Theoretical Underpinnings of Snow Interception and Canopy Snow Ablation Parameterisations

Vegetation structure is considered one of the most important factors shaping the spatial variation of snow accumulation under forest canopies. However, fine scale relationships between canopy density, snow interception, wind redistribution and sub‐canopy accumulation are poorly understood and difficult to observe, and their influence governing stand‐scale snow distributions that determine snow covered area depletion during melt is largely unknown. In this study, fine‐scale observations of forest structure and sub‐canopy snow accumulation were analysed over two mid‐winter snowfalls to a sub‐alpine forest in Marmot Creek Research Basin, Canadian Rockies, Alberta, to identify the impact of snow‐canopy interactions on spatial patterns of sub‐canopy snow accumulation. High spatial resolution (5 and 25 cm) snow accumulation estimates and canopy structure metrics were calculated from the combination of repeated UAV‐lidar observations with snow and photographic surveys, utilizing novel resampling methods including voxel ray sampling of lidar (VoxRS) to improve metric robustness and reduce bias. Over 50% of the spatial variance in forest snow accumulation was found at length scales less than 2 m, supporting the role of local scale canopy structure in governing variation in subcanopy snow accumulation. Additionally, subcanopy snow accumulation showed significant angular spread in relationships with overhead canopy structure; the vertical asymmetry coinciding with local windflow directions during snowfall. Detailed angular analysis showed nontrivial snow‐vegetation relationships that likely reflect multiple snowfall‐vegetation processes, including unloading and entrainment of intercepted snowfall during wind gusts and funnelling of entrained particles by downwind vegetation. These fine‐scale findings suggest several emergent processes which may influence snow accumulation at the scale of forest stands, with novel considerations for representing snow water equivalent distributions under dense evergreen canopies under varying environmental and canopy conditions. Similar studies over a broad range of conditions and forests will help refine and generalize the effects observed here for further snow hydrology and forestry applications.

Abstract. Multiple options for representing physical processes in forest canopies are added to FSM, which is a model with multiple options for representing physical processes in snow on the ground. The canopy processes represented are shortwave and longwave radiative transfer; turbulent transfers of heat and moisture; and interception, sublimation, unloading, and melt of snow in the canopy. There are options for Beer's law or two-stream approximation canopy radiative transfer, linear or non-linear canopy snow interception efficiency, and time- and melt-dependent or temperature- and wind-dependent canopy snow unloading. Canopy mass and energy balance equations can be solved with one or two model layers. Model behaviour on stand scales is compared with observations of above- and below-canopy shortwave and longwave radiation, below-canopy wind speed, snow mass on the ground, and subjective estimates of canopy snow load. Large-scale simulations of snow cover extent, snow mass, and albedo for the Northern Hemisphere are compared with observations and land-only simulations by state-of-the-art Earth system models. Without accounting for uncertainty in forest structure metrics and parameter values, the ranges of multi-physics ensemble simulations are not as wide as seen in intercomparisons of existing models. FSM2 provides a platform for rapid investigation of sensitivity to model structure and parameter values or ensemble-based data assimilation for snow in open and forested environments.

Recent work has examined ultimate factors limiting deer (Odocoileus spp.) and elk (Cervus elaphus) populations during winter, such as temperature and forage, but there has been inadequate examination of the influence of snow, especially in concert with foraging decisions. We examined deer and elk habitat selection on winter range in the temperate mountains of southeastern British Columbia. The life histories of radiocollared mule deer (O. hemionus) and elk included seasonal elevational migrations (1,000–1,400 m) and long-distance movements (up to 50–63 km, respectively). Late-winter, deep-snow habitat is limited in wet, mountainous environs and may explain the relatively low densities of ungulates present. Snow-track transects conducted during late winter suggested that deer (mule deer and white-tailed deer [O. virginianus] combined) avoided areas with >40 cm of snow and elk areas with >50 cm. Late-winter snow depth was positively related to elevation and negatively related to slope and solar radiation (hours/day), all of which can be obtained from existing databases and used to map relative late-winter snow depth. The snow-depth model can be used to map potential winter range regardless of current vegetation cover. During late winter deer selected older forests and stands with greater amounts of Douglas-fir (Pseudotsuga menziesii) in the overstory in forested sites. Older stands probably were selected because they had lower snow depths, while mature Douglas-fir trees offered more litterfall forage than other tree species. In contrast, elk selection among forested stands was weak, which suggested that forested stands were not preferred portions of their late-winter habitat. Track data during late winter confirmed that both deer and elk also used areas with low canopy cover, likely to acquire browse. We demonstrated that it is possible to map potential winter range using topographic variables as surrogates for relative snow depth, and we present a model applicable to portions of the temperate interior mountains. We suggest it is important to consider both forage production and snow interception in habitat management because winter energy budgets are a balance between nutrient intake and cost of locomotion.

