Stem Density Research Articles

Insect pest predation by arthropods and birds in different land use types with varying woody vegetation composition in agroecosystems of central Oromia, Ethiopia

Biological control by predators of insect pests is an important benefit of biodiversity, having a contribution to agricultural production. By preying on crop infesting insect pests, predatory arthropods and birds can provide an important ecosystem service. They support agricultural productivity, boosting crop yield and reducing demand for pesticides expense. Habitat quality of land use types, i.e., explained by vegetation cover, can impact the provision of ecosystem services thereby influencing the prevalence of the predators and their predation rates. In order to better understand the level of insect pest control service by predators, we conducted a field experiment to investigate levels of predation, using an attack on artificial caterpillars in response to land use types varied in vegetation cover. We found the attack rate by arthropods was more consistent across land use types than by birds, and the attack by birds was higher in modified land use types with sparse woody vegetation. Moreover, the attack rate for birds showed a decreasing tendency with increasing woody species richness, cover and stem density, while it showed less variation for arthropods. We conclude that biological control by birds is more effective in habitats with simplified vegetation cover than for arthropods in agricultural landscapes. Therefore, we recommend the prevalence of shade trees and small forest patches in agricultural landscapes for supporting the increased levels of insect pest control services provided by predatory birds and arthropods.

Carbon accumulation over 70 years of old-field succession driven by live biomass in a Mediterranean continental environment

Forest expansion in abandoned agricultural lands entails the fixation of atmospheric CO2 in the live biomass, the soil as well as in other ecosystem compartments, and in turn, has strong implications for C budgets and the design of actions to mitigate climate change all over the world. However, changes in C stocks in these compartments are still poorly understood. We assessed the main patterns and drivers of C accumulation over spontaneous colonization of abandoned agricultural lands, considering the above- and below-ground biomass (AGB and BGB, respectively), the woody debris (WD), the litter and the surface soil (SS; 0–6 cm depth), in an area of Central-North Spain. To attain this objective, we established a chronosequence of 30 plots (0.0625 ha) located in agricultural lands abandoned in 1956–1977, 1977–2005 and 2005–2017, in four different forest types. We found that the AGB and the SS accounted for the major proportion of the total C stock, but the BGB was also relatively important. Carbon stocks in all these major compartments increased linearly with the age of tree colonization. But C in the SS did not significantly differ among plots abandoned in the three periods considered and showed decreasing rates of change from youngest (i.e. those in plots abandoned in 2005–2017) to oldest (i.e. those in plots abandoned in 1956–1977) stands. Carbon accumulation was mainly driven by adult stem density and age of tree colonization in the AGB and the BGB, and by the total nitrogen content in the SS. Our findings indicate that, in these new forests, C accumulation in the live biomass is still ongoing and proceeds relatively fast and at an increasing rate, which points toward a clear potential for atmospheric CO2 fixation over the next few decades. This process, however, proceeds more slowly and shows signals of an apparent deceleration in the SS. The C stock in the surface soil is, in fact, largely disconnected from that of live biomass and varies depending on pre-abandonment land-use differences among the study sites.

Açaí palm intensification reorganizes woody plant assemblages at multiple spatial scales in an Amazonian estuarine forest

AbstractThe exploitation of nontimber forest products has been proposed as a sustainable way to exploit tropical forests, but such an opportunity remains to be examined case‐by‐case. We examine the impact of the intensification of the açaí palm (Euterpe oleracea) management for fruit production via increments in palm clumps/stems density on the woody plant assemblages (adult and regenerating) in an estuarine forest landscape in the eastern Amazon region, Brazil. Across 30 forest stands açaí stem density correlated negatively with stem density and taxonomic diversity considering both adult and regenerating woody plant assemblages, but it posed a positive effect on beta diversity via species turnover. Soil fertility and forest stand accessibility played a complementary role. Moreover, açaí clump density affected the abundance of particular woody plant species, including a set of species declining before the 400‐açaí clump density threshold imposed by current regulation. Accordingly, açaí clump density influenced the taxonomic organization of woody plant assemblages at the landscape spatial level. Finally, it is worth mentioning a group of 105 species, which were recorded across the regenerating assemblages but not in the adult assemblages. Among them, a large number of small‐statured woody plant species typical from the forest understory (i.e., the shade‐tolerant assemblage), such as those from Miconia, Piper, Bactris, Anonna and Geonoma genera. As intensification is still spreading it can be considered a threat to the integrity of the Amazon estuarine forest and thus questions the ecological sustainability through which the current Amazonian “black gold” is now produced.

