Suzanne E. Bayley

HUMAN ACTIVITY MEDIATES A TROPHIC CASCADE CAUSED BY WOLVES

Experimental evidence of trophic cascades initiated by large vertebrate predators is rare in terrestrial ecosystems. A serendipitous natural experiment provided an opportunity to test the trophic cascade hypothesis for wolves (Canis lupus) in Banff National Park, Canada. The first wolf pack recolonized the Bow Valley of Banff National Park in 1986. High human activity partially excluded wolves from one area of the Bow Valley (low-wolf area), whereas wolves made full use of an adjacent area (high-wolf area). We investigated the effects of differential wolf predation between these two areas on elk (Cervus elaphus) population density, adult female survival, and calf recruitment; aspen (Populus tremuloides) recruitment and browse intensity; willow (Salix spp.) production, browsing intensity, and net growth; beaver (Castor canadensis) density; and riparian songbird diversity, evenness, and abundance. We compared effects of recolonizing wolves on these response variables using the log response ratio between the low-wolf and high-wolf treatments. Elk population density diverged over time in the two treatments, such that elk were an order of magnitude more numerous in the low-wolf area compared to the high-wolf area at the end of the study. Annual survival of adult female elk was 62% in the high-wolf area vs. 89% in the low-wolf area. Annual recruitment of calves was 15% in the high-wolf area vs. 27% without wolves. Wolf exclusion decreased aspen recruitment, willow production, and increased willow and aspen browsing intensity. Beaver lodge density was negatively correlated to elk density, and elk herbivory had an indirect negative effect on riparian songbird diversity and abundance. These alternating patterns across trophic levels support the wolf-caused trophic cascade hypothesis. Human activity strongly mediated these cascade effects, through a depressing effect on habitat use by wolves. Thus, conservation strategies based on the trophic importance of large carnivores have increased support in terrestrial ecosystems.

Climate-induced changes in the dissolved organic carbon budgets of boreal lakes

During 20 years of climatic warming, drought and increased forest firesbetween 1970 and 1990, DOC concentrations declined by 15--25%in lakesof the Experimental Lakes Area, northwestern Ontario, allowing increasedpenetration of both UV and photosynthetically-active radiation (PAR), andcausing deeper euphotic zones and thermoclines. Decreased input to thelakes of DOC from terrestrial catchments and upstream lakes was theprimary reason for the decline, although in-lake removal also increasedslightly. Decreased streamflow caused by drought was more important thanforest fires in affecting DOC exports from catchments. Experimentalacidification of lakes caused even greater losses in DOC, by enhancing ratesof in-lake removal. DOC in Lake 302S, acidified to pH 4.5 during the1980’s, declined to less than 10% of preacidificationvalues.

Natural and man-caused factors affecting the abundance and cycling of dissolved organic substances in precambrian shield lakes

Effects of natural factors (drought and forest fire), and experimental perturbations (fertilization and acidification) on dissolved organic carbon (DOC) concentrations and ratios to other nutrients in lakes of the Experimental Lakes Area are examined using data obtained over a period of 20 years. DOC concentration, and the ratio of dissolved iron to DOC in lakes of the area were strongly correlated with the relative size of the catchment to the lake.

The mycorrhizal status of the dominant vegetation along a peatland gradient in southern boreal Alberta, Canada

We investigated the mycorrhizal status of the dominant vascular plant species occurring in ten peatlands along a bog—fen—marsh gradient in southern boreal Alberta in 1997. All members of the Ericaceae were ericoid mycorrhizal, and members of the Salicaceae and Pinaceae were ectomycorrhizal. Also, some members of the Salicaceae and Betulaceae were simultancously ecto- and vesicular-arbuscular mycorrhizal (VAM). Fruiting bodies of the known ectomycorrhizal fungal generaCortinarius, Lactarius, andRussula were collected in late fall. Furthermore, the cosmopolitan ectomycorrhizal taxonCenococcum geophilum was associated with trees and shrubs in all fens and bogs. VA-mycorrhizal fungi were not found in any of the dominant herbaceous plant species in these peatlands; however, vesicles suggesting the presence of VAM fungi were found inCalamagrostis canadensis in the riverine marsh andRubus chamaemorus in the bog. NeitherCarex species in fens and marshes, norTypha latifolia in the lacustrine marsh were mycorrhizal; however, microsclerotia, sclerotial plaques, septate, aseptate, and clamped hyphae were observed to grow on and within cortical cells of their roots. Many of these hyphae were dematiaceous and may belong to theMycelium radicis atrovirens complex (MRA), partially consisting of the endophytic fungal generaPhialocephala andLeptodontidium. Hyphac resemblingRhizoctonia were also observed, although definitive identifications were not attempted. The ecological significance of MRA genera remains largely unknown. Thus, the dominant vegetation in southern boreal bogs and fens is mycorrhizal, possibly enabling these plant species to proliferate in these nutrient-poor ecosystems by accessing otherwise unavailable nutrient pools. In contrast, marsh vegetation is generally non-mycorrhizal, possibly due to higher surface-water nutrient concentrations and fluctuating water levels.

