Mixed Stands Research Articles

Regularly Planted Rather Than Natural Understory of Norway Spruce (Picea abies H. Karst.) Contributes to the Individual Stability of Canopy Silver Birch (Betula pendula Roth.)

Forest plantations, particularly high-density planted stands, are considered to be more prone to wind damage compared to naturally regenerated stands. The wind resistance (mechanical stability) of plantations can, however, be improved by close-to-natural management, for example, combining pioneer and shade-tolerant species. Presumably, the stability of such stands would be enhanced by the reduced competition of canopy trees and stronger root contacts provided by understory trees, which depend on spatial distribution. In the hemiboreal forest zone, silver birch (Betula pendula Roth.) and Norway spruce (Picea abies (L.) H.Karst.) form such a combination naturally. In this study, the static tree-pulling tests were performed to estimate the mechanical stability of canopy silver birch growing with random Norway spruce understory in naturally regenerated (post-clear-cut) and regularly planted bi-species mixed stands. The regular mixing of the high-density bi-species stand significantly improved the loading resistance of canopy silver birch compared to the naturally regenerated stands of similar composition and age. Such an effect might be related to the stratification of the canopy space between pioneer birch and shade-tolerant spruce, which improved the individual stability of the canopy trees. Further, a regular rooting network of the planted stands likely contributed to the stability by reducing weak spots. Accordingly, the wind resistance of trees in regularly planted bi-species stands might be improved, avoiding additional management.

Using Airborne Lidar, Multispectral Imagery, and Field Inventory Data to Estimate Basal Area, Volume, and Aboveground Biomass in Heterogeneous Mixed Species Forests: A Case Study in Southern Alabama

Airborne light detection and ranging (lidar) has proven to be a useful data source for estimating forest inventory metrics such as basal area (BA), volume, and aboveground biomass (AGB) and for producing wall-to-wall maps for validation of satellite-derived estimates of forest measures. However, some studies have shown that in mixed forests, estimates of forest inventory derived from lidar can be less accurate due to the high variability of growth patterns in multispecies forests. The goal of this study is to produce more accurate wall-to-wall reference maps in mixed forest stands by introducing variables from multispectral imagery into lidar models. Both parametric (multiple linear regression) and non-parametric (Random Forests) modeling techniques were used to estimate BA, volume, and AGB in mixed-species forests in Southern Alabama. Models from Random Forests and linear regression were competitive with one another; neither approach produced substantially better models. Of the best models produced from linear regression, all included a variable for multispectral imagery, though models with only lidar variables were nearly as sufficient for estimating BA, volume, and AGB. In Random Forests modeling, the most important variables were those derived from lidar. The following accuracy was achieved for linear regression model estimates: BA R2 = 0.36, %RMSE = 31.26, volume R2 = 0.45, %RMSE = 35.30, and AGB R2 = 0.41, %RMSE = 31.31. The results of this study show that the addition of multispectral imagery is not substantially beneficial for improving estimates of BA, volume, and AGB in mixed forests and suggests that the investigation of other variables to explain forest variability is necessary.

Determination of some factors leading to the infestation of Ips sexdentatus in crimean pine stands

Large infestations of bark beetles result in the death of many trees in large forest areas.Ecological-based modeling approaches that include the factors causing infestations are important for accurately predicting whether these infestations will occur, suggesting ways to avoid large infestations, and understanding sustainable forest management. In the present study, the effects of some stand characteristics and topographical and climatological factors on the of Ips sexdentatus infestation at pure and mixed Crimean pine stands were evaluated. Ten factors were considered as important for predicting the predisposition of a pine forest to infestation: stand structure, site index, crown closure, stand age, aspect, slope, elevation, maximum temperature, precipitation, and solar radiation. Ten conditioning layers were overlayed separately with a beetle infestation map using geographic information system (GIS) to investigate how the beetle damage changed according to these factors and how much damage it caused. Binary logistic regression analysis was used to determine how combinations of the 10 factors affected beetle infestations and which of the factors were most damaging. It was found that the stand structure, crown closure, site index, stand age, slope, elevation, maximum temperature, precipitation, and solar radiation were definite factors in I. sexdentatus infestation; the aspect was not found to be a strong factor. The crown closure was the most significant factor affecting I. sexdentatus infestation followed by maximum temperature, elevation, slope, precipitation, solar radiation, stand age, site index, and stand structure. The crown closure, stand structure, maximum temperature, solar radiation, and forest stand area variables were significantly included in the logistic regression model.