Soil seed banks provide a storage effect in post-logging regrowth forests of southeastern Australia

Despite the importance of soil seed banks in diversity maintenance, our understanding of plant response to changes in resource availability is largely limited to above-ground vegetation. We investigated how forest structure and edaphic properties influenced the above-ground vegetation and soil seed banks following logging in montane regrowth forests dominated by Eucalyptus regnans in the Central Highlands of southeastern Australia. We surveyed above-ground vegetation, soil seed banks, forest structure and soil properties across 20 harvest units, aged 16 to 20 years. A total of 80 species were identified in above-ground vegetation with 72 species in the soil seed bank, with only 34% of species co-occurring in both species’ pools. Climate, soil, topography, and light availability shaped plant composition but the relative importance of these properties varied among individual species and pools of diversity (combined, above-ground, soil seed bank, life form). Annual heat moisture index (AHMI) was the most important factor that influenced plant community composition across all species pools with individual species positively associated with AHMI. Acacia, but not Eucalyptus stem density further moderated plant response via effects on both light availability and soil nitrogen at the stem exclusion phase of stand development. Structurally mediated controls on above-ground community composition flow through to the soil seed bank via above-ground diversity effects on below-ground composition. For the combined species pool, individual species were most frequently related to Acacia stem density that on average explained 20% of model variation. Soil nutrients accounted for most of the model variation for individual species in above-ground (26%), soil seed bank (20%) and non-woody (32%) pools of diversity, with AHMI accounting for most of the model variation for woody species (18%). The differential response of individual species and community composition to gradients in resource availability across different pools of species diversity and life forms clearly demonstrates a storage effect in wet temperate forests of southeastern Australia that promotes post-disturbance recruitment and persistence. Our work suggests logging interacts with broad environmental controls to shape species diversity. The key role of Acacia stem density as a biotic filter of plant diversity provides opportunity to shape future plant diversity through management interventions such as thinning in the early stages of stand development. With native forest harvesting of these forests set to end from 2024, our findings provide important information on future patterns of plant diversity as logged forests recover over time, opportunities for management interventions in shaping plant composition, and potential impacts of future wildfire.

Tree-ring δ15N as an indicator of nitrogen dynamics in stands with N2-fixing Alnus rubra.

Tree-ring δ15N may depict site-specific, long-term patterns in nitrogen (N) dynamics under N2-fixing species, but field trials with N2-fixing tree species are lacking and the relationship of temporal patterns in tree-ring δ15N to soil N dynamics is controversial. We examined whether the tree-ring δ15N of N2-fixing red alder (Alnus rubra Bong.) would mirror N accretion rates and δ15N of soils and whether the influence of alder-fixed N could be observed in the wood of a neighboring conifer. We sampled a 27-year-old replacement series trial on south-eastern Vancouver Island, with red alder and coastal Douglas-fir (Pseudotsuga menziesii [Mirb.] Franco) planted in five proportions (0/100, 11/89, 25/75, 50/50 and 100/0) at a uniform stem density. An escalation in forest floor N content was evident with an increasing proportion of red alder, equivalent to a difference of ~750kgNha-1 between 100% Douglas-fir versus 100% alder. The forest floor horizon also had high δ15N values in treatments with more red alder. Red alder had a consistent quadratic fit in tree-ring δ15N over time, with a net increase of $\sim$1.5‰, on average, from initial values, followed by a plateau or slight decline. Douglas-fir tree-ring δ15N, in contrast, was largely unchanged over time (in three of four plots) but was significantly higher in the 50/50 mix. The minor differences in current leaf litter N content and δ15N between alder and Douglas-fir, coupled with declining growth in red alder, suggests the plateau or declining trend in alder tree-ring δ15N could coincide with lower N2-fixation rates, potentially by loss in alder vigor at canopy closure, or down-regulation via nitrate availability.