Oil sands mining and reclamation cause massive loss of peatland and stored carbon

We quantified the wholesale transformation of the boreal landscape by open-pit oil sands mining in Alberta, Canada to evaluate its effect on carbon storage and sequestration. Contrary to claims made in the media, peatland destroyed by open-pit mining will not be restored. Current plans dictate its replacement with upland forest and tailings storage lakes, amounting to the destruction of over 29,500 ha of peatland habitat. Landscape changes caused by currently approved mines will release between 11.4 and 47.3 million metric tons of stored carbon and will reduce carbon sequestration potential by 5,734–7,241 metric tons C/y. These losses have not previously been quantified, and should be included with the already high estimates of carbon emissions from oil sands mining and bitumen upgrading. A fair evaluation of the costs and benefits of oil sands mining requires a rigorous assessment of impacts on natural capital and ecosystem services.

Aboveground net primary production along a bog-fen-marsh gradient in southern boreal Alberta, Canada

Abstract:Total aboveground plant production in a bog, three rich fens and two marshes were determined via the multiple harvest and cranked wire techniques. These peatlands follow a gradient of increasing pH, water flow, and surface water nutrient concentrations from the bog to the rich fens to the eutrophic marshes. The net primary production (NPP) values were as follows: (i) bog, 390 g m-2 year-1, (ii) three rich fens (riverine sedge fen, lacustrine sedge fen, and floating sedge fen), 409 g m-2 year-1, 277 g m-2 year-1 and 356 g m-2 year-1, respectively, and (iii) one riverine and one lacustrine marsh, 323 g m-2 year-1 and 757 g m-2 year-1, respectively. Overall, the bog and the three fens had a similar NPP but they were significantly less productive than the marshes. Along this bog-fen-marsh gradient, moss and shrub production decreased and herb production increased. Herb and moss production exhibited a greater variation between years than among sites within each year. Shrub production remained similar ...

ABOVEGROUND PEAT AND CARBON ACCUMULATION POTENTIALS ALONG A BOG-FEN-MARSH WETLAND GRADIENT IN SOUTHERN BOREAL ALBERTA, CANADA

Production-to-decomposition quotients and asymptotic limits of peat accumulation were determined to estimate peat and carbon accumulation potentials along a bog-fen-marsh wetland gradient in southern boreal Alberta. The wetlands were a bog, a poor fen (PF), a wooded moderate-rich fen (WRF), a lacustrine sedge fen (LSF), a riverine sedge fen (RSF), a riverine marsh (RM), and a lacustrine marsh (LM). First year mass losses increased along this gradient (bog 14%, fens 25–61%, marshes 57–62%), with second year total mass losses increasing from 18 to 38% from the bog to the moderate-rich fens. Ratios of aboveground net primary production to decomposition and asymptotic limits of peat accumulation showed decreasing trends from the bog to the fens to the marshes as decay rates increased along the same gradient. TheSphagnum-dominated sites (bog, PF) showed greater peat accumulation potentials than the brown moss-dominated sites (WRF, LSF) and those sites with an insignificant-to-no moss stratum (RSF, RM, LM), which is paralleled by their decreasing peat thicknesses. Rates of litter accumulation in the first year averaged 170 g m−2 yr−1 inSphagnum-dominated sites, 130 g m−2 yr−1 in brown moss-dominated sites, and 103 g m−2 yr−1 in sites with an insignificant-to-no moss stratum. All three wetland types showed similar carbon accumulation potentials (83, 67, and 50 g m−2 yr−1, respectively) after the first year of decomposition. Peat depth, asymptotic limits of peat accumulation, and production-to-decomposition ratios correlated negatively with water levels, pH, and Ca2+, and they correlated positively with moss and woody plant production (shrubs, trees). Peatlands with strong moss and shrub/tree strata (bog, PF, WRF) accumulate more peat than those wetlands dominated by graminoids (LSF, RSF, RM, LM). In the bog, high peat accumulation potentials may be related to low rates of decomposition. The peat accumulation potentials of some fens (PF, WRF) are similar to the bog and may be maintained by higher decomposition rates, which are offset by higher litter inputs. In the graminoid-dominated fens and marshes, peat accumulation potentials are lowest and may be related to higher litter quality, resulting in higher decomposition rates.

