Increasing Tree Cover Research Articles

Sustainable Evolution of the Geographic System in the Regional Park “Carrascoy y El Valle” in the Region of Murcia (Southeast Spain)

The region of Murcia, located in the southeast of Spain, has historically been affected by deforestation and desertification processes that favour natural risks, sometimes ending in tragic personal consequences. To address this, at the end of the 19th century an ambitious plan was launched to reforest the mountains in the most problematic river basins. This article aims to study the changes experienced in the geographic mountain system “Carrascoy y El Valle” after reforestation, and their effects on different environmental processes. Two areas were selected to compare the evolution of the tree cover, using photographs from 1928 and current satellite images, and small grids were designed to analyze the current herbaceous and shrub cover. The results show a significant increase in tree cover in parallel to the mulch cover, which was higher in the shady than in the sunny orientation. The distribution of the herbaceous and shrub cover was irregular and unexpectedly higher in the sunny than in the shady areas, probably due to intensive trampling in the shady areas. Overall, the evolution of the geographic system “Carrascoy y El Valle” has been sustainable, with favourable effects on the ecosystem, erosion, landscape, and climate conditions, thus slowing down desertification.

Human infrastructure, surface water and tree cover are important drivers of bird diversity across a savanna protected area-mosaic landscape

ContextProtected areas are important in mitigating threats to biodiversity, including land conversion. Some of the largest protected areas are located in biodiverse savanna systems where a mosaic of land-uses exist beyond their borders. The protected areas located in such systems are often host to threatened species and diverse animal communities. In spite of the ecosystem services birds provide, we do not know how functionally and evolutionary diverse the community is in north-eastern South Africa, or what the drivers of such diversity are inside and outside one of the world’s largest savanna protected areas: Kruger National Park (KNP).ObjectivesFirstly, we aimed to investigate how bird species richness, functional richness, phylogenetic and beta diversity (including its components), and rarity differed across the KNP protected area and its adjacent mosaic. Secondly, we aimed to investigate the habitats and proximity to the KNP boundary that drove patterns across three biodiversity metrics. We also investigated whether differences in sample sizes of the citizen science data we employed, impacted results in a significant manner.MethodsTo investigate our aims, we used bird species records from the Southern African Bird Atlas Project 2 (a citizen science project that collects data at a 5 min latitude by 5 min longitude resolution), and for elucidating drivers of community composition, we used a finer scale remotely sensed product.ResultsHuman infrastructure, water sources and tree cover were overall the most significant and strongest drivers of bird diversity in the region; however, the patterns were complex. Specifically, we found that species richness was strongly and positively influenced by seasonal water and infrastructure mostly inside the protected area (KNP). Most significantly and somewhat concerning, though, were the strong negative effects that infrastructure had on bird functional and phylogenetic diversity inside KNP and, to a lesser extent, inside the mosaic. Seasonal water had a similarly strong but positive effect on species richness in the protected area, a random sub-sample of the former and the mosaic. Tree cover also had a negative and significant effect across the region on phylogenetic diversity and was the strongest driver of this diversity metric.ConclusionsOur results displayed the significant but negative influence that relatively little infrastructure had on bird functional- and phylogenetic diversity inside the KNP protected area despite its positive effect on species richness. Water sources across the protected area-mosaic landscapes also significantly affected regional savanna bird community richness. An increase in tree cover negatively affected phylogenetic diversity inside and outside the protected area as well as the mosaic: a similar finding to other studies in South African savanna systems. We showed the importance of habitat heterogeneity, specifically its components such as infrastructure, freshwater systems and tree cover, and how these impact independently and differently on bird communities across a large biogeographical savanna region.

