Frédéric Archaux

Effects of sampling time, species richness and observer on the exhaustiveness of plant censuses

Abstract Question: How may sampling time affect exhaustiveness of vegetation censuses in interaction with observer effect and quadrat species richness? Location: French lowland forests. Methods: Two data sets comprised of 75 timed, one-hour censuses of vascular plants carried out by five observers on 24 400-m2 forest quadrats were analysed using mixed-effect models. Results: The level of exhaustiveness increased in a semi-logarithmic way with sampling time and decreased with quadrat species richness. After one hour, 20 to 30% of the species remained undetected by single observers. This proportion varied among observers and the discrepancy increased with increasing sampling time. Fixing the sampling time may make richness estimates vary less between observers but the time limit should be at least 30 min to reduce the bias in exhaustiveness between rich and poor quadrats. Conclusions: We advocate the use of sampling methods based on spatially or temporally-replicated censuses and statistical analyses that correct for the lack of census exhaustiveness in vegetation studies. Nomenclature: Kerguélen (2002). Abbreviation: AICc = consistent Akaike information criterion.

Long-term seed bank dynamics in a temperate forest under conversion from coppice-with-standards to high forest management

ABSTRACT Questions: How do changes in forest management, i.e. in disturbance type and frequency, influence species diversity, abundance and composition of the seed bank? How does the relationship between seed bank and vegetation change? What are the implications for seed bank dynamics? Location: An ancient Quercus petraea - Carpinus betulus forest in conversion from coppice-with-standards to regular Quercus high forest near Montargis, France. Methods: Seed bank and vegetation were sampled in six replicated stand types, forming a chronosequence along the conversion pathway. The stand types represented mid-successional stages of stands in transition from coppice-with-standards (to high forest (16 plots) and early- and mid-successional high forest stands (32 plots). Results: Seed bank density and species richness decreased with time since last disturbance. Adjusting for seed density effects obscured species richness differences between stand types, but species of later seres were nested subsets of earlier seres, implying concomitant shifts in species richness and composition with time since disturbance. Later seres were characterized by species with low seed weight and high seed longevity. Seed banks of early seres were more similar to vegetation than to later seres. Conclusions: Abandonment of the coppice-with-standards regime altered the seed bank characteristics, as well as its relationship with vegetation. Longer management cycles under high forest yield impoverished seed banks. For their persistence, seed bank species will increasingly rely on management of permanently open areas in the forest landscape. Thus, revegetation at the beginning of new high-forest cycles may increasingly depend on inflow from seed sources. Nomenclature: Lambinon et al. (1998).

Contribution of forest management artefacts to plant diversity at a forest scale

Abstract• IntroductionMost temperate forests are managed for wood production, and some forestry practices generate typical environmental features such as roads, paths, ditches and tractor ruts, which are likely to affect forest species distribution.• MethodsWe studied the influence of forestry artefacts on the overall forest-understory plant diversity in an ancient oak-dominated French forest with a long history of management. Two designs (grid design and paired design) were built in order to record the occurrence frequency of artefacts and to estimate the originality of the plant assemblage that they host.• ResultsWe recorded 897 plots on the grid design: 68.3% of the plots were more than 4 m away from any artefact, 23.3% were within 4 m of an artefact and 8.4% were located on an artefact. The artefact contribution to total floristic richness would lie between 8.0% and 22.6%, depending on whether the artefact surroundings were included or not in the artefact contribution. Road verges were the least frequent artefacts but provided the richest contribution to overall plant diversity (82%), whereas paths were the poorest (with only a 42% contribution). Thirteen species appeared to prefer artefacts over control plots: six forest species, five non-forest species and two generalist species.• DiscussionWe show that forestry artefacts are key components of the floristic diversity in managed forests; therefore, forest management should take them into consideration.