Growth and formation of Scots pine stands in Eastern Polissia of Ukraine

Abstract The purpose of the research is to study the current state, features of growth and formation of Scots pine (Pinus sylvestris L.) stands in Eastern Polissia of Ukraine. The structure of pine stands by origin, age, the density of stocking, site indices, forest types and health condition was analysed. Features of the formation of stands were studied at the permanent sample plots. Visual assessment of health condition, as well as signs of pest and disease damage of trees, other defects and external signs that caused stem defects was carried out. The age structure of pine stands was not optimal: there was an excess of mature stands and a lack of young stands. The health condition of mixed pine stands was relatively better than that of pure pine stands. Mixed pine stands were characterised by high biological resistance and accumulated significant wood stock under regular sylvicultural maintenance. The dynamics of forestry and evaluation indicators of reference pine stands were evaluated and comparison of their growth with stocked pine stands was performed.

Patterns of pollen dispersal and pollen capture in the hybridizing cattails,Typha latifoliaandTypha angustifolia

Pollen dispersal regulates the formation of the invasive, wind-pollinated hybrid cattail Typha × glauca Godron, the F1offspring of the broadleaf ( Typha latifolia L.) and narrowleaf ( Typha angustifolia L.) cattail. An earlier study suggested that pollen dispersal by T. latifolia might be spatially restricted, with most dispersal occurring over distances less than 2 m. Restricted pollen dispersal would imply that hybrid formation primarily occurs within mixed stands of cattails. Hybrid formation might also be affected by preferential receipt of conspecific pollen, but this has not been investigated for cattails. We compared patterns of pollen dispersal for T. latifolia and T. angustifolia using a wind tunnel. We then tested whether patterns of pollen receipt were biased toward the capture of conspecific versus heterospecific pollen using monospecific cattail stands with a single local pollen source. Results from the wind tunnel partially supported the previous finding of spatially restricted pollen dispersal for T. latifolia, the paternal parent of F1hybrids. Pollen receipt by T. angustifolia was biased toward the capture of conspecific pollen. Localized pollen dispersal by T. latifolia and preferential conspecific pollen capture by T. angustifolia should reduce rates of hybrid formation below that expected under random mating.

Growth and Adaptive Capacity of Douglas Fir Genetic Resources from Western Romania under Climate Change

The most recent climate change scenarios show that Southern and Eastern Europe will be affected by a significant increase in temperature and drought frequency by the end of the 21st century. Romania has already recorded very high temperatures and long periods of drought over recent decades, the most affected regions being the south, west and east of the country. Considering that successful forest management requires suitable species and high-quality reproductive material for reforestation, the aim of this study was to evaluate and compare the growth and drought response of Douglas fir (Pseudotsuga menziessi var. menziesii) and Norway spruce (Picea abies) in two stands installed at the end of the 19th century in western Romania. The growth traits, wood characteristics and drought parameters (resistance, recovery, resilience and relative resilience) of Douglas fir and Norway spruce trees have been analyzed and compared. The climate–growth relationship was determined using growth response functions over the period 1938–2017. Additionally, to simulate the potential impact of climate change on Douglas fir in this region, the RCP4.5 scenario was used over two periods: 2041–2070 and 2071–2100. The results reveal that Douglas fir has an exceptional growth capacity, overcoming the Norway spruce since the early ages in both site conditions. The highest growth performances were seen in the low-productivity site. From analyzing the responses to drought events, considerable differences were found between species. The results highlight the high resistance and relative resilience to extreme droughts of Douglas fir compared to Norway spruce. However, autumn–winter temperatures play an important role in the adaptation of Douglas fir to site conditions in Romania. The use of appropriate provenances of Douglas fir in mixed stands with native broadleaved species may be an option for climatically exposed sites, thus increasing the value of these stands.

