The research, led by Martin Béland of Laval University’s Digital Forest Lab together with Gordon Bonan of the NSF National Center for Atmospheric Research, Hideki Kobayashi of the Japan Agency for Marine-Earth Science and Technology, and Dennis Baldocchi of the University of California, Berkeley, tackles a stubborn blind spot in radiative transfer modeling. Computer models that simulate forest canopy microclimates, from the air temperature at the forest floor to the fluxes that link land surfaces to the global atmosphere, all begin with the same calculation: how much solar radiation does the canopy reflect, and where does the rest go? Classic one-dimensional schemes such as the Norman model from 1979 and the two-stream formulations of Dickinson and Sellers divide that absorbed energy among sunlit leaves, shaded leaves, and soil. Wood simply does not appear in the ledger.

Yet recent work has shown that woody structures absorb a significant fraction of incoming near-infrared radiation in dense forests and store it as heat. Because stems are massive, they warm slowly through the day and release that stored heat at night, shifting the diurnal rhythm of air temperature inside the canopy. That matters for the organisms living in the understory and on the forest floor, for the closure of energy budgets at eddy covariance flux towers, and for land surface models such as the Community Land Model, which currently lumps leaves and stems together into a single plant area index with weighted optical properties, never resolving their separate absorption.

The challenge is structural. Stems and branches are wildly heterogeneous in size, orientation, and density, and their exposure to sunlight depends on where they sit within the canopy. The team’s solution was to modify the radiative transfer component of the CanVeg2 multilayer canopy model, which uses the Norman scheme, so that wood is explicitly represented. The mathematics is elegant: the projected areas of leaves and stems are combined in the Beer-Lambert extinction equation, and each canopy layer’s intercepted radiation is partitioned between leaves and wood in proportion to their projected areas in that direction, with leaf area index and wood silhouette area index weighted by their respective projection factors and clumping indices. The full system is solved as a tridiagonal set of equations, keeping the model fast enough for routine microclimate simulation.

One subtlety the researchers had to confront is that stems, like leaves, are not randomly distributed in space, and this clumping affects how much radiation they intercept. With no modern data available, the team mined a remarkable historical dataset: light transmission measurements collected in the 1980s by a tram system shuttling PAR sensors back and forth through a temperate deciduous forest near Oak Ridge, Tennessee, during leaf-off conditions in January 1981. Inverting Beer’s law against those measurements, and correcting for the fact that bark scatters more light than leaves and thus inflates ground-level transmission, the team arrived at a wood clumping index of 0.75 for a temperate deciduous forest. Sensitivity tests showed this parameter matters: shifting it from 0.75 to 0.6 or 0.9 changed the radiation absorbed by stems by roughly 16 percent in both directions, even though canopy albedo barely moved.

Validating a one-dimensional model requires a trustworthy benchmark, and here the team turned to ground-based lidar and three-dimensional ray tracing. At four broadleaf deciduous sites spanning a structural gradient, Harvard Forest in Massachusetts, Morgan-Monroe State Forest in Indiana, the Smithsonian Environmental Research Center in Maryland, and the Pasoh Forest Reserve in Malaysia, each plot was scanned from 121 lidar positions to build dense 3D voxel grids, 30 centimeters on a side, that separately map leaf area density and wood silhouette area density. These voxel maps fed the FLiESvox ray tracing model, which tracks photons through the full three-dimensional canopy, including multiple scattering within clumped foliage using the recollision probability theory of Smolander and Stenberg. Running FLiESvox was computationally demanding: covering varying sun angles and diffuse fractions required 81 simulations in the PAR waveband and 81 in the near-infrared.

The agreement between the modified one-dimensional model and the 3D benchmark was strikingly good. Across all four sites, root mean square errors between vertically integrated absorbed fluxes came to about 12 watts per square meter in the PAR and about 8 watts per square meter in the near-infrared. Vertical profiles of absorption by sunlit leaves, shaded leaves, and wood agreed with mean errors per layer of a few tenths of a watt per square meter. A leaf-off test case, where only wood remains in the canopy, also showed strong agreement between the two models, suggesting the approach works year-round. The step-by-step model comparisons revealed why each modification mattered: adding foliage clumping lowered albedo and let light penetrate deeper, adding wood further reduced both albedo and the radiation reaching the soil, and adding multiple scattering within clumped layers significantly cut near-infrared albedo while boosting leaf absorption.

