Spruce regeneration on woody microsites in a subalpine

by L Bujoczek · Cited by 5 — 208 p. Holeksa J., Ciapała S. (1998). Usuwanie martwych drzew a naturalne odnowienie świerka w gór- noreglowych borach świerkowych Beskidu Wysokiego.

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1Leszek Bujoczek 1211Spruce regeneration on woody microsites in a subalpine forest in the western Carpathians (2015). Spruce regeneration on woody microsites in a subalpine forest in the western Carpathians. Silva Fennica vol. 49 no. 3 article id 1337. 21 p. HighlightsThe occurrence probability of Picea abies seedlings on fallen deadwood was found to increase with diameter and decay stage of deadwood and with the volume of living trees, and to decrease with the density of living trees, sapling density, and land slope; it was also higher on stumps with greater diameter and in plots with higher sapling density, but decreased with increasing stump height.The density of Picea abies [L.] Karst. regeneration on different microsites, the quantity and quality of woody microsites, and seedling occurrence probability on stumps and fallen deadwood were studied in a subalpine forest in the Gorce Mountains, part of the western Carpathians, which has been under protection for approximately 30Œ40 years. Thirty percent of seedlings and 29% of saplings grew on stumps and fallen deadwood, while the remaining regeneration occurred on the Picea seedlings on fallen deadwood increased with deadwood diameter and decay stage and with the volume of living trees, and decreased with increased density of living trees, sapling density, and land slope. Furthermore, seedlings were more likely to grow on stumps with a greater diameter and in plots with higher sapling density, but less likely to grow on higher stumps. Stumps and fallen deadwood covered about 408 m2 exceeding 30 cm, which are the most important for promoting regeneration, took up only about 22 m2/ha. In the studied subalpine forest, which has been protected for 30Œ40 years, tree regenera – coarse woody debris; regression model; fallen deadwood; stumps; decomposition; Picea abies 1 Department of Forest Management, Geomatics and Forest Economics, Faculty of Forestry, University of Agriculture in Krakow, Al. 29 Listopada 46, 31Œ425 Krakow, Poland ; 2 Department of Forest Biodiversity , Faculty of Forestry, University of Agriculture in Krakow, Al. 29 Listopada 46, 31Œ425 Krakow, Poland E-mail 17 March 2015 6 May 2015 7 May 2015 http://dx.doi.org/10.14214/sf.1337

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21 Introduction In areas with harsh climate the occurrence of suitable microsites for seedlings and saplings, pro -viding better conditions for their survival and growth, is an important aspect of phytocoenosis regeneration (Harmon et al. 1986; Kuuluvainen 1994; Hörnberg et al. 1995; Kupferschmid and Bugmann 2005a). The presence of different types of microsites creates diverse environmental conditions in terms of temperature, moisture, and light. In a windthrow area of boreal old-growth forest, Kuuluvainen and Kalmari (2003) found that the spatial distribution of Picea abies [L.] Karst. regeneration establishment was nonrandom and varied between different microsite types. Picea seedlings were found in microsites created by windthrow disturbance, and particularly on advanced-decay wood and uprooted pits and mounds. Sixty-three percent of Picea seedlings occurred in these microsites, although they only covered approx. 28% of the study area. The results positive effect of several site parameters on Picea regeneration. More Picea saplings grew on rough surfaces and near hindrances, such as stumps, uprooted stumps, rocks, and fallen snags. In turn, high ground vegetation coverage and humus thickness negatively affected regeneration. In correlation with the presence of mosses of low thickness. Their results also pointed to microsites covered with litter and decaying wood as preferred ones.In subalpine forests, the role of coarse woody debris (CWD) in the regeneration process is particularly pronounced (Kupferschmid and Bugmann 2005a). In the Carpathians, this mountain zone is dominated by Picea abies (Jaworski and Karczmarski 1995; Chwistek 2001; Holeksa et Picea seed germination, while the sites most suitable for the growth of young Picea plants are logs, stumps, and