Effects of climate on the radial growth of mixed stands of Nothofagus nervosa and Nothofagus obliqua along a precipitation gradient in Patagonia, Argentina

Climate models for North Patagonia in Argentina project dryer conditions, due to a decrease in mean precipitation combined with an increase in mean temperatures. The temperate mixed Nothofagus forest, which exists along a steep precipitation gradient, could be directly impacted. For this study, we evaluated the influence of mean climate on the growth of the significant deciduous species: N. nervosa and N. obliqua. For the first time in Argentina, dendroclimatological analyses were done on both species using a network of 14 chronologies, covering their longitudinal distribution along a gradient of declining precipitation from west to east. Seasonal correlation analysis revealed that temperature has a negative effect on the growth of both species across all sites, particularly during summer of the previous and current growth season. Precipitation has a positive effect on the growth of trees for both species, which is more significant for N. nervosa. The relationship between early-summer climate and growth remained relatively stable over time for N. nervosa; however, for N. obliqua the detrimental effects of temperature increased towards the end of the 20th century, and the positive effects of precipitation decreased, particularly at the driest end of the gradient. These results suggest that a continued decrease in rainfall with a rise in temperature could impact growth for both of these species.

Long-Term Productivity of Monospecific and Mixed Oak (Quercus petraea [Matt.] Liebl. and Quercus robur L.) Stands in Germany: Growth Dynamics and the Effect of Stand Structure

Wood production is one of the most important ecosystem service that forests provide to society. However, under changing climatic conditions, this appears to be subject to increasing uncertainties. In the present study we analyzed how long-term productivity of oak (Quercus petraea [Matt.] Liebl. and Quercus robur L.) stands has developed, how oak behaved on tree and stand level depending on the stand structure and which trade-offs can be observed. For the analyses, data from 147 long-term monospecific and mixed stands were investigated, which have been regularly recorded since 1898. Firstly, long-term stand productivity has increased up to 21% until 2020 as compared to 1960. This trend was observed for both, monospecific as well as mixed oak stands. Secondly, stand productivity was on average 19% higher in mixed compared to monospecific oak stands. This superiority can be explained by higher stand densities, a vigorous understory and the admixture of beech in particular. With increasing age, the observed positive effect of stand density was higher. Thirdly, individual oak productivity slowed down under interspecific competition, especially in young to mid-aged stands. In this context, the productivity of individual oaks depended strongly on their social position within the stand. Fourthly, in terms of growth partitioning larger trees contributed most in young oak stands, regardless of mixture. In order to preserve oak as a productive component of future mixed forests, the results suggest a silvicultural promotion of oak. Consistent management of dominant and vital oaks can achieve high productive trees while maintaining the positive characteristics of highly structured and mixed forests. A vigorous secondary stand can increase overall stand productivity at lower densities and allows silvicultural flexibility at the stand level. Creating vertical stand structure to reduce competition has only a limited positive effect on productivity of individual oaks that is highly related to its social status. Special attention should still be paid to beech as admixed tree species, which can continue to crowd oak even at higher stand ages.

Insect infestations and the persistence and functioning of oak-pine mixedwood forests in the mid-Atlantic region, USA.

