Tree Density Research Articles

Densities of Eurasian Three-toed Woodpecker Picoides tridactylus and sap trees correlate across a latitudinal gradient in Sweden

Densities of Eurasian Three-toed Woodpecker Picoides tridactylus and sap trees correlate across a latitudinal gradient in Sweden

Restoration thinning accelerates small tree growth but may slow large tree growth in a multi‐age flood‐dependent forest

Abstract Large tree decline is occurring globally with critical implications for biodiversity and carbon sequestration. Restoration thinning is a potential management action to accelerate tree growth and promote large tree development in forests, yet trials have been limited and results have been mixed. We conducted a large‐scale trial to determine whether restoration thinning could accelerate the development of large trees in river red gum forests in Australia that had experienced widespread woody thickening and a decline of large trees due to long‐term commercial timber harvesting and river regulation. Thinning was conducted on 44 9‐ha plots by removing trees <40 cm diameter from around retained trees at a range of spacings. Initial tree densities ranged from ~260 to ~1860 trees per ha and 8%–86% of trees were removed by thinning. We monitored 1980 trees prior to thinning, and annually for 5 years post‐thinning. We tested the effects of thinning intensity on diameter growth of different sized trees and explored whether long‐ and short‐term water availability affected outcomes. Thinning promoted the growth of small trees <56 cm diameter, especially in drier sites during wet years. Higher thinning intensities reduced the growth rates of large trees (no smaller than 79.5 cm diameter) in wetter sites. For medium‐ and large‐sized trees, long‐ and short‐term water availability were stronger drivers of tree growth than competition due to tree density. Synthesis and applications. Restoration thinning may accelerate tree growth in young river red gum forests where all trees are small. But restoration thinning may be ineffective or detrimental in multi‐aged forests where the goal is to promote the growth rates of trees that are already medium to large in size.

Growth dynamics of an Amazonian forest: Effects of reduced impact logging and recurring atypical climate events during a 20-year study

Although forest management with reduced impact logging (RIL) practices is regarded as a way to generate income from tropical forests without losing their overall conservation values, the behavior of forests following logging is a topic that has been little studied in the southwestern Brazilian Amazon (SWA), where the predominant forest type is open with low density of commercial timber species. This study examined the growth dynamics of a logged forest in the SWA through monitoring of permanent sample plots (PSP) over twenty years post logging. Following logging, the forest fully recovered its original tree density (439. ha−1) and aboveground biomass (AGB) stocks (188.4 Mg. ha−1) but did not recover extracted timber volume in the commercial size class (DBH > 50 cm, 28 m3. ha−1 before logging and 22.6 m3. ha−1 in 2022). Tree growth, recruitment and mortality rates presented a high fluctuation during the monitoring period, increasing immediately after logging (0.43 cm. yr.−1, 4.1 % and 4.7 % respectively), declining five years after, (0.25 cm. yr.−1, 0.7 % and 1.5 % respectively) and presenting a new peak sixteen years after logging (0.35 cm. yr.−1, 3.9 % and 7.4 % respectively) which persisted to the end of the study period. Consequently, forest turnover was very high, with stand half-life and doubling life of 29.6 and 27.2 years, respectively. The results show that in terms of forest dynamics and production, the behavior of logged forests was also affected by atypical climate events, such as recurring droughts across Amazonia. Consequently, in the forest type studied, and under the prescribed logging cycle of 25 years, RIL alone was not sufficient to guarantee the sustainability of long-term production of the main timber species harvested. Following the current growth trend (0.46 m3. ha−1. yr.−1 for trees above 10 cm DBH and 0.22 m3. ha−1. yr.−1 for trees above 50 cm DBH) the time to recover the total commercial volume and commercial volume for trees above 10 cm DBH and above 50 cm DBH would be 34 and 45 years respectively. Our findings suggest the need for adoption of silvicultural treatments to increase forest productivity in areas under RIL in SWA.

