Forest Expansion Research Articles

Responses of streamflow to forest expansion in a typical subhumid watershed under future climate conditions

Water availability in the subhumid region is highly vulnerable to frequent droughts. Water scarcity in this region has become a limiting factor for ecosystem health, human livelihood, and regional economic development. A notable pattern of land cover change in the subhumid region of the United States is the increasing forest area due to afforestation/reforestation and woody plant encroachment (WPE). Given the distinct hydrological processes and runoff generation between forests and grasslands, it is important to evaluate the impacts of forest expansion on water resources, especially under future climate conditions. In this study, we focused on a typical subhumid watershed in the United States – the Little River Watershed (LRW). Utilizing SWAT + simulations, we projected streamflow dynamics at the end of the 21st century in two climate scenarios (RCP45 and RCP85) and eleven forest expansion scenarios. In comparison to the period of 2000–2019, future climate change during 2080–2099 will increase streamflow in the Little River by 5.1% in the RCP45 but reduce streamflow significantly by 30.1% in the RCP85. Additionally, our simulations revealed a linear decline in streamflow with increasing forest coverage. If all grasslands in LRW were converted into forests, it would lead to an additional 41% reduction in streamflow. Of significant concern is Lake Thunderbird, the primary reservoir supplying drinking water to the Oklahoma City metropolitan area. Our simulation showed that if all grasslands were replaced by forests, Lake Thunderbird during 2080–2099 would experience an average of 8.6 years in the RCP45 and 9.4 years in the RCP85 with water inflow amount lower than that during the extreme drought event in 2011/2012. These findings hold crucial implications for the formulation of policies related to afforestation/reforestation and WPE management in subhumid regions, which is essential to ensuring the sustainability of water resources.

The role of dispersal limitation in the forest biome shifts of Europe in the last 18,000 years

AbstractAimHow the ability of plants to move towards newly favourable habitats (dispersal limitation) impacts the change of biome distribution and transition under fast climate warming is still debated. Analysing vegetation change in the past may help to clarify the relative importance of underlying ecological processes such as climate, biotic interactions, and dispersal. In this study, we investigated how dispersal limitation affected the distribution of European forests in the last 18,000 years.LocationSouthern and Central Europe.TaxonSpermatophyta.MethodsUsing the LPJ‐GM 2.0 model (an extension of LPJ‐GUESS), we simulated European vegetation from the end of the Last Glacial Maximum (18.5 ka) to the current time (0 ka). Using biome reconstructions from pollen data as reference, we compared the performance of two dispersal modes: with no migration constraints or seed limitation (free dispersal mode), and with plant establishment depending on seed dynamics and dispersal (dispersal limitation mode).ResultsThe model run, including migration processes, was better at capturing the post‐glacial expansion of European temperate forests (and the longer persistence of boreal forests) than the setting assuming free dispersal, especially during periods of rapid warming. This suggests that a number of (temperate) tree taxa experienced delayed occupancy of climatically suitable habitats due to a limited dispersal capacity, i.e., post‐glacial migration lags.Main ConclusionsOur results show that including migration processes in model simulations allows for more realistic reconstructions of forest patterns under rapid climate change, with consequences for future projections of carbon sequestration and climate reconstructions with vegetation feedback, assisted migration and forest conservation.

Vegetation diversity in response to monsoonal variability in the Eastern Himalaya, India over the past ~13 000 yrs

