Granivores and Restoration: Implications of Invasion and Considerations of Context-dependent Seed Removal

Granivores are important components of sagebrush communities in western North America. These same regions are being altered by the invasion of the exotic annual Bromus tectorum (cheatgrass) that alters physical and biological dynamics in ways that appear to promote its persistence. This research directly relates to the restoration of B. tectorum-dominated systems in two inter-related ways. First, because these landscapes have large quantities of seeds applied during restoration, it is important to determine the major granivore communities in intact sagebrush communities and in nearby cheatgrass-dominated communities. Second, it is important to develop an understanding of patterns of seed harvest by granivores. In addition to the data chapters there are two review chapters; Chapter 1 highlights factors contributing to seed removal and Chapter 7 provides ecologically based techniques that could minimize the negative consequences of granivores during ecological restoration. Common groups of ants showed increased abundances; uncommon species and functional groups were generally negatively impacted by cheatgrass (Chapter 2). Conversely, rodents were negatively impacted by conversion to cheatgrass (Chapter 4). Ant seed removal was highly context-dependent (Chapter 3), depending on the background vegetation (large-scale among-patch effects), foraging distance from the nest mound (small-scale among-patch effects), and the presence of other seed species in mixture (within-patch effects). In addition, cheatgrass provided associational resistance to native seeds in mixture, meaning the presence of cheatgrass increased native seed survival. In Chapter 5 a novel statistical technique in the ecological sciences showed that rodents have marked preferences for some seeds over others and that more seeds were removed in sagebrush compared to cheatgrass-dominated sites, although associational effects among seed mixtures were not detected. In Chapter 6 we show that the amount of seed harvested depended on both intraspecific and interspecific seed density. B. tectorum seeds had associational susceptibility (increased harvest) in the presence of native seeds. Although the reciprocal effect may occur, we did not find statistical support for it. These sets of studies are not only of basic ecological interests, but are also important for developing management strategies for restoration of these degraded lands

Short-term Response of Holcus lanatus L. (Common Velvetgrass) to Chemical and Manual Control at Yosemite National Park, USA

One of the highest priority invasive species at both Yosemite and Sequoia and Kings Canyon national parks is Holcus lanatus L. (common velvetgrass), a perennial bunchgrass that invades mid-elevation montane meadows. Despite velvetgrass being a high priority species, there is little information available on control techniques. The goal of this project was to evaluate the short-term response of a single application of common chemical and manual velvetgrass control techniques. The study was conducted at three montane sites in Yosemite National Park. Glyphosate spotspray treatments were applied at 0.5, 1.0, 1.5, and 2.0% concentrations, and compared with hand pulling to evaluate effects on cover of common velvetgrass, cover of other plant species, and community species richness. Posttreatment year 1 cover of common velvetgrass was 12.1% 6 1.6 in control plots, 6.3% 6 1.5 averaged over the four chemical treatments (all chemical treatments performed similarly), and 13.6% 6 1.7 for handpulled plots. This represents an approximately 50% reduction in common velvetgrass cover in chemically- treated plots recoded posttreatment year 1 and no statistically significant reduction in hand pulled plots compared with controls. However, there was no treatment effect in posttreatment year 2, and all herbicide application rates performed similarly. In addition, there were no significant treatment effects on nontarget species or species richness. These results suggest that for this level of infestation and habitat type, (1) one year of hand pulling is not an effective control method and (2) glyphosate provides some level of control in the short-term without impact to nontarget plant species, but the effect is temporary as a single year of glyphosate treatment is ineffective over a twoyear period

Germination and Growth of Native and Invasive Plants on Soil Associated with Biological Control of Tamarisk (Tamarix spp.)

Introductions of biocontrol beetles (tamarisk beetles) are causing dieback of exotic tamarisk in riparian zones across the western United States, yet factors that determine plant communities that follow tamarisk dieback are poorly understood. Tamarisk-dominated soils are generally higher in nutrients, organic matter, and salts than nearby soils, and these soil attributes might influence the trajectory of community change. To assess physical and chemical drivers of plant colonization after beetle-induced tamarisk dieback, we conducted separate germination and growth experiments using soil and litter collected beneath defoliated tamarisk trees. Focal species were two common native (red threeawn, sand dropseed) and two common invasive exotic plants (Russian knapweed, downy brome), planted alone and in combination. Nutrient, salinity, wood chip, and litter manipulations examined how tamarisk litter affects the growth of other species in a context of riparian zone management. Tamarisk litter, tamarisk litter leachate, and fertilization with inorganic nutrients increased growth in all species, but the effect was larger on the exotic plants. Salinity of 4 dS m 1 benefitted Russian knapweed, which also showed the largest positive responses to added nutrients. Litter and wood chips generally delayed and decreased germination; however, a thinner layer of wood chips increased growth slightly. Time to germination was lengthened by most treatments for natives, was not affected in exotic Russian knapweed, and was sometimes decreased in downy brome. Because natives showed only small positive responses to litter and fertilization and large negative responses to competition, Russian knapweed and downy brome are likely to perform better than these two native species following tamarisk dieback