Modeling structural traits of Aleppo pine (Pinus halepensis Mill.) forests with low-density LiDAR

ABSTRACT Mediterranean forests of Aleppo pine (Pinus halepensis Mill.) have a crucial role in climate change, as they are extremely adaptive and provide valuable timber or carbon stocks. However, greater detail quantifying those attributes is needed: although National Forest Inventories are acceptable, continuous cover maps are normally lacking. Here, we use the public Spanish low-density LiDAR flights to model above-ground biomass, volume, tree density, basal area and dominant height of naturally regenerated Mediterranean Aleppo pine forests, comparing individual-tree detection and area-based approach. We found R2 and RRMSE among 0.51–0.66 and 40–34% for above-ground biomass, 0.54–0.70 and 34–28% for volume, 0.23–0.45 and 33–28% for tree density, 0.48–0.62 and 32–27% for basal area, and 0.70–0.69 and 11–11% for dominant height. In all cases but dominant height, the area-based approach outperformed the individual-tree detection. Neither time difference between LiDAR flight and ground measurement or past land use affected the area-based approach models, yet the latter had a strong effect on observed productivity. The different definitions of dominant height were equivalent and did not influence the dominant height models. We believe these models, and their corresponding maps, will be a great asset for policymakers and different stakeholders for Aleppo pine forests throughout the Mediterranean basin.

Characterizing heterogeneous forest structure in ponderosa pine forests via UAS-derived structure from motion

Increasingly, dry conifer forest restoration has focused on reestablishing horizontal and vertical complexity and ecological functions associated with frequent, low-intensity fires that characterize these systems. However, most forest inventory approaches lack the resolution, extent, or spatial explicitness for describing tree-level spatial aggregation and openings that were characteristic of historical forests. Uncrewed aerial system (UAS) structure from motion (SfM) remote sensing has potential for creating spatially explicit forest inventory data. This study evaluates the accuracy of SfM-estimated tree, clump, and stand structural attributes across 11 ponderosa pine-dominated stands treated with four different silvicultural prescriptions. Specifically, UAS-estimated tree height and diameter-at-breast-height (DBH) and stand-level canopy cover, density, and metrics of individual trees, tree clumps, and canopy openings were compared to forest survey data. Overall, tree detection success was high in all stands (F-scores of 0.64 to 0.89), with average F-scores > 0.81 for all size classes except understory trees (< 5.0 m tall). We observed average height and DBH errors of 0.34 m and − 0.04 cm, respectively. The UAS stand density was overestimated by 53 trees ha−1 (27.9%) on average, with most errors associated with understory trees. Focusing on trees > 5.0 m tall, reduced error to an underestimation of 10 trees ha−1 (5.7%). Mean absolute errors of bole basal area, bole quadratic mean diameter, and canopy cover were 11.4%, 16.6%, and 13.8%, respectively. While no differences were found between stem-mapped and UAS-derived metrics of individual trees, clumps of trees, canopy openings, and inter-clump tree characteristics, the UAS method overestimated crown area in two of the five comparisons. Results indicate that in ponderosa pine forests, UAS can reliably describe large- and small-grained forest structures to effectively inform spatially explicit management objectives.

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.

Comparative analysis of gut microbiome of mangrove brachyuran crabs revealed patterns of phylosymbiosis and codiversification.

The acquisition of microbial symbionts enables animals to rapidly adapt to and exploit novel ecological niches, thus significantly enhancing the evolutionary fitness and success of their hosts. However, the dynamics of host-microbe interactions and their evolutionary implications remain largely underexplored in marine invertebrates. Crabs of the family Sesarmidae (Crustacea: Brachyura) are dominant inhabitants of mangrove forests and are considered keystone species there. Their rapid diversification, particularly after adopting a plant-feeding lifestyle, is believed to have been facilitated by symbiotic gut microbes, enabling successful colonization of intertidal and terrestrial environments. To investigate the patterns and mechanisms shaping the microbial communities and the role of microbes in the evolution of Sesarmidae, we characterized and compared the gut microbiome compositions across 43 crab species from Sesarmidae and other mangrove-associated families using 16S metabarcoding. We found that the gut microbiome assemblages in crabs are primarily determined by host identity, with a secondary influence from environmental factors such as microhabitat and sampling location, and to a lesser extent influenced by biological factors such as sex and gut region. While patterns of phylosymbiosis (i.e. when microbial community relationships recapitulate the phylogeny of their hosts) were consistently observed in all beta-diversity metrics analysed, the strength of phylosymbiosis varied across crab families. This suggests that the bacterial assemblages in each family were differentially shaped by different degrees of host filtering and/or other evolutionary processes. Notably, Sesarmidae displayed signals of cophylogeny with its core gut bacterial genera, which likely play crucial functional roles in their hosts by providing lignocellulolytic enzymes, essential amino acids, and fatty acids supplementation. Our results support the hypothesis of microbial contribution to herbivory and terrestrialization in mangrove crabs, highlighting the tight association and codiversification of the crab holobiont.

