Tree Cover Research Articles

Fire, environmental and anthropogenic controls on pantropical tree cover

AbstractExplaining tropical tree cover distribution in areas of intermediate rainfall is challenging, with fire’s role in limiting tree cover particularly controversial. We use a novel Bayesian approach to provide observational constraints on the strength of the influence of humans, fire, rainfall seasonality, heat stress, and wind throw on tropical tree cover. Rainfall has the largest relative impact on tree cover (11.6–39.6%), followed by direct human pressures (29.8–36.8%), heat stress (10.5–23.3%) and rainfall seasonality (6.3–22.8%). Fire has a smaller impact (0.2–3.2%) than other stresses, increasing to 0.3–5.2% when excluding human influence. However, we found a potential vulnerability of eastern Amazon and Indonesian forests to fire, with up to 2% forest loss for a 1% increase in burnt area. Our results suggest that vegetation models should focus on fire development for emerging fire regimes in tropical forests and revisit the linkages between rainfall, non-fire disturbances, land use and broad-scale vegetation distributions.

A Spectral–Spatial Approach for the Classification of Tree Cover Density in Mediterranean Biomes Using Sentinel-2 Imagery

Tree canopy cover is an important forest inventory parameter and a critical component for the in-depth mapping of forest fuels. This research examines the potential of employing single-date Sentinel-2 multispectral imagery, combined with contextual spatial information, to classify areas based on their tree cover density using Random Forest classifiers. Three spatial information extraction methods are investigated for their capacity to acutely detect canopy cover: two based on Gray-Level Co-Occurrence Matrix (GLCM) features and one based on segment statistics. The research was carried out in three different biomes in Greece, in a total study area of 23,644 km2. Three tree cover classes were considered, namely, non-forest (cover < 15%), open forest (cover = 15%–70%), and closed forest (cover ≥ 70%), based on the requirements set for fuel mapping in Europe. Results indicate that the best approach identified delivers F1-scores ranging 70%–75% for all study areas, significantly improving results over the other alternatives. Overall, the synergistic use of spectral and spatial features derived from Sentinel-2 images highlights a promising approach for the generation of tree cover density information layers in Mediterranean regions, enabling the creation of additional information in support of the detailed mapping of forest fuels.

Planning eco-sensitive zones for promoting tree diversity and ecosystem services in urban academic landscapes: a case study from the North-western Indo-Gangetic plain

ABSTRACT Urban academic greenspaces provide a protective environment for the conservation of plants and animals and ecological health benefits to human beings. Several anthropogenic activities and landscape practices lead to patches of natural and built-up areas; therefore, a better understanding of campus tree diversity and ecosystem services among natural and built-up areas may help in biodiversity management. Considering this, we assessed how landscape heterogenicity (i.e. the proportion of natural and built-up/paved surface area) and planning principles influence tree density and diversity patterns in three zones (buffer zone: natural/remnant woodland; transition zone: mixed open grassland and woody plantation; core zone: paved/built-up, grassland, and scattered woody plantation) in the Indian Institute of Science Education and Research (IISER) Mohali campus (Punjab) India. We found a total of 1,993 trees belonging to sixty-eight species, mostly native flora. We found that landscape planning principles significantly influenced tree diversity patterns, with the highest tree diversity in the B3 buffer zone (H: 2.9, PIE: 0.9), which integrated elements of the original landscape and new plantations to optimise ecological value and the lowest diversity in the B2 buffer zone (i.e. H: 0.4; PIE: 0.2) with a monoculture plantation of exotic agroforestry species. We also observed that tree density was negatively influenced by impervious surface area (r = -0.68, p < 0.05) in the core zones and by the plantation of exotic species in the natural areas. The campus diversity supports birds of different feeding guilds (insectivore: 41%, omnivore: 25%, carnivore: 25%, frugivore/nectarivore: 13%, graminivore: 4%, and piscivore: 2%). Additionally, academic buildings planned with high canopy cover and density (45% and 95 ha−1) had reduced the wall temperatures of academic buildings from 12°C to 6°C compared to neighbouring buildings without tree cover. This highlighted the importance of maintaining tree diversity in urban academic institutions to promote urban sustainability.

Changes in morphological and physiological traits of urban trees in response to elevated temperatures within an Urban Heat Islands.

