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

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

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

Effects of Rodent Species, Seed Species, and Predator Cues on Seed Fate

Seed selection, removal and subsequent management by granivorous animals is thought to be a complex interaction of factors including qualities of the seeds themselves (e.g., seed size, nutritional quality) and features of the local habitat (e.g. perceived predator risk). At the same time, differential seed selection and dispersal is thought to have profound effects on seed fate and potentially vegetation dynamics. In a feeding arena, we tested whether rodent species, seed species, and indirect and direct predation cues influence seed selection and handling behaviors (e.g., scatter hoarding versus larder hoarding) of two heteromyid rodents, Ord’s kangaroo rat (Dipodomys ordii) and the Great Basin pocket mouse (Perognathus parvus). The indirect cue was shrub cover, a feature of the environment. Direct cues, presented individually, were (1) control, (2) coyote (Canis latrans) vocalization, (3) coyote scent, (4) red fox (Vulpes vulpes) scent, or (5) short-eared owl (Asio flammeus) vocalization. We offered seeds of three sizes: two native grasses, Indian ricegrass (Achnatherum hymenoides) and bluebunch wheatgrass (Pseudoroegneria spicata), and the non-native cereal rye (Secale cereale), each in separate trays. Kangaroo rats preferentially harvested Indian ricegrass while pocket mice predominately harvested Indian ricegrass and cereal rye. Pocket mice were more likely to scatter hoard preferred seeds, whereas kangaroo rats mostly consumed and/or larder hoarded preferred seeds. No predator cue significantly affected seed preferences. However, both species altered seed handling behavior in response to direct predation cues by leaving more seeds available in the seed pool, though they responded to different predator cues. If these results translate to natural dynamics on the landscape, the two rodents are expected to have different impacts on seed survival and plant recruitment via their different seed selection and seed handling behaviors

Impacts of large-scale teleconnection indices on chill accumulation for specialty crops in California.

Although the impacts of teleconnection indices on climate metrics such as precipitation and temperature in California have been widely studied, less attention has been given to the impact on integrated climate indices such as chill accumulation. This study investigates the linkages between large-scale teleconnections and winter chill accumulation for specialty crops in California, which may enable more effective and dynamic adaptation to in-season climate variability. Three large-scale teleconnection indices were selected: Oceanic Nino Index (ONI), Pacific-North American teleconnection pattern (PNA), and Pacific Decadal Oscillation (PDO) index to assess their effects on chill accumulation. The Chill Hours Model and Dynamic Model are adopted to calculate chill accumulation in Chill Hours (CH) and Chill Portions (CP) from November to January. Three major crop-producing regions, including the Central Coast, Sacramento Valley, and San Joaquin Valley, are used as the focused regions. Our results suggest CP generally has a stronger response to teleconnection patterns than CH in California. The correlations between chill accumulation and teleconnections are generally weaker during the summer than other seasons, and significant correlation can be observed 2-10 months before the start of the chill accumulation period. Among the three teleconnection indices, ONI is most weakly correlated to chill accumulation in focused regions, while PDO shows the strongest positive correlation and explains up to 39% variability of CP. PNA presents the most widespread negative correlation with chill accumulation. When aggregated to different teleconnection modes, +3.6 above-average CP is expected during ONI positive mode; +2.3 above-average CP is expected during PDO positive mode, while +2.1 above-average CP is expected during PNA negative mode. This study provides insights on early-season chill prediction and feasible management and adaptation strategies, and the methodology presented here can be used to develop decision support tools of risk control for agricultural producers and policymakers

California wine grape growers need support to manage risks from wildfire and smoke

California has experienced an increase in the size, frequency, and severity of wildfires in recent years, with wide-ranging impacts to agriculture. The 2020 wildfire season was particularly catastrophic, causing billions of dollars in damage to the state’s world-renowned wine industry. Wine grape growers and wine producers statewide recently took a survey to help us better understand the wildfire informational resources available to producers, as well as the role wildfire risk plays in operational management decisions. The survey results show that the negative impacts of wildfires on wine production may be the result of wildfire smoke more than of the actual wildfires. We also show that managers do not always make operational changes, even when they perceive increased wildfire risk. Despite diverse sources of wildfire-related information and operational guidance, there is not enough information to effectively manage fire risk

California wine grape growers need support to manage risks from wildfire and smoke

California has experienced an increase in the size and severity of wildfires in recent years, with wide-ranging impacts to agriculture. The 2020 wildfire season was particularly catastrophic, causing billions of dollars in damage to the state's world-renowned wine industry. Wine grape growers and wine producers statewide were recently surveyed to better understand the wildfire informational resources available to producers, as well as the role wildfire risk plays in operational management decisions. The survey results show that the negative impacts of wildfires on wine production may be the result of wildfire smoke more than of the actual wildfires. We also show that managers do not always make operational changes, even when they perceive increased wildfire risk. Despite diverse sources of wildfire-related information and operational guidance, there is not enough information to effectively manage fire risk

Technical Assistance Providers Identify Climate Change Adaptation Practices and Barriers to Adoption among California Agricultural Producers

Climate change will challenge California agriculture, requiring producers (i.e., farmers and ranchers) to adopt climate-adaptive management practices to sustain production. Agricultural technical assistance providers (TAPs) play a significant role in supporting producers’ efforts to adopt climate-smart management practices. It is therefore important to understand current TAP perceptions of climate change, TAP recommendations for climate adaptation, and the barriers to adopting climate-smart practices. To understand these issues, we held four focus group discussions with small groups of TAPs from across the state and evaluated transcripts from the discussions to identify common themes and concepts. The TAPs that participated in the focus groups understood climate change and its impacts on California agriculture, with climate extremes and water-related issues being the most frequently cited climate-related challenges. Focus group discussions and subsequent evaluation revealed that while TAPs recommend science-backed practices for adapting California agriculture to climate change, producers may not be accepting of some recommendations. Critically, the TAP focus groups cited insufficient monetary support—both for themselves and for producers—and insufficient information and messaging around climate-adaptive practices as key barriers to practice adoption. This improved understanding of the intersection of TAPs’ work on climate change and climate adaptation in California agriculture is useful for the development of information and resources that can bridge these identified barriers