Magnus Löf

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.

Mechanical site preparation for forest restoration

Forest restoration projects have become increasingly common around the world and planting trees is almost always a key component. Low seedling survival and growth may result in restoration failures and various mechanical site preparation techniques for treatment of soils and vegetation are important tools used to help counteract this. In this article, we synthesize the current state-of-knowledge concerning mechanical site preparation for improved tree establishment when carried out in different forest restoration situations, point out critical research gaps and provide some recommendations for future directions. Mechanical site preparation often results in improved seedling survival and growth. However, if not intensive methods with much soil disturbance are used, it is a rather ineffective tool for controlling competing vegetation. Methods such as scarification, mounding and subsoiling also lead to multiple interactions among soil physical and chemical properties that affect plant survival and growth, and it may be difficult to determine the actual cause–effect relationship of any positive seedling responses. Most research to date on mechanical site preparation and plantation performance has been conducted using a few conifer tree species. Seedling responses differ among tree species and alternative species are often used during restoration compared to production forestry indicating a need for additional research for improved understanding. Several management objectives such as soil protection and increased biodiversity are many times relevant during forest restoration, and mechanical site preparation methods should be implemented carefully because they can have large impacts on the environment.

Germination and early growth of sown Quercus robur L. in relation to soil preparation, sowing depths and prevention against predation.

A field experiment was established in the autumn of 1992 in order to study predation of acorns, germination and early growth of oak seedlings. The experiment was established on a clearcut and an adjacent oak shelterwood in southern Sweden. In the experiment, a total of 6 840 acorns were sown. The sowing was carried out with different vegetation control and soil preparation treatments and with different planting depths.The germination percentage was highest for acorns sown at five cm depth and lowest for acorns sown on top of the soil, and lower for acorns sown in areas where the humus layer had been removed than in areas where the humus layer was retained. There was no difference in the percentage germination after two growing seasons between acorns sown inside the shelterwood and acorns sown on the clearcut. The height of the seedlings was lowest when the humus was removed while the number of leaves per seedling was lowest for seedlings in untreated areas after two growing seasons. Furthermore, seedlings in untreated areas showed the lowest relative height growth rate during the second growing season. In spite of higher biomass of ground vegetation in undisturbed areas compared to treated areas, no effect of the soil and vegetation control treatments could be found on soil water potentials. The soil temperature and photosynthetic active radiation at seedling level were higher in areas where soil preparation and vegetation control had been performed. However, it was concluded that neither low soil water availability nor low light levels could be the only cause of lower relative height growth rate during the second growing season for seedlings in undisturbed areas.

Interacting effects of irradiance and water stress on dry weight and biomass partitioning in Fagus sylvatica seedlings

Abstract Actual climate models for central Europe predict prolonged summer droughts. Knowledge on how the interaction between light and water availability affects regeneration will hence be of major importance. In an experiment carried out under controlled conditions, newly emerged beech seedlings were grown in pots with sand during 54 days. Three treatments applying three different light levels (2, 9 and 43% relative light intensity) were combined with two soil water treatments (control and drought). At the end of the experiment, seedlings were separated into leaves, stem and root and the seedlings’ dry mass, leaf area and stem length was determined. Low irradiance (2%) had a strong negative effect on dry weights of seedling components, leaf area and specific leaf mass. Drought clearly affected biomass partitioning for seedlings at high irradiance levels (43%). An interaction between irradiance and drought on biomass partitioning in beech seedlings was observed at medium irradiance level (9%). Within a wide range of light levels in the forests, both light and drought may affect biomass partitioning in young seedlings.