It has been proposed that forests will act as a sink for -50% of the anthropogenic C02 projected to be released into the atmosphere by the year 2050 as global net primary productivity in forests increases (DeLucia et al. 1999). Coniferous forest ecosystems dominate a large portion of the Earth's land area, and fire plays an important role in the natural disturbance regime of these ecosystems (Archibald 1995). Quantifying the components of the carbon cycle during ecosystem recovery from fire is fundamental for determining how fire and changes in fire frequency alter regional and global carbon budgets (Auclair and Carter 1993, Houghton 1996, Burke et al. 1997). Clearly, if we are to model the effects of terrestrial ecosystems on global carbon budgets, we must develop a better understanding of the role that natural disturbance plays in the carbon dynamics of these systems. Processes that occur after fire may be more important for carbon cycling than the immediate return of carbon to the atmosphere through biomass oxidation (Auclair and Carter 1993). For example, primary productivity following fire is reduced or eliminated until new chlorophyll is synthesized in new leaf area. In addition, aboveground detrital inputs are greatly altered and formerly live roots become available for decomposition. Moreover, litter quality changes with the oxidation of fine fuels; soils and litter become warmer with the removal of overstory shading and a change in albedo; and soils become wetter because of essentially no post-fire transpiration and very little interception of rain and snow. These changes can increase decomposition and soil respiration (Burke et al. 1997), releasing as much as three times more carbon to the atmosphere as the amount released by the initial fire (Auclair and Carter 1993). Notably, carbon is assimilated by new plant growth in fire-adapted ecosystems, with perhaps little net effect on atmospheric C02 (Crutzen and Goldhammer 1993). In addition to large effects on carbon budgets at the stand scale, fire and landscape variables interact to produce a mosaic of different vegetation types (Anderson and Romme 1991, Turner et al: 1997a and b, Foster et al. 1998). The resulting spatial heterogeneity in tree density, herbaceous cover, and species composition in Yellowstone National Park (YNP) will influence primary production and carbon storage for many years. Therefore, to determine the long-term effects of fire on carbon release and storage following fire, information is needed on how processes differ among sites as a function of community structure and stand age. YNP is an ideal study area for this kind of research. Our objective is to answer two questions: 1) How does the relative abundance of trees, shrubs, and herbs influence above- and belowground carbon storage and flux values in young post-fire stands? 2) How do above- and belowground carbon storage and fluxes in young post-fire stands differ from those in nearby mature forests?

IDERIS, N. K. H, JAAFAR, S. MD. & SUKRI, R. S. 2025. Impact of road construction on tree diversity and forest structure in an intact Bornean mixed dipterocarp forest. Reinwardtia 24(1): 1–15. — Road construction has previously been shown to negatively impact biodiversity and is an urgent threat to Bornean tropical forests. We investigated changes in tree species diversity and forest structure of the Andulau Forest Reserve in Brunei Darussalam, following the construction of the Telisai-Lumut Highway. Within nine 20 × 20 m plots set up at varying distances from the forest edge where the road was located, we measured all trees ≥ 1 cm in diameter at breast height for their stem diameter, height and crown characteristics, and identified all trees ≥ 5 cm dbh. Although mean tree abundance and diversity between plots were similar, we detected significant differences in forest structure, particularly stem diameter, basal area, and crown characteristics. Plots closest to the road recorded the highest total tree species richness, although not significant, and contained a mixture of pioneer tree species and remnant interior forest species, while no pioneers were recorded in the interior forest plots. We documented the presence of high conservation value species, including three critically endangered species (Gonystylus bancanus, Hopea micrantha, and Vatica venulosa). Our work illustrates the potential impacts on forest structure from road construction and highlights the need for further studies to assess the long-term impacts on tree diversity and forest dynamics.