Phytosociology and Stand Structure of Tropical Dry Deciduous Forest of Dalma Wildlife Sanctuary, Jharkhand, Eastern India

Assessing the composition and structure of ecosystems is of the utmost importance for the conservation of forests. Tree species diversity, distribution pattern and stand structure provide baseline information for conservation and management of the forest. The present study was conducted in the Dalma Wildlife Sanctuary to assess the diversity, composition, richness and stand structure. Standard sampling method was used for vegetation sampling and data collection. An aggregate of 2876 individuals belonging to 41 species, 34 genera and 22 families were identified from 2.5 ha sampling area. The sanctuary recorded tree density of 1151 ind./ha with a total basal area of 510.807 sq. m. Analysis of IVI value revealed that S. robusta (65.207), B. cochinchinensis (22.451), A. latifolia (18.071), T. tomentosa (15.604) and D. melanoxylon (12.449) were the dominant tree species in the sanctuary. The family Fabaceae was the most species-rich family with 9 species. Over 70% of tree species showed contiguous distribution pattern in the studied area. The sanctuary recorded diversity index (H') of 3.204, richness index (R') of 4.504 and evenness index (E) of 0.863. The stand structure indicates a natural satisfactory regeneration and healthy population in the studied forest areas. Density-girth class distribution showed that more than 75% of the total population was dominated by seedlings and saplings. The research findings suggests that the sanctuary is an ecolologically rich site with an expanding population. An efffective management and conservation strategy will ensure a sustained biodiversity and richness of this protected site.

Urban trees' potential for regulatory services in the urban environment: an exploration of carbon sequestration.

Urbanisation has emerged as a formidable challenge for urban policymakers, reaching unparalleled heights and unsettling the ecological equilibrium of the cities. Urban areas now grapple with many issues encompassing climate change, resource depletion, population surges and increased pollution levels. Many planned cities have planted trees and other vegetation within the urban sectors to enhance air quality, mitigate climate effects and provide valuable ecosystem services. This study assessed tree species diversity and their potential for carbon sequestration in Panjab University Campus, Chandigarh. We established 188 plots, each comprising randomly selected quadrats measuring 10 m × 10 m, encompassing areas with varying levels of vegetation, ranging from low to moderate and high density. We used four different allometric equations to estimate tree biomass and carbon stock. Our findings revealed that 92 tree species belong to 72 genera and 35 families, with a total tree density of 975 ha-1. The total CO2 sequestration in form of carbon stock was 18,769.46 Mg C ha-1, with Manilkara hexandra (1239.20 Mg C ha-1), Ficus benghalensis (1072.24 Mg C ha-1), Kigelia pinnata (989.89 Mg C ha-1) and Lagerstroemia floribunda (716.88 Mg C ha-1) being the top contributors. Specifically, the equation of Chave et al. (2005) without tree height yielded the highest biomass and carbon stock estimates than other equations. The present study underscores the vital role of trees on the campus as potent carbon reservoirs meet to maintain an aesthetic sense for biotic components and alleviate rising levels of CO2 in the atmospheric environment. By emphasising the role of urban trees as potent carbon reservoirs, the study underscores the importance of integrating green infrastructure into urban planning strategies. Furthermore, it offers valuable guidance for urban planners. It suggests that strategic tree planting and maintenance can enhance green spaces, regulate temperatures and ultimately support regional and global climate change mitigation goals. Incorporating these findings into urban planning processes can aid policymakers in developing resilient, ecologically sustainable cities worldwide.