Germination and Growth of Native and Invasive Plants on Soil Associated with Biological Control of Tamarisk (Tamarix spp.)

Introductions of biocontrol beetles (tamarisk beetles) are causing dieback of exotic tamarisk in riparian zones across the western United States, yet factors that determine plant communities that follow tamarisk dieback are poorly understood. Tamarisk-dominated soils are generally higher in nutrients, organic matter, and salts than nearby soils, and these soil attributes might influence the trajectory of community change. To assess physical and chemical drivers of plant colonization after beetle-induced tamarisk dieback, we conducted separate germination and growth experiments using soil and litter collected beneath defoliated tamarisk trees. Focal species were two common native (red threeawn, sand dropseed) and two common invasive exotic plants (Russian knapweed, downy brome), planted alone and in combination. Nutrient, salinity, wood chip, and litter manipulations examined how tamarisk litter affects the growth of other species in a context of riparian zone management. Tamarisk litter, tamarisk litter leachate, and fertilization with inorganic nutrients increased growth in all species, but the effect was larger on the exotic plants. Salinity of 4 dS m 1 benefitted Russian knapweed, which also showed the largest positive responses to added nutrients. Litter and wood chips generally delayed and decreased germination; however, a thinner layer of wood chips increased growth slightly. Time to germination was lengthened by most treatments for natives, was not affected in exotic Russian knapweed, and was sometimes decreased in downy brome. Because natives showed only small positive responses to litter and fertilization and large negative responses to competition, Russian knapweed and downy brome are likely to perform better than these two native species following tamarisk dieback

A variety-specific analysis of climate change effects on California winegrapes

California contains a broad geography over which climate conditions can be suitable for cultivating multiple varieties of winegrapes. However, climate change is projected to make winegrape cultivation more challenging across many of California's winegrowing regions. In order to understand the potential effects of climate change on winegrapes, this study models variety-specific phenology for six winegrape varieties and quantifies the change in phenology and viticulturally-important agroclimate metrics over 12 of California's American Viticultural Areas (AVAs) by the mid-21st century. Results show more rapid development for winegrapes with earlier budburst, flowering, veraison, and maturation across all varieties and AVAs. Cabernet Sauvignon shows the greatest change in phenology timing, while Chardonnay shows the least change. Likewise, the West Sonoma Coast AVA shows the greatest average change in phenology timing across varieties and development stages and Lodi AVA shows the least. Projected changes in agroclimatic metrics include an additional month of potentially damaging heat days (above 35 °C) in some AVAs, and decreases in frost days. These results have implications for numerous factors related to viticultural production, including water resources management and crop yield and quality, and underscore the need for California winegrape growers to improve their resilience to climate change by adopting strategies such as increasing soil health and water use efficiency and selecting cultivars suited for future climate conditions. By conducting climate effects analyses at the variety-specific and AVA scale, important information is provided to the winegrowing industry at a resolution that can support decision-making towards resilience

Vegetation response to invasive Tamarix control in southwestern U.S. rivers: a collaborative study including 416 sites