Monsoon precipitation plays a crucial role in shaping the diversity of vegetation in the Himalayas, both in terms of temporal and spatial distribution. While palynology has traditionally been employed to reconstruct the past climate of the Himalaya, there has been limited understanding of how monsoon-related changes affect the structure and distribution of vegetation. To address this, we analysed pollen data from a 3 m deep sedimentary profile in the higher Sikkim Himalaya to reconstruct monsoon driven changes in vegetation diversity. Our results show a highly fluctuating trend of pollen and diversity parameters at late-Pleistocene-Holocene transition for which fluctuating hydroclimatic conditions and differential pollen preservation in coarser sediments is attributed. During the Early Holocene (10,438–7934 cal yrs BP) favourable hydroclimatic conditions led to a rapid expansion of mixed broad-leaved forests, marked by higher values of richness and alpha diversity. Between 7934 and 5481 cal yrs BP, the region experienced moderate hydroclimatic conditions that facilitated expansion and diversification of woody taxa, and correlated with the global Holocene Climate Optimum (HCO). Conversely, from 5481 to3949 cal yrs BP, declining total pollen count (TPC), species richness, and alpha diversity indicates significant shifts in vegetation composition under deteriorating climatic conditions, which corresponds with the 4.2 ka event worldwide. From 3949 to 2049 cal yrs BP, an increasing yet variable trend in TPC and diversity indices, suggests warm-humid conditions prevailed in the region. During the last 1086 cal yrs, an increasing trend is recorded in the palyno assemblage and diversity parameters suggesting ameliorating climate, matches well with the Mediaeval Climate Anomaly (MCA). Our inferences suggest that the palyno assemblage and diversity parameters are quiet sensitive to warm and humid conditions.

A paleoecological context for forest distribution and restoration in Grootbos Nature Reserve, Agulhas Plain, South Africa

Grootbos Nature Reserve falls within the Cape Floristic Region of South Africa and comprises fynbos and forest vegetation elements, which exist as alternate stable states and are naturally maintained by feedbacks between vegetation, fire, topography and climate. The objective of this study was to investigate changes in forest extent in the Baviaansfontein valley in Grootbos Nature Reserve in order to understand whether current forest coverage was greater or lesser prior to colonial settlement. Incorporating paleoecology has the potential to define historical ranges of landscape variability that can guide forest restoration programs that are aligned to historical forest occurrence. Not all landscapes are suited for tree planting initiatives as they harbor indigenous open vegetation, which is of conservation value. Historical and palaeoecological information is especially valuable as tree planting initiatives and reforestation programs are becoming more popular. Here we present a combined palynological (pollen, spores, charcoal) and geochemical approach (X-ray fluorescence elemental ratios, Loss-on-ignition), to evaluate the historic extent and distribution of forest and fynbos vegetation for the past ~250 years at Baviaansfontein in the Grootbos Nature Reserve. The start of the record was dominated by pollen typical of asteraceous fynbos, with evidence of forest elements also present, though in low abundance. After 200 years (c.1750 CE–1950 CE) of increased input of micro- and macrocharcoal, the subsequent decline in charcoal indicates a decrease in fire occurrence. This decline coincides with increased input of forest pollen taxa, suggesting that fire suppression most likely triggered forest expansion and perhaps initiated the beginning of a biome boundary shift. The continued decline in fire promoted the development of the present-day proteoid fynbos type around ~1980 CE and was responsible for the replacement of the previously more asteraceous-dominated fynbos type. The results show that changes in fire occurrence have driven compositional changes over time within fynbos but also contributed to the expansion of forest at the expense of fynbos. Considering the palaeoecological record and the expected warmer climate with more fires, forest expansion at Baviaansfontein is not recommended. The proteoid-dominated fynbos biome might be similarly negatively affected by warmer climate and a shift to an asteraceous fynbos community could occur in the future.

Spatio-Temporal Dynamics of Land Use and Land Cover, and Small-Scale Forest Expansion in Northwestern Ethiopian Highlands

Spatio-Temporal Dynamics of Land Use and Land Cover, and Small-Scale Forest Expansion in Northwestern Ethiopian Highlands

Plant-soil interactions alter nitrogen and phosphorus dynamics in an advancing subarctic treeline.

