Ecological Applications最新文献

Revealing the ecological impact of reclaimed water (RW) replenishment on bacterioplankton communities is crucial to promote RW utilization, yet less attention has been paid to the RW headwater urban stream with continuous RW recharge. Here, we collected water samples from Lujia stream to investigate the bacterioplankton community diversity, network, and assembly in spatiotemporal variation. Based on statistical analyses, bacterioplankton diversity in the midstream section was the lowest, especially in the dry season. Furthermore, spatial heterogeneity was more significant than seasonal heterogeneity for both biotic and abiotic factors. Dissolved oxygen and nitrite were the environmental driving factors of the bacterioplankton community in the wet and dry seasons, respectively. Intriguingly, a series of indicator bacteria related to nutrient nitrogen cycling were identified in the midstream section. Meanwhile, co-occurrence network analysis showed that the midstream section had the strongest competitive antagonism. Furthermore, the results of community assembly also showed that the midstream section harbored the highest proportions of stochastic processes, which were obviously different from the two other sections. Consequently, the midstream section was presumed to be a community coalescence area. Overall, our findings not only filled gaps in understanding the characteristics of bacterioplankton communities in long-term RW headwater urban streams but also highlighted the importance of the midstream section as a key objective of river restoration and management.

The misalignment of species adaptations with current environmental conditions can cause ecosystems to lose resilience, accumulate resilience debt, and transition to another state. Such a state change is evident in eastern North American broadleaf forests where dominant tree species are shifting from oaks (Quercus spp.) to mesophytic species such as maples (Acer spp.). The replacement of oaks is widespread and threatens the ecosystem services these forests provide, generating interest in using forest management to halt or reverse this change. The national Fire and Fire Surrogate (FFS) study was a large-scale study of forest management practices, and the Green River FFS site in western North Carolina (initiated in 2001) offers the opportunity to understand how management actions affect oak forest resilience. The Green River FFS site implemented three experimental treatments replicated across three spatial blocks: mechanical felling of saplings and ericaceous shrubs (Mech), prescribed fire (Fire), and a combination (Mech + Fire), which were compared to untreated controls (Control). Here, we used this long-running experiment to evaluate oak forest resilience by examining changes in overstory basal area and forest composition among overstory trees, saplings, and seedlings. We found that basal area increased in the Control and Mech treatments, was unchanged in the Fire treatment, and decreased in the Mech + Fire treatment as a result of mortality. Oak sapling abundances increased with reduced basal area, a pattern not found with the major mesophytic representative, maples. This suggests that oaks are well positioned to recruit to the overstory where basal area has decreased due to overstory mortality, and at the Green River FFS site, this was best achieved in the Mech + Fire treatment. Creating conditions where oak saplings have an advantage over maples requires the mortality of some overstory trees, including desirable oaks. Taken together, our findings suggest that the misalignment of oak traits and current environmental conditions has led to resilience debt, which may be reduced when management actions mimic a severe disturbance that results in the opening of the canopy. Thus, management actions that combine mechanical felling and repeated prescribed fires may promote sustained oak dominance in the future.

Climate change and novel fire regimes increasingly challenge stewardship of forests adapted to infrequent, stand-replacing fire. Novel fire regimes may disrupt mechanisms that sustained postfire regeneration historically, and whether fire management can promote forest resilience to future fires is uncertain. We used the individual-based forest simulation model iLand to explore how fire exclusion zones that mimic historical burn mosaics may affect postfire tree regeneration in conifer forests of Grand Teton National Park (Wyoming, USA). We asked: (1) How do the amount and configuration of potential fire exclusion zones influence postfire tree regeneration throughout the 21st century under alternative climate scenarios? (2) How do “operational” fire exclusion zones affect postfire tree regeneration within burned patches and across the landscape by the end of the 21st century? We first conducted a factorial simulation experiment with varying amounts (10%, 30%, 50% of the landscape) and configurations (dispersed vs. clumped) of fire exclusion zones. Informed by this experiment and logistical firefighting considerations, we developed an operational scenario in which we designated mature forests surrounded by defensible fuel breaks as fire exclusion zones. Simulations were conducted under four future climate scenarios (warm-wet, hot-wet, warm-dry, hot-dry), and postfire tree regeneration densities with fire exclusion zones were compared to reference scenarios without fire exclusion zones. Regeneration of fire-avoiding conifers (subalpine fir, Abies lasiocarpa and Engelmann spruce, Picea engelmannii) was consistently greater with fire exclusion zones, especially with ≥30% of the landscape in dispersed configuration. Fire exclusion zones had minimal effects on regeneration of fire embracers (lodgepole pine, Pinus contorta var. latifolia) and fire resisters (Douglas-fir, Pseudotsuga menziesii var. glauca). In the operational scenario, postfire regeneration of fire-avoiding species was greater compared to the reference scenario, especially in hot climate scenarios. Although regeneration of fire avoiders declined in operational and reference scenarios throughout the 21st century, regeneration densities were up to 10 times greater in the operational relative to the reference scenario. Our results suggest that mimicking historical burn mosaics by establishing fire exclusion zones could sustain seed sources and afford more time for subalpine conifer forests to adapt to a warmer world with more fire.

