Quantification of Hydrologic Response to Forest Disturbance in Western U.S. Watersheds

Forested watersheds produce more than half of the water supply in the United States. Forests affect how precipitation is partitioned into available water versus evapotranspiration. This dissertation investigated how water yield and snowpack responded to forest disturbance following recent disturbances in western U.S. forests during the period 2000-2019. Chapter 2 systematically reviewed 78 recent studies that examined how water yield or snowpack changed after forest disturbances. Water yield and snowpack often increased after disturbance, but decreased in some circumstances. Decreased water yield was most likely to occur following disturbances that did not remove the entire forest canopy. It was also more likely to occur in more arid watersheds at lower latitudes, such as in the southwestern U.S., and on south-facing aspects. Chapter 3 examined 159 watersheds across the western U.S. to determine how often and where water yield increased or decreased following forest disturbance. Overall, more severe forest disturbances, particularly in relatively wet watersheds such as in the Northern Rocky Mountains or Pacific Northwest, were more likely to produce larger water yield. However, forest disturbances in very arid watersheds, such as those in the southwestern U.S., were more likely to result in less water yield. Chapter 4 developed a new method for more precisely mapping forest canopies and understory forest vegetation. This method used data collected by the U.S. Forest Service’s Forest Inventory and Analysis Program. The maps of separate forest canopy and understory vegetation layers are expected to allow hydrologists to make more accurate predictions regarding the effects of future vegetation changes on water supply. Previous studies that monitored water yield before and after clearcut timber harvests concluded that forest disturbances would lead to increased water yield. In contrast, the work presented here found that disturbances that do not remove the entire canopy (e.g., due to insects, drought, disease, thinning, low-severity wildfire) may lead to different water yield and snowpack responses than disturbances that remove the entire canopy (e.g., clearcut harvesting, severe wildfire). This work has therefore helped us better understand how future water supply, for people and for ecosystems, will be affected by future forest changes

Temporal, Spatial, and Environmental Influences on the Demographics and Harvest Vulnerability of American Black Bears (Ursus americanus ) in Urban Habitats in New Jersey, Pennsylvania and West Virginia

