High Tree Density Research Articles

Factors affecting early red oak (Quercus rubra L.) regeneration near its northern distribution limit in Quebec

Red oak is an important species within the North American landscape, with climate change projections indicating a potential northward shift in its distribution. However, understanding the factors influencing its regeneration success at the northern limit remains limited. Site conditions and seed provenance adaptability may play critical roles. To bridge this knowledge gap, we conducted a seed transfer study in two northern red oak stands in Quebec. We firstly investigated stand regeneration history through dendrochronological characterization. Then, we monitored the survival and growth of saplings for four red oak provenances across a south-to-north gradient in field and greenhouse settings, with varying soil nutrient levels due to fertilization, and with or without protection from large herbivores. Results indicated that stands have similar age structures with red oak establishment coinciding with the last major fire disturbance in the early 1920s. However, tree species composition and density differed, suggesting differences in fire disturbance regime or ecological succession status prior to fire. Site had the largest influence on red oak regeneration, with the highest tree density and soil water availability site exhibiting a 29% higher survival rate. Protection against large herbivores also significantly impacted red oak seedling performance, leading to a 16% higher survival rate. Germination, survival and growth also significantly differed between provenances. The local (northernmost) provenance exhibited the poorest overall performance with 28 to 42% lower germination, survival and growth rates, while the two southernmost provenances exhibited superior germination and sprout survival. An increase in soil nutrient availability was beneficial to red oak in the greenhouse, but only marginally benefited survival and growth in the field, suggesting that this factor is of less importance than other factors (e.g., water and light availability) for red oak early regeneration. The findings of this study suggest that silvicultural efforts to favor red oak should focus on site and provenance selection, and that water availability is currently limiting red oak regeneration success at acorn and early seedling life stages (i.e., 1 year old seedlings) near its northern distribution limit.

Diversity, structure, and composition of melliferous and non-melliferous vegetation surrounding meliponaries of the Yucatan Peninsula, Mexico

Background: Although the loss of Melipona beecheii colonies in meliponaries suggests insufficient availability of melliferous blooming plants, there is limited knowledge about the diversity and conditions of the surrounding vegetation. Question: What is the diversity, structure, and composition of the melliferous and non-melliferous vegetation surrounding meliponaries, and how does it affect the availability of food sources for bees? Study site and dates: The vegetation surrounding nine meliponaries, three in each political state of the Yucatán Peninsula encompassing the main vegetation types, was studied in 2022 and 2023. Methods: Four 150-meter-long transects with the point-centered quadrants method were traced in each meliponary to estimate plant species composition, the availability of melliferous and blooming plants (IVI), diversity parameters (Hill-numbers), tree density, and diameter per strata. Results: 312 taxa, 250 genera, and 73 plant families were recorded. In five meliponaries, blooming melliferous plants accounted for less than 9 % of the IVI, with one meliponary having no blooming species. The highest diversity was found in a meliponary surrounded by semi-evergreen forest. The high stratum had a mean tree height of 5.5 (SD ± 2.9) meters and 3,390 (SD ± 2,702) trees/hectare across vegetation types. The tree diameter was lowest in meliponaries located in the semi-deciduous forest. Conclusions: The meliponaries are surrounded by young secondary vegetation with high density of small trees and predominance of the low stratum. We found a similar vegetation diversity among meliponaries and scarce blooming melliferous plants. Human activity seems to impact plant diversity and food availability for M. beecheii.

