Treesearch

In recent years, the pocket penetrometer (PPT) test has been used to measure soil compaction and has gained attention due to its simplicity, high speed, and low cost. This study aimed to predict soil strength using a regression relationship between unconfined compressive strength (UCS) and PPT. We collected 45 large soil samples from a forest district in a part of the Hyrcanian Forest. In the laboratory, soil samples were classified according to unified soil classification system. Samples were classified as either silt or clay with a low or high liquid limit. These four soil groups were,...

Tree mortality associated with drought and concurrent bark beetle outbreaks is expected to increase with further climate change.When these two types of disturbance occur in concert it complicates our ability to accurately predict future forest mortality. The recent extreme California USA drought and bark beetle outbreaks resulted in extensive tree mortality and provides a unique opportunity to examine questions of why some trees die while others survive these co-occurring disturbances. We use plot-level data combined with a three-proxy tree-level approach using radial growth, carbon...

The phylogenetic and functional diversity of microbial communities in tropical rainforests, and how these differ from temperate communities remain poorly described but are directly related to the increased fluxes of greenhouse gases such as nitrous oxide (N2O) from the tropics. Towards closing these knowledge gaps, we analyzed replicated shotgun metagenomes representing distinct life zones from four locations in the Luquillo Experimental Forest (LEF), Puerto Rico. These soils had a distinct microbial community composition and lower species diversity when compared to temperate grasslands or...

California’s high density, fire-excluded forests experienced an extreme drought accompanied by warmer than normal temperatures from 2012 to 2015, resulting in the deaths of millions of trees. We examined tree mortality and growth of mixed-conifer stands that had been experimentally treated between 2011 and 2013 with two different thinning treatments, one with more structural variability (HighV) and one with less structural variability (LowV), applied alone or in combination with prescribed burning. Tree mortality between 2014 and 2018 varied by species ranging from 42% of white fir (Abies...

Non-native insects and pathogens can alter the composition and successional trajectories of forests and, in exceptional cases, drive their host trees functionally extinct. Emerald ash borer has killed millions of ash trees in its invaded range across eastern North America. Predicting the future ecological role of ash requires information on the extent of ash regeneration and recruitment in the wake of invasion. Variable levels of ash regeneration have been observed in stands invaded by emerald ash borer, although recruitment rates of young ash trees into the overstory remain unclear. Here,...

Reduction in faunal diversity is suggested to reduce litter decomposition, whereas increases in ultraviolet (UV) radiation may directly enhance or indirectly retard litter decomposition. Here we examined the effect of soil arthropods and UV radiation on litter decomposition in burned and unburned plots during a 469-day field experiment in a subtropical pastureland of Puerto Rico. Prescribed burn reduced soil arthropod diversity and increased UV radiation during the initial period of 240 days following the burn, and consequently reduced plant litter decomposition. The density of predators...

The forced flow driven flame spread behavior along an array of discrete wooden fuel elements was ex- perimentally investigated, which could be an important step to understanding the flow-flame interactions that govern fire spread. Fuel arrays with fiv e different spacings (0.75, 0.875. 1.00, 1.125, and 1.25 cm) were subject to flow speeds ranging from 2.2 to 4.3 m/s at approximately 0.2 m/s intervals. For spacing-flow speed conditions tested in the current study, the flame spread behavior was categorized into three different regimes, continuous, discrete, and quenching, and the regimes...

Pine barrens are open-canopy ecological communities once prevalent on sandy soils across the northern Great Lakes Region of the U.S. and Canada, though fire suppression and plantation forestry have now reduced them to a few isolated areas. Efforts to restore pine barrens are underway on some public lands, but lack of knowledge on the social and ecological issues and challenges that affect these projects impedes fuller progress. As a precursor to designing a public preference survey for pine barrens restoration, we sought input from those with expert knowledge about pine barrens. Using a...

Computational Fluid Dynamics (CFD) models are powerful research tools for studying fire dynamics. However, their application to wildland fire scenarios requires evaluation against relevant experimental data. To progress our current understanding of the fidelity of a CFD approach to simulating wildland fire dynamics, a dataset from an experimental fire was used as a test case. First, implications of the level of detail provided to the model, in the form of fuel structure and wind, are evaluated. Second, the predictions of both fire behavior (e.g. spread rate) and the driving combustion...

The effects of freestream flow on fire spread behaviors of a discrete wooden fuel array were studied. The spacing between fuel elements was varied, and the flame spread behavior under 1, 2, and 3 m/s forced flow velocities was investigated. The fastest spread rate was not observed for the smallest spacing. Furthermore, increasing spacing did not necessarily lead to a slower spread, as seen with the flame spread along the 0.75 cm spaced array which was as fast or faster than the 0.5 cm spacing condition. At a spacing of 1 cm, fragmented flames were observed at wind speeds of 3 m/s that...