Line Rochefort

North American approach to the restoration of Sphagnum dominated peatlands

Sphagnum dominated peatlands do not rehabilitate well after being cutover (mined) for peat and some action needs to be taken in order to restore these sites within a human generation. Peatland restoration is recent and has seen significant advances in the 1990s. A new approach addressing the North American context has been developed and is presentedin this paper. The short-term goal of this approach is to establish a plant cover composed of peat bog species and to restore a water regime characteristic of peatland ecosystems. The long-term objective is to return the cutover areas to functional peat accumulating ecosystems. The approach developed for peatland restoration in North America involves the following steps: 1)field preparation, 2) diaspore collection, 3) diaspore introduction, 4) diaspore protection, and 5) fertilization. Field preparation aims at providing suitable hydrological conditions for diaspores through creation of microtopography and water retention basins, re-shaping cutover fields and blocking ditches. It is site specific because it depends largely onlocal conditions. The second step is the collection of the top 10 centimetres of the living vegetation in a natural bog as a source of diaspores. It is recommended to use a ratio of surface collected to surface restored between 1: 10 and 1: 15 in order to minimize the impact on natural bogs and to insure rapid plant establishment in less than four years. Diaspores are then spread as a thin layer on the bare peat surfaces to be restored. It has been demonstrated that too scant or too thick a layer decreases plant establishment success. Diaspores are then covered by a straw mulch applied at a rate of 3 000 kg ha-1 which provides improved water availabilityand temperature conditions. Finally, phosphorus fertilization favours more rapid substrate colonization by vascular plants, which have been shown to help stabilize the bare peat surface and act as nurse plants to the Sphagnum mosses.

Energy and moisture considerations on cutover peatlands: surface microtopography, mulch cover and Sphagnum regeneration

This study examined (i) the effect of artificially created microtopography and straw mulch on the soil moisture and (ii) energy balance and the establishment of a Sphagnum cover on a cutover peatland. Straw mulch caused rainfall interception approaching 2 mm per event. Although interception represented 44% of the total rainfall over the measurement period, water that evaporated from the mulch used energy that would otherwise have been used to evaporate soil water. Thus, the net effect of interception by mulch was negligible. The soil heat flux below the mulch was only 13% of the bare soil value and was decoupled from the daily net radiation. Net radiation over the bare soil was 15% greater than over the mulch. However, because of the greater heat flux into the bare peat, the energy available for sensible and latent heat fluxes was similar between the mulch covered and bare peat. Average evaporation from mulch and bare soil was estimated to be 2.6 and 3.1 mm d 1 , respectively. Soil water tension 1 cm below the surface remained above 100 cm (mb) all season (100% of the time) when a mulch was used, compared to only 30% of the time in the bare soil. Correspondingly, the water table was sustained above the 40 cm depth, 60% of time in the mulch covered site, compared to only 40% of the time in the bare peat site. Negative relief

Response of vegetation and net ecosystem carbon dioxide exchange at different peatland microforms following water table drawdown

[1] Northern peatlands are significant stocks of terrestrial soil carbon, and it has been predicted that warmer temperatures and lower water tables resulting from climate change will convert these ecosystems into sources for atmospheric carbon dioxide (CO2). However, these predictions do not consider the potential for hydrologically induced ecological succession or the spatial variability of carbon accumulation rates between different microforms in peatlands. To address these issues, the vegetation community was described, and the rates of gross ecosystem photosynthesis (GEP), ecosystem respiration (Rtot) and net ecosystem CO2 exchange were determined along poor fen microtopographic gradients at a control site and at a site which experienced a water table drawdown of � 20 cm 8 years prior to the study (drained). Sampling plots within these sites were classified as microforms of hummocks, lawns, or hollows. The coverage of Sphagnum moss declined on drained hummocks, drained lawns were invaded by sedges, and hollows shifted from open water plots at the control site to Sphagnum-dominated plots with sparse vascular plant cover at the drained site. As a result, Rtot was significantly greater at the drained site at all microforms while maximum rates of GEP declined at drained hummocks and were enhanced at drained lawns and hollows compared to similar control microforms. These results suggest that predictions about the response of northern peatland carbon exchange to climate change must consider the interaction between ecology and hydrology and the differential responses of microforms related to their initial ecohydrological conditions.

