Natural Forest Dynamics Research Articles

The dynamics of forest species composition in the Eastern Moscow Region

Abstract The forests of urbanised areas provide multiple ecosystem services and are highly dynamic. Determining the trends in species composition changes can help to predict their future capacity to fulfil ecological and resource-maintaining functions. We examined the direction of forest successions in the Northeast Moscow region under the canopy of different tree species. Field data were obtained from 78 permanent test plots monitored for more than a 15-year period; field studies were complemented by archival data. The cluster analysis made it possible to divide all plots into five groups by current species composition and structure and into eight groups by the importance of broadleaved species in the undergrowth. Gradual evolution (cohort dynamics) was found to be typical for middle-aged secondary forests; patch dynamics was described in mature stands of late succession species after non-critical natural disturbances; drastic changes were observed in spruce (Picea abies (L.) Karst.) stands after pest attacks. Two main trends were revealed in species composition shift: restoration of mixed spruce-broadleaved forests and development of lime-dominated broad-leaved forests, the latter being the prevailing one in the stands of composite forest types. Intensive development of oak-associated species is probably related to the climate conditions in the Moscow megacity. The content of this article may be of interest for researchers studying natural forest dynamics and can be used for prospective planning of target species composition in the forestries of the Moscow region.

Morfometria de Araucaria angustifolia em diferentes altitudes no Sul do Brasil

Os índices morfométricos podem ser usados para subsidiar o entendimento da dinâmica de florestas naturais. Diante disso, objetivou-se descrever e avaliar as características morfométricas e dendrométricas de Araucaria angustifolia, como subsídio para compreensão da estrutura da floresta natural de araucária. Os dados foram mensurados em três municípios de Santa Catarina, considerando diferentes altitudes de ocorrência da espécie, com amostragem de 247 árvores, utilizando o método de Bitterlich, sendo medida a circunferência a 1,30 m do solo, altura total e de inserção de copa e raios de copa. As relações interdimensionais das árvores foram descritas por meio de índices morfométricos. O sítio 2 apresentou árvores de maior porte em relação ao diâmetro e área de copa. O sítio 3 apresentou a maior densidade de árvores (403 árvores ha-1), enquanto nos sítios 1 e 2 foram observadas 362 e 232 árvores ha-1, respectivamente. No sítio 3, a maior parte das árvores apresentou proporção de copa superior a 50% e formal de copa menor que 1, indicando árvores de copas mais estreitas e largas. O diâmetro da árvore apresentou correlação negativa e superior a 70% com o grau de esbeltez. Nos três sítios, o diâmetro apresentou correlação positiva com o diâmetro de copa.

Natural forest dynamics have more influence than climate change on the net ecosystem production of a mixed Mediterranean forest

Natural forest dynamics have more influence than climate change on the net ecosystem production of a mixed Mediterranean forest

Wind-Generated Seed Shadow in Southern Brazil: The Influence of the Mother Plant and Wind Direction

Abstract Diaspore dispersal is an essential function of plant species, with effects on plant populations and natural forest dynamics. This study examines how traits of the mother plant (height, crown spread and distance from the diaspores) and the wind (wind speed) affect the spatial distribution of anemochorous diaspores of Apuleia leiocarpa, Peltophorum dubium, and Jacaranda micrantha in Southern Brazil. The number of diaspores from A. leiocarpa, P. dubium, and J. micrantha decrease with the increase in distance from the mother plant and there was no influence of wind direction on the spatial distribution of diaspores. Diaspore sizes of these plants were not related to their dispersal distances. Diaspore dispersal for A. leiocarpa was negatively correlated to the plant height and the crown spread. The dispersal of Peltophorum dubium and Jacaranda micrantha were not influenced by the diaspores and plants traits considered in this study.

