Natural disturbances from wind and bark beetles have increased strongly in recent decades across Central Europe. As climate change will likely amplify disturbance activity further, disturbances are ...increasingly threatening the sustainable supply of ecosystem services to society. Management strategies to mitigate disturbances are thus urgently needed. In Central Europe, managing for complex, uneven-aged forests has been suggested as a measure to reduce disturbance risk. However, the scientific evidence for a dampening effect of uneven-aged management on disturbances remains weak and inconclusive. Here, our objective was to assess differences in the disturbance regimes of uneven-aged and even-aged conifer forests during the years 1986 to 2020. We used remote sensing to quantify wind and bark beetle disturbances across four study sites in Austria. The sites span a large environmental gradient and have been under uneven-aged management for many decades. Here, we contrast them with surrounding even-aged forests with similar environmental conditions (uneven-aged forests: 13,440 ha, even-aged forests: 27,910 ha). Specifically, we used a paired-landscape approach, matching uneven-aged with even-aged forests at the level of sublandscapes and controlling for differences in elevation, slope, exposition, topography and the proportion of coniferous species. For each pair of sublandscapes (n= 5000) we quantified differences in disturbance rate, frequency, size and severity between uneven-aged and even-aged forests. Our findings revealed that in uneven-aged forests, disturbance rates were on average 31.3% lower, disturbances returned with a 36.3% lower frequency, and maximum patch sizes were 15.7% smaller than in surrounding even-aged forests. The proportion of high severity disturbance patches was only marginally influenced, being 3.8% lower in uneven-aged versus even-aged forests. Topography strongly modulated the effect of management on disturbance regimes. While disturbance rate was lower in uneven-aged forests overall, it exceeded the rate of surrounding even-aged forests on steep slopes >20° and elevations >1500 m asl. In conclusion, our results suggest that uneven-aged management may partly counteract increases in natural disturbances in Central European forests. However, we also caution that uneven-aged management is not a silver bullet solution for managing forest change, and highlight that adapted forest management approaches should be tailored to local needs and conditions.
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•We compared wind and bark beetle disturbances in different management regimes.•We studied 41,350 ha of managed forests in Austria.•Using a paired landscape approach, we controlled for site and stand conditions.•Disturbance rate, frequency, and size were lower in uneven-aged forests.•Topography modulates disturbance differences between uneven- and even-aged forests.
Despite a general lack of knowledge on the effects of different strategies, conversion of even-aged stands to uneven-aged forest is ongoing across Europe. Conversion of Bavarian Norway spruce stands ...under the present climate scenario was simulated using the individual tree simulator SILVA. Three conversion strategies initiated at two different stand ages, 30 and 60 years, were simulated to develop uneven-aged mixed stands of Norway spruce, silver fir and European beech: gap creation, shelterwood and passive conversion. The three conversion strategies were furthermore combined with different harvesting rates. These conversion scenarios were compared with maintaining the even-aged Norway spruce management as reference. Scenarios were evaluated in terms of mean annual increment and structural development over a 150-year conversion period as well as the expectation value (EV) for eternal future rotations. Compared to the reference scenario, conversion scenarios reduced mean annual increment (6–43%) and also generally EV (−5–78%), except for some scenarios when stand age at conversion was 60 and applying a 3% discount rate. Conversion by shelterwood always reduced EV (both compared to the reference and other conversion scenarios) when initiated at age 30. With passive conversion, the effect on EV was dependent on the assumptions regarding regeneration costs. Gap conversion generally resulted in high EV and increased stand heterogeneity fastest among the different strategies. Other scenarios, especially passive conversion, were dependent on heavy thinning for developing heterogeneity faster (although still slower than with creation of gaps). Most conversion scenarios eventually resulted in similar structural heterogeneity, but the time it took to get to this stage varied greatly (50–120 years). Conversion by creation of smaller gaps in combination with a high rate of target diameter harvesting resulted in a favorable conversion in terms of economic returns and development of stand heterogeneity due to early income and differentiated regeneration.