Trophic Interactions in a High Arctic Snow Goose Colony

Abstract We examined the role of trophic interactions in structuring a high arctic tundra community characterized by a large breeding colony of greater snow geese (Chen caerulescens atlantica). According to the exploitation ecosystem hypothesis of Oksanen et al. (1981), food chains are controlled by top-down interactions. However, because the arctic primary productivity is low, herbivore populations are too small to support functional predator populations and these communities should thus be dominated by the plant/ herbivore trophic-level interaction. Since 1990, we have been monitoring annual abundance and productivity of geese, the impact of goose grazing, predator abundance (mostly arctic foxes, Alopex lagopus) and the abundance of lemmings, the other significant herbivore in this community, on Bylot Island, Nunavut, Canada. Goose grazing consistently removed a significant proportion of the standing crop (∼40%) in tundra wetlands every year. Grazing changed plant community composition and reduced the production of grasses and sedges to a low-level equilibrium compared to the situation where the presence of geese had been removed. Lemming cyclic fluctuations were strong and affected fox reproduction. Fox predation on goose eggs was severe and generated marked annual variation in goose productivity. Predation intensity on geese was closely related to the lemming cycle, a consequence of an indirect interaction between lemming and geese via shared predators. We conclude that, contrary to the exploitation ecosystem hypothesis, both the plant/herbivore and predator/prey interactions are significant in this arctic community.

Sphagnum regeneration on bare peat surfaces : field and greenhouse experiments

The re-establishment of Sphagnum mosses on bare peat surfaces is one of the main challenges faced in the restoration of post-harvested peatlands. One suggested approach to ensure moss recolonization is to use fragments of Sphagnum plants collected from a natural area as diaspores. The regeneration and recolonization potential of fragments of different species of Sphagnum were tested on bare peat, both in the field and in a greenhouse. We examined how diaspore size, density and depth of origin influence recolonization and re-establishment success. The greenhouse experiment also tested the impact of water level on Sphagnum regeneration and recolonization. Field and laboratory experiments showed that only the surface layer (0-10 cm) of a peat profile contained enough viable material to be of practical use as a source of diaspores. Small (0.5-cm), medium (1-cm) or large (2-cm) diaspores had similar recolonization success. Obtaining a precise and even size of fragments will not, therefore, be an important aspect to consider when scaling up to the quantities needed for restoring large surfaces. Greenhouse experiments showed that water level in the peat column greatly influences the recolonization success of Sphagnum diaspores. Most species reacted positively to wetter conditions, with the notable exception of S. fuscum. A density of 450 Sphagnum plants per m 2 resulted in some Sphagnum species covering up to 50% of the peat surface in 3 months and 100% in 6 months, when the water table was close to the peat surface in the greenhouse experiment. Sphagnum cover reached 5-10% after 3 mqnths in the drier treatments of the greenhouse experiment and was generally comparable to the results obtained in the field after one season of growth under shade cloth. Improving the humidity conditions offered to diaspores is by far the most promising approach to reduce the quantity of diaspores needed to re-establish a significant moss cover rapidly on a post-harvested surface. The selection of appropriate species and densities according to the dryness of the surface to be restored are two other elements to consider in minimizing the amount of source material needed for restoration.

LANDSCAPE CHARACTERISTICS INFLUENCE POND OCCUPANCY BY FROGS AFTER ACCOUNTING FOR DETECTABILITY

2 Departement de phytologie, Pavillon Paul-Comtois, UniversiteLaval, Quebec, Quebec, G1K 7P4, Canada Abstract. Many investigators have hypothesized that landscape attributes such as the amount and proximity of habitat are important for amphibian spatial patterns. This has produced a number of studies focusing on the effects of landscape characteristics on am- phibian patterns of occurrence in patches or ponds, most of which conclude that the land- scape is important. We identified two concerns associated with these studies: one deals with their applicability to other landscape types, as most have been conducted in agricultural landscapes; the other highlights the need to account for the probability of detection. We tested the hypothesis that landscape characteristics influence spatial patterns of amphibian occurrence at ponds after accounting for the probability of detection in little-studied peatland landscapes undergoing peat mining. We also illustrated the costs of not accounting for the probability of detection by comparing our results to conventional logistic regression anal- yses. Results indicate that frog occurrence increased with the percent cover of ponds within 100, 250, and 1000 m, as well as the amount of forest cover within 1000 m. However, forest cover at 250 m had a negative influence on frog presence at ponds. Not accounting for the probability of detection resulted in underestimating the influence of most variables on frog occurrence, whereas a few were overestimated. Regardless, we show that conven- tional logistic regression can lead to different conclusions than analyses accounting for detectability. Our study is consistent with the hypothesis that landscape characteristics are important in determining the spatial patterns of frog occurrence at ponds. We strongly recommend estimating the probability of detection in field surveys, as this will increase the quality and conservation potential of models derived from such data.