Increasing tree cover on Irish dairy and drystock farms: The main attitudes, influential bodies and barriers that affect agroforestry uptake

Agroforestry has been cited as a means to increase sustainability and biodiversity at a farm level while allowing farming to continue on the same parcel of land. However, even with profitable financial incentives currently in place to promote agroforestry uptake, uptake remains low in Ireland. This highlights that farmer decision-making regarding the adoption of agri-environmental measures do not follow the assumed economic rationality. To better understand the factors that influence farmer decision-making with respect to tree planting on farms, this study used an extended Theory of Planned Behaviour (TPB) to identify the main attitudes, influencers and intentions of Irish dairy and drystock farmers to planting trees on their land. The barriers to these farmers adopting agroforestry were also investigated. An online cross-sectional survey using a semi-structured questionnaire was administered to a nationally representative sample of the farmers in Ireland. Structural Equation Modelling (SEM) was used to assess the direct and indirect effects of TPB constructs on intention towards adopting agroforestry. According to the SEM analysis, the TPB constructs explained 74% of the variance in intention to plant trees. The results demonstrate that these farmers are mainly driven by their attitude and moral norms which in turn are shaped through the views of their influential people such as advisors and local farmers. The current method of increasing agroforestry uptake is mainly top-down driven and focused on the economic incentives currently in place. New methods to increase agroforestry should focus on encouraging people of influential status within the farming community to promote agroforestry, and through promoting co-design and co-creative systems.

Predator types, urbanization, and tree cover drive top-down control of herbivorous and carnivorous preys in an urban agroecosystem

ABSTRACT Prey-predator interactions hold significant importance, widely acknowledged as crucial processes within ecosystems. Yet, there is a scarcity of empirical data that effectively illustrates the influence of urbanization on such interactions. We performed a common garden experiment utilizing 1250 clay models to assess the predation risks faced by herbivorous and carnivorous prey in an urban agroecosystem in the southern Philippines. Our findings revealed significant differences in attack risks between the trophic levels, with herbivorous caterpillars (n = 246; 53.25%) experiencing higher predation rates compared to carnivorous lizards (n = 216; 46.75%). Interestingly, while the trophic level of the prey did not directly predict predation risk, the presence of predators showed significant effects. Arthropods emerged as the dominant predators of herbivorous prey compared to other predators, whereas mammalian predators predominantly attacked carnivorous prey. The landscape variable also had a strong influence on the risk of predation. We found that increasing tree cover was significantly related to increased predation risk, while built-up showed the opposite. Our research findings support the ‘increasing disturbance hypothesis’, suggesting that rising urbanization rates reduce predator diversity, resulting in a decrease and loss of predation pressure.

Satellite-based evidence highlights a considerable increase of urban tree cooling benefits from 2000 to 2015.

Tree planting is a prevalent strategy to mitigate urban heat. Tree cooling efficiency (TCE), defined as the temperature reduction for a 1% tree cover increase, plays an important role in urban climate as it regulates the capacity of trees to alter the surface energy and water budget. However, the spatial variation and more importantly, temporal heterogeneity of TCE in global cities are not fully explored. Here, we used Landsat-based tree cover and land surface temperature (LST) to compare TCEs at a reference air temperature and tree cover level across 806 global cities and to explore their potential drivers with a boosted regression tree (BRT) machine learning model. From the results, we found that TCE is spatially regulated by not only leaf area index (LAI) but climate variables and anthropogenic factors especially city albedo, without a specific variable dominating the others. However, such spatial difference is attenuated by the decrease of TCE with tree cover, most pronounced in midlatitude cities. During the period 2000-2015, more than 90% of analyzed cities showed an increasing trend in TCE, which is likely explained by a combined result of the increase in LAI, intensified solar radiation due to decreased aerosol content, increase in urban vapor pressure deficit (VPD) and decrease of city albedo. Concurrently, significant urban afforestation occurred across many cities showing a global city-scale mean tree cover increase of 5.3 ± 3.8% from 2000 to 2015. Over the growing season, such increases combined with an increasing TCE were estimated to on average yield a midday surface cooling of 1.5 ± 1.3°C in tree-covered urban areas. These results are offering new insights into the use of urban afforestation as an adaptation to global warming and urban planners may leverage them to provide more cooling benefits if trees are primarily planted for this purpose.