Sparse large trees in secondary and planted forests highlight the need to improve forest conservation and management

Large trees are essential for carbon storage and biodiversity conservation. While an increasing number of studies have focused on large trees in primary forests, little is known about them in secondary and planted forests. We surveyed 86,936 trees in secondary forests and 91,294 trees in planted forests in Zhejiang, China, to investigate the distribution patterns and determinants of large trees in these forests. We found a mean density of large trees (DBH ≥ 30 cm) of 15 ± 13 stems ha−1 in secondary forests and 11 ± 9 stems ha−1 in planted forests. Moreover, the mean density of trees with DBH ≥ 60 cm was 0.36 stems ha−1, indicating that large trees are particularly rare in secondary and planted forests. These large trees were primarily occurred in secondary forests that living in high-elevation area with less human exploitation and colder and wetter climates, and in planted forests with higher species richness and lower tree density. In addition, the density of large trees in these forests significantly increased with tree species richness and decreased with increasing tree density. These results indicate that the sparse large trees were the legacy of historical human activities in the studied area, but currently, the development of large trees is still limited by the improper forest structure characterized by low species diversity and high tree density. To better conserve large trees, there is an urgent need for enhanced conservation policies for secondary forests, such as establishing forest parks for forests with large trees, and implementing near-natural forest management practices for planted forests, which include planting mixed native tree species and maintaining moderate tree density.

Assessing structure, spatial patterning, and size class distribution of miombo woodland species along a precipitation gradient

Our study investigates the intricate ecological mechanisms shaping miombo woodlands across a rainfall gradient in Zimbabwe. We comprehensively analysed vegetation structure, tree morphology, and spatial patterning across three distinct ecological regions characterized by varying mean annual precipitation (MAP). Results reveal that taller and larger trees are prevalent in the more humid site, while higher tree density is observed in the drier site. The spatial analysis highlights a significant aggregation of adult miombo species across all sites, with juveniles exhibiting a propensity to cluster around adult trees. These findings underscore the pivotal role of ecological gradients, such as precipitation, in shaping miombo woodland structure. However, the absence of clear spatial patterns across the rainfall gradient suggests that precipitation may have less influence on the spatial distribution of miombo trees. Understanding these complex ecological dynamics is essential for developing targeted conservation and management strategies that align with the unique attributes of miombo woodlands, critical ecosystems within the African landscape particularly vulnerable to global climate change.

Comparison of nectar and pollen resources in various Tilia species. A case study from southern Poland

Management of food resources is considered fundamental for supporting insect pollinators, whose abundance shows a downward trend on the global scale. Here, the nectar and pollen production (per flower, per 1 m2 of tree crown), the composition of nectar carbohydrates and the levels of pollen proteins was evaluated in eight Tilia species (Malvaceae) growing in SE Poland. In the warm-summer continental climate, Tilia species can improve nectar and pollen resources mainly in June/July. Although the flowering period of each species is short (8.0–14.7 days), appropriate selection of species can extend the availability of food for more than a month. However, the considerable variations in the flowering onset (11.2–20.1 days) may cause significant inter-seasonal shifts in food accessibility.The nectar with its highly changeable sugar concentration (29.5–77.4%) was composed of sucrose, glucose, and fructose; protein content in pollen was 7.2–16.8%. The mean sugar yield was in the range of 0.95–19.1 g per 1 m2 (T. amuriensis – T. platyphyllos, respectively), whereas the mean pollen yield was 1.37–4.1 g per 1 m2 of tree crown (T. amuriensis – T. × euchlora, respectively). Significant year-to-year fluctuations of sugar and pollen yield in linden trees have to be taken into account in conservation schemes, and the introduction of other flowering plants with more stable sugar and pollen production should be considered in an area with a high density of linden trees. Linden flowers mainly support honey bees; nevertheless, wild pollinators (bumble bees, solitary bees, and dipterans) can also benefit from linden floral resources.

