Local spatial pattern in the occurrence of two congeneric wood-decaying fungi in an old-growth boreal forest

Abstract

This paper characterizes spatial patterns in the occurrence of two congeneric wood-decaying fungi (Aphyllophorales: Polyporaceae) in an old-growth boreal forest in eastern Finland. The spatial patterns are used to evaluate indirectly the short-distance dispersal ability of the species. Fomitopsis rosea is a specialist on Picea abies occurring mainly in forests with large amounts of dead wood, whereas Fomitopsis pinicola is a substrate generalist and also abundant in managed forests. Within a forest reserve, a 25 ha study area was divided into 25 m×25 m grid (n=400), and all dead trees and fruiting bodies of the two polypore species were recorded. Spatial patterns were analysed with Spatial Analysis by Distance IndicEs methodology (SADIE). Downed spruce logs were highly aggregated within the study area. After this distribution was accounted for, the spatial pattern of F. pinicola and F. rosea on logs was random. The lack of spatial aggregation suggests that within old-growth forest stands dispersal of the two fungal species is not a limiting factor for their occurrence.     

Carbon and nitrogen dynamics along the log bark decomposition continuum in a mesic old-growth boreal forest

Narrowing the uncertainties in carbon (C) and nitrogen (N) dynamics during decomposition of coarse woody debris (CWD) can significantly improve our understanding of forest ecosystem functioning. We examined C, N and pH dynamics in the least studied CWD component—tree bark in a 66-year-long decomposition chronosequence. The relative C concentration decreased by ca. 32% in pine bark, increased by ca. 18% in birch bark and remained stable in spruce and aspen bark. Nitrogen increased in bark of all tree species. In conifer bark, it increased along with epixylic succession. Over 45 years, the relative C/N ratio in bark decreased by 63 and 45% for coniferous and deciduous species, respectively. Bark pH did not change. Due to bark fragmentation, the total C and N amounts in bark of individual logs of aspen, birch, pine and spruce decreased at average rates of 0.03, 0.02, 0.26 and 0.05 year^?1, and 0.02, 0.02, 0.03 and 0.03 year^?1, respectively. At the forest stand level, the total amounts of C and N in log bark were 853 and 21 kg ha^?1 or 11.2 and 45.5% of the C and N amounts stored in downed logs and ca. 2.3–3.8 and 2.2–2.4%, respectively, of total C and N amounts stored in forest litter. In boreal forests, decomposing log bark may act as a long-term source of N for wood-inhabiting communities.     

The effects of burning and dead-wood creation on the diversity of pioneer wood-inhabiting fungi in managed boreal spruce forests

The loss of natural forest habitats due to forestry is the main reason for the decline in boreal forest biodiversity of the Nordic countries of Europe. Ecological rehabilitation may provide means to recover and sustain biodiversity. We analyzed the effects of controlled burning and dead-wood creation (DWC) on the diversity of pioneer wood-inhabiting fungi in managed Norway spruce (Picea abies) forests in southern Finland. Altogether 18 stands were first subjected to a partial cutting with ordinary logging residues in form of cut stumps and treetops left on site. The subsequent rehabilitation treatments consisted of a controlled burning applied in half of the stands and three levels of dead-wood creation (5, 30 and 60 m³ ha⁻¹). The DWC involved creation of logs; felling of whole trees to mimic downed logs formed by natural disturbance processes. Each treatment was replicated three times. Inside each stand, substrates were sampled in two different biotopes; one on mineral soil and one on mineral soil with a thin peat layer. We surveyed the fungal flora on the logs (n = 364) and the ordinary residue stumps (n = 1767) and tops (n = 845) five years after the treatments.When comparing different stands, controlled burning had a significant effect on species composition; certain species were significantly more frequent on substrates in burned stands than in unburned stands, indicating that these species were favored by controlled burning. By contrast, we found no significant effects of DWC levels or biotope on species composition or richness. When comparing different substrates, 99% of the logs hosted at least one species and the occurrence probability of certain species was significantly higher on logs than on ordinary residue stumps and tops. Yet, volume-based rarefaction analyses showed that residues were more species dense than the logs, indicating that ordinary logging residues constitute important resources for many pioneer species.We conclude that controlled burning combined with DWC have strong effects on biodiversity; it modifies the composition of the pioneer wood-inhabiting fungal species found in managed forests and may thereby also influence the further succession and diversity of the secondary fungal flora.     