The influence of site preparation on growth in Quercus robur L. seedlings in a southern Sweden clear-cut and shelterwood

Natural regeneration of Quercus spp. is regarded as a method with major problems for establishing new stands. A number of factors like quantity and quality of acorn production, heavy predation and browsing on acorns and seedlings and low growth rate of oak seedlings contribute in regeneration failures. To study the influence of light, nutrients and water on growth in Quercus robur L. seedlings in relation to site preparation, a field experiment was established. The experiment was carried out in a clear-cut and a shelterwood in southern Sweden from 1992 until 1995. Five different treatments were applied and acorns were then planted. The treatments were: herbicide, herbicide and mixing of the humus layer and the top 10 cm of the mineral soil, herbicide and removal of the humus layer, herbicide and deep cultivation down to 40 cm with the humus layer in the bottom and undisturbed control. Irrespective of the method, the different site preparation treatments after three years equally well prevented the growth of ground vegetation and increased the seedling growth. PPFD (photosynthetic photon flux density) at seedling level was about 20% of full light in the shelterwood and in the undisturbed control plots in the clear-cut. PPFD at the seedling level were about 60% of full light in the different site preparation treatments in the clear-cut. The mean cumulative soil water potential was about the same in undisturbed control plots in the clear-cut and shelterwood. In the different site preparation treatments, mean cumulative soil water potential indicated lower values in the clear-cut compared to the shelterwood. According to measurements of the leaf water potential, seedlings seemed to be more affected by water stress in the clear-cut. Nitrogen concentration in leaves was about the same in all treatments. Longer periods with shelterwoods in combination with the additional site preparation for ground vegetation control was recommended for practical forestry for improved growth of oak seedlings during natural regeneration. It does not seem to be important which method of additional ground vegetation control is chosen as long as the amount of ground vegetation is reduced. It was concluded that light level alone is not the key factor controlling growth of oak seedlings during natural regeneration. However, light and soil water content may interact and influence the growth of oak seedlings.

Effects of roe deer browsing and site preparation on performance of planted broadleaved and conifer seedlings when using temporary fences

Abstract The effects of fencing and site preparation on performance of birch (Betula pendula Roth), oak (Quercus robur L.), pine (Pinus sylvestris L.) and spruce [Picea abies (L.) Karst.] seedlings were studied over four growing seasons in southern Sweden. The experiment was composed of four browsing treatments, from which roe deer (Capreolus capreolus L.) were excluded for 0, 12, 24 or 42 months, and four soil treatments. Natural browsing was combined with artificial browsing (clipping). It was demonstrated that browsing by roe deer could be isolated from browsing by moose (Alces alces L.) by selective fencing. Except for birch, browsing had little effect on seedling survival. Browsing reduced height growth by more than 100% for oak and pine, and more than 60% of pine seedling developed multiple stems. Except for oak, site preparation increased seedling survival. Inverting site preparation, in combination with or without fertilization, produced positive growth responses in seedlings, whereas patch scarification did not. There was no interaction between browsing and soil treatments on seedling performance. It was concluded that long-term protection against browsing by roe deer is needed for oak and pine, whereas short-term fences might be used for birch, and that spruce is relatively unaffected by browsing.

Influence of patch scarification and insect herbivory on growth and survival in Fagus sylvatica L., Picea abies L. Karst. and Quercus robur L. seedlings following a Norway spruce forest.

Southern Sweden is dominated by relatively uniform coniferous forests where Norway spruce is the most common tree species. Ecological and economic considerations have created an interest in re-establishing broadleaves in these forests. To study the influence of patch scarification and compare the influence of insect herbivory on growth and survival in beech (Fagus sylvatica L.), Norway spruce (Picea abies L. Karst.) and oak (Quercus robur L.) seedlings, a field experiment was established. The experiment was carried out on a new clear-cut following Norway spruce, and in a Norway spruce shelterwood. Seedlings were spring-planted in two consecutive years in untreated ground (control) and in patch site preparation treatment in combination with or without repeated insecticide treatment. The influence of patches on seedling growth and survival of all species studied was low. No pronounced differences in photosynthetic photon flux density at seedling level and recolonization of ground vegetation were observed between patch scarification and control. Patches had higher soil water potentials than the control in the shelterwood, but this did not result in any positive growth response in the seedlings. The number of trapped pine weevils (Hylobius abietis L.) was about equal in both patch scarification and control treatment. Insecticide treatment had a significant influence on growth and survival of seedlings. On the clear-cut, herbivory by pine weevils was lower on beech and oak seedlings than on Norway spruce seedlings. In the shelterwood, herbivory by pine weevils was low on all species. The conclusion is that less efforts are needed to protect beech and oak from herbivory by pine weevil compared to Norway spruce. Herbivory by short-snouted weevils (Strophosoma melanogrammum Forst. and Otiorhynchus scaber L.) constitutes another threat, but was about the same on beech, oak and Norway spruce. Although the highest growth in the seedlings occurred in the open, this study shows that high survival can be achieved without using site preparation and insecticides when beech and oak are planted under shelterwood trees of Norway spruce.