Water purification – an essential service from forest ecosystems, and farming practices in the Pong River Basin, Northeast Thailand

Deforestation often results in biodiversity depletion, land degradation, and loss of forest ecosystem services such as water purification. This research examined the relationship between natural forest areas in the Pong River Basin (PRB), northeast Thailand, and water quality in the Pong River system, one of the country's most polluted rivers. Water parameters were measured in 15 tributaries where samples were collected 500 m upstream from the outlets, and 2–5 m from the streambanks during summer, rainy, and winter seasons in 2021. Land use and land cover (LULC) were classified by a supervised classification method in QGIS using LANDSAT8 satellite imagery and USGS SRTM data. Vegetative surveys were conducted near the sampling locations which included species richness and density. Water characteristics at all the sites were under Thailand's Water Quality Standard, except a level of biological oxygen demand (avg. BOD = 3.52 mg/L). The upper PRB, covered with more forested areas with higher tree densities along streambanks (∼43 % of the basin, 619 trees/ha), revealed better water quality including a higher concentration of dissolved oxygen (avg. DO = 7.57 mg/L) and a lower level of fecal coliform bacteria (avg. FCB = 642 MPN/100 mL). In contrast, the lower PRB having larger areas of farmlands and smaller forests (∼63 % and 23 %, respectively) yielded higher concentrations of FCB (avg. = 1,353 MPN/100 mL) and phosphates (avg. PO43- = 0.34 mg/L). Positive correlations were found between the amount of forestlands (% of the sub-basin) with DO and nitrate concentrations (r = 0.468 and 0.409, p-value < 0.05, respectively), while agricultural areas were correlated with FCB (r = 0.414, p-value < 0.05). Amounts of forests determine water purity, while farmlands denoting dirtiness. These findings show that water purification is an essential forest ecosystem service, critical for stream health.

Mangrove vegetation response to alteration in coastal geomorphology after an earthquake in Andaman Islands, India

The 2004 Sumatra-Andaman earthquake caused a devastating tsunami and shifts in land elevations, which had an instantaneous as well as the long-term impact on the Andaman Islands. Especially, the coastal uplift and subsidence has altered the tidal regime, leading to mass mortality and degradation of mangroves (∼150 sq. km). The tectonic shift in the Andaman archipelago has created three broader geographical units: North Andaman with coastal uplift (∼1.3 m) – sea level drop (SLD) scenario; Middle Andaman with minor to no change in coastal geomorphology – no change scenario; and South Andaman with coastal subsidence (∼1.1 m) – sea level rise (SLR) scenario. How these changes in the tidal regime have influenced mangrove vegetation remains less understood. Therefore, we assessed mangrove vegetation characteristics across the Andaman Islands to examine mangrove response to coastal uplift and subsidence after 18 years since the disturbance. The uplifted sites mimicking the SLD scenario appeared more destructive to mangroves (tree density - 771/ha) in comparison to subsided sites mimicking the SLR scenario (tree density - 937/ha), while no change sites with the highest tree density (1288/ha) showed lowest impacts to mangrove. The species diversity (H’=Shannon-Wiener index) within recruitment cohorts (seedlings: <1 cm DBH and saplings: ≥1 cm and <5 cm DBH) sapling (H’=1.57), and seedling (H’=1.48) was significantly higher than the trees (H’=1.20). Rhizophora apiculata and Ceriops tagal were the dominant species (cumulative IVI 60%) found in survived mangrove forests demonstrating their high resilience for sudden changes in tidal regime. Our study provided a comprehensive account of mangrove vegetation response after a major disruptive event in 2004. Long-term monitoring of these novel sites would enhance our understanding of mangrove response to sea level change, which can also provide significant insights for the restoration and management of mangroves.