mounds created by uprooted trees (Holeksa 1998). The importance of these microsites has been reported in numerous papers (e.g., Hytteborn and Packham 1987; Hofgaard 1993; Hörnberg An abundance of deadwood does not guarantee the formation of woody microsites suitable for the emergence and survival of Picea seedlings. Shortly after their death, fallen trees are inaccessible to vascular plants (Zielonka 2006a, Holeksa et al. 2008). The process of decomposition changes the physical and chemical properties of wood and therefore affects the conditions for the functioning of the organisms associated with it. The decomposition of Picea deadwood is accompanied by a decrease in its density and increased moisture. Its chemical composition becomes altered as well of the white-rot fungi Armillaria spp. and Phellinus nigrolimitatus was positively correlated with both seedling and sapling density, and conversely the presence of the brown-rot fungus Fomitopsis pinicola was negatively correlated with regeneration density. According to data from various regions of the world, the decomposition rates of Picea wood expressed as mean k et al. 2008). Numerous studies have shown the complexity of the process (Edmonds and Eglitis 1989; Busse 1994; Zhou et al. 2007). In the Carpathians, the mean total residence time of Picea logs was studied in reference to their diameter and amounted to 71 years for logs with a diameter of under 23 cm, 90 years for 23Œ35 cm, and 113 years for more than 35 cm (Holeksa et al. 2008). On an eight-level scale, the mean time to decay stage III is about 28 years, to stage V Œ 45 years, and to stage VII Œ 60 years (Zielonka 2006b). The succession pattern of Picea regeneration on logs in relation to decay stage has been discussed in several publications (Narukawa et al. 2003; Mori et. al. 2004). In the western Car –

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3survive for decades. The most abundant Picea recruitment occurs on logs 30Œ60 years after tree death, when the wood is in decay stages IVŒVII (Zielonka 2006a). It has also been found that the optimum period for seedling emergence and survival occurs before mosses completely cover the Studies conducted in the Alps have shown that microsites undergo dynamic changes. It has tree number and species composition (Kupferschmid and Bugmann 2005b; Kupferschmid et al. 2006). Of particular importance at the subalpine level are light conditions, as the demand of young Picea plants for light increases with altitude (Jaworski 1995). Light conditions depend on both Christensen et al. (2005) reported a positive correlation between the time an area has been under strict protection and the amount of CWD remaining in stands. For a long time, montane Picea forests in Central Europe have been used for timber production (Svoboda et al. 2010). However, (Kräuchi et al. 2000). Woody microsites play an important role in the functioning of forest eco -forest biodiversity (Siitonen 2001; Stokland et al. 2012). Therefore, the quantity and quality of such microsites and their impact on regeneration are issues of great interest, and research in this addresses the following questions:Which microsite types are favorable / suitable for Picea regeneration in a subalpine forest that PiceaWhich characteristics of stands and parameters of woody microsites have an effect on the occur -rence of Picea2 Materials and methods 2.1 Study area The study was conducted in the subalpine forest located in its entirety in Gorce National Park, in the south of Poland. The Gorce Mountains are situated in the western Carpathians and cover an area of approximately 550 km2, extending between 19°53´Œ 20°26´E and 49°26´Œ 49°40´N. A subalpine forest occurs between the isotherms of 4 and 2°C (Hess 1965), from an altitude of about 1100 m Plagiothecio-Piceetum tatricum The forest is dominated by Picea abies (93% of stand volume and 87% of tree number), with other species (albeit less abundant, particularly in lower locations) being Fagus sylvatica L. (6% and 11%, respectively) and Abies alba Mill (in both cases 1%). Single occurrences of Sorbus aucuparia L. and Acer pseudoplatanus L. have been recorded (Chwistek 2001). The mean stand volume recorded in the years 1992Œ2007 was 357Œ403 m 3 haŒ1 with a basal area of 32Œ35 m2 haŒ1, and the number of trees being 408Œ479 per ha (Chwistek 2010).

