Drivers of understory plant communities in Sierra Nevada mixed conifer forests with pyrodiversity

Background Fire suppression in western North America increased and homogenized overstory cover in conifer forests, which likely affected understory plant communities. We sought to characterize understory plant communities and their drivers using plot-based observations from two contemporary reference sites in the Sierra Nevada, USA. These sites had long-established natural fire programs, which have resulted in restored natural fire regimes. In this study, we investigated how pyrodiversity—the diversity of fire size, severity, season, and frequency—and other environment factors influenced species composition and cover of forest understory plant communities. Results Understory plant communities were influenced by a combination of environmental, plot-scale recent fire history, and plot-neighborhood pyrodiversity within 50 m. Canopy cover was inversely proportional to understory plant cover, Simpson’s diversity, and evenness. Species richness was strongly influenced by the interaction of plot-based fire experience and plot-neighborhood pyrodiversity within 50 m. Conclusions Pyrodiversity appears to contribute both directly and indirectly to diverse understory plant communities in Sierra Nevada mixed conifer forests. The indirect influence is mediated through variability in tree canopy cover, which is partially related to variation in fire severity, while direct influence is an interaction between local and neighborhood fire activity.

Efficacy of Chemical and Biological Stump Treatments for the Control of Heterobasidion occidentale Infection of California Abies concolor

We conducted an experimental evaluation of treatments to limit Heterobasidion occidentale infection of white fir (Abies concolor) stumps and wounds in California mixed conifer forests. We tested the efficacy of urea, borate, and a mixture of two locally collected Phlebiopsis gigantea strains in preventing pathogen colonization of fir stumps and separately, urea and borate as infection controls on experimental stem wounds. These were paired with a laboratory test on ~100 g wood blocks with and without a one-week delay between inoculation and treatment. Urea, borates, and Phlebiopsis treatments all significantly reduced the stump surface area that was colonized by H. occidentale at 84%, 91%, and 68%, respectively, relative to the controls. However, only the borate treatments significantly lowered the number of stumps that were infected by the pathogen. The laboratory study matched the patterns that were found in the stump experiment with a reduced area of colonization for urea, borates, or P. gigantea treatments relative to the controls; delaying the treatment did not affect efficacy. The field wound experiment did not result in any Heterobasidion colonization, even in positive control treatments, rendering the experiment uninformative. Our study suggests treatments that are known to limit Heterobasidion establishment on pine or spruce stumps elsewhere in the world may also be effective on true firs in California.

Biophysical Settings that Influenced Plantation Survival During the 2015 Wildfires in Northern Rocky Mountain Moist Mixed-Conifer Forests

Fire suppression and the loss of western white pine (WWP) have made northern Rocky Mountain moist mixed-conifer forests less disturbance resilient. Although managers are installing hundreds of plantations, most of these plantations have not experienced wildfire since establishment. In 2015, wildfires burned through one hundred WWP plantations in this region, providing an opportunity to evaluate the effects of wildfires on sapling survival. A Weibull distribution approach was used to characterize the variation of fire severity pixels, as indicated by the differenced normalized burn ratio. The distribution parameters provided a method to identify the biophysical setting and plantation characteristics influencing fire severity and sapling survival. Plantations located on lower slope positions were more resistant to wildfires than plantations located midslope or close to the ridges. Snow water equivalent was positively correlated with wildfire resistance and resilience. Results will help focus reforestation efforts and identify locations where future plantations can potentially survive wildfires. Study Implications This study examined wildfire effects on western white pine plantations, with the intention to inform managers where to locate plantations that will be more resistant to wildfires and determine which plantations may require postfire reforestation. Plantations were more resilient and resistant to wildfires when they occurred on lower slopes, even when steep, indicating these places may be better suited for future plantations. Plantations located on upper slopes and ridges are vulnerable to wildfire even when located on moist habitat types and will likely need reforestation.

Inter-specific competition among trees in pythagorean fuzzy soft environment

A Pythagorean fuzzy set is very effective mathematical framework to represent parameter-wise imprecision which is the property of linguistic communication. A Pythagorean fuzzy soft graph is more potent than the intuitionistic fuzzy soft as well as the fuzzy soft graph as it depicts the interactions among the objects of a system using Pythagorean membership grades with respect to different parameters. This article addresses the content of competition graphs as well as economic competition graphs like k-competition graphs, m-step competition graphs and p-competition graphs in Pythagorean fuzzy soft environment. All these concepts are illustrated with examples and fascinating results. Furthermore, an application which describes the competition among distinct forest trees, that grow together in the mixed conifer forests of California, for plant resources is elaborated graphically. An algorithm is also designed for the construction of Pythagorean fuzzy soft competition graphs. It is worthwhile to express the competing and non-competing interactions in various networks with the help of Pythagorean fuzzy soft competition graphs wherein a variation in competition relative to different attributes is visible.

Mid-Scale Drivers of Variability in Dry Mixed-Conifer Forests of the Mogollon Rim, Arizona

The structure and composition of southwestern dry mixed-conifer forests have changed significantly, decreasing forest resiliency to uncharacteristic disturbances which also threaten ecosystem services. Restoration of these forests can be informed by historical conditions; however, managers and researchers still lack a full understanding of how environmental factors influence forest conditions. We investigated historical and contemporary variability in dry mixed-conifer forests in northern Arizona and identified important environmental drivers. We utilized forest sample plots and dendrochronological reconstruction modelling to describe forest conditions in 1879 and 2014, respectively. We used correlogram analysis to compare spatial autocorrelation of average diameter, basal area and tree density, and structural equation modeling to partition the causal pathways between forest structure, forest composition, and a suite of environmental factors reflecting climate, topography, and soil. Historical (1879) reconstructed forests had significantly fewer trees, lower basal area, and higher average diameter than contemporarily (2014). Composition has shifted from ponderosa pine dominance towards a more mixed-species composition. Historically, forest structure did not exhibit strong spatial autocorrelation, but contemporary tree density and diameter were strongly autocorrelated. Environmental factors described little variation in historical forest conditions but are more important for contemporary conditions. Managers can utilize this increased understanding of variation to tailor silvicultural prescriptions to environmental templates.