Pine Canopy Research Articles

Do heavy-metal grassland species survive under a Scots pine canopy during early stages of secondary succession?

The highly specialized flora of localities affected by former metal ore mining and metallurgy is endangered by succession or intentional afforestation all over Europe. Its last remnants therefore deserve our attention. We examined whether Scots pine encroaching on a heavy-metal grassland (Olkusz Zn-Pb mining area, S Poland) is outcompeting specialized herbaceous species, as has been observed elsewhere. Plant species composition and richness sampled at 124 plots were analysed in relation to pine stand parameters (canopy cover, stand age, stand basal area), abiotic environmental factors (e.g. soil properties) and spatial variables (e.g. plot coordinates). Plots were divided into three shading categories and compared in terms of vegetation and habitat parameters. Scots pine outcompeted several light-demanding species, leading to a decrease of total species richness and cover. Characteristic species of this grassland (Biscutella laevigata, Silene vulgaris) and some metal-tolerant plants were clearly insensitive to shading. For these early successional species, more important was the availability of microsites with shallow skeletal soil or bare subsoil. Tree stand parameters differently affected grassland vegetation: canopy cover caused primarily a compositional shift in the community, while stand age was the principal agent of decline in species richness. Scots pine increased the soil concentrations of available Ca and Mg, and negatively affected soil development (organic matter and mineral particle accumulation), which might be beneficial to some shade-tolerant grassland species. Maintaining the studied grassland’s present species richness and composition would require cutting woody plants less frequently than recommended for dry grasslands of non-metalliferous sites, and disturbing the soil surface.

Alteration of forest succession and carbon cycling under elevated CO2.

Regenerating forests influence the global carbon (C) cycle, and understanding how climate change will affect patterns of regeneration and C storage is necessary to predict the rate of atmospheric carbon dioxide (CO2 ) increase in future decades. While experimental elevation of CO2 has revealed that young forests respond with increased productivity, there remains considerable uncertainty as to how the long-term dynamics of forest regrowth are shaped by elevated CO2 (eCO2 ). Here, we use the mechanistic size- and age- structured Ecosystem Demography model to investigate the effects of CO2 enrichment on forest regeneration, using data from the Duke Forest Free-Air Carbon dioxide Enrichment (FACE) experiment, a forest chronosequence, and an eddy-covariance tower for model parameterization and evaluation. We find that the dynamics of forest regeneration are accelerated, and stands consistently hit a variety of developmental benchmarks earlier under eCO2 . Because responses to eCO2 varied by plant functional type, successional pathways, and mature forest composition differed under eCO2 , with mid- and late-successional hardwood functional types experiencing greater increases in biomass compared to early-successional functional types and the pine canopy. Over the simulation period, eCO2 led to an increase in total ecosystem C storage of 9.7 Mg C ha(-1) . Model predictions of mature forest biomass and ecosystem-atmosphere exchange of CO2 and H2 O were sensitive to assumptions about nitrogen limitation; both the magnitude and persistence of the ecosystem response to eCO2 were reduced under N limitation. In summary, our simulations demonstrate that eCO2 can result in a general acceleration of forest regeneration while altering the course of successional change and having a lasting impact on forest ecosystems.

Observations and snow model simulations of winter energy balance terms within and between different coniferous forests in southern boreal Finland

Variation of canopy properties between different forest types is seldom taken into account in hydrological and climate models, and consideration of variation inside a forest is normally omitted. In this work, three data sets on near surface energy balance terms (incoming shortwave and longwave radiation; air and snow–soil interface temperatures) were collected in the southern boreal coniferous zone in Finland during three winters below different types of forest canopies. The aim was to evaluate the ability of a snow mass and energy balance model with a canopy module to reproduce the observed differences in below-canopy incoming radiations and snow–soil interface temperature. Clear differences were seen between pine and spruce forest sites (higher snow–soil interface temperatures and incoming shortwave fluxes, and lower incoming longwave fluxes at the pine site). Differences were also observed between the sparse and dense pine canopy locations. Canopy parameter values had a great effect on the quality of the model simulations. The combination of optically obtained leaf area index (LAI) values with a needle clumping correction and either optical or empirical sky view fraction (SVF) values as a canopy parameterization gave better correspondence to observations than the use of uncorrected effective LAI and any SVF.

