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A GIS map of the variation in slope across the Mänoa watershed with the locations of all seven study sites.
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Browsing and trampling by nonnative feral pigs (Sus scrofa) negatively impact native flora and fauna in forested ecosystems and cause soil compaction. However, their impact on runoff and erosion is largely unknown. This study addressed this knowledge gap by investigating effects of feral pigs on runoff volume and total suspended solids (TSS) in run...
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Context 1
... study was conducted in the Mänoa wa- tershed on the island of O'ahu, Hawai'i. The watershed encompasses approximately 2,528 ha, with both steeply sloping mountainous and flat coastal lands within a relatively small area ( Figure 1). Runoff from the Mänoa wa- tershed is carried by two main streams, M änoa and Pälolo, which join before emptying into the Ala Wai Canal. ...
Context 2
... areas in the upper forested regions of Pacific island watersheds with <9% slope are not common (the average slope of the Mänoa watershed is 47%). Using a Geo- graphic Information System (GIS), a map of slope characteristics throughout the water- shed was created, and areas with slopes be- tween 5% and 30% were identified as poten- tial sites (Figure 1). Assessment of slopes steeper than 30% was not attempted because runoff plots are problematic on these steeper slopes. ...
Citations
... Their presence also raises concern for water quality as they frequent riparian areas where they defecate and disturb soil by rooting for food and wallowing (Strauch et al. 2016). Although visual evidence of riparian disturbance is often evident, prior research has shown variable success at detecting water quality degradation from pig activity (Doupe et al. 2009;Dunkell et al. 2011;Brooks et al. 2020;Bolds et al. 2021). Increases in Escherichia coli have commonly been detected, but the effects on parameters such as suspended solids and nutrients have been inconsistent. ...
Wild pigs (Sus scrofa) are capable of causing significant agricultural and environmental damage, but previous research to determine their effects on water quality has yielded variable results. We collaborated on a wild pig removal study to assess selected water quality parameters as indicators of pig presence. Monthly grab samples from tributaries in agricultural and conservation lands were collected and analyzed for parameters including total suspended solids (TSS), NO3-N, NH4-N, soluble reactive phosphorus (SRP), and eDNA. Three continuous water quality sensors were installed to measure temperature, specific conductance, and turbidity in 15-minute intervals. Monthly water samples showed tributaries in agricultural areas with dense wild pig populations had elevated TSS, but inorganic N and P were not elevated. Environmental DNA (eDNA) was detectable across the study area but in low concentration. Sensor data suggest specific conductance and turbidity are useful for detecting instances of instream wildlife disturbances. Our future work will utilize measures of wild pig density for further interpretation of water quality response to wild pig management.
... Soil stability strongly correlates to vegetation cover; when large areas are cleared, soil becomes vulnerable to erosion. As land is exposed to direct rainfall and surface water runoff, sedimentation increases, particularly along human-made structures such as roads and landing sites [1,2]. ...
... In forested areas, litter cover acts as a protective layer to slow down runoff and prevent the loss of nutrients from the soil [8]. The impact of wild ungulates on runoff and sedimentation is often overlooked, with only a few studies investigating this interaction [2,9,10]. Mammalian herbivores influence ecosystem-level processes, but the effects and their extent are context-dependent, thus generalizations remain elusive [11,12]. ...
Forest soils are shaped by various processes, like runoff, erosion, sedimentation and bioturbation. A better understanding of the interactions between abiotic and biotic soil-forming processes, including wild boar (Sus scrofa) rooting (i.e., subsurface foraging), enhances adequate management of forest ecosystems. We hypothesized that intense soil sedimentation influences wild boar rooting occurrence and that wild boars modify the outcome of the sedimentation process by redistributing soil layers. This study was conducted in the Babat Valley, Hungary. We estimated the availability of sedimented and non-sedimented patches and the occurrence of boar rooting. Surveys and samplings were done along transects, over consecutive months, where the impact of rooting on the physical and chemical characteristics of soil was measured by comparing them between control and rooted sites. We found that non-sedimented, steep areas were preferred areas for rooting. Sedimentation processes have a higher impact on soil chemical characteristics and soil layer composition than wild boar rooting. We conclude that mitigation of soil degradation can be more effective by reducing adverse abiotic processes rather than wild boar population control.
