Palle Madsen

Adaptive forest management in central Europe: Climate change impacts, strategies and integrative concept

Abstract Climatic warming may lead to increased or decreased future forest productivity. However, more frequent heat waves, droughts and storms and accompanying pathogen attacks are also expected for Europe and are considered to be increasingly important abiotic and biotic stress factors for forests. Adaptive forestry can help forest ecosystems to adapt to these new conditions in order to achieve management goals, maintain desired forest ecosystem services and reduce the risks of forest degradation. With a focus on central Europe, this paper presents the following management strategies: (1) conservation of forest structures, (2) active adaptation, and (3) passive adaptation. The feasibility and criteria for application of the different strategies are discussed. Forest adaptation may entail the establishment of “neonative” forests, including the use and intermixing of native and non-native tree species as well as non-local tree provenances that may adapt better to future climate conditions. An integrative adaptive management concept is proposed that combines (1) species suitability tests and modelling activities at the international scale, (2) priority mapping of adaptation strategies at the national to regional scale, and (3) implementation at the local scale. To achieve this, an international experimental trial system is required to test suitable adaptive measures throughout Europe and worldwide.

Natural regeneration of beech (Fagus sylvatica L.) with respect to canopy density, soil moisture and soil carbon content

Abstract The purpose of the present study is to model the regeneration success using quantifiable growth factors. The hypothesis is that the regeneration success can be predicted from a model that incorporates canopy and ground flora leaf area indexes (LAI), soil water content and soil carbon content. In April 1992, 10 plots (1 m2) were established in each of 22 Danish beech stands with natural regeneration originating from the 1989 seed fall. The regeneration success was investigated until autumn 1994. In each of the 220 plots the light conditions, soil water supply and soil carbon content were quantified. The survival was high during the study period. From spring 1992 to autumn 1993 the mean number of saplings decreased from 58 m−2 to 54 m−2. The sapling number was reduced by increased canopy density but it was neither influenced by water supply nor by soil carbon content. The height growth variation was evident. After the fifth growing season (autumn 1994) the height of the tallest sam3pling per plot ranged from 7 to 120 cm. Generally, an increased canopy opening increased the potential for and variance of height growth. Increased soil water content caused a significant increase in the growth of the saplings; whereas, a significant reduction in growth occurred with increased soil carbon content. The shading from the competing ground flora had no significant effect. However, the contribution to the total sum of squares from the quantitative variables of the relevant statistical models was only 3%–13%. Therefore, the models were unable to predict regeneration success satisfactorily and it was not possible to establish the causal effects underlying silvicultural treatments and site. It is concluded that the beech saplings probably were so well established at the beginning of the study that they had become tolerant to poor growing conditions, such as the drought in 1992. This indicates that the growing conditions during the early phases of seedling establishment may be crucial for the regeneration success. For silviculturists, these conclusions stress the importance of creating favourable growth conditions prior to the first growing season. Future research should examine the early phases of seedling establishment by quantifying growth factors in more detail than was done in the present study.

Effects of soil water content, fertilization, light, weed competition and seedbed type on natural regeneration of beech (Fagus sylvatica)

Abstract Natural regeneration of beech (Fagus sylvatica) is regarded as an inexpensive and generally satisfactory, though unreliable, method fo forest regeneration. In order to improve the understanding of the ecological conditions behind the growth and survival of beech seedlings, factorial experiments were carried out in each of two beech stands with different canopy openings. The effects of soil water content and nutrient supply in relation to light intensity, weed competition and seedbed type were studied. Under the open canopy (13% light) the seedling growth was increased three to four times when both fertilized and irrigated in a mineral soil seedbed compared with seedlings that were neither fertilized nor irrigated. The seedling response to treatments was small in the mixed soil seedbed under the open canopy and in both seedbed types under the closed canopy (5% light). Seedling growth was increased only with increased soil water content under the open canopy in fertilized plots. Weed competition did not reduce seedling growth significantly. Fertilization reduced soil water content up to about 20%. It was concluded that primary growth factors like light intensity, soil water content and nutrient supply should all be quantified or manipulated when the growth of beech seedlings is investigated. Otherwise, the correct interpretation of complex effects such as silvicultural treatments, soil types and weed competition must be regarded as very difficult or impossible to make.