Treelines advance due to climate warming. The impacts of this vegetation shift on plant-soil nutrient cycling are still uncertain, yet highly relevant as nutrient availability stimulates tree growth. Here, we investigated nitrogen (N) and phosphorus (P) in plant and soil pools along two tundra-forest transects on Kola Peninsula, Russia, with a documented elevation shift of birch-dominated treeline by 70 m during the last 50 years. Results show that although total N and P stocks in the soil-plant system did not change with elevation, their distribution was significantly altered. With the transition from high-elevation tundra to low-elevation forest, P stocks in stones decreased, possibly reflecting enhanced weathering. In contrast, N and P stocks in plant biomass approximately tripled and available P and N in the soil increased fivefold toward the forest. This was paralleled by decreasing carbon (C)-to-nutrient ratios in foliage and litter, smaller C:N:P ratios in microbial biomass, and lower enzymatic activities related to N and P acquisition in forest soils. An incubation experiment further demonstrated manifold higher N and P net mineralization rates in litter and soil in forest compared to tundra, likely due to smaller C:N:P ratios in decomposing organic matter. Overall, our results show that forest expansion increases the mobilization of available nutrients through enhanced weathering and positive plant-soil feedback, with nutrient-rich forest litter releasing greater amounts of N and P upon decomposition. While the low N and P availability in tundra may retard treeline advances, its improvement toward the forest likely promotes tree growth and forest development.

Hydrological responses to historical and predicted land use/land cover changes in the Welmel watershed, Genale Dawa Basin, Ethiopia: Implications for water resource management

Study regionWelmel watershed, Genale-Dawa Basin, Ethiopia. Study focusThis study aimed to analyze the hydrological impacts of land use/land cover (LULC) changes in the Welmel watershed for 1990–2020 and to predict the LULC change impact on the hydrological status in the year 2050. The hybrid land use classification technique for classifying Landsat images; Cellular-Automata Markov (CA-Markov) for prediction of the 2035 and 2050 LULC; and the Soil and Water Assessment Tool (SWAT) for hydrological modeling were employed in the analyses. New hydrological insights for the regionThe findings revealed that from 1990 to 2020, significant alterations in the hydrological regime occurred due to historical LULC changes in the Welmel watershed, which are expected to continue in the 2035 and 2050 periods. Forest cover loss and expansion of agricultural areas, which occurred from 1990 to 2020, have resulted in increased annual flow (6.18%), wet seasonal flow (10.21%), and surface runoff (25.32%), and reduced dry seasonal flow (6.34%), groundwater flow (17.17%, and evapotranspiration (0.36%). The 2035 and 2050 LULC indicate further increased annual flow, wet seasonal flow, and surface runoff, and reduced dry seasonal flow, groundwater flow, and evapotranspiration. The study also stated the hydrological impacts of the LULC changes at the sub-watershed scales. More noticeable changes in hydrological components have been observed at the sub-watershed scale, mainly associated with the uneven spatial distribution of LULC changes. The findings provide valuable insights for policymakers, water resource managers, and local communities in formulating strategies to enhance water resource management practices in the Welmel watershed and similar regions. It could also be for researchers and Academia who can be benefited and it can be used to supplement global goals like Sustainable Development Goal 6 (SDG 6): ensure the availability and sustainable management of water and sanitation for all.

Quantitative Holocene climate reconstruction and anthropogenic impact analysis based on the pollen records in peat sediment in Southern China

The quantitative reconstruction of Holocene paleoclimate is pivotal for unraveling the evolution of East Asian Monsoon (EAM). Some recent studies have highlighted the escalating human activities in the late Holocene, which could potentially pose significant challenges to the precise quantitative reconstruction of paleoclimate. In this study, we undertake a quantitative reconstruction of Holocene climate and human influence index (HII) based on pollen data from the Shiwangutian (SWGT) in Southern China. This is achieved by developing and applying a pollen-based calibration model utilizing Locally Weighted Average-Partial Least Squares Regression (LWWA-PLS) and the Modern Analogue Technique (MAT). Our findings reveal that evergreen forests experienced expansion between 11.6 and 9.0 cal ka BP, coinciding with elevated Mean Annual Precipitation (Map) and Mean Annual Temperature (Mat) levels. These patterns signify a progressively warm and wet climate during this period. Subsequently, evergreen forests achieved their maximum abundance between 9.0 and 4.0 cal ka BP, aligning with a notable increase in vegetation richness, indicating a warmer and wetter climate during the mid-Holocene. Notably, during the interval of 6.0–4.0 cal ka BP, the Map, Mat, and Precipitation of Warmest Month (Mpwa) reached the Holocene optimum, approximately 14% higher than modern. Consequently, we deduce that in the early and middle Holocene, when the monsoon was particularly strong, synchronous changes in precipitation fostered the regional expansion of evergreen broad-leaved forests. Furthermore, the record demonstrates a substantial reduction in forest cover and a noteworthy increase in the HII value since 4.0 cal ka BP, likely attributable to anthropogenic impacts. Our analysis suggests that the influence of anthropogenic activities surpassed that of natural climate factors in shaping regional vegetation cover. These findings offer insights into potential drivers of climate change. As a preliminary conclusion, we propose that the summer insolation, ice sheets, and meltwater fluxes were the primary controlling factors for climate variations during the early to mid-Holocene in Southern China.