Recreating structurally realistic tree maps with airborne laser scanning and ground measurements

The estimation of forest attributes representing aspects of structural biodiversity from vast areas is difficult not only because of the lack of agreement on what constitutes a structurally diverse forest, but also due to difficulties in the detection of small trees. However, a structurally diverse forest should have large variation in tree size (i.e., height and diameter), as well as some clustering of trees, as regular tree pattern is typical for managed forests. In this work we developed a framework for building structurally representative tree maps using airborne laser scanning data and a limited number of ground measurements using data from two locations in Finland. In the proposed method, an individual tree detection algorithm is optimized so that the number of undetected trees and false detections is minimized. The ground measurements are then used to train models for predicting the number and location of undetected trees and false detections by resampling the attributes of undetected trees in the training data. This model can then be applied to other areas in the proximity of the ground measurements to build tree maps, with the location, height, and diameter for each tree. The methodology was shown to reproduce the number of trees, the height distribution, and the spatial pattern of the trees with sufficient accuracy for practical use in large-scale mapping of forest attributes. For example, the individual tree detection could find at best about 54% of the trees with an additional 7% of false detections, resulting in a bias of approximately −30%, while with the new method the bias was reduced to ±10% of the stem density. Further research is needed on how to account for tree species when building tree maps.

Defaunation is known to have pervasive, negative effects on tropical forests, but this is not the whole story.

Ecosystem functioning and integrity are affected by the loss of large-bodied animals, and comprehending when and how ecosystems are affected is an important goal of defaunation ecology. Despite considerable investigation, our understanding is incomplete. Previous research is biased towards the study of seed dispersal in the Neotropics. This study examined whether and how defaunation affects stem density, species diversity, species composition, spatial distribution, and dispersal mode composition of young understorey plants in an Afrotropical setting. Rectangular plots along transects and wedge-shaped plots under focal trees of five mammal-dispersed species were used to compare three sites representing a defaunation gradient in the Dja faunal reserve in Cameroon. Results showed no change in stem density. Woody plant diversity was highest in the most defaunated site, and compositional differences were noted. Under focal trees, the overall abundance of both seedlings and juveniles was similar. The most defaunated site had the highest number of seedlings far from parent trees. More juvenile stems occurred near parent trees in the least defaunated site. This surprising trend might result from fruit dispersal by small, surviving animals and humans more easily collecting fruits, for food or medicinal purposes, in defaunated, more accessible sites. Negligible or no differences in the abundance of animal-dispersed species and other dispersal modes emerged. This study highlights the roles of extant taxa as surrogate providers of ecological services in defaunated Afrotropical forests. Hence, functional compensation is a serious possibility. Additionally, conceptual models of defaunation consequences that exclude the role of humans may not reflect real-world situations. Overall, these investigations suggest that tropical forests, especially those where ecological niches are less partitioned, may be more resilient to defaunation pressures than is often assumed. Effectively conserving extant, and perhaps less iconic, animal species provides hope for defaunated forests.

Tropical Forests Stand Recovery 30-year After Selectively Logged in Peninsular Malaysia

This article analysed the 25–30 years of growth of dipterocarps forests that were logged under the Selective Management System (SMS) at three sites in Peninsular Malaysia to understand how management regimes affected forest stem density and basal area. The management regimes were (1) unlogged, (2) moderately logged forests that logged all dipterocarps ≥ 65 cm diameter at breast height (dbh) and all non-dipterocarps ≥ 60 cm dbh, and (3) intensely logged forests that logged all dipterocarps ≥ 50 cm dbh and non-dipterocarps ≥ 45 cm dbh. The intensely logged regime is similar to the SMS practices in Peninsular Malaysia. This result showed that one-year post-logging, there was no difference in the total stem density and basal area between forests logged according to the two management regimes. Forest stem density decreased over time in all management regimes, significantly greater in unlogged forests (-15.1 stems/ha/yr, confidence interval (CI): -16.9 to -13.3). This decline in stem density reflected that mortality exceeded recruitment in all management regimes. Despite the consistent decline of forest stem density, the basal area increased over time, and the rate of increase in the intensely logged forest (0.22 m2 /ha/yr, CI: 0.19 to 0.25) was significantly greater than the other management regimes. Our study showed that 30 years post-logging, the effect of selective logging remained evident. Both logged forest stem density and the basal area did not recover to that of unlogged forests, indicating the importance of enrichment planting and extending the cutting cycles beyond 30 years for the sustainability of dipterocarps forests.