Natural forest dynamics have more influence than climate change on the net ecosystem production of a mixed Mediterranean forest

Climate models predict increased drought conditions for the Mediterranean region, putting forests under increasing risk from direct or indirect effects of droughts. On the other hand, increasing CO2 and longer growing seasons could compensate the negative impacts of more intense droughts on forest productivity and carbon sequestration. Furthermore, large areas of Mediterranean forests are relatively young and unmanaged, and maturing usually tends to decrease carbon sequestration.We conducted a simulation study to explore the interplay between climate, CO2, and maturing, on forest net primary production (NPP) and net ecosystem production (NEP) over the 2000–2100 period. We used the Not Only Tree/Grass (NOTG) model, which is individual-based, process-oriented, and spatially explicit. We applied the model to the Font-Blanche experimental site, a typical mixed Mediterranean forest dominated by Aleppo pines and holm oaks.Simulations under three climate scenarios (current, moderate change, severe change) suggest that NPP could be enhanced by climate change, both due to higher CO2 and longer growing seasons. On the other hand NEP would only be temporarily enhanced by climate change. The largest effect, however, was a decrease of NEP over time for all scenarios, due to forest maturing, with heterotrophic respiration progressively catching up with NPP. This implies that, regardless of climate change, the sink capacity of large unmanaged forest areas in southern Europe could strongly diminish during the 21st century.

Modelling Post-Disturbance Successional Dynamics of the Canadian Boreal Mixedwoods

Natural disturbances, such as fire and insect outbreaks, play important roles in natural forest dynamics, which are characterized over long time scales by changes in stand composition and structure. Individual-based forest simulators could help explain and predict the response of forest ecosystems to different disturbances, silvicultural treatments, or environmental stressors. This study evaluated the ability of the SORTIE-ND simulator to reproduce post-disturbance dynamics of the boreal mixedwoods of eastern Canada. In 1991 and 2009, we sampled all trees (including seedlings and saplings) in 431 (256 m2) plots located in the Lake Duparquet Research and Teaching Forest (western Quebec). These plots were distributed in stands originating from seven wildfires that occurred between 1760 and 1944, and which represented a chronosequence of post-disturbance stand development. We used the 1991 inventory data to parameterize the model, and simulated short- to long-term natural dynamics of post-fire stands in both the absence and presence of a spruce budworm outbreak. We compared short-term simulated stand composition and structure with those observed in 2009 using a chronosequence approach. The model successfully generated the composition and structure of empirical observations. In long-term simulations, species dominance of old-growth forests was not accurately estimated, due to possible differences in stand compositions following wildfires and to differences in stand disturbance histories. Mid- to long-term simulations showed that the secondary disturbance incurred by spruce budworm did not cause substantial changes in early successional stages while setting back the successional dynamics of middle-aged stands and accelerating the dominance of white cedar in late-successional post-fire stands. We conclude that constructing a model with appropriate information regarding stand composition and disturbance history considerably increases the strength and accuracy of the model to reproduce the natural dynamics of post-disturbance boreal mixedwoods.

Effect of Temperature and Precipitation on the Vegetation Dynamics of High and Moderate Altitude Natural Forests in India

In the present study, the high-altitude vegetation dynamics of natural forest cover were analyzed to find the effect of local hydrology for about 10 years. Vegetation dynamics in four different topographical and climatic conditions in India were studied using normalized difference vegetation index (NDVI) data from vegetation sensor of SPOT satellite, and daily temperature and precipitation data from Asian Precipitation–Highly Resolved Observational Data Integration Towards Evaluation project. The main objective was to understand how and to what extent the natural vegetation reciprocates in various climatic conditions. First, the vegetation data was denoised by using empirical mode decomposition technique. The relation between the vegetation growth and hydrological parameters was studied to find the anomalies. Then, the wavelet analysis of the hydrological data was carried out to find the frequency and extent of the anomalies. Finally, nonparametric Mann–Kendall trend analysis and Sen’s slope analysis were applied to find the trend of the vegetation, temperature, and precipitation dynamics. Results indicate that the growth of the vegetation starts when the average temperature is 10 °C or higher. Beyond that the increase in temperature may have a negligible effect on growth of vegetation. The vegetation also shows positive change in monthly NDVI with the increase in precipitation depending forest type and local climate. However, with excessive rainfall, a declining trend in vegetation growth was observed. The NDVI data show positive trend in all four sites. In northern region, the temperature showed positive trend, while precipitation had negative trend. In eastern and western regions, the temperature had negative trend and precipitation had positive trend.

