Microsite variation and climate result in stand dynamics variation in pristine Pinus sylvestris mires: Evidence from a stand structure study

Questions: How do climate conditions and the site's ecohy‐ drological properties affect the age and size structure of natural Pinus sylvestris stands on pristine boreal mires? How do the long‐term stand dynamics on mires proceed as stands age? Do the mire stands reach a balanced, old‐growth stage? Location: Boreal mire forests in southern and northern Finland. Methods: Tree age and diameter distributions were analysed in 52 stands in two climate areas and in two mire site types with different ecohydrological properties. Temporal stand dynamics were examined by (1) comparing the graphs of the stands’ mean tree ages by diameter at breast height (1.3 m) classes and (2) describing the changes in stand characteristics and stand age and size structures as a function of stand dominant age in a chronosequence. Results: In the south, the DBH distributions were mostly unimodal and bell‐shaped in both site type groups. Age distributions were multimodal and flat in fully‐stocked sites but more uneven in sparsely forested composite sites. In the north, both the age and size distributions were clearly uneven in both site type groups. Tree age and size variation increased with stand age, but levelled out in the long term. Particularly in the south, the abundance of small trees decreased as stand age increased. Conclusions: The pine stands on pristine boreal mires are more dynamic than anticipated and are generally not characterised by a balanced, self‐perpetuating structure. Their dynamics reflect differences in climate and ecohydrology: on stocked sites in favourable boreal conditions, the stands showed structures typically resultant of inter‐tree competition processes that control tree growth and regeneration, whereas in harsh boreal climates, the tree regeneration process is ongoing diversifying the stand structure.     

Conservation of vascular plants in single large and several small mires: species richness, rarity and taxonomic diversity

1. This study on vascular plant species of boreal spruce and pine mires concentrated on two geometrical principles: whether single large or several small (SLOSS) reserves contain more species and whether patch shape should be as nearly circular as possible.
2. SLOSS and patch shape have usually been tested by using species richness. Only a few studies have taken the rarity of species into account, and taxonomic diversity has never been used. In our study, all three of these factors were used.
3. Our results showed that the number of species was not related to the spruce mire size, but it increased in relation to the pine mire size. In contrast, the rarity score increased in relation to the area of spruce mires, but it was not related to the area of pine mires. Taxonomic diversity was not related to size in the case of spruce mires, but it increased with pine mires.
4. The SLOSS comparison showed that several small mires contained more vascular plant species than a large one of equal size. Several small mires also had higher rarity scores and taxonomic diversity than a single large mire. The number of species, rarity score and taxonomic diversity increased in relation to the number of small mires in a group. The same results were obtained with both spruce and pine mires.
5. Species richness, rarity score and taxonomic diversity were not related to mire shape. The results did not depend on the mire type.     

Vegetationsverhältnisse und Naturumwelt des Beckens Jestřebská kotlina am Ende des Spätglazials und im Holozän (Doksy-Gebiet)

The method of pollen analysis was used to study a profile sample taken from the Jest?ebské blato mire, the Doksy District (northern Bohemia). The aim of the palacobotanical analyses was to perform a reconstruction of vegetation and environment for geobotanical and archaeological research purposes. Sediments dating back to the end of the Late Glacial and to both the Early and Middle Holocene were pollenanalytically studied. The results of the pollen analyses recorded the development of vegetation during the end of the Late Glacial, Preboreal, Boreal and Atlantic Periods. Parkline pine stands of the end of the Late Glacial developed to closed pine forests, during the Preboreal. Even during the Boreal, the dominant pine formed forest communities were typical of the area under study, though trees with greater demands on temperature and moisture conditions continued to penetrate the existing communities. During the Lower and the first half of the Upper Atlantic Period, spruce forests and alder woods formed the dominant forest communities in mire. Nevertheless,Pinus was still dominant on extreme sites (both from the edaphic and geomorphological points of view). An early occurrence ofAlnus andPicea is another characteristic feature of the studied area. The conclusions drawn from pollenanalytical results were used for the reconstruction of the past environment of the Mesolithic and Neolithic Ages.     