Using prescribed fires in young forests: A pyrosilvicultural approach

Prescribed burning is an effective treatment to reduce the risk of very severe wildfires. Many forests, however, are ill-suited for prescribed fire, because of high fuel loads, high tree densities, or young stands that are vulnerable to low intensity fires. Utilizing prescribed fire in reforested stands established after high-severity fires can protect against further losses from subsequent wildfires (“reburn” fires). Only a handful of studies provide practical guidance on how and when to burn young forests. We apply the concept of “pyrosilviculture” to suggest ways in which pre-fire silvicultural treatments can make prescribed burns more effective across a variety of age classes and structures. We also update results from a study in which several age classes of stands (12-, 22-, 32-, and 100-year-old) were burned experimentally on the same day. This focuses on a key question for managers: how to determine the right stand age at which prescribed fires may become feasible. As expected, older stands were more resistant to damage and had higher survival rates. If tree survival during prescribed fires is a primary objective, then a conservative approach is to wait until stands are age 30 before instituting prescribed fire. This is likely an overestimate of the minimum age, given that the prescribed fires applied in this study occurred during especially dry conditions. Under different objectives, higher mortality may be considered beneficial if it creates low-density, high-complexity stands that are similar to historic conditions.

Demography, Structure, and Composition of a Low-Disturbance Forest in Luzon, Philippines

Tropical forests continue to face deforestation in countries such as the Philippines. To look at the long-term behavior of forests in response to intrinsic and extrinsic factors, continual monitoring of forest dynamics is needed. To do this, we established a 2-ha permanent tropical forest plot in a low-disturbance area in Maluyon, Philippines. We addressed three main questions: 1) How does the plot change through time? 2) How do different species in the plot change through time? 3) Would the responses differ by tree size? We measured, mapped, and identified all trees &gt;1 cm in diameter in 2011. In 2015, we re-measured surviving trees and measured, mapped, and identified recruits. A total of 177 tree species were found in the plot. The forest exhibited a mean growth rate of 0.054 cm/year, mortality rate of 0.011%/year, and recruitment rate of 0.019%/year. Overall growth and mortality rates were lower in Maluyon than in other plots, possibly due to the forest’s high tree density and low disturbance. Species-specific rates revealed the presence of both the growth-survival and the stature-recruitment trade-offs. Size class analysis showed higher growth rates in large-sized than in small-sized trees. In contrast, small-sized trees exhibited a higher mortality rate compared to large-sized trees, likely due to density dependence. Key findings of the study may be utilized to increase the success rate of restoration efforts in this watershed. Using a mix of fast-growing, generalist species with high survival rates (e.g., Allophyllus cobbe and Anisoptera thurifera) is highly recommended.

More trees and fewer roads: the importance of local and landscape features for insectivorous bats in open urban green spaces

Context Urbanisation poses new challenges for wildlife worldwide, and recent research suggests that urban parks, although highly modified, may act as important refuges. Insectivorous bats can persist in urban landscapes and play an important role in keeping insect populations in balance. Previous research on use of urban landscapes by these bats has often focused on patches of remnant bushland within cities, but their use of highly modified open spaces is not well understood. Aims We aimed to determine the use of open green spaces (e.g. open parks, sports ovals) by insectivorous bats in Melbourne, Australia and to identify landscape factors that influence their presence and activity level. Methods We conducted passive acoustic surveys at 35 sites across greater Melbourne. Once species were identified from the echolocation call data, we modelled species richness, total activity and activity of individual species against landscape and weather variables, using Generalised Linear Mixed Models and Generalised Additive Mixed Models. Key results Across 557 detector nights, we identified at least 11 of the 17 species recorded to occur in Melbourne. Both species richness and activity were greater in areas with more nearby trees and lesser in areas with more roads. There were weaker species-specific relationships between bat activity and both distance to the nearest water source and Normalised Difference Vegetation Index. Species richness and activity levels were lower on nights with a lower temperature at dusk, higher rainfall and stronger wind. Conclusions Our results show that multiple bat species consistently use Melbourne’s open green spaces, highlighting the potential habitat value of these areas, especially those surrounded by high tree densities and fewer roads. Implications Insectivorous bats play important roles within ecosystems and bring benefits to human society. To encourage the diversity and activity of insectivorous bats in urban landscapes, we recommend retaining and increasing indigenous vegetation surrounding open areas in urban parks, as well as more strategic planning of new urban parks that further increases tree density in cities.

