Resistance of African tropical forests to an extreme climate anomaly.

The responses of tropical forests to environmental change are critical uncertainties in predicting the future impacts of climate change. The positive phase of the 2015-2016 El Niño Southern Oscillation resulted in unprecedented heat and low precipitation in the tropics with substantial impacts on the global carbon cycle. The role of African tropical forests is uncertain as their responses to short-term drought and temperature anomalies have yet to be determined using on-the-ground measurements. African tropical forests may be particularly sensitive because they exist in relatively dry conditions compared with Amazonian or Asian forests, or they may be more resistant because of an abundance of drought-adapted species. Here, we report responses of structurally intact old-growth lowland tropical forests inventoried within the African Tropical Rainforest Observatory Network (AfriTRON). We use 100 long-term inventory plots from six countries each measured at least twice prior to and once following the 2015-2016 El Niño event. These plots experienced the highest temperatures and driest conditions on record. The record temperature did not significantly reduce carbon gains from tree growth or significantly increase carbon losses from tree mortality, but the record drought did significantly decrease net carbon uptake. Overall, the long-term biomass increase of these forests was reduced due to the El Niño event, but these plots remained a live biomass carbon sink (0.51 ± 0.40 Mg C ha-1 y-1) despite extreme environmental conditions. Our analyses, while limited to African tropical forests, suggest they may be more resistant to climatic extremes than Amazonian and Asian forests

Resistance of African tropical forests to an extreme climate anomaly

The responses of tropical forests to environmental change are critical uncertainties in predicting the future impacts of climate change. The positive phase of the 2015–2016 El Niño Southern Oscillation resulted in unprecedented heat and low precipitation in the tropics with substantial impacts on the global carbon cycle. The role of African tropical forests is uncertain as their responses to short-term drought and temperature anomalies have yet to be determined using on-the-ground measurements. African tropical forests may be particularly sensitive because they exist in relatively dry conditions compared with Amazonian or Asian forests, or they may be more resistant because of an abundance of drought-adapted species. Here, we report responses of structurally intact old-growth lowland tropical forests inventoried within the African Tropical Rainforest Observatory Network (AfriTRON). We use 100 long-term inventory plots from six countries each measured at least twice prior to and once following the 2015–2016 El Niño event. These plots experienced the highest temperatures and driest conditions on record. The record temperature did not significantly reduce carbon gains from tree growth or significantly increase carbon losses from tree mortality, but the record drought did significantly decrease net carbon uptake. Overall, the long-term biomass increase of these forests was reduced due to the El Niño event, but these plots remained a live biomass carbon sink (0.51 ± 0.40 Mg C ha−1 y−1) despite extreme environmental conditions. Our analyses, while limited to African tropical forests, suggest they may be more resistant to climatic extremes than Amazonian and Asian forests

Consistent patterns of common species across tropical tree communities

Trees structure the Earth’s most biodiverse ecosystem, tropical forests. The vast number of tree species presents a formidable challenge to understanding these forests, including their response to environmental change, as very little is known about most tropical tree species. A focus on the common species may circumvent this challenge. Here we investigate abundance patterns of common tree species using inventory data on 1,003,805 trees with trunk diameters of at least 10 cm across 1,568 locations 1–6 in closed-canopy, structurally intact old-growth tropical forests in Africa, Amazonia and Southeast Asia. We estimate that 2.2%, 2.2% and 2.3% of species comprise 50% of the tropical trees in these regions, respectively. Extrapolating across all closed-canopy tropical forests, we estimate that just 1,053 species comprise half of Earth’s 800 billion tropical trees with trunk diameters of at least 10 cm. Despite differing biogeographic, climatic and anthropogenic histories 7, we find notably consistent patterns of common species and species abundance distributions across the continents. This suggests that fundamental mechanisms of tree community assembly may apply to all tropical forests. Resampling analyses show that the most common species are likely to belong to a manageable list of known species, enabling targeted efforts to understand their ecology. Although they do not detract from the importance of rare species, our results open new opportunities to understand the world’s most diverse forests, including modelling their response to environmental change, by focusing on the common species that constitute the majority of their trees

Consistent patterns of common species across tropical tree communities

Trees structure the Earth’s most biodiverse ecosystem, tropical forests. The vast number of tree species presents a formidable challenge to understanding these forests, including their response to environmental change, as very little is known about most tropical tree species. A focus on the common species may circumvent this challenge. Here we investigate abundance patterns of common tree species using inventory data on 1,003,805 trees with trunk diameters of at least 10 cm across 1,568 locations1,2,3,4,5,6 in closed-canopy, structurally intact old-growth tropical forests in Africa, Amazonia and Southeast Asia. We estimate that 2.2%, 2.2% and 2.3% of species comprise 50% of the tropical trees in these regions, respectively. Extrapolating across all closed-canopy tropical forests, we estimate that just 1,053 species comprise half of Earth’s 800 billion tropical trees with trunk diameters of at least 10 cm. Despite differing biogeographic, climatic and anthropogenic histories7, we find notably consistent patterns of common species and species abundance distributions across the continents. This suggests that fundamental mechanisms of tree community assembly may apply to all tropical forests. Resampling analyses show that the most common species are likely to belong to a manageable list of known species, enabling targeted efforts to understand their ecology. Although they do not detract from the importance of rare species, our results open new opportunities to understand the world’s most diverse forests, including modelling their response to environmental change, by focusing on the common species that constitute the majority of their trees