Decomposition along A moderate-rich fen-marsh peatland gradient in boreal Alberta, Canada

Losses of dry mass of the dominant litter, a standard litter (Carex aquatilis), and cellulose (Whatman filterpaper) were examined by the litter bag technique in three fens (riverine sedge fen, lacustrine sedge fen, floating sedge fen) and two marshes (lacustrine marsh, riverine marsh). LocalCarex lasiocarpa had a similar mass loss in marshes (mean of 63%) and in fens (mean of 59%) over 456 days in 1993 and 1994.Typha latifolia decomposed at a similar rate as the localC. lasiocarpa in the lacustrine marsh, whereasSalix pedicellaris decomposed significantly slower than the localC. lasiocarpa in the floating sedge fen (FSF). Overall, the mass loss of the standard plant litter was not significantly different between the fens (mean of 72%) and the marshes (mean of 69%). However, cellulose decomposed significantly faster in the marshes (mean of 67%) than it did in the fens (mean of 28%) over 100 days in 1994. Decay ofCarex aquatilis was best related to ammonium (NH4+) (r=0.73) in fens and the water level relative to the peat surface (r= 0.74) in marshes. Standard plant litter decomposition was best explained by surface water concentrations of NH4+(r=0.89) in fens and by soluble reactive phosphorus (SRP)(r=0.89) in marshes. Cellulose decomposition was best related to SRP in fens (r=0.70) and marshes (r=0.64) alike. An arithmetic/logarithmic decay model most accurately described plant mass losses during decomposition (59%) compared to the widely used logarithmic/arithmetic model (12%).

Aboveground plant production and nutrient content of the vegetation in six peatlands in Alberta, Canada

We examined the effects of water level, surface water chemistry, and climatic parameters on aboveground primary plant production, and the tissue nutrient concentrations in the dominant herb species in a bog, three fens, and two marshes. In the fens, total NPP correlated best with NO3- and total phosphorus surface water concentrations in 1993 and 1994. Total NPP in the marshes correlated best with alkalinity in 1993, and with soluble reactive phosphorus in 1994. Climatic parameters, such as mean annual growing season temperature, growing degree days, and precipitation, had the most notable effect on moss growth, whereas shrub and herb production correlated significantly with the water level relative to the moss surface. Herb production correlated positively and shrub production correlated negatively with the water level relative to the moss surface. Tissue nutrient concentrations of carbon (C), nitrogen (N), and total phosphorus (TP), and the C:N quotient in Carex lasiocarpa exhibited similar trends in the fens and the marshes. Carbon tissue concentrations in C. lasiocarpa remained unchanged, whereas N and TP tissue levels decreased throughout the growing season. In the site with the highest NPP and presumably the highest stand density, C. lasiocarpa exhibited the highest tissue N and TP levels. Furthermore, TP tissue concentrations in C. lasiocarpa were substantially higher in the marshes than in the fens. Tissue nutrient concentrations in Eriophorum vaginatum in the bog showed variable response patterns. N tissue levels increased, whereas tissue TP concentrations decreased from late June to late August. In the bog, E. vaginatum exhibited similar tissue TP levels to C. lasiocarpa in the fens; however, they were both substantially lower than those found in C. lasiocarpa from the marshes.

Effects of forest fire and drought on acidity of a base-poor boreal forest stream: similarities between climatic warming and acidic precipitation

In a boreal forest catchment in the Experimental Lakes Area in northwestern Ontario, wildfire caused an increase in the concentrations of strong acid anions and base cations of the stream. In the naturally base-poor Northwest (NW) Subbasin, a 1980 wildfire caused exports of strong acid anions to increase more than export of base cations, causing a 2.5 fold increase in the acidity of the stream. Mean annual stream pH declined from 5.15 prior to fire to 4.76 two years after fire. Acid-neutralizing capacity (ANC), calculated as the difference between total base cations and strong acid anions, decreased to 20% of pre-fire values. Sulfate and chloride were the strong acid anions responsible for the decline in ANC, increasing four-fold. While nitrate increased eleven-fold, concentrations were too low to significantly affect ANC. There was a significant correlation between weekly sulfate concentration and base cation concentration (r2 = 0.83) in the two years after fire. Recovery of ANC was caused by the more rapid decline in concentration of sulfate than by changes in base cations. Drought produced a similar but weaker response than fire, with increased sulfate concentrations and decreased stream pH. Climatic warming that increases drought and fire frequency would have effects that mimic the impacts of acidic precipitation (i.e. higher sulfate concentrations and acidic stream waters). Areas which have higher concentrations of stored S from past acid precipitation or have large areas of peatlands in the watershed may have aggravated losses of S and H+ after drought and fire.