Old-growth Abies Research Articles

Spatial structure and richness of ectomycorrhizal fungi colonizing bioassay seedlings from resistant propagules in a Sierra Nevada forest: comparisons using two hosts that exhibit different seedling establishment patterns

In this study we analyzed the spatial structure of ectomycorrhizal fungi present in the soils as resistant propagules (e.g. spores or sclerotia) in a mixed-conifer forest in the Sierra Nevada, California. Soils were collected under old-growth Abies spp. stands across approximately 1 km and bioassayed with seedlings of hosts that establish best in stronger light (Pinus jeffreyi) or that are shade-tolerant (Abies concolor). Ectomycorrhizal fungi colonizing the roots were characterized with molecular techniques (ITSRFLP and DNA sequence analysis). Wilcoxina, five Rhizopogon species and Cenococcum were the most frequent of 17 detected species. No spatial structure was detected in the resistant propagule community as a whole, but P. jeffreyi seedlings had higher species richness and associated with seven Rhizopogon species that were not detected on A. concolor seedlings. We drew two conclusions from comparisons between this study and a prior study of the ectomycorrhizal community on mature trees in the same forest: (i) the resistant propagule community was considerably simpler and more homogeneous than the active resident community across the forest and (ii) Cenococcum and Wilcoxina species are abundant in both communities.

Spatial structure and richness of ectomycorrhizal fungi colonizing bioassay seedlings from resistant propagules in a Sierra Nevada forest: comparisons using two hosts that exhibit different seedling establishment patterns

In this study we analyzed the spatial structure of ectomycorrhizal fungi present in the soils as resistant propagules (e.g. spores or sclerotia) in a mixed-conifer forest in the Sierra Nevada, California. Soils were collected under old-growth Abies spp. stands across approximately 1 km and bioassayed with seedlings of hosts that establish best in stronger light (Pinus jeffreyi) or that are shade-tolerant (Abies concolor). Ectomycorrhizal fungi colonizing the roots were characterized with molecular techniques (ITS-RFLP and DNA sequence analysis). Wilcoxina, five Rhizopogon species and Cenococcum were the most frequent of 17 detected species. No spatial structure was detected in the resistant propagule community as a whole, but P. jeffreyi seedlings had higher species richness and associated with seven Rhizopogon species that were not detected on A. concolor seedlings. We drew two conclusions from comparisons between this study and a prior study of the ectomycorrhizal community on mature trees in the same forest: (i) the resistant propagule community was considerably simpler and more homogeneous than the active resident community across the forest and (ii) Cenococcum and Wilcoxina species are abundant in both communities.

Structural segregation and scales of spatial dependency in Abies amabilis forests

Question: Is a mosaic structure apparent in the spatial distribution of trees in old-growth Abies amabilis forests? Location: Montane forests of the western Cascade Range, Washington, USA. Methods: Maps of tree locations were created for study areas located in two, 300-year old stands and a single 600-year old stand. Stand structure parameters were calculated using several subsample quadrats sizes (56.25 - 306.25 m 2 ), which were drawn randomly with replacement at a density of 250 quadrats per ha from the stem maps in the computing environment. Spatial cross-covariance functions between different canopy strata were estimated using the spline cross-correlogram. Results: Negative spatial correlation (segregation) between subcanopy tree density and areas of high overstorey occupancy was detected. Understorey and midstorey tree densities were positively spatially correlated. These general trends were apparent across the range of observational scales investigated. Significant spatial correlation between canopy strata was observed at spatial scales of 12 - 44 m and extended to the largest scales in the 600-year old stand. Conclusion: The observed spatial segregation between canopy strata supports the hypothesis that old A. amabilis forests form fine-scale structural mosaics. Structural segregation at small scales may be due to competitive interactions as well as exogenous forcing of tree locations (e.g. by mortality due to pathogens or disturbance), however segregation at large scales in the 600-year old stand is likely due to exogenous factors alone. This study reinforces the idea that horizontal heterogeneity is an emergent property of old-growth forests.