... These species are opportunistic foragers and have been documented depredating all levels of the food web, including seeds, insects, crabs, sea turtle eggs, and seabirds. Furthermore, in the case of pigs, their contribution to erosion is likely greater than just the denuding of landscapes as their rooting behavior (i.e., turning over the soil) causes soil disturbance, furthering sedimentation within streambeds (Dunkell et al., 2011;Fig. 3c). ...
... Thus increasing vegetation simply decreases groundwater recharge on many low-lying atolls and transpiration dominates total evapotranspiration. Sedimentation to the marine environment can have significant impacts on ecosystem functioning and resilience in the long term across island types(Aumack et al. 2007;Dunkell et al. 2011). Sedimentation occurs through a number of mechanisms, all of which involve destabilization of surface sediments and lead to increased suspended sediments in surface runoff. ...
... Invasive ungulates have been known for decades to overgraze native vegetation, particularly riparian vegetation(Roper & Saunders 2020), causing shifts in community structure that generally decrease streambank stability(Gaston 2015;Allen & Lee 2006). Less stable streambanks contribute to increased suspended sediments in stream water, and consequently in nearshore marine habitats such as coral reefs and kelp forests(Beschta & Ripple 2009 Golbuu et al., 2011;Dunkell et al., 2011). Therefore, we can expect islands with more cover of vegetation and specifically more complex riparian vegetation to exhibit less sedimentation to the nearshore marine environment. ...
... Invasive poeciliid fish also increase the amount and forms of N and P in invaded streams (Holitzki et al. 2013). Feral ungulates, such as pigs (Sus scrofa L.), also degrade water quality through increased nutrient, sediment, and bacteria loading (Dunkell et al. 2011a(Dunkell et al. , 2011bSidle et al. 2006;Singer et al. 1984;Strauch et al. 2016a). ...
The book addresses biological responses to stream nutrients throughout U.S. Forest Service experimental forests and ranges. Chapter 16, which I co-authored, entitled "Ecoregion 11.1.1 California Coastal Sage, Chaparral, and Oak Woodlands: San Dimas Experimental Forest, California," addressed nutrients and their impacts in the San Dimas Experiment Forest, specifically.
... Invasive poeciliid fish also increase the amount and forms of N and P in invaded streams (Holitzki et al. 2013). Feral ungulates, such as pigs (Sus scrofa L.), also degrade water quality through increased nutrient, sediment, and bacteria loading (Dunkell et al. 2011a(Dunkell et al. , 2011bSidle et al. 2006;Singer et al. 1984;Strauch et al. 2016a). ...
This report reviews existing research and datasets from 17 U.S. Forest Service-affiliated experimental forests and ranges (EFRs) that are relevant to science needs of state and federal water quality regulatory agencies. A focus group of regulatory personnel chose “biological responses to stream nutrients” as the focus for this synthesis, and identified a broader array of science topics that could be of regulatory interest. Additional research needs of regulators that could potentially be filled by future studies at these sites were identified as (1) the composition of biotic communities and responses to nutrient enrichment in low-nutrient reference streams, (2) effects on streams of forest management practices, and (3) aquatic impacts of air pollution and of climate change.
Monitoring of relatively undisturbed EFR reference watersheds provides data on baseline stream conditions useful for developing water quality criteria with the reference waterbody method. Studies at EFRs in eight ecoregions may provide a basis for nutrient stressor-response models, a second method for developing water quality criteria.
Management experiments at EFRs have been used to formulate and test best management practices for forests. Hypothesis-testing research into ecological mechanisms underlying stream processes at EFRs can be used to develop models of stream responses.
EFRs offer opportunities to expand research on classes of streams that are underrepresented in the regulatory science base, particularly headwater streams with detritus-based food webs and ephemeral and intermittent flows. Research networks containing multiple EFRs could be used to produce science needed to address large-scale regulatory issues that span multiple ecoregions. Cooperative research at EFRs involving water quality regulatory agencies and land management agencies could potentially produce mutual benefits.