Consistent patterns of common species across tropical tree communities

Trees structure the Earth's most biodiverse ecosystem, tropical forests. The vast number of tree species presents a formidable challenge to understanding these forests, including their response to environmental change, as very little is known about most tropical tree species. A focus on the common species may circumvent this challenge. Here we investigate abundance patterns of common tree species using inventory data on 1,003,805 trees with trunk diameters of at least 10 cm across 1,568 locations1-6 in closed-canopy, structurally intact old-growth tropical forests in Africa, Amazonia and Southeast Asia. We estimate that 2.2%, 2.2% and 2.3% of species comprise 50% of the tropical trees in these regions, respectively. Extrapolating across all closed-canopy tropical forests, we estimate that just 1,053 species comprise half of Earth's 800 billion tropical trees with trunk diameters of at least 10 cm. Despite differing biogeographic, climatic and anthropogenic histories7, we find notably consistent patterns of common species and species abundance distributions across the continents. This suggests that fundamental mechanisms of tree community assembly may apply to all tropical forests. Resampling analyses show that the most common species are likely to belong to a manageable list of known species, enabling targeted efforts to understand their ecology. Although they do not detract from the importance of rare species, our results open new opportunities to understand the world's most diverse forests, including modelling their response to environmental change, by focusing on the common species that constitute the majority of their trees

Liana Distribution And Abundance In Moist Tropical Forest In Ghana 40 Years Following Silvicultural Interventions

Lianas are an important structural aspect of tropical forest ecosystems, but may have negative impacts on tree growth and productivity. We censused lianas in plots that were subjected to three different types of silvicultural intervention in Bobiri forest in Ghana in order to answer two questions: 1) does liana cutting during the initial years of a cutting cycle influence liana densities, basal area and vine loads in tree crowns relative to unlogged forest?; 2) does the duration, intensity and sequence of silvicultural interventions in the initial years of a cutting cycle influence vine loads? Data were gathered from six onehectare plots in each of the three silviculturally-treated stands, with comparative data collected from four one-hectare plots in an unlogged part of the same forest. Lianas were categorised into small (stems =2 - 5 cm DBH) and large sizes (DBH >5 cm) and censused in nested subplots within the one-hectare plots. The extent of liana loading or ‘infestation’ of individual trees ? 20cm DBH was investigated using a 5-point score 0, 1, 2, 3 and 4 within the plots. A total of 697 liana stems were inventoried in both the silviculturally-treated and the unlogged forest. The density of small lianas was relatively higher in the unlogged forest than in treated forest. However, mean densities of large lianas were similar across treatments. For all lianas with DBH = 2 cm, mean densities were lower in the treated forest than in the unlogged forest. Liana loading or ‘infestation’ was dependent on silvicultural treatment consequent to the timing of interventions; while about 9% of stems were completely covered by lianas in forest where climber cutting followed timber harvesting; only about 1% of trees were completely covered by lianas in unlogged forest and forest where liana cutting preceded timber harvesting. Approximately 90% of trees DBH ? 20cm were free of lianas in forest where liana cutting preceded timber harvesting, with ~81% of stems in the same category free of lianas in unlogged forest. However, in forest where liana cutting followed timber harvesting only about 46% of stems were free of lianas. We conclude, from the lower densities of lianas in the silvicultural intervention sites relative to the unlogged sites that even 40 y later the impact of climber cutting was measurable. Although the density of large lianas was not distinct among the silviculturally-treated stands, the interventions promoted greater access to tree crowns by lianas when applied after timber harvesting. Thus the timing of silvicultural interventions in the initial years of a cutting cycle is important since it influences liana load in tree crowns in the long term. Keywords: Silvicultural systems, Liana load, Tropical Shelterwood System, Post-Exploitation System, Liana inventor

A comparison of tree seedling growth in artificial gaps of different sizes in two contrasting forest types.

One of the major concerns in forestry in the tropics is the lack of information on the impact of canopy disturbance through logging. The degree of canopy opening that should be allowed during logging to enhance natural regeneration of timber tree species is not known. Information on the seedling ecology of individual species and ecological species groups on which to base management decisions are also lacking. Experiments to determine the ecophysiological responses of seedlings of timber tree species to different irradiances in two forest sites were carried out. The two forest reserves are Nkrabia and Tinte Bepo in the Moist Evergreen and Moist Semi-Deciduous Forest Types, respectively. Eight species, representing three Shade Bearers, four Non-Pioneer Light Demanders and one Pioneer species, were grown in a series of artificially-created gaps in two forest sites differing in annual rainfall. The forest shade received 1-2% irradiance, while the artificial gaps received 5, 10, 15, 30 and 65% irradiance. Seedling growth was greater at Nkrabia Forest Reserve (Moist Evergreen Forest Type) than at Tinte Bepo Forest Reserve (Moist Semi-Deciduous Forest Type). This is probably due to the lower soilmoisture stress at Nkrabia as a result of more rainfall. Lower moisture stress at Nkrabia may also explain the greater leaf area and specific leaf area ratios, lower leaf turnover and lower number of small leaves on plants than those at Tinte Bepo. Response of height growth to irradiance of Shade Bearers and Non-Pioneer Light Demanders was similar but different from that of Pioneer species.Keywords: Forest types; Canopy disturbance; Irradiance; Seedling growth; Ecological species group