,9,10,11,12,13,14,15]. The Sky Island ecosystems of southwestern North
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