Contrasting Responses of Land Surface Temperature and Soil Temperature to Forest Expansion During the Dormant Season on the Qinghai‐Tibet Plateau

AbstractAs one of the important ecological responses of ecosystem to global climate change, forest expansion can alter land surface energy budget and local microclimate. Land surface temperature (LST) and soil temperature (ST) indicate the above‐ and below‐ground thermal state, respectively. However, the lack of studies on the relationships between LST and ST changes after forest expansion hinders our understanding of the vegetation‐microclimate interactions, especially during the dormant season. We quantified the change of LST (∆LST) and ST (∆ST) after forest expansion in the dormant season on the Qinghai‐Tibet Plateau (QTP), and then explored their differences and linkages. The results showed that forest expansion significantly decreased LST by 0.75 ± 0.20°C, while significantly increased ST in three layers (0–7, 7–28, and 28–100 cm) by 0.31 ± 0.06, 0.29 ± 0.05, and 0.20 ± 0.04°C, respectively. The decreased LST was conducive to the preservation of snow, leading to larger snow depth, larger fractional snow cover and more snow cover days in forests than grasslands, which further promoted the increased ST through enhanced thermal insulation. Furthermore, it is suggested that the cooling impact of forest expansion on LST and warming impact on ST would both be stronger at humid sites than at dry sites. These findings will contribute to understand the vegetation‐microclimate‐snow interactions and the decoupling phenomenon between LST and ST in the dormant season influenced by vegetation change.

Chemistry-albedo feedbacks offset up to a third of forestation's CO2 removal benefits.

Forestation is widely proposed for carbon dioxide (CO2) removal, but its impact on climate through changes to atmospheric composition and surface albedo remains relatively unexplored. We assessed these responses using two Earth system models by comparing a scenario with extensive global forest expansion in suitable regions to other plausible futures. We found that forestation increased aerosol scattering and the greenhouse gases methane and ozone following increased biogenic organic emissions. Additionally, forestation decreased surface albedo, which yielded a positive radiative forcing (i.e., warming). This offset up to a third of the negative forcing from the additional CO2 removal under a 4°C warming scenario. However, when forestation was pursued alongside other strategies that achieve the 2°C Paris Agreement target, the offsetting positive forcing was smaller, highlighting the urgency for simultaneous emission reductions.

Land use land cover change intensity analysis for sustainable natural resources management: The case of northwestern highlands of Ethiopia