Damage from infestations of Lymantria dispar L. in oak-dominated stands and southern pine beetle (Dendroctonus frontalis Zimmermann) in pine-dominated stands have far exceeded impacts of other disturbances in forests of the mid-Atlantic Coastal Plain over the last two decades. We used forest census data collected in undisturbed and insect-impacted stands combined with eddy covariance measurements made pre- and post-disturbance in oak-, mixed and pine-dominated stands to quantify how these infestations altered forest composition, structure and carbon dynamics in the Pinelands National Reserve of southern New Jersey. In oak-dominated stands, multi-year defoliation during L. dispar infestations resulted in > 40% mortality of oak trees and the release of pine saplings and understory vegetation, while tree mortality was minimal in mixed and pine-dominated stands. In pine-dominated stands, southern pine beetle infestations resulted in > 85% mortality of pine trees but had minimal effect on oaks in upland stands or other hardwoods in lowland stands, and only rarely infested pines in hardwood-dominated stands. Because insect-driven disturbances are both delaying and accelerating succession in stands dominated by a single genus but having less effect in mixed-composition stands, long-term disturbance dynamics are favoring the formation and persistence of uneven age oak-pine mixedwood stands. Changes in forest composition may have little impact on forest productivity and evapotranspiration; although seasonal patterns differ, with highest daily rates of net ecosystem production (NEP) during the growing season occurring in an oak-dominated stand and lowest in a pine-dominated stand, integrated annual rates of NEP are similar among oak-, mixed and pine-dominated stands. Our research documents the formation of mixedwood stands as a consequence of insect infestations in the mid-Atlantic region and suggests that managing for mixedwood stands could reduce damage to forest products and provide greater continuity in ecosystem functioning.

Root-soil facilitation in mixed Eucalyptus grandis plantations including nitrogen-fixing species

The success of mixed plantation systems is ultimately the net result of positive and negative interactions, including belowground interactions, among the respective species. Despite increasing knowledge on positive interactions on biomass and productivity in mixed-species plantations, relatively little is known about the mechanisms underlying belowground interactions. Based on biodiversity data from four mixed Eucalyptus grandis plantations, we determined the optimal ecological facilitative interactions of mixed plantation, i.e., E. grandis and Alnus formosana. We then investigated in situ root exudation of E. grandis using a cuvette-based method and analysed root patterns, defence chemicals, bacterial communities, and biochemical properties of rhizosphere soils in mixed E. grandis with alder. Compared with pure Eucalyptus plantations, the fine root production by E. grandis was higher in subsoil layers (40–80 cm) in mixed plantations with alder. Autotrophic root respiration and associated enzymes were also increased in mixed plantations. Root exudates and defence allelochemicals of E. grandis changed in the presence of alder. Compared with the pure Eucalyptus plantations, E. grandis roots in mixed plantations reduced the release of potential allelochemicals, such as phenolic acids, flavonoids, unsaturated lactone, and glycosides. Methyl jasmonate, a common signal chemical, was significantly decreased in mixed-species plantations. The bacterial community of E. grandis rhizosphere soil was improved in mixed stands and recruited more nitrifying, N-fixing, and cellulose-decomposing bacteria, such as family Nitrosomonadaceae, genera MND1, Marmoricola, and Rikenellaceae RC9 gut groups. Thus, belowground ecological facilitative interactions occurred in mixed plantations with alder, which were due to E. grandis altering its rooting pattern, reducing the levels of released allelochemicals, recruiting more beneficial bacteria, and improving the biochemical properties of rhizosphere soil. This mechanism may be useful in reforestation programs for Eucalyptus monocultures that are suffering from problems associated with low biodiversity and reduced soil fertility.

The retention of non-commercial hardwoods in mixed stands maintains higher avian biodiversity than clear-cutting

