The size at reproduction of canopy tree species in central Africa

The Relationship Between Maturation Size and Maximum Tree Size From Tropical to Boreal Climates

The fundamental trade-off between current and future reproduction has long been considered to result in a tendency for species that can grow large to begin reproduction at a larger size. Due to the prolonged time required to reach maturity, estimates of tree maturation size remain very rare and we lack a global view on the generality and the shape of this trade-off. Using seed production from five continents, we estimate tree maturation sizes for 486 tree species spanning tropical to boreal climates. Results show that a species' maturation size increases with maximum size, but in a non-proportional way: the largest species begin reproduction at smaller sizes than would be expected if maturation were simply proportional to maximum size. Furthermore, the decrease in relative maturation size is steepest in cold climates. These findings on maturation size drivers are key to accurately represent forests' responses to disturbance and climate change.

Comprehensive conservation assessments reveal high extinction risks across Atlantic Forest trees

Biodiversity is declining globally, yet many biodiversity hotspots still lack comprehensive species conservation assessments. Using multiple International Union for Conservation of Nature (IUCN) Red List criteria to evaluate extinction risks and millions of herbarium and forest inventory records, we present automated conservation assessments for all tree species of the Atlantic Forest biodiversity hotspot, including ~1100 heretofore unassessed species. About 65% of all species and 82% of endemic species are classified as threatened. We rediscovered five species classified as Extinct on the IUCN Red List and identified 13 endemics as possibly extinct. Uncertainties in species information had little influence on the assessments, but using fewer Red List criteria severely underestimated threat levels. We suggest that the conservation status of tropical forests worldwide is worse than previously reported.

Latitudinal shift in the timing of flowering of tree species across tropical Africa: insights from field observations and herbarium collections

Temporal and spatial patterns in flowering phenology were assessed for eight tropical African tree species. Specifically, the frequency and seasonality of flowering at seven sites in central Africa were determined using field data, graphical analysis and circular statistics. Additionally, spatial variation in the timing of flowering across species range was investigated using herbarium data, analysing the relative influence of latitude, longitude and timing of the dry season with a Bayesian circular generalized linear model. Annual flowering was found for 20 out of the 25 populations studied. For 21 populations located at the north of the climatic hinge flowering was occurring during the dry season. The analysis of herbarium collections revealed a significant shift in the timing of flowering with latitude for E. suaveolens, and with the timing of the dry season for M. excelsa (and to a lesser extent L. alata), with the coexistence of two flowering peaks near the equator where the distribution of monthly rainfall is bimodal. For the other species, none of latitude, longitude or timing of the dry season had an effect on the timing of flowering. Our study highlights the need to identify the drivers of the flowering phenology of economically important African tree species.

Assessing the Landscape Pattern and Population Status of the Timber Species Mansonia altissima A. Chev. For Restoration Purposes in Moist Semi-Deciduous Forest

Mansonia altissima A. Chev., a redwood producer species in tropical Africa, occurs as one small, isolated population in a highly anthropized landscape in Republic of Benin. We accessed the landscape pattern and population status to inform restauration action for the species. We established 20 one-ha permanent plots divided in 320 subplots (25 m × 25 m) in-situ and counted and measured M. altissima plants with diameter ≥ 1cm at base and 1.30 m above ground (DBH) in February 2017, 2018 and 2019. Based on the main disturbance factors, such as fire, human-caused damage to seedlings, harvesting of wood for fuel, and agriculture, we assigned the plots to one of three disturbance levels: poor, moderate, and strong. We grouped the plants into four life stages according to diameter size (cm): seedling (1 ≤ DBH < 5), sapling (5 ≤ DBH < 10), premature (10 ≤ DBH < 20), and mature (DBH ≥ 20). We used Landsat data of years 1986, 2002 and 2017 to quantify and analyze landscape changes and fragmentation. Results showed that the landscape was dramatically changed and fragmented between 2002 and 2017 due to disturbance increase. Semi-deciduous forest (SDF) containing M. altissima decreased, whereas woodlands and savannas increased. SDF was severely fragmented and disaggregated. In plots with strong disturbance, mortality rate was higher, whereas in plots with poor disturbance, it was lower and recruitment was highest. Mortality rate differed significantly among life stages and disturbance levels. Experimental restoration is required to identify locations where the species can establish young viable populations. Fire and other anthropogenic disturbance have to be controlled to ensure this natural population can provide seeds for restoration and conservation projects.

Spatio-temporal patterns of orchids flowering in Cameroonian rainforests

We characterized the flowering patterns of 45 epiphytic orchid species occurring in Cameroonian rainforests to explore the environmental and evolutionary forces driving their phenology. We used a dataset of 3470 flowering events recorded over a period of 11 years in the Yaoundé living collection (82% of the flowering events) and from in situ observations (18% of the flowering events) to (i) describe flowering frequency and timing and synchronization among taxa; (ii) test flowering patterns for phylogenetic relatedness at the generic level; and (iii) investigate the spatial patterns of phenology. An annual flowering pattern prevailed among the species selected for this study. The species-rich African genera Angraecum and Polystachya are characterized by subannual and annual frequency patterns, respectively. However, in terms of flowering time, no phylogenetic signal was detected for the four most diverse genera (Ancistrorhynchus, Angraecum, Bulbophyllum, and Polystachya). Results suggest also an important role of photoperiod and precipitation as climatic triggers of flowering patterns. Moreover, 16% of the taxa cultivated ex situ, mostly Polystachya, showed significant differences in flowering time between individuals originating from distinct climatic regions, pointing toward the existence of phenological ecotypes. Phenological plasticity, suggested by the lack of synchronized flowering in spatially disjunct populations of Polystachya, could explain the widespread radiation of this genus throughout tropical Africa. Our study highlights the need to take the spatial pattern of flowering time into account when interpreting phylogeographic patterns in central African rainforests.