Thomas Cordonnier

Effects of increasing landscape heterogeneity on local plant species richness: how much is enough?

Contemporary landscape ecology continues to explore the causes and consequences of landscape heterogeneity across a range of scales, and demands for the scientific underpinnings of landscape planning and management still remains high. The spatial distribution of resources can be a key element in determining habitat quality, and that in turn is directly related to the level of heterogeneity in the system. In this sense, forest habitat mosaics may be more affected by lack of heterogeneity than by structural fragmentation. Nonetheless, increasing spatial heterogeneity at a given spatial scale can also decrease habitat patch size, with potential negative consequences for specialist species. Such dual effect may lead to hump-backed shape relationships between species diversity and heterogeneity, leading to three related assumptions: (i) at low levels of heterogeneity, an increase in heterogeneity favours local and regional species richness, (ii) there is an optimum heterogeneity level at which a maximum number of species is reached, (iii) further increase in spatial heterogeneity has a negative effect on local and regional species richness, due to increasing adverse effects of habitat fragmentation. In this study, we investigated the existence of a hump-shaped relationship between local plant species richness and increasing forest landscape heterogeneity on a complex mosaic in the French Alps. Forest landscape heterogeneity was quantified with five independent criteria. We found significant quadratic relationships between local forest species richness and two heterogeneity criteria indicators, showing a slight decrease of forest species richness at very high heterogeneity levels. Species richness–landscape heterogeneity relationships varied according to the heterogeneity metrics involved and the type of species richness considered. Our results support the assumption that intermediate levels of heterogeneity may support more species than very high levels of heterogeneity, although we were not able to conclude for a systematic negative effect of very high levels of heterogeneity on local plant species richness.

Reconciling Biodiversity Conservation and Timber Production in Mixed Uneven-Aged Mountain Forests: Identification of Ecological Intensification Pathways

Mixed uneven-aged forests are considered favorable to the provision of multiple ecosystem services and to the conciliation of timber production and biodiversity conservation. However, some forest managers now plan to increase the intensity of thinning and harvesting operations in these forests. Retention measures or gap creation are considered to compensate potential negative impacts on biodiversity. Our objectives were to assess the effect of these management practices on timber production and biodiversity conservation and identify potential compensating effects between these practices, using the concept of ecological intensification as a framework. We performed a simulation study coupling Samsara2, a simulation model designed for spruce-fir uneven-aged mountain forests, an uneven-aged silviculture algorithm, and biodiversity models. We analyzed the effect of parameters related to uneven-aged management practices on timber production, biodiversity, and sustainability indicators. Our study confirmed that the indicators responded differently to management practices, leading to trade-offs situations. Increasing management intensity had negative impacts on several biodiversity indicators, which could be partly compensated by the positive effect of retention measures targeting large trees, non-dominant species, and deadwood. The impact of gap creation was more mitigated, with a positive effect on the diversity of tree sizes and deadwood but a negative impact on the spruce-fir mixing balance and on the diversity of the understory layer. Through the analysis of compensating effects, we finally revealed the existence of possible ecological intensification pathways, i.e., the possibility to increase management intensity while maintaining biodiversity through the promotion of nature-based management principles (gap creation and retention measures).

Reconstructing harvesting diameter distribution from aggregate data

Abstract• ContextDistribution of removed trees among species and diameter classes is usually used to characterize selection harvesting. This information is, however, rarely available when analysing past time series. The challenge is then to determine the minimal level of information required to characterize harvests.• AimsWe tested in this work whether an algorithm based on the total number of trees and volume to be removed enabled the reconstruction of harvesting diameter distributions, when combined with stand diameter distribution before harvest.• MethodsWe tested the algorithm against empirical data in the case of selection system, comparing distributions by χ² tests, and extended its evaluation to more diversified theoretical situations.• ResultsObserved harvesting distributions were well-reconstructed in most empirical cases, with better results when considering mean simulated distributions. The algorithm was also effective for other thinning and harvesting strategies: low thinning, thinning of dominants, and mechanical thinning, whatever the structure of the stand before being cut.• ConclusionTotal number of trees and volume harvested appeared thus sufficient to reconstruct DBH distribution of removed trees in diverse situations, provided that the distribution before harvest was known. This algorithm, therefore, enables the simulation of complex harvesting operations with minimal information.

Is generalisation of uneven-aged management in mountain forests the key to improve biodiversity conservation within forest landscape mosaics?

ContextUneven-aged management systems based on selection silviculture have become popular in European mountain forests and progressively replace other silvicultural practices. In time, this trend could lead to a homogenisation of the forest mosaic with consequences on structural indices recognised as beneficial to forest biodiversity.AimsThis study was conducted to investigate the potential effects of a generalisation of the selection silvicultural system on structural diversity in the forest landscape with consequences for forest biodiversity conservation.MethodsWe compared four structural indices (tree species richness, diameter heterogeneity, deadwood volume and basal area of mature trees) in five different stand types typical of the northern French Alps, using forest plot data in the Vercors mountain range. Through virtual landscape simulations, we then calculated predicted mean proportions of stand types under two different conservation strategies: (i) maximising mean index values at the landscape level and (ii) maximising the number of plots in the landscape with index values above given thresholds.ResultsMulti-staged forests did not maximise all indices, the best solution being to combine the five stand types in uneven proportions to improve biodiversity conservation.ConclusionThe expansion of selection silviculture in European heterogeneous forest landscapes could enhance biodiversity conservation if other stand types with complementary structural characteristics are maintained.

