Top-down and bottom-up factors affecting invasive populations are rarely considered simultaneously, yet their interactive responses to disturbances and management interventions can be essential to understanding invasion patterns. We evaluated post-fire responses of the exotic perennial forb Chondrilla juncea (rush skeletonweed) and its biocontrol agents to landscape factors and a post-fire combined herbicide (imazapic) and bacteria (Pseudomonas fluorescens strain MB906) treatment that targeted invasive annual grasses in a sagebrush steppe ecosystem. Biocontrol agents released against C. juncea in previous decades included Cystiphora schmidti (gall midge), Aceria chondrillae (gall mite), and Puccinia chondrillina (rust fungus). C. juncea abundance was greater in sprayed than unsprayed plots, and where soils were coarser, slopes faced southwest, solar heat loads and topographic water accumulation were greater, and cover of deep-rooted native perennials was lower. Mite infestation was greater in unsprayed plots, midge infestation was greater at higher elevations on steeper slopes, and midges were more abundant while rust was less abundant on gravelly soils. Biocontrol infestation levels varied considerably between years and could not be predicted in 2019 from 2018 infestation levels. Multiple biocontrol species were often present at the same plots but were rarely present on the same C. juncea individuals. These results suggest that spatial patterns of invasion by C. juncea are related to deep-soil water availability, warmer conditions, and alleviation of competition. Treatments designed to reduce invasive annual grasses may inadvertently release C. juncea by both reducing plant competition for soil resources and affecting biocontrol agent (mite) abundance.

Invasive-plant treatments often target a single or few species, but many landscapes are diversely invaded. Exotic annual grasses (EAGs) increase wildfires and degrade native perennial plant communities in cold-desert rangelands, and herbicides are thus sprayed to inhibit EAG germination and establishment. We asked how EAG-target and nontarget species responded to an herbicide mixture sprayed over a large, topographically diverse landscape after wildfire. We focused on how whole-community and natural EAG-pathogen treatment responses varied over years and physical properties of sites. We monitored plant cover and diversity in 41 pairs of plots located inside or outside areas (486 ha total) treated with a combined aerial broadcast spray of pre-emergent herbicide (imazapic) and weed-suppressive bacteria (Pseudomonas fluorescens, “MB906”) to target EAGs after wildfires in southwest Idaho, USA.

Invasive-plant treatments often target a single or few species, but many landscapes are diversely invaded. Exotic annual grasses (EAGs) increase wildfires and degrade native perennial plant communities in cold-desert rangelands, and herbicides are thus sprayed to inhibit EAG germination and establishment. We asked how EAG-target and nontarget species responded to an herbicide mixture sprayed over a large, topographically diverse landscape after wildfire. We focused on how whole-community and natural EAG-pathogen treatment responses varied over years and physical properties of sites. We monitored plant cover and diversity in 41 pairs of plots located inside or outside areas (486 ha total) treated with a combined aerial broadcast spray of pre-emergent herbicide (imazapic) and weed-suppressive bacteria (Pseudomonas fluorescens, “MB906”) to target EAGs after wildfires in southwest Idaho, USA.

Twenty quadrats within the burn perimeter of a September 2021 wildfire outside of Boise, Idaho were surveyed for the abundance of fire effects, biocrusts and vascular plants immediately post-fire. The fire was too small to be named. Char was measured as a proxy for fire intensity. Biocrusts were surveyed by morphogroup (crustose lichens, cup lichens, fruticose lichens, gelatinous lichens, short moss, tall moss) and vascular plants were surveyed by functional group (annual forbs, perennial grasses). Char was measured ocularly and biocrust/plant abundance was measured via point-vertex intercept at 40 points per quadrat.

Twenty quadrats within the burn perimeter of a September 2021 wildfire outside of Boise, Idaho were surveyed for the abundance of fire effects, biocrusts and vascular plants immediately post-fire. The fire was too small to be named. Char was measured as a proxy for fire intensity. Biocrusts were surveyed by morphogroup (crustose lichens, cup lichens, fruticose lichens, gelatinous lichens, short moss, tall moss) and vascular plants were surveyed by functional group (annual forbs, perennial grasses). Char was measured ocularly and biocrust/plant abundance was measured via point-vertex intercept at 40 points per quadrat.