Impact of Disturbances on the Carbon Cycle of Forest Ecosystems in Ukrainian Polissya

Climate change continues to threaten forests and their ecosystem services while substantially altering natural disturbance regimes. Land cover changes and consequent management entail discrepancies in carbon sequestration provided by forest ecosystems and its accounting. Currently there is a lack of sufficient and harmonized data for Ukraine that can be used for the robust and spatially explicit assessment of forest provisioning and regulation of ecosystem services. In the frame of this research, we established an experimental polygon (area 45 km2) in Northern Ukraine aiming at estimating main forest carbon stocks and fluxes and determining the impact caused by natural disturbances and harvest for the study period of 2010–2015. Coupled field inventory and remote sensing data (RapidEye image for 2010 and SPOT 6 image for 2015) were used. Land cover classification and estimation of biomass and carbon pools were carried out using Random Forest and k-Nearest Neighbors (k-NN) method, respectively. Remote sensing data indicates a ca. 16% increase of carbon stock, while ground-based computations have shown only a ca. 1% increase. Net carbon fluxes for the study period are relatively even: 5.4 Gg C·year−1 and 5.6 Gg C C·year−1 for field and remote sensing data, respectively. Stand-replacing wildfires, as well as insect outbreaks and wind damage followed by salvage logging, and timber harvest have caused 21% of carbon emissions among all C sources within the experimental polygon during the study period. Hence, remote sensing data and non-parametric methods coupled with field data can serve as reliable tools for the precise estimation of forest carbon cycles on a regional spatial scale. However, featured land cover changes lead to unexpected biases in consistent assessment of forest biophysical parameters, while current management practices neglect natural forest dynamics and amplify negative impact of disturbances on ecosystem services.

A mixture of human and climatic effects shapes the 250-year long fire history of a semi-natural pine dominated landscape of Northern Latvia

Fire has been shown to shape successional pathways and dynamics of forest vegetation. However, its role in European hemiboreal forests remains poorly understood. Here we provide the first annually resolved reconstruction of fire history from the Eastern Baltic Sea region, developed in the pine-dominated landscape of Slitere National Park (SNP), northwestern Latvia, over the last 250 years. Our results suggest that forest fires have been a common disturbance factor in the studied landscape. In total, we dated 62 single fire years, with the mean-point scale fire return interval of 46 years and the length of the fire cycle ranging from 45 to 80 years. We identified periods of high (1750–1950) and low (1960–2000) fire activity, with the corresponding lengths of fire cycles being 45–68 and 58–80 years, respectively. Although both long-term (century and decade-long) and annual dynamics of fire activity in SNP was closely linked to socio-political changes in Latvia, fire activity in SNP was also affected by climate, as indicated by the close positive association of years with increased area burned and positive SST anomalies in the Baltic and North Seas. Future management of SNP should make fire an important element of natural forest dynamics and consider using prescribed fires of various spatial extent and severity.

Stand Dynamics and Structure of Two Primary Champlain Valley Clayplain Forests, Vermont