Stand-level drivers of tree-species diversification in Mediterranean pine forests after abandonment of traditional practices

The progressive abandonment of traditional forest management over the last few decades has led to significant densification processes in most Mediterranean pine stands. In parallel, some of these stands have also shown tree-species diversification processes, the occurrence of which is considered essential for future adaptability and resilience to change. Here we aim to gain further understanding of the main factors driving these diversification processes via a case-study approach using the long-term-managed black pine (Pinus nigra Arn. ssp. salzmannii) forests of the Catalan Pre-Pyrenees (NE Spain). For this purpose, we sampled 155 plots distributed in 8 different stands and analyzed the role played by a number of microsite factors and stand attributes (including canopy openness and heterogeneity) on the abundance of seedlings (h<1.3m) and saplings (h>1.3m; dbh<7.5cm) of the main tree-species in the area (i.e. black pine, evergreen oak and marcescent oaks). Results revealed ongoing black pine recruitment limitation processes mainly associated to the high canopy cover of the overstory and the increasing abundance of shrubs, which may compete with pines for light resources. In contrast, we found that current environmental and stand-level conditions favor the progressive advance of the recruitment of evergreen and marcescent oaks, which are able to establish successfully under the dominant pine canopy. However, in the absence of canopy openings, light levels may not allow the established oaks (in particular the evergreen Quercus ilex) to grow and progress to higher developmental stages. Our findings bring deeper insight into the role of stand-level factors regulating species diversification, and can be used by forest managers to adjust their practices (e.g. by modifying the spatial and temporal patterns of silvicultural treatments such as thinnings or selection cuttings) in order to favor this natural process and increase stand resilience.

Atmospheric Deposition and Interactions with Pinus pumila Regal Canopy on Mount Tateyama in the Northern Japanese Alps

To estimate the impact of atmospheric deposition on alpine ecosystems, we evaluated the interactions between atmospheric deposition and the Pinus pumila canopy close to the summit of Mount Tateyama, central Japan. We analyzed the chemical characteristics of rain, fog, and throughfall under the canopy in the summertime for 5 years. The concentrations of inorganic nitrogen and sulfate in precipitation at the summit (2839 m a.s.l.) were lower than at the base (13 m a.s.l.), but the total amounts deposited tended to be larger, because the precipitation was greater at the summit and highly concentrated fog water was deposited on the pine canopy. Large fluctuations in the quality and quantity of deposition were due to interannual variations in the meteorological conditions. About 80% of NO3 --N and NH4 +-N (0.40 and 0.47 kg ha-1 month-1) from rain and fog were retained in the P. pumila canopy, and contributions from fog were twice those from rain. Considerable amounts of K+, Mg2+, and Ca2+ ions (0.97, 0.13, and 0.13 kg ha-1 month-1) were leached out from the canopy to the soil as throughfall. The leaching did not increase with rainfall, but increased as the duration of the fog and dew increased.

Estimation of temporal and spatial variations in groundwater recharge in unconfined sand aquifers using Scots pine inventories

Abstract. Climate change and land use are rapidly changing the amount and temporal distribution of recharge in northern aquifers. This paper presents a novel method for distributing Monte Carlo simulations of 1-D sandy sediment profile spatially to estimate transient recharge in an unconfined esker aquifer. The modelling approach uses data-based estimates for the most important parameters controlling the total amount (canopy cover) and timing (thickness of the unsaturated zone) of groundwater recharge. Scots pine canopy was parameterized to leaf area index (LAI) using forestry inventory data. Uncertainty in the parameters controlling sediment hydraulic properties and evapotranspiration (ET) was carried over from the Monte Carlo runs to the final recharge estimates. Different mechanisms for lake, soil, and snow evaporation and transpiration were used in the model set-up. Finally, the model output was validated with independent recharge estimates using the water table fluctuation (WTF) method and baseflow estimation. The results indicated that LAI is important in controlling total recharge amount. Soil evaporation (SE) compensated for transpiration for areas with low LAI values, which may be significant in optimal management of forestry and recharge. Different forest management scenarios tested with the model showed differences in annual recharge of up to 100 mm. The uncertainty in recharge estimates arising from the simulation parameters was lower than the interannual variation caused by climate conditions. It proved important to take unsaturated thickness and vegetation cover into account when estimating spatially and temporally distributed recharge in sandy unconfined aquifers.

