Sierra Nevada meadows experienced intense livestock grazing in the 19th Century, resulting in a shift from deep-rooted highly productive perennial clonal sedges to short-lived and shallow-rooted plants. The current meadow vegetation contains >20% bare ground and <10% cover of highly-productive clonal sedges and rushes. We hypothesized that the existing vegetation was insufficiently productive to have formed or to maintain the 2000-year-old carbon-rich meadow soils. We established a multiyear experiment (2016-2019) to determine if planting Carex scopulorum seedlings into Tuolumne Meadow, in Yosemite National Park, could reverse the impacts of legacy grazing and restore the soil carbon storage function. Planted C. scopulorum had a high survival rate over four years (75.2%) with slow but significantly-increasing belowground biomass production (1.34 g plant-1 yr -1). Field-measured and gap-fill modeled carbon fluxes indicate an annual average ecosystem respiration (ER) of 0.96 kg C m-2 yr-1 and gross primary productivity (GPP) of 0.59 kg C m-2 yr-1, resulting in a net ecosystem exchange (NEE) loss of 0.37 kg C m-2 yr-1. This represents an annual loss of 1.3% of the 29.4 kg C m-2 of soil organic carbon. The transplanted sedges would need to increase meadow GPP by 63%, or ER decreases by 39%, to achieve a net annual storage of soil carbon to reestablish the processes that formed the organic rich soil. Active planting to increase the currently sparse high-productivity plant species is a good option to boost GPP, but climate change could accelerate ER and increase net ecosystem carbon loss.

Modification of food webs is a frequent cause of shifts in ecosystem states that resist reversal when the food web is restored to its original condition. We used the restoration of the large carnivore guild including gray wolves (Canis lupis), cougars (Felis concolor), and grizzly bears (Ursus arctos horribilis) to the northern range of Yellowstone National Park as a model system to understand how ecosystems might resist reconfiguration after the restoration of apex predators to the food web. The absence of wolves, cougars, and grizzly bears for nearly a century from the northern range was the primary cause of dramatic changes in riparian plant communities. Willows (Salix spp.) were suppressed in height by intense browsing by the dominant herbivore, elk (Cervus canadensis). The loss of activity by beavers (Castor canadensis) coincided with the loss of tall willows. We hypothesized that intense elk browsing interrupted the mutualism between willow and beavers: ecosystem engineering by beavers was a critical component of willow habitat and tall willows were a critical component of habitat for beavers. This interruption made riparian communities resilient to the disturbance caused by the restoration of apex predators. We hypothesized further that reductions in elk browsing attributable to reductions in elk population size were not sufficient to prevent the suppression of willow growth. To test these hypotheses, we conducted a 20-year, factorial experiment that crossed simulated beaver dams with the exclusion of browsing. We found that willows grew to heights expected for restored communities only in the presence of dams and reduced browsing. Willows experiencing ambient conditions remained well below this expectation. We found no difference in heights or growth rates of willows in experimental controls and willows in 21 randomly chosen sites, confirming that the results of the experiment were representative of range-wide conditions. A reorganized community of large herbivores was implicated in the suppression of willow growth. We conclude that the restoration of large carnivores to the food web failed to restore riparian plant communities on Yellowstone's northern range, supporting the hypothesis that this ecosystem is in an alternative stable state caused primarily by the extirpation of apex predators during the early 20th century.

Dataset of soil carbon stocks collected from tropical mountain peatlands in Sajama, Bolivia.

Adding chipped wood to soil ameliorates compaction, allowing faster plant growth that is critical to successful wetland restorations. Following the filling and planting of an erosion gully in Halstead Meadow, Sequoia National Park, the tallest leaf height and maximum clone width of transplanted Scirpus microcarpus seedlings were negatively correlated with soil compaction. Plant height decreased by 9.8 cm and width decreased by 11.9 cm per MPa of soil compaction (range of 0.74–4.50 MPa). We experimentally amended mineral soil in a test trench and found that every 0.10 cm3/cm3 addition of wood chips (range of 0.00–0.75 cm3/cm3) reduced compaction by 0.174 MPa. Had the Halstead Meadow gully fill contained an equivalent volume of wood chips to the reference area soil organic matter content (0.64 cm3/cm3), we predict compaction would have been reduced by 1.11 MPa, increasing individual transplant width spread by 36%, approximately doubling the vegetated area after two growing seasons. In a greenhouse phytometer experiment, conifer bark leachate (phenolics 211 mg/L) significantly reduced plant growth and, in the presence of added nutrients, increased the production of the enzyme polyphenol oxidase (PPO). However, phenolics concentration in bark‐free conifer wood leachate (12 mg/L), similar to field‐sampled concentrations, did not affect plant growth or PPO production. Pure conifer bark is not recommended as a soil amendment, but the addition of low‐bark‐content wood chips to gully fill may be a feasible and effective means of reducing soil compaction, accelerating plant establishment, and lowering wetland restoration project costs.

The population model used to generate a static age distribution of a stable willow population.