Urban Heat Islands (UHI) are a common phenomenon in metropolitan areas worldwide where the air temperature is significantly higher in urban areas than in surrounding suburban, rural or natural areas. Mitigation strategies to counteract UHI effects include increasing tree cover and green spaces to reduce heat. The successful application of these approaches necessitates a deep understanding of the thermal tolerances in urban trees and their susceptibility to elevated urban temperatures. We evaluated how the photosynthetic thermal optimum (Topt), photosynthetic heat tolerance (T50), and key leaf thermoregulatory morphological traits (leaf area, specific leaf area, leaf width, thickness and LDMC) differ between conspecific trees growing in 'hot [UHI]' vs. 'cool' parts of Montreal, Canada (with a difference of 3.4°C in air temperature), to assess the ability of seven common tree species to acclimation to higher temperatures. We hypothesized that individuals with hotter growing temperatures would exhibit higher Topt and T50, as well as leaf thermoregulatory morphological traits aligned with conservative strategies (e.g., reduced leaf area and increased leaf mass) compared to their counterparts in the cooler parts of the city. Contrary to our a priori hypotheses, leaf area increased with growing temperatures and only four of the seven species had higher T50 and only three had higher Topt values in the hotter area. These results suggest that many tree species cannot acclimate to elevated temperatures and that the important services they provide, such as carbon capture, can be negatively affected by high temperatures caused by climate change and/or the UHI effect. The ability vs inability of tree species to acclimate to high temperatures should be considered when implementing long term tree planting programs in urban areas.

Large changes in vegetation composition seen over the last 50 years in British limestone pavements

Abstract Limestone pavements contain a unique flora, dominated by ferns with a mix of herbaceous species more often found in woodlands, heathlands and grasslands. The crevices between the rocks are known as grikes, they provide a shaded habitat which, depending on pavement structure, can protect plants from grazing. Despite being of conservation importance and supporting a number of rare and scarce plant species there has been very little research into vegetation change in limestone pavements. This study repeated a survey originally conducted between 1972 and 1975. The Ward and Evans survey visited 535 limestone pavement units spread across England, Scotland and Wales and recorded grike vegetation. This study was able to resurvey 516 of those pavements and repeat the survey using the original methods. Expansion of tree and shrub cover has been observed in some pavements but not previously quantified so tree cover was assessed using historic aerial photographs and satellite imagery. On average species richness per pavement increased but there was a very wide range of change in species richness across individual pavement units ranging from a loss of 56 species to an increase of 38. Dissimilarity averaged 0.41. The area of pavement covered by trees or large shrubs increased by 62% between the two surveys but the number of pavements with zero tree cover also increased. Breaking down pavement units into those with low (&lt;5%), medium (5%–30%) and high (&gt;30%) current tree cover shows that species richness increased in open pavements but was reduced in pavements with high tree cover. Pavement units with high tree cover also showed higher dissimilarity and lower levels of indicators of disturbance. In pavements with high tree cover Ellenberg light (L) values were significantly lower than in open pavements. Open pavements showed higher levels of competitive species (based on Grime CSR values) but no change difference in Ellenberg nutrient (N) values. Vegetation in limestone pavements has changed considerably in the period between the two surveys with negative effects of high tree and shrub cover particularly problematic. There is an urgent need for investigation to support management decisions in this habitat. Read the free Plain Language Summary for this article on the Journal blog.

Non‐breeding home range and habitat use by European Pied Flycatcher (Ficedula hypoleuca) in northwest Liberia: apparent resilience to forest degradation?

Identifying population drivers of migratory birds requires knowledge of species' ecology throughout their annual cycle. For most Afro‐Palaearctic migratory species, little is known about non‐breeding habitat use, despite extensive land use change in non‐breeding areas of sub‐Saharan Africa being a key factor implicated in population decline. We radio‐tracked 54 Pied Flycatchers Ficedula hypoleuca at two sites of differing levels of forest disturbance, in Liberia, western Africa, over three non‐breeding seasons to determine home range size and site fidelity, and describe habitat and tree species preference within home ranges. We found high territory fidelity both within and between years, and a preference for well‐wooded landscapes. We found that Pied Flycatcher presence was positively associated with large and mature trees, and areas with a higher density of trees. Pied Flycatchers preferred several tree species that were uncommon within home ranges, and several non‐native tree species likely to support a high invertebrate abundance. Pied Flycatchers preferentially selected areas burnt in the same or previous winter, possibly related to enhanced food resources associated with vegetation regrowth following burning. We also found no significant difference in home range size between sites and similar habitat associations despite differences in habitat disturbance. This suggests that human‐modified habitats may remain suitable for Pied Flycatchers, as long as they retain moderate tree cover, especially larger, taller and more mature trees, whether native or non‐native.