Disrupted montane forest recovery hinders biodiversity conservation in the tropical Andes

AbstractAimAndean montane forests are biodiversity hotspots and large carbon stores and they provide numerous ecosystem services. Following land abandonment after centuries of forest clearing for agriculture in the Andes, there is an opportunity for forest recovery. Field‐based studies show that forests do not always recover. However, large‐scale and long‐term knowledge of recovery dynamics of Andean forests remains scarce. This paper analyses tropical montane forest recovery trajectories over a 15‐year time frame at the landscape and tropical Andean scale to inform restoration planning.MethodsWe first detect “potential recovery” as areas that have experienced a forest transition between 2000 and 2005. Then, we use Landsat time series analysis of the normalized difference water index (NDWI) to classify four “realized recovery” trajectories (“ongoing”, “arrested”, “disrupted” and “no recovery”) based on a sequential pattern of 5‐yearly Z‐score anomalies for 2005–2020. We compare these results against an analysis of change in tree cover to validate against other datasets.ResultsAcross the tropical Andes, we detected a potential recovery area of 274 km2 over the period. Despite increases in tree cover, most areas of the Andes remained in early successional states (10–25% tree cover), and NDWI levelled out after 5–10 years. Of all potential forest recovery areas, 22% showed “ongoing recovery”, 61% showed either “disrupted” or “arrested recovery”, and 17% showed “no recovery”. Our method captured forest recovery dynamics in a Peruvian arrested succession context and in landscape‐scale tree‐planting efforts in Ecuador.Main conclusionsForest recovery across the Andes is mostly disrupted, arrested or unsuccessful, with consequences for biodiversity recovery and provision of ecosystem services. Low‐recovery areas identified in this study might be good candidates for active restoration interventions in this UN Decade on Restoration. Future studies could determine restoration strategies and priorities and suggest management strategies at a local planning scale across key regions in the biodiversity hotspot.

Spatio-temporal dynamics of tree cover change in semi-arid Ghana: evidence from Sentinel-2 time series data

ABSTRACT Trees provide vital ecosystem services, yet anthropogenic activities have continued to reduce tree cover (TC) globally, leading to disparities in the distribution of ecosystem services at various scales. Similarly, empirical analysis of indicators that measure variations in TC at various temporal and spatial scales is limited in the semi-arid regions where global environmental challenges such as climate change are already affecting TC distribution. This paper quantified recent (2017 - 2019) TC changes in the semi-arid region of Ghana using Sentinel-2 times series data and the application of landscape metrics. The results showed that TC declined by 30% within two years. Urbanizing areas showed more rapid TC depletion rates, while some rural areas experienced a slight increase in TC. The findings suggest the need for local environmental governance by consolidating actions towards conserving semi-arid TC. Sustainable charcoal and fuelwood production are imperative for a long-term sustainable supply of ecosystem services.

Distinguishing forest types in restored tropical landscapes with UAV-borne LIDAR

Forest landscape restoration is a global priority to mitigate negative effects of climate change, conserve biodiversity, and ensure future sustainability of forests, with international pledges concentrated in tropical forest regions. To hold restoration efforts accountable and monitor their outcomes, traditional strategies for monitoring tree cover increase by field surveys are falling short, because they are labor-intensive and costly. Meanwhile remote sensing approaches have not been able to distinguish different forest types that result from utilizing different restoration approaches (conservation versus production focus). Unoccupied Aerial Vehicles (UAV) with light detection and ranging (LiDAR) sensors can observe forests` vertical and horizontal structural variation, which has the potential to distinguish forest types. In this study, we explored this potential of UAV-borne LiDAR to distinguish forest types in landscapes under restoration in southeastern Brazil by using a supervised classification method. The study area encompassed 150 forest plots with six forest types divided in two forest groups: conservation (remnant forests, natural regrowth, and active restoration plantings) and production (monoculture, mixed, and abandoned plantations) forests. UAV-borne LiDAR data was used to extract several Canopy Height Model (CHM), voxel, and point cloud statistic based metrics at a high resolution for analysis. Using a random forest classification model we could successfully classify conservation and production forests (90% accuracy). Classification of the entire set of six types was less accurate (62%) and the confusion matrix showed a divide between conservation and production types. Understory Leaf Area Index (LAI) and the variation in vegetation density in the upper half of the canopy were the most important classification metrics. In particular, LAI understory showed the most variation, and may help advance ecological understanding in restoration. The difference in classification success underlines the difficulty of distinguishing individual forest types that are very similar in management, regeneration dynamics, and structure. In a restoration context, we showed the ability of UAV-borne LiDAR to identify complex forest structures at a plot scale and identify groups and types widely distributed across different restored landscapes with medium to high accuracy. Future research may explore a fusion of UAV-borne LiDAR with optical sensors, and include successional stages in the analyses to further characterize and distinguish forest types and their contributions to landscape restoration.

