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Carbon density in boreal forests responds non-linearly to temperature: an example from the Greater Khingan Mountains, northeast China

Publication . Liu, Yang; Trancoso, Ralph; Ma, Qin; Ciais, Philippe; Gouvêa, Lidiane; Yue, Chaofang; Assis, Jorge; Blanco, Juan A.

Boreal forests play a crucial role in the global carbon (C) cycle and in climate stabilization. To better predict global C budgets, it is important to accurately estimate the size of forest C pools, and to identify the factors affecting them. We used national forest inventory data for the Greater Khingan Mountains, northeast China from 1999 to 2018 and 149 additional field plots to estimate C storage and its changes in forest vegetation, excluding C stored in soils, and to calculate the total C density in forest ecosystems. From 1999 to 2018, the vegetation C storage and density increased by 92.22 Tg and 4.30 Mg C ha-1, respectively, while the mean C sink was 4.61 Tg C yr-1. Carbon storage and density showed the same pattern, with the largest stocks in trees, followed by herbs, shrubs, and then litter. Mean C density was higher in mature forests than in young forests. The maximum C density was recorded in Populus davidiana forests, and was 2.2-times larger than in Betula davurica forests (the minimum). The mean (& PLUSMN; standard error) total C density of forest ecosystems was 111.3 & PLUSMN; 2.9 Mg C ha-1, including C stored in soils. Mean annual temperature (MAT) controlled total C density, as MAT had positive effects when it was lower than the temperature of the inflection point (-2.1 to -4.6 degrees C) and negative effects when it was above the inflection point. The rate of change in the total C density depended on the quantile points of the conditional distribution of total C density. Natural and anthropogenic disturbances had weaker effects on C density than temperature and precipitation. In conclusion, our results indicate that there might be a temperatureinduced pervasive decrease in C storage and an increase in tree mortality across Eastern Asian boreal forests with future climate warming.

2023Journal article

Open Access

Global impacts of projected climate changes on the extent and aboveground biomass of mangrove forests

Publication . Gouvêa, Lidiane; A, Serrão; Cavanaugh, Kyle; Gurgel, Carlos F. D.; Horta, Paulo A.; Assis, Jorge

Aim: Over the past 50 years, anthropogenic activities have led to the disappearance of approximately one-third of the world's mangrove forests and their associated ecosystem services. The synergetic combined effect of projected climate change is likely to further impact mangroves in the years to come, whether by range expansions associated with warming at higher latitudes or large-scale diebacks linked to severe droughts. We provide an estimate of future changes in the extent and aboveground biomass (AGB) of mangrove forests at global scales by considering contrasting Representative Concentration Pathway scenarios (decade 2090-2100 under RCP 2.6 in line with the Paris Agreement expectations, and RCP 8.5 of higher emissions). Location: Global. Methods: Boosted regression trees fitted occurrence and AGB of mangroves against high-resolution biologically meaningful data on air temperature, precipitation, wave energy, slope and distance to river Deltas. Results: On the global scale, models produced for present-day conditions retrieved high accuracy scores and estimated a total area of 12,780,356 ha and overall biomass of 2.29 Pg, in line with previous estimates. Model projections showed poleward shifts along temperate regions, which translated into comparable gains in total area, regardless of the RCP scenario (area change RCP 2.6: 17.29%; RCP 8.5: 15.77%). However, biomass changes were dependent on the emission scenario considered, remaining stable or even increasing under RCP 2.6, or undergoing severe losses across tropical regions under RCP 8.5 (overall biomass change RCP 2.6: 12.97%; RCP 8.5: -11.51%). Such losses were particularly aggravated in countries located in the Tropical Atlantic and Eastern Pacific, and the Western and Eastern Indo-Pacific regions (regions with losses above similar to 20% in overall biomass). Conclusions: Our global estimates highlight the potential effect of future climate changes on mangrove forests and how broad compliance with the Paris Agreement may counteract severe trajectories of loss. The projections made, also provided at the country level, serve as new baselines to evaluate changes in mangrove carbon sequestration and ecosystem services, strongly supporting policy-making and management directives, as well as to guide restoration actions considering potential future changes in niche availability.