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4The density of seedlings (on average 9587 per ha) and saplings (1094 per ha) and their spe-cies composition in the entire subalpine forest were described in detail as of 2003 Picea, whose share in seedlings and saplings was 88% and 34%, Sorbus aucuparia (1% and 48% ), Fagus sylvatica (8% and 8%), and Abies alba (3% and 6%). Some individuals belonging to the species Larix decidua Mill., Betula pendula Acer pseudoplatanus, Salix caprea L., and Populus tremula L. were also found. The ground vegetation was dominated by Vaccinium myrtillus , Polytrichum attenuatum , Athyrium distentifolium, Calamagrostis sp., and Oxalis acetosella.Due to the history of protection and silvicultural interventions, the studied subalpine forest is not homogeneous. Most of the forest (an area of approx. 1038 ha) has been under protection since 1979 (Fig. 1). That area consists of several smaller sub-areas. In the 1980s and 1990s, due to an outbreak of Cephalcia alpina Klug (= C. falleni Dalm.), the forest was under active pro -tection (Capecki 1982), involving sanitation cutting and removal of dead trees. Currently, strict protection has been reestablished. The forest area is a mosaic of different developmental stages, from parts in the break-up stage and undergoing succession processes, through optimum stages, to old-growth forest.Fig. 1. Location of the study area and the arrangement and characteristics of sample plots.

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5has been under strict protection continuously since 1970 (some of the forest was included in the protection plan in 1979). It forms a mosaic of even-storied medium-aged stands and old-growth forest, marked by disturbances initiated in recent years.These two forest areas were studied separately in the years 2003 and 2007.2.2 Field methods grew on were recorded (Table 1). Data were collected from 221 circular sample plots, distributed was 100 m2a large area, thus 4 subplots were delineated for counting seedlings, each of an area of 1.25 m 2, with their centers located at a distance of 3 m towards N, W, S, and E from the center of the plot. The second study was carried out in the summer of 2007 in the second part of the subalpine forest, with an area of 45 ha. The amount of regeneration, CWD parameters, and stand characteristics were recorded (Table 1). Measurements were taken in 20 permanent circular sample plots, each with an area of 500 m 2, distributed regularly at the nodes of a grid formed by 150 × 100 m rectangles (Fig. 1). 15Œ22.9, 23Œ30.9 cm, etc. Measurement was limited to inside the circumference of the circular sample plots, so if a piece of deadwood was situated across the plot border, only the part that lay within the plot was counted. The stage of CWD decomposition was recorded on an eight-level scale (Table 2). In total, 959 pieces of fallen deadwood and 193 stumps were examined. All fallen deadwood pieces and stumps were thoroughly checked for the occurrence of Picea seedlings (excluding current-year seedlings). No other species of seedlings grew on CWD. Saplings occurred infrequently on woody microsites and in numbers too low to enable statistical analysis. Additionally, in each plot, standing cm were measured, the slope of the sample plot was recorded, saplings of all species were counted, and canopy closure was determined (as a percentage of ground area shaded by overhead foliage and estimated visually). Moreover, based on 1992 data concerning the studied forest areas, the volume of trees that died over the past 15 years (tree losses) was estimated. The volume of living and standing dead trees, as well as tree losses, was estimated with the and snags was calculated according to Smalian™s formula (Eq. 1): ˜˚˛˜˚˚˛˜˚˛˝˝˙where: ebss, Œ cross-sectional area at the beginning and end of a CWD piece and lŒ length of the piece. The cross-sectional area of each end of a CWD piece, depending on its shape, was cal —

