The Regeneration of a Highly Disturbed Ecosystem: A Mined Peatland in Southern Québec

We studied the natural regeneration of an ombrotrophic peatland (Cacouna bog) located in southern Québec that was disturbed by peat mining and other anthropogenic activities over a 200-year period. Using an extensive collection of historical documents, as well as dendrochronological data, we reconstructed the history of the peatland. We also sampled vegetation and environmental variables, and integrated the data in a geographic information system. More than 60% of the total area of the bog was mined between 1942 and 1975, and 98 km of ditches were dug to drain the site. The peatland lost 34% of its initial peat volume between 1946 and 1998. Although the bog was severely disturbed, the spontaneous revegetation of the site by vascular plants was successful (90%–100% cover). However, only 10% of the total mined area has been recolonized by Sphagnum species, mainly because drainage ditches are still operational and contribute to drying out the bog. Water table level, peat deposit thickness, and pH are abiotic factors strongly influencing the vegetation composition in the bog. Spatial and historical factors are also important components in this study since they explain, either alone or in interaction with abiotic factors, 44% of the variation of the species data. The intensity of mining activities and the pattern of abandonment of mined sectors strongly influenced abiotic factors, which in turn affected the revegetation process. Even if the Sphagnum cover of the bog is low, the rapid “recovery” of the vegetation cover in the peatland indicates that after the reestablishment of an appropriate hydrological regime, a highly disturbed peatland has a considerable potential for regeneration. Received 24 April 2001; accepted 30 October 2001.     

Mechanisms involved in the re-establishment of Sphagnum-dominated vegetation in rewetted bog remnants

Restoration of peat bog vegetation inhighly degraded peatlands is generallyattempted by improving the hydrology ofthese areas. The present paper discussesand explains various restoration strategiesrelating to peat quality, water chemistryand hydrology. In some cases, (shallow)inundation of bog remnants leads to a rapidredevelopment of (floating) Sphagnumvegetation, usually when poorly humifiedSphagnum peat is still present. Afterinundation, the peat either swells up tothe newly created water table or becomesbuoyant, in both cases creating a favorablesubstrate for Sphagnum mosses. Bulkdensity and methane production rate play animportant role in the buoyancy of floatingpeat, methane providing buoyancy to thesubstrates. The presence of (slightly)calcareous groundwater in the peat base mayenhance the development of floating raftsby stimulating decomposition processes.Alternatively, the growth of submerged Sphagnum species can also lead to thedevelopment of floating rafts. This dependson the penetration of light into the waterlayer and the availability of carbondioxide in the water layer.Many bog remnants, however, only havestrongly humified peat, which does notfavor the redevelopment of Sphagnumcarpets after deep inundation. On the otherhand, most peat moss species appear to dovery well on surface soaked black peat,which is why shallow inundation (< 0.3 m)is to be preferred in such cases.Compartmentalization of the terrain willprobably be necessary to ensure a more orless constant water table.An important prerequisite for thesuccessful restoration of bog remnants isthe development of a hydrologicallyself-regulating acrotelm. Key speciesinvolved in this development are Sphagnum magellanicum, Sphagnumpapillosum and Sphagnum rubellum.These typical hummock and lawn species areusually very slow colonizers compared tohollow species such as Sphagnumcuspidatum and Sphagnum fallax.Introduction of key species in carpetsdominated by hollow species or on baresubstrates appears to be very successful,indicating that the main constraint iscolonization.     

Xylem traits of peatland Scots pines reveal a complex climatic signal: A study in the Eastern Italian Alps

Long-term climate reconstructions are frequently based on tree-ring high-resolution proxies extracted from subfossil peatland trees. Peatlands are peculiar ecosystems characterized by high moisture in the upper soil part which creates a harsh living environment for trees. The climate mostly indirectly influences tree growth determining seasonal variations in the water table level. Within this framework, the aim of this study was to investigate climate responses of trees (Pinus sylvestris L.) growing inside and outside a Southern Alpine peat bog, by using tree-ring and wood anatomical traits (e.g. tracheid number and dimension, cell-wall thickness). Our results showed differences in the xylem structure and climate signal recorded by peatland and mineral soil trees. Peatland trees were characterized by narrow rings and tracheids with thinner cell wall. Summer temperature and precipitation were the major drivers of xylem formation in peatland trees. At intra-annual level wood anatomical traits revealed a complex within-ring signal during the growing season. The multi-parameters approach together with the high-resolution gained by using tree-ring sectors allowed us to obtain new detailed information on the xylem development of peatland trees and climate drivers that influenced it.     