A quantitative assessment of the ecological value of sycamore maple habitats in the French Alps

Abstract• Naturalness is an important criterion in nature conservation assessment. At the stand-level, such assessment must be based on objective and quantifiable indicators measurable in the field.• In this study, we used a multi-criterion method based on the difference between a Natural Value (NV) and a Conservation Value (CV) to quantify the ecological value of sycamore maple patches compared to the surrounding mixed forests. Indeed, sycamore habitats are considered of high natural and conservation value both by naturalists and by European institutions.• Our results showed that the natural and conservation values were significantly higher for the sycamore forests than for the surrounding mixed forests and that this assessment did not depend on abiotic factors such as elevation or aspect. Actually, naturalness of structure and composition in the sycamore habitats was higher than for mixed forests and allowed us to differentiate between the two habitats.• Managers could easily use this method in order to assess the ecological value of small habitats in mountainous regions and to provide guidelines for close-to-nature and conservation-related silviculture.Résumé• La naturalité est un critère important pour l’évaluation de mesures conservatoires des écosystèmes. Au niveau local, une telle évaluation doit être basée sur des indicateurs objectifs et quantifiables sur le terrain.• Dans cette étude, nous avons utilisé une méthode multicritères basée sur la différence entre Valeur Naturelle (NV) et Valeur Conservatoire (CV) pour quantifier la valeur écologique des érablaies de versant à érable sycomore (Acer pseudoplatanus L.) par comparaison avec les peuplements mixtes de hêtraie-sapinière-pessière avoisinants. En effet, les naturalistes ainsi que l’Union Européenne considèrent que les érablaies de versant ont une valeur de conservation et de naturalité élevée.• Nos résultats montrent que les valeurs naturelle et de conservation sont significativement plus élevées pour l’érablaie que pour la forêt mixte avoisinante et que cette évaluation ne dépend pas de facteurs abiotiques tels que l’altitude ou l’exposition. En fait, la naturalité de structure et de composition des érablaies de versant sont plus fortes que celles des forêts mixtes et permettent de différencier les deux habitats en termes de valeur écologique.• Les gestionnaires peuvent facilement utiliser cette méthode pour évaluer la valeur écologique de petits habitats en zone de montagne, ce qui permet d’établir des orientations sylvicoles pour une gestion conservatoire et proche de la nature.

Projected regional forest plant community dynamics evidence centuries-long effects of habitat turnover

Co-ordinating Editor: Hans Henrik Bruun Abstract Questions: Many Western European and North American countries have been experiencing strong reforestation in the last two centuries due to agricultural abandonment. Other landuse changes, such as urbanization, can simultaneously trigger forest erosion. In this context of habitat turnover, forest understorey plant dynamics depend on the balance between immigration credit in postagricultural forest and extinction debt in ancient forest. The transient and final community properties following concomitant habitat creation and destruction are poorly known. In this contribution, we study the projected transient regional forest plant dynamics and identify the determinants of the relaxation duration at both landscape and patch scales. Location: SeineetMarne region, France. Methods: Species’ incidences are projected in 9,208 patches of the SeineetMarne region characterized by strong development of postagricultural forests and a moderate erosion of ancient forests during the period 1840–2000. We use a metapopulation model with static biodiversity data and landscape history to project forest plant dynamics. We focus on 33 generalist forest species that are able to colonize both ancient and postagricultural forests. Results: Our analyses reveal that (1) extinction in ancient forests slows the colonization process, which lasts between 250 and 990 years after habitat turnover, depending on species characteristics; (2) the species incidence in postagricultural forests converges towards that in ancient forests long before the overall species incidence stabilizes at the landscape scale (i.e. long before the relaxation time); (3) landscapeand patchscale relaxation times depend on species colonization ability and patch functional connectivity; (4) the colonization process is rather slow for ancient forest species; and (5) the incidence of ancient forest species becomes larger than the incidence of other species at the end of the colonization dynamics thanks to their strong persistence. Conclusions: Ancient forest species may potentially benefit from a large immigration credit but need centuries to use it. On such time scales, many perturbations are likely to jeopardize the realization of this potential credit.