Completion Form

2022

We used both remote sensing and on the ground evaluation to address the primary objectives of the project. Drone imagery and GIS tools were used to map the spatial pattern of brome abundance in the high production year (2020) at White Dome based on residual litter cover a year later in 2021, a year of very low annual brome production. We also obtained drone imagery to examine annual brome abundance at Beehive Dome in 2021. We then used four years of drone monitoring imagery (nine 0.6 ha permanent plots at Beehive Dome, and seven at White Dome) and on the ground reproductive output monitoring (2019-2022) to evaluate and compare patterns of recruitment, survival, growth, and reproductive output at the two study populations. We used both drone imagery and on the ground studies to examine whether the increased levels of annual brome invasion at White Dome in 2020 were related to increased levels of rodent herbivory, insect foliar and capsule herbivory, and fungal pathogen-caused disease in comparison to Beehive Dome, where brome abundance had remained low. Lastly, we carried out a pilot GIS analysis of LANDSAT imagery using the greenness differencing methodology for two contrasting brome production years at White Dome and the surrounding area to determine the feasibility of tracking annual brome abundance across years with imagery from the LANDSAT archive with 30 m pixel resolution.

Our first project objectives were to use drone imagery to map annual brome patterns of invasion at White Dome and Beehive Dome in 2020, a high-precipitation year that resulted in a large increase in brome cover at White Dome, and to use these maps along with surface cover habitat classification and poppy census maps to determine the amount of overlap between invaded habitat and core poppy habitat. At Beehive Dome there was too little litter cover to use this method, which was not surprising based on field observations of low levels of brome invasion there except along washes. Mapped annual brome cover over the 209 ha flight area on the east side of the White Dome Preserve based on litter from the 2020 high-production year was 6.0% overall. The brome cover was not uniformly distributed. It was much higher and more continuous in areas closer to the northern, northeastern, and southern preserve boundaries, areas with large infestations in adjacent areas, showing the potential importance of propagule pressure. The core of the preserve area was much less invaded, and the area inside the fenced research area in the southwest corner had annual brome cover of only 2.3%, almost three times lower than the flight area considered overall. 
When annual brome distribution was examined relative to the surface cover classification based on surface soil color, brome cover values were three times higher on the dark crust and light crust surface cover classes than on the white cover class, whereas dwarf bear poppy densities from the 2018 drone census were five times higher on the white cover class than on the dark or light crust cover classes. This shows that the white knoll top habitat that supports most of the poppies is much less invaded than habitats where poppy densities are low, both locally and at a landscape scale. A total of 87% of the poppies in the 2021 flight area were found within the fenced research area in the 2018 census.
 In spite of this apparent habitat non-overlap and the lower overall brome cover within the research area, a spatial analysis of these two distribution data sets determined that 85% of the poppy points were <10m from a brome point, even in the research area. The likely explanation for this is that annual bromes can colonize the areas beneath shrub canopies, even on knoll tops in the white surface cover class, creating a polka-dot-like spread of very small invasion foci within poppy-occupied habitat. The poppies are rarely if ever found under shrub canopies, resulting in <1% intersection between brome and poppy points, and <5% of poppy points were within 1 m of a brome point in the research area where the majority of the poppies occurred. Values were similar for the flight area as a whole. Another factor in the relatively close proximity of brome points to poppy points in spite of low overall brome cover is the fact that the surface cover classes can also occur in close proximity on the landscape scale, placing more invaded habitat immediately adjacent to uninvaded habitat that supports poppies. 
We used the four-year dwarf bear poppy drone monitoring data set to determine whether brome invasion had a deleterious effect on population dynamics at White Dome relative to Beehive Dome, which was minimally invaded. The population of adult poppies that was present on the 0.6 ha monitoring plots was similar (923 plants at White Dome and 931 plants at Beehive Dome, respectively) when monitoring plots were established in 2019. These were either reproductively mature two-year-old plants from the large 2017 recruitment event or adults still present from previous recruitment events. The plants are not long-lived, so that survival curves that showed steep linear decline at both populations from 2019 to 2022 were not surprising. These survival curves were similar for the two populations over this period, and survival was actually higher in 2022 at White Dome (13% of original plants) than at Beehive Dome (1.2%) These results suggest that annual brome invasion has not impacted adult dwarf bear poppy survival. In addition, adult poppy mortality rates were not related to inter-annual variation in precipitation patterns, even though there was a dramatic difference between wet and dry years during this period.  Patterns of year-to-year change in plant diameter were also very similar at the two sites.
Seed production in dwarf bear poppy is generally high, but reproductive output monitoring at the two populations over the four-year monitoring period revealed some between-population differences. In 2019 and 2020, fruit set was uniformly high at both locations, above 95%. In 2021, both populations had reduced fruit set, but the effect was much more pronounced at White Dome (53% vs. 92%). In 2022, fruit set was <50% at both populations. These lower fruit-set years coincided with dry winters that may have affected pollinator abundance or plant resource status. Filled seed number per capsule was higher at Beehive Dome than at White Dome in all but the final year of monitoring. This resulted in higher filled seed number per flower (fruits per flower x seeds per fruit) at Beehive Dome in the first three years. In spite of high fruit abortion in 2022, the White Dome plants were able to produce as many seeds per flower as Beehive Dome plants due to exceptionally high seed fill that year. These results indicate that the White Dome plants overall are likely to have lower seed production, but there is no evidence that the year of high brome abundance resulted in reduced reproductive output there, as that was the best year of the four for White Dome in terms of seed production per flower. 
We evaluated rodent activity-related mortality using drone imagery across four years at the two sites. The rodents responsible were surmised to be antelope ground squirrels (Ammospermophilus leucurus), diurnal herbivorous rodents commonly observed at both sites. We evaluated a 1 m circle centered on each point where a poppy was newly missing each year in all of the monitoring plots at each site. We scored each circle as 'no new disturbance', 'rodent hole' when a hole was found instead of the poppy that was present the previous year, or as 'rodent digging' when fresh mounds of soil were observed. Over the three-year period, there was somewhat higher rodent-associated mortality at Beehive Dome than at White Dome, but the major difference between the sites was in the timing of rodent-associated mortality, which was much higher at White Dome in 2020 and much higher at Beehive Dome in 2021. Neither site had significant rodent-associated mortality in 2022.  The reason for this site difference in the year of peak rodent activity is not known, but there is no strong evidence that annual brome cover in 2020 was implicated in rodent-associated mortality there, especially as even higher mortality was observed the following year at Beehive Dome in the absence of significant annual brome cover.
We also evaluated herbivory at the scale of foliar and capsule damage for plants included in the reproductive output study. Most of this damage was due to a variety of insects. Levels of herbivory were similar at the two sites but trended higher at Beehive Dome. The most striking pattern in the data set was very low levels of herbivory in the high rainfall years the first two years of the study, but much higher levels during the dry years, especially the final year of the study. There was no indication that associated high brome cover increased small-scale herbivory on poppies, which rarely caused major damage to the plants. 
We attempted to carry out evaluation of disease levels on poppy plants in the reproductive output study each year, but the accuracy was hampered by the timing of data collection, which may not have coincided with the time of maximum disease development. We determined through genetic ITS fingerprinting using cultures grown from infected tissue that the major pathogen causing both foliar and inflorescence damage was a species of the fungal genus Alternaria. Disease symptoms were present across the first three years at White Dome and present at levels as high as or higher than those observed at Beehive Dome each of those years. Beehive Dome only had significant disease incidence in 2020, and both populations exhibited a lack of disease symptoms in 2022. These results are hard to interpret, but there is no compelling case for an association with annual brome invasion at White Dome, as in the 2020 high brome production year, both populations had similarly high levels of disease (ca. 40% of plants with symptoms). There was little direct evidence that disease was a cause of mortality, but this could be because the timing of data collection did not permit us to fully make this connection. 
In summary, we did not obtain any evidence that the brome invasion at White Dome at its current level has substantially increased any indirect threats to dwarf bear poppy persistence. The population and individual level data from two populations with dramatically different levels of brome invasion showed largely similar patterns across four years of monitoring. However, annual brome invasion may still pose a threat in and of itself, in spite of the habitat segregation between annual bromes and poppies evident in the analysis. The presence of annual bromes under shrub clumps throughout the preserve has placed an annual brome seed source within occupied poppy habitat. This is a scenario that has unfolded in other places that initially seemed to have relatively low invasion potential. Given the right sequence of years, it could be possible for the annual bromes modify the surface at the local invasion edges sufficiently with their own litter to enable slow but inexorable spread into the interspaces between the shrubs. Once the fine fuel layer of brome standing litter becomes continuous, the risk of fire increases exponentially. This means that dealing with the annual brome problem before it escalates to this level should be a high priority in dwarf bear poppy habitat throughout its range.