CONTEXT : Climate change is expected to increase forest vulnerability through disturbances such as windstorms and droughts. Forest managers are therefore investigating strategies to increase forest ...resistance and resilience, especially by promoting uneven-aged and mixed forests through group selection, and by reducing stand stocking and large trees proportion. However, there is little information on the long-term impacts of these two practices. AIMS : The objectives of this study were (1) to develop an original silviculture algorithm designed for uneven-aged management and (2) to use it to assess the effects of the above-mentioned management methods in long-term simulations. METHODS : We simulated individual and group selection techniques in order to study the effects of group size, harvesting intensity and their interactions on wood production, stand heterogeneity, and regeneration in mountain spruce–fir forests. We used the spatially explicit individual-based forest model Samsara2 to simulate forest dynamics. RESULTS : Our simulation results confirmed the positive effect of group selection practices on structure diversity and regeneration but not on spruce maintenance. Increasing harvesting intensity enabled forest destocking but decreased structure diversity and led to non-sustained yields for the most intensive scenarios. CONCLUSION : As adaptation measure, we thus recommend moderate group selection harvesting creating 500 m² gaps.
The conversion to uneven-aged, mixed-species stands represents one possible way to mitigate the consequences of disturbances in Norway spruce forests in Central Europe. A better understanding of the ...establishment and growth dynamics of the understory can contribute to a more effective conversion process. Here we investigate the structure of understory, light climate and growth of natural regeneration of Norway spruce and silver fir in two forest stands undergoing conversion to continuous cover forestry. Stand-wise forest inventory was conducted in 1993 and 2013. The natural regeneration was surveyed, and the light conditions and inter-tree competition were quantified in 51 sample plots established across the stands in 2013. Our results suggest that the diffuse radiation strongly affects the height growth of fir and spruce natural regeneration. We do not confirm the effect of local sapling density on the regeneration dynamics. The results further show that fir trees grow faster than spruce under less intensity of diffuse light. Most of the spruce and fir trees reached the upper limit of the lower overstory (DBH 12 cm) at approximately 50 years of age. Thus, more substantial reductions in stand density can lead to a well-differentiated structure in less than five decades. To control the prospective representation of spruce and fir in mixed-species forests undergoing the conversion, managing of light conditions is crucial.
► Long-term influence of single-tree selection system on forest structure was analysed. ► High variability of harvest intensity during last 130
years was recorded. ► Species mixture was regulated by ...canopy closure, silviculture and SO
2 emissions. ► Improvement of the system is possible by spatiotemporal combination of diverse fellings.
The single-tree selection system is an important option for management of Norway spruce (
Picea abies (L.) Karst.) and silver fir (
Abies alba Mill.) forests because it provides continuous cover, requires low investments for tending, and promotes natural regeneration as well as high stand resistance and elasticity. It is often regarded as a very conservative system that usually results in only minor spatiotemporal changes in forest structure and composition. We studied management history, structural changes, regeneration dynamics, and light climate of a traditional single-tree farmer selection silver fir-Norway spruce forest (site typology
Bazzanio-Abietetum). Stand structure was analyzed on five 0.25
ha permanent plots in 1994, 2001, and 2008. Regeneration density and height growth, forest floor vegetation, and light climate were also assessed on 1.5
×
1.5
m regeneration subplots in 2001 and 2008. Tree cores extracted from dominant trees from both species in two plots were used for reconstructing stand history and age structure of the canopy layer. We documented the forest response to three types of selection management regimes: excessive, normal, and conservative. Excessive management with harvest intensity significantly above the increment was documented until the late 1950s, including two peaks of heavy fellings (diameter limit cut) in the 1880s and 1930s, which favoured establishment of Norway spruce and released regeneration. The period that followed was characterized by normal selection management, but was nevertheless marked by a decline of silver fir as a result of air pollution and several droughts. This led to sanitary fellings that were carried out from the late 1970s to the early 1990s. In the last two decades conservative management followed, which led to suppression and decline of regeneration, especially of Norway spruce, and loss of selection structure. Although we recorded lower regeneration potential of silver fir compared with Norway spruce within the seedling category, silver fir outcompeted Norway spruce within the small-sized tree category (1
cm
<
dbh
⩽
10
cm) because of its superior height growth in low light levels (diffuse light <6%) and occupied a greater share of the canopy. Nevertheless, we anticipate that over the long-term the low light regime will also cause regeneration decline of silver fir and broadleaves. Our research revealed significant structural changes in a single-tree farmer selection forest during the last 150
years. These were a result of variable management regime and environment. A farmer single-tree selection system could better mimic the natural disturbance regime if spatiotemporal combinations of diverse felling regimes would be used.
