Evenness mediates the global relationship between forest productivity and richness

1. Biodiversity is an important component of natural ecosystems, with higher species richness often correlating with an increase in ecosystem productivity. Yet, this relationship varies substantially across environments, typically becoming less pronounced at high levels of species richness. However, species richness alone cannot reflect all important properties of a community, including community evenness, which may mediate the relationship between biodiversity and productivity. If the evenness of a community correlates negatively with richness across forests globally, then a greater number of species may not always increase overall diversity and productivity of the system. Theoretical work and local empirical studies have shown that the effect of evenness on ecosystem functioning may be especially strong at high richness levels, yet the consistency of this remains untested at a global scale. 2. Here, we used a dataset of forests from across the globe, which includes composition, biomass accumulation and net primary productivity, to explore whether productivity correlates with community evenness and richness in a way that evenness appears to buffer the effect of richness. Specifically, we evaluated whether low levels of evenness in speciose communities correlate with the attenuation of the richness–productivity relationship. 3. We found that tree species richness and evenness are negatively correlated across forests globally, with highly speciose forests typically comprising a few dominant and many rare species. Furthermore, we found that the correlation between diversity and productivity changes with evenness: at low richness, uneven communities are more productive, while at high richness, even communities are more productive. 4. Synthesis. Collectively, these results demonstrate that evenness is an integral component of the relationship between biodiversity and productivity, and that the attenuating effect of richness on forest productivity might be partly explained by low evenness in speciose communities. Productivity generally increases with species richness, until reduced evenness limits the overall increases in community diversity. Our research suggests that evenness is a fundamental component of biodiversity–ecosystem function relationships, and is of critical importance for guiding conservation and sustainable ecosystem management decisions

Evenness mediates the global relationship between forest productivity and richness

1. Biodiversity is an important component of natural ecosystems, with higher species richness often correlating with an increase in ecosystem productivity. Yet, this relationship varies substantially across environments, typically becoming less pronounced at high levels of species richness. However, species richness alone cannot reflect all important properties of a community, including community evenness, which may mediate the relationship between biodiversity and productivity. If the evenness of a community correlates negatively with richness across forests globally, then a greater number of species may not always increase overall diversity and productivity of the system. Theoretical work and local empirical studies have shown that the effect of evenness on ecosystem functioning may be especially strong at high richness levels, yet the consistency of this remains untested at a global scale. 2. Here, we used a dataset of forests from across the globe, which includes composition, biomass accumulation and net primary productivity, to explore whether productivity correlates with community evenness and richness in a way that evenness appears to buffer the effect of richness. Specifically, we evaluated whether low levels of evenness in speciose communities correlate with the attenuation of the richness–productivity relationship. 3. We found that tree species richness and evenness are negatively correlated across forests globally, with highly speciose forests typically comprising a few dominant and many rare species. Furthermore, we found that the correlation between diversity and productivity changes with evenness: at low richness, uneven communities are more productive, while at high richness, even communities are more productive. 4. Synthesis. Collectively, these results demonstrate that evenness is an integral component of the relationship between biodiversity and productivity, and that the attenuating effect of richness on forest productivity might be partly explained by low evenness in speciose communities. Productivity generally increases with species richness, until reduced evenness limits the overall increases in community diversity. Our research suggests that evenness is a fundamental component of biodiversity–ecosystem function relationships, and is of critical importance for guiding conservation and sustainable ecosystem management decisions

Evenness mediates the global relationship between forest productivity and richness

Biodiversity is an important component of natural ecosystems, with higher species richness often correlating with an increase in ecosystem productivity. Yet, this relationship varies substantially across environments, typically becoming less pronounced at high levels of species richness. However, species richness alone cannot reflect all important properties of a community, including community evenness, which may mediate the relationship between biodiversity and productivity. If the evenness of a community correlates negatively with richness across forests globally, then a greater number of species may not always increase overall diversity and productivity of the system. Theoretical work and local empirical studies have shown that the effect of evenness on ecosystem functioning may be especially strong at high richness levels, yet the consistency of this remains untested at a global scale. 2. Here, we used a dataset of forests from across the globe, which includes composition, biomass accumulation and net primary productivity, to explore whether productivity correlates with community evenness and richness in a way that evenness appears to buffer the effect of richness. Specifically, we evaluated whether low levels of evenness in speciose communities correlate with the attenuation of the richness–productivity relationship. 3. We found that tree species richness and evenness are negatively correlated across forests globally, with highly speciose forests typically comprising a few dominant and many rare species. Furthermore, we found that the correlation between diversity and productivity changes with evenness: at low richness, uneven communities are more productive, while at high richness, even communities are more productive. 4. Synthesis. Collectively, these results demonstrate that evenness is an integral component of the relationship between biodiversity and productivity, and that the attenuating effect of richness on forest productivity might be partly explained by low evenness in speciose communities. Productivity generally increases with species richness, until reduced evenness limits the overall increases in community diversity. Our research suggests that evenness is a fundamental component of biodiversity–ecosystem function relationships, and is of critical importance for guiding conservation and sustainable ecosystem management decisions. © 2023 The Authors. Journal of Ecology published by John Wiley & Sons Ltd on behalf of British Ecological Society