Modeling the effects of climate change and management on the dead wood dynamics in boreal forest plantations

The present research examines the joint effects of climate change and management on the dead wood dynamics of the main tree species of the Finnish boreal forests via a forest ecosystem simulator. Tree processes are analyzed in stands subject to multiple biotic and abiotic environmental factors. A special focus is on the implications for biodiversity conservation thereof. Our results predict that in boreal forests, climate change will speed up tree growth and accumulation ending up in a higher stock of dead wood available as habitat for forest-dwelling species, but the accumulation processes will be much smaller in the working landscape than in set-asides. Increased decomposition rates driven by climate change for silver birch and Norway spruce will likely reduce the time the dead wood stock is available for dead wood-associated species. While for silver birch, the decomposition rate will be further increased in set-aside in relation to stands under ordinary management, for Norway spruce, set-asides can counterbalance the enhanced decomposition rate due to climate change thereby permitting a longer persistence of different decay stages of dead wood.     

Spatial distribution of dead wood and the occurrence of five saproxylic fungi in old-growth timberline spruce forests in northern Finland

Abstract

Adequate understanding of the factors that determine the establishment and survival of dead-wood-dependent species in natural forests is a prerequisite to the successful maintenance of these species in managed forests. This study investigated the factors affecting the occurrence of five wood-inhabiting polypores in old-growth timberline spruce forests in northern Finland, including the substrate availability and the spatial arrangement of large-diameter logs. The volume of coarse woody debris (CWD) varied significantly between the sites (range 15–30 m³ ha^?1), large-diameter logs comprising on average 35% of the total CWD volume. However, the within-site variation in CWD volume was 10–15 times larger than the between-site variation. The spatial distribution of large-diameter logs was aggregated or initially aggregated on four sites and random on one site, creating local patches of high CWD volume. An individual target species occurred on average on 8% of all large-diameter logs, and on 11% of optimal logs (as determined by the decay stage). The characteristics of the logs and stand variables explained partly the occurrence of the target species; furthermore, the mortality pattern of trees (stem breakage versus uprooting) and the presence of primary decomposers also significantly affected the occurrence of the target species. The results indicate that besides substrate availability and quality, local habitat factors and species interactions also play a role in the occurrence of wood-inhabiting fungi in boreal timberline forests.     

The diversity of wood-decaying fungi in relation to changing site conditions in an old-growth mountain spruce forest,Central Europe

Studies on the relation of the diversity of wood-decaying fungi to elevation are scarce, and their results are not consistent. We found that the elevation gradient and structural characteristics of a Picea abies forest underlie changes in the species richness and composition of wood-decomposing fungi. The occurrence of macrofungal sporocarps on logs on the ground was recorded over 3 years in 12 study plots (total area 2.4 ha) on a mountain slope (1,220–1,335 m) in the Bohemian Forest, Czech Republic. The majority of species was more abundant in plots with a high mean volume of logs. The mean volume of logs was negatively related to elevation, which in turn had a negative influence on the occurrence of fungi. A negative relation of the high total volume of standing snags to the occurrence of fungi may be due to recent mortality caused by a bark beetle outbreak, albeit followed by the input of fresh logs that favoured a limited group of species. The diversity of fungi was also explained by the mean volumes of logs separated into decay classes. Numbers of red-listed species increased with the mean volume of logs and decreased with elevation. Large logs in later stages of decay provide essential habitat for the formation of sporocarps of red-listed species.     