Various studies conducted in the northwestern highlands of Ethiopia from 2001 to 2020 indicated two contrasting directions of change in land use land cover. One direction is the expansion of farmlands at the expense of the natural vegetation, and the other direction is expansion of plantation forest on farm and grazing lands. But, the net effect of land use land cover change is not as such clear. A clear understudying of such dynamics in land use land cover and the net effect of the change helps design effective land use planning policy, which enhances sustainable natural resources management. Accordingly, the study analyzed intensity of land use land cover change for three-time periods (1990–2000; 2000–2010 and 2010–2020). The findings of this study can be applicable to different parts of the globe where two contrasting directions of change in land use land cover exist. The study employed both qualitative and quantitative methods, which were specifically applied through carrying out step-by-step: satellite image acquisition, preprocessing, classification, accuracy assessment, and intensity analysis. Result of the analysis indicated that land use land cover change over the three intervals showed considerable variation where intensity was consistently increasing from the first (1990–2000) interval to the subsequent (2000–2010) interval, and it was fast (8.24%) during the third interval (2010–2020). The analysis also indicated considerably high transition from bare land to grazing land and bush land during the third interval, especially on areas where the community practiced controlled management of grazing lands (zero grazing) and protection of bush lands. From the total bare land cover in 2010, 21% converted to grazing land and 17% converted to bush land. LULC transition from bush land to cultivated land was rising due to encroachment of bush lands by farming. Transition from bush land to cultivated land increased by 4%, 16% and 50% in the period 1990–2000, 2000–2010, and 2010–2020, respectively. On the other hand, transition from cultivated land to forest land was considerably high during the third interval. From the total cultivated land cover in 2010, 25% converted to forest land, where the change is mainly associated to the introduction of woodlot plantation on individual farmland holdings. In general, the finding suggests that controlled management of grazing lands; comparing environmental and economic benefits of quarry/stone extraction sites; and plantation of economically viable and environmentally sound tree species are key policy issues which needs due attention in land use planning and management practices.

Effect of watershed characteristics on river flow for the case of two watersheds, Megech and Gumaro, Upper Blue Nile Basin, Ethiopia

Land degradation is a series of problems in Ethiopia’s highlands, particularly in the Upper Blue Nile River Basin reflected in the form of soil erosion and reduce soil fertility from time to time. The effect of watershed characteristics on the river flow of those watersheds was evaluated by distributing a physically based hydrological model known as the soil and water assessment tool model. The model was calibrated for the river flow from 1992 to 2006 and validated for the period from 2007 to 2014. The performance of the model was evaluated based on performance rating criteria, coefficient of determination, and Nash and Sutcliff efficiency on monthly based value, the coefficient of determination (R2) and Nash–Sutcliffe coefficient was greater than 0.6 and 0.5 for all scenarios on both watersheds, respectively. The land-use land-cover change scenario, the climate characteristics, and the slope change scenario was developed, from those analyses, it was found that has been a substantial decrease or increase in forest land, shrubland, grassland, and expansion of agricultural land. The mean annual streamflow of 2010 LULC decreased by 1.44% for 2010 from 2003 LULC and 5.23% for 2018 from 2010. Because of reduced cultivated land from 2010 up to 2018 and increased grassland and plantation in the Megech watershed and 2010 LULC decreased by 0.9% for 2010 from 2003 LULC and 2.04% in 2018 from 2010. This distributed physically based hydrological model has been applied for the evaluation of physical catchment characteristics with significant differences which was Cropland for Megech and Gumaro watersheds which were 67.28% and 61.5%, respectively, for the 2003 LULC, 64.94% Megech, and 58.89% for Gumaro watershed for 2010LULC and 51.95% for Megech and 42.12% for Gumaro watershed, similarly, Eutric Cambisols were covering large areas for both watersheds.

Effect of the Moso Bamboo Pyllostachys edulis (Carrière) J.Houz. on Soil Phosphorus Bioavailability in a Broadleaf Forest (Jiangxi Province, China)

Moso bamboo (Phyllostachys edulis (Carrière) J.Houz.) is a fast-growing species that commonly invades neighboring broadleaf forests and has been widely reported in subtropical forest ecosystems. However, little is known about the effect on soil phosphorus (P) bioavailability and its potential influence factor during the P. edulis expansion. Here, the four soil P bioavailable fractions (i.e., CaCl2-P, Citrate-P, Enzyme-P, and HCl-P), acid phosphatase activity, iron and aluminum oxides (Fed and Ald), and soil total P pool at depths of 0–10 cm, 10–20 cm, and 20–40 cm were measured in three expanding interfaces (a broadleaf forest, a mixed bamboo–broadleaf forest, and a pure P. edulis forest) in subtropical forests of southern China. Regardless of soil depths, the CaCl2-P content was significantly lower in the mixed bamboo–broadleaf forest than the other two forest types, with contents ranging from 0.09 to 0.16 mg/kg, whereas the HCl-P content was significantly lower in the broadleaf forest, with contents ranging from 3.42 to 14.33 mg/kg, and the Enzyme-P content and acid phosphatase activity were notably lower in P. edulis forest with contents of 0.17–0.52 mg/kg and 68.66–74.80 μmol MUF released g−1 min−1, respectively. Moreover, the soil total P pool was enhanced in the mixed bamboo–broadleaf forest in 0–10 cm depth compared to broadleaf and P. edulis forests, with increases of 27.40% and 31.02%, respectively. The redundancy analysis showed that soil pH plays an important role in regulating soil P bioavailability during the P. edulis expansion (p < 0.01). From the above results, the invasion of P. edulis into broadleaf forests has resulted in soil P bioavailability and storage capacity. The results of this study suggest that when P. edulis invades broadleaf forests, it could affect the soil P bioavailability by elevating soil pH, which in turn drives and facilitates the completion of the expansion. This is important for understanding P cycling during the P. edulis forest expansion in subtropical regions.