Initial Vegetation Response to Fuel Mastication Treatments in Rare Butterfly Habitat of the Spring Mountains, Nevada

Current dense forests in the Spring Mountains, Nevada, attributed to land management practices including fire exclusion, are considered to provide sub-optimal habitat for the rare endemic Mount Charleston blue butterfly (Plebejus shasta charlestonenesis). To reduce fuel loads in these forests, managers have used various treatments, including tree thinning and mechanical mastication. This study analyzed potential negative and positive effects of deposition of masticated slash (post-tree thinning material such as branches and logs) on host plants within Mount Charleston blue habitat. We manipulated depth of woodchip beds in 1-m2 quadrats at a Pinus ponderosa (ponderosa pine) site and monitored understory vegetation and butterfly host-plant response to the treatments. We also performed a germination experiment on seeds of the butterfly larval host plant Astragalus calycosus var. calycosus (Torrey's milkvetch) by applying various treatments combinations which included shading, liquid smoke, cold stratification and scarification. We found no significant effect (P>0.05) to any of the plant community variables (e.g., species richness, plant cover, and A. c. var. calycosus density, cover, and flowering) from forest-floor treatments during the first reproductive season after treatments. Cover and leaf number of A. c. var. calycosus declined over all treatments, suggesting that the pine tree canopy inhibited butterfly host plants, despite thinning of the pine canopy, or other factors limited the host plant. In the germination experiment, scarification significantly increased germination but all other treatment effects were not significant (P>0.05). The lack of a short-term response of the plant community to forest-floor manipulation is consistent with experiments in other P. ponderosa forests (including longer-term research) and indicates that these treatments did not substantially alter the vegetative characteristics of butterfly habitat. Given the potential detrimental effects of wood chip deposition on butterfly habitats, this small-scale experiment indicates that such effects will not result in short-term changes in Mt. Charleston blue butterfly host plants in wood chips layers less than 5 cm in depth.

Intensity of haemosporidian infection of parids positively correlates with proximity to water bodies, but negatively with host survival

In birds, haemosporidian parasites have been found to have direct pathogenic effects on the host with important consequences for their fitness. However, less is known about distribution patterns of parasite vectors, which may significantly affect parasite prevalence, infection intensity and, thus, pathogenicity in hosts. Here, we tested for relationships between infection intensity, survival, predation and distance from water bodies of mixed-species tit flocks. We found that the prevalence of Haemoproteus and Plasmodium infections decreased with increasing distance from forest lakes and bogs outside the bird breeding season. Haemoproteus and Plasmodium parasites were found to be associated with a low survival rate of willow tits (Poecile montanus) in the vicinity of water bodies, while crested tits (Lophophanes cristatus) were affected only by Haemoproteus. Crested tits, a dominant species of parid social groups, had a lower parasite prevalence and they survived better than the subordinate willow tit. This can be explained by the crested tits foraging higher in the pine canopy as parasite vectors supposedly cannot reach hosts in the upper canopy as equally as in lower parts of the canopy. We show that individuals staying in flocks further from the forest water bodies and spending more time foraging in the upper parts of the canopy have higher chances of survival into the next breeding season. This suggests that different forest and canopy areas may differ in terms of parasite risk and associated mortality. Finally, we found that the infection status of parids increases the probability of predation by the pygmy owl (Glaucidium passerinum). We conclude that distance from water bodies and foraging location in the forest canopy may affect the intensity of parasite infection with fitness consequences in wintering parids.

Is this the end? Dynamics of a relict stand from pervasively deforested ancient Iberian pine forests

A drier climate together with intense management can be detrimental for species when they are found at their xeric limit. We analyzed the dynamics of Pinus sylvestris in Central Spain in relation to colonization by more drought-tolerant Quercus pyrenaica. The studied forest presents high biodiversity and is one of the last stands relict from a widespread pine-dominated forest in West-Central Iberian Mountains demised by human deforestation. The observed age patterns could suggest a natural regeneration origin of the current stand for both species. However, while oaks regenerated continuously since the 1950s, there was almost no pine regeneration after the 1870s. Therefore, the lack of pine regeneration was previous to recent climatic changes. Pine stands with ongoing oak colonization were likely thinned in the 1920s in opposition to pure pine stands. Mixed and pure stands expressed certain differences in their response to climate. Pines suffered more from high temperatures from spring to fall, which would reflect their lower tolerance to drought than oaks. Cross-wavelet analysis showed that pine exhibited an increase in their sensitivity to drought intensity in the last years. However, the dominant pine canopy established in the nineteenth century does not show symptoms of growth decline in response to climate change. The factors determining the disruption of pine regeneration need to be determined. Management could have played a dominant role constraining stand dynamics, threatening pine sustainability through modifications of the understory vegetation and soil properties.

