Post-Fire Seedling Recruitment and Morpho-Ecophysiological Responses to Induced Drought and Salvage Logging in Pinus halepensis Mill. Stands

Abstract

Salvage logging is the commonest post-fire emergency action, but has unclear ecological effects. In the Mediterranean Basin, drought periods and fire regimes are changing and forest management should be adapted. In summer 2009, a mid-high severity fire burned 968 ha of Aleppo pine (Pinus halepensis Mill.) forest in southeast Spain, which was submitted to salvage logging six months later. In spring 2010, plots were set in untreated and logged areas to monitor the recruitment and survival of the main tree species and three companion species: Stipa tenacissima L. (resprouter), Cistus clusii Dunal and Rosmarinus officinalis L. (obligate seeders). We evaluated responses to different scenarios in relation to intensification of summer droughts and forest management to obtain differences in water stress, growth, and gas exchange to cope with summer drought. Drought was induced by using rain-exclusion shelters and recorded ecophysiological characteristics were obtained with a portable gas exchange system. The main tree species recruitment was poor, but companion species showed a high survival ratio. Lower water stress was found for obligate seeder seedlings, which was higher in logged areas with induced drought. The initial post-fire stage was similar for the studied areas. However, after two drought periods (2010 and 2011), significant differences were found in the morphological and ecophysiological responses. In the unmanaged area, the biggest size of individuals due to the most marked increases in height and coverage were observed mainly in resprouter S. tenacissima. In the area submitted to salvage logging, the growth ratios in plots with induced drought were OPEN ACCESSForests 2015, 6 1859 lower, mainly for seeders. Greater productivity was related to higher transpiration, stomatal conductance, and net photosynthetic ratio, but lower water use efficiency was found in obligate seeders with no drought induction, and S. tenacissima obtained higher values in untreated areas. Our results confirm that both forest management and intensification of summer droughts influenced the resilience and productivity of the ecosystems in the short term. Adaptive forest management after fire can imply successful survival and recovery of plant communities in the mid to long term. This study provide a scientific basis to develop tools for the post-fire restoration of serotinous pine forests occurring in low-altitudinal areas of the Mediterranean Basin, prone to summer droughts and fire events.

Interactions between large high-severity fires and salvage logging on a short return interval reduce the regrowth of fire-prone serotinous forests

“…Unexpectedly, there were no interactive (synergistic) effects between fire and salvage logging after a single large high-severity fire (F vs. F-iSL and F-dSL), as the removal of the burned wood did not decrease pine seedling recruitment and performance more than did fire alone. Particularly, in the studied stands, immediate (<1 year after fire) salvage logging had no detrimental effects on the natural regeneration of the vegetation; contrarily to previous results by other authors that demonstrated the negative impact of harvesting operations on pine seedling emergence and mortality, plant species composition and diversity, shrub regrowth, and plant facilitative interactions (e.g., Castro et al, 2011;Leverkus et al, 2014;Lindenmayer & Noss, 2006;Moya et al, 2015). Firstly, the high number of mature trees bearing serotinous cones in the studied maritime pine population (Tapias et al, 2004) very likely resulted in a large number of recruited seedlings (Calvo et al, 2008;Hernández-Serrano et al, 2013) that were either very abundant to counterbalance mortality (Martínez-Sánchez et al, 1999) or not seriously damaged by the prompt harvesting operations, as trunks were manually handled without heavy machinery (see Blair et al, 2016;Castro et al, 2011;Leverkus et al, 2014, and references therein).…”

“…While twice-burned plots had (1) high density of immature pines with low reproductive ability (i.e., small canopy seed bank; Espelta et al, 2008), (2) a well-developed shrub layer, and, thus, (3) greater regrowth of the understorey. In addition, no differences between once-and twice-burned plots were observed for the recovery of obligate seeder shrubs that are tolerant to high-severity fires and variable water conditions (Moya et al, 2015), and slowly regenerated from their persistent soil seed banks (Pausas & Keeley, 2014).…”

“…However, their recovery after a large high-severity fire that eliminates most of the vegetation can be undermined with prolonged deleterious effects (González-De Vega et al, 2016). We, therefore, expect that the occurrence of two consecutive large high-severity fires at a short return interval (<15 years) will lessen forest regrowth as it will (i) lower the reproductive ability, recruitment and performance of serotinous pines (Espelta et al, 2008;Eugenio et al, 2006) and (ii) favour either fast-growing resprouter shrubs adapted to frequent fires (Calvo et al, 2012;Pausas & Vallejo, 1999) or obligate seeder shrubs with fire-stimulated germination and tolerant to high-severity fires (Pausas & Keeley 2014) and high water limitation (Moya et al, 2015).…”

Soil Respiration Changes after Prescribed Fires in Spanish Black Pine (Pinus nigra Arn. ssp. salzmannii) Monospecific and Mixed Forest Stands

“…Our results indicated high SR rates in summer, which is associated with higher soil surface temperature levels and microclimate aspects [42,43]. In addition, Austin and Vivanco [44], or Brandt et al [45], have observed that an increase in UV radiation in soil favours litter decomposition, which may be due to microbial facilitation [46], and consequently increases SR [47].…”

Transpiration in recovering mixed loblolly pine and oak stands following wildfire in the Lost Pines region of Texas

“…The severely burned site had the most stable water availability of the three sites across time, likely due to low total biomass and competition, but the shallow‐rooted pine saplings were not as able to capitalize on this advantage as the deep‐rooted resprouts. The roots of regenerating pines are likely restricted to the upper part of the profile, whereas the resprouting oaks have deep root systems remaining from mature trees (Clemente, Rego, & Coreia, ; Moya, de las Heras, López‐Serrano, & Ferrandis, ; Vilagrosa, Hernandez, Luis, Cochard, & Pausas, ). The resprouts' greater root : shoot ratios help increase hydraulic efficiency over that of mature trees.…”