Using the Viability Theory to Assess the Flexibility of Forest Managers Under Ecological Intensification

AbstractGreater demand for wood material has converged with greater demand for biodiversity conservation to make balancing forest ecosystem services a key societal issue. Forest managers, owners, or policymakers need new approaches and methods to evaluate their ability to adapt to this dual objective. We analyze the ability of forest owners to define sustainable forest management options based on viability theory and a new flexibility index. This new indicator gauges the adaptive capacity of forest owners based on the number of sustainable actions available to them at a given time. Here we study a public forest owner who regulates harvest intensity and frequency in order to meet demand for timber wood at forest scale and to meet a biodiversity recommendation via a minimum permanently maintained volume of deadwood per hectare at stand scale. Dynamical systems theory was used to model uneven-aged forest dynamics—including deadwood dynamics—and the dynamics of timber wood demand and tree removals. Uneven-aged silver fir forest management in the “Quatre Montagnes region” (Vercors, France) is used as an illustrative example. The results explain situations where a joint increase in wood production and deadwood retention does not reduce the flexibility index more than increasing either one dimension alone, thus opening up ecological intensification options. To conclude, we discuss the value of the new flexibility index for addressing environmental management and ecological intensification issues.

Reconciling Environment and Production in Managed Ecosystems: Is Ecological Intensification a Solution?

The overall demand for both agricultural and forest goods and services has strongly increased and is likely to continue to rise in the future, leading to more intensive practices in many managed ecosystems with potential negative effects for biodiversity and the environment (Cassman 1999; Tilman et al. 2002; Brussaard et al. 2010; Verkerk et al. 2014). Regarding agriculture, the challenge is to feed increasing numbers of people (food security) as well as to contribute to the development of bioenergy (Valentine et al. 2012). In the same vein, more forest products are required to satisfy new ambitious energy and construction policies (Jonsson 2013). Meanwhile, the concept of ecosystem services (ESs) has emerged and has been established in the environmental research and public spheres, exemplifying the complexity of ecosystems and their multiple relationships with human needs, including provisioning and regulating as well as social and cultural services (Tilman et al. 2002; Messier et al. 2015). Although conflicts or trade-offs between ESs have often been emphasized, positive interactions between, for example, regulating and provisioning ESs have paved the way to designing new management systems promoting ecological processes and reducing practices based on heavy mechanical or chemical means (Gaba et al. 2015). Overall, this is creating possibilities to reconcile production and the environment through a new type of ecologically driven intensification. According to Dore et al. (2011), ecological intensification (EI) consists in reducing artificial inputs while maintaining high production levels through biological regulation. It can thus be related to all practices that consist in intensifying the use of natural functions provided by ecosystems to support production (Chevassus au Louis and Griffon 2008). By nature, EI is closely related to biodiversity, which can directly or indirectly support production and other ESs through functional processes (Bommarco et al. 2013; Gaba et al. 2014). Although to date it has for the most part been mentioned in discussions on crop systems in agriculture, with some adjustments it can be generalized to other managed ecosystems dedicated to production (Rey et al. 2015). For instance, in forest science, concepts such as close-to-nature forestry, which explicitly integrates the reduction of inputs using natural processes, can fall under EI (Bauhus et al. 2013). As highlighted by Tittonell (2014), EI must be considered as designing ecosystem-based ‘‘[...] multifunctional agroecosystems that are both sustained by nature and sustainable in their nature.’’ From all these principles, it appears that EI contains all the ingredients to reconcile production and the environment (Fig. 1): (1) it aims at supporting and maximizing production; (2) it promotes practices that are based on functional ecological processes and that favor synergies between ESs (especially between regulating and provisioning ESs); and (3) it aims at reducing negative impacts of intensive management practices designed to increase productivity. So far, some important steps have been taken toward EI in both forestry and agriculture. For instance, in forestry, favoring species mixture in planted or natural forest stands may increase ecosystem productivity through temporal and spatial species niche complementarities (Forrester 2014). Silviculture practices based on natural processes (natural & Thomas Cordonnier thomas.cordonnier@irstea.fr

Ecological research and environmental management: We need different interfaces based on different knowledge types

The role of ecological science in environmental management has been discussed by many authors who recognize that there is a persistent gap between ecological science and environmental management. Here we develop theory through different perspectives based on knowledge types, research categories and research-management interface types, which we combine into a common framework. To draw out insights for bridging this gap, we build our case by:We point out the complementarities as well as the specificities and limitations of the different types of ecological research, ecological knowledge and research-management interfaces, which is of major importance for environmental management and research policies.