Tall, large-diameter trees and dense shrub layer as key determinants of the abundance and composition of bird communities in oak-dominated forests

Increasing human activity is altering the structure of forests, which affects the composition of communities, including birds. However, little is known about the key forest structure variables that determine the richness of bird communities in European temperate oak forests. We, therefore, aimed to identify key variables in these habitats that could contribute to the design of management strategies for forest conservation by surveying 11 oak-dominated forest sites throughout the mid-mountain range of Hungary at 86 survey points to reveal the role of different compositional and structural variables for forest stands that influence the breeding bird assemblages in the forests at the functional group and individual species levels. Based on decision tree modelling, our results showed that the density of trees larger than 30 cm DBH was an overall important variable, indicating that large-diameter trees were essential to provide diverse bird communities. The total abundance of birds, the foliage-gleaners, primary and secondary cavity nesters, residents, and five specific bird species were related to the density of high trunk diameter trees. The abundance of shrub nesters was negatively influenced by a high density of trees over 10 cm DBH. The density of the shrub layer positively affected total bird abundance and the abundance of foliage gleaners, secondary cavity nesters and residents. Analysis of the co-dominant tree species showed that the presence of linden, beech, and hornbeam was important in influencing the abundance of various bird species, e.g., Eurasian Treecreeper (Certhia familiaris), Marsh Tit (Poecile palustris) and Wood Warbler (Phylloscopus sibilatrix). Our results indicated that large trees, high tree diversity, and dense shrub layer were essential for forest bird communities and are critical targets for protection to maintain diverse and abundant bird communities in oak-dominated forest habitats.

Exploring Tree Density Increases after Fire Exclusion in the Northern Front Range and Great Plains, Colorado, USA

Since Euro-American settlement and associated fire exclusion, grasslands and open forests have converted to forests throughout the United States. Contributing to the weight of evidence, we determined if forestation also occurred in forests and grasslands of Colorado. Our study extent encompassed landscapes of the 0.5 million ha Arapaho and Roosevelt National Forests in the northern Front Range (eastern side) of the southern Rocky Mountains and the 1 million ha Weld County, which contains Pawnee National Grassland, in the Great Plains grasslands. We quantified tree composition, cover, and densities from historical (years 1863 to 1886) tree surveys, current surveys (2002 to 2011), and land cover (2016) to identify departures. In the Arapaho and Roosevelt, historical lack of tree presence and overall low tree densities suggested an open landscape, due to about 70% of 7134 survey points without two trees within 60 m. The treed landscape, which was not continuously forested, had density estimates of about 153 trees/ha. In contrast, the current landscape was 68% forested with high tree densities; fire-dependent pines decreased relative to subalpine fir (Abies lasiocarpa) increases. In Weld County, seven trees were surveyed historically, whereas currently, woody cover totaled 2555 ha. Uniquely applying historical surveys at landscape scales, we documented an open landscape in the northern Front Range, unlike previous research, and rare tree presence in the relatively understudied grasslands of Colorado. Forestation corresponded with changes in U.S. grasslands and forests following Euro-American settlement and associated fire exclusion.

Dynamic cocoa agroforestry: 25 years of experience in Alto Beni, Bolivia

Despite cocoa traditionally being grown in agroforestry systems, monoculture farming now dominates in major producing countries like Côte d’Ivoire and Ghana. Globally, interest is growing to return once more to cocoa agroforestry, due to its many benefits, including biodiversity conservation, temperature and water cycle regulation, and carbon sequestration. The article reports on a study which analysed cocoa agroforestry plots of smallholder farmers in Alto Beni, Bolivia. These systems are characterised by the high diversity and density of companion trees. The model plot, managed under dynamic agroforestry principles, showed variability in cocoa yields but these increased over time. Additional income was also yielded from companion crops, which provide timber for harvest and fruits for sale and consumption, improving income diversification, food security and food sovereignty. Dynamic agroforestry systems, therefore, have higher labour intensity but also higher income compared to monocrop cocoa production systems, which is supported by the the SysCom Bolivia trial of 2017–2019. Dynamic agroforestry systems are also shown to increase biodiversity, offer resilience against climate change, and improve farmer’s ratings of happiness. The article emphasises the importance of agroforestry systems for sustainable cocoa production, highlighting its provision of economic benefits alongside environmental and social advantages. To maximise the potential of agroforestry systems, there is a need for continued research and long-term data collection for continuous improvement of management practices.

