Structural Complexity Enhancement increases fungal species richness in northern hardwood forests

Forest management practices directly influence microhabitat characteristics important to the survival of fungi. Because fungal populations perform key ecological processes, there is interest in forestry practices that minimize deleterious effects on their habitats. We investigated the effects on fungal sporocarp diversity of modified uneven-aged forest management practices in northern hardwood ecosystems, including a technique called Structural Complexity Enhancement (SCE). SCE is designed to accelerate late-successional stand development; it was compared against two conventional selection systems (single tree and group) and unmanipulated controls. These were applied in a randomized block design to a mature, multi-aged forest in Vermont, USA. Eight years after treatment, fungal species richness was significantly greater in SCE plots compared to conventional selection harvests and controls (p < 0.001). Seven forest structure variables were tested for their influence on fungal species richness using a Classification and Regression Tree. The results suggested that dead tree and downed log recruitment, as well as maintenance of high levels of aboveground biomass, under SCE had a particularly strong effect on fungal diversity. Our findings show it is possible to increase fungal diversity using forestry practices that enhance stand structural complexity and late-successional forest characteristics.     

A novel tight cylindrical mold for epoxy resin embedding allows enhanced microscopic analysis of microcores extracted from woody plants

A novel mold was devised to embed microcores extracted from stems of trees in epoxy resin, which has been widely used for optical and electron microscopic analysis of xylem formation. The embedding mold of a tight cylindrical shaped tube was designed to avoid displacement of microcores from the right position during the process of resin embedding. Microcores of a ring-porous hardwood species, Quercus crispula, with higher wood density and much larger differentiating vessel elements laid down on the boundary between the current xylem and the previous one, which generally cause difficulty in thin sectioning and breaks in sections, respectively, were embedded in the cylindrical molds full of epoxy resin. Locations of the three principal planes of wood anatomy could be determined in cylindrical resin-embedded microcores as follows: the transverse plane could be found on their side of cylinder, the radial one was vertical to the transverse, and the tangential ones were their circular ends of cylinder. The present embedding mold, therefore, can provide all three principal sections for microscopic wood anatomy from the side or ends of the same cylindrical microcore in principle. To confirm the usefulness of the resin-embedded microcores, we examined the differentiation of vessel elements during the period of earlywood formation on their transverse sections under microscopes, consequently could observe cell division in the cambial zone and sequential stages of vessel element differentiation, including cell expansion and deposition of the secondary cell wall. The present embedding mold for epoxy resin is simple but highly useful and innovative for a wide range of applications of microcores in microscopy for studies on tree-ring formation.     

Red Spruce Stand Dynamics, Simulations, and Restoration Opportunities in the Central Appalachians

Red spruce (Picea rubens)–dominated forests occupied as much as 600,000 ha in West Virginia prior to exploitive logging era of the late nineteenth and early twentieth centuries. Subsequently, much of this forest type was converted to northern hardwoods. As an important habitat type for a number of rare or sensitive species, only about 12,000 ha of red spruce forests presently remain in the state. In order to assess the prospects for restoration, we examined six northern hardwood stands containing understory red spruce to (1) characterize stand dynamics and regeneration patterns and (2) simulate the effectiveness of restoration silviculture to enhance red spruce overstory recruitment. Stands originated in the late 1800s to early 1900s and are currently in the (late) stem exclusion or understory reinitiation stages. Five of the six stands had even‐aged overstories that originated after clear‐cutting. Tree‐ring chronologies show high initial growth rates consistent with stand initiation. One stand, partially harvested in 1915, was uneven aged with older, legacy residuals in the canopy. Most stands had two cohorts of understory red spruce, with more than 40% of these individuals showing prior release. Our 100‐year growth simulation suggested that a 50% basal area thinning from above could double red spruce basal area to support a mixed spruce–hardwood stand in approximately 20–40 years. These results indicate that restoration silviculture could be an effective tool for increasing the amount and quality of this reduced forest type in the central Appalachians.     

High white-tailed deer densities benefit graminoids and contribute to biotic homogenization of forest ground-layer vegetation

Biotic homogenization, with its emphasis on invasions, extinctions, and convergence in taxonomic similarity, provides an important framework for investigating changes in biodiversity across scales. Through their selective foraging, large populations of white-tailed deer are altering population sizes, driving extirpations, and facilitating invasions of plants throughout the eastern United States. I hypothesize that deer can drive biotic homogenization in forest understory communities by shifting species composition to one dominated by grasses, sedges, and ferns (all wind-pollinated plants). I report the effects of 16 years of deer exclusion in a hemlock-northern hardwood stand in N Wisconsin using a block design. Species composition showed greater convergence in control plots than exclosure plots, indicating deer can drive biotic homogenization at the stand level. Total percent cover is nearly 4 times greater in exclosure plots. Percent cover by woody plants, broadleaf herbs, and ferns is 150, 63, and 20 times greater in exclosure plots, respectively, while cover by sedges and grasses is 3.8 and 2.2 times greater in control plots. Cover by species with showy, insect-pollinated flowers is 79 times greater in exclosures. Graminoid-dominated control plots represent a novel state not observed fifty years ago, and could reflect the emergence of a grazing lawn. The increase in graminoids at this study area and throughout the region could under some global change scenarios be an early stage of conversion from forest to savanna or wood pasture.     