Abstract
The decision to change forest management system from the traditional even-aged to the selection one based on statistical inventory is often limited by a missing previous inventory. To avoid ...this issue, we used available forest inventory data from ca 2 000 ha of mixed uneven-aged beech-fir-spruce-pine forest and tree ring data from 831 trees to reconstruct forest status from one decade ago. For this purpose, we have created three sets of species-specific models: 1) diameter-stump models to reconstruct the diameter of missing trees, 2) diameter-increment models based on tree ring data to estimate past diameters, and 3) height-diameter models to estimate past tree heights. This approach has allowed us to completely reconstruct the state of the forest as it was ten years ago and use the results as a substitution for a previously missing inventory.
Background and Purpose: Beech-fir forests cover about 13% of forest land in Croatia, thus being a significant forest resource that is dominantly managed by uneven-aged selection management system. ...Continuous and successful regeneration is an essential prerequisite for this kind of forest management. Therefore updated and sound information on the present state of regeneration is important, especially in the context of climate change and the actual structure of beech and fir forests. The aim of this paper is to present and analyse current state of regeneration in beech and silver fir forests of Gorski kotar region, with regard to forest ownership (management model), forest communities and habitat characteristics.
Materials and Methods: Field measurement has been done on 313 plots in the beech and fir forests of Gorski kotar region, Croatia. The assessment of regeneration was based on measurement of trees ranging from 0 to 10 cm dbh (species, number of trees, average height) and also the estimation of seedlings up to 1.30 m high (regenerated area in 10% classes, the share of tree species, the origin of stand establishment, regeneration quality).
Results: Attributes like the success of regeneration, the structure of seedlings by species and the recruitment of saplings were analysed with regards to ownership, forest communities and the aim of forest management. The results indicate poor incidence of regeneration especially of silver fir (more than 50% percent of field plots with no regeneration). Silver fir saplings (height>1.3 m, dbh ≤10 cm) are registered on 9% of plots, average number being only 165 per ha (all species together 2044 per ha). The estimated average share of the regenerated area is 16.3% of total forest area, contributed by 5.2% of conifers and 3.8% silver fir. A total of 14 tree species were recorded on regenerated areas, clearly dominated by broadleaves, especially beech (over 50%).
Conclusions: Significant differences in regeneration attributes were proven by ANOVA between ownership categories, forest communities and habitat characteristics. In order to get better insight on the structure of regeneration, it is recommended to improve future assessment by establishing special sub-plots for measurement of seedlings by species.
A period of stagnation in silver fir development has been recorded in all felled trees in selection forests of Serbia (233 trees on Mt. Goc and 451 trees on Mt. Tara). In the selection forests on Mt. ...Goc, the stagnation stage ranges between 40 and 330 years, but on Mt. Tara, it ranges from 15 to 185 years. It was concluded that the duration was caused not by the ecological and productivity potential (site class) of the soil for fir development, but primarily by the growth space, resulting from the application of single-tree selection or group selection systems. It was also found that the duration of latent state and tree sizes attained over that phase (except for height, and that was to a lesser extent) did not affect the silver fir tree development in the post-stagnation period.
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