Effects Of Multiple Drivers Research Articles

Vaccinium dwarf shrubs responses to experimental warming and herbivory resistance treatment are species- and context dependent

Climate change impacts on species and ecosystem functioning may depend on climatic context and study systems. Climate warming and intensified herbivory are two stressors to plants that often appear in combination and are predicted to increase in cold environments. Effects of multiple drivers on plant performance are difficult to predict and warrant studies that use experimental manipulations along climatic gradients to produce more realistic knowledge. Our three study sites by the Sognefjord in Norway, that differed mainly in climatic conditions (ca. 5°C growing season difference), ranged from hemi-boreal lowland (100 masl, Low), via boreal mid-montane (500 masl) to alpine timberline (900 masl, High) bioclimates. At each site, in a randomized block design, we simulated growing-season warming using open-top chambers (OTCs) and experimentally induced herbivory resistance using the plant hormone methyl jasmonate (MeJA). We recorded growth, mortality, flower and fruit numbers, and insect herbivory on tagged ramets in permanent plots across three years (2016-2018) in three open woodland populations of two functionally important plant species with contrasting traits, Vaccinium myrtillus (bilberry) and V. vitis-idaea (lingonberry). Growth of both dwarf shrubs decreased with warming in the warm lowland populations (Low) but increased in the alpine populations (High). Shoot mortality increased most with warming at Low but was reduced at High. Reproduction, both flowering and fruiting, decreased with induced resistance treatment, but the effect was larger when warmed for bilberry and increased with elevation for both species. Leaf herbivory in bilberry increased with warming at Low but decreased at High. The combined warming and resistance treatment had only synergistic negative interaction effects on fruit numbers in bilberry. The clear context- and species-dependent effects of climate warming and increased resistance in this study may predict a potential decline in performance, as well as abundance and distribution, of these functionally important Vaccinium species at our lowest site. Bilberry reproduction appeared to be particularly susceptible to both climate warming and induced resistance in the manipulated populations. Such combined negative effects on plant performance are likely to have considerable knock-on effects via altered species’ interactions and ecosystem functioning.

Non‐stationary effects of multiple drivers on the dynamics of Japanese sardine (Sardinops melanostictus, Clupeidae)

AbstractNon‐stationary driver‐response relationships are increasingly being recognized by scientists, underlining that a paradigm shift out of conventional stationary relationships is crucial. Japanese sardine (Sardinops melanostictus, Clupeidae) is a typical small pelagic fish in the northwestern Pacific with considerable fluctuations in productivity, bringing about great economic and ecological concerns. Numerous studies suggest that the population dynamics of Japanese sardine is an integrated process affected by multiple density‐dependent, fishing and climatic drivers. However, little has hitherto been done to incorporate the non‐stationary effects of multiple drivers, impeding progresses in understanding the population dynamics and in developing management strategies. In this study, we adopted variable coefficients generalized additive models to reveal the non‐stationary effects of density dependence, fishing pressure and climatic conditions on the population dynamics of Japanese sardine. Results suggest that the dynamics of Japanese sardine from 1976 to 2018 could be divided into four periods: the 1980s when suitable climatic conditions from strong Siberian High pressure system sustained high abundance; the 1990s when negative density‐dependent effects and degrading climatic conditions due to temperature increase led to population collapse; the 2000s when negative triple effects, particularly high fishing pressure, restricted the population increase; and the 2010s when favourable climatic conditions with re‐strengthening Siberian High pressure system accompanied by low fishing pressure contributed to the population recovery. The study highlights that precise identifications of population status and climatic conditions are helpful to achieve good trade‐offs between resource exploitation and protection and to facilitate ecosystem‐based management for Japanese sardine fisheries.

