Analysis of Litterbag Cover Across Drylands

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Description
Arid and semiarid ecosystems (known as drylands) cover 45% of global land area and are predicted to expand to encompass half of the world’s land area by the end of the century. Litter decomposition plays a large role in nutrient…

Arid and semiarid ecosystems (known as drylands) cover 45% of global land area and are predicted to expand to encompass half of the world’s land area by the end of the century. Litter decomposition plays a large role in nutrient and carbon cycling in dryland ecosystems, yet it remains poorly understood. Models that accurately predict decomposition in mesic ecosystems fail to accurately describe decomposition in drylands due to differing drivers of decomposition but also because litter in drylands accumulates around litter retention elements (LREs). LREs can be any object or surface that inhibits the movement vectors (e.g., wind) that push litter across drylands, creating a “pool” of litter around the LRE. Litter pooling increases the amount of mixing between litter and soil, creating a microclimate more conducive to microbial decomposition. Due to the increase in microbial decomposition, the decomposition rate for litter around LREs can be markedly different than that of litter not in LREs. To further understand how much litter accumulates in LREs, I studied the differences in litter accumulation between LREs and open areas in five drylands across the Southwestern United States. To do this, I visually analyzed photos of 424 litterbags to determine the cover percentages of four different types of organic litter (grass, broadleaf, reproductive, woody) and rock litter. Visual analysis of litterbags consisted of manually delineating the percent coverage of each of these litter categories. Litterbags had been placed in both open intercanopy areas as well as woody sub-canopy areas in which the plant canopy acted as the LRE. Additionally, 45 of these litterbags were randomly selected for analysis in the computer program FIJI (FIJI is Just ImageJ) to assess the litter area find the percent difference between visual and digital analysis. Areas underneath woody sub-canopies accumulated far more organic matter litter over time than open areas between canopies did but displayed a similar amount of rock litterbag cover. Shrub microsites also displayed far more varied litterbag cover percentages than open microsites. Data also suggested that litter does not always accumulate underneath shrubs or open intercanopy areas and may dissipate as time progresses. These results support the idea that litter accumulation varies throughout drylands, and that soil and litter mix frequently in LREs such as under woody plant canopies. The percent difference between FIJI analysis and visual analysis was generally negative, reflecting that visual estimation of litterbag cover was typically smaller than digital estimates. Cumulatively, litter was shown to accumulate much more around LREs and even move from them – supporting the idea that litter decomposition models need to account for litter movement in drylands to be accurate.
Date Created
2022-05
Agent

Studying Litter Decomposition in Deserts Across the Western United States

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Description

Drylands cover almost half of the land surface on Earth, yet there is still little understood of the processes in these ecosystems. This project studied the impact of macroclimate (precipitation and temperature in large regions) in comparison to microclimate (the…

Drylands cover almost half of the land surface on Earth, yet there is still little understood of the processes in these ecosystems. This project studied the impact of macroclimate (precipitation and temperature in large regions) in comparison to microclimate (the climate under canopy versus in the open) to learn more about the drivers of litter decomposition in drylands.

Date Created
2021-12
Agent

What Causes a Locust Swarm: A Hierarchical Patch Dynamics Approach

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Description
Ecological phenomena act on various spatial and temporal scales. To understand what causes animal populations to build and decline depends heavily on abiotic and biotic conditions which vary spatiotemporally throughout the biosphere. One excel- lent example of animal populations dynamics…