Spatio-Temporal Heterogeneity of the Ecological Environment and Its Response to Land Use Change in the Chushandian Reservoir Basin

Conducting ecological monitoring assessments and revealing the effects of driving factors are crucial for enhancing ecological safety and promoting sustainable development. Taking the Chushandian Reservoir basin as the research object, this paper employed the Remote Sensing Ecological Index (RSEI), constructed based on remote sensing data, to monitor and assess the ecological environment of the study area from 1990 to 2021, and predicted its future development trend through the Hurst index. On this basis, we integrated land use data to elucidate the response of the ecological environment to human activities. The results show that: (1) The mutation test indicates that selecting 1990, 2004, 2008, 2013, and 2021 as the study time nodes can comprehensively reflect the spatio-temporal information regarding changes in ecological quality in the study area. Specifically, both 1990 and 2021 exhibit higher ecological quality ratings, while 2008 has the lowest ecological quality rating. The spatial distribution of ecological quality is strongly clustered, with high–high clustering and low–low clustering dominating. (2) The overall trend of ecological quality in the study area appears in a pattern of initial decline followed by subsequent improvement. From 1990 to 2004, the degraded area constituted the largest proportion, accounting for 87.82%. After 2008, the quality of the ecological environment began to rebound. Between 2008 and 2013, the proportion of regions with improved ecological conditions was 57.91%, and from 2013 to 2021, 46.74% of the regions showed improvement. (3) In the research area, 36.70% of the regions exhibit a trend of sustainable stability into the future, representing the highest proportion. Approximately 34.3% of the areas demonstrate a trend of sustainable improvement, while the regions exhibiting sustainable degradation account for only 5.72%. While the ecological environment is demonstrating a positive overall developmental trend, it is crucial to stay vigilant regarding areas of ongoing degradation and implement appropriate protective measures. (4) Land use change significantly impacts the ecological environment, with the expansion of land for urban build up causing some ecological deterioration, while the later expansion of forest improves ecological quality. The results provide theoretical approaches and a foundation for decision-making in the ecological management of the Chushandian Reservoir basin.

Projections of Land Use Change and Water Supply–Demand Assessment Based on Climate Change and Socioeconomic Scenarios: A Case Study of Guizhou Province, China

