After a more than a century of fighting to keep fire out of forests, reintroducing it is now an important management goal. Yet changes over the past century have left prescribed burning with a big job to do. Development, wildfire suppression, rising global temperatures, extended droughts, exotic species invasions, and longer fire seasons add complexity to using this practice.
Managers must consider how often, how intensely, and what time of year to burn; for insights they often look to how and when fires burned historically. However, attempting to mimic historical wildfires that burned in hot, dry conditions is risky. Burning in fall or spring when temperature and humidity are low reduces the risk of prescribed fires becoming uncontrollable, but does it have the intended effects? How do forest ecosystems that historically were adapted to fire respond when fire is reintroduced after so much time without it?
Forest Service researchers Becky Kerns and Michelle Day conducted a long-term experiment in the Malheur National Forest, Oregon, to assess how season and time between prescribed burns affect understory plant communities in ponderosa pine forests. They found that some native plants persisted and recovered from fire but didn’t respond vigorously, while invasive species tended to spread. These findings may help forest managers design more effective prescribed-fire treatments and avoid unintended consequences.
Exotic grasses are a widespread set of invasive species that are notable for their ability to significantly alter key aspects of ecosystem function. Understanding the role and importance of these invaders in forested landscapes has been limited but is now rising, as grasses from Eurasia and Africa continue to spread through ecosystems of the Americas, Australia, and many Pacific islands, where they threaten biodiversity and alter various aspects of the fire regime. The ecological, social and economic impacts of the grass-fire cycle associated with species such as cheatgrass (Bromus tectorum) have been long recognized in aridlands such as the iconic sagebrush ecosystems of the western US. However, the damaging impacts of invasive grasses in forestlands have received considerably less attention. We review literature, conceptual models, model output, and empirical evidence that indicate grass invasion in forest ecosystems may be an important yet largely under-recognized phenomenon. In combination with climate change, wildfire, and overstory management, invasive grasses could create a “perfect storm” that threatens forest resilience. Invasive grasses can be successful in forested environments or develop strongholds within forested mosaics and could provide the literal seeds for rapid change and vegetation type conversion catalyzed by wildfire or changes in climate. Although invasive grass populations may now be on the edge of forests or consist of relatively rare populations with limited spatial extent, these species may disrupt stabilizing feedbacks and disturbance regimes if a grass-fire cycle takes hold, forcing large portions of forests into alternative nonforested states. In addition, forest management actions such as thinning, prescribed fire, and fuel reduction may actually exacerbate invasive grass populations and increase the potential for further invasion, as well as broader landscape level changes through increased fire spread and frequency. Lack of understanding regarding the ecological consequences and importance of managing invasive grasses as a fuel may lead to unintended consequences and outcomes as we enter an age of novel and rapid ecological changes. This paper focuses on the contributory factors, mechanisms, and interactions that may set the stage for unexpected forest change and loss, in an effort to raise awareness about the potential damaging impact of grass invasion in forested ecosystems.
Environmental DNA (eDNA) assays for single‐ and multi‐species detection show promise for providing standardized assessment methods for diverse taxa, but techniques for evaluating multiple taxonomically divergent assemblages are in their infancy. We evaluated whether microfluidic multiplex metabarcoding on the Fluidigm Access Array™ platform and high‐throughput sequencing could identify diverse stream and riparian assemblages from 48 taxon‐general and taxon‐specific metabarcode primers. eDNA screening was paired with electrofishing along a stream continuum to evaluate congruence between methods. A fish hatchery located midway along the stream continuum provided a dispersal barrier, and a point source for non‐native White Sturgeon (Acipencer transmontanus). Microfluidic metabarcoding had 87% accuracy with respect to electrofishing and detected all 13 species electrofishing observed. Taxon‐specific barcoding primers were more successful than taxon‐general universal metabarcoding primers at classifying sequences to species. Both types of markers detected a transition from downstream sites dominated by multiple fish species, to upstream sites dominated by a single species; however, we failed to detect a complementary transition in amphibian occupancy. White Sturgeon was only detected at the hatchery outflow, indicating eDNA transport was not detectable ~2.4 km from its source. Overall, we identified 878 predicted taxa. Most sequences (50.1%) derived from fish (Actinopteri, Petromyzontidae), oomycetes (21.3%), arthropoda (classes Insecta, Decapoda; 16.5%), and apicomplexan parasites (3.8%). Taxa accounting for ~1% or less of sequences included freshwater red algae, diatoms, amphibians, and beaver. Our work shows that microfluidic metabarcoding can survey multiple phyla per assay, providing fine discrimination required to resolve closely related species, and enable data‐driven prioritization for multiple forest health objectives.
