Impact of Competition on the Growth of Pinus Tabulaeformis in Response to Climate on the Loess Plateau of China

With climate change, understanding tree responses to climate is important for predicting trees’ growth, and plant competition as a nonnegligible biotic factor plays a key role in such response. However, few studies have investigated how competition affects the response of Pinus tabulaeformis plantations to climate . In our study, we investigated nine 29-year-old P. tabulaeformis plantation plots (three density gradients). The dendroecological method was used to analyze the impact of competition on trees response to drought and interannual climate variation. Stand density index was used to indicate the intensity of competition. The results showed that competition modified the climate-growth relationship. Competition increased trees’ sensitivity to drought but the relationship between competition and sensitivity to drought was nonlinear. The competition effect slightly increased under intense competition conditions. Additionally, competition reduced trees’ sensitivity to interannual climate variation. After 1999, the effect of competition was obvious. The sensitivity of small-diameter trees, especially those in middle- and high-density stands, declined. Thus, in the future these trees presumably may exhibit a reduced sensitivity to interannual climate variation and a greater sensitivity to drought.

Bayesian Predictions of Bark Beetle Attack and Mortality of Three Conifer Species During Epidemic and Endemic Population Stages

Bark beetles naturally inhabit forests and can cause large-scale tree mortality when they reach epidemic population numbers. A recent epidemic (1990s–2010s), primarily driven by mountain pine beetles (Dendroctonus ponderosae), was a leading mortality agent in western United States forests. Predictive models of beetle populations and their impact on forests largely depend on host related parameters, such as stand age, basal area, and density. We hypothesized that bark beetle attack patterns are also dependent on inferred beetle population densities: large epidemic populations of beetles will preferentially attack large-diameter trees, and successfully kill them with overwhelming numbers. Conversely, small endemic beetle populations will opportunistically attack stressed and small trees. We tested this hypothesis using 12 years of repeated field observations of three dominant forest species (lodgepole pine Pinus contorta, Engelmann spruce Picea engelmannii, and subalpine fir Abies lasiocarpa) in subalpine forests of southeastern Wyoming paired with a Bayesian modeling approach. The models provide probabilistic predictions of beetle attack patterns that are free of assumptions required by frequentist models that are often violated in these data sets. Furthermore, we assessed seedling/sapling regeneration in response to overstory mortality and hypothesized that higher seedling/sapling establishment occurs in areas with highest overstory mortality because resources are freed from competing trees. Our results indicate that large-diameter trees were more likely to be attacked and killed by bark beetles than small-diameter trees during epidemic years for all species, but there was no shift toward preferentially attacking small-diameter trees in post-epidemic years. However, probabilities of bark beetle attack and mortality increased for small diameter lodgepole pine and Engelmann spruce trees in post-epidemic years compared to epidemic years. We also show an increase in overall understory growth (graminoids, forbs, and shrubs) and seedling/sapling establishment in response to beetle-caused overstory mortality, especially in lodgepole pine dominated stands. Our observations provide evidence of the trajectories of attack and mortality as well as early forest regrowth of three common tree species during the transition from epidemic to post-epidemic stages of bark beetle populations in the field.

The importance of large-diameter trees to the creation of snag and deadwood biomass

Background Baseline levels of tree mortality can, over time, contribute to high snag densities and high levels of deadwood (down woody debris) if fire is infrequent and decomposition is slow. Deadwood can be important for tree recruitment, and it plays a major role in terrestrial carbon cycling, but deadwood is rarely examined in a spatially explicit context. Methods Between 2011 and 2019, we annually tracked all trees and snags ≥1 cm in diameter and mapped all pieces of deadwood ≥10 cm diameter and ≥1 m in length in 25.6 ha of Tsuga heterophylla / Pseudotsuga menziesii forest. We analyzed the amount, biomass, and spatial distribution of deadwood, and we assessed how various causes of mortality that contributed uniquely to deadwood creation. Results Compared to aboveground woody live biomass of 481 Mg ha−1 (from trees ≥10 cm diameter), snag biomass was 74 Mg ha−1 and deadwood biomass was 109 Mg ha−1 (from boles ≥10 cm diameter). Biomass from large-diameter trees (≥60 cm) accounted for 85%, 88%, and 58%, of trees, snags, and deadwood, respectively. Total aboveground woody live and dead biomass was 668 Mg ha−1. The annual production of downed wood (≥10 cm diameter) from tree boles averaged 4 Mg ha−1 yr−1. Woody debris was spatially heterogeneous, varying more than two orders of magnitude from 4 to 587 Mg ha−1 at the scale of 20 m × 20 m quadrats. Almost all causes of deadwood creation varied in importance between large-diameter trees and small-diameter trees. Biomass of standing stems and deadwood had weak inverse distributions, reflecting the long period of time required for trees to reach large diameters following antecedent tree mortalities and the centennial scale time required for deadwood decomposition. Conclusion Old-growth forests contain large stores of biomass in living trees, as well as in snag and deadwood biomass pools that are stable long after tree death. Ignoring biomass (or carbon) in deadwood pools can lead to substantial underestimations of sequestration and stability.