Please see the attached report document for a more complete description of our studies.

Based on this study as well as an earlier long-term monitoring study at a different population, the basic population dynamic pattern for dwarf bear poppy could be described as a 'boom and bust' cycle, with high recruitment success during favorable periods, that is, years with high winter-spring precipitation, followed by high seed production for a few years as well as steady mortality rates regardless of weather patterns. If the period between recruitment years is longer than the life span of most adult plants, densities can fall to very low levels. However, the presence of a large persistent seed bank enables population recovery in response to subsequent favorable years. This means that habitat once occupied is still potentially occupied and is likely to support adult poppies in the future. The causes of mortality vary with environmental conditions, but the overall pattern remains the same. 
	Direct anthropogenic disturbance can disrupt this pattern, making protection from disturbance the key component in management of existing populations regardless of their current status in terms of density, as is the recommendation of the USFWS and also the current management practice. The apparently recent spread and encroachment of annual bromes into some gypsum badlands habitats that support dwarf bear poppies adds another layer of complexity to management. We propose examining these invasion patterns in more detail both historically from LANDSAT imagery and through drone-based mapping in years with more living brome cover that would permit use of greenness differencing or multispectral mapping methods. This would include evaluation of potential source populations that may be driving invasion into poppy habitat through increased propagule pressure. 
We also propose a continuation of our pilot studies on the feasibility of safely using pre-emergent herbicides to control annual bromes in the gypsum badlands habitat, that is, without any negative effects on dwarf bear poppy. We believe that the best approach to annual brome control would be to accurately map the infestations using drone technology, then use precision herbicide application with a spray drone that can apply the chemical to small, well-defined areas that are programmed into its flight plan. This technology is already available at relatively low cost for agricultural use. This would minimize surface disturbance, cost, and labor associated with on the ground herbicide application and would permit a level of control that would be impossible with traditional aerial herbicide application. We look forward to working with land managers across the multiple land ownerships that support dwarf bear poppy to explore this option.

Susan Meyer

09/07/2022 11:57:01