Systematic acoustic surveys inform priority conservation areas for koalas in a modified landscape

ContextLandscape modification due to urbanisation, agriculture and other human activity can have considerable impact on species’ distributions. Understanding the influence of both site and landscape level characteristics is essential for guiding conservation actions.ObjectivesOur study aimed to determine the influence of site and landscape level characteristics on the distribution of koalas and to identify areas for conservation action in a modified landscape.MethodsWe used passive acoustic surveys undertaken from October 2019 to January 2020 to determine site occupancy by koalas at 123 sites on the Mornington Peninsula, Victoria, Australia. We extracted variables for each site (within 100 m of recorders) and landscape (within 1 km of recorders) within a GIS. Site variables were tree cover, land use and soundscape, and landscape variables were tree cover, fragmentation, road density, and watercourse length.ResultsSite variables did not have an influence on site occupancy by koalas. Landscape-scale tree cover positively influenced, and road density negatively influenced site occupancy. We used our model to predict site occupancy in one-hectare grid cells across the landscape and found that public land was three times as likely as land under private tenure to have high probability of koala presence. Based on our results, increasing tree cover in landscapes where there already is 30% to 68% tree cover and a sealed road density of < 1 m per hectare would have the greatest benefit for koalas. Approximately 85 km2 (11%) of the Mornington Peninsula meets these criteria, with 87% of that land under private tenure.ConclusionsLandscape context is of primary importance for conservation of koalas in a modified landscape. Modelling should be used to improve the effectiveness of conservation actions.

Carbon Sequestration Potential of Commercial Agroforestry Systems in Indo-Gangetic Plains of India: Poplar and Eucalyptus-Based Agroforestry Systems

Climate change, land degradation, and desertification lead to the loss of carbon present in the soil and plants. The carbon dioxide (CO2) concentration in the atmosphere has reached 412 ppm. This is a rise of 47% since the start of the industrial period, when the concentration was close to 280 ppm. Therefore, the sequestration of carbon from the atmosphere to earth is the need of the hour. Many scientists have suggested agroforestry as a potent instrument for climate change mitigation as well as to fetch lucrative benefits. The Indian government is also promulgating tree-based systems for increasing tree cover up to 33% of the total geographical area to mitigate climate change. Therefore, the expansion of the commercial agroforestry system of fast-growing tree species producing higher biomass could be a sustainable and ecologically benign technique to sequester carbon, increase green cover, and improve the financial status of farmers. This review highlights the commercial agroforestry systems, biomass and carbon sequestration potential, and case studies of poplar and eucalyptus. The species such as poplar (Populus deltoides), nilgiri (Eucalyptus spp.), subabul (Leucaena leucocephala), tree of heaven (Ailanthus excelsa), willow (Salix spp.), malabar neem (Melia dubia), cadamba (Neolamarckia cadamba), and white teak (Gmelina arborea) are the suitable tree species for carbon sequestration under agroforestry. Among these species, poplar and eucalyptus are major agroforestry tree species that have been adopted by millions of farmers in India since the 1990s. Indo-Gangetic plains are considered the birthplace of commercial or industrial agroforestry, as poplar and eucalyptus are widely planted. This review reports that poplar and eucalyptus have the potential to sequester carbon stock of 212.7 Mg C ha−1 and 237.2 Mg C ha−1, respectively. Further, the net carbon sequestration rate in poplar and eucalyptus was 10.3 and 12.7 Mg C ha−1 yr−1, respectively. In conclusion, the commercial agroforestry system was very successful in the Indo-Gangetic regions of the country but needs further expansion with suitable compatible crops in different parts of the country.