Understanding natural forest dynamics is critical for informing forest restoration and conservation efforts. However, such information is often difficult to generate for areas that have a long history of intense land use, such as the Champlain Valley of Vermont. We used dendroecological methods and assessments of forest structural conditions to describe the tree recruitment history and structural dynamics of 2 examples of valley clayplain forest, a rare natural community that has been drastically reduced in extent by agricultural land use in the Champlain Valley. Although historic selective harvesting had occurred in the areas sampled, these sites represent the best remaining examples of semi-natural valley clayplain forests in the region, thus providing an opportunity to document long-term patterns of structural and compositional conditions and tree recruitment in areas with limited land-use. Age structures in these 2 areas were strongly uneven-aged, with older cohorts composed of Quercus alba (White Oak), including an individual dating to the 1640s, and recruitment over the past 2 centuries dominated by Tsuga canadensis (Eastern Hemlock). Size distributions of live trees also reflected these patterns of recruitment, with White Oak occurring exclusively in larger diameter classes (>35 cm) and Eastern Hemlock predominating across all smaller size classes. We observed sparse regeneration of Quercus spp. (oaks) in these areas, suggesting that this historically important component of valley clayplain forests may disappear over time in the absence of large, stand-scale natural disturbances or management activities focused on the perpetuation of this species group.

Gap dynamics of natural Populus euphratica floodplain forests affected by hydrological alteration along the Tarim River: Implications for restoration of the riparian forests

Due to climate change and excessive human activities, runoff dynamics of the Tarim River in northwest China become more pronounced. Understanding the effects of hydrological alteration on the life strategy and dynamics of the Populus euphratica riparian forests is becoming increasingly important. Forest gaps led by such disturbances change the structure and function of the desert riparian forest ecosystems. However, there is a lack of research on the gap formation and dynamics of this special forest type, for which the main driving force of the gap disturbance has always been unknown. In this study, we investigated several parameters of P. euphratica forest gap, such as gap size, gap age, gap fraction, and gap makers to quantify the gap disturbance regimes in the natural floodplain forests along the Tarim River in arid northwest China. In the middle reaches of the Tarim River, a total number of 263 gap makers and 60 gaps in six 50 m × 50 m plots with a total area of 1.5 hm2 were investigated. The result showed that gap fraction was <5%, and approximately 28.5% of the expanded gaps were from 1.0 to 1.2 in size (ratio of gap diameter to tree height), especially when formed around 1997–2006. The median size of the expanded gap (140.57 m2) in the desert riparian forests was smaller than in tropical forests. P. euphratica was the most abundant gap maker, and its share among gap makers was 12–14 times larger than another species. Furthermore, gap makers contributed to the forest gap size, as shown by a significant correlation between the number of gap makers and the size of expanded gaps, especially those that had been created 50–60 years ago (R2 = 0.455, P < 0.01). The DBH distribution of living trees versus dead trees showed that most P. euphratica mortality occurred in small size classes. However, living trees were equally frequent in large classes, which suggested that large trees were not exclusively injured or died in these P. euphratica stands that were affected by poor habitats, such as water scarcity. We concluded that climate change and anthropogenic activities (increasing water use for irrigation) since the 1970s led to the progressive decrease in water resources at the regional scale and resulted in a higher frequency of forest gaps in the riparian forests along the Tarim River. The results of this study provide useful implications for ecological restoration of P. euphratica to improve sustainable management of desert riparian forests.

Spatial patterns of dominant species and their implication for natural secondary forest ecosystem dynamics in a reserved forest of north China

Spatial pattern analysis is useful to elucidate the type and importance of the ecological processes in forest ecosystem. To better understand the dynamics of the natural secondary forest ecosystem and to provide information regarding the interactions between arbors and shrubs, the spatial patterns of dominant species in a natural secondary forest was examined in this paper. We developed a 2 ha secondary forest plot by mapping the location of all woody plants (diameter at breast height ≥1 cm). Univariate and bivariate Ripley’s L(r) functions were utilized to evaluate the spatial patterns and association of the three dominant plants (P. davidiana, B. platyphylla and C. mandshurica). It was found that aggregated distribution was the main pattern in the dominant populations of the total and size-specific individuals of arbors at most scale. The degree of aggregation gradually decreased with size in B. platyphylla due to self-thinning while increased in P. davidiana which may attribute to the effects of logging for large- and medium-size woods in 1940s or 50s. In associations of intra-/interspecies pairs, positive association was the majority of intraspecies, whereas negative association was the domination in interspecies. Remarkable, mutual independence dominated in C. mandshurica vs. size-specific B. platyphylla pairs at most scales, and positive association emerged at greater than 8 m scales in C. mandshurica vs. size-specific B. platyphylla-large, may contribute to different niche occupying that generated less competitions for resources, even the large ones could provide preferable shelter for shrubs.