Faidherbia albida (Delile) Tree Dieback Effects on Crop Production in the Parkland Agroforests of Southwestern Niger

Faidherbiaalbida is an agroforestry tree species playing important agroecological and socioeconomic roles in arid and semiarid zones in Africa. For many years, anthropogenic and abiotic stresses were considered as the main threats for the species in West African parkland agroforests. Considerable dieback has recently occurred in F. albida trees of parkland agroforests in central southwestern Niger, and the causes are unknown. The objectives of this study are to (i) investigate the magnitude of dieback of F. albida trees and (ii) assess local community perceptions of the effects of F. albida dieback on crop production. The health status and phenology of 213 F. albida trees were observed in the area where the dieback is occurring. Similarly, a sample of 144 people, 86% of which were farmers, was surveyed. Dieback incidence of F. albida trees was 19%, with mortality of 6%. Large-diameter trees had greater dieback than small-diameter trees. The most affected parts of the tree were the branches at 54% and the trunks at 39%. The populations noted a 33–55% reduction in the yields of major crops. This dieback of F. albida trees poses a serious threat to the survival of rural communities. Further studies can be conducted to identify the cause or cause of the dieback to guide the suitable agroforestry parkland management strategies.

Feasibility of a Harvesting System for Small-Diameter Trees as Unutilized Forest Biomass in Japan

In order to secure a supply of forest biomass, as well as promote further utilization following the completion of the Feed-in-Tariff Scheme for Renewable Energy (FIT), small-diameter trees such as cleanings from young planted forests and broad-leaved trees from coppice forests are prospective resources in Japan. The goal of this study was to discuss effective methods for harvesting the small-diameter trees that are unutilized forest biomass in Japan. This study assumed a simplified model forest and conducted experiments and time studies of the harvesting of small-diameter trees with a truck-mounted multi-tree felling head. As a result, the machine used in the experiment could fell a maximum of six trees inward in a row from a forest road. However, the harvesting cost (felling, accumulating and chipping) was cheapest when the machine felled five trees inward in a row. Lengthening the maximum reach of a felling head to fell trees deeper inward in a row appeared effective in increasing the number of harvested trees. From the perspective of minimizing the harvesting cost, however, there were upper limits to the number of trees felled inward as well as to the maximum reach of a felling head. The results of a sensitivity analysis suggested the following machine improvements could be considered in future policy: increasing the moving velocity of a felling head and the maximum number of trees that can be held at a time are effective if it is possible to lengthen the maximum reach of a felling head. Meanwhile, shortening the machine’s moving time among operation points is also effective if the maximum reach of a felling head cannot be lengthened.

Basic Examination of the Harvesting of Small-Diameter Trees as Unutilized Forest Biomass in Japan

In order to secure the supply source as well as promote the further utilization of forest biomass following the completion of the Feed-in Tariff Scheme for Renewable Energy (FIT), small-diameter trees, including samples from not only young planted forests but also broad-leaved trees from coppice forests, can be expected to be a prospective solution in Japan. With the aim of discussing the most effective method of harvesting such small-diameter trees as unutilized forest biomass appropriate for Japan, a simplified model forest was assumed in this study, while the harvesting of small-diameter trees was investigated with a truck-mounted multi-tree felling head and time-studied. As a result, the machine used in the experiment could fell a maximum of six trees in a row from a forest road, but the harvesting (felling, accumulating, and chipping) cost was the lowest when the machine felled five trees in a row.

Pilot study on low-density binderless bark particleboards manufacture from gelam wood (Melaleuca sp.) bark

The production of low-density binderless bark particleboards (LDBBP) from gelam wood bark (GWB) using a hot pressing method at low temperature (128 °C) and pressure (30 kg × cm-2) was explored by examining their physical properties according to SNI 03-2105-2006 (2006). They were also examined via scanning electron microscope (SEM)-energy dispersive X-ray (EDX) observation. The LDBBPs were manufactured using two types of GWB particles: (1) bark waste that was peeled off of small-diameter trees < 10 cm (A) and, (2) bark that was directly peeled off from a standing tree with an average diameter of 10 cm to 15 cm (B). Results showed that the average values of the physical properties of LDBBP(A) and LDBBP(B) met the SNI 03-2105-2006 (2006) requirements in terms of density, moisture content, and thickness swelling after being immersed for 24 h for particleboard type 24-10 and type 17.5-10.5 with maximum thickness swelling requirement 20%. However, they failed to meet the maximum thickness swelling criterion of 12% for other particleboard types. Subsequent internal morphology observation using SEM indicated the presence of cracks on LDBBP (A), so only LDBBP (B) could be manufactured without delamination. Gelam bark could potentially be used to produce non-adhesive particleboards.

Simulation-Based Cost Analysis of Industrial Supply of Chips from Logging Residues and Small-Diameter Trees

Research Highlights: The use of terminals can increase supply costs by 5–11% (when compared to direct supply), but terminals help secure supply during peak demand and cope with operational problems in the supply fleet in cases where direct supply chains would be unable to meet demand on time. Background and Objectives: This work analyses the supply cost of chipped logging residues and small-diameter trees, from chipping at roadside storages to delivery to the end-user. Factors considered include demand curves (based on the requirements of a theoretical combined heat and power plant or biorefinery); demand volume; and mode of supply (direct or combined via terminal). The impact of longer trucking distances from the sites, and supply integration between forest and other land (varying relocation distances) was also assessed. Materials and Methods: The operational environment and work of a theoretical chip supplier in northern Sweden were modelled and simulated in ExtendSim®. Results: The mean supply cost of chips was 9% higher on average for combined chains than for direct chains. Given a high demand, 8% of the annual demand could not be delivered on time without using a terminal. High supply integration of forest and other land reduced supply costs by 2%. Contractors’ annual workloads were evened out by direct supply to the biorefinery (which has a relatively steady demand) or supply via-terminal independently of the end-user. Keeping distinct chips from different sites (implying that trucks were not always fully loaded) instead of mixing chips from different sites until the trucks were fully loaded increased supply costs by 12%. Conclusions: Terminals increase supply costs, but can enable demand to be met on time when direct supply chains alone might fail. Integrated supply planning could reduce supply costs by increasing the utilization of residual biomass from other land.