Differentiation in adaptive traits between neighbouring bog and mineral soil populations of Scots pine Pinus sylvestris

I used a reciprocal sowing experiment in the field to reveal differentiation in adaptive traits between two neighbouring northern populations of Scots pine Pinus sylvestris. 1 compared a peat bog population with a mineral soil population. Seedling survival was monitored during seven growing seasons and the plants were then harvested to obtain data on pine traits associated with growth and resource allocation, i.e. height, needle length, total dry weight, relative growth, proportion root and proportion needles. Seeds from the peat bog populations had lower germination capacity and were smaller than those from the mineral soil population. Despite their smaller size, the seeds from the bog population were superior for establishment of pines on the bog. On the mineral soil, the traits were strikingly similar in the two pine populations. In contrast, the traits were more variable and differentiated on the bog. Here, the native bog pines grew faster and had a larger proportion root than those originating from the population on the adjacent mineral soil. It is suggested that the differentiation between peat bog populations and mineral soil populations might represent a major direction of differentiation in northern Scots pine populations.     

Trade-Offs between Growth Rate,Tree Size and Lifespan of Mountain Pine (Pinus montana) in the Swiss National Park

A within-species trade-off between growth rates and lifespan has been observed across different taxa of trees, however, there is some uncertainty whether this trade-off also applies to shade-intolerant tree species. The main objective of this study was to investigate the relationships between radial growth, tree size and lifespan of shade-intolerant mountain pines. For 200 dead standing mountain pines (Pinus montana) located along gradients of aspect, slope steepness and elevation in the Swiss National Park, radial annual growth rates and lifespan were reconstructed. While early growth (i.e. mean tree-ring width over the first 50 years) correlated positively with diameter at the time of tree death, a negative correlation resulted with lifespan, i.e. rapidly growing mountain pines face a trade-off between reaching a large diameter at the cost of early tree death. Slowly growing mountain pines may reach a large diameter and a long lifespan, but risk to die young at a small size. Early growth was not correlated with temperature or precipitation over the growing period. Variability in lifespan was further contingent on aspect, slope steepness and elevation. The shade-intolerant mountain pines follow diverging growth trajectories that are imposed by extrinsic environmental influences. The resulting trade-offs between growth rate, tree size and lifespan advance our understanding of tree population dynamics, which may ultimately improve projections of forest dynamics under changing environmental conditions.     

排水沟蓄水条件下农田与排水沟水盐监测

为了查明盐碱地排水沟蓄水条件下农田与排水沟之间的水盐交换,基于两年现场观测试验数据,分析了农田与排水沟的水位响应以及电导率变化规律。结果发现:研究区排水沟蓄水条件下,相邻排水沟水位与农田地下水位变化基本一致,作物生长期较为强烈的蒸发蒸腾作用进一步降低了田间地下水位;排水沟水位变化可以直接或间接地影响周围农田的地下水位和水质状况,在无外界来水干扰的情况下,农田地下水和排水沟水样的电导率变化趋势一致,当排水沟受到外来淡水补给时,沟内浓缩的盐分得到稀释,电导率明显低于农田地下水。研究结果可为类似地区盐碱地治理和生态环境保护提供参考依据。     

Assessing long‐term hydrological and ecological responses to drainage in a raised bog using paleoecology and a hydrosequence

