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An emerging trend in tree-ring research is use of multiple species for reconstructing paleoclimates, but the possible simultaneous use of boreal-cordilleran species is untested. In this study, ring-width chronologies of sympatric Pinus contorta (lodgepole pine, n = 116 series) and Picea albertiana (western white spruce, n = 348 series) were constructed to assess their temporal (dis)similarities and correlative relationships with meteorological variables. Chronology construction was based on multiple Regional Curve Standardization. Most (97.5%) Pinus chronology values occurred within ±1 SD of their Picea counterparts, but Picea values tended to be slightly less (sign-test, p < 0.001, n = 201). Pinus ring widths were more frequently (16 versus 9) and more strongly correlated (U-test, p < 0.009) with 1942–2013 meteorological variables than Picea. Both species were correlated with moisture variables, but Picea was not correlated with those of temperature. Pinus and Picea ring-width variation was best explained by summer (r = –0.434) and annual (r = –0.426) heat-moisture index values (p < 0.001, n = 72) among tested variables, respectively. Although seldom used, P. contorta appears as suitable as conventionally-used P. albertiana based on chronology similarity, but a greater diversity of significant correlation outcomes suggest Pinus is potentially more useful for boreal-cordilleran paleoclimate reconstruction.
Edge effects are a major cause of natural dynamics of fragmented forests; however, studies that evaluate edge effects during the lifetime of trees are relatively rare. Through a long-term perspective of tree growth, dendroecology can contribute to a better understanding of the influence of edge effects. In order to frame our interpretation, we raised the following hypotheses: (1) trees located close to a forest edge have lower growth rates compared to trees growing far from edges, and (2) climate sensitivity of trees naturally growing on the forest edge is different from the trees in the interior. This study was conducted in Southern Brazil, where 21 Araucaria angustifolia located 50 m from the edge and 19 individuals located 4000 m from the forest edge were sampled. Dendrochronological study followed the usual procedures and growth patterns were evaluated using basal area increment, specific threshold value of fast and slow growth, and principal components analysis. During the 54 years analyzed, results indicated that the edge effect reduced growth by 30% in diameter increment and wood production of A. angustifolia trees. Regarding the influence of climatic variability on tree growth, we observed that edge effects may exert strong pressure on growth responses to climate in A. angustifolia located on forest edges, making individuals in those environments potentially more sensitive to variations in temperature and rainfall, mainly at warmer times of year. We therefore emphasize the importance of considering edge trees as potential bioindicators of historical environmental changes and forest fragmentation. Future studies should be carried out in other forest types and with different tree species (e.g. pioneer vs. shade-tolerant, trees vs. shrubs) to test the reliability of our results and provide more robust conclusions about this phenomenon.
Fire is a critical ecosystem process that has played a key role in shaping forests throughout the Beartooth Mountains in northwestern Wyoming. The highly variable topography of the area provides ideal conditions to compare fire regimes across contiguous forest types, yet pyro-dendrochronological research in this area is limited. We reconstructed fire frequency, tree age structure, and post-fire tree growth response in the Clarks Fork Ranger District of the Shoshone National Forest to infer variations in historical fire behavior and stand effects. We collected fire-scarred trees and plot-based tree ages on plots ranging 0.5-5 km2 in size across two forest types separated by 2 km: a lower-elevation forest of mixed Douglas-fir and lodgepole pine and a higher elevation treeline forest dominated by whitebark pine. Fires occurred in the lower-elevation forest in 1664, 1706, 1785, 1804, 1846, and 1900 with a mean fire return interval of 47 years. The fires in 1804 and 1900 were also recorded in the higher elevation forest, with significant tree mortality at high elevation in the 1900 fire. Both forests were multi-aged with little evidence of tree cohorts in response to severe, stand-replacing events. On average, tree growth increased after fires, with mean ring widths after fire 39% wider in Douglas-fir and 40% wider in lodgepole pine than pre-fire averages, suggesting that some tree mortality likely occurred in association with lower-elevation forest fires. Burns were more frequent in the lower-elevation forest and were occasionally able to spread into the upper-elevation whitebark stand. Although we suspect the transition of fires from low-to high-elevation occurred during drier years, we did not find any relationship between fire years and available climatic reconstructions via superposed epoch analysis. Regeneration during the 20th Century in the whitebark forest documents recovery of this forest after the 1900 moderate-severity fire event. Finally, especially in the lower-elevation Douglas-fir forest, the period since the last recorded fire (1900) appears to be longer than any fire-free period in the historical record, suggesting that fire exclusion may be creating changes in landscape and patch-scale stand structures, which will likely impact future fire behavior, especially the extent of crown-replacing fire, in these forests.
Forest fires are an important factor shaping Mediterranean ecosystems and determine the distribution of different species. Information about past forest fires can be obtained with pyrodendroecology. Here, we present a fire history for three sites in the mountain forest belt on the island of Corsica in the Mediterranean Basin. The dating of scars from cores, stem discs, and wedges from 101 pine trees (Pinus nigra and Pinus pinaster) allowed the reconstruction of six definite fire events between 1800 and 2017. Additionally, we reconstructed the spatial extent of a large fire event at AD 2000 with remote sensing data. The study sites are affected by different types of fires. The even-aged forest structure at two sites is clear evidence of past lethal fires, whereas the old-growth Pinus nigra forest at the third site represents the final stage of succession under current climate conditions. The current distribution of both pine species can at least partly be regarded as a result of varying fire frequency at different sites. Although Pinus pinaster stands dominate in areas with frequent fires and can even replace Pinus nigra in cases of high fire frequency, Pinus nigra dominates in areas with low fire frequencies.
Injury from sampling increment cores may induce defense responses in trees, which may vary between species and reflect differing defense allocation strategies against attack by insects and pathogens. We recorded presence of systemic induction of traumatic resin ducts from early-season increment coring in mature white spruce (Picea glauca) and lodgepole pine (Pinus contorta var. latifolia) trees. In the year of coring, traumatic resin ducts formed three months later, 20 cm below the initial coring site in the xylem of white spruce and showed little variation in response among the spruce families. In contrast, lodgepole pine did not form traumatic resin ducts in trees cored earlier in the growing season. Although traumatic resin ducts are induced by biotic and abiotic disturbances, we found a species-specific defense response to increment coring in two common boreal forest tree species.