Pinus nigra Arn. ssp. salzmannii seedling recruitment is affected by stand basal area, shrub cover and climate interactions

Abstract

Abstract& Key message Shrub cover has visible effects on Pinus nigra Arn ssp. salzmannii seedling emergence, but only in drier years under moderate basal area (25-30 m 2 ha −1 ). In the wetter year, shrub cover favours seedling survival without basal area influence. & Context Shrubs are known to favour tree seedling recruitment in difficult climate environments, but facilitation may prove optimal in intermediate-level rather than harsh conditions, although such an effect remains to be specified. & Aims The main aim of this work was to evaluate the influence of stand basal area (15-20, 25-30 and 35-40 m 2 ha −1 ) × with/without shrub facilitation on seedling recruitment in Spanish black pine (P. nigra Arn. ssp. salzmannii), which has been struggling to regenerate natural forests since the late nineteenth century, sometimes jeopardizing stand persistence. & Methods In spring 2012 and 2013, 72 subplots of 25 × 25 cm were established in Cuenca Mountains, centraleastern Spain (four replicates, each counting three subplots × 2 shrub conditions, both under and outside shrub cover, in three different stand basal areas). All plots were randomly distributed at least 500 m apart within each stand basal area. Each subplot comprised 20 seeds previously collected at the experimental forest site. Seedling emergence and early survival were monitored every month in 2012 and 2013. Handling Editor: Laurent BergèsContribution of the co-authors ME Lucas-Borja and D Candel-Pérez conceived the research, obtained the field data, run the data analysis and wrote the manuscript. PA Tíscar, T Onkelinx and P Balandier run the data analysis and wrote the manuscript. FA García Morote obtained the field data and wrote the manuscript.

Seed Origin and Protection Are Important Factors Affecting Post-Fire Initial Recruitment in Pine Forest Areas

“…Thus, the micrometeorological and light conditions found in totally burned areas would have generated a better environment for P. nigra upland and midland seedling survival in the wetter spring of 2011. Our results also agreed with those of Lucas-Borja et al [48], who found that survival was higher away from orthogonal shrub projection under favourable climate conditions in 2013, which also suggests a light effect consistent with reports by [49].…”

“…In places where summer drought negatively affects initial seedling recruitment, higher sunlight reaching soil surface can be promoted with lower overstorey densities, and, thus, higher seedling growth can be generated [48]. Data from this study show that P. pinaster natural regeneration in midland altitudes from central-eastern Spain is difficult to achieve.…”

Direct Seeding of Pinus halepensis Mill. for Recovery of Burned Semi-Arid Forests: Implications for Post-Fire Management for Improving Natural Regeneration

“…Referring to drought, previous studies have shown that the scarce summer rainfall should be considered the first cause of low emergence and early seedling mortality in Mediterranean areas [18,30,32]. In our research, the scarce precipitation after seed germination (8 mm in May-June 2015) and the first summer drought affected the initial survival rate of revegetation.…”

“…However, our results suggest that in a very intense summer drought, grass does not facilitate pine seedlings. Recently, the facilitation hypothesis and the stress-gradient hypothesis have been discussed because if environmental conditions become very severe, facilitation can collapse [30,32,65]. In a severe drought scenario, the effects of grass on Pinus halepensis seedlings might include reduced soil water availability, which may not be counterbalanced by improvements in microclimate or shade [38].…”

“…On a global scale, the factors that affect pine recruitment in the Mediterranean Basin are more diverse and include changes in land use, forest succession, disturbance (fires), drought, gradients of light and nutrients, seed production, grazing pressure, or soil properties (for a review, see [29]). On a low scale, the studies that have focused on the recruitment dynamics of Mediterranean conifer species have found increasing seedling mortality in the summer [17][18][19][30][31][32]. Mediterranean ecosystems are characterized by long hot summers, with high irradiance and little, or no, precipitation, and these conditions strongly limit carbon assimilation [30,33].…”