Germinazione dei semi e sopravvivenza dei semenzali di leccio (Quercus ilex L.) in interventi finalizzati alla rinaturalizzazione delle pinete di pino d’Aleppo (Pinus halepensis Mill.) dell’isola di Pianosa (Arcipelago Toscano, L

Abstract: Interventions aimed at promoting Quercus ilex spread in the Island of Pianosa (Tuscan Archipelago National Park) have been carried out within LIFE Nature Project “Tuscan Islands: new actions for sea birds and habitats”. In Pinus halepensis stands from afforestation, 810 acorns have been sown in 9 areas under the pine canopy with different presence of Mediterranean scrub. Germination and seedlings survival, five years after sowing, have been very satisfactory only in areas with a dense shrub layer.

On the SAR Backscatter of Burned Forests: A Model-Based Study in C-Band, Over Burned Pine Canopies

A discrete scattering model, based on the radiative-transfer theory, is used to simulate the backscattering of burned pine canopies at C-band. The model is first parameterized either with direct field measurements on a selected burned area in Greece or with proper estimations of the required variables, for which direct measurements were not possible. The simulated backscatter at VV polarization was compared against European Remote Sensing 2 (ERS-2) observations. The comparison was based on the observed backscattering of nine burned plots, during four different postfire acquisitions $(n=36)$ . In general, the model provides satisfying estimations of the backscattering with a root-mean-square error of 1.01 dB. The copolar signal for both HH and VV showed a mild decrease with increasing fire impacts and was considerably affected by the incidence angle. From the experiments performed in the simulated environment, it is concluded that the SAR copolar (C-band) backscatter varies with respect to certain fire impact levels. Other important acquisition- or stand-dependent variables (such as incidence angle and snag age) were also found to impact the relationship between backscatter and fire impacts. Finally, the backscattering variability on increasing volumetric soil moisture (VSM) and snag moisture was examined. The increase of VSM from 20% to 30% amplified the signal in both copolarized bands by 1.2–1.5 dB. This amplification was more apparent on VV polarization than in HH polarization. Instead, the HH signal proved to be more sensitive on the increase of snag moisture, which was tested under a stable dry soil.

Native North American pine attenuates the competitive effects of a European invader on native grasses

Strong direct competitive interactions between two species can be attenuated or exacerbated by the asymmetric effects of other species. In this context we explored a natural pattern in which an exotic invader, Centaurea stoebe, was much less abundant under ponderosa pines than in open grassland. In a field experiment Centaurea had strong competitive effects on the native Pseudoroegneria spicata in open grassland. Pines had no effects on either Centaurea or Pseudoroegneria when they were grown alone, but the strong competitive effects of Centaurea on Pseudoroegneria found in open grassland did not occur under pine canopies. In common garden experiments we found that shade mimicking one effect of pine canopies inhibited Centaurea but did not affect the native Festuca idahoensis. Shade did not alter competitive outcomes between the native and the invader. In the same experiment, soil from under pines increased Centaurea size and its competitive effects on Festuca, the opposite of what would be predicted from natural patterns in the field. However, pine litter strongly suppressed Centaurea in field and greenhouse experiments, inhibited growth of Festuca when grown alone, and importantly also eliminated competition between Festuca and Centaurea. Overall, our results suggest that ponderosa pine may resist Centaurea invasion both directly and by attenuation of the invader’s competitive effects. This biotic resistance appears to occur in part through asymmetric direct effects of pine litter, and in part from ways in which the litter, canopy effects, and soil under pines modify interactions between Centaurea and natives.