COMPOSICIÓN DE COMUNIDADES DE HONGOS MICORRÍZICOS ARBUSCULARES EN AGROECOSISTEMAS DEL ÁREA DE PROTECCIÓN DE FLORA Y FAUNA CAÑÓN DEL USUMACINTA EN TABASCO, MÉXICO

&lt;p&gt;&lt;strong&gt;Background.&lt;/strong&gt; The mutualistic interaction with Arbuscular Mycorrhizal Fungi (AMF) is one of the main strategies used by plants to improve their absorption of nutrients and cope with adverse environmental conditions. They are ubiquitous microorganisms that help maintain soil health and crop nutrition, which is why they are considered an essential component in agroecosystems. However, its presence is affected by multiple biotic and abiotic factors such as tree cover and management intensity. &lt;strong&gt;Objective. &lt;/strong&gt;Evaluate and compare the AMF communities and tree cover of the main agroecosystems present in the Usumacinta Canyon Flora and Fauna Protection Area (APFFCU) in the humid tropics of southeastern México. &lt;strong&gt;Methodology.&lt;/strong&gt; The abundance of spores and the number of AMF morphospecies and the density and diversity of trees were counted in 25 plots of the agroecosystems Potrero (P), Milpa (M), Huerto Familiar (HF), Acahual (A) and Plantación Forestal (PF). An Analysis of Variance (ANOVA) was applied to the set of data obtained from each variable to detect the presence of significant differences between each of the agroecosystems evaluated. Likewise, to observe the effect between the variables, the Pearson correlation analysis was carried out. Finally, Principal Component Analysis (PCA) was carried out to visualize the grouping of the study plots. &lt;strong&gt;Results.&lt;/strong&gt; The ANOVA detected significant differences when comparing the variables of interest. The highest abundance of spores was found in P and PF, while A and PF presented the highest richness of AMF morphospecies. Acaulosporaceae and Glomeraceae were the most representative families and &lt;em&gt;Acaulospora kentinensis&lt;/em&gt; was the only morphospecies that was observed in all the agroecosystems evaluated. The highest values of tree density and diversity were observed in A. The lowest tree density was present in P and the lowest tree diversity in PF. The PCA allowed us to group the plots with the highest tree density, spore abundance and morphospecies richness on average. &lt;strong&gt;Implications.&lt;/strong&gt; The information derived from this study highlights the importance of the presence of trees in agricultural productivity and the design of long-term sustainable agroecosystems. &lt;strong&gt;Conclusion.&lt;/strong&gt; It was concluded that the AMF communities of the agroecosystems evaluated in the APFFCU vary in spore abundance and morphospecies richness, which is correlated with the characteristics of their tree cover.&lt;/p&gt;

Hornbill abundance and habitat relationships in a human-impacted protected area in the Indian Eastern Himalaya

