Jürgen Bauhus

Retention Forestry to Maintain Multifunctional Forests: A World Perspective

The majority of the worlds forests are used for multiple purposes, which often include the potentially conflicting goals of timber production and biodiversity conservation. A scientifically validated management approach that can reduce such conflicts is retention forestry, an approach modeled on natural processes, which emerged in the last 25 years as an alternative to clearcutting. A portion of the original stand is left unlogged to maintain the continuity of structural and compositional diversity. We detail retention forestrys ecological role, review its current practices, and summarize the large research base on the subject. Retention forestry is applicable to all forest biomes, complements conservation in reserves, and represents bottom-up conservation through forest manager involvement. A research challenge is to identify thresholds for retention amounts to achieve desired outcomes. We define key issues for future development and link retention forestry with land-zoning allocation at various scales, expanding its uses to forest restoration and the management of uneven—age forests.

Community assembly during secondary forest succession in a Chinese subtropical forest

Subtropical broad-leaved forests in southeastern China support a high diversity of woody plants. Using a comparative study design with 30 × 30 m plots (n = 27) from five successional stages ( 1 m in height in each plot and counted all woody recruits (bank of all seedlings ≤1 m in height) in each central 10 × 10 m quadrant of each plot. In addition, we measured a number of environmen...

Designing forest biodiversity experiments: general considerations illustrated by a new large experiment in subtropical China

Summary 1. Biodiversity–ecosystem functioning (BEF) experiments address ecosystem-level consequences of species loss by comparing communities of high species richness with communities from which species have been gradually eliminated. BEF experiments originally started with microcosms in the laboratory and with grassland ecosystems. A new frontier in experimental BEF research is manipulating tree diversity in forest ecosystems, compelling researchers to think big and comprehensively. 2. We present and discuss some of the major issues to be considered in the design of BEF experiments with trees and illustrate these with a new forest biodiversity experiment established in subtropical China (Xingangshan, Jiangxi Province) in 2009/2010. Using a pool of 40 tree species, extinction scenarios were simulated with tree richness levels of 1, 2, 4, 8 and 16 species on a total of 566 plots of 25� 8 9 25� 8m each. 3. The goal of this experiment is to estimate effects of tree and shrub species richness on carbon storage and soil erosion; therefore, the experiment was established on sloped terrain. The following important design choices were made: (i) establishing many small rather than fewer larger plots, (ii) using high planting density and random mixing of species rather than lower planting density and patchwise mixing of species, (iii) establishing a map of the initial ‘ecoscape’ to characterize site heterogeneity before the onset of biodiversity effects and (iv) manipulating tree species richness not only in random but also in trait-oriented extinction scenarios. 4. Data management and analysis are particularly challenging in BEF experiments with their hierarchical designs nesting individuals within-species populations within plots within-species compositions. Statistical analysis best proceeds by partitioning these random terms into fixed-term contrasts, for example, species composition into contrasts for species richness and the presence of particular functional groups, which can then be tested against the remaining random variation among compositions. 5. We conclude that forest BEF experiments provide exciting and timely research options. They especially require careful thinking to allow multiple disciplines to measure and analyse data jointly and effectively. Achiev

Mechanisms for carbon and nutrient release and retention in beech forest gaps

Nutrient cycling and water balance in forest gaps has received little attention until now, although gap regeneration is important to natural dynamics of temperate forests. Gaps of 30 m diameter, cut in a mature beech forest, exhibited a distinct change in microclimatic conditions in comparison with the surrounding stand. Soil moisture in gaps remained very high throughout the observation period. Disruption of the N cycle in gaps led to substantial nitrate losses; seepage water nitrate concentrations were 10–18 mg NO3-N L-1. Excess nitrification was a significant cause of soil acidification and aluminium release. The pH in subsoil seepage water decreased by 0.25. Liming in gaps promoted the establishment of a herbaceous vegetation, which functioned as an important nutrient sink, and thus is recommended for tree regeneration in highly acidified forest ecosystems as it increases the resilience of the ecosystem to nutrient losses.