Vegetation structure and decreased moth abundance limit the recolonisation of restored habitat by the European Nightjar

Woodland ecosystems of Europe have undergone major transitions in the last centuries. Changes in land use and the loss of natural forest dynamics have often led to structurally poor, uniform and dense stands. Not surprisingly, open forest species relying on a heterogeneous stand structure have suffered dramatic population declines. The European Nightjar Caprimulguseuropaeus, a nocturnal insectivorous bird, has undergone such a decline in its main Swiss stronghold in Valais. Despite the species’ potential to colonize new sites and habitat restoration measures implemented since 2001, recolonisation of restored sites has not taken place, suggesting problems with the current habitat restoration strategy. In order to refine management recommendations, we compared habitat structure and moth abundance, a key Nightjar food source, at sites that are still occupied and at sites that had been abandoned but have recently been restored. Vegetation structure was more heterogeneous and moth abundance greater at occupied than at abandoned sites. More specifically, occupied sites harboured a greater coverage of bare ground, while abandoned sites exhibited a higher amount of regeneration and intermediate shrub layer. The occurrence of natural perches was also higher in occupied sites. Abandoned sites are thus characterised by lower prey abundance and denser vegetation cover, the combination of which is likely to lead to lower prey availability for hunting Nightjars. Restoration action would benefit from maintaining snags and dead branches and by targeting unproductive habitats characterised by mineral soils, thereby slowing down regeneration and shrub regrowth. For future successful management of Nightjar habitats, it seems thereby essential trying to find the balance between actions that allow opening the lower and mid-strata of the forest while sustaining high moth populations.

Changes in Species Composition in Alder Swamp Forest Following Forest Dieback

It is generally hypothesized that forest dieback is a characteristic of alder swamp forests (alder carrs, Alnion glutinosae alliance). Different internal and external factors may trigger this process, including human disturbance, changes in river discharge, unusually severe and prolonged flooding, terminal age of an even-aged alder forest (ca. 100–150 years) and others. Although forest dieback in this type of forest may cause major changes in environmental conditions, the influence of this change on the floristic composition has not been well recognized. The study aimed to detect any possible changes in floristic variation in alder swamp forest following forest dieback. Vegetation plots in alder swamp forests affected by forest dieback were resurveyed 20 years after a previous study. PERMANOVA was used to test the significance of the compositional change and nonmetric multidimensional scaling (NMDS) with passively fitted means of the Ellenberg’s Indicator Values were used to interpret its ecological meaning. In addition, different structural and diversity indices were compared, including species richness, percentage cover of vegetation layers, Shannon and Simpson diversity and evenness. Finally, we analyzed changes in the frequency of vascular plant species using Chi square tests. We recorded clear and significant compositional changes following alder swamp forest dieback. This change was most related to the gradient of moisture, followed by the gradients of light and temperature. The analysis of the individual species showed that the species of hummocks declined, while the species of hollows increased. Moreover, the current communities are dominated by some hydrophytes that were not recorded 20 years ago. Forest dieback resulted in profound changes in the hydrological regime. The observed changes are consistent with a model of cyclic succession as proposed for alder swamps. In addition, we conclude that the natural forest dynamics have to be taken into consideration while interpreting the results of re-survey studies.