Understory plant communities fail to recover species diversity after excluding deer for nearly 20 years

White-tailed deer ( Odocoileus virginianus) have been overabundant in eastern North America for more than five decades, resulting in depauperate understories and ricocheting effects on higher trophic levels. Even after deer populations are reduced, understory plant communities may fail to recover for an unknown length of time due to persistent legacy effects. We surveyed understory plant communities in six deer exclosures and paired reference plots in northwestern Pennsylvania to determine the degree to which 19 years of deer exclusion was sufficient for recovery of species richness, diversity, percent cover, and understory structural complexity. We observed a 2.3-fold increase in tree cover and a 60% reduction in fern cover in the ground layer, as well as a 114-fold increase in foliage density between 80 and 200 cm above ground level, in exclosures compared to reference plots. However, the exclosures did not permanently support higher overall percent cover, species richness, or diversity in the ground layer, nor did we detect any meaningful divergence in community composition between exclosures and reference plots. We conclude that 19 years of release from chronic over-browsing are sufficient to restore understory structural complexity, but recovery of diversity in the ground layer will require more time or direct intervention.

Steal the rain: Interception loses and rainfall partitioning by a broad-leaf and a fine-leaf woody encroaching species in a southern African semi-arid savanna.

Woody plant encroachment (WPE) has been found to alter ecosystem functioning and services in savannas. In rain-limited savannas, increasing woody cover can reduce streamflow and groundwater by altering evapotranspiration rates and rainfall partitioning, but the ecological relevance of this impact is not well known. This study quantified the altered partitioning of rainfall by two woody plant structural types (fine- and broad-leaved trees) across a gradient of encroachment in a semi-arid savanna in South Africa. Averaged across both plant functional types, loss of rainfall through canopy interception and subsequent evaporation roughly doubled (from 20.5% to 43.6% of total rainfall) with a roughly 13-fold increase in woody cover (from 2.4 to 31.4m2/ha tree basal cover). Spatial partitioning changes comprised fourfold increases in stemflow (from 0.8% to 3.9% of total rainfall) and a decline in throughfall proportion of about two-fifths (from 80.2% to 47.3% of total rainfall). Changes in partitioning were dependent on plant functional type; rainfall interception by the fine-leaved multi-stemmed shrub Dichrostachys cinerea was almost double that of the broad-leaved tree Terminalia sericea at the highest levels of woody encroachment (i.e., 49.7% vs. 29.1% of total rainfall intercepted at tree basal area of 31.4m2/ha). Partitioning was also dependent on rainfall characteristics, with the proportion of rainfall intercepted inversely related to rainfall event size and intensity. Therefore, increasing tree cover in African grassy ecosystems reduces the amount of canopy throughfall, especially beneath canopies of fine-leaved species in smaller rainfall events. Rainfall interception traits may thus confer a selective advantage, especially for fine-leaved woody plant species in semi-arid savannas.

Determining the Temporal Change in Tuz Gölü between 2000-2020 by Remote Sensing

Changes in the landscape become extremely destructive and many heritage values and resources are irreversibly lost. The speed, frequency and magnitude of these changes in the landscape increased in the second half of the 20th century, especially with the impact of human activities. Remote sensing is the most widely used method for determining the change in the landscape. In the research, MNDWI, NDVI and NDMI techniques, which are frequently applied in remote sensing, were used in order to determine the landscape change in Salt Lake. Thus, the changes in the built area, water surface and land cover between the years 2000-2020 in Salt Lake were determined. According to the MNDWI and NDMI Analysis results, a decrease was observed in the water surface width and moisture content in Salt Lake between 2000 and 2020. In the steppe areas south of Salt Lake, the increase in tree cover due to the change in land use type was determined by NDVI analysis. Therefore, it is possible to say that there is an increase in the amount of moisture in these areas. In addition, it was determined that the increase in agricultural activities in the region caused a change in land use types and the amount of green space in the region changed at this rate. With the mentioned methods, negative changes in the landscape as a result of human activities on the landscape can be determined practically. Thus, it will be possible to predict the negative consequences of climate change and take precautions.