2022Journal article

Open Access

Biophysical modelling and graph theory identify key connectivity hubs in the Mediterranean marine reserve network

Publication . Abecasis, David; Fragkopoulou, Eliza; Claro, Bruno; Assis, Jorge

Connectivity plays a key role in the effectiveness of MPA networks ensuring metapopulation resilience through gene flow and recruitment effect. Yet, despite its recognized importance for proper MPA network functioning, connectivity is not often assessed and is very seldomly used in marine spatial planning. Here, we combined biophysical modelling with graph theory to identify Mediterranean marine reserves that support connectivity between different ecoregions through stepping-stone processes, thus preventing network fragmentation, and those that have an important role as propagule source areas contributing to the recruitment and rescue effects. We identified 19 reserves that play a key role towards the functioning of the network, serving either as stepping-stones or as propagule sources, yet with distinct patterns between ecological groups with contrasting propagule duration (PD). The Cote D'Azur marine reserves are important both as stepping-stones and propagule sources for several ecological groups. Also, key is the Capo Rizzuto and Plemmirio marine reserves due to their role as stepping stones between different marine ecoregions, particularly for species with longer PD (Pisces, Crustacea and Echinodermata). These results provide stakeholders and managers with crucial information for the implementation and management of an efficient marine reserve network in the Mediterranean.

2023-01Journal article

Open Access

Artificial intelligence convolutional neural networks map giant kelp forests from satellite imagery

Publication . Marquez, L.; Fragkopoulou, Eliza; Cavanaugh, K. C.; Houskeeper, H. F.; Assis, J.

Climate change is producing shifts in the distribution and abundance of marine species. Such is the case of kelp forests, important marine ecosystem-structuring species whose distributional range limits have been shifting worldwide. Synthesizing long-term time series of kelp forest observations is therefore vital for understanding the drivers shaping ecosystem dynamics and for predicting responses to ongoing and future climate changes. Traditional methods of mapping kelp from satellite imagery are time-consuming and expensive, as they require high amount of human effort for image processing and algorithm optimization. Here we propose the use of mask region-based convolutional neural networks (Mask R-CNN) to automatically assimilate data from open-source satellite imagery (Landsat Thematic Mapper) and detect kelp forest canopy cover. The analyses focused on the giant kelp Macrocystis pyrifera along the shorelines of southern California and Baja California in the northeastern Pacific. Model hyper-parameterization was tuned through cross-validation procedures testing the effect of data augmentation, and different learning rates and anchor sizes. The optimal model detected kelp forests with high performance and low levels of overprediction (Jaccard's index: 0.87 +/- 0.07; Dice index: 0.93 +/- 0.04; over prediction: 0.06) and allowed reconstructing a time series of 32 years in Baja California (Mexico), a region known for its high variability in kelp owing to El Nino events. The proposed framework based on Mask R-CNN now joins the list of cost-efficient tools for long-term marine ecological monitoring, facilitating well-informed biodiversity conservation, management and decision making.

2022Journal article

Open Access

The invasive alga Gracilaria vermiculophylla in the native northwest Pacific under ocean warming: Southern genetic consequence and northern range expansion

Publication . Liu, Yi-Jia; Zhong, Kai-Le; Jueterbock, Alexander; Satoshi, Shimada; Choi, Han-Gil; Weinberger, Florian; Assis, Jorge; Hu, Zi-Min

Ocean warming is one of the most important factors in shaping the spatial distribution and genetic biodiversity of marine organisms worldwide. The northwest Pacific has been broadly illustrated as an essential seaweed diversity hotspot. However, few studies have yet investigated in this region on whether and how past and ongoing climate warming impacted the distribution and genetic pools of coastal seaweeds. Here, we chose the invasive species Gracilaria vermiculophylla as a model, and identified multiple genetic lineages in the native range through genome-scale microsatellite genotyping. Subsequently, by reconstructing decadal trends of sea surface temperature (SST) change between 1978 and 2018, we found that SST in northern Japan and the East China Sea indeed increased broadly by 0.25-0.4 degrees C/decade. The projections of species distribution models (SDMs) under different future climate change scenarios (RCP 2.6, RCP 4.5, RCP 6.0 and RCP 8.5) indicated that a unique genetic pool of G. vermiculophylla at its current southern range limit (i.e. the South China Sea) is at high risk of disappearance, and that the populations at its current northern range limit (i.e. in Hokkaido region) will undergo poleward expansions, particularly by the year 2100. Such responses, along with this species' limited dispersal potential, may considerably alter the contemporary distribution and genetic composition of G. vermiculophylla in the northwest Pacific, and ultimately threaten ecological services provided by this habitat-forming species and other associated functional roles.

2022-09Journal article

Open Access