Improving restoration success through microsite selection: an example with planting sagebrush seedlings after wildfire

Abstract

Post‐fire restoration of foundation plant species, particularly non‐sprouting shrubs, is critically needed in arid and semi‐arid rangeland, but is hampered by low success. Expensive and labor‐intensive methods, including planting seedlings, can improve restoration success. Prioritizing where these more intensive methods are applied may improve restoration efficiency. Shrubs in arid and semi‐arid environments can create resource islands under their canopies that may remain after fire. Seedlings planted post‐fire in former canopy and between canopies (interspace) may have different survival and growth. We compared planting Wyoming big sagebrush (Artemisia tridentata Nutt. ssp. wyomingensis Beetle & Young) seedlings post‐fire in former sagebrush canopy and interspace microsites at five locations. Four growing seasons after planting, seedling survival was 46 and 7% in canopy and interspace microsites, respectively. Sagebrush cover was 5.8 times greater in canopy compared to interspace microsites. Sagebrush survival and cover were likely greater because of less competition from herbaceous vegetation as well as benefiting from resource island effects in canopy microsites. Initially, post‐fire abundance of exotic annual grasses was less in canopy microsites, but by the third year post‐fire it was substantially greater in canopy microsites, indicating that resource availability to seedlings was greater, at least initially, in canopy microsites. These results suggest microsites with greater likelihood of success should be identified and then utilized to improve restoration success and efficiency. This is important as the need for restoration greatly exceeds resources available for restoration.

Re-introducing fire in sagebrush steppe experiencing decreased fire frequency: does burning promote spatial and temporal heterogeneity?

“…If mountain big sagebrush does not establish well in the first couple of years after fire, sagebrush recovery is slow (Ziegenhagen and Miller 2009). Sagebrush also establishes better in microsites that are largely devoid of herbaceous vegetation Davies et al 2020). In our study, limited-to-no fire-induced mortality of perennial grasses resulted in few open spaces for establishment of sagebrush seedlings.…”

Reestablishing a foundational species: Limitations on post‐wildfire sagebrush seedling establishment

“…We found that sufficient mortality occurred such that in unseeded and seeded areas, nearly half of the populations found to be occupied 1–2 years post‐fire were unoccupied 2–3 years post‐fire. Increased mortality of shrubs can be attributed to resource limitations, especially water (e.g., O'Connor et al, 2020), and increased competition with seeded non‐shrub species and non‐native species (Davies et al, 2020; Rinella et al, 2015). Within 3 years since sowing, aerial seeding of sagebrush either resulted in enough seedlings to reduce the likelihood of complete population mortality, or as mentioned previously, this apparent seeding effect may reflect manager decision‐making regarding which particular areas to restore.…”

“…We found that sufficient mortality occurred such that in unseeded and seeded areas, nearly half of the populations found to be occupied 1-2 years post-fire were unoccupied 2-3 years post-fire. Increased mortality of shrubs can be attributed to resource limitations, especially water (e.g., O'Connor et al, 2020), and increased competition with seeded nonshrub species and non-native species (Davies et al, 2020;Rinella et al, 2015). Within 3 years since sowing, aerial F I G U R E 6 Nonparametric multiplicative regression modeled relationships between sagebrush seedling occupancy rate (y-axis), native perennial grass cover (x-axis), and aerial sagebrush seeding status (colored line series; gray line is visible along x-axis; "+" indicates sagebrush seed applied, "À" indicates no sagebrush seed applied) in 103 populations sampled 1-2 years post-fire in areas with minimal fertile island microsite cover (0%-1.25%) and no remnant sagebrush plants detected within 150 m. This model was developed to simulate conditions where no mature sagebrush exited pre-fire.…”

“…Fertile islands associated with shrubs are well documented in arid‐land ecosystems (Garner & Steinberger, 1989; Hassan & West, 1986; Ochoa‐Hueso et al, 2018). These microsites are locations where mature sagebrush canopies burn and subsequently leave behind an area with unique soil characteristics that may facilitate sagebrush establishment, while inhibiting invasive annuals for 1–2 years (Barnard et al, 2019; Davies et al, 2020; Germino et al, 2018; Figure 1a). These findings have important implications for sagebrush restoration.…”

“…It is thought that these microsites influence seedling establishment by providing favorable soil texture, compaction, color, nutrient, and water infiltration conditions, while also providing an area of relatively low competition (Davies et al, 2009; Sankey et al, 2012). Competition may be reduced because perennial grasses are often less abundant under shrub canopies before fire, and non‐native annuals are likely removed from the seedbank after fire due to high burn severity under the shrub canopy (Davies et al, 2017; Davies et al, 2020; Huber‐Sannwald & Pyke, 2005; Liu et al, 2020). If fertile island microsites are as important throughout the Great Basin as suggested by previous case studies, that would amount to a critical role for former sagebrush in the establishment of new populations in post‐fire environments.…”