Asian forest hornbills play an important functional role as seed dispersers. Three of the large-bodied hornbill species in the Eastern Himalaya are declining globally. To understand their global population status, it is important to obtain reliable abundance estimates across their range. Protected areas are the strongholds for hornbill species in the Eastern Himalaya but differ in degree of disturbances and human pressures. We estimated the abundances of four hornbill species (Great Hornbill, Wreathed Hornbill, Rufous-necked Hornbill, and Oriental Pied-Hornbill) in the human-impacted Buxa Tiger Reserve in northern West Bengal. This is the first study in Asia to obtain abundance estimates of the hornbill species through comprehensive spatial coverage of the reserve. The densities of the three large-bodied species were low (< 1 bird per km2), while that of the small-bodied Oriental Pied hornbill was around 11 birds per km2. Abundance estimates ranged from a mean of 27 birds for the Rufous-necked Hornbill that is confined to the hilly areas to 161 for the Great Hornbill, 375 for the Wreathed Hornbill and 8050 for the Oriental Pied-Hornbill. Habitat quality was poor in most of the reserve with low tree density and basal area with only a few patches with higher tree density. Oriental Pied-Hornbills were associated with lower elevations and higher fruiting tree density. Despite the relatively low abundance of the large-bodied hornbill species, Buxa is an important site for hornbill conservation due to the presence of breeding populations and nests. While past and ongoing human pressures have resulted in habitat degradation, poaching pressures are low and hornbills are able to persist and breed in this landscape. Ecologically meaningful forest restoration with diverse native tree species is urgently needed to improve the habitat quality for hornbills and other wildlife.

The Potential Health Benefits of Urban Tree Planting Suggested through Immersive Environments

Disruptive change in urban landscapes, such as large-scale tree planting, is complicated by the different priorities of the wide range of urban stakeholders. Here, we demonstrate an approach to the planning of urban green spaces using virtual reality simulations. We evaluate the health benefits (restorative benefits) and safety concerns of participants using virtual reconstructions of 10 urban parks in Bradford, UK, to simulate changes in woodland cover. Participants experienced each of the 10 parks as immersive environments with each of three scenarios: (i) no trees, (ii) real tree distribution, and (iii) doubling of tree numbers. Participants answered a short questionnaire while in each virtual park to quantify their feelings of safety and the restorative benefit that they thought they would experience. The results show that our VR approach produces reported restorative benefits that are not significantly different from those reported in the physical parks during visits by participants. We then demonstrate that increased tree cover is associated with significant increases in perceived restorative benefit, with some evidence of saturation at higher tree densities. Reductions in tree cover lead to a reduction in reported restorative benefit. We suggest that immersive technologies present a useful tool for the consultation and co-design of urban landscapes.

Understanding predictors of mistletoe infection across an urban university campus in Southwest China

Due to the importance of trees in urban ecosystems, it is crucial to understand the distribution, prevalence, and intensity of parasitic mistletoe infection across urban landscapes. In this study, we aimed to understand how various tree-related factors (e.g., tree taxonomy, size, pruning history, nativity, foliage, density, and diversity) might influence mistletoe prevalence and infection intensity across a typical subtropical urban greenspace. We surveyed 6,012 trees representing 96 species, 76 genera, and 44 families across a large, urban university campus in a major Southwest Chinese city. In total, we found 353 mistletoe host trees (prevalence: 5.87%), largely concentrated on the eastern part of campus, partially due to the proximity of waterbodies and a large adjacent greenspace, as well as higher tree density. To understand how predictors affected the prevalence and intensity of mistletoe infection, we used a hurdle model fitting our zero-inflated count data. Four independent variables significantly affected the prevalence of mistletoe infestation, with three demonstrating positive correlations (crown width, tree density, and tree diversity). One variable (evergreen foliage) negatively correlated with mistletoe prevalence. However, only one factor was found to significantly affect mistletoe infection intensity (crown width, positively). Due to the variety of ecosystem services mistletoes provide, more studies are necessary to assess the impact of various mistletoe management strategies, especially on urban biodiversity.

