Gauthier Ligot

Enrichment of Central African logged forests with high-value tree species: testing a new approach to regenerating degraded forests

ABSTRACT In natural forests of Central Africa, several studies indicate a dramatic decrease in commercial trees, including species of concern for conservation. Enrichment planting with these species will favor both the long-term recovery of their populations and biodiversity conservation in logged forests. In this study, we analyzed the survival and growth of 23 species in plantations. Fourteen 0.2–1.1 ha mixed species plantations consisting of single-species 15 × 15 m blocks were studied for 5 years in a logging concession of southeastern Cameroon. The plantation design considered both species light requirements and sensitivity to damage by pests. To identify the best species for enrichment planting, we assessed both species performance and plantation costs. We also tested for relationships between species traits and species performance. Mean annual diameter growth increments ranged from 1.67 to 42.9 mm. No significant relationship was found between growth and survival. Herbivory by wild Bovidae was the main cause of mortality and should be carefully considered in rehabilitation efforts. We found a significant negative relationship between wood density and maximum growth rate. The other traits tested were not good predictors of species performance in plantations. The two best-performing species, Triplochiton scleroxylon and Terminalia superba, could reach the minimum cutting diameter during a 30-year cutting cycle. Costs were high and mechanized site preparation is suggested to reduce them. Widespread adoption of such plantations will only occur if financial incentives or national regulations for assuring regeneration are implemented. EDITED BY Nicholas Brokaw

Assessing and Harmonizing Lying Deadwood Volume with Regional Forest Inventory Data in Wallonia (Southern Region of Belgium)

Using lying deadwood or coarse woody debris (CWD) as an indicator of biodiversity and of sustainable forest management is on the rise among national and local forest inventories. Nevertheless choosing the most suitable sampling method is difficult as it depends mostly on CWD abundance and dimensions. In addition the CWD volume estimates of different regional inventories are rarely comparable. We therefore tested two generally recommended methods for lying deadwood: line intersect sampling and fixed area sampling. We assessed both methods in plots of the regional forest inventory of Wallonia (southern region of Belgium). Next we developed bridging functions that converts CWD volume estimates to estimates that would have been obtained with different thresholds. Results about precision and time requirement are very slightly in favour of the line intersect sampling method. Nevertheless, we have noted that this method has several drawbacks, especially in the context of a regional and multi-resource inventory. Beside the established bridging functions indicate that CWD volume estimate from the Walloon forest inventories should be reduced by 20% in order to be internationally harmonized.

Architectural differences associated with functional traits among 45 coexisting tree species in Central Africa

1.Architectural traits that determine the light captured in a given environment are an important aspect of the life‐history strategies of tropical tree species. In this study, we examined how interspecific variation in architectural traits is related to the functional traits of 45 coexisting tree species in central Africa. 2.At the tree level, we measured tree diameter, total height and crown dimensions for an average of 30 trees per species (range 14–72, total 968 trees) distributed over a large range of diameters (up to 162 cm). Using log‐log models, we fitted species‐specific allometric relationships between tree diameter, height and crown dimensions. At the species level, we derived architectural traits (height and crown dimensions) at 15 cm and maximum diameters from species‐specific allometries. The architectural traits were then related to functional traits, including light requirements, wood density, leaf habit, and dispersal mode. 3.Among the 45 coexisting tree species, we identified strong variations in height and crown allometries, along with architectural traits derived from these species‐specific allometries. There was a positive correlation among architectural traits, suggesting that large‐statured canopy species were taller and had larger and deeper crowns than small‐statured understory species at all ontogenic stages. The relationships between architectural and functional traits highlighted a continuum of species between the large‐statured canopy species and the small‐statured understory species. In this moist and seasonal forest, large‐statured canopy species tended to be light‐demanding, wind‐dispersed, deciduous and large contributors to forest biomass (high basal area), while small‐statured understory species tended to be shade‐tolerant, animal‐dispersed, evergreen and most abundant in terms of stem density. 4.Our results highlighted strong architectural differences among coexisting tropical tree species in central Africa. The relationships between architectural and functional traits provided insights into the life‐history strategy of tropical tree species.

Dosage de la lumière pour maintenir la coexistence d’espèces d’ombre et de demi-ombre dans la régénération de la futaie irrégulière

Le traitement en futaie irrégulière et mélangée, au couvert continu dont le renouvellement est assuré par la régénération naturelle (de Türckheim et Bruciamacchie, 2005), a de plus en plus d’adeptes. L’engouement pour ce traitement est tel qu’il a récemment été imposé dans certaines conditions en forêts publiques de Wallonie [circulaire “Pro Silva” imposée pour les forêts publiques de Wallonie (Sanchez, 2013)]. Néanmoins, cette sylviculture demande une bonne connaissance des processus naturels dont le sylviculteur essaye de tirer profit. L’une des principales difficultés réside certainement dans le maintien du mélange à partir de la régénération naturelle. En effet, si le peuplement n’est pas suffisamment ouvert, les semis des espèces tolérantes à l’ombre s’installent plus efficacement que les semis des espèces moins tolérantes à l’ombre. Peu à peu, les espèces les plus tolérantes à l’ombre dominent la composition du peuplement et compromettent ainsi l’objectif de maintien d’un cortège d’espèces compagnes diversifié. À l’inverse, si l’on ouvre fortement le peuplement, une vague de régénération dense et peu diversifiée s’installe souvent. Dominée par l’espèce la plus performante, et notamment celle qui a pu s’établir dans l’ombre, elle compromet également le maintien de la diversité spécifique et conduit à des travaux sylvicoles supplémentaires.