The choice of definition has a large effect on reported quantities of dead wood in boreal forest

A survey was conducted to assess the impact of the choice of definition on reported quantities of dead wood in Swedish forests, which to more than 90% are located in the boreal zone. The data collection was made on a subsample of the permanent plots of the Swedish national forest inventory. The objects included were standing dead trees and snags down to 5-cm diameter at breast height, dead lying stems and branches down to a threshold diameter of 1 cm and stumps down to a threshold diameter of 5-cm at normal stump height. Standing trees, snags and stumps were inventoried on 10-m radius circular plots while the downed objects were inventoried using both circular plots and line intersect sampling; thin objects (diameter 1–5 cm) were assessed only through line intersect sampling. The results showed that the estimated volume of dead wood was as high as 25 m³ ha^?1 when all components were included. With the standard Swedish definition, the corresponding estimate was only 10.9 m³ ha^?1, or 43% of the total value. Since definitions of dead wood vary greatly between countries we conclude that great caution must be exercised when figures are compared in connection with international reporting. For example, adding stumps to the Swedish definition would increase the amounts of dead wood from 10.9 to 15.7 m³ ha^?1, i.e. with 44%.     

Tree mortality and habitat shifts in the regeneration trajectory underneath canopy of an old-growth subalpine forest

To better understand tree regeneration trajectories and the resultant coexistence of Abies with co-dominants, Picea jezoensis var. hondoensis, Tsuga diversifolia and Betula ermanii, in an old-growth subalpine forest, we investigated spatial mortality patterns during the regeneration of Abies mariesii and A. veitchii, which are abundant in the understory reflecting their shade tolerance. Regeneration of these Abies spp. from shaded understory to canopy status is affected by other canopy co-dominants. Snags of understory Abies spp. were common, suggesting that the primary mortality agent is suppression by the overstory. Although live, small Abies trees in the understory were positively associated with a Picea canopy, the long-term survival was reduced among Abies trees close to the canopy, suggesting that shading by large Picea in the overstory negatively affects understory Abies plants. The existence of shade-intolerant canopy co-dominants such as Picea and also Tsuga, which are larger and longer lived than the shade-tolerant Abies, may play an important role in preventing the Abies spp. from competitively displacing these other tree species, which are much rarer in the understory, though common in the canopy. Moreover, in spite of the fact that Betula canopies fostered recruitment and growth of Abies saplings, Abies showed no association with Betula canopy and their survival at later-stage was rather reduced near or beneath Betula canopies at the subsequent understory small tree stage. Based on spatially significant events related to tree death, this study detected such “habitat shifts” in the trajectory of tree regeneration. Accordingly, it can be concluded that careful consideration of the regeneration habitat is required for a fuller understanding of ecological processes in spatially complex old-growth forest systems.     

Red-listed wood-inhabiting fungi in natural and managed forest landscapes adjacent to the timberline in central Sweden

Many wood-inhabiting fungi are today threatened as modern forestry practices drastically reduce the amount of dead wood available in various forest ecosystems. We investigated whether the occurrence of red-listed wood-inhabiting fungi differed between natural and managed forest landscapes adjacent to the timberline in the middle part of Sweden. We assessed whether environmental variables such as the degree of human impact, length of forest roads, dead wood volume and quality affected species richness and abundance. The effects of forestry on wood-inhabiting fungi have been assessed in several studies in lowland Swedish forests. Few studies have, however, been conducted in forest landscapes adjacent to the timberline in Sweden. This is potentially important since forests close to the Swedish mountains have been pointed out as one of few intact forest landscapes in Fennoscandia and they are subjected to increasing logging pressure. Similar to other studies, species numbers and abundances were positively correlated with larger volumes of logs in various decay stages. However, never shown previously, the length of forest roads was negatively correlated with species abundance and occurrence of red-listed species. We suggest that a low amount of forest roads can be used as a conservation indicator to localize still-intact forest landscapes.     

A dendroecological reconstruction of disturbance in an old-growth Fagus-Abies forest in Slovenia

The scarcity of large old-growth forests has made it challenging to quantify disturbance regimes in Central Europe. The objective of this study was to reconstruct the history of disturbance in an old-growth Fagus-Abies forest reserve in Slovenia using a dendroecological approach. We extracted cores from canopy trees blown down during a recent windthrow event and identified growth releases in the tree-ring series using boundary-line release criteria to infer past disturbances. A total of 216 release events were identified from 88 trees. Between 1790 and 1990, moderate, asynchronous release events were present in nearly every decade of the disturbance chronology, suggesting a history of frequent, low severity disturbance. However, there were also peaks in the chronology corresponding to synchronous release events in a large proportion of the trees, suggesting that less frequent, intermediate severity disturbance events played an important role in forest development. These events are likely caused from wind damage associated with local thunderstorms, which seem to occur at intervals between 20–80 years on the study site. Thus, in addition to the small-scale gap phase processes operating in the forest, the results indicate that periodic intermediate severity disturbance events are an important component of the disturbance regime in mountain forests of Central Europe.     