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6Table 1. Measurements taken on sample plots in 2003 and 2007.Measured characteristicMeasurements on an area of 1038 ha in 2003, on 221 sample plots Picea seedlings were not included):1. small: height < 26 cm Seedling height was measured and two types of microsites were distinguished: and also the exposed mineral soil formed by tree fall) and mounds (formed by the root plates of uprooted trees)2. decaying wood (stumps and fallen deadwood) Picea saplings (eight classes): 2. DBH1 < 1 cm Sapling height or DBH were measured and four types of microsites were distinguished: 2. mounds 3. stumps4. fallen deadwood For last three classes of saplings, microsite categories were Measurements on an area of 45 ha w 2007, on 20 sample plots Deadwood typeStanding entire dead trees with DBH 7 cmDBH and height of treesSnags Œ standing snapped trees with stump height 1.3 m and DBH 7 cm)Height and two diameters: under the ground and at the top of snagStumps with height < 1.3 m and diameter above the Height and two diameters: under the ground and at the top of stumpFallen deadwood: plates ) trunk or large branches etc.) Deadwood thinner than 7 cm in diameter was not taken into account.-egories during measurement, each category having a span of 8 cm in diameter: 7Œ14.9, 15Œ22.9, 23Œ30.9, etc. At the end of each deadwood piece, the width and height of the cross-sectional area were measured. The length of the piece and stage of decomposition were recorded on an 8 level scale (Table 2). Piceawere not included):1. small: height < 26 cm Height of seedling and the type of microsite it grew on deadwood and coarse woody debris decomposition were recorded.Saplings on woody microsites were not taken into account because they occurred infrequently and in numbers too low to enable statistical analysis.Other characteristics measured on sample plotsLiving trees Œ all trees with DBH 7 cm (all species were included)DBH and height of trees.Tree losses Œ all trees that died over 15 years before the 2007 measurement It was recorded which trees died relative to the 1992 measurement (tree coordinates and DBH were known from 1992).Saplings Œ all individuals with height 0.5 m but with DBH < 7 cm (all species were included)Number of saplings on the sample plot.Slope of sample plot [°]Slope of the land on which the sample plot was located.Canopy closure [%]-head foliage and estimated visually. 1DBH - diameter at breast height PAGE - 8 ============ 8trees by 1 unit calculated for 1 ha did not lead to perceptible changes in the odds ratio, which was -pendent variables by one unit increased or decreased Picea seedling probability by the odds ratio. Interdependencies among the independent variables were tested by the existence of correla -tions, and additionally by multivariate regression analysis and the corresponding tolerance values. A model was built using the stepwise forward method. Initially, only one explanatory variable was applied, and subsequently other variables were included in the model. The new model was compared with the preceding one with the use of the likelihood ratio Chi-squared test. McFadden, 2 values were used as quality characteristics of the model (Larose Pearson™s residuals were calculated (Menard 2001). The Spearman rank correlation was used to assess the relationship between all independent variables in a given sample plot (volume, basal area, density of living trees, losses over 15 years prior to measurement, canopy closure, sapling density, slope of sample plot, volume of fallen deadwood and stumps, total volume of CWD).3 Results3.1 Density of Picea seedlings and saplings on different microsites Based on data obtained from 221 sample plots in 2003, total Picea regeneration, that is, the total number of seedlings and saplings (excluding current-year seedlings) was 7587 ha-1. The average Picea seedling density was 7167 haŒ1 (Fig. 2). The density of Picea saplings was 395 haŒ1 for those with a DBH of less than 4 cm and 25 ha-1 for those with a DBH of 4Œ6.9 cm.Fewer seedlings grew on decaying wood (30%, Student™s t = 3.4; p < 0.001) than on the on stumps and fallen deadwood was 33% and 11%, respectively (Fig. 3). Microsite type was also important for Picea saplings with a DBH of less than 4 cm (ANOVA; on mounds created by uprooted trees. In terms of regeneration on decaying wood, the most numer-Table 3. Characteristics of stands and coarse woody debris as measured on twenty 0.05 ha sample plots in 2007.Variables MeanMinŒMaxStandard deviationVolume of living trees [m 3 ha-1]375131Œ724170Density of living trees [trees ha-1]52080Œ1205287Basal area of living trees [m2 ha-1]37.916.4Œ63.213.4Sapling density [individuals