Proposed Multi-ST Model for Collaborating Multiple Robots in Dynamic Environments

Coverage path planning describes the process of finding an effective path robots can take to traverse a defined dynamic operating environment where there are static (fixed) and dynamic (mobile) obstacles that must be located and avoided in coverage path planning. However, most coverage path planning methods are limited in their ability to effectively manage the coordination of multiple robots operating in concert. In this paper, we propose a novel coverage path planning model (termed Multi-ST) which utilizes the spiral-spanning tree coverage algorithm with intelligent reasoning and knowledge-based methods to achieve optimal coverage, obstacle avoidance, and robot coordination. In experimental testing, we have evaluated the proposed model with a comparative analysis of alternative current approaches under the same conditions. The reported results show that the proposed model enables the avoidance of static and moving obstacles by multiple robots operating in concert in a dynamic operating environment. Moreover, the results demonstrate that the proposed model outperforms existing coverage path planning methods in terms of coverage quality, robustness, scalability, and efficiency. In this paper, the assumptions, limitations, and constraints applicable to this study are set out along with related challenges, open research questions, and proposed directions for future research. We posit that our proposed approach can provide an effective basis upon which multiple robots can operate in concert in a range of ‘real-world’ domains and systems where coverage path planning and the avoidance of static and dynamic obstacles encountered in completing tasks is a systemic requirement.

The Phenology of Coffea arabica var. Esperanza L4A5 Under Different Agroforestry Associations and Fertilization Conditions in the Caribbean Region of Costa Rica

This study focused on the phenology of Coffea arabica var. Esperanza L4A5, an F1 interspecific hybrid obtained by crossing commercial varieties with wild genotypes from Ethiopia and Sudan. Most phenological studies on C. arabica have been conducted in traditional high-altitude regions, leaving a gap in the understanding of its behavior in non-traditional areas such as the Caribbean region of Costa Rica. To establish a baseline on the phenological behavior of the Esperanza L4A5 hybrid in this region, we conducted a four-year study examining the effects of different agroforestry associations: (1) Albizia saman; (2) Hymenaea courbaril and Erythrina poeppigiana; (3) Anacardium excelsum and Erythrina poeppigiana; and coffee plots under full sun. Additionally, the phenology of the coffee plants was evaluated under differentiated fertilizations (physical, chemical, and without fertilization), considering meteorological factors such as temperature, humidity, and rainfall. The observed variables included the development of floral nodes, pre-anthesis, anthesis, and fruiting stages. To analyze the relationships between environmental factors, tree cover, fertilization, and the phenological stages, we employed multiple linear regression (MLR), which revealed that both tree cover and physical and chemical fertilizations had significant effects on the presence of developed floral nodes and, consequently, on fruit production. Furthermore, the random forest (RF) model was applied to capture complex interactions between variables and to rank the importance of meteorological factors, tree cover, and fertilization practices. These analyses demonstrated that the Esperanza L4A5 hybrid exhibited viable phenological development under the atypical conditions of the Caribbean region of Costa Rica, suggesting its potential to adapt and thrive in non-traditional coffee-growing areas.

More extremely hot days, more heat exposure and fewer cooling options for people of color in Connecticut, U.S.

It is well-documented that people of color in the U.S. are disproportionately exposed to extreme urban heat. However, most studies have focused on large cities for one point in time, and less is known about how heat exposure changes over time in smaller cities. Here, we present a study of the changing nature of urban heat exposure and cooling strategies for ten cities in Connecticut in the U.S. Our results show that people of color experience more heat exposure and fewer adaptation strategies. They experienced higher overall temperatures, more extremely hot days, and larger increases in heat exposure. Also, they have lower air conditioning ownership rates and lower tree cover. Taken together, the results indicate that people of color are not only exposed to higher temperatures but also disproportionately exposed to increasing temperatures over time. With lower heat adaptation capacity, people of color are more vulnerable to increasing urban heat.