Fire exclusion vs. a fire-free interval following repeated prescribed fire: Consequences for forest stand structure and species composition in an upland oak forest

In the Central Appalachian forest region, oaks (Quercus L.) and other disturbance-dependent tree species are experiencing widespread regeneration failure after decades of fire suppression. Managers use prescribed fire to decrease basal area with the aim of facilitating oak regeneration and shifting species composition toward pyrophytic species that dominate the overstory. Although fire may set the stage for improved oak regeneration, a fire-free period is necessary for oak seedlings to develop into fire-resistant stems. The effects of prescribed fire have been amply investigated across the region, but few studies have examined changes to stand structure and oak regeneration after cessation of burning. We followed the effects of three treatments, fire-excluded, 3x-burned, and 4x-burned, for 20 years. After a fire-free interval of approximately ten years, burned treatments had significantly lower total basal area and greater relative density of oaks in the subcanopy (10–20 cm DBH) than the fire-excluded treatment. The 4x-burned, which had the greatest reduction in basal area, also had greater relative density of midstory oaks (2–10 cm DBH), and higher stem density of oak regeneration (<2 cm DBH) than the fire-excluded. Despite these trends towards increased regeneration of oaks and other pyrophytes, red maple (Acer rubrum L.) stem density also increased in the midstory of burned treatments, suggesting a legacy effect of decades of fire suppression and the concomitant mesophication that has occurred. We also examined the effects of continued fire exclusion on the fire-excluded reference treatment. Additional evidence of mesophication on this treatment was demonstrated by increased overstory (≥20 cm DBH) and subcanopy red maple stem density as well as midstory (2–10 cm DBH) eastern white pine (Pinus strobus L.) stem density, a prominent mesophyte on these sites. This study supports the idea that repeated prescribed burning followed by a 10-year fire-free interval can alter stand structure and lead to improved oak regeneration by increasing canopy openness. However, the results were variable across burned treatments (3x vs. 4x) and the ingrowth of red maple and other mesophytes after only 10 years of fire exclusion will require additional control measures. Successful maintenance of oak-dominated forests on upland sites in the Central Appalachian hardwoods region may be contingent on a subsequent canopy disturbance that further increases light availability followed by a fire-free interval. Importantly, in the absence of burning or other disturbance, red maple and other mesophytic species will continue to increase in relative stem density.

Woody species diversity and carbon stock potentials in homegarden agroforestry and other land use systems, northern Ethiopia

Homegarden agroforestry (HGAF) provides wider ecosystem services in the agricultural landscapes in the tropics. However, the potentials of the homegardens for floristic species conservation and climate change mitigation were less empahsized. The present study was designed to investigate woody species diversity, carbon stock, and the relationships between woody plant species and carbon stock in the HGAF and other land use types. Three land use types were purposively selected, totalling 60 nested sample plots. The stand structure and woody plant species diversity were determined. Biomass carbon stocks were estimated employing appropriate allometric equations. Soil Organic Carbon (SOC) stocks (at 0–30 and 30–60 cm layers) were calculated. The result of the study showed a total of 38 woody plant species recorded from both HGAF and exclosures, but no report from cropland. The abundance, basal area, stem density, species richness, and Shannon and Simpson diversity indices were significantly higher in the HGAF than in exclosures. The mean SOC stock was the highest in HGs (122.13 ± 19.12 Mg ha-1). The estimated mean total ecosystem carbon stock of HGAF, cropland, and exclosure was 171.17 ± 37.25, 78.06 ± 11.97, and 92.5 ± 17.33 Mg ha-1, respectively, which was statistically significant among land use types. A positively significant correlation was observed between diversity, richness, and abundance of woody species and carbon stocks both in the HGAF and exclosure land use systems. The current study confirmed that increased woody species diversity in HGAF enhanced carbon sequestration. The HGAF land use in the northern parts of the country is scanty as compared to the southern part, where there is a rich woody species diversity. Therefore, it is recommendable to promote HGAF across agricultural landscapes of the study area, which enhances biodiversity conservation and mitigation of climate change impacts.