Abstract A diverse landscape can support a more diverse range of species and allow for more complex community structures. In forested habitats, openings and changes in tree composition allow for a higher species richness due to the greater chance of niche occupancy. Knowledge about these relationships may be useful for adapting forest harvesting strategies to, for example, support bird diversity conservation and studies are required to understand how different harvesting strategies influence forest structure and bird diversity. Here, we used Autonomous Recording Units (ARU) to record dawn signalling of forest birds between two forest-harvesting treatment types (complete clear-cuts and hardwood-retention patches) vs control forest patches in the John Prince Research Forest, British Columbia, Canada. We compared Species Richness and Shannon diversity as detected through identifying species in audio recordings, across treatments. The observed Species Richness and Shannon diversity did differ between the Retention treatment and Forest controls when controlling for number of individuals sampled, but both had higher Species Richness and Shannon diversity of passerine species than the Clear-cut treatments. When comparing species composition, we found that forest-associated species were disproportionately detected in Forest controls compared to Clear-cut treatments but detected at intermediate levels in Retention treatments. Species associated with early-seral habitats, though, had disproportionate detection in Clear-cut treatments compared to Forest controls, but also showed expected detections in Retention treatments. These results suggest that partial harvesting and retention of non-commercial hardwoods, can help retain forest-associated species while also helping attract early-seral avian species; this can help increase the overall diversity of the landscape while still making logging profitable. Further research should be conducted to determine the value of this retained habitat at different spatial scales to understand the impacts that it may have for larger-scale deployment.

The distribution of carbon stocks between tree woody biomass and soil differs between Scots pine and broadleaved species (beech, oak) in European forests.

While the impacts of forest management options on carbon (C) storage are well documented, the way they affect C distribution among ecosystem components remains poorly investigated. Yet, partitioning of total forest C stocks, particularly between aboveground woody biomass and the soil, greatly impacts the stability of C stocks against disturbances in forest ecosystems. This study assessed the impact of species composition and stand density on C storage in aboveground woody biomass (stem + branches), coarse roots, and soil, and their partitioning in pure and mixed forests in Europe. We used 21 triplets (5 beech-oak, 8 pine-beech, 8 pine-oak mixed stands, and their respective monocultures at the same sites) in seven European countries. We computed biomass C stocks from total stand inventories and species-specific allometric equations, and soil organic C data down to 40 cm depth. On average, the broadleaved species stored more C in aboveground woody biomass than soil, while C storage in pine was equally distributed between both components. Stand density had a strong effect on C storage in tree woody biomass but not in the soil. After controlling for stand basal area, the mixed stands had, on average, similar total C stocks (in aboveground woody biomass + coarse roots + soil) to the most performing monocultures. Although species composition and stand density affect total C stocks and its partitioning between aboveground woody biomass and soil, a large part of variability in soil C storage was unrelated to stand characteristics.Supplementary InformationThe online version contains supplementary material available at 10.1007/s10342-022-01453-9.

Long-Term Effects of Crop Tree Release on Growth and Quality in White-Oak (Quercus alba L.)-Dominated Stands

Abstract Crop tree release (CTR) can be an effective intermediate silvicultural treatment for culturing high-value stems in mixed hardwood stands. The lengthy rotation of hardwoods requires long-term evaluations if silvicultural treatment effectiveness is to be fully evaluated. Our study provides a 35-year evaluation of individual-tree and stand response to CTR imposed in small sawtimber-sized white-oak (Quercus alba L.)-dominated stands. The focus on white oak is justified based on the significant biologic and economic values of the species, and this study furthers our ability to optimize use of CTR as management tool for sustaining our oak resources. The replicated experiment included three treatment levels: 20 crop trees ac−1, 34 crop trees ac−1, and a control. Using a repeated-measures framework, we analyzed (1) how CTR affects growth and stem quality of white oak crop trees and (2) stand-level effects of CTR on basal area, stocking, and ingrowth. CTR increased crop tree diameter growth and proportion of crop trees reaching their maximum potential grade. However, crop tree diameter growth and proportion achieving maximum potential grade did not differ between the 20 and 34 crop trees ac−1 treatments. Finally, CTR stimulated stand-wide growth without altering the patterns of ingrowth density or species distributions.