Ecological phenomena act on various spatial and temporal scales. To understand what causes animal populations to build and decline depends heavily on abiotic and biotic conditions which vary spatiotemporally throughout the biosphere. One excel- lent example of animal populations dynamics is with locusts. Locusts are a subset of grasshoppers that undergo periodical upsurges called swarms. Locust swarms have plagued human history by posing significant threats to global food security. For example, the 2003-2005 desert locust (Schistocerca gregaria) swarm destroyed 80%-100% of crops in the impacted areas and cost over US $500 million in mitigation as estimated by the Food and Agriculture Organization of the United Nations. An integrative multi-scale approach must be taken to effectively predict and manage locust swarms. For my dissertation, I looked at the ecological causes of locust swarms on multiple scales using both the Australian plague locust (Chortoicetes terminifera) and desert locust as focal species. At the microhabitat scale, I demonstrated how shifts in the nutritional landscape can influence locust gregarization. At the field level, I show that locust populations avoid woody vegetation likely due to the interactive effect of plant nutrients, temperature, and predators. At the landscape level, I show that adaptations to available nutrient variation depends on life history strategies, such as migratory capabilities. A strong metapopulation structure may aid in the persistence of locust species at larger spatial scales. Lastly, at the continental scale I show the relationship between preceding vegetation and locust outbreaks vary considerably between regions and seasons. However, regardless of this variation, the spatiotemporal structure of geographic zone > bioregion > season holds constant in two locust species. Understanding the biologically relevant spatial and temporal scales from individual gregarization (e.g. micro-habitat) to massive swarms (e.g. landscape to continental) is important to accurately predicting where and when outbreaks will happen. Overall, my research highlights that understanding animal population dynamics requires a multi-scale and trans-disciplinary approach. Into the future, integrating locust re- search from organismal to landscape levels can aid in forecasting where and when locust outbreaks occur.
Date Created
2021
Agent

Image Recognition Software Reveals Potential for Detection of Hypolith Colonization in the Namib Desert

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Description

Drylands, though one of the largest biomes, are also one of the most understudied biomes on the planet. This leaves scientists with limited understanding of unique life forms that have adapted to live in these arid environments. One such life…

Drylands, though one of the largest biomes, are also one of the most understudied biomes on the planet. This leaves scientists with limited understanding of unique life forms that have adapted to live in these arid environments. One such life form is the hypolithic microbial community; these are autotrophic cyanobacteria colonies that can be found on the underside of translucent rocks in deserts. With the light that filters through the rock above them, the microbes can photosynthesize and fix carbon from the atmosphere into the soil. In this study I looked at hypolith-like rock distribution in the Namib Desert by using image recognition software. I trained a Mask R-CNN network to detect quartz rock in images from the Gobabeb site. When the method was analyzed using the entire data set, the distribution of rock sizes between the manual annotations and the network predictions was not similar. When evaluating rock sizes smaller than 0.56 cm2 the method showed statistical significance in support of being a promising data collection method. With more training and corrective effort on the network, this method shows promise to be an accurate and novel way to collect data efficiently in dryland research.

Date Created
2021-05
Agent

Effects of Net Illumination on Fish Assemblages in Baja California Sur, Mexico

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Description

Globally, the incidental capture of non-target species in fisheries (bycatch) has been linked to declines of ecologically, economically, and culturally important marine species. Gillnet fisheries have especially high bycatch due to their non-selective nature, necessitating the development of new bycatch…

Globally, the incidental capture of non-target species in fisheries (bycatch) has been linked to declines of ecologically, economically, and culturally important marine species. Gillnet fisheries have especially high bycatch due to their non-selective nature, necessitating the development of new bycatch reduction technologies (BRTs). Net illumination is an emerging BRT that has shown promise in reducing bycatch of marine megafauna, including sea turtles, cetaceans, and seabirds. However, little research has been conducted to understand the effects of net illumination on fish assemblages, including bony fish and elasmobranchs (i.e. sharks, rays, and skates). Here, I assessed a 7-year dataset of paired net illumination trials using four different types of light (green LEDs, green chemical glowsticks, ultraviolet (UV) lights, and orange lights) to examine the effects of net illumination on fish catch and bycatch in a gillnet fishery at Baja California Sur, Mexico. Analysis revealed no significant effect on bony fish target catch or bycatch for any light type. There was a significant decrease in elasmobranch bycatch using UV and orange lights, with orange lights showing the most promise for decreasing elasmobranch bycatch, resulting in a 50% reduction in bycatch rates. Analysis of the effects of net illumination on elasmobranch target catch was limited due to insufficient data. These results indicate that the illumination of gillnets may offer a practical solution for reducing fish bycatch while maintaining target catch. More research should be conducted to understand the effects of net illumination in different fisheries, how net illumination affects fisher profit and efficiency, and how net illumination affects fish behavior. Further optimization of net illumination is also necessary before the technology can be recommended on a broader scale.