Observations of the association by early-juvenile western rock lobsterPanulirus cygnuswith seagrass assemblages (Decapoda: Achelata: Palinuridae)

AbstractThe fishery of the western rock lobster, Panulirus cygnusGeorge, 1962, is Australia’s most valuable wild-caught single-species fishery. Recruitment in some regions of the fishery was observed to be significantly lower than expected after the 2010/2011 West Australian marine heatwave that caused extensive disturbance of dominant coastal habitats. This event generated interest in the study of the factors influencing survival and recruitment of post-larval benthic P. cygnus after settlement. The habitat associations of the highly cryptic post-settlement early-juveniles were previously unknown, with only anecdotal observations of individuals within limestone crevices in nearshore habitats. Our study used early-juveniles derived from ongoing monitoring of puerulus settlement to examine their habitat association mechanism in mesocosm experiments. Comparison of common nearshore habitat assemblages (bare sand, limestone crevices, and seagrasses (Posidonia and Amphibolis) at varying seagrass densities) found that most early-juveniles associated strongly with Amphibolis assemblages at high stem densities (~2,100 stems m–2). A shift in association between Amphibolis fronds and stems at high stem density to Amphibolis-shaded sand and leaf debris at low stem density indicated active habitat selection by early-juveniles. Habitat choices were tested with the scents of prey items and habitat types within Amphibolis assemblages using Y-maze bioassays. No significant olfactory choices were found, suggesting that habitat associations may be driven by multiple cues. Our study provides new laboratory-based insights into the habitat association of early-juvenile P. cygnus and suggests changes in seagrass assemblage identity and density are likely to be important. Further experimentation is needed to define the cues driving these patterns. The impact of habitat change on recruitment in this important fishery remains unknown and should be an objective of future research.

Sustainable management of rainforest in cross river state, nigeria

The study evaluate the matric models using trees stand parameters such as stem density, in-growth, rates of growth and mortality rate to predict the tree stand structure of the most complex tropical rainforest ecosystem in Cross River State, Nigeria. The model represented all tree species covering matrix for 6 years. The forest decline due to dominant eigenvalue (A) of the matrix R was 0.977, which is the intrinsic rate of natural increase with less than zero. A sensitivity analysis revealed that large recruitment rate of 87% was required to restore stability to the forest while only 16% improvement in growth rate would ensure sustenance and hence stabilized the forest.

Distribution patterns of lianas from subtropical to subboreal zones of the Japanese archipelago and the difference between climbing types

Several factors related to liana abundance have been shown at broad scales, however, the information on factors affecting liana distribution in temperate zones is limited. Climbing types of lianas appear to be associated with interspecific variations of lianas and may be related to the broad-scale distribution and functions of lianas. We aimed to assess the environmental factors related to the abundance of all lianas and those of each climbing type from subtropical to subboreal forests in the Japanese archipelago to better understand the geographical gradient of the liana community.We established six 400 m2 subplots within each of 19 forest plots and recorded the species, stem diameter, and climbing types of lianas with stem diameters ≥ 1 cm. We used generalised linear mixed effects models and model selection based on Akaike's information criterion to examine the effects of climate, soil, and forest structural attributes on liana stem density and basal area.Liana abundance varied substantially among the 19 plots and some forests were characterized by abundant lianas in temperate zones. Twining and root climbers were the major climbing types. Mean annual temperature positively affected the stem density of twining climbers and negatively affected the basal area of root climbers. Maximum snow depth positively affected the stem density of root climbers and negatively affected the basal area of twining climbers. Carbon:nitrogen ratio and dry mass of the soil organic layer had negative effects on the abundance of twining climbers and stem density of both climbers, respectively. Tree basal area positively affected the basal area of root climbers.This study demonstrated the effects of environmental factors, including unique factors such as snow accumulation, on liana distribution at a broad scale from the subtropical to the subboreal zone. Furthermore, the difference between climbing types in distribution may contribute to the gradient of forest ecosystem functions along the environmental factors.