Retention harvests are promoted as an alternative to clearcuts to enhance ecological values in managed forests. Understanding how retention affects carbon (C) dynamics over time and in various forest types is important for balancing objectives like timber production and C storage. This is particularly crucial now, as the climate mitigating effects of boreal forests are weakening due to both forest harvests and natural disturbances. Using data from a relatively long-term experiment (pre-harvest to 18-years post-harvest) in previously unharvested boreal mixedwood forest, we compared C pools (mature trees, regenerating trees and shrubs, deadwood, and soil) among harvest levels (clearcuts, 10%, 20%, 50%, 75% retention, and unharvested reference). Soil C appeared to be invariant at the scale of this study, so we focused our analyses on biomass in living and dead vegetation. Total pre-harvest C storage was greater in conifer-dominated and mixed stands than in deciduous (broadleaf)-dominated stands, reflecting mainly greater biomass in live trees but also in downed deadwood. Net loss of C from the forest up to 3-years post-harvest scaled with harvest intensity in all forest types. At 3- and 18-years post-harvest in deciduous and 3-years post-harvest in conifer stands, all retention harvests resulted in larger C stocks than clearcuts; only higher retention levels provided this benefit at 3- and 18-years post-harvest in mixed (75% retention) and at 18 years in conifer stands (50%, 75% retention). In some forest types, the highest retention levels (75% for deciduous and mixed stands, 50% and 75% for conifer stands) maintained total C stocks statistically equivalent to unharvested forest at both 3- and 18-years post-harvest. Deciduous stands became net C sinks by 3–7 years post-harvest, likely due to prolific aspen regeneration and growth. Mixed and conifer stands, however, were nearly C-neutral or were C sources until 12–18 years post-harvest. This reflected persistent effects of pre-harvest forest type, including less aspen regeneration, slower growth of conifer seedlings, and mortality of retained conifers. Our results suggest that strategic retention harvesting could serve as a practical option to couple C storage options to other management considerations.

Prey depletion, direct poaching, and habitat fragmentation are driving global declines of carnivore species, but the specific consequences of these impacts on population demography have not been widely studied, obscuring an understanding of why some populations recover while others flounder. This 11-year study sought to uncover what constrains recovery of a low-density tiger population in Thailand, by investigating population dynamics with respect to three key mechanisms potentially affecting vital rates: tiger poaching, prey depletion, and immigration. Our site resembled most Southeast Asian tiger populations in that tiger and prey abundance were both low, but it was unusual in sharing landscape connectivity with the largest tiger population remaining in Southeast Asia. We identified tigers with camera traps and applied a Pradel robust design model to estimate survival, recruitment, immigration, and population growth rate. We obtained information on cub production through observations of dependent young with their mother. The small population (7–11 adults) was stable over time but did not increase ($��\lambda �$ = 1.006). This inertia corresponded with the status of key prey species, which occurred at low density and had flat population trends. Female survival rate was high (0.823), but reproduction rate (0.514) and cub survival (0.313) were 2–3 times lower than other tiger populations in Asia where prey availability is higher. This pattern of flat population trend, high adult survival, and low reproduction is indicative of the effects of prey scarcity, rather than direct poaching, as the essential constraint on recovery. Most recruitment of new tigers came from immigration, with 67% of the resident females being born outside, rather than locally. High female survival plus immigration were critical to sustaining this population, and represent an essential foundation for future recovery, but this potential is impeded by prey scarcity which suppresses reproductive success. Managers can unblock the path to recovery by increasing abundance and distribution of preferred prey. This would allow resident females to reproduce more consistently and boost survival rates of their cubs, while creating new high-quality habitats for additional females to settle in, whether they are locally born or arrive through immigration.