Restoration concepts for temperate and boreal forests of North America and Western Europe

ABSTRACT Throughout the boreal and temperate zones, forest restoration efforts attempt to counteract negative effects of conversion to other land use (afforestation and remediation) and disturbance and stress on existing forests (rehabilitation). Appropriate silvicultural practices can be designed for any forest restoration objective. Most common objectives include timber, wildlife habitat for game species, or aesthetics. Increasingly other objectives are considered, including carbon sequestration, biological diversity, non-game mammals and birds, endangered animals and plants, protection of water quality and aquatic resources, and recreation. Plantation forestry remains the most effective approach to restoration of forest cover to large areas, and recent trends toward more complex plantations are explored. Rehabilitation of degraded forests increasingly relies on re-establishing natural disturbance regimes and emphasizes “close-to-nature” approaches to regeneration and stand management. The objectives of this paper are to clarify concepts of forest restoration and to present examples of restoration activities in temperate and boreal forests of North America and Western Europe.

Growth and survival of Fagus sylvatica seedlings in relation to light intensity and soil water content

Previous investigations have shown different growth and root/shoot ratio increases of beech seedlings (Fagus sylvatica) with increased light intensity. In the present investigation both light intensity and soil water content were regulated on four levels in a factorial experiment. At the highest level of soil water content the seedling growth increased linearly with light intensity while the root/shoot ratio decreased with light intensity. At low levels of soil water content both the growth and root/shoot ratio slightly increased with increased light. The soil water content was also affected by the light intensity indicating that the soil water content may have caused unobserved effects in responding to increased light in previous investigations. It is concluded that both light intensity and soil water content should be quantified or manipulated even if only the effect of one of the two growth factors are investigated.

Restoring forests: What constitutes success in the twenty-first century?

Forest loss and degradation is occurring at high rates but humankind is experiencing historical momentum that favors forest restoration. Approaches to restoration may follow various paradigms depending on stakeholder objectives, regional climate, or the degree of site degradation. The vast amount of land requiring restoration implies the need for spatial prioritization of restoration efforts according to cost-benefit analyses that include ecological risks. To design resistant and resilient ecosystems that can adapt to emerging circumstances, an adaptive management approach is needed. Global change, in particular, imparts a high degree of uncertainty about the future ecological and societal conditions of forest ecosystems to be restored, as well as their desired goods and services. We must also reconsider the suite of species incorporated into restoration with the aim of moving toward more stress resistant and competitive combinations in the longer term. Non-native species may serve an important role under some circumstances, e.g., to facilitate reintroduction of native species. Propagation and field establishment techniques must promote survival through seedling stress resistance and site preparation. An improved ability to generalize among plant functional groups in ecological niche adaptations will help to overcome site-limiting factors. The magnitude and velocity of ongoing global change necessitates rapid responses in genetics that cannot be naturally induced at valid temporal and spatial scales. The capacity for new concepts and technologies to be adopted by managers and accepted by society will depend on effective technology transfer and a community-based approach to forest restoration. The many benefits human society gains from forests requires that forest restoration considers multiple objectives and approaches to minimize trade-offs in achieving these objectives.