Time series analysis of forest carbon dynamics: recovery of Pinus palustris physiology following a prescribed fire

Frequency and intensity of fire determines the structure and regulates the function of savanna ecosystems worldwide, yet our understanding of prescribed fire impacts on carbon in these systems is rudimentary. We combined eddy covariance (EC) techniques and fuel consumption plots to examine the short-term response of longleaf pine forest carbon dynamics to one prescribed fire at the ends of an edaphic gradient (mesic and xeric sites). We also introduce novel (to the EC research community) statistical time-series approaches to quantify the drivers of carbon dynamics in these systems. We determined that our mesic site was a moderate sink of carbon (−157.7 ± 25.1 g C m−2 year−1), while the xeric site was carbon neutral (5.9 ± 32.8 g C m−2 year−1) during the study. The fire released 408 and 153 g C m−2 year−1 for the mesic and xeric sites, respectively. When loss associated with fire was combined with net ecosystem exchange rates, both sites became moderate carbon sources for the year. Analyses of assimilation and respiration parameters (e.g., maximum photosynthesis, quantum efficiency, and daytime ecosystem respiration) showed a positive trend over time pre-fire and a negative trend over time post-fire for maximum ecosystem CO2 uptake rates, and the opposite relationship for daytime ecosystem respiration rates. Within 30 days following fire, ecosystem physiological activity was statistically similar to pre-fire and appeared to be driven by the pine canopy. Our results suggest that prescribed fire (low intensity, high frequency) maintains the existing structure and function (in this case, carbon flux rates) because longleaf pine ecosystems have evolved with fire. This study, 1 year in length, provides a foundational understanding of the complex interaction between fire and carbon dynamics for longleaf pine ecosystems. Moreover, it provides a case study for applying time series analysis methods to EC data where there are complex relationships between ecosystem physiological activity and environmental drivers. However, to elicit a broader understanding of the complex interaction occurring between fire and carbon dynamics long- term studies are needed.

Can vegetation types work as an indicator of soil organic carbon? An insight from native vegetations in Nepal

Soil is the largest pool of carbon after the ocean. The assessment of soil organic carbon (SOC) stocks under different types of vegetations is critical for evidence-based implementation of soil carbon trading under different market mechanisms. Using data from 490 permanent soil sample plots with elevations ranging from 271m to 3238m above sea level, from three different watersheds in Nepal, this study aims to compare SOC under five different forest types and determine whether forest types could be indicator of SOC: Shorea robusta; mixed broadleaf; Schima-Castanopsis; pine; and Rhododendron-Quercus forests. In each vegetation type forests with dense canopies (≥70% canopy cover) have higher amounts of SOC than that of open canopy forests (<70% canopy cover). On average, with up to 30cm soil depth, dense canopy Rhododendron-Quercus forest has the highest amount of SOC (14,136gC/m2), followed by dense canopy mixed broadleaf forest (12,576gC/m2). One-way analysis of variance (ANOVA) indicates significant differences in soil organic carbon (SOC) amounts across the five forest types (df=485, F=17.299, p=0.000) and therefore forest types could be indicator of SOC. Moreover, within the similar altitudinal zone and topographic, edaphic and climatic environments: soils under the mixed species forests have higher amounts of SOC than that of single species dominated forests; and soils under forests with nitrogen fixing trees have a higher amount of SOC than those from other forests. Therefore, in addition to forest types these two conditions within the given vegetation types could work as sub-indicators of SOC. In comparison with global studies, all Nepalese forest types had much higher levels of SOC. Only two of the seven factors/indicators investigated (altitude and average age of dominant trees) were found to have significant impacts (r=0.33 to 0.64) on SOC and only in the dense and sparse canopy pine forests. The reasons of not having any impacts of all other factors on SOC in different vegetation types have been discussed.

Restoration of rain forest beneath pine plantations: A relay floristic model with special application to tropical South Asia