The team then compared modeled albedos against tower observations of reflected sunlight, the only component of the radiation budget routinely measured in the field. Both models overestimated broadband albedo by roughly 4 to 7 percent, but the modified Norman model came noticeably closer to the observations than its predecessor, thanks to stem absorption and the treatment of multiple scattering. The characteristic U-shaped diurnal pattern of albedo, higher when the sun sits low, was successfully reproduced. The residual overestimate could stem from uncertain optical properties of leaves, soil, or bark, which vary with moisture, or even from the metallic tower structure itself slightly biasing the measurements. The authors also note that the recollision probability theory was developed for needleleaf shoots, and its extension to broadleaf shoots, while supported by the results, deserves dedicated testing with models that represent every leaf as an explicit mesh.

The practical consequences ripple outward. Because stems absorb far more near-infrared than photosynthetically active radiation, including them will barely change carbon and latent heat fluxes, but it will strongly alter sensible heat fluxes and biomass heat storage, with implications for the persistent energy budget closure problem at flux towers. More dramatically, the simulations showed that omitting stems nearly doubles the radiation absorbed by the soil in both wavebands, a major distortion of the energy balance at the soil-air interface that may explain why land surface models have needed empirical corrections to under-canopy wind speeds. With the modified model, wood absorption is computed directly from canopy structure, resolved vertically, and free of ad-hoc partitioning, and the code and data are openly available on Zenodo for other modeling groups. Validation in needleleaf forests, savannas, and sparse canopies lies ahead, but for dense broadleaf forests, the trunks and branches that were once invisible to climate models can now finally be counted, and the forest’s hidden heat economy is coming into focus.

Subject of Research: Radiation absorption by woody stems in forest canopy microclimate modeling

Article Title: Consideration of radiation absorption by stems in forests for microclimate modeling

Article References: Béland, M., Bonan, G., Kobayashi, H., & Baldocchi, D. (2026). Consideration of radiation absorption by stems in forests for microclimate modeling. Geoscientific Model Development, 19(18), 9019-9033. https://doi.org/10.5194/gmd-19-9019-2026

Image Credits: AI Generated

DOI: 10.5194/gmd-19-9019-2026

Keywords: forest microclimate, radiative transfer, wood heat storage, ground lidar, canopy albedo, Norman model, near-infrared radiation, leaf clumping, eddy covariance, land surface modeling, 3D ray tracing, deciduous forests

The research, published in Biosphere: A Scientific Journal under the title Risks to Unique Dialects of Birdsong: The Case of Chaffinch (Fringilla coelebs) Song Dialects in Southern and Eastern Ukraine During the Russia–Ukraine War, was carried out by Eugenia Yablonovska-Grishchenko and Vitaly Grishchenko. Its starting point is a fundamental fact of songbird biology. Unlike the calls that birds produce instinctively from birth, the songs of many songbird species are learnt behaviours, passed down from one generation to the next through listening and imitation. Over time, local populations develop their own recognisable variants of a species’ song, and these variants persist because young birds learn from the older birds around them. The result is a form of non-hereditary cultural transmission that has evolved independently in birds just as it has in human language.

The Common Chaffinch is one of the best-studied examples of this phenomenon in Europe. Populations across its range maintain distinct, geographically bounded song dialects, and the steppe zone of southern and eastern Ukraine is home to several such regional vocal complexes that had been documented and mapped in previous scientific work. Those earlier maps are what made the new study possible. Because the geographic distribution of chaffinch dialects in the region had already been described, the researchers could identify the specific forest plots that had been used to characterise each regional vocal complex, and then check, plot by plot, whether those forests were still standing.

Since February 2022, active combat across southern and eastern Ukraine has destroyed forests, triggered large-scale fires, and displaced wildlife populations. The research team identified 41 forest plots that had been used in earlier work to describe and map the regional dialects, and assessed each one using satellite images from summer and autumn 2025. Every plot was classified into one of three conditions: normal, damaged, or destroyed. The classification was necessarily remote, because fieldwork inside active combat zones is impossible, but the satellite record allowed a systematic, plot-by-plot assessment of the habitat on which each dialect depends.

