Physiological Mechanisms of Foliage Recovery after Spring or Fall Crown Scorch in Young Longleaf Pine (Pinus palustris Mill.)

Abstract

We hypothesized that physiological and morphological responses to prescribed fire support the post-scorch foliage recovery and growth of young longleaf pine. Two studies conducted in central Louisiana identified three means of foliage regrowth after fire that included an increase in the gas exchange rate of surviving foliage for 3 to 4 months after fire. Saplings also exhibited crown developmental responses to repeated fire that reduced the risk of future crown scorch. Starch reserves were a source of carbon for post-scorch foliage regrowth when fire was applied in the early growing season. However, the annual dynamics of starch accumulation and mobilization restricted its effectiveness for foliage regrowth when fire was applied late in the growing season. As such, post-scorch foliage regrowth became increasingly dependent on photosynthesis as the growing season progressed. Additionally, the loss of foliage by fire late in the growing season interrupted annual starch dynamics and created a starch void between the time of late growing season fire and mid-summer of the next year. The occurrence of drought during both studies revealed barriers to foliage reestablishment and normal stem growth among large saplings. In study 1, spring water deficit at the time of May fire was associated with high crown scorch and poor foliage and stem growth among large saplings. We attribute this lag in stem growth to three factors: little surviving foliage mass, low fascicle gas exchange rates, and poor post-scorch foliage recovery. In study 2, May fire during a short window of favorable burning conditions in the tenth month of a 20-month drought also reduced stem growth among large saplings but this growth loss was not due to poor post-scorch foliage recovery. Application of this information to prescribed fire guidelines will benefit young longleaf pine responses to fire and advance efforts to restore longleaf pine ecosystems.

Assessing the potential impact of retaining native off‐site tree species in woodland restoration

“…Southern pines vary in their allocation to bark with longleaf allocating more early growth to bark than slash, loblolly, and (presumably) shortleaf pine (Jackson et al 1999). However, all southern pines eventually develop sufficiently thick bark to withstand surface fires with minimal impacts; some southern pines can also reflush following fires that kill needles (Sayer et al 2021). Another fire adaptation is the hastening of crown lifting to avoid foliage and bud damage from convective heating (McGuire et al 2021).…”

Integrating plant physiology into simulation of fire behavior and effects

“…3b,c ; Michaletz & Johnson, 2007 ; Hood et al ., 2018 ; Michaletz, 2018 ; Bär et al ., 2019 ). Postfire environmental conditions and species‐specific traits determine whether resulting functional and growth limitations will lead to vegetation recovery or mortality (Bär et al ., 2019 ; Sayer et al ., 2020 ; Hood, 2021 ; Ruswick et al ., 2021 ). For instance, traits such as water stress resistance are observed to differ between disturbance‐dependent and obligate sprouters in Mediterranean‐type climate regions (Pratt et al ., 2012 ), with implications for postfire community composition.…”

“…3c ) as for mortality from drought and herbivory, where sufficiently high PLC or low NSC results in mortality. This is consistent with recent work linking mortality and recovery from low‐intensity fire to prefire water status (van Mantgem et al ., 2018 ; Partelli‐Feltrin et al ., 2020 ) and concentrations of NSC (Zhu et al ., 2012 ; Sayer et al ., 2020 ). In addition, smoldering consumption can impact water uptake directly through root loss (O'Brien et al ., 2010 ).…”

“…In conifers, trade‐offs have also been documented between resistance to cavitation and to fire, likely mediated by allocation of carbon to either building thick bark or dense xylem, but not both (Resco de Dios et al ., 2018 ). These trade‐offs have implications for woody vegetation recovery from fire under climate change, where drought conditions can predispose woody vegetation to hydraulic (Partelli‐Feltrin et al ., 2020 ) and carbon (Sayer et al ., 2020 ) limitations, impacting capacity to recover from fire‐induced injury and/or resprout. Indeed, intense postfire drought can also cause significant resprout mortality resulting from simultaneous loss of hydraulic conductivity and depletion of root starch (Pratt et al ., 2014 ).…”

Seasonality of Biennial Burning Has No Adverse Effects on Mature Longleaf Pine Survival or Productivity

“…Previous research has indicated that growing season burns can inhibit root growth leading to speculation that dormant season burns are preferable for maintaining longleaf pine productivity (Sayer and Haywood, 2006). Growing season burns may also negatively affect non-structural carbohydrate stocks, which could further constrain recovery and productivity (Guo et al, 2004;Sayer et al, 2020). Such negative effects may be magnified in locations where fire has long-been excluded, as burning in stands with accumulated understory vegetation and duff can produce higher fire intensity (Menges and Deyrup, 2001), reduce non-structural carbohydrate reserves (Varner et al, 2009), and enhance post-fire physiological stress (O'Brien et al, 2010).…”