Between 1987 and 1988, twenty-four approximately 2-acre plots were established in Jones County, Georgia on the Hitchiti Experimental Forest which is also known as the Brender Demonstration Forest. These plots have not burned since prior to 1939. Treatments were applied to track site changes over time from five short return interval underburn treatments. These treatments, replicated 4 times, were comprised of: biennial dormant season headfires, triennial dormant season headfires, triennial dormant season backfires, triennial growing season headfires, growing season headfires every 6 years, and unburned controls. Triennial dormant season treatments were eventually combined. Variables tracked over time include the impact of fire on overstory pine growth, midstory (in this study midstory includes understory plants > 4.5 feet high) structure and composition, seedling (in this study including all woody plants < 4.5 feet high and all other plants regardless of height) species dominance, percent cover, pine seedling establishment and mortality, and forest floor consumption. Several thousand overstory and midstory trees were tagged, GPS coordinates recorded and their survival and growth followed over time. Vegetation was measured in nested circular plots and on line transects. Live and dead overstory trees on two 0.2 acre (1/5 ac) subplots per treatment plot were tallied annually by species with diameter at breast height and height, measured and pest damage/mortality by pathogen, lightning and wind damage recorded. Basal area was calculated periodically. Some overstory pines were bored to determine age (typically after death). Midstory live and dead trees were tallied annually on six 0.02 acre subplots per treatment plot. Seedlings were tallied on eighteen 0.001 acre (MA = milacre) subplots per treatment plot by species/species group, and percent of the subplot area in vines, herbs, moss, live woody material, dead plant material, and void of plant material (exposed mineral soil). Six 33 feet line transects per treatment plot were divided into 6 inch segments and dominant seedling species/species group tallied annually. Over 150 species/species groups were identified and tracked over time. Weights of likely available live fuel were determined by species/species group prior to each burn, as were weights of likely available dead fuel for various categories/size classes. Paired postburn samples were collected to determine consumption of various fuel categories. Overstory and midstory pine crown scorch, foliage consumption, and hardwood mortality were tallied within two weeks following each burn. Other vegetation datasets include pine seedling establishment and survival over time on the 18 MA subplots per treatment plot. Red cockaded woodpecker (RCW) related information was collected annually by Region 8 (Southern Region) of the USFS and is available from them. Live and dead fuel moisture data were sampled prior to every burn and can include preburn moisture content grab samples, 10-hour fuel stick readings, and random lumber probe readings. Fire behavior records of headfires and backfires can include rate of spread, flame length, flame angle, flame zone depth, short distance spotting, slopovers, burnout time, and percent of plot burned. The study plan called for observations of fire residence time as well, but such observations were rarely recorded. Weather data include on-plot hand-held instrument observations of surface wind velocity, ambient temperature and relative humidity (RH). On-site data collected can include precipitation, ambient temperature, RH and wind traces from recording gauges. Keetch Byram Drought Index (KBDI) calculation and National Fire danger Rating System NFDRS predictions and other weather observations taken at two nearby Georgia Forestry Commission weather stations were also included.

Fifteen fires from the Chronosequence dataset (see Knutson et al. 2014) were visited in 2012 and 2013 and surveyed for cover of lichens and mosses. Fires were selected to cover the range of average precipitation for each of three water years following fire, fire severity, time since fire, season of ignition, total acres burned and grazing intensity. Cattle grazing was characterized by distance from water sources for cattle, cow dung density counts and Animal Unit Months from the Rangeland Administration System of the Bureau of Land Management. Fire was characterized by whether or not a site burned, time since fire, the area burned, and an estimated amount of shrub cover consumed by the fire as compared to seemingly comparable unburned sites. In total, 99 plots were surveyed.

Fifteen fires from the Chronosequence dataset (see Knutson et al. 2014) were visited in 2012 and 2013 and surveyed for cover of lichens and mosses. Fires were selected to cover the range of average precipitation for each of three water years following fire, fire severity, time since fire, season of ignition, total acres burned and grazing intensity. Cattle grazing was characterized by distance from water sources for cattle, cow dung density counts and Animal Unit Months from the Rangeland Administration System of the Bureau of Land Management. Fire was characterized by whether or not a site burned, time since fire, the area burned, and an estimated amount of shrub cover consumed by the fire as compared to seemingly comparable unburned sites. In total, 99 plots were surveyed.

These data summarize postfire resprouts and seedling counts for Ceanothus species in subgenus Ceanothus based on published data that is cited and personal observation by the author and other co-authors of the publication.

These data summarize postfire resprouts and seedling counts for Ceanothus species in subgenus Ceanothus based on published data that is cited and personal observation by the author and other co-authors of the publication.