How does silviculture affect storm damage in forests of south-western Germany? Results from empirical modeling based on long-term observations

Storms represent the most important disturbance factor in forests of Central Europe. Using data from long-term growth and yield experiments in Baden-Wuerttemberg (south-western Germany), which permit separation of storm damage from other causes of mortality for individual trees, we investigated the influence of soil, site, forest stand, and tree parameters on storm damage, especially focusing on the influence of silvicultural interventions. For this purpose, a four-step modeling approach was applied in order to extract the main risk factors for (1) the general stand-level occurrence of storm damage, (2) the occurrence of total stand damage, and (3) partial storm damage within stands. The estimated stand-level probability of storm damage obtained in step 3 was then offset in order to describe the damage potential for the individual trees within each partially damaged stand (4). Generalized linear mixed models were applied. Our results indicate that tree species and stand height are the most important storm risk factors, also for characterizing the long-term storm risk. Additionally, data on past timber removals and selective thinnings appear more important for explaining storm damage predisposition than for example stand density, soil and site conditions or topographic variables. When quantified with a weighting method (summarizing the relative weight of single predictors or groups of predictors), removals could explain up to 20% of storm risk. The stepwise modeling approach proved an important methodological feature of the analysis, since it enabled consideration of the large number of observations without damage (“zero inflation”) in a statistically correct way. These results form a reliable basis for quantifying forest management’s direct impact on the risk of storm damage.

Silvicultural alternatives to conventional even-aged forest management - what limits global adoption?

BackgroundThe development of forestry as a scientific and management discipline over the last two centuries has mainly emphasized intensive management operations focused on increased commodity production, mostly wood. This “conventional” forest management approach has typically favored production of even-aged, single-species stands. While alternative management regimes have generally received less attention, this has been changing over the last three decades, especially in countries with developed economies. Reasons for this change include a combination of new information and concerns about the ecological consequences of intensive forestry practices and a willingness on the part of many forest owners and society to embrace a wider set of management objectives. Alternative silvicultural approaches are characterized by a set of fundamental principles, including avoidance of clearcutting, an emphasis on structural diversity and small-scale variability, deployment of mixed species with natural regeneration, and avoidance of intensive site-preparation methods.MethodsOur compilation of the authors’ experiences and perspectives from various parts of the world aims to initiate a larger discussion concerning the constraints to and the potential of adopting alternative silvicultural practices.ResultsThe results suggest that a wider adoption of alternative silvicultural practices is currently hindered by a suite of ecological, economic, logistical, informational, cultural, and historical constraints. Individual contexts display their own unique combinations and relative significance of these constraints, and accordingly, targeted efforts, such as regulations and incentives, may help to overcome specific challenges.ConclusionsIn a broader context, we propose that less emphases on strict applications of principles and on stand structures might provide additional flexibility and facilitate the adoption of alternative silvicultural regimes in a broader set of circumstances. At the same time, the acceptance of alternative silvicultural systems as the “preferred or default mode of management” will necessitate and benefit from the continued development of the scientific basis and valuation of a variety of ecosystem goods and services. This publication is aimed to further the discussion in this context.

Estimating fine-root biomass and production of boreal and cool temperate forests using aboveground measurements : A new approach

Information of fine-root biomass and production is critical for quantifying the productivity and carbon cycle of forest ecosystems, and yet our ability to obtain this information especially at a large spatial scale (e.g., regional to global) is extremely limited. Several studies attempted to relate fine-root biomass and production with various aboveground variables that can be measured more easily so that fine-root biomass and production could be estimated at a large spatial scale, but found the correlations were generally weak or non-existed at the stand level. In this study, we tested a new approach: instead of using the conventional way of analysing fine-root biomass at the stand level, we analysed fine-root data at the tree level. Fine-root biomass of overstory trees in stand was first separated from that of understory and standardized to a common fine-root definition of < 2 mm or < 5 mm diameter. Afterwards, we calculated fine-root biomass per tree for a ‘representative’ tree size of mean basal area for each stand. Statistically significant correlations between the fine-root biomass per tree and the diameter at the ground surface were found for all four boreal and cool temperate spruce, pine, fir and broadleaf forest types, and so allometric equations were developed for each group using a total of n = 212 measurements. The stand-level fine-root biomass of trees estimated using the allometric equations agrees well with the measurements, with r2 values of 0.64 and 0.57 (n = 171), respectively, for fine-roots < 2 mmand < 5 mm diameter. This study further estimated fine-root production as the product of fine-root turnover rate and fine-root biomass, and determined the turnover rate as a function of fine-root biomass, stand age, and mean annual temperature. The estimates of tree fine-root production agree well with reported values, with r2 value of 0.53 for < 2 mm and 0.54 for < 5 mm diameter (n = 162) at the stand level.