Regeneration patterns and tree species coexistence in old-growth Abies– Picea forests in southwestern China

We analyzed the population structure (size, age, spatial patterns) and radial growth patterns of Abies faxoniana Rehder & Wilson, Picea purpurea Mast., and Betula sp. to investigate the role of dwarf bamboo abundance, gap disturbance, and species life history on the coexistence of canopy dominants in old-growth forests in the Wang Lang Natural Reserve in southwestern China. Four stands were sampled with a single large plot (0.4–0.5 ha). There were fewer tree seedlings and saplings in the two plots with a dense bamboo understory, and A. faxoniana seedlings and saplings were much more abundant than those of P. purpurea. Picea purpurea and Betula sp. seedlings established more frequently on raised surfaces than those of A. faxoniana. Seedling density of A. faxoniana, and B. utilis was also higher beneath open than closed canopy conditions in the plots with little bamboo. Young A. faxoniana and Betula sp. trees were clumped at small to intermediate scales (25–900 m 2), which are scales of clumping consistent with past regeneration in canopy gaps. Frequent peaks in radial growth releases in the canopy trees in the plots suggest a prevailing regime of small-scale gap disturbances. In each plot, A. faxoniana tree density and basal area was greater than that of P. purpurea. Picea purpurea trees were present in a wide range of age-classes in each plot indicating a pattern of intermittent regeneration in each stand for at least 500 years. In contrast, Abies faxoniana were abundant in age-classes <250 years, and few A. faxoniana were >350 years old. Betula sp. were mainly <120 years old. Betula sp. and P. purpurea preferred different seed-beds than A. faxoniana for establishment and regeneration of A. faxoniana, and especially Betula, is associated with gaps. Longevity and high survivorship are key life history traits of P. purpurea that prevent its replacement by A. faxoniana. In Wang Lang, stable coexistence is maintained by differences in species regeneration niche, species demographic characteristics, and species responses to the gap disturbance regime.

Canopy tree development and undergrowth bamboo dynamics in old-growth Abies– Betula forests in southwestern China: a 12-year study

Interactions between forest canopy characteristics and plants in the forest understory are important determinants of forest community structure and dynamics. In the highlands of southwestern, China the dwarf bamboo Bashania fangiana Yi is an understory dominant beneath a mixed canopy of the evergreen Abies faxoniana (Rheder & Wilson) and the deciduous Betula utilis (D. Don). The goal of this study was to better understand the role of bamboo dominance, canopy characteristics, and periodic bamboo dieback on forest development. To achieve this goal, we measured tree seedling, tree saplings, and trees, forest canopy characteristics, and bamboo cover in permanent forest ( n = 4) and gap plots ( n = 31) in a mixed A. faxoniana and B. utilis forest in Sichuan, China. Dwarf bamboos died off in 1983 in the gap plots, and in three of the four forest plots. Forest development was assessed for the period 1984–1996. The seedling bank in forest and gap plots increased after bamboo die-off. A. faxoniana seedlings increased more than B. utilis in forest plots; the opposite pattern characterized gap plots. The proportion of seedlings on raised micro-sites on the forest floor also changed and new seedling were more abundant on the forest floor. By 1996, bamboo seedling cover and biomass had recovered to ca. 45% or their pre-flowering values. Rates of bamboo seedling recovery were faster beneath canopy gaps and deciduous trees than beneath forest or evergreen trees. Tree mortality exceeded recruitment in plots with dense bamboo; the opposite pattern was found in the plot with little bamboo. The mortality rate for B. utilis trees (2.4% year −1) was higher than that for A. faxoniana (0.8% year −1) and forests with dense bamboos became more open over the census period. Tree mortality was size-dependent and intermediate sized trees had the lowest rates of mortality. Stand basal area increased mainly due to greater basal area gain than loss for A. faxoniana. Interactions between tree species life history, canopy type, and bamboo life-cycles create heterogeneous conditions that influence tree and bamboo regeneration and contribute to the coexistence of A. faxoniana and B. utilis in old-growth forests in southwestern China.