Rodent impact on establishment of direct-seeded Fagus sylvatica, Quercus robur and Quercus petraea on forest land

Abstract Seed predation by granivorous rodents constitutes a major problem during reforestation using direct seeding. Acorns or beech nuts were sown at 14 different sites in Denmark and southern Sweden, and seedling establishment was inventoried during the first three growing seasons. Around the time of sowing, rodents were either snap-trapped or live-trapped. At some sites, perches for raptors were installed, and at other sites, signs of predation were investigated or predation was monitored by camera surveillance. Granivorous rodents had a profound negative influence on sowings, and the removal of beech nuts occurred rapidly following sowing. Establishment of oak was better when surroundings consisted of mixed forests rather than broadleaved forests. Fewer rodents were caught, and establishment was better, in large reforestation areas. Rodent captures indicated that forest edges, slash piles and stone wall remains were suitable rodent microhabitats. Snap-trapping or raptor perches did not result in increased oak establishment. Neither sowing in summer nor increased seeding depth decreased predation by rodents on beech nuts. In conclusion, seeds need protection from rodents immediately at the time of sowing. Choosing large regeneration areas combined with removal of suitable rodent habitats seems to be a practical alternative for the development of successful strategies for direct seeding.

What is forest landscape restoration

The extent and distribution of global forests is a matter of considerable concern. The overall rate of deforestation remains high although recent reports suggest it is finally beginning to decline (FAO 2011). But this hides regional differences. In temperate regions net forest cover is increasing because of afforestation and natural expansion of forests. By contrast, net forest cover in most tropical regions continues to decline and few of the remaining forests are being managed on a sustainable basis (Asner et al. 2010; Foley et al. 2005). This means that more and more tropical countries are changing from being exporters of forest products to being importers. Across the globe most deforestation has been carried out to create agricultural lands but a large proportion of these lands have subsequently been abandoned (Ramankuty and Foley 1999).

Evaluation of different approaches for modelling individual tree seedling height growth

We compared different approaches for modelling height growth of individual beech seedlings in a controlled factorial experiment as well as in field data from naturally regenerated beech seedlings under the canopy of overstorey mature beech trees. Several competition indices, a model of overstorey fine root density, relative photosynthetically active radiation (PAR) values, and soil water values were used in these approaches. In the factorial experiment relative PAR and soil water content were measured and used for the prediction of seedlings height growth. In the field experiment this was done by using relative PAR and estimated fine root biomass as a surrogate for below ground resource availability. The latter approach was compared with a model where we used various competition indices representing the impact of overstorey trees on beech seedlings. Our results suggested that (1) models which combine resource based growth functions are suitable for the prediction of individual height growth of beech seedlings. Resource based models offer the opportunity to investigate on the independent multiplicative effect of irradiance and water supply and their interactions on tree seedlings. It was (2) shown that a combined model could be used not only to predict individual height growth of beech seedlings in a controlled experiment but also in the field. The model parameters of a pure light response function for the controlled factorial experiment are comparable to those obtained in the field study. The results showed (3) that the precision of predicting beech seedlings height growth is comparable between the model types tested within this study. Approximately half of the observed variation in seedlings relative height growth rate could be explained. However, the simple competition index approach provides no information on the environmental factors constraining tree seedlings growth; whereas the multiplicative combined models can be used to get a better understanding of growth dynamics in the field.

Effects of seedbed type on wintering of beech nuts (Fagus sylvatica) and deer impact on sprouting seedlings in natural regeneration

Abstract Natural regeneration of beech ( Fagus sylvatica ) is often initiated by soil preparation before seed fall in the mast years. The wintering of beech nuts and the sprouting of beech seedlings in mixed and mineral soil seedbeds were investigated in six Danish beech stands after the 1989 seed fall. Previously, the mineral soil seedbed was considered to give the best wintering conditions for beech nuts owing to a relative low level of fungal attack. In the present investigation average number of undamaged nuts and sprouting seedlings were up to ten times larger in the mineral soil seedbed compared with the mixed soil seedbed within the same stand. However, the fungal attack was not significantly affected by the seedbed type. It is suggested that rodents collect undamaged nuts, leaving empty and damaged nuts behind, and that they prefer to seek for nuts in the mixed soil seedbed. Thereby, the method used for the collection of samples in previous investigations may have yielded misleading results concerning the effects of seedbed type on fungal attack.