Date Created
2021-05
Agent

Physiological Response to Environmental Stress in Drylands Ecosystems: Examining Prosopis velutina Seedling Responses to Temporal Water Availability Gradients

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Description
Climate change is increasing global surface temperatures, intensifying droughts and increasing rainfall variation, particularly in drylands. Understanding how dryland plant communities respond to climate change-induced rainfall changes is crucial for implementing effective conservation strategies. Concurrent with climate change impacts on…

Climate change is increasing global surface temperatures, intensifying droughts and increasing rainfall variation, particularly in drylands. Understanding how dryland plant communities respond to climate change-induced rainfall changes is crucial for implementing effective conservation strategies. Concurrent with climate change impacts on drylands is woody encroachment: an increase in abundance of woody plant species in areas formerly dominated by grasslands or savannahs. For example, the woody plant, Prosopis velutina (velvet mesquite), has encroached into grasslands regionally over the past century. From an agricultural perspective, P. velutina is an invasive weed that hinders cattle forage. Understanding how P. velutina will respond to climate change-induced rainfall changes can be useful for management and conservation efforts. Prosopis velutina was used to answer the following question: Is there a significant interactive effect of mean soil water moisture content and pulse frequency on woody seedling survival and growth in dryland ecosystems? There were 256 P. velutina seedlings sourced from the Santa Rita Experimental Range in southern Arizona grown under four watering treatments where mean and pulse frequency were manipulated over two months. Data were collected on mortality, stem height, number of leaves, instantaneous gas exchange, chlorophyll fluorescence, biomass, and the leaf carbon to nitrogen (C:N) ratio. Mortality was low across treatments. Pulse frequency had less impact across response variables than the mean amount of water received. This may indicate that P. velutina seedlings are relatively insensitive to rainfall timing and are more responsive to rainfall amount. Prosopis velutina in the low mean soil moisture treatments lost a majority of their leaves and had greater biomass allocation to roots. Prosopis velutina’s ability to survive in low soil moisture conditions and invest in root biomass can allow it to persist as drylands are further affected by climate change. Prosopis velutina could benefit ecosystems where native plants are at risk due to rainfall variation if P. velutina occupies a similar niche space. Due to conflicting viewpoints of P. velutina as an invasive species, it’s important to examine P. velutina from both agricultural and conservation perspectives. Further analysis on the benefits to P. velutina in these ecosystems is recommended.
Date Created
2020
Agent

Effects of Grazing Management on Carbon Stocks in an Arid Rangeland

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Description
Rangelands are an extensive land cover type that cover about 40% of earth’s ice-free surface, expanding into many biomes. Moreover, managing rangelands is crucial for long-term sustainability of the vital ecosystem services they provide including carbon (C) storage via soil…

Rangelands are an extensive land cover type that cover about 40% of earth’s ice-free surface, expanding into many biomes. Moreover, managing rangelands is crucial for long-term sustainability of the vital ecosystem services they provide including carbon (C) storage via soil organic carbon (SOC) and animal agriculture. Arid rangelands are particularly susceptible to dramatic shifts in vegetation cover, physical and chemical soil properties, and erosion due to grazing pressure. Many studies have documented these effects, but studies focusing on grazing impacts on soil properties, namely SOC, are less common. Furthermore, studies testing effects of different levels of grazing intensities on SOC pools and distribution yield mixed results with little alignment. The primary objective of this thesis was to have a better understanding of the role of grazing intensity on arid rangeland soil C storage. I conducted research in long established pastures in Jornada Experimental Range (JER). I established a 1500m transect in three pastures originating at water points and analyzed vegetation cover and SOC on points along these transects to see the effect of grazing on C storage on a grazing gradient. I used the line-point intercept method to measure and categorize vegetation into grass, bare, and shrub. Since soil adjacent to each of these three cover types will likely contain differing SOC content, I then used this vegetation cover data to calculate the contribution of each cover type to SOC. I found shrub cover and total vegetation cover to decrease, while grass and bare cover increased with decreasing proximity to the water source. I found areal (g/m2) and percent (go SOC to be highest in the first 200m of the transects when accounting for the contribution of the three vegetation cover types. I concluded that SOC is being redistributed toward the water source via foraging and defecation and foraging, due to a negative trend of both total vegetation cover and percent SOC (g/g). With the decreasing trends of vegetation cover and SOC further from pasture water sources, my thesis research contributes to the understanding of storage and distribution of SOC stocks in arid rangelands.
Date Created
2018
Agent