Spruce (Picea abies L.) planting leads post-clearcut bird assemblages to a novel successional pathway\u2014a comparative study in hemiboreal mixed forests

Key messageBird assemblages in planted spruce (Picea abies L.) forests were compositionally distinct from those in naturally regenerated mixed stands. Despite rapid stand development on productive soils, even-aged silviculture cannot host most old-forest species. However, their habitat quality could be supported in landscape mosaics with retention forestry and set-asides.ContextThe most productive forest lands have naturally the richest bird assemblages but tend to be also most intensively managed. Sustainable solutions to this conflict are unclear.AimTo assess bird assemblages and their successional dynamics in planted Norway spruce (Picea abies L.) stands compared to naturally developing stands.MethodsWe mapped breeding bird assemblages in forty 5-ha plots on highly productive soils in Estonia. The plots included sets of naturally regenerated and planted stands, and (as successional endpoints) clear-cuts and old stands.ResultsPlanted stands had fewer bird species and pairs than naturally regenerated stands; the latter having a species composition resembling late-successional deciduous-dominated stands. Importantly, the species composition in mature spruce plantations converged toward the composition observed in late-successional conifer-dominated stands. Downed dead wood, stand age, deciduous trees, and stock density were the most significant stand characteristics shaping bird assemblages.ConclusionThe habitat value of established spruce plantations can be primarily improved by allowing for some deciduous trees and gaps with deciduous undergrowth. At the landscape scale, the bird diversity of even-aged systems would be enhanced by multi-scale applications of retention forestry—from retention trees to old-growth set-asides.

Mixed forest specific calibration of the 3-PGmix model parameters from site observations to predict post-fire forest regrowth

Fire disturbance has been one of the main reasons for the alteration of forest succession trajectory and forest composition in the Daxing’anling Mountain of Inner Mongolia. Therefore, predicting the dynamic process of post-fire regrowth is critical for understanding the specific forest succession trajectory of this region. The 3-PGmix model (i.e., Physiological Principles in Predicting Growth for mixed stands) has been reported as a powerful tool for predicting the growth of mixed forest species. However, simulating post-fire regrowth of mixed forest with 3-PGmix remains challenging due to the uncertainty of species-specific as well as site-specific model parameters. Based on the field measurements from a wide range of environmental conditions, the 3-PGmix model was calibrated by conducting the sensitivity analysis and optimization of species-specific parameters for mixed forest stands of larch (Larix gmelinii) and birch (Betula platyphylla) with the PEST model (Model-Independent Parameter Estimation), and by using our newly developed methods to accurately estimating site-specific parameters (e.g., fertility rating, stand density, climate factors). The calibrated 3-PGmix model was tested against the independent sites and predicted the characteristic of post-fire forest regrowth. The sensitivity analysis shows that the parameters describing the forest canopy are more sensitive to the objective function of the PEST model. The calibrated 3-PGmix model performed well on independent sites, resulting in agreement with the field-measured diameter at breast height (DBH), the biomass of components, and stand density with a bias of less than 15% on most sites. The 3-PGmix model prediction of post-fire forest recovery characteristics found that the highest recovery rate of 5.5% per year was predicted from the moderate burn severity scenarios. A higher fertility rating was predicted to accelerate the process of post-fire forest successional and shorten the duration time when the species proportion achieves balance. The mixed-forest specific calibration of the 3-PGmix model in this study enables the explicit prediction of post-fire forest succession, and more simulations over different spatial scales with a wide range of environmental conditions by coupling with remote sensing observations can be expected.

Landscape and stand-scale factors drive the infestation of an endemic fungal pathogen: The role of leaf traits