In the wet forest regions of southwest Sri Lanka and the Western Ghats, India, Pinus caribaea was a common tree species for reforestation on public lands that were originally cleared of native forest for agriculture but subsequently succeeded to fire tolerant grasses and ferns. Much of this reforestation occurred during the 1970s and 1980s. The ecological literature suggests that in many temperate broadleaf forest regions pine is an important component of early succession on old fields, beneath which second growth hardwood can establish and eventually dominate. More recent studies have demonstrated the establishment of native rain forest regeneration beneath a variety of exotic tree plantations. We review nearly twenty-five years of research on this topic for South Asia through a series of studies done in southwest Sri Lanka. Results demonstrate that native species recruitment of both pioneers and site generalist late-successional trees grow well beneath exotic pine plantations. Diversity and density increase from plantation interior to edge. Protection from groundstory fire is the single most important component of promoting regeneration recruitment beneath pine. Establishing late-successional site and dispersal restricted species requires planting beneath pine rather than reliance on natural establishment. Best establishment and growth occur in openings where rows of canopy pine have been removed. Species considered for planting comprise the major late-successional canopy tree species of the forest in the genera Dipterocarpus, Shorea (Dipterocarpaceae) and Mesua (Clusiaceae). Native species that produce non-timber forest products (NTFP) need to be planted with best results in canopy openings. The most valuable NTFP’s comprise a sugar palm (Caryota urens), rattan (Calamus spp.) and a medicinal liana (Coscinium fenestratum). Financial analyses reveal that pine plantations that are enrichment planted and cultivated with rain forest timber and non-timber species can provide superior economic benefits as compared to land cultivated singly for tea.

Effects of overstory retention, herbicides, and fertilization on sub-canopy vegetation structure and functional group composition in loblolly pine forests restored to longleaf pine

The desirable structure of longleaf pine forests, which generally includes a relatively open canopy of pines, very few woody stems in the mid-story, and a well-developed, herbaceous ground layer, provides critical habitat for flora and fauna and contributes to ecosystem function. Current efforts to restore longleaf pine to upland sites dominated by second-growth loblolly pine require information about how restoration treatments affect sub-canopy vegetation. We established a field experiment at Fort Benning in Georgia and Alabama, USA to determine the effects of four levels of approximately uniform canopy density (Control [∼16m2/ha basal area], MedBA [∼9m2/ha basal area], LowBA [∼5m2/ha basal area], and Clearcut [0m2/ha basal area]) and three cultural treatments (NT [untreated], H [chemical control of woody and herbaceous vegetation] and H+F [chemical control plus fertilization]) on vegetation structure and functional group composition for three growing seasons following canopy removal. In general, cover (a measure of abundance) of ground layer vegetation increased with the amount of canopy removal. The ground layer was dominated by herbaceous vegetation in each year. Canopy trees generally suppressed the cover of graminoids in the first two years after treatment but only the Control plots had lower graminoid cover than Clearcut plots after the third growing season. Forb cover was significantly lower on Control plots than on Clearcut plots after only the first growing season, and woody stems/shrubs had lower cover on Control plots than on LowBA or Clearcut plots in each year. Vegetation cover increased following the first year after canopy removal, and the relative dominance of functional groups did not change through time. Canopy retention limited the development of mid-story woody stems, with the greatest stem densities in the Clearcut plots. The herbicide treatment (on both H and H+F) significantly reduced woody stem density in the mid-story in 2009, but the effect was no longer significant in 2010. Traditional methods for converting stands of other pine species to longleaf pine commonly include clearcutting followed by planting, but our results suggest that clearcutting may release woody vegetation to increase mid-story stem densities and will reduce the amount of pine needles in the fuel bed. Retaining low to moderate levels of canopy density (5–9m2/ha basal area) in loblolly pine stands may provide an effective balance for reaching multiple restoration objectives that include maintaining desirable vegetation structure and creating fuel conditions for a frequent fire regime.

Inter-specific competition and management modify the morphology, nutrient content and resorption in Scots pine needles

Influence of tree-to-tree competition on nutrient resorption is still not well understood. To contribute filling this gap, we assessed the effects of thinning (0, 20 and 30 % extraction of basal area) and canopy type (beech–pine vs. pine subplots) on needle dry weight, needle length, nutrient content and nutrient resorption (N, P and K) in Scots pine (Pinus sylvestris) needles of different cohorts, 8–9 years after thinning. Thinning and canopy type often concurrently affected needle morphology (e.g. lighter and shorter needles in 30 % thinning, heavier and longer needles in pine canopy on the first year of study) and nutrient content (e.g. decrease in N, P and K in 30 %; N, P and K higher in pine canopy on the first year of study). However, effects of thinning appeared only in older cohorts for N and P but were found in old and new cohorts for needle dry weight, needle length and K, indicating that some thinning effects remained after 8–9 years. Canopy effects on morphology and nutrient content were more frequent in recent cohorts, in relation to an increase in beech cover over time. While no clear effects of thinning on the nutrient resorption were observed, higher values were observed in the pine than in the mixed canopy, which could be related to a higher Scots pine stem growth in those patches. The observed differences between treatments will likely increase as the stand develops, probably leading to beech trees being dominant, and as future thinnings are carried out.