Trends in socioeconomic disparities in urban heat exposure and adaptation options in mid-size U.S. cities

There is ample evidence that Environmental Justice communities experience high levels of extreme heat. However, it is unknown how disparities in urban heat exposure and adaptation options change over time. This study investigates socioeconomic disparities over time in urban heat exposure and adaptation options in eight mid-sized Northeastern cities. We ask: How were socioeconomic factors associated with heat exposure and adaptation options over time? We analyzed disparities at the census block group level and census block level, respectively. At the census block group level, we ran spatial regression models between socioeconomic variables, including race, income, gender, and age, and heat exposure and adaptation variables, including land surface temperature, normalized different vegetation index (NDVI), tree cover, and air conditioning ownership rate. We found that: Low median household income is always associated with high LST and low NDVI from 1990 to 2020; Low percentage of females is always associated with high LST and low NDVI from 1990 to 2020. High percentage of POC is associated with high LST in 2010 and 2020, but not in 1990 and 2000; Low median household income and low percentage of elderly are associated with lower tree cover; High percentage of POC, low percentage of elderly, and low median household income are associated with lower AC rates. In analysis at the census block level by city, we found that disparities in urban heat exposure between predominantly POC and predominantly white communities increased in most cities during 1990-2020. Predominantly POC communities consistently have lower vegetation cover over time in most cities. Disparities in vegetation cover per unit area increased in most cities, whereas disparities in vegetation cover per capita decreased in most cities. Our findings of the trends in disparities in heat exposure and adaptation are useful for forecasting disparities in the future. These findings also suggest that interventions should prioritize cities with increasing disparities in heat exposure and adaptation.

Impact of urbanization on soapnut Sapindus trifoliatus L. tree cover and the need for community involvement: a case study from Kochi, Kerala, India

ABSTRACT The South Indian soapnut tree, Sapindus trifoliatus L, is a midsized evergreen tree from the Indian subcontinent whose fruit can produce natural detergents, biodiesel, and biopesticides. In this study, we document the systematic destruction of soapnut trees through a citizen-supported tree census in an emerging Tier 2 city, Kochi, in South India. In the study, 3580 respondents allowed us to find and map 210 locations of soapnut trees across 411.57 km2. Kochi expanded suddenly in the early 2000s, with a drastic increase in built-up area (126%) and a steady decline in wetlands (57.6%) and croplands (15%). Habitat loss and removal from home gardens has quartered soapnut tree density, to 0.11 km−2. With only 50 trees remaining, the population of the South Indian soapnut will reach the brink of local extinction by 2080.

Chasing cool: Unveiling the influence of green-blue features on outdoor thermal environment in Roorkee (India)

Urban environments in humid subtropical climates, like Roorkee, India, often experience high summer temperatures and uncomfortable outdoor thermal conditions. However, the impact of green-blue landscape configurations on cooling intensity (ΔTa) and outdoor thermal comfort (OTC) is insufficiently understood. This study, conducted in Roorkee during summer 2022, assessed the effect of green-blue landscape configurations on OTC using Physiological Equivalent Temperature (PET) and mean radiant temperature (Tmrt). PET values ranged from slight to extreme heat stress, with statistically significant differences in cooling intensity across varied landscape configurations. Tree shaded canal front locations registered lower Ta (1.6 °C) and Tmrt (9.3 °C). Similarly, shaded canal front locations registered 4.7 °C lower PET than sun-exposed locationsDifferent tree species showed significant variation in ΔTa, with the highest cooling effect (maximum average ΔTa of 3 °C) occurring during the morning hours. Notably Morus alba and Mangifera indica yielded the highest cooling effect, outperforming artificial and mixed shade. Eucalyptus alba, on the other hand, registered adverse comfort conditions. Denser tree canopies and attributes - canopy diameter, leaf area index, and height were strongly correlated to improved cooling performance.Additionally, increasing pervious surfaces and tree cover within 100 m of intervention areas enhanced cooling, with significant effects noted within a 25–50 m radius. This study highlights the role of green-blue infrastructure, particularly the combination of low sky-view factor (SVF), dense canopy trees, and proximity to water, in reducing heat stress. These findings offer crucial insights for climate-responsive open space design, particularly in Indian cities facing rampant urbanization and global warming.

