Invasive alien acacias rapidly stock carbon, but threaten biodiversity recovery in young second-growth forests.

Under the UN-Decade of Ecosystem Restoration and Bonn Challenge, second-growth forest is promoted as a global solution to climate change, degradation and associated losses of biodiversity and ecosystem services. Second growth is often invaded by alien tree species and understanding how this impacts carbon stock and biodiversity recovery is key for restoration planning. We assessed carbon stock and tree diversity recovery in second growth invaded by two Acacia species and non-invaded second growth, with associated edge effects, in the Brazilian Atlantic Forest. Carbon stock recovery in non-invaded forests was threefold lower than in invaded forests. Increasingly isolated, fragmented and deforested areas had low carbon stocks when non-invaded, whereas the opposite was true when invaded. Non-invaded forests recovered threefold to sixfold higher taxonomic, phylogenetic and functional diversity than invaded forest. Higher species turnover and lower nestedness in non-invaded than invaded forests underpinned higher abundance of threatened and endemic species in non-invaded forest. Non-invaded forests presented positive relationships between carbon and biodiversity, whereas in the invaded forests we did not detect any relationship, indicating that more carbon does not equal more biodiversity in landscapes with high vulnerability to invasive acacias. To deliver on combined climate change and biodiversity goals, restoration planning and management must consider biological invasion risk. This article is part of the theme issue 'Understanding forest landscape restoration: reinforcing scientific foundations for the UN Decade on Ecosystem Restoration'.

Vegetation and seed bank of an open-scrub bush restinga formation in the Southeastern coast of Brazil

Introduction: Restingas are coastal plain ecosystems located along Eastern Brazil, corresponding to about 5 000 km.The restinga vegetation is associated with the Atlantic rainforest biome and comprises four distinct main formation zones: coastal grasslands, shrublands, open-forests and marsh zones. Especially due to coastal urbanization, this is a threatened ecosystem that, through its different shrub formations, exhibits a unique mosaic as a result of the vegetation distribution in nuclei of different covering, physiognomy and floristic composition. Objective: We aimed to characterize the above and belowground composition of a conserved, non-flooded, open-scrub, nuclei (patches of bushes) formation of restinga in Linhares, ES, southeastern Brazil. Methods: The vegetation survey was conducted using the line intercept method. Diameter and height of the first six nuclei were measured in five transects separated by 50 m, totaling 30 nuclei up to 350 m away from the shore line. The phytosociology and Shannon Index of the aboveground vegetation community were calculated. In the same 30 nuclei, leaf litter and topsoil layer (15 x 15 x 10 cm) samples were collected to survey the viable seed bank, which was later placed in a greenhouse for germination and seedling identification. The Sørensen Similarity index (SSi) was used to compare the floristic composition between the leaf litter and topsoil layer seed banks. Nuclei volume and number of species were calculated as well. Results: In the aboveground vegetation, 54 plant species belonging to 32 families were identified, totaling 1 098 individuals. The nuclei showed a diversity (H') of 3.08 nats, and an average diameter of 11.5 m (s = 9.1), area of 526.4 m2 (s = 1 081.7), and height of 2.9 m (s = 1.1). Davilla flexuosa, followed by Smilax rufescens, presented the highest IVI (Importance Value Index). A total of 1 839 seedlings from 32 species and 19 families were identified in the seed bank. Enydra sessilis (Asteraceae) had the highest seed density (544), while the family with highest species richness was Cyperaceae. A low similarity between the vegetation surveyed and the seed bank composition was found (only 5 species in common, SSi = 0.10). Conclusions: The results indicate that a post-disturbance early community, established from the seed bank, would have a substantially different species composition, but with other potential species to restore vegetation over the long-term succession.