Context dependency in interference competition among birds in an endangered woodland ecosystem

AbstractAimMuch research has quantified species responses to human‐modified ecosystems. However, there is limited work on how human‐modified ecosystems may reshape competitive interactions between species. Using a 19‐year study across 3 million ha, we aimed to answer the question: Are levels of interference competition between bird species context dependent and influenced by habitat structure and productivity? We focussed on the hyper‐aggressive behaviour of the Noisy Miner (Manorina melanocephala), which is recognized as a key threatening process for other woodland bird species in Australia. Whether environmental conditions such as amount of forest cover and net primary productivity (NPP) mediate the Noisy Miners' impact remains untested at large spatiotemporal scales.LocationTemperate woodlands of south‐eastern Australia.MethodsWe gathered data on bird site occupancy from repeated surveys of field sites and assembled satellite data on tree cover and NPP. We constructed Bayesian multi‐species occupancy/detection models of bird species in woodland patches and tested the fixed and interactive effects of Noisy Miner presence, the amount of tree cover, NPP, and time. We quantified the responses of 31 species, many with known interactions with the Noisy Miner documented previously at fine spatial scales.ResultsWe identified negative associations between the Noisy Miner and 18 bird species, including, unexpectedly, both small and large bodied taxa. Site occupancy in some species was influenced by interactions between Noisy Miner presence and increasing amounts of tree cover or productivity. For some species, interference competition by the Noisy Miner is context‐dependent and mitigated by increasing tree cover and/or increasing NPP.Main ConclusionsOur analyses revealed that woodland bird conservation in our study region will be promoted by protecting refugia characterized by areas of high NPP and high tree cover. Preventing vegetation clearing that reduces tree cover could reduce interference competition by the Noisy Miner on parts of the remaining woodland bird community, including species of conservation concern.

Woody encroachment affects multiple dimensions of ant diversity in a neotropical savanna

Abstract Although savanna woody encroachment has become a global phenomenon, relatively little is known about its effects on multiple dimensions and levels of savanna biodiversity. Using a combination of field surveys, a species‐level phylogeny, and functional metrics drawn from a morphological dataset, we evaluated how the progressive increase in tree cover in a fire‐suppressed savanna landscape affects the taxonomic, functional, and phylogenetic diversity of neotropical ant communities, at both the alpha and beta levels. Ants were sampled along an extensive tree cover gradient, ranging from open savannas to forests established in former savanna areas. Variation in tree cover had a significant influence on all facets of diversity at the beta level, whereas at the alpha level tree cover variation affected the taxonomic and functional but not the phylogenetic diversity of the ant communities. In general, ant community responses to variation in tree cover were largely non‐linear as differences in taxonomic alpha diversity and in the taxonomic, functional, and phylogenetic composition of the sampled communities were often much stronger at the savanna/forest transition than at any other part of the gradient. This indicates that savanna ant communities switch rapidly to an alternative state once the savanna turns into forest. Ant communities in the newly formed forest areas lacked many of the species typical of the savanna habitats, suggesting that the maintenance of a fire suppression policy is likely to result in a decrease in ant diversity and in the homogenisation of the ant fauna at the landscape scale.

Grassland conservation and restoration in India: a governance crisis

Grasslands are contested ecosystems due to our scant understanding of their ecological and socioeconomic roles and also due to the ambiguity in understanding what exactly constitutes them. This problem escalates in the absence of proper governance. In this paper, we explore the historical accounts of Indian grasslands to trace how they have shaped contemporary grassland conservation and restoration policies. The paper draws from the concept of Biome Awareness Disparity and links it to grassland degradation through misleading nomenclature and flawed interventions rooted in misplaced governance. We found that Indian grasslands are negatively affected by India's commitment to global goals (with quantified targets of increasing tree cover) and the involvement of multiple government bodies in grassland management. This conundrum is fueled by the strong forest bias within government bodies and nongovernmental organizations. Based on the findings, we propose that India needs a more cohesive national policy framework and a robust ecosystem classification system to successfully conserve and restore grasslands.