Predicting the outcomes of land management on biodiversity is difficult without a mechanistic understanding of how management approaches, ecosystem structure, environmental conditions, and biodiversity interact. Management effects may be direct or indirect, context- or scale-dependent, or obscured by local environmental conditions. Resolving these relationships at the regional scale may be difficult, given heterogeneity in local environmental conditions, yet understanding broad-scale patterns can elucidate context dependencies and improve restoration outcomes. We confronted these challenges within globally rare oak savannas in the midwestern United States, which have been altered by fire exclusion and resulting woody encroachment. By modeling direct and indirect pathways by which management influences diversity, we test a general framework for savanna restoration. Across 100 oak savannas spanning five US states, management by prescribed fire and mechanical thinning of woody vegetation affected groundlayer plant species richness through changes to ecosystem structure (canopy openness and litter depth), and these effects were both context- and scale-dependent. Frequent prescribed fires and canopy thinning promoted greater canopy openness, which in turn increased richness at small (1 m²), but not larger (1000 m²) scales. Frequent fire additionally increased richness at small and larger scales through effects independent of ecosystem structure. While management effects were large relative to the influence of local edaphic conditions, soil productivity had two largely offsetting effects on small-scale richness, increasing richness directly but decreasing richness indirectly by promoting closed canopy structure. These results suggest using a combination of fire and canopy thinning to reverse the effects of decades of fire exclusion. However, management effects were also context-dependent, emphasizing that management outcomes vary regionally. Here, 1-m² plant species richness increased with both fire frequency and canopy thinning under low, but not high, productivity soil conditions. By demonstrating how specific management practices influence savanna structure and biodiversity by manipulating ecological processes across broad geographic and edaphic gradients, our findings provide a framework for understanding management outcomes at short and medium intervals (e.g., within and between decades, respectively), in the form of a model that can be refined by testing additional hypotheses to better predict savanna restoration outcomes.

The extensive restoration of fragmented woodlands calls for practices appropriate to large-scale efforts. These simultaneously require an understanding of ecosystem-level processes and the plant-scale environment. The recruitment niche of the target species is crucial, that is conditions required for seed germination to seedling establishment. Our study contributes to underpinning the science behind successfully promoting the utilization of natural regeneration in woodland restoration in a subarctic environment. We identified the recruitment niche of the only native forest-forming species in Iceland. From 2018 to 2020, we quantified mountain birch seed accumulation, germination, and early seedling survival in relation to substrate types within 500-m-long transects at two study sites on Skeiðarársandur outwash plain, southeast Iceland. At the time of the study, the founding population in this early successional environment had recently reached reproductive maturity. Mountain birch seeds were most likely to accumulate on vegetated surfaces and to germinate in low-growing vegetation, with unimpeded sunlight. Survival was not significantly influenced by substrate types, but was surprisingly high (generally >50%) for the first 1–2 years, although most seedlings were still very small. Overall, recruitment was consistently greater than expected in thin moss (~1 cm), which may be considered a key substrate type for mountain birch recruitment success. Due to high cover of suitable substrate types in the study area, the spatial pattern of the first locally recruited generation of mountain birch was determined at the earliest life history stage, by dispersal limitation. Our study highlights the importance of the recruitment niche for successful restoration and of securing seed input when dispersal may be limited. This allows for scaling up the restoration of severely fragmented woodlands, for which the pending restoration of Icelandic woodlands serves as a case study. The rapid mountain birch establishment on Skeiðarársandur shows that woodland restoration may not need major interventions; however, they must be based on profound knowledge of colonizing processes. Thus, restoration with minimal human assistance can be a practical, low-cost option.

