Jerzy Szwagrzyk

Spatial patterns of trees in natural forests of East-Central Europe

The analysis of spatial patterns is one of the ways to estimate the role of competition among trees in forest dynam- ics. Three hypotheses concerning distribution patterns in old- growth stands were tested: (1) fine-scale spatial patterns of trees are regular; (2) patterns do not differ significantly from a random distribution, and (3) spatial patterns at larger scales are clumped because of site heterogeneity. Old-growth forest stands in Poland and the Czech Republic were analysed with a modified Ripley K function, using distribution maps of tree stems. Fine-scale spatial patterns (with distances among trees not exceeding 15 m) were usually intermediate between random and regular. Trends towards a regular distribution occurred more often among dead than among live individuals. No significant relationships between tree species were found at smaller scales; however, at larger scales (distances from 15 - 25 m) negative associations between some species were found. This reflects site heterogeneity rather than any direct influence of one tree species upon another.

Dynamics of seedling banks in beech forest: results of a 10-year study on germination, growth and survival

The dynamics of a seedling bank was studied in four plots located in the Krynica Experimental Forest, southern Poland. Each sample plot was divided into eight sectors, in which germinants and seedlings were mapped, measured, and labelled; their survival was checked twice a year between 1989 and 1996. Maps of relative light intensities on the forest floor in sample plots were produced on the basis of measurements conducted in June and August 1991. During the entire period of study, European beech (Fagus sylvatica L.) made up over 96% of germinants and seedlings. Numbers of beech germinants varied strongly (from 0 to 1178) among plots and years. Each year of abundant germination was followed by one or two years of scarce germination, and there was an increasing trend in the number of germinants in three plots between 1989 and 1996. Seedling emergence was almost independent of relative light intensity and first-season survival was positively, but weakly correlated with it. Long-term survival of seedlings was low and strongly related to relative illumination. Results of analyses of spatial patterns in seedlings suggested that some microsites were more conducive than others to germination and early survival of seedlings. Survival among taller germinants was greater than among shorter ones. A true seedling bank was observed only in two plots, where relative light intensities were 9 and 15% of full sunlight. In a plot with relative light intensity of 4%, the seedling bank was unstable and in the least illuminated plot (<3% of full sunlight) no seedling bank was formed. Results indicate that, even in a strongly shade-tolerant species like beech, formation of a seedling bank requires the occurrence of canopy openings in the close proximity.

Above-ground standing biomass and tree species diversity in natural stands of Central Europe

Abstract Questions: 1. Is the above-ground biomass in natural temperate forests positively correlated with tree species diversity? 2. Is this biomass related to the diversity of tree functional groups? Location: We used published data from over 100 permanent plots located in natural temperate forests in the Czech Republic, Poland and Slovakia. Methods: We related the number of tree species and Simpsons index of tree species diversity to the above-ground biomass in natural forest stands, and we repeated the same calculations for the identification of functional groups of trees using PCA analysis of functional traits. Results: Analysed sites ranged from almost pure subalpine spruce stands to mixed deciduous lowland forests with eight tree species per stand. The above-ground biomass accumulation ranged from 169 to 536 tons of dry mass per hectare. For the analysed data set the relationship between tree species diversity and biomass accumulation was not significant but showed a negative trend. Similar results were obtained in analyses employing tree functional groups instead of tree species. A significant negative relationship was found after four stands located in the highest elevations had been removed from the data set. Conclusions: There is a weak negative relationship between tree species diversity and above-ground biomass in natural forests of Central Europe. Nomenclature: Tutin et al. (1964–1980).

Tree mortality and effects of release from competition in an old-growth Fagus-Abies-Picea stand

. In a montane mixed Fagus-Abies-Picea forest in Babia Gora National Park (southern Poland), the dynamics of an old-growth stand were studied by combining an 8-yr annual census of trees in a 1-ha permanent sample plot with radial increments of Abies and Picea growing in the central part of the plot. The mortality among the canopy trees was relatively high (10% in 8 yr), but the basal area increment of surviving trees slightly exceeded the losses caused by tree death. DBH increment was positively correlated with initial diameter in Abies and Picea, but not in Fagus. For individual trees smaller than the median height, basal area increment was positively related to the basal area of old snags and the basal area of recently deceased trees in their neighbourhood, but negatively related to the basal area of live trees. Dendrochronological analysis of the past growth patterns revealed numerous periods of release and suppression, which were usually not synchronized among the trees within a 0.3 ha plot. The almost normal distribution of canopy tree DBH and the small number of young individuals in the plot indicated that stand dynamics were synchronized over a relatively large area and, hence, were consistent with the developmental phase concept. On the other hand, the lack of synchronization among periods of growth acceleration in individual mature Abies and Picea trees conforms more closely to the gap-dynamics paradigm.