Invasive species have had well-documented impacts to native biodiversity in many locations around the world via predation, competition, parasitism, and/or habitat or ecosystem process modification (Pimentel, Zuniga & Morrison 2005; McGeoch et al. 2010). However, many non-native species integrate into native ecosystems without having quantifiably significant negative impacts (Daehler & Carino 2000), or are even intentionally introduced for their beneficial effects (Howarth 1991), which can sometimes lead to unforeseen negative outcomes (Louda 1997). However, the terminology surrounding non-native species is not standardized (Colautti & MacIsaac 2004), and so labels such as “invasive”, “weed”, and “noxious” are often attached to non-native species without significant supporting science documenting their implied negative impacts to native ecosystems and resources. Because invasive species can be extremely difficult to eradicate once established, it is prudent and costeffective to accurately identify which species are currently, or are likely to be, causing harm to ecosystems (Keller, Lodge & Finnoff 2007).

A broad sample of 79 montane fens in the Sierra Nevada revealed that underlying geology and topography exert strong control over the distribution and vegetation of these ecosystems. Distinct granodiorite, metamorphic, volcanic, carbonate and serpentine bedrock geology resulted in very different water chemistry, which had significant effects on the particular plant species found at each site. Wide-ranging values of pH (4.28–8.00) and dissolved cation concentrations (1.6–62.0 mg L^-1^) spanned the categories of transitional poor–rich to extremely rich fens. The vegetation of a pair of fens on carbonate bedrock and two floating mat fens was markedly different from the vegetation recorded at any other study sites. Once these outlier fens were removed from the analyses, the environmental variables that correlated most closely with the vegetation data were pH, altitude, presence of volcanic bedrock and fen slope. The measured environmental parameters explained 9.7 % of the variability in the vegetation data. Species richness was primarily (and negatively) correlated with altitude. Peat thickness (15–253 cm) was constrained in smaller catchments and on steeper slopes, and was positively correlated with soil organic matter content (16–92 %). Of the four typical fen landforms (bedrock contact, slope, spring mound and basin), sloping fens were the most common (63 % of the 79-fen sample).

Study Region: We analyzed the effects of groundwater pumping on a mountain wetland complex, Yosemite National Park, California, USA.Study Focus: Groundwater pumping from mountain meadows is common in many regions of the world. However, few quantitative analyses exist of the hydrologic or ecological effects of pumping.New Hydrological Insights for the Region: Daily hydraulic head and water table variations at sampling locations within 100 m of the pumping well were strongly correlated with the timing and duration of pumping. The effect of pumping varied by distance from the pumping well, depth of the water table when the pumping started, and that water year's snow water equivalent (SWE). Pumping in years with below average SWE and/or early melting snow pack, resulted in a water table decline to the base of the fen peat body by mid summer. Pumping in years with higher SWE and later melting snowpack, resulted in much less water level drawdown from the same pumping schedule. Predictive modeling scenarios showed that, even in a dry water year like 2004, distinct increases in fen water table elevation can be achieved with reductions in pumping. A high water table during summers following low snowpack water years had a more significant influence on vegetation composition than depth of water table in wet years or peat thickness, highlighting the impact of water level drawdown on vegetation. (C) 2014 The Authors. Published by Elsevier B.V.

(1) The high-altitude (4,500+ m) Andean mountain range of north-western Bolivia contains many peatlands. Despite heavy grazing pressure and potential damage from climate change, little is known about these peatlands. Our objective was to quantify carbon pools, basal ages and long-term peat accumulation rates in peatlands in two areas of the arid puna ecoregion of Bolivia: near the village of Manasaya in the Sajama National Park (Cordillera Occidentale), and in the Tuni Condoriri National Park (Cordillera Real). (2) We cored to 5 m depth in the Manasaya peatland, whose age at 5 m was ca. 3,675 yr. BP with a LARCA of 47 g m^-2^ yr^-1^. However, probing indicated that the maximum depth was 7–10 m with a total estimated (by extrapolation) carbon stock of 1,040 Mg ha^-1^. The Tuni peat body was 5.5 m thick and initiated ca. 2,560 cal. yr. BP. The peatland carbon stock was 572 Mg ha^-1^ with a long-term rate of carbon accumulation (LARCA) of 37 g m^-2^ yr^-1^. (3) Despite the dry environment of the Bolivian puna, the region contains numerous peatlands with high carbon stocks and rapid carbon accumulation rates. These peatlands are heavily used for llama and alpaca grazing.

Loheide et al.(2009) proposed a conceptual framework describing the groundwater-ecosystem connection in wet meadows of the Sierra Nevada and Cascade Ranges. This framework, based on field observations and hydrologic modeling, provides an understanding of how groundwater flow processes, both within meadow aquifers and at the watershed scale, affect vegetation patterning in the meadow. In the models presented, meadows with higher hydraulic conductivity than the surrounding bedrock were considered.