Forest vegetation management under debate: an introduction

is anintegral part of silvicultural practices in many parts of theworld (Wagner et al. 2006; Richardson et al. 2006; Newton2006). However, there are substantial differences betweenthe continents with regard to the preferred methods. Theimplementation of tending measures to control woodycompetitors is common in European even-aged stands as inother parts of the world. In contrast, the use of herbicidesfor weed control is much less common in Europe than forexample in North America, South Africa, Australia andNew Zealand where chemical vegetation control, inparticular, is used and promoted strongly in plantationforestry (Newton 2006). If at all, in Europe, herbaceousvegetation is controlled predominantly by mechanical sitepreparation, mulching or other techniques (McCarthy et al.2010, this issue). An overwhelming amount of literaturehas shown that chemical vegetation control can result inhuge gains in wood volume (Wagner et al. 2006). This hadlet to favourable reports of chemical vegetation control asthe following statements may indicate: ‘in most instances,forests cannot be managed economically without herbi-cides if the goal is to grow seedlings at the potential of thesite and the plant community includes sprouting hardwoodsand shrubs of rhizomatous forbs and ferns’ (McDonald andFiddler 1993); ‘most regeneration efforts around the worldwould fail or be severely delayed without effective forestvegetation management … primarily using herbicides’(Wagner et al. 2006); ‘reducing competition for desirabletrees with modern chemicals has less impact on soil andwildlife habitat and lowers human health risk per unitof effectiveness than mechanical or manual methods’(Newton 2006). In contrast, in Europe at present there ispolitical consensus for a reduction in the use of herbicidesas much as possible (i.e. The EU Thematic strategy on theSustainable Use of Pesticides). Society perceives Europeanforests as the last quasi-natural compartments of a land-scape which has been entirely manipulated for more than2,000 years. In this context, herbicides are view by thepublic as a serious threat for the maintenance of the set ofmultiple functions that forests provide (Merlo and Croitoru2005; Schmithu¨sen 2007; Ammer and Puettmann 2009).

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.

Non-market forest ecosystem services and decision support in Nordic countries

ABSTRACT The need to integrate non-market ecosystem services into decision-making is widely acknowledged. Despite the exponentially growing body of literature, trade-offs between services are still poorly understood. We conducted a systematic review of published literature in the Nordic countries (Denmark, Norway, Sweden and Finland) on the integration of non-market forest ecosystem services into decision-making. The aim of the review was two-fold: (1) to provide an overview of coverage of biophysical and socio-economic assessments of non-market ecosystem services in relation to forest management; (2) to determine the extent of the integration of biophysical and socio-economic models of these services into decision support models. Our findings reveal the need for wider coverage of non-market ecosystem services and evidence-based modelling of how forest management regimes affect ecosystem services. Furthermore, temporal and spatial modelling of ecosystem impacts remains a challenge. We observed a few examples of multiple non-market services assessments. Integration of non-market services into decision support was performed with either biophysical or socio-economic models, often using proxies and composite indicators. The review reveals that there is scope for more comprehensive and integrated model development, including multiple ecosystem services and appropriate handling of forest management impacts.