Land use change and water supply–demand assessment are critical to achieving regional sustainable development and improving human wellbeing. In the context of complex climate change and socioeconomic development, there is an urgent need for systematic assessment and forecasting studies on how to combine physical, geographical, and socioeconomic factors to clarify patterns of change in the land use change and water supply–demand, as well as to respond appropriately to different climate and socioeconomic development scenarios in the future. Based on the Shared Socioeconomic Pathways-Representative Concentration Pathway (SSP-RCP) scenarios, a framework for simulating future land use change and assessing water supply–demand in the coupled SD-PLUS-InVEST model was constructed. The land use change in Guizhou Province from 2020 to 2050 was simulated using the SD-PLUS model, and the water supply–demand conditions were projected for 2030, 2040, and 2050 under multiple scenarios (SSP126, SSP245, and SSP585). The research results indicated that (1) The land use change in the study area has significant spatial heterogeneity. It showed similar trends in the land use change in the SSP126 and SSP245 scenarios, with both artificial surfaces and forest showing an expansion trend, but the expansion of forest was most typical in the southwestern region in the SSP126 scenario, and there is a significant increase in the northeastern region in the SSP245 scenario. Additionally, there is a rapid expansion of artificial surfaces in the central region in the SSP585 scenario, and a more rapid expansion of cultivated land in the southeastern region, with a significant increase in the area of water bodies. (2) The changes in water supply from 2020 to 2050 under the three scenarios show a smaller increase (5.22–11.88%), a significant increase in water demand (29.45–58.84%), and an increase in the area of water shortage by about 2708.94–9084.40 km2, with the extent of the shortage increasing by about 23.71–79.50%. (3) According to the results of the SSP-RCP scenario projections, socioeconomic development has a significant impact on the growth of water demand, and climate and land use change may exacerbate the spatiotemporal heterogeneity of water supply–demand in the karst region. The systematic study of land use change and water supply–demand in Guizhou can provide a scientific basis for the sustainable management of regional ecosystems and the rational allocation of land and water resources.

Evolutionary and ecological trends in the Neotropical cycad genus Dioon (Zamiaceae): An example of success of evolutionary stasis

AbstractCycads represent an example of the success of evolutionary stasis. Despite their early origin, they survived multiple events of mass extinction and diversified in modern tropical ecosystems during the Cenozoic without major changes in their morphology. What factors have allowed their persistence and diversification despite their conservative nature? We reviewed documentation on the micro‐ and macro‐evolutionary processes involved in the diversification of the Neotropical genus Dioon. Dioon comprises 18 species from varied habitats in Mexico and Honduras, and serves as a model to understand the patterns of cycad diversification. Here, we synthesize evidence reached from different fields, especially biogeography, phylogenetics, population ecology, and speciation, to propose a mechanism that can explain the current patterns of biodiversity in Dioon. At the macroevolutionary scale, a Paleogene origin for Dioon is more likely than an alternative hypothesis of a Neogene origin. Dioon lineages have dispersed along with the expansion of tropical forests throughout main mountain chains. Subsequently, climate change, and particularly aridification, promoted the fragmentation of the tropical forests, allowing the main Dioon clades to evolve in isolation at distinct biogeographic regimes. At the microevolutionary scale, low seed dispersal capability, stochastic demographic processes, and niche conservatism restrict the lineages to isolate themselves at narrow habitats, promoting local adaptation in populations. Local adaptation seems to be a process achieved through many generations under stabilizing selection. Altogether, these processes shaped the diversification in Dioon. This review attempts to stimulate further research on cycads and other biological groups that have diversified despite their apparent evolutionary stasis.

Invasion by Cedrela odorata threatens long distance migration of Galapagos tortoises.

Invasive alien species are among the most pervasive threats to biodiversity. Invasive species can cause catastrophic reductions in populations of native and endemic species and the collapse of ecosystem function. A second major global conservation concern is the extirpation of large-bodied mobile animals, including long-distance migrants, which often have keystone ecological roles over extensive spatial extents. Here, we report on a potentially catastrophic synergy between these phenomena that threatens the endemic biota of the Galapagos Archipelago. We used GPS telemetry to track 140 migratory journeys by 25 Western Santa Cruz Island Galapagos tortoises. We plotted the spatial interaction between tortoise migrations and recently established non-native forest dominated by the invasive tree Cedrela odorata (Cedrela forest). We qualified (a) the proportion of migratory journeys that traversed Cedrela forest, and (b) the probability that this observed pattern occurred by chance. Tortoise migrations were overwhelmingly restricted to small corridors between Cedrela forest blocks, indicating clear avoidance of those blocks. Just eight of 140 migrations traversed extensive Cedrela stands. Tortoises avoid Cedrela forest during their migrations. Further expansion of Cedrela forest threatens long-distance migration and population viability of critically endangered Galapagos tortoises. Applied research to determine effective management solutions to mitigate Cedrela invasion is a high priority.