Small-scale spatial patterns of trees in a mixed Pinus sylvestris-Fagus sylvatica forest

Abstract The fine-scale spatial patterns of trees were analysed in 20 circular plots established in mixed forests dominated by pine and beech in Ratanica Valley, a small forested catchment in the Carpathian foot-hills, southern Poland. Within each plot exact locations of individuals were recorded in circles of radii proportional to the sizes of measured trees. Pattern analysis was conducted using modified Ripleys K method. A part from a general pattern for all trees and for beech and pine separately, spatial relationships between these two species were analysed using the K function for bivariate processes. Distribution of theoretical competition intensity measures for the central part of each plot was calculated using two ‘influence functions’. The prevailing spatial pattern in all size classes of analysed trees was intermediate between purely random and regular. However, statistically significant regularity in tree distribution was recorded only in a few plots. Clumped distribution was extremely rare, and so were the departures from randomness towards aggregation. Therefore, the hypothesis of any positive interactions among individuals, leading to their clumped distribution, should be rejected. On the other hand, the role of crowding-dependent mortality in shaping patterns of trees was only partly confirmed by the results. Analyses of spatial relationships between beech and pine revealed that these two species were distributed independently, apart from two cases when a kind of ‘attraction’ between them occurred. Global sums of competitive influences, calculated with two different formulae, gave generally similar results: there was a great diversity in sums of influences both within and among analysed plots. Nonetheless, high levels of tree crowding were very rarely achieved, the majority of analysed stands being well below the stocking level which could be attained under prevailing site conditions.

Natural regeneration of forest related to the spatial structure of trees : a study of two forest communities in Western Carpathians, southern Poland

The existence of a relationship between the spatial pattern of trees and the distribution of young individuals beneath the canopy has been tested in the beech (Fagus sylvatica) and spruce (Picea abies) — fir (Abies alba) forests in the mountainous region, using two different methods. The first method was the analysis of spatial pattern of individuals, the second one was based on calculating sums of influences of all trees occurring within analysed plot on a given point on the forest floor. Results of spatial pattern analyses were surprisingly consistent: almost all mature trees and seedlings didplayed a random pattern of spatial arrangement. However, there is a clear, although statistically insignificant tendency towards uniformity of spatial pattern with increasing sizes of analysed trees. Results of comparing sums of influences on regularly distributed points with sums of influences on seedlings or saplings revealed no tendency in forest regeneration to concentrate in places, where the sums were smaller than the average for a plot. This, coupled with the dominance of random spatial pattern of trees, suggests, that viewed on a small spatial scale, influence of competition among forest trees on their spatial arrangement is obscured by other factors, which are not closely related to the distribution of individuals.

Small-scale spatial pattern and size structure of Rubus hirtus in a canopy gap

. The response of a Rubus hirtus population to the creation of a new forest gap was analysed. All individuals in two 30-m2 plots – one in a gap and one with full canopy cover – were mapped and the length of Rubus shoots measured. This was done 1, 2, 3, 4, and 7 yr after creation of the gap. Spatial patterns were analysed using Ripleys K-method. Although the density of Rubus in the gap increased from 3 to 24 rooting points/m2, the change in spatial pattern of individuals over 7 yr was very limited. During the first four years a clumped pattern appeared at distances of > 0.5 m. After seven years the pattern was random at all distances. Young shoots spread in all directions with equal probability. The expansion was achieved by establishment of new ramets, increase in the number of shoots per rooting point playing a minor role. Individual plants contributed to gap filling very unequally; few of them produced many rooting points. The average size of canes and the proportion of tip-rooting canes were highest in the second year after the gap formation.

Spatial and temporal variability of natural regeneration in a temperate old-growth forest