EVALUATION OF PLANTS BASED ON ECOLOGICAL TOLERANCE CRITERIA: A CASE STUDY OF URBAN OPEN GREEN SPACES IN RIZE, TURKIYE

In addition to aggressive urbanization, climate change and ecological challenges also have serious negative effects on urban green areas. Moreover, the selection of inappropriate plants in urban green space landscape projects increases the severity of these negatives. Therefore, inappropriate plant selection is considered a significant threat to the sustainability of urban green spaces. This situation highlights the importance of selecting plants with high ecological tolerance in urban park landscape projects. In this study, all tree, shrub, and ground cover plants identified in 11 urban parks and open green areas in Rize province were evaluated in terms of ecological tolerance criteria (air pollution, drought, wind, temperature, cold, and salinity). A total of 223 plant taxa were examined (77 native, 3 semi-native, 143 exotic), and it was determined that 149 taxa (49 native, 100 exotic) were sensitive to at least one of these criteria, while the remaining 74 taxa (27 native, 47 exotic) had sufficient tolerance to all ecological variables examined. Prunus serrulata Lindl. ‘Kanzan’ was identified as the taxon with the weakest ecological tolerance, and the resilience statuses of the other taxa were presented in the assessment table created. As a result, it was found that there are taxa used in Rize urban open green areas that pose risks against ecological factors, and recommendations were made for future landscape planting projects.

Widespread forest-savanna coexistence but limited bistability at a landscape scale in Central Africa

Abstract Tropical forest and savanna frequently coexist under the same climatic conditions, which has led to the hypothesis that they could represent alternative ecosystem states, stabilized by internal feedbacks. An implication of this hypothesis is that forest and savanna may be bistable and exhibit tipping behavior in response to changing conditions. However, we pose that the local presence of forest and savanna within coexistence landscapes is not sufficient evidence that these are alternative stable states at larger ecosystem scales. Therefore, we explore forest-savanna coexistence and bistability at landscape scale in Central Africa. Using remote sensing data on tree cover, we classify 0.1° x 0.1° (approx. 10 x 10 km) landscapes as homogeneous forest, homogeneous savanna, or coexistence, and analyze the roles of climate, topography and soil sand content in driving their distributions. We find that local coexistence of forest and savanna within landscapes is common and occurs for the whole range of mean annual precipitation in our study area. At low precipitation, however, coexistence increases with topographic roughness and is therefore likely driven by local redistribution of resources rather than internal feedbacks. Coexistence within intermediate and high precipitation landscapes remains unexplained by the studied variables, and may be caused either by heterogeneity in unmeasured drivers or by feedback-driven bistability. At landscape scale, the precipitation ranges for which homogeneous forest and savanna occur have only limited overlap, and this overlap can be largely explained by other external drivers, such as seasonality, soil sand content, and topography. This lack of evidence that homogeneous forest and savanna in Central Africa are alternative ecosystem states at this landscape scale means that transitions between them may be mostly local, resulting in coexistence states. Therefore, we conclude that the likelihood of large-scale tipping between homogeneous forest and savanna ecosystems may be lower than previously thought.

Socio-economic gradients in urban green space access and respiratory health

Abstract Background This study investigates social disparities as one of the drivers influencing the access to green spaces and exposure to natural environments, potentially exacerbating disparities in respiratory health in children. Methods Longitudinal ELSPAC birth cohort study data included 4384 complete case participants born in cities of Brno and Znojmo, examined throughout the years 1990-2010. Estimates on socio-economic status (SES) scores of children’s parents and their education were used as socio-economical predictors. Tree cover density (TCD) calculated as mean canopy closure percentage in the individual walking distance neighbourhoods and the ownership and accessibility of a garden were used as indicators of green space accessibility. Multiple logistic regression models were employed to estimate odds ratios for predictors of respiratory health outcomes, controlling for several confounders. Results Parents’ SES was found to be positively associated with neighbourhood TCD, and this effect was even more pronounced for garden owners. Higher tree cover was then significantly negatively associated with development of acute bronchitis (OR 0.88, CI 95 % 0.84-0.94 for 1 SD of tree cover), while not having a garden (OR 1.81, CI 95 % 1.42-2.33) and living in area with lower tree cover (OR continuously decreasing from 1.88 to 1.68 for lowest and highest quartile respectively) was significantly associated with progression of acute bronchitis into chronic bronchitis in a fully adjusted model. Vice versa, higher tree cover was statistically significantly positively associated with development of allergic rhinitis (OR 1.09, CI 95 % 1.03-1.15), suggesting viability of the novel method of estimation of individual neighbourhood greenness. Conclusions The results suggest protective effect of access to urban green spaces against adverse respiratory outcomes in children. The socially uneven distribution of access emphasizes the importance of urban policies in promoting urban health. #NGEU Key messages • There is a significant protective effect of access to green spaces against respiratory diseases and their progression. • There’s an unequal, but varied distribution of access to green spaces, and social gradient in health, highlighting the importance of urban green space distributive politics.