Legacies from natural forest dynamics: Different effects of forest management on wood-inhabiting fungi in pine and spruce forests

The species composition of wood-inhabiting fungi (polypores and corticoids) was investigated on 1138 spruce logs and 992 pine logs in 90 managed and 34 natural or near-natural spruce and pine forests in SE Norway.Altogether, the study included 290 species of wood-inhabiting fungi. Comparisons of logs with similar properties (standardized tree species, decay class, dimension class) in natural and managed forests showed a significant reduction in species number per log in managed spruce forests, but not in managed pine forests. The species number per log in managed spruce forests was 10-55% lower than on logs from natural spruce forests. The reduction was strongest on logs of large dimensions. A comparison of 200-400 spruce logs from natural and managed forests showed a 25% reduction in species richness corresponding to a conservative loss of ca. 40 species on a regional scale.A closer inspection revealed that species confined to medium and very decayed spruce logs were disfavored in managed forests, whereas species on early decay classes and decay generalists were unaffected. Similarly, species preferring large spruce logs were disfavored in managed forests. Forest management had strongest impact on low-frequent species in the spruce forests (more than 50% reduction), whereas common species were modestly affected. Corticoid fungi were more adversely affected than polypore fungi.These results indicate that wood-decaying fungi in pine forests are more adapted to forest disturbances than spruce-associated species. Management measures securing a continuous supply of dead wood are more important in spruce forests than in pine forests.     

A review of habitat thresholds for dead wood: a baseline for management recommendations in European forests

In contemporary forest management, also of commercial forests, threshold values are widely used for consideration of biodiversity conservation. Here, we present various aspects of dead-wood threshold values. We review published and unpublished dead-wood threshold data from European lowland beech–oak, mixed-montane, and boreo-alpine spruce–pine forests separately to provide managers of European forests with a baseline for management decisions for their specific forest type. Our review of dead-wood threshold data from European forests revealed 36 critical values with ranges of 10–80 m³ ha⁻¹ for boreal and lowland forests and 10–150 m³ ha⁻¹ for mixed-montane forests, with peak values at 20–30 m³ ha⁻¹ for boreal coniferous forests, 30–40 m³ ha⁻¹ for mixed-montane forests, and 30–50 m³ ha⁻¹ for lowland oak–beech forests. We then expand the focus of dead-wood threshold analyses to community composition. We exemplify the two major statistical methods applied in ecological threshold analysis to stimulate forest researchers to analyze more of their own data with a focus on thresholds. Finally, we discuss further directions of dead-wood threshold analysis. We anticipate that further investigations of threshold values will provide a more comprehensive picture of critical ranges for dead wood, which is urgently needed for an ecological and sustainable forestry.     

Canopy gaps in an old-growth fir-beech forest remnant of Western Carpathians

The old-growth forest remnants of Western Carpathians provide a unique possibility to study the disturbance regimes of forest ecosystems without human influence. This study investigated the gap dynamics in beech-dominated old-growth forest Badínsky prales in Central Slovakia. Considering the decline of silver fir in last decades, the study analyzed the main characteristics of disturbance regime with the emphasis on the role of fir. On a 5-ha research plot, the dominant tree species was beech, the proportion of fir reached about 10%. However, a significantly higher proportion of fir (>30%) was observed in the coarse woody debris. In total, 45 canopy openings were recorded. Canopy gaps and expanded gaps covered 11.3 and 37.9% of the forest area, respectively. Despite the highest frequency of small gaps <100 m², their proportion of the overall gap area reached only 20%, what suggests the important role of intermediate and large gaps in the gap dynamics as well. The analysis of gapmakers’ crown projections confirmed a rather low contribution of fir (14.6%) to the gap formation despite its relatively intensive mortality. A high variability of the next generation age between the gaps (6–44 years) was recorded what suggests a large temporal variation of the disturbance events. The lateral expansion of adjacent trees was found to be the determining process for the closure of small canopy openings. The intermediate and large gaps are more likely closed by the height growth of natural regeneration and understory trees that are present on the majority of the area.     