Quantifying the impact of Great Green Wall and Corporate plantations on tree density and biomass in Sahelian Senegal

The Great Green Wall (GGW) is an international initiative to combat land degradation and restore native plant life in the Sahel, but due to a lack of monitoring tools, it remains unknown to be considered as success or failure. Here, we quantify the impact of GGW plantations and Corporate plantations (privately owned) in Sahelian Senegal based on remote sensing data and deep learning by mapping individual trees and their biomass across the Sahel region. Tree features (cover, density and above-ground biomass) have been computed in every hectare of 42 plantations (of both, corporate and GGW) and their surrounding non-planted areas, subsequently used for a comparative analysis of tree features. Results showed that gains in tree features varied substantially between plantations. At plot scale, among Corporate plantations, the average gain in tree density was 61.16±42.12 trees/ha while it was 5.7±5.8 trees/ha for GGW plantations. In regards to tree cover, the average gain was 618.5±588.5 m2/ha for Corporate plantations and 71.72±108.89m2/ha for GGW plantations. For the above-ground biomass, the average gain was 3.36±3.29 tons/ha in the Corporate plantations and 0.46±0.67 tons/ha in the GGW plantations. The average gain in foliar biomass in the Corporate plantations was 0.15±0.13 tons/ha and in the GGW plantations, it was 0.02±0.03 tons/ha. The average gain in wood biomass was 3.21±3.12 tons/ha among the Corporate plantations and was 0.43±0.64 tons/ha among the GGW plantations. Notably, regarding the relative benefit in terms of ecosystem services per unit of density, each tree in GGW plantations contribute more to ecosystem services per unit of density compared to Corporate plantations. In GGW, each gained tree contributes 18 m2 of cover, 116.1 kg of above-ground biomass, 5.6 kg of foliar biomass, and 114.2 kg of woody biomass, while in corporate plantations, on the other hand, each gained tree adds 9 m2 of cover, 48.4 kg of above-ground biomass, 2.3 kg of foliar biomass, and 46.3 kg of woody biomass. These findings are opposed to conventional paradigms, suggesting that the Great Green Wall, while perhaps missing its tree density targets, has succeeded in its mission to produce ecosystem services per tree. This raises important questions about the redefinition of objectives in reforestation projects, focusing on quality rather than quantity, a perspective that could transform our understanding of the successes and failures of these essential ecological restoration initiatives. However, the assessment primarily relies on indicators such as cover and biomass, potentially overlooking other crucial ecosystem services. Therefore, while our conclusions underscore the effectiveness of reforestation initiatives, future research should aim to establish a more comprehensive understanding of ecosystem services by incorporating additional indicators beyond cover and biomass, such as species diversity, soil health, water retention, and habitat quality.

Temporal changes in species richness, composition and diversity of the forest stands over 36-year period, Western Himalaya, India

This study investigates the temporal changes in species richness, composition, and diversity in forest stands spanning a 36-year period in the Western Himalaya. Four forest stands (subtropical Sal-forest, subtropical Chir-pine forest, temperate Banj-oak forest, and temperate Mixed-oak Forest) studied in 1980-1981 were resurveyed using similar methods. Over the past 36 years, 19 new species have been recorded in the four stands; eight species planted and eleven species naturally introduced. Dominant species continue to dominate in the forest stands. However, their contribution to the total tree density has decreased over the year. Species diversity, richness, and evenness increased in all forests except the Sal stand. Three species were newly introduced in the Sal stand, seven in the Chir-pine stand, eight in the Banj-oak stand, and seven in the Mixed-oak stand. The highest similarity in species composition was observed in the Sal stand (59%), followed by the mixed-oak stand (57%), Chir-pine stand (50%), and Banj-oak stand (47%). The results indicate an increase in tree density across all sites, with the Mixed-oak forest exhibiting the highest increase in tree density due to least biotic pressure. The findings of this study, based on two-time composition datasets, provide valuable insights into forest dynamics, supporting biodiversity conservation and management planning.