Planting native trees in degraded grassy woodland does not restore species composition

SummaryRestoration of degraded former Cumberland Plain Woodland by planting of native trees and shrubs was undertaken by Greening Australia (NSW) on the Cumberland Plain, west of Sydney, Australia, from the mid‐1990s. Our study examined the success of this restoration in stands of two ages using species composition as the criterion. The starting point (pasture) and the target (reference woodland) were sampled to document the extent of progress of species composition from pasture through young (3–5 years) and old (9–11 years) restoration stands to reference woodland across three sites at two surveys. Comparisons showed restored stands of both ages differed significantly from pasture, and from each other, showing decreasing similarity between the restoration stands and pasture at all sites. Despite this, species composition in restored stands at all three sites was still significantly different from reference sites, showing that none had achieved the target reference state after 11 years. The trajectory of restored sites between the two surveys was not towards the reference state. Restoration resulted in the establishment of 20 (71%) of the planted species. Recruits from five planted species were found. A further 40 unplanted native ground layer species were found in restoration. Structurally, tree cover increased with time since restoration and was higher in the restored sites. Ground cover, which was very high in pasture was lower in some restored sites. The majority of the unplanted native species were resprouters, and their presence in the above‐ground vegetation was most likely by vegetative resprouting from the bud‐and‐tuber bank as ground cover was lower with the increase in tree cover and shade. Tree and shrub planting by itself has not yet progressed the restored areas to the species composition of reference sites. Additional tools will be needed to assist restoration, specifically the addition of re‐seeder native plants not able to persist through vegetative resprouting after restoration. Measures to control the burden of weeds present in the pasture seed bank are also required.

Monitoring Tree Cover Change Using the CuSum Algorithm: A Case Study in the Southern Western Ghats of Kerala

Monitoring Tree Cover Change Using the CuSum Algorithm: A Case Study in the Southern Western Ghats of Kerala

Rising forest exposure and fire severity from climate warming amplify tree cover losses from wildfire in California

Abstract Warmer temperatures and severe drought are driving increases in wildfire activity in the western United States, threatening forest ecosystems. However, identifying the influence of fire severity on tree cover loss (TCL) is challenging using commonly used categorical metrics. In this study, we quantify regional trends in wildfire-driven TCL as the product of annual burned area, average forest exposure (pre-fire tree cover), and average fire severity (relative loss of tree cover). We quantified these trends with Landsat-based 30 m resolution fire and tree cover datasets for California wildfires from 1986–2021. Rates of TCL rose faster than trends in burned area, with the magnitude of tree cover area loss per unit of area burned increasing by 70% from 0.20 ± 0.05 during 1986–1996 to 0.34 ± 0.10 during 2011–2021. Forest exposure (pre-fire tree cover) within fires increased by 41% from a decadal mean of 23.4% ± 5.5% (1986–1996) to 33.1% ± 7.8% (2011–2021). Increasing forest exposure is associated with a recent expansion of fires in dense northern forests. Concurrently, fire severity (relative TCL) rose by 30% from a decadal mean of 50.4% ± 7.2% during 1986–1996 to 65.6% ± 6.5% during 2011–2021. We developed and applied a simple conceptual framework to quantify the combined effect of wildfires affecting denser forests and burning more severely. The combined effect of these two processes contributed to nearly half (47%) of the TCL since 1986, highlighting that recent changes in burned areas alone cannot explain observed tree cover trends. Linear regression analysis revealed that warmer summers and drier winters were significant drivers of increasing forest exposure, fire severity, and burned area (R 2 from 0.54 to 0.80, p ⩽ 0.001), particularly in the northern forests. Climate extremes had a disproportionate impact on dense forests that were once more resistant to wildfire but now face risks from a shifting wildfire regime.