Structural diversity is a key driver of above-ground biomass in tropical forests

ABSTRACT Background A gamut of abiotic and biotic factors is related to the amount of above-ground biomass (AGB) produced in ecosystems. Some factors have direct and others indirect relationships with AGB. Detailed analyses in tropical forests are few but much needed for better understanding the potential impacts of global change drivers and for mitigating impacts. Aims Here, we examined the relationship between AGB and different predictor variables and quantitatively evaluated their relative importance in lowland to lower montane deciduous and lower montane – montane evergreen forest types. We hypothesised that the relationship between AGB and climate, topography, structural diversity, species diversity (alpha and beta) and phylogenetic diversity would differ between the two forest types. Methods We inventoried trees from 114 plots (each 0.1 ha) and used partial least square structural equation modelling to test the direct and indirect relationship between AGB and the predictor variables. Results We found that structural diversity variables, stem density and tree girth, were significantly and positively related to AGB in both forest types, displaying a stronger relationship in montane evergreen forests (w = 0.65 for density and 0.89 for tree girth). In the deciduous forest, alpha and phylogenetic diversity were also important factors, whereas beta and phylogenetic diversity were important in the evergreen forest. The effects of topography and climate varied between forest types, with elevation and precipitation being related to AGB directly and indirectly through their relationship with structural diversity. Conclusion Our results suggest that structural diversity is a key driver of tropical forest biomass, both directly and indirectly. This fundamental understanding can aid in the predictive efforts of biodiversity conservation and forest management.

Vision-Aided Localization and Mapping in Forested Environments Using Stereo Images.

Forests are traditionally characterized by stand-level descriptors, such as basal area, mean diameter, and stem density. In recent years, there has been a growing interest in enhancing the resolution of forest inventory to examine the spatial structure and patterns of trees across landscapes. The spatial arrangement of individual trees is closely linked to various non-monetary forest aspects, including water quality, wildlife habitat, and aesthetics. Additionally, associating individual tree positions with dendrometric variables like diameter, taper, and species can provide data for highly optimized, site-specific silvicultural prescriptions designed to achieve diverse management objectives. Aerial photogrammetry has proven effective for mapping individual trees; however, its utility is limited due to the inability to directly estimate many dendrometric variables. In contrast, terrestrial mapping methods can directly observe essential individual tree characteristics, such as diameter, but their mapping accuracy is governed by the accuracy of the global satellite navigation system (GNSS) receiver and the density of the canopy obstructions between the receiver and the satellite constellation. In this paper, we introduce an integrated approach that combines a camera-based motion and tree detection system with GNSS positioning, yielding a stem map with twice the accuracy of using a consumer-grade GNSS receiver alone. We demonstrate that large-scale stem maps can be generated in real time, achieving a root mean squared position error of 2.16 m. We offer an in-depth explanation of a visual egomotion estimation algorithm designed to enhance the local consistency of GNSS-based positioning. Additionally, we present a least squares minimization technique for concurrently optimizing the pose track and the positions of individual tree stem[s].

Restoration of low-intensity fire in Quercus-Pinus mixedwoods following a prolonged period of fire exclusion

Low-intensity surface fire is required to restore and maintain Quercus-Pinus mixedwood composition, structure, and function. However, historical fire exclusion has resulted in altered vegetation-fuel-fire feedbacks in long-unburned mixedwoods. Fire is now being reintroduced to reduce fire-intolerant understory and midstory stem density, consume excessive litter accumulation, eradicate the duff layer, and achieve various other goals; however, the consequences of restoring fire are poorly understood. The goal of this study was to quantify the effects of fire reintroduction on intra-stand Pinus echinata neighborhoods in a mixed Quercus-P. echinata stand following an extended period of fire exclusion. We report results from a 3-year sampling of the effects of one dormant season and one early growing season fire on woody plant dynamics, understory light, fuel conditions, and P. echinata basal duff-ring accumulation. The sapling assemblage was unaffected by one fire, but the second fire resulted in shoot mortality across all taxa. Understory light availability was unchanged after two fires, and litter depth was significantly reduced after the first and second fire. We found that fire seasonality was likely more important than fuel conditions to achieve desired fire effects. Our results indicated that continued fire and midstory treatment will be required to regenerate P. echinata.