Peatland restoration: A brief assessment with special reference to Sphagnum bogs.

Recent literature on peatland restorationindicates as a general goal repairing orrebuilding ecosystems by restoringecosystem structure, trophic organization,biodiversity, and functions to thosecharacteristic of the type of peatland towhich the damaged ecosystem belonged, or atleast to an earlier successional stage.Attainment requires provision of anappropriate hydrological regime,manipulating surface topography, improvingmicroclimate, adding appropriate diaspores,manipulating base status where necessary,fertilizing in some cases, excludinginappropriate invaders, adaptively managingthrough at least one flood/drought cycle toensure sustainability, and monitoring on ascale of decades. Several matchingconditions favoring or opposing restorationare suggested.In the restoration of peatlands, successeshave generally been those of short-termrepair. Periods of restoration have beenmuch too short to ensure progression to, oreven well toward, a fully functionalpeatland reasonably compatible with thepristine state of similar peatlandselsewhere, although with altered surfacepatterns.Long-term monitoring ofpeatland-restoration projects is essentialfor a better understanding of how to carryout such restoration successfully.Paleoecology is suggested as anunderutilized tool in peatlandrestoration.

The natural revegetation of a harvested peatland in southern Québec: A spatial and dendroecological analysis

Abstract:In North America peat has been harvested for horticultural use since the beginning of the 20th century. Many peatlands are now abandoned after decades of mining, and natural revegetation o...

Water and peat chemistry comparisons of natural and post-harvested peatlands across Canada and their relevance to peatland restoration

Water and peat chemistry comparisons of four post-harvested and neighboring, undisturbed peatlands across Canada show that harvesting alters chemical conditions. Commercial harvesting removes the surface peat and exposes layers farther down the peat deposit. The newly exposed peat layers that were formed in earlier developmental stages of the peatland can be more minerotrophic and/or more variable in chemical composition than undisturbed bog peat. All the harvested sites were originally bogs. Only one site, which had minimal peat removed, presently has chemical conditions somewhat similar to the original surface, with low elemental levels typical of bogs. Two sites are now chemically similar to poor fens and one site is similar to a moderate-rich fen. Levels of sodium, potassium, calcium, magnesium, sulphate and chloride in three of the harvested sites are higher than normal values found in natural, unharvested bogs, and result from the exposure of fen peat. Higher levels of ammonium-nitrogen and nitrate-nitrogen in the peat and water of all the harvested sites are present, with higher ammonium associated with wetter sites and higher nitrate levels associated with drier sites.

Effect of Grazing by Greater Snow Geese on the Production of Graminoids at an Arctic Site (Bylot Island, NWT, Canada)

1 Arctic ecosystems are sensitive to grazing because of their low overall net primary production. We therefore studied the effect of greater snow geese on the production of arctic graminoids. 2 At Bylot Island, NWT (73?N), breeding snow geese graze Eriophorum scheuchzeri and Dupontiafisheri in lowland polygon fens. Vegetation in seasonal exclosures was sampled at 2-week intervals from mid-June to mid-August 1990, 1991 and 1993 (ungrazed areas) and compared with plant growth in short-term exclosures set up over grazed areas. Standing crop (above-ground biomass), net above-ground primary production (NAPP) and nitrogen content were determined for both plant species. 3 Goose faeces were used as an index of grazing intensity. Cumulative faeces counts increased from 2.2 faeces m-2 in 1990-9.9 faeces m-2 in 1993. 4 Peak above-ground dry biomass of ungrazed areas averaged 33 g m2. In all years, goose grazing significantly reduced the above-ground biomass of Eriophorum and Dupontia. Over the 3 years, we estimated that geese consumed from 65 to 113% of the cumulative NAPP of Eriophorum, and from 30 to 78% of the cumulative NAPP of Dupontia. Consumption of Dupontia, but not Eriophorum, was related to grazing intensity. 5 Cumulative NAPP of grazed areas was slightly lower than that of ungrazed areas at the end of the summer. On an individual plant basis, cumulative NAPP of Dupontia, but not of Eriophorum, was reduced by grazing. Nitrogen content of plants after grazing was higher than in ungrazed plants. 6 Although grazed plants were able to grow new foliage, goose grazing did not enhance NAPP at Bylot Island as has been reported elsewhere. This could be either because grazing occurs too late in the season when the regrowth capacity of plants is low or because nutrients released from goose faeces are absorbed by mosses and are not immediately available to graminoids.