Contribution à la gestion sylvicole des forêts humides ivoiriennes à travers l'analyse des dispositifs permanents de Mopri et Irobo

Avec les exigences croissantes pour une exploitation durable des écosystèmes forestiers tropicaux et l'avènement de la certification environnementale, la Société de Développement des Forêts ivoiriennes (SODEFOR) s'est mise très tôt en quête de nouvelles méthodes de gestion sylvicole des peuplements naturels, répondant à la fois aux besoins de l'environnement et de l'industrie. En collaboration avec le CIRAD-FORET, les chercheurs ont alors expérimenté une technique d'éclaircie. S'inspirant davantage de l'économie forestière, elle vise à éliminer une certaine catégorie d'arbres afin d'accroître le rendement d'une autre catégorie présentant un intérêt commercial immédiat. L'essai sylvicole a été simultanément conduit dans deux types différents de forêt humide : les types semi-décidu et sempervirente respectivement représentés par les dispositifs permanents de Mopri et d'Irobo. Dans les deux dispositifs, l'analyse chronologique de la surface terrière entre 1978 et 1994 a révélé un effet positif des éclaircies sur le taux d'accroissement et l'enrichissement naturel du peuplement commercial. Mais cet effet paraît second par rapport à l'influence des caractéristiques initiales des sites telles que la surface terrière totale, la proportion restante des arbres non commercialisables et la composition floristique commerciale. En espèces commerciales, la forêt de Mopri (46,8%) est deux fois plus riche que celle d'Irobo (23,5%). En revanche, le gain de productivité annuel par rapport aux témoins y est deux fois moins important : 0,19 m2/ha/an contre 0,34 m2/ha/an à Irobo. Le meilleur taux d'accroissement des arbres commerciaux est obtenu, après éclaircie, pour une surface terrière totale de l'ordre de 17,5 à 20 m2/ha à Mopri et approximativement de 22,5 à 25 m2/ha à Irobo. L'ouverture de la canopée profite surtout aux gros arbres. Elle favorise davantage l'enrichissement naturel à Mopri qu'à Irobo. En 16 ans, les placettes de Mopri se sont en moyenne enrichies de 4,5 nouvelles essences commerciales contre 1,4 à Irobo. Ce processus d'enrichissement naturel concerne seulement un petit nombre d'espèces commerciales. Ce sont notamment (i) à Mopri, Antiaris africana, Terminalia superba, Chorophora regia, Chorophora excelsa, Entandrophragma cylindricum, Lannea welwitschii et Copaïfera salikounda; et (ii) à Irobo, Canarium schweinfurthii, Fagara macrophylla, Ricinodendron africanum et Pycnanthus angolensis. Suite à une exploitation forestière antérieure au traitement sylvicole mais relativement récente, les deux peuplements ne sont pas stables. Ils continuent de se reconstituer tant en surface terrière qu'en richesse spécifique. Bien que cette dynamique générale soit fonction des placettes, la richesse en essences commerciales semble se stabiliser autour de 29 (s = 4) espèces/ha à Mopri et 17 (s = 3) espèces/ha à Irobo.LYON1-BU.Sciences (692662101) / SudocSudocFranceF

Diversité floristique et infiltration humaine de la forêt classée de la Besso (Côte d’Ivoire)