Question: We studied vegetation succession after drainage in a bog, as an analogue for potential persistent water table drawdown due to climate change. We asked: (1) how does bog vegetation change following a long‐term water table lowering and (2) how are effects of drainage on hydrology and vegetation distributed temporally and spatially? Location: Mer Bleue peatland, Ontario, Canada (45.41°N, 75.48°W). Methods: Analyses of changes in vegetation and hydrology associated with drainage were examined spatially along a hydrosequence and temporally using paleoecological reconstructions from peat cores (testate amoebae, pollen) in a drained portion of a peatland untouched for 85 years following drainage. Relationships between modern vegetation and water table were assessed through clustering and ordination analyses of vegetation relevés. Results: Post‐drainage increases in tree cover, especially Betula and Larix, decreases in Sphagnum cover and shifts in species composition of dominant shrubs were observed. Present‐day vegetation patterns along the hydrosequence were primarily related to seasonal variability of water table depth. Paleoecological records reveal that where the present‐day vegetation has been impacted by drainage, persistent water table lowering occurred in response to drainage. However, in an area with relatively natural vegetation, a transient drop in water table depth occurred at the time of drainage. Conclusions: Temporal and spatial patterns revealed that the bog response to drainage was spatially and temporally heterogeneous, and probably mediated by feedbacks among vegetation, peat structure and hydrology. Spatial patterns along the hydrosequence were similar to those observed in paleoecological reconstructions, but the use of the two complementary techniques provides additional insights.     

Fatal interactions between Scots pine and Sphagnum mosses in bog ecosystems

In this study, we explore how Sphagnum mosses and Scots pine, Pinus sylvestris , interact on different spatial and temporal scales in a boreal bog ecosystem. We were particularly interested in relationships between the occurrence of Sphagnum- dominated habitats and the occurrence of Scots pines of different age and size.
Juvenile and adult pines occurred in different habitats. While juveniles mainly occurred in Sphagnum- dominated habitats, predominantly with Sphagnum rubellum , adult pines were found in habitats dominated by lichens, or with a sparse vegetation cover. Examination of surface peat cores sampled close to adult pines revealed that almost all pines (97%) had established in a Sphagnum -dominated environment and that the habitat had changed since pine establishment. Scots pine is thus capable of changing and exterminating the Sphagnum -dominated environment preferred for germination and establishment. Pines impede Sphagnum growth and peat accumulation significantly once they have reached a stem diameter of approximately 20 mm. It takes from 30 to 90 yr for a pine to reach that size.
Our results show the importance of interactions between Scots pine and Sphagnum mosses in bog ecosystems. We conclude that interactions between trees and Sphagnum mosses are important driving forces behind the vegetation change that has characterised boreal bogs during the Holocene.     

大连市黑松树木水分利用效率的环境响应

以生长于大连城区的黑松为研究对象,建立了1951—2010年间的树木径向生长、树轮稳定碳同位素比率(δ¹³C)和水分利用效率的时间序列,研究了三者的变化特点及其与主要气候因子的关系.结果表明: 1980年以来,黑松树木径向生长有减缓趋势,δ¹³C值降低,但是水分利用效率显著增加(P<0.05).年轮宽度、稳定同位素比率和水分利用效率的变化均受气候因素的影响,并随季节波动:夏季温度与树木径向生长呈负相关,而冬季则呈正相关;6月降水和相对湿度的波动与年轮宽度变化基本呈正相关;3—9月各月温度与δ¹³C和水分利用效率呈弱正相关,其他月份基本呈弱负相关;全年降水和相对湿度分别与δ¹³C和水分利用效率基本呈负相关.快速暖干化的城市气候环境促进了树木水分利用效率的提高.     

Change in fluxes of carbon dioxide,methane and nitrous oxide due to forest drainage of mire sites of different trophy

Northern peatlands accumulate atmospheric CO₂ thus counteracting climate warming. However, CH₄ which is more efficient as a greenhouse gas than CO₂, is produced in the anaerobic decomposition processes in peat. When peatlands are taken for forestry their water table is lowered by ditching. We studied long-term effects of lowered water table on the development of vegetation and the annual emissions of CO₂, CH₄ and N₂O in an ombrotrophic bog and in a minerotrophic fen in Finland. Reclamation of the peat sites for forestry had changed the composition and coverage of the field and ground layer species, and increased highly the growth of tree stand at the drained fen. In general, drainage increased the annual CO₂ emissions but the emissions were also affected by the natural fluctuations of water table. In contrast to CO₂, drainage had decreased the emissions of CH₄, the drained fen even consumed atmospheric CH₄. CO₂ and CH₄ emissions were higher in the virgin fen than in the virgin bog. There were no N₂O emissions from neither type of virgin sites. Drainage had, however, highly increased the N₂O emissions from the fen. The results suggest that post-drainage changes in gas fluxes depend on the trophy of the original mires.     