A comprehensive study of how urban morphological parameters impact the solar potential, energy consumption and daylight autonomy in canyons and buildings

Over the past two decades, global greenhouse gas emissions have surged, leading to rising sea levels and climate change. Solar energy has emerged as an excellent solution to this problem. This study aims to assess daylight availability and energy consumption in urban canyons and blocks in a semi-arid climate while exploring the correlation between the heterogeneity of urban morphological parameters and key research variables. The study employed field measurements and simulations using Ladybug Tools and UMI. Data were collected from urban canyons and blocks in three areas, amounting to 1,366,982 m2. The findings indicate that areas with abundant greenery and H/W ratios exceeding 1.8 experience the most significant shading effects in urban canyons. Selecting suitable trees and placing them in strategic locations can enhance energy efficiency. Furthermore, broad urban canyons (H/W < 0.5) receive four times more solar radiation than narrow urban canyons (H/W > 1.8) with high tree density, peaking at 240 kWh/m2 during summer. In urban blocks, rooftops have the highest solar potential, with imbalances between building heights and interbuilding shading as factors that reduce solar capabilities. Tree coverage significantly affects the solar potential of facades, with some urban blocks receiving less than 5,000 kWh/m2 of solar radiation on the southern facades each month. Finally, this study examined the impact of heterogeneity within urban morphological parameters on the principal research variables. The results indicate that the heterogeneity observed in urban morphological parameters affects daylight availability and energy consumption within urban blocks.

Elevation-Dependent Natural Regeneration of Abies georgei var. smithii Forest in Southeastern Tibet

The comprehensive impacts of biotic and abiotic factors on the natural regeneration of Abies georgei var. smithii (Abies) forests in Tibet are not thoroughly understood. To address this gap, our study focused on the regeneration densities of Abies seedlings, saplings, and small trees across 21 plots (each 20 m × 20 m) along an elevation gradient from 3730 m to 4330 m in the Sygera Mountains of Southeastern Tibet. We meticulously measured a suite of 11 variables that describe stand structures and ecological conditions. Through analyses using Spearman’s correlation analysis, hierarchical partitioning, and multiple linear regression, we identified key ecological drivers for successful Abies regeneration. Our results highlighted a peak in the abundance of seedlings, saplings, and small trees at an elevation of 3930 m. As the elevation rose from 3730 m to 4330 m, we observed an initial increase followed by a decrease in canopy cover (canopy), mother tree density (MotherT), 1000-seed weight (SeedW), litter thickness (LitterT), moss cover (MossC), moss thickness (MossT), soil moisture (SM), and soil bulk density, while mean annual temperature and soil depth to permafrost consistently decreased. The critical ecological drivers for Abies natural regeneration were identified as follows: MossT was pivotal for seedling density; canopy and MossC were influential for sapling density, and MotherT was the main factor affecting the density of small trees. This study suggests that a high density of mother trees and a thick and highly covered layer of moss are conducive to the natural regeneration of Abies in the Sygera Mountains. Understanding the current status of regeneration is vital for informing conservation and management strategies for Abies forests in Tibet.

Relações entre o espaçamento arbóreo e características do campo nativo em sistemas silvipastoris no bioma Pampa

ABSTRACT: The current study assessed the association of eucalyptus-tree spacing with forest growth and yield, as well as with the floristic composition, diversity and yield of natural grassland grown in silvopastoral systems in Pampa biome. Data were collected in six family cattle-ranching area in Bagé County (RS). The effect of two different genetic materials (seminal-origin Eucalyptus dunnii plant and one Eucalyptus grandis clone) on shading features of plants grown in 3 planting-spacing dimensions(625, 312 and 208 trees ha-1) was assessed, as well as their association with herbaceous extract (bare soil; green cover; forage dry matter; floristic composition; species richness; and grass, legumes and winter - and summer-growth species rates) and forestry (litter accumulation, diameter at breast height, total height and volume per hectare) variables. Planting carried out at the highest tree density (625 trees ha-1) has increased forest yield. However, it reduced green cover, herbaceous extract dry-matter yield and species richness, mainly in grasses and legumeswith greater forage potential. Conversely, it is possible combining forestry and animal yield to the preservation of native forage species at low tree densities (204 to 312 trees ha-1).