Sources and Decomposition of Dissolved Organic Matter in Desert Streams

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Description
Dissolved organic matter (DOM) is an important part of aquatic foodwebs because it contains carbon, nitrogen, and other elements required by heterotrophic organisms. It has many sources that determine its molecular composition, nutrient content, and biological lability and in turn,…

Dissolved organic matter (DOM) is an important part of aquatic foodwebs because it contains carbon, nitrogen, and other elements required by heterotrophic organisms. It has many sources that determine its molecular composition, nutrient content, and biological lability and in turn, influence whether it is retained and processed in the stream reach or exported downstream. I examined the composition of DOM from vascular wetland plants, filamentous algae, and riparian tree leaf litter in Sonoran Desert streams and its decomposition by stream microbes. I used a combination of field observations, in-situ experiments, and a manipulative laboratory incubation to test (1) how dominant primary producers influence DOM chemical composition and ecosystem metabolism at the reach scale and (2) how DOM composition and nitrogen (N) content control microbial decomposition and stream uptake of DOM. I found that differences in streamwater DOM composition between two distinct reaches of Sycamore Creek did not affect in-situ stream respiration and gross primary production rates. Stream sediment microbial respiration rates did not differ significantly when incubated in the laboratory with DOM from wetland plants, algae, and leaf litter, thus all sources were similarly labile. However, whole-stream uptake of DOM increased from leaf to algal to wetland plant leachate. Desert streams have the potential to process DOM from leaf, wetland, and algal sources, though algal and wetland DOM, due to their more labile composition, can be more readily retained and mineralized.
Date Created
2018
Agent

Photosynthesis under Rocks: Hypolith Distribution across the Namib Desert Rainfall Gradient

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Description
“Extremophile” is used to describe life that has adapted to extreme conditions and the conditions they live in are often used to understand the limits of life. In locations with low precipitation and high solar radiation, photosynthetic cyanobacteria can colonize…

“Extremophile” is used to describe life that has adapted to extreme conditions and the conditions they live in are often used to understand the limits of life. In locations with low precipitation and high solar radiation, photosynthetic cyanobacteria can colonize the underside of quartz fragments, forming ‘hypoliths.’ The quartz provides protection against wind, reduces solar radiation, and slows the rate of evaporation following infrequent rain or fog events. In most desert systems, vascular plants are the main primary producers. However, hypoliths might play a key role in carbon fixation in hyperarid deserts that are mostly devoid of vegetation. I investigated hypolith distribution and carbon fixation at six sites along a rainfall and fog gradient in the central Namib Desert in Namibia. I used line point intersect transects to assess ground cover (bare soil, colonized quartz fragment, non-colonized quartz fragment, non-quartz rock, grass, or lichen) at each site. Additionally, at each site I selected 12 hypoliths and measured cyanobacteria colonization on quartz and measured CO2 flux of hypoliths at five of the six sites.
Ground cover was fairly similar among sites, with bare ground > non-colonized quartz fragments > colonized quartz fragments > non-quartz rocks. Grass was present only at the site with the highest mean annual precipitation (MAP) where it accounted for 1% of ground cover. Lichens were present only at the lowest MAP site, where they accounted for 30% of ground cover. The proportion of quartz fragments colonized generally increased with MAP, from 5.9% of soil covered by colonized hypoliths at the most costal (lowest MAP) site, to 18.7% at the most inland (highest MAP) site. There was CO2 uptake from most hypoliths measured, with net carbon uptake rates ranging from 0.3 to 6.4 μmol m-2 s-1 on well hydrated hypoliths. These carbon flux values are similar to previous work in the Mojave Desert. Our results suggest that hypoliths might play a key role in the fixation of organic carbon in hyperarid ecosystems where quartz fragments are abundant, with MAP constraining hypolith abundance. A better understanding of these extremophiles and the niche they fill could give an understanding of how microbial life might exist in extraterrestrial environments similar to hyperarid deserts.
Date Created
2016-12
Agent
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