To date, no research studies in the eastern United States have addressed the spatial ecology of black bears (Ursus americanus) in urban and suburban habitats, and there is limited information regarding black bear space use, habitat selection, and harvest vulnerability. I assessed the harvest vulnerability, home range size, and spatial ecology of black bears in New Jersey, Pennsylvania, and West Virginia in collaboration with the New Jersey Division of Fish and Wildlife, Pennsylvania Game Commission, and the West Virginia Division of Natural Resources. The major objectives of my study were to identify and quantitatively assess: (1) if black bears shift home ranges seasonally with respect to urban/suburban habitats; (2) harvest vulnerability and cause-specific mortality of black bears in urban/suburban habitats; (3) if black bears captured as result of nuisance complaints are transient or reside in urban/suburban habitats; (4) habitat characteristics of movement corridors utilized by black bears in urban/suburban habitats; and (5) if corridors likely to be used by black bears accessing urban/suburban environments can be predicted by habitat modeling.;Over the course of the study (2010-2012), agency employees trapped, handled, and fit 119 bears with GPS-GSM collars. Individual study areas in each state were centered around West Milford, Stillwater/Branchville, and Vernon, NJ; Johnstown, Scranton/Wilkes-Barre, and State College, PA; Beckley, Charleston, and Morgantown, WV. A total of 57,816 bear locations were recorded in New Jersey, 114,451 locations were recorded in Pennsylvania, and 33,217 in West Virginia.;Black bears shifted spatial distribution on the landscape in response to resource availability, and consequently I expected bears in urban areas to shift their home ranges seasonally in urban environments. On average, bears were most often found near city limits (\u3c5 km). Home range centers of male bears were twice as far from city limits as female bears (2.31 km vs. 0.91 km, respectively). Bear home range size did not differ among seasons, but did differ between sexes (male home ranges were 5.6 times larger than female bears) and among study areas. Bears did not shift their home ranges closer to urban areas during times of food shortage (spring or late fall). Urban bears lived near town and were resident to the edge of the urban area, but this distance varied with the study area in which they resided. As a result, managers seeking to understand where potential bear conflicts may occur should focus their efforts on the edge of urban and suburban areas (known as the exurban areas) in the Mid-Atlantic Region.;Regulated harvests have reduced mortality and allowed black bear populations to increase throughout the eastern United States over the past 30 years. This rapid and dramatic recovery in population size has led to increased human-bear interactions in New Jersey, Pennsylvania, and West Virginia. Harvest vulnerability of black bears is dependent on a variety of factors and therefore difficult to estimate. I measured harvest vulnerability by generating maximum entropy (Maxent) models of bear occurrence during the prehunting period and hunting season for each study area. I used Maxent to generate models of bear occurrence. In all but one study area, black bear occurrence was 5-75% less in the hunting season than in the prehunting period. Bear occurrence decreased from prehunting period to hunting season in both public hunting lands and urban areas. Bear occurrence probability shifted from public hunting areas to the periphery of the public hunting areas between the prehunting period and hunting season. Annual harvest rates of urban bears were highest in Pennsylvania (20.2%) and lower in New Jersey (5.9%) and West Virginia (17.3%). Despite the short timeframe (3 years) of my study, regulated hunting was effective in killing urban black bears Pennsylvania and West Virginia. Hunters in Pennsylvania harvested a similar proportion of urban bears to the long-term harvest rate of all bears in the state (20.2% vs. 20.0%, respectively). Probability of urban bear occurrence shifted from public hunting areas during the prehunting period to private lands on the periphery of urban areas during the hunting season. Average overall mortality rates of urban bears were highest in Pennsylvania (28.1%) and lower in West Virginia (17.5%) and New Jersey (15.1%). Despite the short timeframe of the study, regulated hunting was effective in killing a high number of urban black bears in New Jersey, Pennsylvania, and West Virginia, when all mortality sources were taken into account.;Black bear populations have increased nationwide over the past 4 decades due to reduction in direct mortality. Bear population sizes have increased over time and as a result, human-bear conflicts have increased. I sought to determine whether nuisance bears in urban/suburban areas are residents to the area or transient. I predicted that the majority of bears found in urban/suburban areas form resident populations on the urban perimeter, rather than transient individuals that leave the core forests and enter the urban areas periodically. There was considerable support for my prediction that bear populations in urban areas are resident and spend much of their time on the city\u27s edge. Black bears used private lands on the periphery of urban areas. I posit that this may have been because these areas likely had abundant food and provided reduced risk of disturbance (e.g., hunting, human disturbance).;Given the recent explosive increase in urban bear populations, managers are charged to determine which areas of urban/suburban centers are likely to be used by bears. It is unknown whether black bears use travel corridors within urban/suburban matrix to travel between habitat patches. There exists a paucity of information on how black bears use urban and suburban habitats. We used boosted regression trees to create two predictive models of bear occurrence in urban and suburban habitats for (1) New Jersey and Pennsylvania, and (2) West Virginia. We separated West Virginia from New Jersey and Pennsylvania in the modeling process because West Virginia\u27s topography is more rugged and the population density of people was the lowest of all three states. We randomly selected a subset of 40,000 bear locations in New Jersey and Pennsylvania, as well as, 30,000 bear locations in West Virginia from the full database of locations. We generated 40,000 random points within the study areas in New Jersey and Pennsylvania and 30,000 random points within the study areas of West Virginia. We built three models (1) for New Jersey and Scranton/Wilkes-Barre, PA, (2) State College and Johnstown, PA, and (3) West Virginia. We found that probability of bear occurrence was highest in New Jersey and Scranton/Wilkes-Barre study areas when bears were: (1) \u3c1 km from edge forest, (2) \u3c7.5 km from the nearest road, (3) \u3c7.5 km from the nearest urban area, (4) land use/ land cover was forested, (5) \u3c12 km from public land, and (6) NDVI \u3c 0.3. We found that probability of bear occurrence was highest in Johnstown and State College study areas when bears were: (1) \u3c1 km from edge forest, (2) \u3c1 km from the nearest road, (3) \u3c7 km from the nearest urban area, and (4) \u3c7 km from public land. The highest probability of bear occurrence in West Virginia occurred when (1) NDVI was \u3e0.6, (2) distance to public land was \u3e22.0 km, (3) distance to urban areas was between 1-5 km, (3) topographic position index was \u3e100 (steep, rugged terrain), (4) land use land cover was forested or other , (5) distance to roads was \u3e1.4 km, and (6) distance to core forest was \u3e1.5 km. We found no support for our prediction that urban bears use corridors. Bears spent nearly 95% of their time on the edge of city limits and \u3c5% of their time within city limits. We found no evidence that habitat quality on the edge of city limits was lower than that of non-urban bear habitat. There is likely not a physiological need for bears to traverse urban areas when they can remain in habitats where they would encounter less human disturbance. I found no support for my prediction that bears use corridors. Bears spent nearly 95% of their time on the edge of city limits and \u3c5% of their time within city limits. I had no evidence that habitat quality on the edge of city limits was lower than that of non-urban bear habitat. There likely was no physiological need for bears to traverse urban areas because urban habitat patches are often safe from human disturbance and therefore, they did not use corridors. The final predictive model of the probability of bear occurrence will assist managers by identifying areas where urban bears are most likely to live and areas that require direct management actions