The Effects of Peatland Restoration on Water‐Table Depth,Elemental Concentrations,and Vegetation: 10 Years of Changes

We studied the effects of restoration on water‐table depth (WTD), element concentrations of peat and vegetation composition of peatlands drained for forestry in southern Finland. The restoration aimed to return the trajectory of vegetation succession toward that of undisturbed systems through the blockage of ditches and the removal of trees. Permanent plots established on a bog and a fen were sampled 1 year before, and 1, 2, 3, and 10 years after the restoration. The restoration resulted in a long‐term rise of the water‐table in both peatlands. Ten years after restoration, the mineral element concentrations (Ca, K, Mg, Mn, and P) of peat corresponded to those reported from comparable pristine peatlands. In particular, the increase of K and Mn concentrations at both sites suggests the recovery of ecosystem functionality in terms of nutrient cycling between peat and plants. The restoration resulted in the succession of plant communities toward the targeted peatland vegetation of wetter condition at both sites. This was evident from the decreased abundance of species benefiting from drainage and the corresponding increase of peatland species. However, many species typical of pristine peatlands were missing 10 years after restoration. We conclude that the restoration led to a reversal of the effects of drainage in vegetation and studied habitat conditions. However, due to the slow recovery of peatland ecosystems and the possibility that certain failures in the restoration measures may become apparent only after extended time periods, long‐term monitoring is needed to determine whether the goals of restoration will be met.     

Scots pine growing on forested mires in Abernethy Forest,Strathspey, Scotland

Summary

A substantial proportion of the Abernethy Forest Reserve has Scots pine (Pinus sylvestris) growing on the surfaces of a variety of mires. The hydrology of the mires has been affected by drainage and peat cutting but this area is unusual in having had a long period of protection from grazing by domestic stock. There are three main types of pine populations found on these mires. Woodland bog comprises predominantly bog vegetation with abundant pine seedlings due to the heavy seed rain from the surrounding woodland. Only a few very small trees survive, which are stunted, heavily diseased and have very low seed production. Wooded bog also comprises predominately bog vegetation but there are scattered mature trees of a moderate height with an open canopy. The trees are fertile and can form uneven aged stands with regeneration. Bog woodland is a predominantly woodland vegetation with tall, dense tree cover on deep peat. The trees are well grown with a dense canopy. A few remnants of bog vegetation remain in the ground flora although most have been replaced by woodland bryophytes and shrubs. Each of these three types is described and their development is discussed.     

Fine-root growth in a forested bog is seasonally dynamic,but shallowly distributed in nutrient-poor peat

Background and aims

Fine roots contribute to ecosystem carbon, water, and nutrient fluxes through resource acquisition, respiration, exudation, and turnover, but are understudied in peatlands. We aimed to determine how the amount and timing of fine-root growth in a forested, ombrotrophic bog varied across gradients of vegetation density, peat microtopography, and changes in environmental conditions across the growing season and throughout the peat profile.

Methods

We quantified fine-root peak standing crop and growth using non-destructive minirhizotron technology over a two-year period, focusing on the dominant woody species in the bog: Picea mariana, Larix laricina, Rhododendron groenlandicum, and Chamaedaphne calyculata.

Results

The fine roots of trees and shrubs were concentrated in raised hummock microtopography, with more tree roots associated with greater tree densities and a unimodal peak in shrub roots at intermediate tree densities. Fine-root growth tended to be seasonally dynamic, but shallowly distributed, in a thin layer of nutrient-poor, aerobic peat above the growing season water table level.

Conclusions

The dynamics and distribution of fine roots in this forested ombrotrophic bog varied across space and time in response to biological, edaphic, and climatic conditions, and we expect these relationships to be sensitive to projected environmental changes in northern peatlands.