Impacts of natural and human factors on water-related ecosystem services in the Dongting Lake Basin

Correctly identifying and understanding the drivers of ecosystem change and their impacts on ecosystem services (ESs) could provide comprehensive supporting information for ecological governance decisions. This study aimed to identify the key drivers and influencers of natural and human factors on water-related ecosystem services (WESs) in three aspects: spatial heterogeneity contribution, driving relationships, and constraining relationships. The study area included the Dongting Lake Basin, which was divided into 2816 sub-basins as the spatial unit. The WESs of water production, soil conservation, and water purification (output nitrogen) from 2000 to 2020 were quantified, and the impact of environmental factors on WESs and ES enhancement potential were assessed. The results showed that: (1) From 2000 to 2020, the three WESs increased in varying degrees; water production, soil conservation, and nitrogen export increased by 27.60%, 43.20%, and 1.50%, respectively. (2) Precipitation (PRE), slope (Slope), and percentage of ecological land (ELP) were the dominant factors influencing the spatial heterogeneity pattern of water production, soil conservation, and nitrogen output, respectively; PRE, Slope, and ELP had evident nonlinear relationships with the WESs and displayed segmental regression relationship characteristics. (3) Natural and human factors had significant constraining effects on the WESs, even though the driving effects were not significant. (4) Potential measurement results that integrate the driving and limiting effects of factors showed significant heterogeneity, which allows for the screening of efficient ES enhancement measures and locating the implementation space. Therefore, comprehensively considering the effects of multiple drivers and obtaining a multilateral understanding of the impact of the driving factors on ESs will help refine and optimize environmental management decisions.

Forms and drivers of annual streamflow variability in the headwaters of Canadian Prairies during the 20th century

AbstractHeadwater streamflows in the Rocky Mountain foothills are the key to water availability in the Canadian Prairies. Headwater characteristics, however, have been and continue to be subject to major variability and change. Here, we identify various forms of change in the annual mean streamflow and timing of the annual peak and attempt to distinguish between the effects of multiple drivers using a generalized regression scheme. Our investigation shows that the Pacific Decadal Oscillation (PDO) is the main driver of significant monotonic trends and shifts in the central tendency of annual mean streamflow in major headwaters. In parallel, the cumulative effects of non‐PDO climatic drivers and human‐induced land use and land management are the main causes of significant variations in the timing of the annual peak. Additional analyses show that time sequences with significant trends in annual mean streamflow and timing of the annual peak coincide with those that show significant trends in the PDO or non‐PDO component of the air temperature, respectively. The natural streamflow characteristics are substantially perturbed by anthropogenic river flow regulation, depending on the form of change and/or the level of regulation. Evidence suggests that the general tendency of human regulation is to alleviate the severity of above‐ and below‐average streamflow conditions; however, it may also intensify the variability in natural streamflow characteristics during drier years and/or those with earlier annual peak timing. These are circumstances to which the regional water resource system is vulnerable. Our findings are important for the provision of effective regional water resource management in the Canadian Prairies and contribute to a better understanding of the complex interactions between natural and anthropogenic drivers in coupled human–water systems.

Vascular plant changes in extreme environments: effects of multiple drivers

The Antarctic Peninsula is one of three regions of the planet that have experienced the highest rates of climate warming over recent decades. Based on a comprehensive large-scale resurvey, allowing comparison of new (2009) and historical data (1960s), we show that the two native Antarctic vascular plant species have exhibited significant increases in number of occupied sites and percent cover since the 1960s: Deschampsia antarctica increasing in coverage by 191 % and in number of sites by 104 %. Colobanthus quitensis increasing in coverage by 208 % and number of sites by 35 %. These changes likely occurred in response to increases of 1.2 °C in summer air temperature over the same time period. Both species exhibited changes with elevation due to the interaction of multiple drivers (climatic factors and animal disturbance), producing heterogeneity of responses across an elevation gradient. Below an elevation of 20 m fur seal activity exerted negative impacts. Between 20 and 60 m, both plant species underwent considerable increases in the number of sites and percent cover, likely influenced by both climate warming and nutrient input from seals. Above an elevation threshold of 60 m the maximum elevation of the sites occupied decreased for both species, perhaps as a consequence of physical disturbance at higher elevations due to the permafrost conditions and/or the snow cover thickness and persistence. Understanding the role of disturbance drivers for vegetation change in cold regions may become a research priority to enable improved forecasting of biological responses and feedbacks of climate warming on ecosystems in these globally influential regions.

