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Couteron, Pierre; Kokou, Kouami

doi:10.1023/a:1009723906370

Cited by 93 publications

(4 citation statements)

References 32 publications

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“…When vegetation is cleared by people to address the need for land, scarce cover makes semiarid West Africa (SWA) soils prone to degradation (Couteron & Kokou, 1997;Savadogo, Tigabu, Sawadogo, & Odén, 2007;Sop & Oldeland, 2013). In particular, wind and water erosion and decreasing organic matter and nutrient contents in soils (Ganry, Feller, Harmand, & Guibert, 2001;Roose & Barthès, 2001) may lead to the formation of physical crusts on topsoil layers (Bationo, Kihara, Vanlauwe, Waswa, & Kimetu, 2007;Mando & Stroosnijder, 2006).…”

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confidence: 99%

Ramial wood amendments (Piliostigma reticulatum) mitigate degradation of tropical soils but do not replenish nutrient exports

et al. 2018

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Restoring degraded soils to support food production is a major challenge for West African smallholders who have developed local innovations to counter further degradation. The objective of this study was to evaluate a local farmer's technique that uses ramial wood (RW) as soil amendment (Piliostigma reticulatum shrub). Three treatments were applied in an experimental plot in Burkina Faso: control (no amendment), low RW (3 Mg fresh mass·ha−1·yr−1), and high RW (12 Mg fresh mass·ha−1·yr−1). RW was chipped to <5‐cm pieces and either buried or mulched. Topsoil carbon (C), nitrogen (N), and phosphorus (P) in control and low‐RW treatments declined after 7 years of continuous sorghum cultivation. Use of high‐RW amendment stabilized soil C content while N and P declined, thus not replenishing nutrient exports. Net contribution to soil C in the layer measuring 0–15 cm was 15% of the applied C in the high‐RW amendments. Although biomass and grain yields were higher in high‐RW treatments, crop productivity declined throughout the experiment for all treatments. Termite casts on RW treatments evidenced the potential role of wood‐foraging termites in diluting the impact of RW on soil fertility build‐up and soil water content. We conclude that mitigating soil degradation under semiarid conditions in Burkina Faso would require large amounts of woody amendments, particularly if the level of termite activity is high. Additional nutrient sources would be needed to compensate for removal in exported products so that biomass and grain production can be stabilized or increased.

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confidence: 99%

Ramial wood amendments (Piliostigma reticulatum) mitigate degradation of tropical soils but do not replenish nutrient exports

et al. 2018

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“…Taken together, tree spatial patterns influence the outcomes of competition by impacting the strength of intra‐relative to interspecific competition (Stoll & Prati, 2001). In addition, in some savannas (Couteron & Kokou, 1997; Skarpe, 1991) and particularly in the Lamto savanna (Barot et al, 1999; Gignoux et al, 2006), trees often show an aggregated spatial distribution. They form clumps leaving an important proportion of the surface covered by grasses.…”

Section: Discussionmentioning

confidence: 99%

Spatial heterogeneity of nitrification contributes to tree–grass coexistence in West African savannas

Konaré,

Koffi,

Boudsocq

et al. 2023

Journal of Ecology

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In savannas, the coexistence between trees and grasses is determined by complex mechanisms based on water partitioning and disturbances. But little is known about the contribution of other resources, such as soil nitrogen (N). In West African savannas, nitrification inhibition by grasses and nitrification stimulation by trees create spatial heterogeneity in nitrification fluxes and N stocks. Savanna trees can also extend part of their roots in the surrounding open area to absorb N. To investigate the role of the spatial heterogeneity of nitrification in tree–grass coexistence, we used a two‐patch model that simulates N dynamics between an open patch (without trees) and a tree clump patch (trees with grasses under their canopy). The open patch was characterized by a low nitrification rate, while the tree clump patch was characterized by a high nitrification rate. Both patches were connected through horizontal fluxes due to soil horizontal exploration by tree roots. We tested coexistence for different spatial tree distributions, as they are known to strongly influence savanna dynamics. Our results show that the spatial heterogeneity of nitrification induces spatial partitioning between ammonium (NH4+) and nitrate (NO3−) promoting tree–grass coexistence. As nitrification inhibition by grasses leads to high NH4+ availability in the open, the possibilities of coexistence are optimized when trees have different preferences in the open versus under their canopy. Thus, tree–grass coexistence is observed when grasses prefer NH4+, while trees prefer NH4+ in the open and NO3− under their canopy. Contrary to random tree distribution, tree clumping enhances tree–grass coexistence. Intraspecific aggregation strengthens the effect of spatial heterogeneity, which decreases interspecific competition and favours tree–grass coexistence. On the contrary, increasing the surface explored by tree roots in the open tends to increase tree–grass competition. This enhances the competitive ability of trees for N acquisition and consequently favours tree invasion. Synthesis. This study shows that this new coexistence mechanism based on mineral N partitioning into NH4+ and NO3− can be determinant in the functioning of West African humid savannas. This mechanism likely interacts with mechanisms based on disturbances, but such interactions should be studied using new models.

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“…8). Thus, this trend might continue in the future and if competition is strong enough even a regular pattern could occur (Couteron and Kokou 1997;Hesselbarth et al 2018).…”

Section: Spatial Patterns Of Alive Trees: Pair-correlation Function G(r)mentioning

confidence: 99%

Tree mortality in mature temperate forests of central Mexico: a spatial approach

et al. 2023

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Tree mortality is an important process of forest stand dynamics and knowledge of it is fundamental to implement adequate management strategies. Subject to several factors, tree mortality can induce different spatial patterns on the remaining live and dead trees. While spatially clustered tree mortality in young forests is often driven by competition, in old-growth forests, spatially clustered tree mortality is often caused by disturbance agents. This study is focused on a spatiotemporal analysis of tree mortality in a mature temperate forest located in central Mexico dominated by Pinus montezumae and Alnus firmifolia. We used tree locations from a permanent plot (300 × 300 m) measured over a 20-year period. The results, from applying point pattern analysis, showed that the spatial pattern of all dead trees was clustered at short to medium distances, but showed no clear deviation from complete spatial randomness at longer distances. Similar results were found for P. montezumae and A. firmifolia. Using the bivariate mark-connection function (alive and dead trees), no tree mortality caused by competition was discernable, only A. firmifolia showed a tendency toward competition-introduced mortality around 15 m. Regarding forest structure, alive trees retained a clustered distribution and size heterogeneity at different distances during the measurement period. Thus, there was evidence that the resulting spatial pattern of tree mortality could be explained by disturbance agents such as droughts rather than tree competition. Therefore, the results of this study can contribute to implement management strategies based on the principles of continuous cover forestry and provide novel information regarding tree mortality in Mexican montane forests.

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Untitled

Cited by 93 publications

References 32 publications

Ramial wood amendments (Piliostigma reticulatum) mitigate degradation of tropical soils but do not replenish nutrient exports

Ramial wood amendments (Piliostigma reticulatum) mitigate degradation of tropical soils but do not replenish nutrient exports

Spatial heterogeneity of nitrification contributes to tree–grass coexistence in West African savannas

Tree mortality in mature temperate forests of central Mexico: a spatial approach

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