Woody debris contribution to the carbon budget of selectively logged and maturing mid-latitude forests

Woody debris (WD) is an important component of forest C budgets, both as a C reservoir and source of CO₂ to the atmosphere. We used an infrared gas analyzer and closed dynamic chamber to measure CO₂ efflux from downed coarse WD (CWD; diameter≥7.5 cm) and fine WD (FWD; 7.5 cm>diameter≥2 cm) to assess respiration in a selectively logged forest and a maturing forest (control site) in the northeastern USA. We developed two linear regression models to predict WD respiration: one based on WD temperature, moisture, and size (R ²=0.57), and the other on decay class and air temperature (R ²=0.32). WD respiration (0.28±0.09 Mg C ha⁻¹ year⁻¹) contributed only ≈2% of total ecosystem respiration (12.3±0.7 Mg C ha⁻¹ year⁻¹, 1999–2003), but net C flux from CWD accounted for up to 30% of net ecosystem exchange in the maturing forest. C flux from CWD on the logged site increased modestly, from 0.61±0.29 Mg C ha⁻¹ year⁻¹ prior to logging to 0.77±0.23 Mg C ha⁻¹ year⁻¹ after logging, reflecting increased CWD stocks. FWD biomass and associated respiration flux were ≈7 times and ≈5 times greater, respectively, in the logged site than the control site. The net C flux associated with CWD, including inputs and respiratory outputs, was 0.35±0.19 Mg C ha⁻¹ year⁻¹ (net C sink) in the control site and −0.30±0.30 Mg C ha⁻¹ year⁻¹ (net C source) in the logged site. We infer that accumulation of WD may represent a small net C sink in maturing northern hardwood forests. Disturbance, such as selective logging, can enlarge the WD pool, increasing the net C flux from the WD pool to the atmosphere and potentially causing it to become a net C source.Electronic Supplementary Material Supplementary material is available for this article at and is accessible for authorized users.     

Predators at bird nests in a northern hardwood forest in New Hampshire

ABSTRACT.   Nest predation is the primary cause of nest failure in most passerine birds, and increases in nest predation associated with anthropogenic habitat disturbance are invoked as explanations for population declines of some bird species. In most cases, however, the identity of the nest predators is not known with certainty. We monitored active bird nests with infrared time-lapse video cameras to determine which nest predators were responsible for depredating bird nests in northern New Hampshire. We monitored 64 nests of 11 bird species during three breeding seasons, and identified seven species of predators during 14 predation events. In addition, we recorded two instances of birds defending nests from predators and, in both cases, these nests were ultimately lost to predation. These results contrast with other studies in terms of the relatively high proportion of nests depredated by raptors and mice, as well as the absence of any predation by snakes. The diverse suite of predators in this and other studies is likely to confound our understanding of patterns of nest predation relative to fragmentation and habitat structure.     

Stemflow nutrient inputs to soil in a successional hardwood forest

Stemflow and throughfall from a regenerating (8-year-old) southern Appalachian hardwood forest were collected to examine the relative importance of tree bole nutrient leaching in response to acid deposition. Samples from nine (2 m²) stemflow collection plots were analyzed for four dormant season and 11 growing season rainstorm events. Results showed that, relative to throughfall fluxes, stemflow accounted, on average, for approximately 8.5% of total water reaching the forest floor during both dormant and growing season storms. Relative to foliar leaching, K-, SO₄-, and PO₄ ions appear to be the most easily leached ions from young tree stems. Proportional nitrate and base cation stemflow fluxes increased significantly (p<0.05) with growing-season storm-event duration, suggesting that the stemsurface nutrient pool is depleted by precipitation more slowly than the foliar pool. On average, proportional stemflow fluxes of SO₄ (12%) and K (14%) were consistently higher than reported maximum values for more mature forest stands, which indicates that small-scale stemflow inputs of ions such as these to the forest floor may be important in early successional ecosystems.     

Variation of cellulose microfibril angles in softwoods and hardwoods-a possible strategy of mechanical optimization

Position-resolved small-angle X-ray scattering was used to investigate the nanostructure of the wood cell wall in two softwood species (Norwegian spruce and Scots pine) and two hardwood species (pedunculate oak and copper beech). The tilt angle of the cellulose fibrils in the wood cell wall versus the longitudinal cell axis (microfibril angle) was systematically studied over a wide range of annual rings in each tree. The measured angles were correlated with the distance from the pith and the results were compared. The microfibril angle was found to decrease from pith to bark in all four trees, but was generally higher in the softwood than in the hardwood. In Norwegian spruce, the microfibril angles were higher in late wood than in early wood; in Scots pine the opposite was observed. In pedunculate oak and copper beech, low angles were found in the major part of the stem, except for the very first annual rings in pedunculate oak. The results are interpreted in terms of mechanical optimization. An attempt was made to give a quantitative estimation for the mechanical constraints imposed on a tree of given dimensions and to establish a model that could explain the general decrease of microfibril angles from pith to bark.