Effects of natural forest dynamics on vascular plant, bryophyte, and lichen diversity in primevalFagus sylvaticaforests and comparison with production forests

AbstractStand structure, mean tree age, deadwood amount and microclimate all change markedly in the course of natural forest dynamics. The last remaining primeval forests of the temperate forest biome are valuable study objects to investigate the effects of forest dynamics and management on forest structure and function as well as phytodiversity, which is not sufficiently understood.Three pairs ofFagus sylvaticaprimeval and production forests in eastern Slovakia were selected for studying the effects of natural forest development stages on vascular plant, bryophyte, and lichen species richness and composition. We further compared the diversity patterns in the initial, optimal and terminal stages of forest development with those of nearby production forests.The plot‐level species richness of epiphytic bryophytes and lichens increased from the initial to the terminal stage, but only lichens exhibited a significantly higher cumulative species richness (γ diversity) in the later (optimal and terminal) stages. No increase in species richness from the initial to the terminal stage was found for deadwood‐inhabiting epiphytes and the ground‐layer vascular plants. Canonical correspondence analyses identified characteristic bryophyte and lichen species for the different development stages, while the bulk of vascular ground layer species occurred across all stages with no stage preference.Stem diameter was an even more important driver of epiphyte diversity and species composition than the development stage. All stages of the primeval forests (including the initial) were more species‐rich in epiphytes and, when investigating larger plot numbers, also in vascular plants than the production forests.Synthesis. In primeval forests of European beech, plant species richness did not differ significantly between the consecutive forest development stages, while species composition did. This is attributable to the small‐scale mosaic structure of the forest, rapid gap closure by beech, and the continuity of deadwood across the stages, which reduces spatio‐temporal differences in microhabitat availability in the forest. Bryophytes and lichens are species‐richer, and vascular plants at least similarly rich, in the primeval as compared to the production forests, if the study area is sufficiently large.

Evaluating restoration success of a 40-year-old urban forest in reference to mature natural forest

We assessed whether forest restoration was successful in Expo ’70 Commemorative Park in Osaka Prefecture, Japan, which was planted in the 1970s with native late-successional tree species. Detailed survey and analysis of species composition, stand vertical stratification, and forest dynamics, including comparison with a reference, natural late-successional forest, were conducted. The restoration plots had grown to larger basal area compared with the reference plots, however, this was a consequence of very high densities of the overstory trees due to low self-thinning rate. Stand vertical structure of the restoration plots was biased toward overstory layers, causing high mortality of understory trees and shrubs. Because there are no mature forests near the restoration site that could act as a seed source, abundance and diversity of understory trees are likely to continue decreasing in the restoration plots, resulting in single-layered forest structure similar to those of monocultures and even-aged forests. Many seedlings of exotic species emerged in the restoration plots and this could lead to a plagiosere where exotic species dominate the vegetation inhibiting regeneration and growth of native species. Ordination analysis using different measures, basal area and abundance, showed apparently contradicting results, suggesting that multiple criteria are needed to evaluate forest restoration success. Our results indicate restoration of mature, late-successional forest cannot be achieved by simultaneous planting of native species. To sustain urban forests into the future, we must conduct long-term monitoring and management referencing natural forest structure and dynamics.

Assessing the structure of primeval and managed beech forests in the Ukrainian Carpathians using remote sensing

Forest structure reflects the forest disturbance regime and can provide important information about the rate of human impact. A better understanding of the structural variability and large-scale dynamics of natural forests is crucial for “close to nature” forest management planning. In this study, we developed a partly automated approach to assess the structure of potential primeval and managed beech forests in the Ukrainian Carpathians using WorldView-2 imagery. We analyzed the local (50 m × 50 m scale) canopy closure of these forests by extracting the canopy gaps and determined four forest structure types ranging from very closed to low density. The occurrence and frequencies of these structure types were significantly different in the primeval and managed beech forests. The four forest structure types were predicted and mapped using multinomial logistic regression based on the textural features derived from the original image bands and two vegetation indices. A 10-fold cross-validation resulted in an overall accuracy of 83% and a kappa coefficient of 75%, with the highest agreement for the very closed structure type (87%) and the lowest agreement for the medium density and low density structure types (79%). The forest structure type maps can be helpful for planning management activities in beech forests.