Most studies assessing vegetation response following control of invasive Tamarix trees along southwestern U.S. rivers have been small in scale (e.g., river reach), or at a regional scale but with poor spatial-temporal replication, and most have not included testing the effects of a now widely used biological control. We monitored plant composition following Tamarix control along hydrologic, soil, and climatic gradients in 244 treated and 172 reference sites across six U.S. states. This represents the largest comprehensive assessment to date on the vegetation response to the four most common Tamarix control treatments. Biocontrol by a defoliating beetle (treatment 1) reduced the abundance of Tamarix less than active removal by mechanically using hand and chain-saws (2), heavy machinery (3) or burning (4). Tamarix abundance also decreased with lower temperatures, higher precipitation, and follow-up treatments for Tamarix resprouting. Native cover generally increased over time in active Tamarix removal sites, however, the increases observed were small and was not consistently increased by active revegetation. Overall, native cover was correlated to permanent stream flow, lower grazing pressure, lower soil salinity and temperatures, and higher precipitation. Species diversity also increased where Tamarix was removed. However, Tamarix treatments, especially those generating the highest disturbance (burning and heavy machinery), also often promoted secondary invasions of exotic forbs. The abundance of hydrophytic species was much lower in treated than in reference sites, suggesting that management of southwestern U.S. rivers has focused too much on weed control, overlooking restoration of fluvial processes that provide habitat for hydrophytic and floodplain vegetation. These results can help inform future management of Tamarix-infested rivers to restore hydrogeomorphic processes, increase native biodiversity and reduce abundance of noxious species

Vegetation response to invasive Tamarix control in southwestern U.S. rivers: a collaborative study including 416 sites

Most studies assessing vegetation response following control of invasive Tamarix trees along southwestern U.S. rivers have been small in scale (e.g., river reach), or at a regional scale but with poor spatial-temporal replication, and most have not included testing the effects of a now widely used biological control. We monitored plant composition following Tamarix control along hydrologic, soil, and climatic gradients in 244 treated and 172 reference sites across six U.S. states. This represents the largest comprehensive assessment to date on the vegetation response to the four most common Tamarix control treatments. Biocontrol by a defoliating beetle (treatment 1) reduced the abundance of Tamarix less than active removal by mechanically using hand and chain-saws (2), heavy machinery (3) or burning (4). Tamarix abundance also decreased with lower temperatures, higher precipitation, and follow-up treatments for Tamarix resprouting. Native cover generally increased over time in active Tamarix removal sites, however, the increases observed were small and was not consistently increased by active revegetation. Overall, native cover was correlated to permanent stream flow, lower grazing pressure, lower soil salinity and temperatures, and higher precipitation. Species diversity also increased where Tamarix was removed. However, Tamarix treatments, especially those generating the highest disturbance (burning and heavy machinery), also often promoted secondary invasions of exotic forbs. The abundance of hydrophytic species was much lower in treated than in reference sites, suggesting that management of southwestern U.S. rivers has focused too much on weed control, overlooking restoration of fluvial processes that provide habitat for hydrophytic and floodplain vegetation. These results can help inform future management of Tamarix-infested rivers to restore hydrogeomorphic processes, increase native biodiversity and reduce abundance of noxious species

Fire Effects on Seed banks and Vegetation in the Eastern Mojave Desert: Implications for Post-fire Management

Area burned has increased during the past few decades in the Mojave Desert due in part to increased dominance of highly flammable invasive non-native annual grasses. Management responses such as post-fire seedings have been implemented during the first 3 post-fire years to suppress the growth of the invasive annual grasses, promote recovery of native species, and facilitate the restoration of plant species diversity and abundance. Although there is a fair amount of information available on the effects of fire on plant diversity, density, and cover, there is very little information available regarding effects on soil seed banks to help guide the development of management prescriptions. This project was designed to evaluate the short-term effects of fire on soil seed bank diversity and density, and vegetation diversity and cover, following the Hackberry Fire Complex of summer 2005 in the eastern Mojave Desert. A secondary objective was to evaluate the correlations between measures of burn severity and seed bank and vegetation abundance to evaluate the utility of burn severity metrics in evaluating fire effects. The study region encompasses upper elevation blackbrush and lower elevation sagebrush ecotones of the Mojave Desert. Fire reduced soil seed bank diversity during the first two post-fire fall seasons, although evenness was slightly higher in burned areas during all three post-fire years, possibly due to loss of annual plant microhabitats previously created by shrub canopies. Fire also reduced seed bank density by 81%, but only during the first post-fire spring. Seed bank reductions were greater for non-natives, Bromus rubens in particular, than for natives. Aboveground vegetation diversity was reduced in burned areas during all three post-fire years due to declines in species richness of perennials, as native species richness was not affected. Fire reduced cover of perennials and increased cover of annuals during all three years, but fire did not affect cover of non-native annual grasses (Bromus rubens, Bromus tectorum, and Schismus spp.). Virtually all of the seed bank and annual plant vegetation metrics evaluated in this study returned to unburned condition by the second or third post-fire years, and varied more among years than due to burning. In addition, the effects of fire on seed bank density during the first year were over an order of magnitude higher than what typically seeding prescriptions would have replaced if they had been implemented. These results call into question the need to seed annual plant species after fires in the Mojave Desert. In contrast, persistent reductions in cover of perennials means that their seed sources were limited and post-fire seedings may have help to overcome this establishment limitation for those species, although further studies are needed to evaluate this dynamic. Both dNBR and CBI burn severity metrics were negatively correlated with total vegetation cover, annual cover in particular, during the first post-fire spring, which appeared to carry over to the seed bank during following fall which was also negatively correlated with dNBR. It therefore appears that dNBR may be a potentially useful tool in estimating reduced cover of annuals during the first post-fire spring, and reduced seed bank density during the following fall