Restoration of managed pine fens: effect on hydrology and vegetation

Question: How does restoration affect the hydrology and the understorey vegetation of managed pine fens? Location: Oligotrophic pine fens in Natura 2000 areas in Kainuu, eastern Finland. Methods: Eleven managed pine fens and eight pristine reference pine fens were chosen for the study in 2005. The managed fens, which had been drained for forestry during the 1970s and 1980s, were restored in 2007. The water table was monitored in all fens over four growing seasons during 2006 to 2009, and vegetation was surveyed from permanent sample plots in 2006 and 2009. Results: Before restoration in 2006, the water table was at a significantly lower level in the managed fens compared with the pristine fens. Immediately after restoration, the water table rose to the same level as in the pristine fens, and this change was permanent. Forest drainage had had little impact on the understorey vegetation of the managed fens in the three decades before restoration, with species typical of pristine fens still dominating the sites. Forest dwarf shrubs and feather mosses had started to increase in cover, but mire dwarf shrubs and Sphagnum mosses still dominated the managed fens. Only the typical hollow species Sphagnum majus, Sphagnum balticum and Scheuzeria palustris were missing from the managed fens. Two years after restoration, the changes in species composition were also marginal, with increased cover of mire dwarf shrubs and sedges being the only significant change. Conclusions: The success of restoration of oligotrophic pine fens seems likely, given that changes in hydrological functioning occurred rapidly, and since little change has occurred in the vegetation composition after draining. Speeding up the regeneration process in these peatland types by restoration may, therefore, be recommended, especially if the drainage effect extends to nearby pristine mires and influences their biodiversity.     

Thiosulfate sulfurtransferase (rhodanese) in forest soils

Concentrations of thiosulfate sulfurtransferase (rhodanese; EC 2.8.1.1) in soils of five types of forest stands (spruce and pine stands without ground vegetation, and mountain ash, birch and pine stands with grass cover) were followed. Soils from grassed stands contained much higher concentrations of the enzyme than soils without ground vegetation. On grassed locations higher enzyme concentrations were found in fermentation horizons, whereas on locations without the ground vegetation they were detected in humus horizons. Urea fertilization and SO₂ pollution did not exhibit any significant effect.     

Regenerative and age dynamic of spruce population in pine plantations under conditions typical for spruce development

We have studied the natural regeneration of spruce (Picea abies L.) under a canopy of pine (Pinus sylvestris L.) on loamy soils. Spruce survival and growth depend on the duration of the regeneration period from the creation of the plantation and the local conditions formed as a result of uneven thinning of pine and spruce canopy. The formation of spruce population is mainly determined by trees that regenerated upon intensive thinning of 20- to 40-year-old pine trees. Spruce regeneration may be enhanced by timely cleaning cutting in pine plantations. The first one, done at the age of 15–20 years, favors pine growth and spruce regeneration. At the normal reproduction of spruce population under the canopy of 80-year-old pine plantations, the second spruce layer is formed. Trunk reserve in this layer is 20–25% of the reserves of the first layer. After its formation, the light regime in the forest depends greatly on the space volume occupied by spruce crowns. Their percentage is especially high at the relative height equal to 0.4–0.7 of the mean spruce height in the second layer. Smaller spruce trees may exist for a long time period, but their development is slowed down and they die at the undergrowth stage. When the plantation is 150 years old, the reserves of spruce trees regenerated under the canopy of pine comprise one-third of the total reserves of the plantation. If the growing conditions are favorable for spruce (C₃), the stability and productivity of pine-spruce plantations exceed those of the pure spruce plantations. The reasonability of natural spruce regeneration for the creation of pine-spruce plantations under C₃ conditions should be substantiated with the consideration of their designation, ages of cuttings, and the possibility of plantation creation and sanitary cuttings according to the valid regulations.     

Shift of Conifer Boreal Forest to Lichen–Heath Parkland Caused by Successive Stand Disturbances