Effect of wind damage on the habitat suitability of saproxylic species in a boreal forest landscape

Many forest-dwelling species are dependent on deadwood. Sources of deadwood include competition- and senescence-related mortality of trees, and various damages. This study described a methodology for predicting the effect of wind damage on the amount of deadwood and suitability of the forest for saproxylic species. The methodology was used in a forested boreal landscape of 360 ha to analyze the effects of wind damage on the habitat quality for 27 groups of saproxylic species differing in their requirements for the species, size and decay stage of deadwood objects. A reference plan maximized net present value (MaxNPV) while others either minimized or maximized height differences between adjacent stands. Maximization of height differences resulted in high amount of wind damage and deadwood while minimizing height differences minimized wind damage and the amount of damage-related deadwood. The fourth plan maximized the average habitat suitability index (HSI) of the 27 groups of saproxylic species. The plans were compiled with and without even-flow harvesting constraints for three 10-year periods. Maximization of height differences between adjacent stands resulted in higher HSI values than obtained in the MaxNPV plan or in the plan than minimized height differences between adjacent stands. The average HSI of shade-demanding species correlated negatively with the amount of harvested timber. No strong correlations were found for light-demanding and indifferent species.     

Identification of boreal forest stands with high herbaceous plant diversity using airborne laser scanning

Boreal forest stands with high herbaceous plant species diversity have been found to be one of the main habitats for many endangered species, but the locations and sizes of these herb-rich forest stands are not well known in many areas. Better identification of the stands could improve both their conservation and management. A new approach is proposed here for locating the mature herb-rich forest stands using airborne laser scanner (ALS) data and logistic regression, or the k-NN classifier. We show that ALS technology is capable of distinguishing the ecologically important herb-rich forests from those growing on less fertile site types, mainly on the basis of unique but quantifiable crown structure and vertical profile that characterise forests on high fertility sites. The study site, Koli National Park, is located on the border of the southern and middle boreal vegetation zones in Finland, and includes 63 herb-rich forest stands of varying sizes. The model and test data comprised 274 forest stands belonging to five forest site types varying from very fertile to poor. The best overall classification accuracy achieved with the k-NN method was 88.9%, the herb-rich forests being classified correctly in 65.0% of cases and the other forest site types in 95.7%. The best overall classification accuracy achieved with logistic regression was 85.6%, being 55.0% for the herb-rich forests and 94.3% for the other forest site types. Both methods demonstrated promising potential for separating herb-rich forests from other forest site types, although slightly better results were obtained with the non-parametric k-NN method, which was capable of utilising a higher number of explanatory variables. It is concluded that ALS-based data analysis techniques are applicable to the detection of mature boreal herb-rich forests in large-scale forest inventories.     

Influence of fire intensity on structure and composition of jack pine stands in the boreal forest of Quebec: Live trees,understory vegetation and dead wood dynamics

North American jack pine (Pinus banksiana Lamb.) stands are generally characterized by an even-aged structure resulting from high intensity fires (HIF). However, non-lethal fires of moderate intensity (MIF), which leave behind surviving trees, have also been reported. The objectives of this study were two-fold: (1) assess the concurrent dynamics of live trees, understory vegetation and different types of coarse woody debris (CWD) during succession after HIF; and (2) document how MIF affects stand structure component dynamics compared to HIF. Stands affected by both HIF and MIF were selected. Tree characteristics and age structure, understory biomass, and CWD volume were assessed. Our results suggest that the structural succession of jack pine stands following HIF comprises three stages: young stands (<48 years), premature and mature stands (58–100 years) and old stands (>118 years). Canopy openness and jack pine density significantly decreased with time since HIF, while black spruce density and CWD volume significantly increased. The highest structural diversity was measured in the premature and mature stands. Compared to HIF, MIF increased mean jack pine basal area, decreased average stand density, delayed the replacement of jack pine by black spruce replacement in the canopy, decreased CWD volume, and significantly increased bryophytes mass. MIF increased the diversity of live trees and generally decreased CWD structural diversity. The study confirms the diversity of natural disturbance magnitude and successional processes thereby initiated. Thereafter, it appeared to be relevant for adjustment of disturbance emulating forest-management systems.     