Robust Trend Analysis in Environmental Remote Sensing: A Case Study of Cork Oak Forest Decline

We introduce a novel methodological framework for robust trend analysis (RTA) using remote sensing data to enhance the accuracy and reliability of detecting significant environmental trends. Our approach sequentially integrates the Theil–Sen (TS) slope estimator, the Contextual Mann–Kendall (CMK) test, and the false discovery rate (FDR) control. This comprehensive method addresses common challenges in trend analysis, such as handling small, noisy datasets with outliers and issues related to spatial autocorrelation, cross-correlation, and multiple testing. We applied this RTA workflow to study tree cover trends in Los Alcornocales Natural Park (Southern Spain), Europe’s largest cork oak forest, analysing interannual changes in tree cover from 2000 to 2022 using Terra MODIS MOD44B data. Our results reveal that the TS estimator provides a robust measure of trend direction and magnitude, but its effectiveness is dramatically enhanced when combined with the CMK test. This combination highlights significant trends and effectively corrects for spatial autocorrelation and cross-correlation, ensuring that genuine environmental signals are distinguished from statistical noise. Unlike previous workflows, our approach incorporates the FDR control, which successfully filtered out 29.6% of false discoveries in the case study, resulting in a more stringent assessment of true environmental trends captured by multi-temporal remotely sensed data. In the case study, we found that approximately one-third of the area exhibits significant and statistically robust declines in tree cover, with these declines being geographically clustered. Importantly, these trends correspond with relevant changes in tree cover, emphasising the ability of RTA to detect relevant environmental changes. Overall, our findings underscore the crucial importance of combining these methods, as their synergy is essential for accurately identifying and confirming robust environmental trends. The proposed RTA framework has significant implications for environmental monitoring, modelling, and management.

Modelling Tree Allometries to Understand the Impact of African Savannah Elephant Herbivory Dynamics on the Vegetation Structure and Tree Cover Change in a Protected Area

ABSTRACTIn landscapes with high elephant density, trees often exhibit more open canopies with fewer branches and foliage due to browsing pressure. This can result in altered tree morphology, with trees exhibiting stunted growth, multiple stems or unusual branching patterns in response to repeated damage from browsing. The objectives of this research were to (i) model the vegetation structure allometries, (ii) assess the impact of African savannah elephant (Loxodonta africana) herbivory on the vegetation structure and (iii) assess tree cover change and vegetation performance over time in Mana Pools National Park in Zimbabwe. We established 26 plots of 30 × 30 m size. Selection of sampling plots was done following several steps. First, a fish net grid with 30 × 30 m polygons was created and projected on the polygon of Mana Pools National Park. The polygons for exclusion zones were then clipped from the fish net grid using the clip tool in ArcGIS Pro 3.0. Then, selection of sampling plots was done initially by stratified random sampling using the Sampling Design Tool add in for ArcGIS Pro 3.0. Landsat images for the years 2003, 2013 and 2023 were used to assess land use land cover (LULC) time series and to calculate Normalised Difference Vegetation Index (NDVI) and Soil Adjusted Vegetation Index (SAVI) for the period. A generalised linear model (GLM) was used to analyse tree allometries. Further statistical investigations were performed using Bayesian piecewise regression (BPR) and Bayesian regression modelling (BRM). Basal area, number of stems, height, long canopy, diameter and basal circumference were all significantly different (p &lt; 0.05) across all sampled plots. The change in growing conditions occurring as a tree grows beyond the reach of the African savannah elephant browsing indicates a natural system breakpoint. The best‐fitting models were a simple linear model and a two breakpoint model for the plant population exposed to elephant herbivory. LULC, NDVI and SAVI confirm evidence of high tree regeneration over 2 decades. Understanding the dynamics in vegetation and LULC changes is critical for effective conservation and management of the habitats for African savannah elephants, as well as for maintaining the health and resilience of forest ecosystems.