We performed a systematic review and meta-analysis of geographic and racial representation and reported success rates of studies of catheter ablation for atrial fibrillation (AF). We searched PubMed, Scopus, and Cochrane databases from 1/1/1990 to 8/1/2016 for trials and observational studies reporting AF ablation outcomes. Major exclusion criteria were insufficient reporting of outcomes, non-English language articles, and ablation strategies that were not prespecified and uniform. We described geographic and racial representation and single-procedure ablation success rates by country, controlling for patient demographics and study design characteristics. The analysis cohort included 306 studies (49,227 patients) from 28 countries. Over half of the paroxysmal (PAF) and nonparoxysmal AF (NPAF) treatment arms were conducted in 5 and 3 countries, respectively. Reporting of race or ethnicity demographics and outcomes were rare (1 study, 0.3%) and nonexistent, respectively. Unadjusted success rates by country ranged from 63.5% to 83.0% for PAF studies and 52.7% to 71.6% for NPAF studies, with substantial variation in patient demographics and study design. After controlling for covariates, South Korea and the United States had higher PAF ablation success rates, with large residual heterogeneity. NPAF ablation success rates were statistically similar by country. Studies of AF ablation have substantial variation in patient demographics, study design, and reported outcomes by country. There is limited geographic representation of trials and observational studies of AF ablation and a paucity of race- or ethnicity-stratified results. Future AF ablation studies and registries should aim to have broad representation by race, geography, and ethnicity to ensure generalizability.

Single species forest systems often suffer from low resistance and resilience to perturbations. Consequently, fostering tree species diversity is discussed as an important management approach to address the impacts of changing climate and disturbance regimes. Yet, the effect of the spatial grain of tree species mixtures remains unknown. We asked whether increasing tree species diversity between stands (beta diversity) has the same effect as increasing tree species diversity within stands (alpha diversity) at similar overall levels of richness (gamma diversity). We conducted a multi‐model simulation experiment under climate change, applying two forest landscape models (iLand and LandClim) across two contrasting landscapes of Central Europe. We analysed the effect of different levels and configurations of diversity on the disturbance impact and the temporal stability of biomass stocks and forest structure. In general, increasing levels of diversity decreased disturbance impacts. Positive diversity effects increased with increasing severity of climate change. Beta diversity buffered disturbance impacts on landscape‐level biomass stocks more strongly than alpha diversity. The effects of the spatial configuration on forest structure were more variable. Diversity effects on temporal stability were less pronounced compared to disturbance impacts, and mixture within and between stands had comparable effects on temporal stability. Diversity effects were context‐dependent, with patterns varying between landscapes and indicators. Furthermore, we found a strong species identity effect, with increasing diversity being particularly beneficial in conifer‐dominated systems of the European Alps. The two models agreed on the effects of different levels and configurations of tree species diversity, underlining the robustness of our findings. Synthesis and application. Enhancing tree species diversity can buffer forest ecosystems against increasing levels of perturbation. Mixing tree species between stands is at least as effective as mixing tree species within stands. Given the managerial advantages of between‐stand mixtures (e.g. reduced need to control competition to maintain diversity, higher timber quality, lower logistic effort), we conclude that forest management should consider enhancing diversity at multiple spatial scales. ​

Tree diversity across different tropical agricultural land use types

Although species richness has been hypothesized to be highest at 'intermediate' levels of disturbance, empirical studies have demonstrated that the disturbance-diversity relationship can be either negative or positive depending on productivity On the other hand, hypothesized productivity diversity relationships can be positive, negative or unimodal, as confirmed by empirical studies. However, it has remained unclear under what conditions each pattern is realized, and there is little agreement about the mechanisms that generate these diverse patterns. In this study, I present a model that synthesizes these separately developed hypotheses and shows that the interactive effects of disturbance and productivity on the competitive outcome of multispecies dynamics can result in these diverse relationships of species richness to disturbance and productivity The predicted productivity diversity relationship is unimodal but the productivity level that maximizes species richness increases with increasing disturbance. Similarly, the predicted disturbance diversity relationship is unimodal but the peak moves to higher disturbance levels with increasing productivity Further, these patterns are well explained by the opposite effects of productivity and disturbance on competitive outcome that are suggested by the change in community composition along these two environmental gradients: higher productivity favours superior competitors while higher disturbance levels favour inferior competitors.