Irrecoverable carbon in mountains and the global mitigation potential of agroforestry and increased tree cover in mountain agricultural systems

Irrecoverable carbon in mountains and the global mitigation potential of agroforestry and increased tree cover in mountain agricultural systems

Ecosystem Functioning of the Loess Plateau in China from Vegetation Restoration Relied Largely on Climate

Climate change and anthropogenic replantation are supposed to greatly change vegetation coverage and ecosystem stability and functions, e.g., net primary productivity (NPP), evapotranspiration (ET) and water use efficiency (WUE). Our study compared WUE of nature- and human-induced forest cover increase on the Loess Plateau since 2000 using satellite-derived Vegetation Continuous Fields (VCF), NPP, ET. This study also applied over 30 years of model-based NPP and meteorological observations to compare the stability and changes brought up by the Grain for Green Project. The result showed that the average forest coverage fraction increased from 7.1% (~4.5 × 104 km2) in 2000 to 11.2% (~7.3 × 104 km2) in 2014. Artificial forest cover increase occupied 76.43% of the significantly increasing tree cover regions. The role of revegetation practice in NPP and ET became gradually more dominant than climate factors in artificial forests from the northern to the southern part of the Loess Plateau. For areas experiencing limited forest coverage increase, artificial forest areas showed higher WUE than natural forest areas under similar mean annual precipitation (MAP). The difference in stability was small between neighboring natural and artificial forest areas. The northwest of the Loess Plateau had an increasing resilience, whereas the south of the Plateau had an increased resistance to precipitation and temperature change. The higher dependency of the northern reforested areas on climate fluctuation indicates a growing threat of water scarcity to the sustainability of anthropogenic reforestation in semi-arid regions.

ARIMA-based forecasting of the effects of wildfire on the increasing tree cover trend and recurrence interval of woody encroachment in grazing land

Invasive tree removal from grazing lands using costly brush management practices is widely employed. However, wildfire-like natural events can also prevent the increasing trend of woody tree encroachment in grazing lands at no cost, instead of expensive prescribed burning. This study aims to estimate the effects of wildfire in 2002 on woody tree encroachment trends during the post-wildfire period (2003–20), as well as the recurrence interval of the encroachment of a wildfire site in the United States. An autoregressive integrated moving average (ARIMA) model was employed to forecast the tree cover during the post-wildfire period. We found that the pre-wildfire tree cover was 4.26% of the total area, which decreased to 1.42% immediately after the wildfire. During 2003–20, wildfire contributed to an average lowering of woody-dominated areas of the wildfire site by 6.59%. The wildfire-recovered grazing area was converted to a woody area again after 8 years, which was due to recurring woody encroachment. Therefore, it is critical to implement brush management strategies to stop the recurrence of woody plant encroachment following wildfire. • Grazing lands in the USA are increasingly being invaded by woody trees. • Wildfire reduces tree cover area immediately. • Wildfire has a long-term reduction effect on invasive tree-dominated areas. • Within a few years, reclaimed grasslands converted into woody areas. • To maintain wildfire-recovered rangelands, proactive and early management strategies are required.

Non-linear effects of meteorological variables on cooling efficiency of African urban trees.

Urban tree cover is widely regarded as an environmentally-friendly and effective urban cooling approach. Meteorological variables, including air temperature, wind speed, and humidity, have complex impacts on the cooling efficiency (CE) of urban trees (i.e., the negative ratio of the land surface temperature change to the tree cover percentage change). This means that increasing the urban tree cover to alleviate heat stress is not necessarily suitable for cities with different climates. African cities are confronted with larger heat risks but lack considerations for the effectiveness of urban tree cooling in urban planning. In this study, 40 African major cities with population greater than 500,000 in different climatic regions were selected, and 1459 CEs during each city's corresponding warmest 3 consecutive months were calculated combined with the availability of meteorological data. The generalized additive models revealed the non-linear impacts of air temperature/temperature dew point difference on CE, which were more evident in arid cities. The CE of urban trees actually increased and then decreased along with the increase of air temperature/temperature dew point difference, and the turning point were 34 °C/26 °C, respectively. African cities would have different frequencies of warm days with an air temperature over 34 °C under different Shared Socioeconomic Pathways within the next 30years. Specially, the cities around Sahel would suffer up to 40-60%days over 34 °C, which meant their urban tree CE would decrease along with air temperature increase. This study highlighted that in African cities, especially those with arid climate, it was unadvisable to only count on increasing tree cover to alleviate urban heat stress in the warming future, which called for other combined cooling strategies.