Biotic and Abiotic Factors Interact to Regulate Northern Peatland Carbon Cycling

Understanding the spatio-temporal variability of controls on peatland carbon (C) cycling is essential to project the effects of future environmental change. While there is understanding of individual drivers of C cycling, the effect of multiple drivers, including interactions, remains poorly understood. Using a spatially and temporally explicit sampling framework, we examined the effects of biotic and abiotic controls on key indicators of peatland functioning: ecosystem respiration (Reco), photosynthesis (Pcal), net ecosystem exchange (NEE), methane (CH4) fluxes, and pore water dissolved organic carbon concentration ([DOC]). Measurements were made over 12 months in a blanket peatland hosting a wind farm in Scotland, UK. Overall, we found that (i) season and plant functional type (PFT) explained most variation in Reco and Pcal, (ii) PFT and spatial location within the wind farm, which integrates several peat properties, were dominant predictors of CH4 fluxes, and (iii) season and location within the wind farm correlated with pore water [DOC]. Examination of predictors indicated that interactions, between and within biotic and abiotic factors, explained a significant amount of variation in greenhouse gas fluxes and [DOC]. These findings indicate that combinations of biotic and abiotic factors could mediate or exacerbate the effects of future environmental change on peatland C cycling. Given this, studies of C cycling need to capture the spatial and temporal variance of biotic and abiotic factors and their interactions to project the likely impacts of environmental change.

Trophic state responses of Onondaga Lake, New York, to reductions in phosphorus loading from advanced wastewater treatment

This study evaluated the response of previously culturally hypereutrophic Onondaga Lake, New York, to major reductions in phosphorus (P) loading from a municipal wastewater treatment plant achieved over a 35-year period. Analysis of the response was based on long-term monitoring of effluent total P concentration (TPMetro) and a robust array of in-lake metrics of trophic state, including (1) TP, (2) chlorophyll a (Chl-a), (3) Secchi disk depth, (4) areal hypolimnetic oxygen deficit (AHOD), (5) the downward flux of volatile suspended solids, and (6) the minimum dissolved oxygen concentration in the upper waters during fall turnover. Substantial positive responses, which were significantly linearly related to the decreases in TPMetro, were documented for all of the metrics over the monitoring period. For example, a 91% reduction in TPMetro resulted in reductions of 84% and 59% in Chl-a and AHOD, respectively. The changes depict a transformation from hypereutrophy to upper mesotrophy, with the exception of AHOD values that remain in the eutrophic range. The delayed response of AHOD reflects slower sediment diagenesis processes. The relationships among the metrics of trophic state are considered in the context of literature expressions, accepted paradigms, and limitations related to variations in food web effects. Empirical models that include the effects of multiple drivers on interannual variations in contemporary trophic state metrics were developed and applied to forecast variability under existing conditions. This case study contributes to the scientific literature describing lake rehabilitation through reductions in P loading.

Environmental perturbation, grazing pressure and soil wetness jointly drive mountain tundra toward divergent alternative states

Summary 1. Plant communities are structured by complex interactions between multiple factors, which veil our understanding of the effects of environmental changes on communities and ecosystems. Besides the relative role of biotic and abiotic factors as community-structuring processes, addressing how they jointly affect the ecological resilience and resistance of plant communities is crucial to understand better the long-term response of communities facing global changes. 2. Here, we used the results from a long-term (23 years) perturbation experiment set up in Fennoscandian mountain tundra to test these mechanisms. The experiment consisted of a transplantation of twenty blocks of Vaccinium myrtillus heath vegetation including upper soil layer from a lower elevation tundra heath habitat to a snowbed habitat 150 m higher in elevation where V. myrtillus lies at its upper limit. In the snowbed with contrasting levels of soil wetness, half of the transplanted blocks were protected from mammalian herbivores. 3. Our results revealed that in addition to the important role of environmental conditions as a structuring force, the joint effects of multiple drivers resulted in divergent patterns in both plant functional composition and species diversity among transplanted communities. Under environmental perturbation (i.e. transplantation to snowbed), the heath vegetation was altered by grazing pressure that reduced the cover of shrubs (especially V. myrtillus). In grazed dry snowbed, a species-rich community with high functional type evenness and diversity developed. Reversely, in dry exclosures, V. myrtillus gained high dominance associated with only few graminoids and forbs. In wet snowbed conditions, shrubs tended to decline both in grazed plots and exclosures whereas bryophytes attained high abundance. Grazing promoted species richness while soil waterlogging tended to promote among-plot heterogeneity (b-diversity) which was highest in wet exclosures. 4. Synthesis. Our long-term experiment reveals that environmental perturbation, grazing and soil wetness exhibit joint effects that induce divergent trajectories of tundra plant communities. We suggest that a strong environmental perturbation triggers mountain tundra heath community to move away from its equilibrium state. The outcome of this shift depends on the interplay between grazing pressure and soil wetness that drive tundra plant communities toward divergent alternative states.