Endemic plant pathogens are important agents of many forest processes and contribute to shaping forest ecosystem dynamics and diversity. However, Marssonina leaf spot of poplar is induced by a pathogenic fungus Drepanopeziza populi, causing increased damage to riparian poplars in recent years. And such endemic diseases have received little attention at the landscape scale, despite the key role of landscape features in the development and spread of certain emerging diseases. Moreover, few studies have sufficiently captured multiple ecological factors driving the infestation of an endemic pathogen acting at the landscape, stand, and individual scales. Here, we measured pathogen load, disease prevalence, and disease severity of Marssonina leaf spot in bitter poplars (Populus laurifolia) in riparian forests, and explored the direct and indirect effects of multiple ecological factors on pathogen infestation using structural equation models. Specifically, we first assessed the effects of landscape and stand-scale factors on leaf traits including leaf area, specific leaf area (SLA), and leaf dry matter content (LDMC), and then examined the role of these factors in shaping disease dynamics. We found that forest cover had no direct impact on host leaf traits and pathogen infestation, but directly affected stand characteristics, with higher forest cover in a landscape increasing host density and tree diversity. Host density was the most important factor of pathogen load, with a higher density of host poplars resulting in greater symptomatic leaf count. Tree diversity had direct effects on disease prevalence, with host poplars growing in mixed forest stands far less infected by pathogens than in pure stands. Disease prevalence was also positively related to pathogen load. Moreover, tree diversity strongly reduced SLA but increased LDMC. Leaves with higher SLA was found to increase pathogen load and disease severity, but leaves with higher LDMC was found to reduce them. Our results show that landscape-scale forest cover indirectly affects Marssonina leaf spot dynamics via stand characteristics and leaf traits. Disentangling the effects of biotic and abiotic factors on pathogen infestation can provide crucial insights into multi-scale ecological factors in driving plant disease expression, and contribute to reducing the overall impact of endemic forest diseases.

Correcting the Results of CHM-Based Individual Tree Detection Algorithms to Improve Their Accuracy and Reliability

Individual tree detection algorithms (ITD) are used to obtain accurate information about trees. Following the process of individual tree detection, it is possible to use additional processing tools to determine tree parameters such as tree height, crown base height, crown volume, or stem volume. However, many of the methods developed so far have focused on parameterising the algorithms based on the study area, height structure or tree species analysed. Applying the parameters of the method can be challenging in areas with dense and heterogeneous forests with a diverse stand structure. Therefore, this work aimed to develop a method to correct the results of ITD algorithms to identify individual trees more reliably, taking into account different ITD methods based on the Canopy Height Model. In the present study, we proposed a three-step approach to correct segmentation errors. In the first step, erroneous (under- and over-segmentation errors) and correct segments were classified. After classification, the second step was to refine the under-segmentation errors. The final step was to merge segments from the over-segmentation class with correct segments based on the specified conditions. The study was conducted in one of the most complex and diverse forest communities in Europe, making tree identification a major challenge. The accuracy of the segmentation improvements varied depending on the method applied and tree species group examined. Thus, based on the results, the paper advocates for the correction method due to its efficiency in mixed forest stands. Therefore, the present study offers a possible solution to reduce segmentation errors by considering different forest types and different CHM-based ITD methods for identifying individual trees.

Catch crop mixtures have higher potential for nutrient carry-over than pure stands under changing environments

Winter catch crops are grown to scavenge nutrients over a period of unfavorable growth conditions and to conserve nutrients for subsequent release to the following main crop. Since environmental conditions have a strong impact on the growth and nutrient capture in roots and shoots of individual catch crop species, we anticipated that mixtures will be more durable and efficient in nutrient capture due to compensatory effects among component species. We tested this hypothesis and determined the nitrogen and phosphorus accumulation in the shoots and roots of four catch crop species grown in pure vs. mixed stands at two sites for two or three years. Element concentrations were determined in the root and shoot biomass of each species and used to calculate the nutrient pool fixed in the root or shoot biomass. A qPCR-based technique was applied to quantify the root biomass of individual species based on species-specific DNA sequences. Despite considerable variation across environments, the overall plant biomass of white mustard (Sinapis alba), lacy phacelia (Phacelia tanacetifolia) and bristle oat (Avena strigosa) was similar and higher than that of Egyptian clover (Trifolium alexandrinum). While pure stands varied 6- to 24-fold in shoot biomass depending on environmental conditions, the variation was only ~3-fold for catch crop mixtures, with less pronounced variation in the root biomass. In general, the root biomass was comparable to the shoot biomass in each species. Roots contributed 26–46% of the nitrogen and 36–48% of the phosphorus to the total accumulation of these nutrients in the catch crop biomass, thus emphasizing the importance of plant roots as belowground nutrient pool for potential carry-over of nutrients to the subsequent crop. Although the mixture was mostly dominated by two of the four species, namely mustard and phacelia, it captured similar or even larger amounts of nutrients than the best-performing pure stand under any growth condition. This was the case for shoot- and for root-bound nutrients. Our results indicate that catch crop mixtures have higher durability than pure cultures to environmental variations. The amount of nitrogen captured by the mixture meets the average postharvest nitrogen that is left over by a wide range of cash crops, thus emphasizing that catch crop mixtures represent an efficient nutrient management tool in crop rotations.