Restoring populations of native keystone species can increase landscape resilience to global change when those species create or modify ecosystems. The North American beaver (Castor canadensis) is an ecosystem engineer that increases river water storage and residence time, increasing fire resilience at the landscape level. Beaver populations in North America are significantly lower than they were historically, but over the last decade, beavers have been increasingly recognized for their ecosystem services, and reintroduction efforts throughout their historic range have become more prevalent. Here, we modeled potential beaver dam-building capacity, associated surface water storage, and fire resilience in California's Sierra Nevada, a region at high risk of drought and wildfire. We estimate that 51% of beaver dam-building capacity remains in this region compared to historical levels, and considerable dam capacity remains in all watersheds. Our conservative estimates suggest that beaver dams have the potential to store a total of 120 million m³ of surface water and create 2200 km² of fire resilience in high fire risk areas. Additionally, streams where beavers have the potential to create the greatest water and fire benefits due to physical landscape and habitat characteristics are frequently found within watersheds that are at high risk for both drought and fire. Specifically, we identified five priority watersheds that have both high risk for drought and fire impacts, and have high potential to benefit from beaver conservation and restoration. Even in areas where fire and drought are less probable, the reestablishment of beavers will likely provide similar benefits. This unique approach to quantifying potential beaver benefits illustrates that wildlife can increase resilience to global change stressors and suggests that biodiversity and nature-based climate solutions are intertwined.

Evaluation of tidal marsh restoration success is typically based on the recovery of habitat size and target species. However, food-web structure may provide valuable insight into ecosystem functioning trajectories. Here, we studied restored tidal marshes of different ages (new, young, old; spanning 1–150 years) in comparison with nearby reference sites along the San Francisco Estuary. We asked: (1) How does restoration help recover energy pathways that support fishes? (2) Do fishes rely more on algal versus detrital pathways in restored sites?; and (3) How does food-web structure vary as a function of species origin and life history? To answer these questions, we sampled fish (n = 806) and basal resources (emergent vegetation and phytoplankton; n = 109) seasonally over two hydrologically contrasting years. Using stable isotopes (δ¹³C, δ¹⁵N, and δ³⁴S), we calculated fish isotopic niche volumes, food chain lengths, and the relative importance of algal versus detrital energy pathways. We found that food chains in restored sites were 8% shorter than in their paired reference sites. Additionally, the young and old restored sites had 37% smaller niche volumes than their references, but the opposite was true for the new restored site (11% larger), illustrating the characteristic trophic surge of early succession. Fishes found in restored sites relied significantly less on detrital energy (7% less) than fishes found in reference sites, and resident fishes showed 12% higher reliance on the detrital pathway than transient species. Finally, most of the native niche volume overlapped with that of introduced fish, which was in turn 38% larger, and a similar pattern was observed when comparing resident to transient fish. Our findings demonstrate that food-web structure does not immediately recover with tidal marsh restoration, even if fish assemblages are species-rich; and show that transient trophic surges may complicate restoration success assessments of newly restored marshes. We contend that incorporating recovery of energy pathways as an indicator of performance may help strengthen monitoring and design of wetland ecosystem restoration projects.

Global changes present significant challenges to biodiversity. However, how plant communities respond to climate change under various anthropogenic disturbances, and how different species groups contribute to these responses, remains poorly understood. Using an 8-year dataset from a temperate grassland and a multidimensional diversity framework (taxonomic, functional, and phylogenetic), we explored the interactive effects of climate change and anthropogenic disturbances (grazing, fertilization, and their combination). We found that (1) increasing water availability consistently boosted multidimensional plant diversity over time across all treatments. (2) However, disturbances, particularly their combination, weakened this positive climatic effect. (3) Differentiating the contributions of rare, common, and dominant species revealed contrasting responses to climate drivers, highlighting the importance of a multidimensional assessment. Grazing also heightened the community's sensitivity to climate change. Our study reveals that anthropogenic disturbances fundamentally modify plant community responses to climate change, providing critical insights for biodiversity conservation and sustainable grassland management under future climate scenarios.