Montpellier broom (Genista monspessulana) and Spanish broom (Spartium junceum) in South Africa: An assessment of invasiveness and options for management

AbstractThe legumes (Fabaceae) Genista monspessulana and Spartium junceum are major invaders in several other parts of the world, but not yet so in South Africa. We determine their current distributions in South Africa at different spatial scales, assess population structure (soil seed banks and size at reproduction) evaluate current management activities, and provide recommendations for control (including assessing the feasibility of nation-wide eradication). G. monspessulana occurs at nine localities in three quarter-degree cells, covering a total of 22.7ha. S. junceum is much more widespread, occurring in 33 quarter-degree cells and is frequently cultivated in private gardens. All naturalised or invasive populations are in disturbed areas, mostly along roadsides. Once established, G. monspessulana and S. junceum accumulate large, persistent soil-stored seed banks, ranging in size between 909 and 22,727 (median 1970)seeds/m2 and 0 and 21,364 (median 455)seeds/m2 for the two species respectively. Both species resprout vigorously after cutting and stump herbicide application (60% of G. monspessulana and 43% of S. junceum plants resprouted) which necessitates regular follow-ups. We estimate that over 10years, at a cost of about ZAR 81,000 (1 ZAR=0.114 US$ as on 6 October 2012), G. monspessulana could be extirpated from South Africa. S. junceum is far more widespread and coupled with low effectiveness of control, abundance of seeds and seed longevity, eradication is unfeasible. We recommend that control methods used for S. junceum be improved to prevent resprouting, and that areas are managed to limit the movement of seeds and avoid further spread and establishment. Further studies are required to understand why these two species have failed to replicate the invasiveness shown in other parts of the world

Integrated Management of Billbugs (Coleoptera: Dryophthoridae) in Intermountain West Turfgrass