Abstract An ecological analysis of wetlands in the high mountain jalca above 3700 m elevation in the Andes near Cajamarca, Peru, indicated that most wetlands are groundwater-supported peat-accumulating fens. The floristic composition of fen communities was controlled largely by groundwater chemistry, which was highly variable and influenced by watershed bedrock composition. Watersheds with highly mineralized rock discharged water as acidic as pH 3.7, which was high in CaSO4, while watersheds with limestone, marble, and skarn produced groundwater as basic as pH 8.2 and high in CaHCO3. Of the 125 plots sampled in 36 wetland complexes, >50% of plots had at least 3 m of peat, and 21 plots had peat thicker than 7 m. Most soil horizons analyzed had 18 to 35% organic carbon, indicating high C storage. A total of 102 vascular plants, 69 bryophytes, and 10 lichens were identified. Study plots were classified using TWINSPAN into 20 plant communities, which were grouped into four broad categories by dominant life form: (1) cushion plant communities, (2) sedge- and rush-dominated communities, (3) bryophyte and lichen communities, and (4) tussock grass communities. Direct gradient analysis using canonical correspondence analysis indicated that Axis 1 was largely a water chemistry gradient, while Axis 2 was a complex hydrology and peat thickness gradient. Bryophytes and lichens were more strongly separated in the ordination space than vascular plants and were better indicators of specific environmental characteristics.

Meadows of the Sierra Nevada and Cascade mountains of California, USA, support diverse and highly productive wet-meadow vegetation dominated by sedges, rushes, grasses, and other herbaceous species. These groundwater–dependent ecosystems rely on the persistence of a shallow water table throughout the dry summer. Case studies of Bear Creek, Last Chance, and Tuolumne meadow ecosystems are used to create a conceptual framework describing groundwater–ecosystem connections in this environment. The water requirements for wet-meadow vegetation at each site are represented as a water-table-depth hydrograph; however, these hydrographs were found to vary among sites. Causes of this variation include (1) differences in soil texture, which govern capillary effects and availability of vadose water and (2) elevation-controlled differences in climate that affect the phenology of the vegetation. The field observations show that spatial variation of water-table depth exerts strong control on vegetation composition and spatial patterning. Groundwater-flow modeling demonstrates that lower hydraulic-conductivity meadow sediments, higher groundwater-inflow rates, and a higher ratio of lateral to basal-groundwater inflow all encourage the persistence of a high water table and wet-meadow vegetation, particularly at the margin of the meadow, even in cases with moderate stream incision.

Wet meadow ecosystems in the highly seasonal climate of the Sierra Nevada, CA, depend on groundwater throughout the dry summer growing season. Meadows in California that have been extensively studied will be used to demonstrate the influence of hydrologic processes on vegetation patterning. These examples will include data on vegetation compostition, water table depth, and remotely sensed images of vegetation patterning.

A decline in the stature and abundance of willows during the 20th century occurred throughout the northern range of Yellowstone National Park, where riparian woody-plant communities are key components in multiple-trophic-level interactions. The potential causes of willow decline include climate change, increased elk browsing coincident with the loss of an apex predator, the gray wolf, and an absence of habitat engineering by beavers. The goal of this study was to determine the spatial and temporal patterns of willow establishment through the 20th century and to identify causal processes. Sampled willows established from 1917 to 1999 and contained far fewer young individuals than was predicted from a modeled stable willow population, indicating reduced establishment during recent decades. Two hydrologically distinct willow establishment environments were identified: fine-grained beaver pond sediments and coarse-grained alluvium. Willows established on beaver pond sediment earlier in time, higher on floodplain surfaces, and farther from the current stream channel than did willows on alluvial sediment. Significant linear declines from the 1940s to the 1990s in alluvial willow establishment elevation and lateral distance from the stream channel resulted in a much reduced area of alluvial willow establishment. Willow establishment was not well correlated with climate-driven hydrologic variables, but the trends were consistent with the effects of stream channel incision initiated in ca. 1950, 20-30 years after beaver dam abandonment. Radiocarbon dates and floodplain stratigraphy indicate that stream incision of the present magnitude may be unprecedented in the past two millennia. We propose that hydrologic changes, stemming from competitive exclusion of beaver by elk overbrowsing, caused the landscape to transition from a historical beaver-pond and willow-mosaic state to its current alternative stable state where active beaver dams and many willow stands are absent. Because of hydrologic changes in streams, a rapid return to the historical state may not occur by reduction of elk browsing alone. Management intervention to restore the historical hydrologic regime may be necessary to recover willows and beavers across the landscape.

In order to understand how human impacts relate to the hydrology of Tuolumne Meadows, we first examine the basin, including basin geology, surface water contributions, surface water delivery to the meadows, and human water use and water supplies. This section focuses on summer 2006 but also uses surface discharge measurements from the Yosemite Hydroclimate Study (Lundquist et al. 2003), which has been operational since summer 2001, to place 2006 in context. Specifically, we address three questions: 1) What are the surface water contributions to Tuolumne Meadows and how did flow volumes change through the 2006 study period? 2) How do surface water fluctuations influence subsurface water tables? 3) How is surface drainage affect by the road, specifically related to culvert locations and functionality?