Effects of species and tree size diversity on recruitment in the Alaskan boreal forest: A geospatial approach

This study empirically evaluates and maps the relationships between recruitment and species and tree size diversity, as measured with the Shannon’s index, within mixed poplar/birch and mixed spruce stands across the boreal forest of Alaska. Data were collected from 438 permanent sample plots re-measured at a 5-year interval. Significant explanatory factors of recruitment, including species and tree size diversity were first identified using hierarchical partitioning. The effects of tree diversity on recruitment were then studied using generalized linear models and universal kriging to account for non-spatial factors and for spatial autocorrelation. We found a consistent positive relationship between recruitment and species diversity and a general negative relationship between recruitment and tree size diversity, indicating a tradeoff between species diversity and tree size diversity in affecting recruitment. These relationships however were not uniform across the landscape, presumably because they were subject to strong spatial autocorrelation attributable to natural disturbances and environmental stressors. In general, diversity had least effect on recruitment in stressful environments where stress, rather than competition, most likely governed recruitment.     

Species-specific partitioning of soil water resources in an old-growth Douglas-fir-western hemlock forest

Although tree- and stand-level estimates of forest water use are increasingly common, relatively little is known about partitioning of soil water resources among co-occurring tree species. We studied seasonal courses of soil water utilization in a 450-year-old Pseudotsuga menziesii (Mirb.) Franco-Tsuga heterophylla (Raf.) Sarg. forest in southwestern Washington State. Soil volumetric water content (theta) was continuously monitored with frequency domain capacitance sensors installed at eight depths from 0.2 to 2 m at four locations in the vicinity of each species. Vertical profiles of root distribution and seasonal and daily courses of hydraulic redistribution (HR), sap flow and tree water status were also measured. Mean root area in the upper 60 cm of soil was significantly greater in the vicinity of T. heterophylla trees. However, seasonal water extraction on a root area basis was significantly greater near P. menziesii trees at all depths between 15 and 65 cm, leading to significantly lower water storage in the upper 65 cm of soil near P. menziesii trees at the end of the summer dry season. Greater apparent efficiency of P. menziesii roots at extracting soil water was attributable to a greater driving force for water uptake rather than to differences in root hydraulic properties between the species. The dependence of HR on theta was similar in soil near individuals of both species, but seasonal maximum rates of HR were greater in soil near P. menziesii because minimum values of theta were lower, implying a steeper water potential gradient between the upper and lower soil that acted as a driving force for water efflux from shallow roots. The results provide information on functional traits relevant for understanding the ecological distributions of these species and have implications for spatial variability of processes such as soil respiration and nutrient cycling.     

Twenty-three years of stand dynamics in an old-growth Chamaecyparis forest in central Japan

Structures and dynamics of old-growth coniferous stands are affected by several types of disturbances including typhoons. We report the forest dynamics of four old-growth Chamaecyparis stands in central Japan that differ in the disturbance history of typhoons over a period of 23 years. The stem number, basal area and mortality were examined. In a predominant stand of C. obtusa (Sieb. et Zucc.) Endl., 24 % of the C. obtusa canopy trees died, mainly as a result of the severe damage of a strong typhoon that caused a single tree-fall gap and the following gap enlargements. In this stand, the total basal area decreased to 76.5 % of the initial value, although the mortality declined in recent years. In contrast, the other three stands decreased only slightly in the stem numbers (0.0–5.6 %) and increased in the basal areas of C. obtusa canopy trees. It is confirmed that the stand-level ingrowths of 300-year-old C. obtusa canopy trees could contribute to the increase in the stock of each stand. Our results support an idea that the dynamics of old-growth Chamaecyparis forests were greatly affected by typhoons. The stand structures will be gradually changed (with the processes of gap dynamics) and C. obtusa will continue to be dominant, potentially over hundreds of years.