A Review of Processes Behind Diversity—Productivity Relationships in Forests

Through complementarity interactions, mixed-species forests can be more productive than monocultures, and this effect can increase with tree-species richness. However, this is not always the case. This review examines the processes and stand structural attributes that can influence diversity-productivity relationships (DPRs); how they influence resource availability, resource uptake, and resource-use efficiency; and also describes some important differences between tree-diversity versus grassland-diversity experiments. The size of the complementarity effects caused by these processes and stand structures varies along spatial and temporal gradients in resource availability and climate. These spatial and temporal dynamics have now been examined in many studies, and the general patterns are summarized using a simple framework; complementarity is predicted to increase as the availability of resource “X” declines (or climatic condition X becomes harsher) if the species interactions improve the availability, uptake, or use efficiency of resource X (or interactions improve climatic condition X). Importantly, this framework differs from the stress-gradient hypothesis to account for a wider range of inter-specific plant interactions (not only facilitation) by considering contrasting methods used to quantify species interactions while accounting for stand structure. In addition, complementarity (as opposed to facilitation) for a given species combination can increase as growing conditions improve in forests, contrary to predictions of the stress-gradient hypothesis with regards to facilitation. This review indicates that while the effects of tree-species diversity on growth and other forest functions are now receiving a lot of attention, far less is known about the effects of structural diversity on growth or forest functioning. Direct measurements of the processes, as opposed to focusing mainly on growth responses, could greatly contribute to our understanding of structural diversity effects.

C and N mineralization in an acid forest soil along a gap-stand gradient

Abstract Using aerobic long-term incubations of 174 days, carbon and nitrogen mineralization, pools of potentially mineralizable C and N, microbial C and N, and leaching of organic CaCl 2 -extractable C and N were determined in forest floor material (O F and O H ) and mineral soil (0–5 cm) collected along a gap-stand gradient. Sample locations were the centre of gaps, the northern part of gaps, the northern edge between gaps and stand, and a mature European beech stand. Conditions changed along the gradient in (a) soil moisture, which was highest in the gap centre, (b) soil temperature, which was elevated in the northern part of the gap and at the northern edge, and (c) active tree roots, which were absent from the gap centre and the northern part. Samples were collected 21 months after gaps (30 m dia) had been created. Because N mineralization in the field during the first year after gap creation was higher in the gap than in the stand but lower in the second year, it was hypothesized that mineralizable substrate had been partially depleted under gap conditions. No differences were found between the gap and the stand in forest floor mass, or forest floor and mineral soil C and N concentrations. In the forest floor, C and N mineralization, and consequently the potentially mineralizable C and N, as derived from first order mineralization kinetics, decreased in the order stand > northern edge > gap centre > gap north. Amounts mineralized were 1053, 861, 761 and 610 g N g −1 and 24.4, 22.6, 22.5 and 20.2 mg C g −1 respectively. In mineral soil, these values were highest in the gap centre. A substantial decrease in microbial biomass occurred in samples from the gap centre during incubation. Other samples showed no marked decrease in microbial biomass during incubation. In the forest floor a shorter turnover time of mineralizable N was observed for gap locations, whereas the turnover of mineralizable C was slower in the northern part of the gap and the northern edge. This suggests that potentially-mineralizable pools of C and N were affected differently by either rooting, moisture or temperature. Similar turnover times (4–11 weeks) for potentially-mineralizable N in both forest floor and mineral soil suggested similar sources of mineralized N. Potentially-mineralizable C consisted of more recalcitrant fractions in mineral soil than in forest floor. Nitrogen immobilization in the form of CaCl 2 -extractable organic compounds was unimportant in this soil. Organic N (N org ) in CaCl 2 -leachates was 4–12% of mineral N. Kinetic parameters indicated that N mineralization in the second year after gaps had been created was lower in the gaps, because mineralizable C and N pools had decreased.

Structural diversity promotes productivity of mixed, uneven-aged forests in southwestern Germany

Forest diversity-productivity relationships have been intensively investigated in recent decades. However, few studies have considered the interplay between species and structural diversity in driving productivity. We analyzed these factors using data from 52 permanent plots in southwestern Germany with more than 53,000 repeated tree measurements. We used basal area increment as a proxy for productivity and hypothesized that: (1) structural diversity would increase tree and stand productivity, (2) diversity-productivity relationships would be weaker for species diversity than for structural diversity, and (3) species diversity would also indirectly impact stand productivity via changes in size structure. We measured diversity using distance-independent indices. We fitted separate linear mixed-effects models for fir, spruce and beech at the tree level, whereas at the stand level we pooled all available data. We tested our third hypothesis using structural equation modeling. Structural and species diversity acted as direct and independent drivers of stand productivity, with structural diversity being a slightly better predictor. Structural diversity, but not species diversity, had a significant, albeit asymmetric, effect on tree productivity. The functioning of structurally diverse, mixed forests is influenced by both structural and species diversity. These sources of trait diversity contribute to increased vertical stratification and crown plasticity, which in turn diminish competitive interferences and lead to more densely packed canopies per unit area. Our research highlights the positive effects of species diversity and structural diversity on forest productivity and ecosystem dynamics.