Despite the fact that tropical dry forests are being exploited on a large scale for various forest products, there has been limited evaluation of the accompanying ecological impacts. In particular, there is no information on the effects of widespread biomass extraction such as grazing and firewood collection. A study was carried out in Sariska Tiger Reserve in northern India, to investigate the effects of biomass extraction on forest vegetation composition, diversity and structure. Biomass extraction caused significant changes in forest vegetation structure and species composition in the tree layer but the extent of these changes varied across the three major vegetation types found in the Reserve. Anogeissus-dominated slope forest showed significantly lower mean canopy cover, tree density, tree basal area and height of trees in disturbed sites in comparison to undisturbed sites. Riparian forest showed lower mean canopy cover, tree basal areas and number of recorded tree species in disturbed sites. Scrub forest had lower mean canopy cover, tree basal area and tree height. There were fewer tall trees but greater number of short trees in disturbed sites of all three vegetation types. Girths of trees similarly shifted towards lower values in riparian and scrub forest. In Anogeissus-dominated forest, disturbed and undisturbed sites did not differ in proportions of trees in various girth-classes. Tree species richness was substantially lower in disturbed sites of Anogeissus-dominated and riparian forest in comparison to undisturbed sites, but was not affected by disturbance in scrub forest. Understorey species richness was higher in disturbed sites of all three vegetation types but understorey changed structurally only in Anogeissus-dominated forest. Overall tree and understorey species composition was significantly different between disturbed and undisturbed sites of Anogeissus-dominated forest, but was unchanged in scrub and riparian forest. Observed changes in vegetation structure, diversity and composition of the different vegetation types due to biomass extraction have implications for biodiversity conservation in tropical dry forest ecosystems, and need to be addressed in future forest management planning.

ABSTRACTVegetation net primary productivity and its variations are important biophysical variables for reflecting climate–vegetation relationship. The Jing–Jin–Ji region in Northern China has important and strategic characteristics for forest resources and ecological environment. This study explores the NPP estimation and its spatial-temporal distribution at the regional scale of Jing–Jin–Ji, based on improved Carnegie-Ames-Stanford Approach model using MODIS. The quantitative evidence presented here suggests that NPP distribution was most strongly correlated with forest structures and climate and showed obvious seasonal changes. The simulated average annual NPP and the total NPP were 658.8and 14884.18, respectively. The results showed that the contribution of NPP of different forest type to total NPP in the study area was different, and the deciduous broadleaf forest had the maximum NPP in per unit area, followed by mixed forest, evergreen needleleaf forest and deciduous needleleaf forest. The simulated total NPP presented a decreasing trend from northwest to southeast. The analysis on NPP spatial–temporal changes concluded that NPP distribution had a close relationship with the climate seasonal changes. This paper provides not only an estimation NPP of different forest types in north China but also a useful methodology for estimating forest carbon storage at regional levels in China.

Mountain treelines are among the most climate-sensitive ecosystems on Earth, yet their fine-scale structural and species level dynamics remain poorly resolved in the Himalayas. In particular, the absence of three-dimensional, crown level measurements have hindered the detection of structural thresholds and species turnover that often precede treeline shifts. To bridge this gap, we introduce UAV LiDAR—applied for the first time in the Hindu Kush Himalayas—to quantify canopy structure and tree species distributions across a steep treeline ecotone in the Manang Valley of central Nepal. High-density UAV-LiDAR data acquired over elevations of 3504–4119 m was used to quantify elevation-dependent changes in canopy stature and cover from a canopy height model derived from the 3D point cloud, while individual tree segmentation and species classification were performed directly on the 3D, height-normalized point cloud at the crown level. Individual trees were delineated using a watershed-based segmentation algorithm while tree species were classified using a random forest model trained on LiDAR-derived structural and intensity metrics, supported by field-validated reference data. Results reveal a sharply defined treeline characterized by an abrupt collapse in canopy height and cover within a narrow ~60–80 m vertical interval. Treeline “threshold” was quantified as a breakpoint elevation from a piecewise model of tree cover versus elevation, and the elevation span over which modeled cover and height distributions rapidly declined from forest values to near-zero. Segmented regression identified a distinct structural breakpoint near 3995 m elevation. Crown-level species predictions aggregated by elevation quantified an ordered turnover in dominance, with Pinus wallichiana most frequent at lower elevations, Abies spectabilis peaking mid-slope, and Betula utilis concentrated near the upper treeline. Species classification achieved high overall accuracy (>85%), although performance varied among taxa, with broadleaf Betula more difficult to discriminate than conifers. These findings underscore UAV LiDAR’s value for resolving sharp ecological thresholds, identifying elevation-driven simplification in forest structure, and bridging observation gaps in remote, rugged mountain ecosystems.