In the southern boreal forest (Québec, Canada), tree harvesting is a major disturbance affecting the dominant black spruce (Picea mariana) stands already suffering from naturally recurrent insect and fire disturbances. Although recovery of the spruce forest after an insect infestation or a fire is possible under current site conditions, it is less likely when both types of disturbance occur during a short period of time. The addition of yet another disturbance, such as tree harvesting, can thus have catastrophic consequences. We analyzed the impact of three successive disturbances—tree harvesting, insect infestation, and fire—on the regeneration of boreal spruce–moss forests within a period of approximately 50 years. The spruce forests were harvested in the 1940s and the 1950s. Recovery from the logging consisted of advance regeneration (spruce layers less than 1 m high that were left intact during clear-cuts), which was burned in 1991. The vegetation cover (mostly heath and lichen species) and soil conditions (acidic, nutrient-poor podzolic soils developed from coarse materials) of the postfire sites that we studied were similar. Stand structure and tree regeneration were documented from large quadrats (0.25 ha) using age, size, and tree ring data from postlogged and postfire spruce. At an early stage of development, the growing advance regeneration was damaged by insect defoliators in the late 1970s and the mid-1980s, and several trees died a few years before the 1991 fire. The successive disturbances considerably reduced the number of seed-bearers, leading to the collapse of postfire regeneration and a shift to parkland. Through a successional trajectory far from the expected trend for boreal forests influenced by single disturbance, the shift resulted in the formation of divergent plant communities. The development of divergent communities at the landscape scale is generally overlooked due to their small size. They indicate, however, the weak resilience of boreal forests faced with cascading perturbations, which are likely to increase in intensively logged areas.     

Non-equilibrium succession dynamics indicate continued northern migration of lodgepole pine

Because species affect ecosystem functioning, understanding migration processes is a key component of predicting future ecosystem responses to climate change. This study provides evidence of range expansion under current climatic conditions of an indigenous species with strong ecosystem effects. Surveys of stands along the northern distribution limit of lodgepole pine (Pinus contorta var. latifolia) in central Yukon Territory, Canada showed consistent increases in pine dominance following fire. These patterns differed strongly from those observed at sites where pine has been present for several thousand years. Differences in species thinning rates are unlikely to account for the observed increases in pine dominance. Rates of pine regeneration at its range limits were equivalent to those of spruce, indicating a capacity for rapid local population expansion. The study also found no evidence of strong climatic limitation of pine population growth at the northern distribution limit. We interpret these data as evidence of current pine expansion at its range limits and conclude that the northern distribution of lodgepole pine is not in equilibrium with current climate. This study has implications for our ability to predict vegetation response to climate change when populations may lag in their response to climate.     

Variation in fine root biomass of three European tree species: Beech (Fagus sylvatica L.), Norway spruce (Picea abies L. Karst.), and Scots pine (Pinus sylvestris L.)

Abstract

Fine roots (<2 mm) are very dynamic and play a key role in forest ecosystem carbon and nutrient cycling and accumulation. We reviewed root biomass data of three main European tree species European beech, (Fagus sylvatica L.), Norway spruce (Picea abies L. Karst.) and Scots pine (Pinus sylvestris L.), in order to identify the differences between species, and within and between vegetation zones, and to show the relationships between root biomass and the climatic, site and stand factors. The collected literature consisted of data from 36 beech, 71 spruce and 43 pine stands. The mean fine root biomass of beech was 389 g m^?2, and that of spruce and pine 297 g m^?2 and 277 g m^?2, respectively. Data from pine stands supported the hypothesis that root biomass is higher in the temperate than in the boreal zone. The results indicated that the root biomass of deciduous trees is higher than that of conifers. The correlations between root biomass and site fertility characteristics seemed to be species specific. There was no correlation between soil acidity and root biomass. Beech fine root biomass decreased with stand age whereas pine root biomass increased with stand age. Fine root biomass at tree level correlated better than stand level root biomass with stand characteristics. The results showed that there exists a strong relationship between the fine root biomass and the above-ground biomass.     

Nutrient pools and fluxes of the ground vegetation in coniferous forests due to fertilizing,liming and amelioration

The effects of fertilization and amelioration treatments on some nutrient pools and fluxes of ground vegetation in mature pine and spruce stands on acid soils in South Germany are described. In N-limited pine forests with moderate canopy density and with Deschampsia flexuosa an additional N-accumulation in biomass of 20–40 kg ha^-1 occurred 3 years after pure N-fertilization. The N, P, K-cycling through ground vegetation was stimulated more than 10 years by a combined N + CaCO₃ + P treatment leading toa shift in dominance from cryptogams and Ericaceae towards Deschampsia flexuosa and ruderal species like Epilobium angustifolium. The effect of a lupine treatment (combined with initial soil preparation, liming and P supply) was far stronger than the effect of the other experimental procedures. But the fertilizer and amelioration effects on the herb layer of pine forests tended to decline after two decades for different reasons.The shade-tolerant ground vegetation in a nitrogen-saturated spruce forest was not able to prevent heavy additional nitrate losses from upper mineral soil after dolomitic liming. But the Ca, Mg and K fluxes through ground vegetation were strongly elevated in the third year after treatment.     