Evidence of mesophication following selective cutting and shelterwood in Virginia’s eastern deciduous forest, USA

The replacement of oaks (Quercus) with mesic tree species in the eastern deciduous forests of North America involves a positive feedback loop being driven by fire suppression and climate change. In this study, we explored the impact of timber harvesting as a potential facilitator of mesophication. Young stands resulting from shelterwoods (on federal lands) and selective cutting (on private lands) were sampled to compare the composition and density of seedlings, saplings, and trees in western Virginia, USA. Oak overstory trees had lower importance values and densities at selective cutting sites compared to shelterwood sites. Among saplings, mesic species had higher importance values and densities than oaks at both selective cutting and shelterwood sites. Evidence of mesophication was found at both selective cutting and shelterwood sites; but a higher level of mesophication appeared to be occurring at the selective cutting sites than at shelterwood sites. At selective cutting sites scarlet oak (Quercus coccinea) was absent from all sampled plots and a dense midstory of subcanopy trees, especially eastern redbud (Cercis canadensis), appeared to be hindering successful oak regeneration. Our results indicate timber harvesting, without regard for the composition of the regeneration layer, may facilitate mesophication in the eastern deciduous forest, with selective cutting resulting in more successful establishment of mesic species compared to shelterwoods. These findings have implications for mesophication on private forest lands, where selective cutting is a very common method of timber harvesting.

The Significance of Tree Height as a Predictor of Tree Mortality during Bark Beetle Outbreaks in a Small Catchment

Bark beetle outbreaks damage forests and kill trees worldwide, but many aspects of their dynamics remain unexplained. Our aim was to identify predictors for individual tree deaths within the small (0.7 km2) Plešné Lake catchment in the Šumava National Park in southwestern Czechia. Within this area, &gt;60,000 trees were geo-referenced and categorized from ten aerial images (20 cm spatial resolution) between 2000 and 2015. For each year for which aerial images were available, we calculated tree densities of different categories and diameters. Tree height was evaluated by means of LiDAR in two terrestrial campaigns (2010 and 2011). A machine learning technique was then used to evaluate the most important variables. The resulting relationships were largely nonlinear and differed among years; however, individual trait tree height proved to be the most influential variable in each year. Higher trees were more likely to have died during either the undisturbed phase (2000 and 2003), the disturbed phase (2005–2011), or the recovery phase (2013). Our results indicate that salvage logging may not be the most effective measure for protecting trees in small catchments.

Examination of Drone Usage in Estimating Hardwood Plantations Structural Metrics

Planting hardwood trees on retired marginal agricultural land is one of the main strategies used to restore forested wetlands. Evaluating effectiveness of wetland restoration requires efficient monitoring to evaluate recovery trajectories and desired conditions. Recent advancements in unmanned aerial system (UAS) technologies have prompted wide-scale adoption of UAS platforms in providing a range of ecological data. In this study, we examined the use of UAS Structure from Motion (SfM) derived point clouds in estimating tree density, canopy height, and percent canopy cover for bottomland hardwood plantations within four wetland reserve easements. Using a local maxima approach for individual tree detection produced plantation level estimates with mean absolute errors of 150 trees per hectare, 0.5 m, and 18.4% for tree density, canopy height, and percent canopy cover, respectively. At the plot level, UAS-derived tree counts (r = 0.53, p < 0.01) and canopy height (r = 0.57, p < 0.01) were significantly correlated with ground-based estimates. We demonstrate that UAS-SfM is a viable method of assessing bottomland hardwood plantations for applications that require precision levels congruent with the mean absolute errors reported here. The accuracy of tree density estimates was reliant upon specific local maxima window parameters relative to stand conditions. Therefore, acquisition of leaf-off and leaf-on imagery may allow for better individual tree detection and subsequently more accurate tree density and other structural attributes.