ha-1]7000Œ2600741Total volume of coarse woody debris [m 3 ha-1]18045Œ422104Volume of fallen deadwood and stumps [m 3 ha-1]6512Œ17248Height of stumps [m]0.550.15Œ1.200.25Canopy closure [%]41.210Œ8522.7Tree losses [m 3 ha-1 year-1] (over the past 15 years)7.00.0Œ20.05.7Slope of sample plot [degrees]17.80Œ308.0 PAGE - 9 ============ 9ous group of saplings was associated with stumps (23%), while those growing on fallen deadwood and other microsites (Tukey test p < 0.001), and between stumps and mounds (p < 0.01). In turn, mounds and fallen deadwood.3.2 Quantity and quality of woody microsites According to data obtained from 20 sample plots in 2007, the fallen deadwood and stumps covered 2 haŒ1). The area occupied by fallen deadwood of different deadwood of small dimensions occupied the largest area, amounting to 166 m 2 haŒ1 for pieces in diameter, covered an area of 109 m 2 haŒ1 60 m2 haŒ1 each. The total area of stumps was 12 m 2 ha-1.In terms of decay stages, the area of deadwood in decay stage I was 92 m2 haŒ1 due to the accumulation of fresh wood (Fig. 4). Decay stages (IIŒVII) showed similar values of approximately Fig. 2. Density of Picea seedling and saplings (with a diameter at breast height of less than 4 cm) on different micro - separate analyses were conducted for seedlings and saplings. PAGE - 10 ============ 10Fig. 3. Picea seedlings and saplings with a DBH (diameter at breast height) of less than 4 cm on different microsites. Fig. 4. Total area of stumps and fallen deadwood in the various decay stages (top chart) and areas of those microsites fallen deadwood in the chart legend. PAGE - 11 ============ 1140Œ50 m2 haŒ1. The most decomposed wood occupied the smallest area (32 m2 haŒ1). The differ -between the sample plots. -cantly positively correlated with the volume of tree losses and total volume of CWD and negatively correlated with the density of living trees and canopy closure (Table 4). 3.3 Picea seedling occurrence on woody microsites Picea seedlings growing on woody microsites occurred in 19 out of 20 sample plots, with a mean of 21.1 individuals per sample plot (SD = 22.7, maximum = 70). They were found in low numbers on 10% of the total number of stumps and fallen deadwood pieces; 92% of the seedlings grew either individually or in groups of up to 9 per 1 stump or piece of fallen deadwood. The highest number of individuals on a single deadwood piece was 23. The mean seedling density on decaying wood was 1.2 individuals per m 2, with 0.6 individuals per m 2 for fallen deadwood and 4.6 individuals per m2 for stumps.Seedling density depended on CWD decay stage (Kruskal-Wallis, H = 51.7; p < 0.001). The greatest number of seedlings were found on wood in decay stage VIII, and their density gradually stages of decay. More seedlings were found on thicker deadwood pieces (23Œ30.9 cm and above 31 excluded from this analysis) (Kruskal-Wallis H = 149.2; p < 0.001). Furthermore, a higher amount of regeneration was found on stumps with a diameter of over 31 cm than on stumps in the other on deadwood that was at least in decay stage V, and with a diameter above 15 cm. In the model of Picea seedling occurrence on fallen deadwood, six independent values and diameter of fallen deadwood, as well as the volume of living trees in the sample plot. In turn, this probability decreased with increasing density of living trees, sapling density, and the slope of the sample plot. The odds ratio for stand parameters, saplings, deadwood diameter, and slope Table 4. Spearman correlation matrix of independent variables (characteristics of 20 sample plots).Basal area of living treesDensity of living treesVolume of living treesTree losses over 15 yearsCanopy closureSapling density (all spe-cies)Slope of sample plotVolume of fallen dead-wood and stumpsTotal volume of coarse woody debrisBasal area of living trees1.000Density of living trees 0.2451.000Volume of living trees 0.932***0.0841.000Tree losses over 15 years -0.414-0.545*-0.3131.000Canopy closure 0.4300.724***0.288-0.612**1.000Sapling density (all species)-0.242-0.378-0.1650.096-0.1691.000Slope of sample plot 0.242-0.1410.2250.006-0.1000.541*1.000Volume of fallen deadwood and stumps -0.206-0.673**-0.1340.597**-0.716***0.2650.2601.000Total volume of coarse woody debris-0.223-0.658**-0.1040.765***-0.650**0.2240.2380.853***1.000 134 KB – 21 Pages