Effects of Chronic Human Activities on Invasion of Longleaf Pine Forests by Sand Pine

Chronic human activities may result in new and permanent successional trajectories in certain ecosystems. The invasion of longleaf pine ecosystems by sand pine in the Florida Panhandle is one such change in the landscape. This study examined the spatial pattern of sand pine expansion and explored the natural and anthropogenic disturbances that fostered this invasion. Aerial photographs (1949, 1994) and Geographic Information Systems analyses confirmed sand pine expansion at Eglin Air Force Base. In 1949, there were 8,982 ha of sand pine in the southern portion of the study area near riparian and coastal lowland forests. By 1994, sand pine had expanded further upland and inland, for a total of 17,147 ha in the study area. Sand pine age data showed that this expansion had started by 1920 but increased rapidly in the 1940s. Historical accounts and structural data from stands suggest that land-use activities associated with the extraction of turpentine promoted the invasion by sand pine. Fires were suppressed in longleaf pine forests to protect turpentine trees, resulting in increased vegetation cover and decreased regeneration of longleaf pine. In addition, stands were typically harvested after turpentining, and there was little or no advanced regeneration of longleaf pine. Sand pine age histograms showed that the onset of high establishment rates (1940s) coincided with changes in land ownership and widespread fire suppression. Sand pine is likely to persist in these ecosystems due to its abundant regeneration. Received 17 March 1999; accepted 28 January 2000.     

Soil CO2 efflux in contrasting boreal deciduous and coniferous stands and its contribution to the ecosystem carbon balance

Similar nonsteady‐state automated chamber systems were used to measure and partition soil CO₂ efflux in contrasting deciduous (trembling aspen) and coniferous (black spruce and jack pine) stands located within 100 km of each other near the southern edge of the Boreal forest in Canada. The stands were exposed to similar climate forcing in 2003, including marked seasonal variations in soil water availability, which provided a unique opportunity to investigate the influence of climate and stand characteristics on soil CO₂ efflux and to quantify its contribution to the net ecosystem CO₂ exchange (NEE) as measured with the eddy‐covariance technique. Partitioning of soil CO₂ efflux between soil respiration (including forest‐floor vegetation) and forest‐floor photosynthesis showed that short‐ and long‐term temporal variations of soil CO₂ efflux were related to the influence of (1) soil temperature and water content on soil respiration and (2) below‐canopy light availability, plant water status and forest‐floor plant species composition on forest‐floor photosynthesis. Overall, the three stands were weak to moderate sinks for CO₂ in 2003 (NEE of ?103, ?80 and ?28 g C m^?2 yr^?1 for aspen, black spruce and jack pine, respectively). Forest‐floor respiration accounted for 86%, 73% and 75% of annual ecosystem respiration, in the three respective stands, while forest‐floor photosynthesis contributed to 11% and 14% of annual gross ecosystem photosynthesis in the black spruce and jack pine stands, respectively. The results emphasize the need to perform concomitant measurements of NEE and soil CO₂ efflux at longer time scales in different ecosystems in order to better understand the impacts of future interannual climate variability and vegetation dynamics associated with climate change on each component of the carbon balance.     

Fire Interval Effects on Successional Trajectory in Boreal Forests of Northwest Canada

Although succession may follow multiple pathways in a given environment, the causes of such variation are often elusive. This paper describes how changes in fire interval mediate successional trajectory in conifer-dominated boreal forests of northwestern Canada. Tree densities were measured 5 and 19 years after fire in permanent plots and related to pre-fire vegetation, site and fire characteristics. In stands that were greater than 75 years of age when they burned, recruitment density of conifers was significantly correlated with pre-fire species basal area, supporting the expectation of stand self-replacement as the most common successional pathway in these forests. In contrast, stands that were under 25 years of age at the time of burning had significantly reduced conifer recruitment, but showed no change in recruitment of trembling aspen (Populus tremuloides). As a result, young-burned stands had a much higher probability of regenerating to deciduous dominance than mature-burned stands, despite the dominance of both groups by spruce (Picea mariana and Picea glauca) and pine (Pinus contorta) before the fire. Once initiated, deciduous-dominated stands may be maintained across subsequent fire cycles through mechanisms such as low on-site availability of conifer seed, competition with the aspen canopy, and rapid asexual regeneration of aspen after fire. We suggest that climate-related increases in fire frequency could trigger more frequent shifts from conifer to deciduous-dominated successional trajectories in the future, with consequent effects on multiple ecosystem processes.     