Morphometric analysis within populations of Hylomyscus walterverheyeni (Rodentia: Muridae) confirms complex relationships between small rodent populations of West Central African forests

Our recent morphometric study on the strictly forest-dwelling small rodent (Praomys misonnei) in West Central Africa revealed complex relationships between populations. The present study tests this hypothesis on another species of forest rodent (Hylomyscus walterverheyeni), and more precisely compares specimens from Kessala (Gabon) with specimens from southern Cameroon. Sixty-eight specimens were used for the morphometric analyses, and four standard external characters were measured: head + body length, tail length, hindfoot length, and ear length. Highly significant morphometric differences were observed between the H. walterverheyeni populations at the local and regional scales. A principal component analysis showed that the Gabonese H. walterverheyeni populations were morphometrically closer to one another than to the Cameroonian ones. Moreover, the body size of the Gabonese H. walterverheyeni populations was smaller than that of the Cameroonian populations. Overall, H. walterverheyeni is characterized by a local morphometric structure pattern similar to that of P. misonnei. These new results further support the scenario of complex relationships between the forest populations of West Central African rodents. This suggests the existence of persistent local biogeographical barriers despite several forest expansion episodes in the upper Pleistocene, as documented by the landscape history of West Central Africa.

Demographic shrinkage promotes ecosystem services supply capacity in the karst desertification control

Although ecological services have been improved in karst desertification control areas, it is still unclear how population shrinkage affects ecosystem service supply capability through ecological assets. In this study, Theil-Sen median, regression analysis, and variance partitioning were applied to explore the linkages of population change (observed data and shared socioeconomic pathways 1-representative concentration pathways 2.6), ecological asset composition (land use), quality (Normalized difference vegetation index [NDVI] and tree height), and ecosystem services in different periods (population growth and decline periods). The results showed that the population change during the growth period (2000–2038) was dominated by migration patterns. In degraded ecoregions (karst desertification) dominated by population out-migration, the net expansion of forest was 15.88 % during 2000–2020, NDVI and tree height increased by 0.57 % and 54.96 %, and ecosystem service supply capability increased by 2.68 %. In contrast, in non-degraded ecoregions (non-karst and karst non-desertification) with population in-migration, change rates of forest (−5.40 % and − 23.68 %), NDVI (0.49 % and 0.53 %), tree height (−8.35 % and − 31.25 %), and ecosystem service supply capability (2.04 % and 2.18 %) were apparently lower than degraded ecoregions. During the population decline period (2039–2100), although the migration pattern between two regions during the growth period was replaced by a population drop within a single region, the positive correlation between population shrinkage with ecological assets and service supply capability was still followed. Overall, the study found that both ways of population shrinkage that involve out-migration and decline can alleviate the land pressure of degraded ecoregions, which enhances ecosystem service supply capability by regulating ecological assets.

Afforestation, Natural Secondary Forest or Dehesas? Looking for the Best Post-Abandonment Forest Management for Soil Organic Carbon Accumulation in Mediterranean Mountains

Forest expansion in Mediterranean mountain areas is a widespread phenomenon resulting from the abandonment of agricultural and pastoral activities during the last century. Therefore, knowledge of the long-term storage capacity of soil organic carbon (SOC) in Mediterranean forests is of great interest in the context of global change. However, the effects of these land uses and covers (natural secondary forest, afforestation with conifers and silvo-pastoral ecosystems (dehesas)) on SOC dynamics are still uncertain. The main objectives of this study were to evaluate physico-chemical soil properties, SOC and nitrogen stocks, and SOC fractions in Mediterranean forests and to assess the effects of tree species, the soil environment (acidic and alkaline), and land management. We selected five land uses and land covers: managed and non-managed afforestation and dehesa (except for alkaline dehesa) and a stage of succession when tree species begin to become established after abandonment. This study concludes that although total SOC stocks are higher in afforested systems with conifers, SOC is stored in less stable carbon pools than in broadleaf forests. In addition, this study confirms that there are marked differences in the results between acidic and alkaline environments. Finally, the management system is also a significant factor, particularly for afforested sites.