Mapping hotspots of potential ecosystem fragility using commonly available spatial data

International audienc

California Wildfire Resilience Core Metrics Rating Process and Results

The California Wildfire & Forest Resilience Task Force (Task Force) has developed regionally-adapted resources to lessen wildfire risk to communities and enhance broader statewide ecosystem resilience. This includes a large set of metrics intended to support a wide range of organizations in prioritizing, planning and/or implementing management actions. The Science Advisory Panel to the Task Force (SAP) was asked to provide expert advice to inform the selection of a subset of “core” metrics for reporting outcomes and progress towards resilience goals. We used survey tools to collect and synthesize the scientific expertise of the SAP as well as other experts regarding existing “Regional Resource Kit” (RRK) metrics as well as potential suggested metrics. This report summarizes the survey process and results. We used two rounds of surveys to collect expert opinion on metrics. Round 1 asked respondents to 1) identify criteria for core metrics, 2) identify metrics from the Regional Resource Kits (RRKs) that were believed to be inadequate based on those criteria, and 3) recommend additional metrics not included in the original set. Round 2 asked respondents to rate the resulting set of 115 metrics. The Round 1 results indicated that selecting a useful set of core metrics depended on their intended application (e.g., planning vs.reporting), the intended audience (e.g., policy makers, scientists, and/or the public), and resilience outcomes (e.g., immediate wildfire risk reduction versus long-term ecological health). In Round 2 we asked respondents to rate each metric on how well it measured each of three broad, overlapping resilience goals identified by the Task Force: 1) reducing wildfire risk, 2) improving ecological integrity, and/or 3) supporting social and/or cultural wellbeing. The Task Force specified the purpose for the metrics: reporting progress to policymakers and the public. Therefore, respondents also evaluated three attributes for each metric: 1) how realistic it was to remeasure (i.e., feasibility), 2) how easy it was to explain to wide audiences (i.e., understandability), and 3) how well it represented the process of interest (i.e., sensitivity). In addition, respondents identified relevant region(s) of California (Sierra Nevada, Southern California, Central Coast, and Northern California) for each metric. For the 115 metrics collectively considered in Round 2 (81 from the RRKs and 34 novel metrics), 66 received an average rating of greater than 4 out of 5 on one or more of the three resilience goals (reduce fire risk, improve ecological resilience, support social/cultural wellbeing). Of these, 13 metrics were rated above 4 out of 5 for two of the three goals, and only “probability of high-severity fire” was rated that highly for all three. Metrics on topics relating to vegetation structure and composition as well as fire behavior and history were most abundant in the RRKs and in our list of highly rated metrics. Topics relating to air quality, water supply, economics, community readiness, environmental justice, and community wellbeing were less abundant in the RRKs and not as highly rated in our surveys; these topic areas could benefit from further expert feedback and development. Top-rated metrics already present in the RRKs included: probability of high severity fire, damage potential in the Wildland-Urban Interface (WUI), standing dead and ladder fuels, vegetative stress during extreme drought, tree mortality, and shrub resilience. Metrics that are not yet in the RRKs but do exist elsewhere include Cal EnviroScreen scores and areas of low potential shrub regeneration. Highly rated novel metrics suggested by the survey respondents include (among others): health outcomes related to air quality/smoke and insurance availability/price. Some considerations for proceeding with selection of core metrics arose through this process. First, metrics selected (and targeted desirable ranges for these metrics) might be ecosystem specific. Second, the tradeoff between the logistical aspects of the metrics (feasibility of remeasurement, understandability) with their scientific accuracy and value needs to be evaluated with the target audience in mind. Third, many metrics can address resilience across multiple topic areas and therefore framing this overlap carefully is important when determining how to track progress towards resilience goals