     

Dendroclimatic signals deduced from riparian versus upland forest interior pines in North Karelia, Finland

Radial growth of boreal tree species is only rarely studied in riparian habitats. Here we investigated chronologies of earlywood, latewood, and annual ring widths and blue intensity (BI; a surrogate to latewood density) from riparian lake shore and upland forest interior pines (Pinus sylvestris L.) growing in boreal forest in eastern Finland. Riparian and upland chronologies were compared to examine differences in the pine growth variability and growth response to climatic variation in the two habitats. It was found that the climatic variables showing statistically significant correlations with the tree-ring chronologies were related to snow conditions at the start of the growing season. Deeper snowpack led to reduced upland pine growth, possibly due to delayed snowmelt and thus postponed onset of the growing season. Warm late winters were followed by increased riparian pine growth because of earlier start of the snow-melt season and thus a lower maximum early summer lake level. Moreover, riparian pines reacted negatively to increased rainfall in June, whereas the upland pines showed a positive response. Latewood growth reacted significantly to summer temperatures. The BI chronology showed a strong correlation with warm-season temperatures, indicating an encouraging possibility of summer temperature reconstruction using middle/south boreal pine tree-ring archives.     

Exploring climate forcing of growth depression in subfossil South Swedish bog pines using stable isotopes

Comparison between growth variability, based on ring-width (RW) analysis, and moisture-sensitive signals in tree-ring carbon and oxygen stable-isotope composition provides increased understanding of how climate and hydrology influenced bog pines (Pinus sylvestris L.) at two sites in southern Sweden during the mid- and late Holocene. Tree-ring sequences from two subfossil trees collected at raised bogs having different hydrology and catchment size were analyzed to probe the stable-isotope signals associated with two bog-wide episodes of growth depression, one during the Holocene Thermal Maximum and the other during the Neoglacial Transition. The occurrence of lower whole-wood δ¹³C and cellulose δ¹³C and δ¹⁸O values immediately prior to the onset of growth depression in both trees, suggesting increased atmospheric relative humidity, is consistent with the notion that excessive effective moisture impeded tree growth. Correlation analysis indicates that the growth response lagged about three years behind the decline in δ¹³C and δ¹⁸O values in each tree, possibly reflecting relatively slow rise in the local water table in response to wetter climate.     

Vegetation changes and development of agriculture at „Kerfontaine“ (Sérent,Massif Armoricain,France)

As part of a new research programme, studies of peat bogs in Brittany are being carried out to trace the changes that have occurred in the course of time, and to determine the different regional stages related to the human activities of land clearance and agriculture. In this context, a palynological study of the Kerfontaine peat bog was undertaken to consider changes in local and regional vegetation dating from after about 7800 B.P. Local vegetation history from Neolithic times until the Middle Ages involved a succession of twelve pollen zones clearly related to variations in water level resulting from natural or anthropogenic influences. The dominant vegetation was alder carr, bog-myrtle mire and birch woods. Heath vegetation, which appeared at the end of the Iron Age, developed during the Gallo-Roman period, finally invading the entire bog in the Middle Ages. Regional vegetation history was characterised, among other things, by the presence of beech woods which developed after 3000 B.P. and then declined during the Middle Ages in conjunction with an increase of cultivation between the 8th and 11th centuries A.D., an indication of great activity during the Carolingian period. Human activity reached its peak around 1800 A.D. at the time of the first pine plantations.     

Carbon fluxes in forested bog margins along a human impact gradient: could vegetation structure be used as an indicator of peat carbon emissions?

Bog ecosystems are sensitive to anthropogenic disturbance, including drainage and air pollution. Carbon (C) balance measurements to determine the effect of disturbance on bog functioning are laborious; therefore reliable proxies for C fluxes that could facilitate upscaling from single studies to a larger scale would be valuable. We measured peat CO₂ emissions (R _s), CH₄ efflux and vegetation characteristics in four bog areas that formed a gradient from pristine to severely disturbed peatlands, affected by drainage, peat mining, alkaline air pollution and underground oil-shale mining. We expected that sites experiencing higher human impact (i.e., the vegetation was more distinct from that of a natural bog) would have higher R _s and lower CH₄ emissions, but differences in peat C emissions between the most disturbed and pristine sites were not significant. Growing period median R _s ranged from 0.5 to 2.2 g C m^?2 day^?1 for our plots; methane emissions, measured from July to December were an order of magnitude lower, ranging from ?5.9 to 126.7 mg C m^?2 day^?1. R _s and CH₄ emissions were primarily determined by water table depth, as was tree stand productivity. Therefore, stand structural parameters could potentially be good indicators of soil C emissions from poorly drained forested bogs.     