Abstract• The natural regeneration of shade-tolerant tree species is characterized by large spatial heterogeneity and temporal variability. The mechanisms producing those patterns are still poorly understood and the knowledge of long-term fluctuations in regeneration processes is very limited.• We used data from long-term study plots in an old-growth stand dominated by European beech and silver fir to address three questions: (1) Is a tendency towards clumping in seedlings associated with a particular spatial scale? (2) Are the spatial patterns in seedlings constant over time? (3) Is the distribution of seedlings related to light intensity?• Over the study period the seedling density varied from 2.5 to 6 ind./m2. Stronger fluctuations occurred at a fine scale. Seedlings were clumped at distances ranging from a few centimeters to a few meters. The distribution of places with high seedling densities was relatively constant over time, especially in beech. Positive but weak rank correlations were found between light intensity and densities of beech and fir seedlings.• Despite large fluctuations in seedlings densities, caused by mast-seeding, a permanent seedling bank was maintained. Very pronounced clumping of tree seedlings found in this study was only partially explained by differences in light intensity.Résumé• La régénération naturelle des essences tolérantes à l’ombre est caractérisée par une grande hétérogénéité spatiale et une variabilité temporelle. Les mécanismes de production de ces modèles sont encore mal compris et la connaissance des fluctuations à long terme des processus de régénération est très limitée.• Nous avons utilisé des données provenant d’études à long terme de parcelles, dans une vieille forêt ancienne dominée par le hêtre et le sapin pectiné, pour répondre à trois questions : (1) Y a-t-il une tendance à des bouquets de semis associée à une échelle spatiale particulière? (2) Les modèles spatiaux des semis sont-ils constants dans le temps? (3) La distribution des semis est-elle liée à l’intensité de la lumière?• Au cours de la période d’étude, la densité des semis a varié de 2.5 à 6 ind./m2. De fortes fluctuations se sont produites à une échelle fine. Les plants étaient distribués en bouquets à des distances allant de quelques centimètres à quelques mètres. La distribution des emplacements avec des densités de semis élevées a été relativement constante au fil du temps, surtout avec le hêtre. Des corrélations positives mais faibles, ont été trouvées entre l’intensité de la lumière et les densités de semis de hêtre et de sapin.• En dépit de fortes fluctuations des densités de semis, causées par la chute des graines, un stock permanent de semis a été maintenu. Des bouquets très marqués de semis, retrouvés dans cette étude n’ont été que partiellement expliqués par des différences dans l’intensité lumineuse.

High Reproductive Effort and Low Recruitment Rates of European Beech: Is There a Limit for the Superior Competitor?

ABSTRACT European beech is a superior competitor among the trees of Central Europe, often growing in pure stands. We proposed a hypothesis, that once beech has reached dominance in forest community, its recruitment could become limited due to the gradual accumulation of pathogens attacking seeds and seedlings. We employed data on seed production and germination along with a field experiment to estimate the germination success of beech in two old-growth forests. Beech produced more seeds than the co-occurring coniferous trees, but less than 1% of beechnuts germinated in the next season. In the field experiment, the percentage of decayed beechnuts was 57% in the Carpathians and 61% in the Alps. Most of the dead germinants and decayed beechnuts were infested by fungi. The average number of fungal colonies per one sample in the Carpathians was significantly higher after mast year than one year before, while the differences between the Alps and Carpathians after mast years were statistically not significant. Fungi have been isolated from practically all dead beechnuts and dead germinants. The number of beechnuts per seed trap, the number of germinants around it and the relative number of fungal colonies obtained from plastic boxes placed in the same sample plot were not significantly correlated. The mortality of germinants continued throughout the spring; the number of life germinants in the middle of May amounted to 0.87% of the initial number of beechnuts in the Carpathians and only 0.28% in the Alps. High rates of beechnut and germinant mortality could probably offset the huge reproductive effort of European beech in old-growth stands and limit the possibility to attain absolute dominance by that species. However, our hypothesis that the build-up of fungal pathogens on the forest floor old-growth stands is able to stop the regeneration of beech still needs to be tested using larger data sets.

Fine-scale spruce mortality dynamics driven by bark beetle disturbance in Babia Góra National Park, Poland

Abstract Bark beetle outbreaks have had major impacts on Norway spruce forests in Europe. The large majority of these forests are located in areas under forest management; thus, few studies have investigated outbreak-driven spruce mortality patterns unaffected by humans. Our study examined spruce mortality resultant from a beetle outbreak in a high-elevation, unmanaged forest over a 17-year span. We analyzed three tree-level survivorship and DBH datasets collected during pre-, mid-, and post-outbreak conditions to evaluate long-term mortality dynamics. We measured changes in mortality severity, topographic and stand structure characteristics, and stand complexity using ANOVAs, and we assessed five topographic and stand structure mortality predictors by employing boosted regression trees. Our results showed that though spruce mortality increased significantly over time, such increases were disproportionate with spatial synchrony. Moreover, the outbreak did not significantly alter the living stand structure and had little effect on stand complexity, exhibiting the effects of an outbreak that spread throughout the forest without causing major stand-level damage. Larger trees at higher elevations on south-facing slopes were targeted most frequently, particularly during the later stages of the outbreak. Aspect, elevation, and slope were the best predictors of mortality, demonstrating moderate forecasting ability. We showed that bark beetle outbreaks can operate on patch-scale gradients, affecting microhabitat conditions, without resulting in sweeping, stand-altering mortality. Small-scale outbreaks may increase forest resilience against more severe outbreaks in the future by creating canopy gaps that facilitate regeneration, which leads to more complex age and size structures within the stand.