... Invasive poeciliid fish also increase the amount and forms of N and P in invaded streams (Holitzki et al. 2013). Feral ungulates, such as pigs (Sus scrofa L.), also degrade water quality through increased nutrient, sediment, and bacteria loading (Dunkell et al. 2011a(Dunkell et al. , 2011bSidle et al. 2006;Singer et al. 1984;Strauch et al. 2016a). ...
This chapter synthesizes the literature from Sagehen Experimental Forest relevant to water quality regulatory agencies, specifically how wildfire and fuels treatments may impact nutrient loads to streams. The chapter is part of a larger general technical report that provides information on the biological responses to stream nutrients from experimental forests located across the United States.
https://www.fs.usda.gov/pnw/publications/biological-responses-stream-nutrients-synthesis-science-experimental-forests-and-ranges
... In terrestrial systems, invasive herbivore eradications can reduce erosion rates, and increase plant production that aids in stabilizing soils [131][132][133][134][135]. On subantarctic Macquarie Island (southwestern Pacific Ocean), the impacts of invasive rabbits and climate change interacted to negatively impact the island ecosystem in a variety of ways [136]. ...
Climate change represents a planetary emergency that is exacerbating the loss of native biodiversity. In response, efforts promoting climate change adaptation strategies that improve ecosystem resilience and/or mitigate climate impacts are paramount. Invasive Alien Species are a key threat to islands globally, where strategies such as preventing establishment (biosecurity), and eradication, especially invasive mammals, have proven effective for reducing native biodiversity loss and can also advance ecosystem resilience and create refugia for native species at risk from climate change. Furthermore, there is growing evidence that successful eradications may also contribute to mitigating climate change. Given the cross-sector potential for eradications to reduce climate impacts alongside native biodiversity conservation, we sought to understand when conservation managers and funders explicitly sought to use or fund the eradication of invasive mammals from islands to achieve positive climate outcomes. To provide context, we first summarized available literature of the synergistic relationship between invasive species and climate change, including case studies where invasive mammal eradications served to meet climate adaptation or mitigation solutions. Second, we conducted a systematic review of the literature and eradication-related conference proceedings to identify when these synergistic effects of climate and invasive species were explicitly addressed through eradication practices. Third, we reviewed projects from four large funding entities known to support climate change solutions and/or native biodiversity conservation efforts and identified when eradications were funded in a climate change context. The combined results of our case study summary paired with systematic reviews found that, although eradicating invasive mammals from islands is an effective climate adaptation strategy, island eradications are poorly represented within the climate change adaptation and mitigation funding framework. We believe this is a lost opportunity and encourage eradication practitioners and funders of climate change adaptation to leverage this extremely effective nature-based tool into positive conservation and climate resilience solutions.
... One such strategy is (passive) upland forest protection. Feral pigs (Sus scofa) in Hawai'i have been observed to negatively impact soil and groundcover, and consequently infiltration and runoff (Dunkell et al., 2011;Strauch et al., 2016). Because pigs and other invasive ungulates are also a major pathway for invasive plant seed dispersal, ungulate exclusion from pristine native forest areas upgradient of the aquifer impedes invasion by alien plant species, which tend to have higher evapotranspiration rates (Giambelluca et al., 2008;Kagawa et al., 2009;Cavaleri et al., 2014) and lower fog capture potential (Takahashi et al., 2011) than native canopy tree species. ...
We develop and operationalize an integrated groundwater and watershed management model using data from the Kīholo aquifer on the west coast of Hawai'i Island. Results from a numerical simulation suggest that investment in fencing (passive management) is preferred to invasive species removal (active management) if we are limited to selecting a single conservation tool. However, using both instruments jointly increases net present value relative to using either instrument independently in most cases tested, and the additional benefit of invasive species removal increases as water becomes scarcer. The general results are largely insensitive to variations in the invasive species uptake rate and recharge benefits of fencing, and in all cases, use of both instruments reduces the loss resulting from the imposition of a safe minimum standard for groundwater-dependent ecosystems more effectively than either instrument alone.