Hydrological differences between bogs and bog-relicts and consequences for bog restoration

The hydrology of bog relicts differs from that in undisturbed bogs. The surface layers of these relicts mostly consist of moderately to strongly humified, secondary weathered peat as a result of drainage and peat cutting. The hydrophysical properties of these layers cause relatively high groundwater level fluctuations. Deep drainage systems, both in the bog relicts and in their surroundings, may have increased the downward seepage. Reduction of these downward water losses may be crucial for the restoration of the required hydrological conditions in certain bog relicts (hydrological bufferzone as external water management option). The potential of internal hydrological modifications, where the increase in storage capacity near the surface is essential, should be emphasized in many bog relicts. Considerable reductions in water level fluctuations can be achieved e.g. when the open water within the area is enlarged and when this water is equally distributed over the area with small peat ridges in between. In general, attention should be given to both the internal and external options in studies on water management.     

Drainage-induced forest growth alters belowground carbon biogeochemistry in the Mer Bleue bog, Canada

Impacts of long-term drying and associated vegetation change on anaerobic decomposition, methane production, and pore water composition in peat bogs are poorly documented. To identify some of these impacts, we analyzed peat humification, pore water solutes, in situ and in vitro respiration rates, and Gibbs free energies of methanogenesis in a bog near a drainage ditch established in 1923. We compared drained peat under open bog vegetation and forest with a bog reference site. Drainage and tree growth induced an enrichment in carboxylic, aromatic, and phenolic moieties in the peat. Short-term in vitro respiration rates significantly decreased with humification (R ²?>?0.6, p?<?0.01). Dissolved inorganic carbon (DIC) and CH₄ concentrations also attained lower maxima in drained areas. However, near the water table in situ respiration intensified as indicated by steeper increases in DIC and CH₄ concentrations than at the reference site, especially under forest. Maximum in situ CO₂ production derived from inverse pore water modeling was 10.3?nmol?cm^?3?d^?1 (forest) and 6.3?nmol?cm^-3?d^-1 (bog) and was one to two orders of magnitude slower than in vitro anaerobic respiration. In the highly decomposed shallow peats under forest, methane production was suppressed and DOC concentration elevated. Raised H₂ concentrations (up to 200?nmol?l^?1) and in situ Gibbs free energies of down to ?60?kJ?mol^?1?(CH₄) suggested an inhibition of hydrogenotrophic methanogenesis by an unidentified factor at these sites. The study documents that several changes in biogeochemical process patterns do occur post-drainage, especially when tree growth is triggered. Most importantly, the establishment of forest on intensely humified peats can lower in situ methane production.     

The effect of anthropogenic activities on the reduction of urban tree sensitivity to climatic change: dendrochronological evidence from Chinese pine in Shenyang city

To understand how urban tree growth has responded to the accelerating expansion in population and urbanization, an understanding of the tree-climate–urban ecosystem relationship is necessary. To this end, a metropolitan, suburban, and rural forest stand in and near Shenyang; and a rural forest stand in Weichang, were sampled in southern Northeast China. Radial growth variability of 109 Chinese pines (Pinus tabulaeformis Carr.), established before 1900 within and around the city, was measured. The contents of trace elements in tree rings were also examined to detect the possible relationship to urban environmental contamination. All sampled trees crossdated well, indicating a homogeneous common influence of regional climate. For the common period of 1901–2000, the radial growth of all trees was significantly affected by local and regional climate, especially temperature and precipitation in winter and spring, respectively. From the rural to the metropolitan areas, a significant decreasing relationship in the response of trees to climatic factors was detected. These decreases occurred over time and in tree stands within the same location or between different sites, and also corresponded with the increasing influence of local urbanization and industrialization on the urban environment during the last century. Particularly strong influences are the increase of population, urban built-up area, and urban agricultural and industrial activities. Decreases in mean sensitivity of Chinese pines were also found and are most likely related to the intensification of anthropogenic activities and environmental change. Based on tree-ring width growth in rural areas, a growth pattern of urban trees without anthropogenic disturbances was established. After removing the climate-related signals from actual urban tree growth, the impact of anthropogenic disturbances was chronologically developed. The results indicate that the periods of heaviest disturbances occurred from 1914 to 1922, 1932 to 1935, 1943 to 1946, 1955 to 1969, and 1973 to 2000.