•The impact of logging and thinning on African tree species diversity was assessed.•We used a long-term controlled experiment on 28 1-ha plots in the Central African Republic.•Disturbance had a weak ...monotonous negative impact on diversity.•This effect mainly resulted from a strong negative effect of disturbance on the species density of the pioneer guild.
Timber production is an important economic sector in most forested countries of Central Africa, where about 14 million hectares of lowland moist forests are now planned for management. This production is expected to be sustainable, but the actual impact of logging on biodiversity is still questioned.
To answer this question, we used a unique long-term controlled experiment implemented more than 20years ago in an old-growth semi-deciduous moist forest of the Central African Republic (CAR). We tested whether (i) anthropogenic disturbances associated with silvicultural operations had an effect on the composition and diversity of tree communities, and (ii) there is a relationship between diversity and disturbance intensity in those forests.
For this, we botanically identified all trees⩾10cm DBH in 28 1-ha plots where no treatment (controls), logging and logging+thinning operations were implemented 24years ago and created a strong gradient of disturbance. We investigated the relationships between five diversity indices and a disturbance index calculated for each 1-ha plot, for all species and separately for three regeneration guilds.
We found a strong positive monotonic relationship between the intensity of disturbance and the percentage of pioneer species in the tree communities, which proved to be equally detrimental, in terms of relative abundance, to the non-pioneer light-demanding and the shade-bearing species.
Overall, disturbance appeared to have a weak monotonous negative effect on diversity, irrespective to the index considered. The diversity of shade-bearers slightly decreased along the disturbance gradient without significant decrease in species density; disturbance had no effect on non-pioneer light demanders, but a clear significant negative effect on the diversity of pioneers, with a significant decrease in species density. This negative effect was associated with the massive recruitment of the early-successional, fast-growing Musanga cecropioides R. Br. (Urticaceae), which rapidly preempted space and resources in the most disturbed plots. Despite this effect, disturbance did not significantly affect the local heterogeneity in species distribution.
These results suggest that the semi-deciduous moist forests of CAR are locally resilient to small-scale disturbances associated with silvicultural operations. This may be a consequence of the past anthropogenic and/or climatic disturbances, which have been stronger and more long-lasting than elsewhere within the tropical forest biome, and would have removed the most vulnerable species. Because logging intensity in these forests is usually low, we do not expect any direct major impact on tree species diversity, at least after the first felling cycle.
► The floristic composition of a forest was monitored from 7 to 23 years after logging. ► Two levels of logging intensity followed or not by thinning were compared. ► Disturbance had little impact on ...the floristic composition. ► In lightly logged subplots, thinning facilitated floristic composition recovery. ► Thinning tended to reduce the ratio of pioneer trees in favor of non-pioneer trees.
In the Congo Basin where most timber species are light-demanding, the low logging intensities commonly implemented (1–2 trees harvested ha
−1) do not provide sufficient canopy gaps to ensure species regeneration. The regeneration of light-demanding timber species may therefore benefit from more intensive logging, or from post-harvest treatments such as thinning by poison girdling that increases light penetration. Little is known of the impact of post-harvest treatments on the floristic composition of tropical moist forests. This study therefore aimed to assess the effects of low and high selective logging (≃2.33 and 4.73 trees harvested ha
−1, and ≃4.96 and 9.16
m
2
ha
−1 of basal area removed (logging
+
damage), respectively) – followed or not by thinning (≃21.14 trees thinned ha
−1, and ≃6.57
m
2
ha
−1 of basal area removed) – on the floristic composition of a tropical moist forest in the Central African Republic, from 7 to 23 years after logging.
We analyzed abundance data for 110 tree genera recorded every year for 14 years in 25 one-hectare permanent subplots. We used multivariate analysis to detect floristic variations between treatments and we assessed changes in floristic composition throughout the period. We compared floristic composition recovery between thinned and unthinned subplots, using unlogged subplots as a reference characterizing the pre-logging floristic composition.
Logging and thinning had little impact on the floristic composition of the subplots as quantified 7 to 23 years later, though they did increase the proportion of pioneer species. Surprisingly, additional thinning at both logging levels failed to further distance floristic composition from that of the unlogged subplots, though it did increase disturbance intensity. Floristic composition recovery appeared to be facilitated when thinning was associated with logging. Thinning seemed to favor the growth and survival of non-pioneer species, to the detriment of pioneer species. These non-pioneer species could either be non-pioneer light demanders or shade-bearers. One explanation for this is that thinning by tree-poison girdling increased light availability without causing major damage to the forest, and thus increased the growth and survival of advance regeneration. The resulting enhanced competition then reduced the survival of pioneer species.
Large tropical trees and a few dominant species were recently identified as the main structuring elements of tropical forests. However, such result did not translate yet into quantitative approaches ...which are essential to understand, predict and monitor forest functions and composition over large, often poorly accessible territories. Here we show that the above-ground biomass (AGB) of the whole forest can be predicted from a few large trees and that the relationship is proved strikingly stable in 175 1-ha plots investigated across 8 sites spanning Central Africa. We designed a generic model predicting AGB with an error of 14% when based on only 5% of the stems, which points to universality in forest structural properties. For the first time in Africa, we identified some dominant species that disproportionally contribute to forest AGB with 1.5% of recorded species accounting for over 50% of the stock of AGB. Consequently, focusing on large trees and dominant species provides precise information on the whole forest stand. This offers new perspectives for understanding the functioning of tropical forests and opens new doors for the development of innovative monitoring strategies.
