The Post-Fire Assembly Processes of Tree Communities Based on Spatial Analysis of a Sierra Nevada Mixed-Conifer Forest

Understanding the mechanisms underlying tree spatial arrangements may provide significant insights into the processes in the maintenance of species coexistence. We examined the potential role of habitat heterogeneity, dispersal limitation, negative density dependence, fire history, and unilateral intraspecific and interspecific interactions of adults on juveniles in shaping the spatial patterns of four dominant tree species (Abies concolor, Pinus lambertiana, Calocedrus decurrens, and Quercus kelloggii) after fire in the Yosemite Forest Dynamic Plot, California, USA. We used the univariate pair correlation function and implemented three point pattern processes (homogeneous Poisson process, inhomogeneous Poisson process, and homogeneous Thomas process) to evaluate the potential contributions of habitat filtering and dispersal limitation. We used a bivariate null model to evaluate unilateral intraspecific and interspecific interactions of adults on juveniles. We also used the pairwise correlation function to investigate the spatial patterns of density dependence. To understand the effect of fire, we used the univariate pair correlation function to investigate pattern changes during the six years following fire. We compared spatial pattern changes in both sprouting species (Quercus kelloggii) and seeding species (Abies concolor), and also examined the changes in patterns of large-diameter individuals of Abies concolor, Pinus lambertiana, and Calocedrus decurrens in 2013 (pre-fire), 2016 (two years post-fire), and 2019. Comparing the contributions of the homogeneous Thomas process and the inhomogeneous Poisson process at different spatial scales showed the importance of dispersal limitation and habitat heterogeneity at finer scales (0 m to 5 m) and coarser scales (5 m to 60 m), respectively, which suggests that the joint effects of dispersal limitation and habitat heterogeneity contribute to the spatial patterns of these three dominant tree species. Furthermore, the results showed that the young individuals of Abies concolor and Pinus lambertiana were more commonly found around the conspecific adults. Juvenile regeneration to the 1 cm diameter threshold was highly aggregated following the fire. Large-diameter trees of Abies concolor, Pinus lambertiana, and Calocedrus decurrens generally did not exhibit patterns different from complete spatial randomness (Calocedrus decurrens), or displayed only slight aggregation (Abies concolor and Pinus lambertiana). In addition, Abies concolor and Pinus lambertiana showed positive and negative conspecific density dependence in the immediate post-fire period, respectively.

Transcontinental dispersal, common ancestry or convergent evolution? New phyllocoptines (Eriophyidae) from American and South African relict conifers

One new genus, three new species and two records of previously described phyllocoptines are reported from American and South African relict conifers. A new monotypic genus Costolobus n. gen. (Epitrimerus-like phyllocoptines with large ridged frontal lobe and bv I missing) is erected for the new species, Costolobus widdringtonis n. gen., n. sp., from South African endemic Widdringtonia wallichii Endl. ex Carrière (Cupressaceae). Two new species, Epitrimerus papillatus n. sp. and Glossilus calocedris n. sp., are described from Araucaria araucana (Araucariaceae) from Chile and Calocedrus decurrens (Cupressaceae) from USA. Two other phyllocoptine species, Calepitrimerus convergens (Keifer 1966) and Phyllocoptes libocedri (Keifer 1939), are recorded from relict North American cupressacean hosts Calocedrus decurrens and Sequoiadendron giganteum collected in California. The genus Glossilus Navia & Flechtmann 2000 is recorded from North America for the first time; a rediagnosis of this genus is provided. Morphological similarity of the Epitrimerus-like phyllocoptines from gymnosperms is briefly discussed. Contemporary distribution of morphologically similar phyllocoptines on relic conifers in geographically remote regions can be explained by 1) their possible common ancestry followed by transcontinental dispersal and coevolution with hosts or by 2) multiple host-shifts from dicots in different continents and convergent morphological evolution. Comparative studies of the whole complex of eriophyoids inhabiting conifers are necessary to reveal phylogenetic structure of this ecological group of mites. Considering that numerous independent host-shifts from dicots to conifers happened in the past in different clades of Eriophyidae s.l., the mites from conifers might be used as “islands” around which their relatives from angiosperms could be grouped using various phylogenetic tools. Such an approach may be useful for future phylogenetic studies of Eriophyoidea.

Composition of the heartwood essential oil of incense cedar (Calocedrus decurrens Torr.)

No abstract available