Public visual preferences for dead wood in natural boreal forests: The effects of added information

This study investigated public preferences for natural boreal forests, including their perceptions of important structural elements for biodiversity like dead and downed wood. We designed an experimental internet survey using nine versions of a questionnaire—with each version featuring a unique combination of original photographs, additional text and digitally edited photographs. Survey participants (N=2701) rated photographs of forest settings with dead wood digitally removed substantially higher than the corresponding original non-edited photographs. However, respondents’ familiarity with the ecological role dead wood provides for forest biodiversity and natural forest dynamics increased their perception of its appearance. Additional text containing information about dead wood’s ecological benefits, either alone or combined with information about its influence on economic benefits, had almost the same effect as pure ecological text. Additional text with information about either economic or socioeconomic aspects of forests including dead wood had no effect on the participants’ ratings. We also observed a learning effect of additional ecological text: text provided in a previous section of the questionnaire affected participants’ ratings of photographs shown later without text. We conclude that well formulated, trusted and targeted information about the ecological role of dead wood can positively influence public support for multi-goal forest policies. Our results may also imply that in cases where the capacity to inform the public about dead wood’s importance is limited, managers might consider removing dead wood from the most frequently visited areas in forests where recreation is the primary management goal.

Drought and frost contribute to abrupt growth decreases before tree mortality in nine temperate tree species

Tree mortality as a crucial element of natural forest dynamics is still a poorly understood process. Abrupt growth decreases are known to occur several years or decades before complete cessation of growth. Hence, identifying and linking these growth decreases to potential inciting factors such as drought and frost will improve our understanding of mortality processes. We analyzed nine Central European tree species including six coniferous species (Abies alba, Picea abies, Larix decidua, Pinus sylvestris, Pinus cembra, Pinus montana) and three broadleaved species (Fagus sylvatica, Quercus spp., Acer pseudoplatanus). Tree-ring data from 848 standing dead trees from 14 forest reserves all over Switzerland were sampled. We applied distributed lag non-linear models to relate abrupt growth decreases to drought and frost. The results indicate for many species that both drought and frost have a moderate to major impact on abrupt growth decreases prior to tree death. While late frost in spring may instantaneously result in sustained abrupt growth decreases in most species except Scots pine and mountain pine, severe drought over several months in spring may either show an immediate negative impact on growth, such as in beech, or feature negative reactions that are lagged by several years, such as in oak and Scots pine. Thus, extreme climatic conditions have an essential influence on abrupt growth decreases that finally result in tree death, although variability of the reactions within and among species is high.

What Happens after the Gap?— Size Distributions of Patches with Homogeneously Sized Trees in Natural and Managed Beech Forests in Europe

A novel but simple approach for describing stand structure in natural and managed forests driven by small-scaled disturbances is introduced. A primeval beech forest reserve in Slovakia and two beech stands in Germany with different management histories were studied, and their forest stand texture was analysed in terms of tree coordinates, stem diameter, and crown radius. Neigh-bouring trees of similar size with estimated contact of their crowns were assigned to tree groups. The study goal was to estimate the number and size of such homogeneous patches. In all cases, the number of tree groups in a particular diameter class decreased exponentially as group size increased. Single trees were predominant. Compared to simulated random tree distributions, the natural stand exhibited a more clumped distribution of small trees and more regular distribution of larger ones. The natural forest generally had smaller groups than the managed even aged stand, but the smallest group sizes were found in the uneven-aged selection forest. The simple analytical approach provided new spatial insights into neighbourhood relations of trees. The continuous scale from single trees to larger tree groups is an important achievement compared to other analytical methods applied in this field. The findings may even indicate a certain degree of self-organization in natural forests. Due to the limitations associated with each method or statistical models, a joint consideration of 1) gap dynamics, 2) forest developmental stages, and 3) size classes of homogeneous tree groups is recommended. Relevant to forest practitioners, the size class distributions enhance an understanding of the complex stand structures in natural forests and therewith support an emulation of natural forest dynamics in managed beech forests.