In the Congo Basin where most timber species are light-demanding, the low logging intensities commonly implemented (1-2 trees harvested ha?1) do not provide sufficient canopy gaps to ensure species ...regeneration. The regeneration of light-demanding timber species may therefore benefit from more intensive logging, or from post-harvest treatments such as thinning by poison girdling that increases light penetration. Little is known of the impact of post-harvest treatments on the floristic composition of tropical moist forests. This study therefore aimed to assess the effects of low and high selective logging (?2.33 and 4.73 trees harvested ha?1, and ?4.96 and 9.16 m2 ha?1 of basal area removed (logging + damage), respectively) - followed or not by thinning (?21.14 trees thinned ha?1, and ?6.57 m2 ha?1 of basal area removed) - on the floristic composition of a tropical moist forest in the Central African Republic, from 7 to 23 years after logging. We analyzed abundance data for 110 tree genera recorded every year for 14 years in 25 one-hectare permanent subplots. We used multivariate analysis to detect floristic variations between treatments and we assessed changes in floristic composition throughout the period. We compared floristic composition recovery between thinned and unthinned subplots, using unlogged subplots as a reference characterizing the pre-logging floristic composition. Logging and thinning had little impact on the floristic composition of the subplots as quantified 7 to 23 years later, though they did increase the proportion of pioneer species. Surprisingly, additional thinning at both logging levels failed to further distance floristic composition from that of the unlogged subplots, though it did increase disturbance intensity. Floristic composition recovery appeared to be facilitated when thinning was associated with logging. Thinning seemed to favor the growth and survival of non-pioneer species, to the detriment of pioneer species. These non-pioneer species could either be non-pioneer light demanders or shade-bearers. One explanation for this is that thinning by tree-poison girdling increased light availability without causing major damage to the forest, and thus increased the growth and survival of advance regeneration. The resulting enhanced competition then reduced the survival of pioneer species. (Résumé d'auteur)
Podocytes are highly specialized epithelial cells on the visceral side of the glomerulus. Their interdigitating primary and secondary foot processes contain an actin based contractile apparatus that ...can adjust to changes in the glomerular perfusion pressure. Thus, the dynamic regulation of actin bundles in the foot processes is critical for maintenance of a well functioning glomerular filtration barrier. Since the actin binding protein, cofilin-1, plays a significant role in the regulation of actin dynamics, we examined its role in podocytes to determine the impact of cofilin-1 dysfunction on glomerular filtration.
We evaluated zebrafish pronephros function by dextran clearance and structure by TEM in cofilin-1 morphant and mutant zebrafish and we found that cofilin-1 deficiency led to foot process effacement and proteinuria. In vitro studies in murine and human podocytes revealed that PMA stimulation induced activation of cofilin-1, whereas treatment with TGF-β resulted in cofilin-1 inactivation. Silencing of cofilin-1 led to an accumulation of F-actin fibers and significantly decreased podocyte migration ability. When we analyzed normal and diseased murine and human glomerular tissues to determine cofilin-1 localization and activity in podocytes, we found that in normal kidney tissues unphosphorylated, active cofilin-1 was distributed throughout the cell. However, in glomerular diseases that affect podocytes, cofilin-1 was inactivated by phosphorylation and observed in the nucleus.
Based on these in vitro and in vivo studies we concluded cofilin-1 is an essential regulator for actin filament recycling that is required for the dynamic nature of podocyte foot processes. Therefore, we describe a novel pathomechanism of proteinuria development.
Traumatic lower extremity fractures with compromised arterial flow are limb-threatening injuries. A retrospective review of 158 lower extremities with traumatic fractures, including 26 extremities ...with arterial injuries, was performed to determine the effects of vascular compromise on flap survival, successful limb salvage and complication rates. Patients with arterial injuries had a larger average flap surface area (255.1 vs 144.6 cm2, P = 0.02) and a greater number of operations (4.7 vs 3.8, P = 0.01) than patients without vascular compromise. Patients presenting with vascular injury were also more likely to require fasciotomy odds ratio (OR): 6.5, confidence interval (CI): 2.3–18.2 and to have a nerve deficit (OR: 16.6, CI: 3.9–70.0), fracture of the distal third of the leg (OR: 2.9, CI: 1.15–7.1) and intracranial hemorrhage (OR: 3.84, CI: 1.1–12.9). After soft tissue reconstruction, patients with arterial injuries had a higher rate of amputation (OR: 8.5, CI: 1.3–53.6) and flap failure requiring a return to the operating room (OR: 4.5, CI: 1.5–13.2). Arterial injury did not correlate with infection or overall complication rate. In conclusion, arterial injuries resulted in significant complications for patients with lower extremity fractures requiring flap coverage, although limb salvage was still effective in most cases.
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