Seasonal ionic fluctuations and annual growth rates in stands of Pinus silvestris L. and Picea abies Karst. (L.)

Seasonal variations in potassium, calcium, nitrogen, phosphorus, and magnesium contents of needles from two different stands of Pinus silvestris L. and Picea abies (L.) Karst. were determined monthly during a period of two years, and the growth rates once a year during five years. The stands were growing on sand or on clay. The supposed transport of potassium to the shoot during autumn could not be demonstrated. The nutrient status of pine and spruce growing on sand and clay was very similar, except for calcium and magnesium. There were only small differences in ion contents between pine and spruce, except for calcium. On soils with low water-holding capacity, the available water in dry years is the limiting factor affecting the growth rate of spruce but not of pine. It is concluded that the nutrient status of the leaves, the growth rates and the available water in the soil are factors that should have an important part in any discussion of fertilization of coniferous forests.     

Insect community response to switchgrass intercropping and stand age of loblolly pine (Pinus taeda) plantations

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长白山云冷杉针阔混交林不同林隙下幼苗幼树密度及空间分布

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Increase of biodiversity in homogeneous Scots pine stands by an ecologically diversified management

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Variable temperature sensitivity of soil organic carbon in North American forests

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Latitudinal response of subarctic tree lines to recent climate change in eastern Canada

Aim The predictions from biogeographical models of poleward expansion of biomes under a warmer 2 × CO2 scenario might not be warranted, given the non‐climatic influences on vegetation dynamics. Milder climatic conditions have occurred in northern Québec, Canada, in the 20th century. The purpose of this study was to document the early signs of a northward expansion of the boreal forest into the subarctic forest‐tundra, a vast heterogeneous ecotone. Colonization of upland tundra sites by black spruce (Picea mariana (Mill.) BSP.) forming local subarctic tree lines was quantified at the biome scale. Because it was previously shown that the regenerative potential of spruce is reduced with increasing latitude, we predicted that tree line advances and recent establishment of seedlings above tree lines will also decrease northwards. Location Black spruce regeneration patterns were surveyed across a > 300‐km latitudinal transect spanning the forest‐tundra of northern Québec, Canada (55°29′–58°27′ N). Methods Elevational transects were positioned at forest–tundra interfaces in two regions from the southern forest‐tundra and two regions from the northern forest‐tundra, including the arctic tree line. The surroundings of stunted black spruce, forming the species limit in the shrub tundra, were also examined. Position, total height and origin (seed or layer) of all black spruce stems established in the elevational transects were determined. Dendrochronological and topographical data allowed recent subarctic tree line advances to be estimated. Age structures of spruce recently established from seed (< 2.5 m high) were constructed and compared between forest‐tundra regions. Five to 20‐year heat sum (growing degree‐days, > 5 °C) and precipitation fluctuations were computed from regional climatic data, and compared with seedling recruitment patterns. Results During the 20th century, all tree lines from the southern forest‐tundra rose slightly through establishment of seed‐origin spruce, while some tree lines in the northern forest‐tundra rose through height growth of stunted spruce already established on the tundra hilltops. However, the rate of rise in tree lines did not slow down with latitude. The density of < 2.5‐m spruce established by seed declined exponentially with latitude. While the majority of < 2.5‐m spruce has established since the late 1970s on the southernmost tundra hilltops, the regeneration pool was mainly composed of old, suppressed individuals in the northern forest‐tundra. Spruce age generally decreased with increasing elevation in the southern forest‐tundra stands, therefore indicating current colonization of tundra hilltops. Although spruce reproductive success has improved over the twentieth century in the southern forest‐tundra, there was hardly any evidence that recruitment of seed‐origin spruce was controlled by 5‐ to 20‐year regional climatic fluctuations, except for winter precipitation. Main conclusions Besides the milder 20th century climate, local topographic factors appear to have influenced the rise in tree lines and recent establishment by seed. The effect of black spruce's semi‐serotinous cones in trapping seeds and the difficulty of establishment on exposed, drought‐prone tundra vegetation are some factors likely to explain the scarcity of significant correlations between tree establishment and climatic variables in the short term. The age data suggest impending reforestation of the southernmost tundra sites, although the development of spruce seedlings into forest might be slowed down by the harsh wind‐exposure conditions.     

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