Introducción: Las restingas son ecosistemas llanos costeros ubicados a lo largo del este de Brasil, que corresponden a unos 5 000 km de la costa atlántica brasileña. La vegetación de restinga está asociada con el bioma de la selva tropical atlántica y comprende cuatro zonas de formación principales: praderas costeras, matorrales, bosques abiertos y zonas pantanosas. Especialmente debido a la urbanización costera, este es un ecosistema amenazado, que, a través de sus formaciones arbustivas, exhibe un mosaico único, como resultado de la distribución de la vegetación en núcleos de diferentes coberturas, fisonomía y composición florística. Objetivo: Caracterizar la composición florística superficial y subterránea de una formación conservada, no inundada, de núcleos de matorral abierto de restinga en Linhares, ES, costa del sureste de Brasil. Métodos: La vegetación se muestreó utilizando el método de la línea de intercepción. El diámetro y la altura de los primeros seis núcleos se midieron en cinco transectos instalados cada 50 m, con un total de 30 núcleos distantes hasta 350 m de la línea de costa. Se muestreó la comunidad de vegetación y se calculó su fitosociología e índice de Shannon. En los mismos 30 núcleos, se recogió la hojarasca más la capa superior del suelo (15 x 15 x 10 cm) para examinar el banco de semillas viable, que luego se colocó en un invernadero para germinar e identificar las plántulas. El índice de similitud de Sørensen se usó para comparar la composición florística entre la hojarasca y el banco de semillas de la capa superficial del suelo y también se calculó la regresión entre el volumen del núcleo y el número de especies. Resultados: En la vegetación superficial se identificaron 54 especies de plantas pertenecientes a 32 familias, con un total de 1 098 plantas. Los núcleos registraron una diversidad (H') de 3.08 nats, y un diámetro promedio de 11.5 m (s = 9.1), área de 526.4 m² (s = 1 081.7) y altura de 2.9 m (s = 1.1). Davilla flexuosa, seguida de Smilax rufescens, presentó el VI (Valor de Importancia) más alto. Se identificaron un total de 1 839 plántulas de 32 especies y 19 familias en el banco de semillas. Enydra sessilis (Asteraceae) tuvo la mayor densidad de semillas viables (544), pero la familia con mayor riqueza de especies fue Cyperaceae. Se encontró una baja similitud entre la vegetación y la composición del banco de semillas (solo 5 especies en común, índice de Sørensen = 0.10). Conclusiones: Los resultados indican que una comunidad recién establecida después de una alteración podría tener una composición de especies sustancialmente diferente, pero con otras especies potenciales para restaurar la vegetación a largo plazo.

Secondary forest fragments offer important carbon and biodiversity cobenefits.

Tropical forests store large amounts of carbon and high biodiversity, but are being degraded at alarming rates. The emerging global Forest and Landscape Restoration (FLR) agenda seeks to limit global climate change by removing carbon dioxide from the atmosphere through the growth of trees. In doing so, it may also protect biodiversity as a free cobenefit, which is vital given the massive shortfall in funding for biodiversity conservation. We investigated whether natural forest regeneration on abandoned pastureland offers such cobenefits, focusing for the first time on the recovery of taxonomic diversity (TD), phylogenetic diversity (PD) and functional diversity (FD) of trees, including the recovery of threatened and endemic species richness, within isolated secondary forest (SF) fragments. We focused on the globally threatened Brazilian Atlantic Forest, where commitments have been made to restore 1 million hectares under FLR. Three decades after land abandonment, regenerating forests had recovered ~20% (72 Mg/ha) of the above-ground carbon stocks of a primary forest (PF), with cattle pasture containing just 3% of stocks relative to PFs. Over this period, SF recovered ~76% of TD, 84% of PD and 96% of FD found within PFs. In addition, SFs had on average recovered 65% of threatened and ~30% of endemic species richness of primary Atlantic forest. Finally, we find positive relationships between carbon stock and tree diversity recovery. Our results emphasize that SF fragments offer cobenefits under FLR and other carbon-based payments for ecosystem service schemes (e.g. carbon enhancements under REDD+). They also indicate that even isolated patches of SF could help to mitigate climate change and the biodiversity extinction crisis by recovering species of high conservation concern and improving landscape connectivity.

Would protecting tropical forest fragments provide carbon and biodiversity cobenefits under REDD+?

Tropical forests store vast amounts of carbon and are the most biodiverse terrestrial habitats, yet they are being converted and degraded at alarming rates. Given global shortfalls in the budgets required to prevent carbon and biodiversity loss, we need to seek solutions that simultaneously address both issues. Of particular interest are carbon-based payments under the Reducing Emissions from Deforestation and Forest Degradation (REDD+) mechanism to also conserve biodiversity at no additional cost. One potential is for REDD+ to protect forest fragments, especially within biomes where contiguous forest cover has diminished dramatically, but we require empirical tests of the strength of any carbon and biodiversity cobenefits in such fragmented systems. Using the globally threatened Atlantic Forest landscape, we measured above-ground carbon stocks within forest fragments spanning 13 to 23 442 ha in area and with different degrees of isolation. We related these stocks to tree community structure and to the richness and abundance of endemic and IUCN Red-listed species. We found that increasing fragment size has a positive relationship with above-ground carbon stock and with abundance of IUCN Red-listed species and tree community structure. We also found negative relationships between distance from large forest block and tree community structure, endemic species richness and abundance, and IUCN Red-listed species abundance. These resulted in positive congruence between carbon stocks and Red-listed species, and the abundance and richness of endemic species, demonstrating vital cobenefits. As such, protecting forest fragments in hotspots of biodiversity, particularly larger fragments and those closest to sources, offers important carbon and biodiversity cobenefits. More generally, our results suggest that macroscale models of cobenefits under REDD+ have likely overlooked key benefits at small scales, indicating the necessity to apply models that include finer-grained assessments in fragmented landscapes rather than using averaged coarse-grained cells.