... These nutrients are often important for terrestrial ecosystems, as well as for adjacent reefs and fish nurseries (Polis & Hurd 1996, Honig and Mahoney 2016, Graham et al. 2018. Through compaction, rooting and grazing, invasive ungulates such as goats (Capra hircus), sheep (Ovis aries), cows (Bos taurus) and pigs (Sus scrofa) alter soil structure and nutrient cycling dynamics, causing sediment and nutrient runoff from land to sea and subsequent terrestrial erosion and eutrophication and sedimentation of coastal marine ecosystems (Peltzer et al. 2010, Dunkell et al. 2011, Beltran et al. 2014. Similarly, invasive herbivores can reduce rates of carbon sequestration through the consumption of woody plants and seeds (Peltzer et al. 2010, Beltran et al. 2014, whereas invasive rodents can indirectly increase rates of aboveground carbon sequestration in islands with seabird populations (e.g., Wardle et al. 2007). ...
The United Nations 2030 Agenda for Sustainable Development sets a framework of universal Sustainable Development Goals (SDGs) to address challenges to society and the planet. Island invasive species eradications have well-documented benefits that clearly align with biodiversity conservation-related SDGs, yet the value of this conservation action for socioeconomic benefits is less clear. We examine the potential for island invasive vertebrate eradications to have ecological and socioeconomic benefits. Specifically, we examine: (1) how SDGs may have been achieved through past eradications; and (2) how planned future eradications align with SDGs and associated targets. We found invasive vertebrate eradication to align with 13 SDGs and 42 associated targets encompassing marine and terrestrial biodiversity conservation, promotion of local and global partnerships, economic development, climate change mitigation, human health and sanitation and sustainable production and consumption. Past eradications on 794 islands aligned with a median of 17 targets (range 13–38) by island. Potential future eradications on 292 highly biodiverse islands could align with a median of 25 SDG targets (range 15–39) by island. This analysis enables the global community to explicitly describe the contributions that invasive vertebrate management on islands can make towards implementing the global sustainable development agenda.
... Soil microbial biomass has been reported to increase following rooting (Risch et al. 2010, Wirthner et al. 2012, but other studies have found that it remains unchanged (Taylor et al. 2011, Wirthner et al. 2011. Other studies have examined the impact of wild pig disturbance on soil erosion, but results were not significant (Dunkell et al. 2011, Strauch et al. 2016, Hancock et al. 2017. The discrepancy in results among studies may be due to different study environments, methods, varying densities of wild pigs, and the measurement of insensitive parameters. ...
... The pattern of increased usage during the wet season is similar to results reported byHancock et al. (2017), who also observed concentrated wild pig activity in a catchment during the wet season in Australia. The authors did not find evidence that wild pig disturbance increased erosion or influenced soil structure, and suggested that any changes may be slow and visible only over a longer period of time.Strauch et al. (2016) andDunkell et al. (2011) studied wild pig ...
Wild pigs (Sus scrofa) are a highly invasive species in the United States and millions of dollars are spent annually on removal efforts and damage reduction. Wild pigs may act as ecosystem engineers in areas where they are established, so it is important to fully understand their impacts to predict how environments they invade may change. Changes in riparian ecosystems should be of special concern as they provide important ecosystem services and are susceptible to disturbance. We examined changes in biogeochemical processes at the terrestrial-aquatic interface at a property that was densely populated by wild pigs. Nitrogen mineralization rates were estimated for floodplain soils disturbed by wild pig rooting, and erosion and accretion of stream bank sediment was recorded to estimate the effects of wild pigs on bank stability. Water quality parameters and fecal bacteria concentrations were measured to determine the impacts of wild pigs on water quality in small forested watersheds. Although the effects of wild pigs may vary depending on local environmental conditions and habitat types, our findings suggest that wild pigs impact nutrient cycling and water quality in riparian areas.