The results showed that 70.7 percent of the plots remained in normal condition, 19.5 percent had been damaged by proximity to combat activity, and 9.8 percent had been completely destroyed following the most intense fighting. In other words, just under a third of the sites that anchor the region’s documented chaffinch dialects have been degraded or erased. The geographic pattern of the damage was not uniform, and it is this unevenness that gives the study its most important ecological insight: the fate of a dialect under bombardment depends largely on what kind of trees grow in the forest that sustains it.

Plots located on the Donetsk Ridge, which is covered primarily by native deciduous forests of oak, ash, and other broadleaf species, showed comparatively lower rates of destruction. Deciduous forests are considerably more resistant to fire than coniferous ones. They retain more moisture, and fire does not carry as readily through their canopies. When combat or associated fires reached the ridge, the broadleaf woodland tended to survive, and with it the local populations of chaffinches that carry the Donetsk Ridge sub-dialect. The authors note that this dialect therefore faces a lower extinction risk than others in the region, precisely because its habitat is comparatively resilient.

The contrast comes from the Lower Dnipro floodplain. The coniferous plantations there are artificial, established decades ago to stabilise sandy soils, and they proved highly vulnerable. In plots within this zone where combat or associated fires occurred, destruction was severe or complete. Unlike the native broadleaf forests of the Donetsk Ridge, these pine plantations burn readily, carrying fire through their canopies and leaving little behind. The dialect associated with the Lower Dnipro floodplain consequently faces a substantially higher risk, given how severely its coniferous forests have burned. The same war, striking different forest types, produces sharply different outcomes for the cultural heritage of the birds living there.

The study draws a distinction that matters enormously for conservation: losing a forest is not the same as losing a dialect, but the two losses are closely linked. Chaffinch song dialects persist because birds living within a defined geographic area learn their local song variant from older birds around them. If the forest is destroyed and the local population is wiped out or scattered, the dialect dies with them. Replanting the forest decades later does not restore the dialect, because there are no local teachers left to transmit it. In this sense, the destruction documented in the study is not simply ecological damage but cultural damage in a biological sense: the erasure of learnt, transmitted behaviours that took generations to develop and that cannot be recovered once broken. A replanted pine stand may one day host chaffinches again, but the songs they sing will not be the songs that were lost.

The authors are careful about the limits of their evidence. The study is constrained by the resolution of available satellite imagery and by the impossibility of conducting fieldwork in active combat zones, meaning that the ground-level state of individual sites could not be directly verified. Satellite classification of normal, damaged, or destroyed condition is a proxy for habitat status, not a census of surviving birds. What the imagery can establish is which habitat patches remain, which have been degraded by proximity to fighting, and which have been erased altogether, and on that basis which dialects are most and least likely to have survived the war so far.

Given those constraints, the researchers call for post-war field surveys to assess which populations and dialects have survived, and for the documentation and recording of remaining dialects to be treated as a conservation priority before further losses occur. The logic is straightforward: a dialect that has been recorded can at least be studied and compared with future populations, while one that disappears unrecorded is gone without trace. The war in Ukraine has already inflicted severe and well-documented damage on the region’s ecosystems, but this study adds a subtler dimension to that accounting. Alongside the forests burned and the wildlife displaced, something intangible is being lost: regional traditions of learnt song, built up over generations of transmission from bird to bird, now at risk of falling silent before anyone can record them. Whether any of them can be heard again after the guns stop will depend on what the satellite images cannot yet show, and on the field surveys that must follow.

Subject of Research: Wartime destruction of forests hosting regional Common Chaffinch song dialects in southern and eastern Ukraine

Article Title: Risks to unique dialects of birdsong

Article References: Risks to unique dialects of birdsong. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: chaffinch, birdsong dialects, Ukraine, Russia–Ukraine war, cultural transmission, satellite imagery, forest destruction, conservation, song learning, deciduous forests, coniferous plantations, Biosphere journal