Billbugs are a serious pest of turfgrass in the Intermountain West. Billbug larvae severely discolor and eventually kill turfgrass by feeding in stems, on roots, and on crowns of the plant. Billbugs are typically managed with preventive, calendar-based applications of insecticides. Most of our knowledge on the biology and management of billbugs comes from research in the eastern U.S, and little is known about billbug biology and best management practices in the Intermountain West. First, I examined the seasonal activity of billbug life stages in Intermountain West turfgrass and developed a predictive degree-day model to better time management strategies against billbugs. I found that compared to the eastern U.S., a regional model that starts earlier (January 13) and has a cooler insect development threshold (3oC) was adequately robust to predict billbugs in Utah and Idaho. Next, I used the Utah-Idaho degree-day model to determine whether preventive and curative timings for billbug management developed in the eastern U.S. were effective in the Intermountain West. Testing four insecticides with the Utah-Idaho model and with eastern U.S. management timings I found that there was support to consider adoption of these same recommendations in Utah and Idaho, particularly for current preventive insecticides such as neonicotinoids and anthranilic diamides. Finally, considering that turf insecticides can negatively impact predatory insects, thought to viisuppress turf pests, I assessed the predatory arthropod community in Intermountain West turf and their impacts on billbugs. I found that the predatory arthropod community consisted primarily of ground beetles and spiders, representing 60% and 28% of all predators, respectively. I found that predators contributed the most by consuming billbug eggs and by changing the behavior of billbug adults with an observed reduction in mating activity. My research not only lays the ground work for development of effective, sustainable integrated management of billbugs in Intermountain West turfgrass, including conservation biocontrol,but also illustrates the necessity of regional predictive models, monitoring, and appropriate timing of management for successful turf pest suppression

Post-release evaluation of the biological control programme against Cereus jamacaru De Candolle (Cactaceae), in South Africa

Cereus jamacaru De Candolle (Cactaceae) is an environment-transforming weed of both agricultural and wildlife habitats in South Africa. Weed infestations reduce carrying capacity of the land, and pose a risk to livestock, wildlife and human safety due to the plant’s spiny thorns. The weed is considered to be under complete biological control in South Africa, due to its introduced control agent, Hypogeococcus festerianus Lizer y Trelles (Hemiptera: Pseudococcidae), although observational reports suggest that the level of success achieved is variable. In this thesis, a formal post-release evaluation of this biological control programme was conducted, specifically to determine the efficacy of H. festerianus as a biological control agent, and to identify factors which may limit or constrain the level of success achieved by the control agent. These data were collected with the intention of improving the control of C. jamacaru in South Africa. A field-based study of C. jamacaru population demographics investigated the efficacy of H. festerianus as a biological control agent of the weed, by integrating weed growth, fecundity and survival metrics with C. jamacaru population dynamics and demographic patterns from 8 sites where H. festerianus was present and 14 sites where the control agent was absent. The findings indicated that H. festerianus significantly reduced weed fecundity, which resulted in fewer seedling recruits, and that levels of plant mortality were greater at sites where H. festerianus was present. The reduction in weed fecundity and survival translated into negative population-level consequences for H. festerianus. Weed-population age frequency distributions in the absence of H. festerianus demonstrated a “reverse J-shaped” distribution, indicative of high recruitment rates and population stability, while C. jamacaru populations infected with H. festerianus were described by bell-shaped distributions, and were typified by limited recruitment, or a complete lack thereof. By constraining recruitment and inhibiting selfregeneration, H. festerianus appears to regulate populations of C. jamacaru. Predation and parasitism of H. festerianus was believed to be a limiting factor for the biological control programme against C. jamacaru in South Africa, although no formal evaluation of this claim had been undertaken. Accordingly, the assemblage of natural enemies acquired by H. festerianus in South Africa was identified by field-collections of infected H. festerianus gall-material. Further, timed point-count surveys of natural enemies associated with H. festerianus were performed and integrated with the data on the impact of H. festerianus on weed population dynamics to assess the impact of two prominent predaceous taxa on H. festerianus efficacy as a biological control agent. Although H. festerianus had acquired a diverse suite of novel natural enemies in South Africa, this has not prevented the biocontrol agent from having an impact on C. jamacaru populations, although other subtler effects cannot be ruled out. This study showed that biological control efforts employing H. festerianus for the management of C. jamacaru have been successful. Furthermore, these data demonstrated the utility of retrospective analyses in developing and improving the science of biological control, specifically how to improve candidate agent prioritisation, determining how many agents are required for successful biological control, and how to evaluate the success of biological control efforts. Improvements in our theoretical understanding of biological control will undoubtedly reduce costs of biological control programmes, improve success rates, and increase the predictability of biological control