In the Pacific Northwest, clearcutting is the preferred method for harvesting wood products from Douglas-fir plantations because it’s economical and mimics a large-scale disturbance. Following a clearcut, Douglas-fir seedlings are planted throughout the recovering native plant community. Yet the newly planted seedlings and native plants aren’t the only vegetation claiming the open ground. Invasive plant species, such as Scotch broom and sweet vernalgrass, can also colonize the site and compete with the seedlings for water, nutrients, and light.
Eradicating Scotch broom requires repeated herbicide applications, but even this approach might not fully control the infestation. Tim Harrington and David Peter, both researchers with the U.S. Forest Service Pacific Northwest Research Station, conducted a 5-year study near Matlock, Washington, to test if logging debris, in combination with herbicide applications, could reduce the spread of Scotch broom and other invasive plants; thereby improving regeneration of Douglas-fir.
They found that leaving logging debris reduced the spread of invasive plants and encouraged the development of the native plant community. Douglas-fir seedlings on these sites also grew faster and had higher survival rates than seedlings on sites where logging debris was removed. These results suggest that retaining logging debris offers a potentially cost-effective and beneficial long-term solution for managing invasive plants.
Scotch broom, Cytisus scoparius (L.) is a globally important nitrogen (N)-fixing invasive plant species that has potential to alter soil water dynamics, soil chemistry, and plant communities. We evaluated the effects of Scotch broom on soil moisture, soil chemistry, soil temperature, photosynthetically active radiation (PAR), and vegetation communities over 4 years at a site recently harvested for timber. Treatments of Scotch broom (either present via planting or absent) and background vegetation (either present or absent via herbicide treatments) were applied to 4 m2 plots. Background vegetation was associated with the greatest decrease of soil water content (SWC) among treatments. During the driest year, Scotch broom showed some evidence of increased early-and late-season soil water usage, and, briefly, a high usage relative to background vegetation plots. On a percent cover basis, Scotch broom had a substantially greater negative influence on SWC than did background vegetation. Surprisingly, Scotch broom was not consistently associated with increases in total soil N, but there was evidence of increasing soil water N when Scotch broom was present. Scotch broom-only plots had greater concentrations of soil water magnesium (Mg2+) and calcium (Ca2+) than other treatments. On a percent cover basis, Scotch broom had a uniquely high demand for potassium (K+) relative to the background vegetation. Average soil temperature was slightly greater, and soil surface PAR lower, with Scotch broom present. Scotch broom-absent plots increased in species diversity and richness over time, while Scotch broom-present plots remained unchanged. Scotch broom presence was associated with an increase in cover of nonnative sweet vernalgrass (Anthoxanthum odoratum L.). Scotch broom generated positive feedbacks with resource conditions that favored its dominance and the establishment of nonnative grass.
This is a Commentary for the 50th Anniversary Issue of Herpetological Review on the Diseases section of the journal which I initiated in December 2007. This section aimed to accelerate the pace and communication of science findings relative to herpetological emerging infectious diseases. Since the section was launched in late 2007, 185 disease articles by 594 authors have been published, including reports on seven disease-causing agents and a geographic scope spanning 42 countries and 35 US states. A world community has engaged in this work, empowering land managers, local biologists, the public, and scientists to partner and develop worthwhile science that can have management implications. These studies are often puzzle pieces of a larger picture, which has been assembled by other synthesis papers and meta-analyses. In Aldo Leopold’s words, “To keep every cog and wheel is the first precaution of intelligent tinkering.” The decade since this section's initiation has seen tremendous change in how disease science is conducted, with blooming collaborations, freer information sharing, and development of coalitions to address regional disease issues. The HR Disease section documents these patterns, and the recent advent of knowledge syntheses to guide further endeavors.