Nitrogen mineralisation and N2O emissions in pure and mixed-species plantations of Eucalyptus urograndis and Acacia mangium

We hypothesised that N inputs to the soil from residues of adult trees of Acacia mangium Willd. increase soil nitrate availability and consequently induce higher nitrous oxide (N2O) fluxes, irrespective of being in pure or mixed stands with Eucalyptus. A randomised block-design experiment was set up on Haplic Planosol in Brazil to study the impact of monospecific stands of Eucalyptus urograndis (Eucalyptus urophylla S. T. Blake × Eucalyptus grandis W. Hill ex Maiden) fertilised with 120 kg N ha−1 (E100+N) and A. mangium (A100), along with the mixture of both species (E50A50) on soil N mineralisation and its relationship with soil N2O emissions. In situ monitoring of N mineralisation, N2O emissions and the soil N stocks was carried out between five- and six-year-old plantations. The total soil net mineralisation of N that was accumulated in plantations A100 and E50A50 was on average 3.5- and 2.5-times greater than in the E100+N plantation. The NO3 − produced throughout the year by the plantations was proportional to the total net mineralisation, according to the following order of production scale: A100 > E50A50 > E100+N. Furthermore, N2O emissions in the plantations that included A. mangium (A100 and E50A50) were significantly higher in some periods of the year, as compared with in the E100+N plantation. This pattern caused a more pronounced curve of accumulated N2O emissions under A. mangium plantations (pure and mixed) as compared with the monospecific Eucalyptus plantation (E100+N). However, the magnitude of N accumulation emissions suggests that mixed plantations could increase the nutritional status of sandy soils.

Development of Tools to Age Grand Fir to Aid in Collaborative Restoration of Federal Lands in Eastern Oregon

Abstract The USDA Forest Service is working closely with collaborative stakeholder groups to accelerate the pace and scale of restoration in fire-prone mixed conifer forests of eastern Oregon. Collaboratively planned restoration projects are typically designed to conserve older trees established before fire exclusion policies and other management practices began to alter forest landscapes beginning in the late 1800s. Tools exist for accurately estimating the age of common species including ponderosa pine, Douglas-fir, and western larch. There are no existing tools available for aging grand/white fir, although an important objective of many restoration projects in mixed conifer stands is to retain older grand/white fir while removing younger individuals that have infilled into stands in the absence of fire to enhance resilience of stands to future climate and disturbance regimes. This article describes the development of tools to age grand fir on the Malheur National Forest by taking simple field measurements of morphological characteristics. Bark fissure depth, height to live foliage, and diameter at breast height were the strongest noncorrelated tree morphological characteristics associated with tree age. Crown class had no predictive power for estimating tree age. A variety of methods are presented that can estimate the age of grand fir with reasonable accuracy and are appropriate for different management objectives. Additional field testing and continued experimentation with different tree aging methods within an adaptive management framework is recommended. Study Implications: Shade tolerant grand fir has expanded dramatically in mixed conifer stands of eastern Oregon in the absence of frequent fire. Collaboratively designed restoration projects in mixed conifer stands usually call for the removal of younger grand fir while maintaining older grand fir that contribute to stand- and landscape-scale biodiversity. It can be difficult to estimate the age of grand fir based on morphological clues because of highly variable growth forms in this species. However, several easy-to-use grand fir aging tools promise to facilitate restoration by making reasonably accurate estimates of tree age.