Disentangling the effects of multiple anthropogenic drivers on the decline of two tropical dry forest trees

Summary1. Tropical plant populations are often subject to multiple types of anthropogenic disturbance. Effective management requires disentangling the effects of these disturbances and prioritizing interventions for the driver(s) most responsible for population decline. However, the effects of multiple drivers on plant population dynamics are rarely examined.2. We assessed the independent and combined effects of common anthropogenic disturbances on the transient and long‐term population dynamics of two economically important, declining tree species in an Indian dry forest. Specifically, we drew on 10 years of demographic monitoring to assess the effects of non‐timber forest product (NTFP) harvest and two invasive species (an understorey shrub Lantana camara and a mistletoe Taxillus tomentosus) on amla (Phyllanthus emblica and Phyllanthus indofischeri) populations.3. Although fruit harvest has been blamed for declining amla populations, the current policy and management strategies implemented to restrict it have little effect on long‐term stochastic growth rates (λs) of amla both with and without invasive species. In contrast, mistletoes significantly decreased λs of both species.4. Lantana had both direct and indirect effects on P. emblica, causing a regeneration bottleneck. Lantana had a direct negative effect on seeding and sapling growth, whereas populations without lantana experienced higher levels of grazing by wild animals. Over 10 years, P. emblica populations dropped to 16% of their original size in areas with invasive species.5. Synthesis and applications. Our results illustrate that mistletoe and lantana, not fruit harvest, are the main drivers of amla decline, and these species are likely to be driving the decline of other Indian dry forest tree species. Management directed only at limiting fruit harvest will be ineffective. Instead, control of both invasive species combined with temporary protection from grazing is urgently needed. The ban on fruit harvest in Indian protected areas is not an effective conservation policy for these species. Harvest is not necessarily the main cause of decline for NTFP species. Management plans for NTFP and other at‐risk species must consider the relative effects of different drivers of decline, including direct and indirect effects of invasive species.

Overcoming the rare species modelling paradox: A novel hierarchical framework applied to an Iberian endemic plant

Rare species have restricted geographic ranges, habitat specialization, and/or small population sizes. Datasets on rare species distribution usually have few observations, limited spatial accuracy and lack of valid absences; conversely they provide comprehensive views of species distributions allowing to realistically capture most of their realized environmental niche. Rare species are the most in need of predictive distribution modelling but also the most difficult to model. We refer to this contrast as the “rare species modelling paradox” and propose as a solution developing modelling approaches that deal with a sufficiently large set of predictors, ensuring that statistical models are not over-fitted. Our novel approach fulfils this condition by fitting a large number of bivariate models and averaging them with a weighted ensemble approach. We further propose that this ensemble forecasting is conducted within a hierarchic multi-scale framework. We present two ensemble models for a test species, one at regional and one at local scale, each based on the combination of 630 models. In both cases, we obtained excellent spatial projections, unusual when modelling rare species. Model results highlight, from a statistically sound approach, the effects of multiple drivers in a same modelling framework and at two distinct scales. From this added information, regional models can support accurate forecasts of range dynamics under climate change scenarios, whereas local models allow the assessment of isolated or synergistic impacts of changes in multiple predictors. This novel framework provides a baseline for adaptive conservation, management and monitoring of rare species at distinct spatial and temporal scales.