Abundance of invasive plants is often attributed to greater competitiveness of these species comp... more Abundance of invasive plants is often attributed to greater competitiveness of these species compared with natives. In a combination of field and glasshouse studies, I examined whether the invasive annual grass Bromus madritensis ssp. rubens is a better competitor than two native winter annuals, Vulpia octoflora and Descurainia pinnata. I examined how timing of Bromus establishment, amount of precipitation, and elevated atmospheric CO2 concentrations contribute to its competitiveness in an intact Mojave Desert shrubland and evaluated Bromus’ impact on growth and reproduction for a variety of perennial life forms. In comparison with ecologically similar native winter annuals, Bromus establishes in diverse habitats of the Mojave Desert because it is less sensitive to changes in nitrogen (N) availability or plant density than native species, and it can rapidly utilize soil water and N for greater biomass and N content. As Bromus continues to integrate into the landscape in the Mojave D...
Background/Question/Methods The increase of large-scale disturbances to vegetation communities ha... more Background/Question/Methods The increase of large-scale disturbances to vegetation communities has ignited interest in rehabilitation efforts. One popular strategy is the application of seed mixes, thereby reestablishing plants more quickly than waiting for seeds to disperse naturally into large disturbed areas. This approach has a mixed record of success in desert regions, largely due to highly unpredictable precipitation patterns. Seeds that were broadcast over large areas after wildfires burned Mojave Desert shrublands during 2005 and 2006 had limited plant establishment in areas that received the lowest rainfall. Under the highly variable environmental conditions typical of deserts, the planting of nursery-grown stock with supplemental moisture may be an alternative, but this strategy has also had mixed success. We planted over 1,300 Nevada ephedra (Ephedra nevadensis) and over 4,500 blackbrush (Coleogyne ramosissima) at five burned sites in the northeast Mojave Desert which var...
Background/Question/Methods Recurring wildfires fueled by non-native annual grasses deplete soil ... more Background/Question/Methods Recurring wildfires fueled by non-native annual grasses deplete soil seed reserves of native desert plants and diminish opportunities for native plants to re-establish. Control of non-native annual brome grasses and forbs and replenishment of native seeds is vital to recovering severely degraded desert shrublands, but post-fire treatments often focus solely on restoring native plants and overlook reducing dominant non-native species. In addition, the success and failure of post-fire treatments are rarely evaluated as a function of effective precipitation. Seeding treatments were implemented in 2006 – helicopter seeding, seeding with incorporation of the seed mixture into the soil, and no seeding treatment – across eight northeast Mojave Desert sites that burned during 2005 and 2006. Within each treatment, we established replicated 0.01 ha plots with pre-emergent herbicide or no herbicide in fall 2008 to evaluate reduction of non-native annuals and re-vege...
Background/Question/Methods In arid environments, demographic changes for long-lived perennials a... more Background/Question/Methods In arid environments, demographic changes for long-lived perennials are difficult to measure because favorable conditions for regeneration occur infrequently. Seedling emergence and survival for many desert plants are sensitive to variability in soil moisture and temperature as well as predation. Understanding the dynamics surrounding plant establishment is important for land managers to effectively mitigate the impacts of disturbances and promote re-vegetation, especially for disturbances such as desert wildfires that are affecting large landscapes dominated by Joshua trees in the Mojave Desert. We investigated the influence of microclimate, season, and residence time on seedling emergence and survival, and seed persistence of Joshua trees after simulated secondary dispersal. We placed seeds in shallow caches and manipulated granivore access (caged versus uncaged), cache placement (beneath shrub canopy versus shrub interspace), and season of placement (s...
Local adaptation is widespread across plant taxa and may influence the responses of species to cl... more Local adaptation is widespread across plant taxa and may influence the responses of species to climate change and the effectiveness of their use in ecological restoration. Natural populations are characterized by fine-scale physiological or phenological adaptations that drive intraspecific variability in responses to altered environmental conditions, including introductions to novel restoration sites. Consequently, restoration practitioners should account for adaptive genetic variability in germplasm from different sites, which may influence seedling establishment and longer-term fitness. Marker-based landscape genomic approaches aim to identify the environmental drivers of adaptive genetic variability and map spatial patterns of gene / environment associations — information that can both guide habitat restoration and improve predictions of species’ responses to climate change. There is a clear need to understand the landscape genomics of Mojave Desert plant taxa because both novel ...