Integrated adoption of controlled grazing and multipurpose fodder trees for enhancing tree cover in dryland farming systems

CONTEXTIntegration of agroforestry with sustainable grazing systems can enhance tree cover in a given landscape. This integration could have a significant economic and ecological impact especially in dryland farming systems. Despite this, the integration is challenged by the lack of combined adoption of both agroforestry and sustainable grazing. OBJECTIVEIn this study, we first examined the factors that determine the integrated adoption of controlled grazing (CG) and multipurpose fodder trees (MFT). More importantly, we investigated whether the integrated adoption of CG and MFT enhances tree cover in dryland farming systems. METHODSBased on primary data collected from a randomly-selected sample of farm households, we used an IV approach to probe into the integrated effect of adopting CG and MFT on tree cover. On the other hand, the bivariate probit model was used to identify the factors that affect the adoption of both CG and MFT. RESULTS AND CONCLUSIONOn average, adopters of both CG and MFT were found to have higher levels of tree abundance and density on their farms. Our model analysis indicates that these higher levels of tree abundance and density are positively related to the integrated adoption of CG and MFT. While the integrated adoption of CG and MFT had a stronger effect, separate adoption of CG or MFT was also correlated with tree abundance. These results generally indicate the importance of integrated silvopastoral systems not only as sustainable livestock management systems but also as promoters of vegetation (tree cover). SIGNIFICANCEGiven the economic and ecological importance of the integrated adoption of CG and MFT, factors that were found to influence integrated adoption including access to improved livestock breeds, skill development (both agroforestry and livestock management training), and agricultural services (such as irrigation and water sources) could give policy a useful direction for targeting and promoting the uptake of such integrated silvopastoral systems both for improving farmers' livelihoods and ecological sustainability.

Investigating the potential of integrated urban greening strategies for reducing outdoor thermal stresses: a case of asymmetrical configuration in the tropical city of Bhopal.

In Indian cities where streets are the only affordable outdoor public space, pedestrians are always exposed to extreme heat related health risk. However, it's a challenge to reduce heat stress in existing streets characterized by asymmetrical urban configuration. Integrating vegetation without reconstituting the original orientation and geometry is one of the feasible ways to alleviate stress. Therefore, current study focuses to analyse the heat stress reduction potential of urban greenery strategy in asymmetrical urban configuration from spatiotemporal perspective. It initiates with the selection of commercial streets in extreme hot climate with an on-site measurement of its climatic and morphological attributes. Furthermore, it leads to the classification and prioritizing of street's sections linked to hot-spots determined by varied sky view factor and asymmetrical aspect ratio. Finally, an Envi-Met model with iterated scenarios at the building and street levels is developed, incorporating three strategies (trees, grass, green-walls). The impact of heat related health risk is quantified using a thermal index Universal Thermal Climate Index along with air temperature and mean radiant temperature. The results suggested that due to asymmetricity a fixed strategy would not be applicable across the street. The highest reduction was observed by trees in asymmetrical sections while lowest was recorded by green-wall. However, it would be worthwhile to adopt green-wall along with dense tree's (leaf area density, 0.3) in order to reduce the heat stress in deeper sections. The evidence-based integration of Urban greenery can assist planners and designers in mitigating extreme heat stress in similar complex urban environment.

Olive grove landscape change: A spatial analysis using multitemporal geospatial datasets

This research examines the evolution of olive landscapes in Cartoceto, Italy, post-World War II. This study investigates the structural and functional attributes of two distinct olive cultivation models, mixed olive groves with a low tree density and high-density olive groves. The research employs remote sensing aerial imagery and land use cartography to reconstruct the past terrain and classify distinct categories of olive orchards. Landscape metrics are utilised to evaluate the impact of human and natural factors on the temporal development of olive landscapes across multiple spatial configurations, defined as Landscape-scale and sub-units or Landscape Units. The results indicate that olive landscapes have experienced noteworthy alterations, characterised by a reduction in the conventional large-scale system and an increase in specialised planting models of smaller sizes, classified as “high intensity”. The region surrounding Cartoceto's historic centre has conserved a greater variety of mixed olive heritage and has witnessed the emergence of novel high densities of trees compared to other areas. Obtaining these results has been facilitated solely by utilising diverse spatial configurations of smaller sub-units than the entire landscape. The outcomes of this investigation provide a foundation for forthcoming enquiries into olive terrains and the development of sustainable rural landscape strategies.