ContextIn northern Europe, changes in forest ecosystem structures are commonly attributed to the ubiquitous impact of modern forestry. However, the starting point for modern forestry was not a pristine forest, but landscapes influenced for centuries by diverse human activities.ObjectivesOur aims were to (1) describe spatial patterns of forest structure and species compositions over large scales in 1920s Finland, and to (2) analyze how these characteristics were influenced by human population and past land-uses.MethodsWe mapped ca. 3000 systematic sample plots measured in the first Finnish National Forest Inventory (1921–1924) and produced a series of maps of large-scale variation in forest characteristics in upland forests. We analyzed forest age and size structures, and species compositions relative to human population and land-use data.ResultsWe found strong geographical and regional gradients in forest age and size structures, and tree species composition. Depending on the variable, these characteristics were at the stand-level best explained by human population density, reflecting the long history of various forest uses. Tree species composition was clearly associated with site productivity, but also with the history of slash-and-burn agriculture and forest grazing.ConclusionsForest landscapes in the early twentieth century Finland exhibited a strong human fingerprint, visible as the abundance of young forests in populated areas, while in remote areas forest characteristics typical of natural forests prevailed. These gradients in human impact a century ago are still reflected as legacies in forest structure, a situation that needs consideration in management and restoration.

Abstract. Computer simulations were used to elaborate hypotheses about controls on forest structure and composition in a 0.7 km ≤ area of boreal forest in Central Sweden. DBH and species of all adult trees and stand conditions were recorded for 57–10 m radius plots. Ordination of these data suggested that nutrient‐availability and time‐since‐disturbance were the main controls of forest composition and structure within the area.The simulation model couples equations representing the effect of tree canopy structure and biomass on light and soil conditions with equations representing the effect of these conditions on reproduction, growth and mortality in height cohorts of trees on a 0.1 ha patch. Nitrogen‐availability levels for each modeled plot were simulated by species‐specific growth multipliers. The model was run for 400 simulated yr at six levels of N availability. Age and N status of each study plot were inferred by matching with the most similar model output. Inferred ages agreed with what is known of the disturbance history, and site factors related to soil fertility were correctly correlated with the inferred N status.The consequences of size‐selective disturbance were explored by model experiments. Biomass was removed from large or small size classes at 100 ‐ 200 yr and the simulations were run for an additional 300 yr. Disturbed stands of high N status often became similar to undisturbed stands of different N status. Size‐selective disturbances produced stands that were different from any in the undisturbed succession, but these differences disappeared within 50 ‐ 100 yr, implying successional convergence in stand structure and composition. Plots of simulated basal area against time and nitrogen‐availability for the four species illustrate the time dependence of species performance along a fertility gradient.

Understanding the relationship between tree species diversity and above-ground carbon (AGC) storage in tropical forests is essential for a sustainable flow of ecosystem goods and services. Although tropical forests of Vietnam are of particular interest due to their high biodiversity and carbon density, few studies have evaluated the relative importance of species composition, tree species diversity and forest structure on AGC storage by forest vegetation type. In this study, we tested for the influence of taxonomic diversity, forest structure and species composition on AGC storage in evergreen broad-leaved and deciduous forests of Southeast Vietnam. Data was collected within 137 rectangular plots (25 m × 20 m), randomly selected across a deciduous forest (DF) and four evergreen broad-leaved forest (EB) categories, with different stand­ing volumes levels: very poor (EBG), poor (EBP), medium (EBM) and rich (EBR). In total, we identified 3687 individuals from 110 tree species belonging to 46 families in 6.85 hectares of sampled area. AGC stor­age significantly differed among forest categories, ranging from 14.81 Mg ha−1 in EBG to 146.74 Mg ha−1 in EBR. There was higher AGC in the medium diameter class (20-40 cm), except for EBR where there was higher AGC within individuals of 40-60 cm in diameter. Taxonomic diversity was weakly correlated with AGC while stand structure (stem density and maximum diameter) were strongly correlated. Our results suggest that maintaining the abundance distributions of remnant tree species, particularly that of large trees, is one important method to enhance AGC storage in the tropical ecosytems of southern Vietnam.