Estimation of canopy fuel characteristics of Aleppo pine (Pinus halepensis Mill.) forests in Greece based on common stand parameters

Canopy fuel characteristics that influence the initiation and spread of crown fires were measured in forty representative Aleppo pine (Pinus halepensis Mill.) stands in Greece. Aleppo pine canopy fuels are characterized by low canopy base height (CBH) (2.0–6.5 m), while available canopy fuel load (CFL) (0.63–1.82 kg/m2) and canopy bulk density (CBD) (0.07–0.22 kg/m3) values are similar to those of other conifers worldwide. Regression equations for the estimation of canopy fuels were developed based on common stand parameters. Stand basal area was the best-fitted predictor for the estimation of CFL and CBD at stand level, explaining 77 and 74 % of the observed variation, respectively. Regression analysis failed to provide any significant estimates for the CBH. Prediction of canopy fuel characteristics based on stand basal area can be useful in fuel management and fire prevention planning since it and can be easily incorporated into existing forest inventory systems and can be used for the Kyoto protocol requirements of carbon changes in Aleppo pine forests located in Greek sites.

Analysing species-specific light transmission and related crown characteristics ofPinus sylvestrisandBetula pendulausing a shoot-level 3D model

This is a first attempt to analyse species-specific light attenuation in mixed boreal forests created by shoot-level 3D tree models. The models are configurations of real individual Scots pine (Pinus sylvestris L.) and silver birch (Betula pendula Roth.) trees grown in mixed-forest stands. We study species-specific differences in radiation transmission by using the ray-casting method. Light transmission was found to be higher in dense birch-dominated stands compared with dense pine-dominated stands because of the higher total foliage area and the higher location of foliage in the pine canopy. Transmission of light per leaf area index (LAI) was nevertheless higher in the pine canopy compared with the birch canopy because of foliage clumping. Especially in clumped canopy, species-specific shoot-level light simulations enable a more realistic estimation of light transmission compared with simpler calculations based on LAI and Beer–Lambert’s law. The observed differences in light-transmission characteristics of the studied species may influence the development of target crowns in the neighbourhood. Light attenuation caused by the dense foliage zone in the upper pine canopy could be avoided in dense stands by mixing species with different vertical foliage distributions.

Evapotranspiration and canopy characteristics of two lodgepole pine stands following mountain pine beetle attack

Over the past decade, British Columbia (BC), has experienced the largest mountain pine beetle (MPB) outbreak on record. This study used the eddy-covariance (EC) technique to examine the impact of the MPB attack on evapotranspiration (E) and associated canopy characteristics of two lodgepole pine stands with secondary structure (trees, saplings and seedlings surviving the attack) located in central BC. MPB-06, an 85-year-old almost pure stand of pine trees, was first attacked in 2006, and by 2010, ~80% of the trees had been killed. MPB-03, a 110-year-old stand with an overstory consisting of over 90% pine and a developed sub-canopy, was first attacked in 2003 and by 2007 had > 95% pine canopy mortality. EC measurements began in August 2006 at MPB-06 and in March 2007 at MPB-03, and continued for four years. Annual total E ranged from 226 mm to 237 mm at MPB-06, and from 280 to 297 mm at MPB-03, showing relatively little year-to-year change at both sites over the four years. Increased E from the accelerated growth of the surviving vegetation (secondary structure, shrubs and herbs) compensated for reduction in E due to the death of the overstory. Monthly average daytime canopy conductance, the Priestley–Taylor (α), and the canopy–atmosphere decoupling coefficient (Ω) steadily increased during the growing season reaching approximate maximum values of 5 mm s−1, 0.75 and 0.12, respectively. Potential evapotranspiration was approximated using a vapour pressure deficit-dependent α obtained at high soil water content. Calculated water deficits indicated some water-supply limitation to the surviving trees and understory at both sites. Rates of root zone drainage during the growing season were low relative to precipitation. Copyright © 2013 John Wiley & Sons, Ltd.