Distance and T-square sampling for spatial measures of tree diversity

Distance sampling and its statistically improved variant, T-square sampling, are important sampling methods in plant ecology. They have often been applied in the context of plant density estimations and are comparatively easy to implement, since they intuitively follow the nearest-neighbour principle and thus do not require the layout of sample plots. Previous research studying distance sampling suggested that T-square sampling may also lead to an improved estimation of spatial tree diversity indices. We simulated distance and T-square sampling in six large fully mapped forest areas for seven tree diversity indices of which some competed for the same diversity aspect, i.e. tree location (dispersion), tree species and tree size diversity. Our results demonstrated that both distance and T-square sampling are indeed robust methods for sampling spatial measures of tree diversity. The sample size required for a sampling error of 10% does not exceed 20% of the total number of trees in a sampling area. T-square sampling has the ability to adapt to different spatial patterns of tree locations and this ability is key to the way the method controls estimation bias. The sample size required for species mingling and size differentiation clearly depends on the underlying spatial tree pattern in the sampling area. With most diversity indices, sample size reductions between 0.06% and 40% could be achieved by the application of T-square sampling compared to traditional distance sampling. All other conditions being equal, we could identify the uniform angle index, the species mingling index and the size differentiation index as those diversity indices achieving lower sampling error values than their competitors. For tree density estimations the Diggle and Byth estimators performed best. Based on our results, T-square sampling can be considered a robust sampling method for spatial tree diversity indices that is easy to apply in the field.

Modelling of sap flux density of oak in a humid region in China

AbstractTranspiration plays a vital role in determining the watershed water cycle. However, we still have little knowledge of the characteristics of tree transpiration in the Hanjiang River Basin, which is the water source for the middle route of South‐to‐North water diversion project. Here, we measured sap flux density of oak trees (Quercus, the dominant species here) at the 10‐min resolution for 2 years and explored its response to the environmental conditions. The incoming short‐wave radiation and vapour pressure deficit well explained the variation of daytime sap flux density, and a statistical model was then proposed to calculate the daytime sap flux density correspondingly; then a nighttime sap flux density module was proposed based on the daytime sap flux density calculation. Sap flux density showed clear counter‐clockwise hysteresis response to incoming short‐wave radiation, and clockwise hysteresis response to vapour pressure deficit. Our sap flux density model can well reproduce the corresponding hysteresis response to incoming short‐wave radiation and vapour pressure deficit. This study unravelled the environmental controls of sap flux density of the oak trees in the Hanjiang River Basin, proposed an efficient model for the sap flux density simulation, provided important knowledge for understanding the corresponding forests' water use, which is of critical significance in determining the water availability for the middle route of the South‐to‐North water diversion project.

Testing extinction events and temporal shifts in diversification and fossilization rates through the skyline Fossilized Birth-Death (FBD) model: The example of some mid-Permian synapsid extinctions.

In the last decade, the Fossilized Birth-Death (FBD) process has yielded interesting clues about the evolution of biodiversity through time. To facilitate such studies, we extend our method to compute the probability density of phylogenetic trees of extant and extinct taxa in which the only temporal information is provided by the fossil ages (i.e. without the divergence times) in order to deal with the piecewise constant FBD process, known as the "skyline FBD", which allows rates to change between pre-defined time intervals, as well as modelling extinction events at the bounds of these intervals. We develop approaches based on this method to assess hypotheses about the diversification process and to answer questions such as "Does a mass extinction occur at this time?" or "Is there a change in the fossilization rate between two given periods?". Our software can also yield Bayesian and maximum-likelihood estimates of the parameters of the skyline FBD model under various constraints. These approaches are applied to a simulated dataset in order to test their ability to answer the questions above. Finally, we study an updated dataset of Permo-Carboniferous synapsids to get additional insights into the dynamics of biodiversity change in three clades (Ophiacodontidae, Edaphosauridae and Sphenacodontidae) in the Pennsylvanian (Late Carboniferous) and Cisuralian (Early Permian), and to assess support for end-Sakmarian (or Artinskian) and end-Cisuralian mass extinction events discussed in previous studies.