Abundance of invasive plants is often attributed to greater competitiveness of these species comp... more Abundance of invasive plants is often attributed to greater competitiveness of these species compared with natives. In a combination of field and glasshouse studies, I examined whether the invasive annual grass Bromus madritensis ssp. rubens is a better competitor than two native winter annuals, Vulpia octoflora and Descurainia pinnata. I examined how timing of Bromus establishment, amount of precipitation, and elevated atmospheric CO2 concentrations contribute to its competitiveness in an intact Mojave Desert shrubland and evaluated Bromus’ impact on growth and reproduction for a variety of perennial life forms. In comparison with ecologically similar native winter annuals, Bromus establishes in diverse habitats of the Mojave Desert because it is less sensitive to changes in nitrogen (N) availability or plant density than native species, and it can rapidly utilize soil water and N for greater biomass and N content. As Bromus continues to integrate into the landscape in the Mojave D...
Background/Question/Methods The increase of large-scale disturbances to vegetation communities ha... more Background/Question/Methods The increase of large-scale disturbances to vegetation communities has ignited interest in rehabilitation efforts. One popular strategy is the application of seed mixes, thereby reestablishing plants more quickly than waiting for seeds to disperse naturally into large disturbed areas. This approach has a mixed record of success in desert regions, largely due to highly unpredictable precipitation patterns. Seeds that were broadcast over large areas after wildfires burned Mojave Desert shrublands during 2005 and 2006 had limited plant establishment in areas that received the lowest rainfall. Under the highly variable environmental conditions typical of deserts, the planting of nursery-grown stock with supplemental moisture may be an alternative, but this strategy has also had mixed success. We planted over 1,300 Nevada ephedra (Ephedra nevadensis) and over 4,500 blackbrush (Coleogyne ramosissima) at five burned sites in the northeast Mojave Desert which var...
Background/Question/Methods Recurring wildfires fueled by non-native annual grasses deplete soil ... more Background/Question/Methods Recurring wildfires fueled by non-native annual grasses deplete soil seed reserves of native desert plants and diminish opportunities for native plants to re-establish. Control of non-native annual brome grasses and forbs and replenishment of native seeds is vital to recovering severely degraded desert shrublands, but post-fire treatments often focus solely on restoring native plants and overlook reducing dominant non-native species. In addition, the success and failure of post-fire treatments are rarely evaluated as a function of effective precipitation. Seeding treatments were implemented in 2006 – helicopter seeding, seeding with incorporation of the seed mixture into the soil, and no seeding treatment – across eight northeast Mojave Desert sites that burned during 2005 and 2006. Within each treatment, we established replicated 0.01 ha plots with pre-emergent herbicide or no herbicide in fall 2008 to evaluate reduction of non-native annuals and re-vege...
Background/Question/Methods In arid environments, demographic changes for long-lived perennials a... more Background/Question/Methods In arid environments, demographic changes for long-lived perennials are difficult to measure because favorable conditions for regeneration occur infrequently. Seedling emergence and survival for many desert plants are sensitive to variability in soil moisture and temperature as well as predation. Understanding the dynamics surrounding plant establishment is important for land managers to effectively mitigate the impacts of disturbances and promote re-vegetation, especially for disturbances such as desert wildfires that are affecting large landscapes dominated by Joshua trees in the Mojave Desert. We investigated the influence of microclimate, season, and residence time on seedling emergence and survival, and seed persistence of Joshua trees after simulated secondary dispersal. We placed seeds in shallow caches and manipulated granivore access (caged versus uncaged), cache placement (beneath shrub canopy versus shrub interspace), and season of placement (s...
Local adaptation is widespread across plant taxa and may influence the responses of species to cl... more Local adaptation is widespread across plant taxa and may influence the responses of species to climate change and the effectiveness of their use in ecological restoration. Natural populations are characterized by fine-scale physiological or phenological adaptations that drive intraspecific variability in responses to altered environmental conditions, including introductions to novel restoration sites. Consequently, restoration practitioners should account for adaptive genetic variability in germplasm from different sites, which may influence seedling establishment and longer-term fitness. Marker-based landscape genomic approaches aim to identify the environmental drivers of adaptive genetic variability and map spatial patterns of gene / environment associations — information that can both guide habitat restoration and improve predictions of species’ responses to climate change. There is a clear need to understand the landscape genomics of Mojave Desert plant taxa because both novel ...
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