Objectif: Contribuer à une meilleure connaissance de la flore de la forêt classée de la Besso et de caractériser les populations infiltrées et les cultures pratiquées dans cette forêt classée.Méthodologie et résultats: La forêt classée de Besso (Côte d’Ivoire) couvre 23 100 ha sur est une forêt dense semi-décidue à Celtis spp. et Triplochiton scleroxylon. La création de clairières culturales entre 1966 et 2012 malgré le classement de la forêt est à l’origine d’une mosaïque de végétations secondaires incluses dans une matrice de forêt « primaire » que nous avons plus particulièrement étudié. Les relevés de surfaces couplés aux inventaires itinérants ont permis d’inventorier 474 espèces, qui se repartissent en 330 genres et 91 familles. Les familles les plus abondantes sont Fabaceae, les Rubiaceae, les Euphorbiaceae, les Moraceae, les Malvaceae, les Meliaceae, les Moraceae, les Annonaceae, les Sapindaceae et les Poaceae. Parmi ces espèces, 79 % sont des phanérophytes et 3 % des hémicryptophytes.Conclusion: Malheureusement, cette forêt est en progressive dégradation à cause des activités humaines qui menacent la biodiversité végétale et animale de cette forêt. Ainsi, pour réduire le phénomène de dégradation des forêts en générale, plusieurs actions de gestion durable pourraient être entreprises par l’État, les ONG et la population. Notamment par la création des zones de conservation de plantes par des mises en défens de jachères.Mots clés: Biodiversité végétale, Forêt classée de la Besso, Côte d’IvoireEnglish AbstractEnglish Title: Floristic diversity and human impact on Besso forest in Ivory CoastObjective: To contribute significantly to the knowledge of the flora of Besso forest and to evaluate the human impact.Methodology and results: The Besso forest in Ivory Coast) covers 23 100 ha and determines a potential vegetation corresponding to the Celtis spp.-Triplochiton scleroxylon semi-deciduous tropical forest. Shifting cultivation between 1966 and 2012 has led to a mosaic of secondary plant communities that are included in an old-growth forest matrix. For hundred seventy for (474) species were recorded in this forest during the field investigations, distributed among 330 genera and 91 families. The most common families were Fabaceae, Rubiaceae, Euphorbiaceae, Moraceae, Malvaceae, Meliaceae, Moraceae, Annonaceae, Sapindaceae and Poaceae. Among those species, 79 % and 3 % are phanerophytes and hemicryptophytes, respectively.Conclusion: Unfortunately, this forest is gradual degradation due to uncontrolled human’s activity. Thus, to reduce the degradation phenomenon of the forets in general, several actions of sustainable managements could be undertaken by the state, Non-Governmental Organisation (NGO) and the population. In particular by the creation of preservation zones of plants, the creation of collective gardens of plants.Keywords: Plant biodiversity, Besso forest, Ivory Coas

Fragmentation is the main driver of residual forest aboveground biomass in West African low forest-high deforestation landscapes

Tropical forests play a crucial role in climate regulation due to their high carbon sequestration capacity. However, degradation and disturbances in these forests may result in significant carbon losses. This study focuses on the impact of various biophysical, anthropogenic, and landscape factors on aboveground biomass (AGB) in heavily disturbed landscapes of Côte d'Ivoire (West Africa), a typical low-forest and high-deforestation country. AGB estimates from a National Forest Inventory dataset have been linked to five categories of variables (Climate, Soil, Topography, Landscape, and Human-related) through a random forest modeling approach that addressed collinearity among variables, selected key variables from each category, and used spatial cross-validation to evaluate model performance. The comprehensive model, combining landscape composition, physical soil properties, and climate variables, demonstrated strong performance with an R-squared of 0.62. Notably, the percentage of landscape occupied by forest within a radius of 1000 m (PLAND1000) had a highly significant impact on AGB, exhibiting a notable increase when PLAND1000 exceeded 80 % and a decrease when it felt below 25 %. Soil properties, both physical (Bulk Density and Coarse Fraction) and chemical (soil pH), significantly influenced AGB, too. Interestingly, climatic, topographic, and other anthropogenic variables had minimal relevance in predicting AGB, suggesting that their effects may have been captured by landscape and soil integrative variables. In order to enhance forest preservation and restoration initiatives in the face of deforestation and fragmentation challenges in the West African region, we recommend (i) evaluating the appropriate landscape scale of effect (a 1000 m radius circle being the most significant in this study); (ii) prioritizing the preservation or restoration of dense forest landscapes; and (iii) integrating landscape composition into forest management policies

Causes and consequences of Cedrela odorata invasion in West African semi-deciduous tropical forests

International audienc

The long-term performance of 35 tree species of sudanian West Africa in pure and mixed plantings

The rapidly growing human population in sudanian West Africa has generated increasing demand for agricultural land and forest products so that most of the original vegetation cover has disappeared and the remainder is highly degraded, meaning that it is urgent to draw up a long-term assessment of the potential of local species to be promoted in pure and mixed plantings as contribution to global forest restoration efforts. We inventoried the survival and growth of 5817 trees belonging to 35 species planted more than 25 years ago in pure and mixed plantings. For a subset of individuals, we estimated heights and volumes of standing timber. We found that (i) the long-term survival (from 50 to 99%.yr−1) and diameter growth (from 1 to 10 mm.yr−1) are highly diverse between species and not correlated to each other, (ii) the annual increase in biomass per tree averages 2.22 kg while the annual increase in stand biomass may be over 6 Mg. ha−1 for three highly-productive species (Khaya senegalensis, Pterocarpus erinaceus and Anogeissus leiocarpa) (iii) the effect of mixture on annual growth is significantly positive with an across-species gain of 0.7 mm.yr−1 while there is no effect on the survival probability. Considering a potential productivity of 10 m3 of timber wood per hectare at 30 years, 13 species have been retained in the list of woody species of interest for planting in the Sudanese zone of West Africa