Climate and soil effects on tree species diversity and aboveground carbon patterns in semi-arid tree savannas

Climatic and edaphic effects are increasingly being discussed in the context of biodiversity-ecosystem functioning. Here we use data from West African semi-arid tree savannas and contrasting climatic conditions (lower vs. higher mean annual precipitation-MAP and mean annual temperature-MAT) to (1) determine how climate modulates the effects of species richness on aboveground carbon (AGC); (2) explore how species richness and AGC relate with soil variables in these contrasting climatic conditions; and (3) assess how climate and soil influence directly, and/or indirectly AGC through species richness and stand structural attributes such as tree density and size variation. We find that greater species richness is generally associated with higher AGC, but more strongly in areas with higher MAP, which also have greater stem density. There is a climate-related influence of soils on AGC, which decreases from lower to higher MAP conditions. Variance partitioning analyses and structural equation modelling show that, across all sites, MAP, relative to soils, has smaller effect on AGC, mediated by stand structural attributes whereas soil texture and fertility explain 14% of variations in AGC and influence AGC directly and indirectly via species richness and stand structural attributes. Our results highlight coordinated effects of climate and soils on AGC, which operated primarily via the mediation role of species diversity and stand structures.

Shelterwood harvests promote high breeding bird diversity and shrubland species for less than 10 years in hardwood forests

We compared forest structure and breeding bird communities between shelterwood harvests (SW; n = 15) and mature upland hardwood forests (M; n = 16) over 17 years (Y). Both were relatively static throughout the study period in M. In contrast, heavy canopy reduction and increased light after timber harvests in SW initiated rapid increases in small tree stem densities and shrub cover driven primarily by blackberry (Rubus spp.) - a clonal shrub that “pioneers” recently disturbed, high-light environments. This open-canopy forest structure with low, dense vegetation was short-lived; young trees reached canopy closure within 10 years, with concomitant reductions in blackberry cover and stem density. Total abundance, species richness, and diversity of breeding birds was greater in SW than M, especially the first several years post-harvest; in Y6 these metrics were more than twice as high in SW as in M. Higher abundance, richness, and diversity in SW was driven by an influx of shrubland associates (indigo buntings (Passerina cyanea), chestnut-sided warblers (Setophaga pensylvanica), Eastern towhees (Pipilo erythrophthalmus)) and positive or neutral responses by most other species; only ovenbirds (Seiurus aurocapilla) were more abundant in M. Abundances of shrubland bird species in particular tracked temporal changes in SW forest structure but each differed slightly in their patterns of increase, peak (with 15–26 times more in SW than M), and decline. By Y10 breeding bird communities in SW resembled those in M, although total abundance, species richness, and diversity remained slightly higher in SW throughout the study period. Total abundance, species richness, diversity, and abundance of shrubland bird species were positively- and ovenbird was negatively correlated with blackberry cover, indicating that it is a suitable stand-alone predictor of post-disturbance young forest and changes in breeding bird communities as forests mature. Our results show that young hardwood forests provide habitat for shrubland bird species and promote high breeding bird diversity for <10 years.

Using Voting-Based Ensemble Classifiers to Map Invasive Phragmites australis

Machine learning is frequently combined with imagery acquired from uncrewed aircraft systems (UASs) to detect invasive plants. Having prior knowledge of which machine learning algorithm will produce the most accurate results is difficult. This study examines the efficacy of a voting-based ensemble classifier to identify invasive Phragmites australis from three-band (red, green, blue; RGB) and five-band (red, green, blue, red edge, near-infrared; multispectral; MS) UAS imagery acquired over multiple Minnesota wetlands. A Random Forest, histogram-based gradient-boosting classification tree, and two artificial neural networks were used within the voting-based ensemble classifier. Classifications from the RGB and multispectral imagery were compared across validation sites both with and without post-processing from an object-based image analysis (OBIA) workflow (post-machine learning OBIA rule set; post-ML OBIA rule set). Results from this study suggest that a voting-based ensemble classifier can accurately identify invasive Phragmites australis from RGB and multispectral imagery. Accuracies greater than 80% were attained by the voting-based ensemble classifier for both the RGB and multispectral imagery. The highest accuracy, 91%, was achieved when using the multispectral imagery, a canopy height model, and a post-ML OBIA rule set. The study emphasizes the need for further research regarding the accurate identification of Phragmites australis at low stem densities.

Intraspecific trait variation as a mechanism of coexistence of congeneric blueberry (Vaccinium) species after forest harvesting

Understorey shrubs of boreal forests grow vigorously after canopy removing disturbance such as clearcutting and fire and dominate the post-disturbance community. Many of these dominant shrubs are morphologically and phylogenetically closely related. How do they coexist despite having similar traits and resource needs? One way the coexisting plants may avoid competition is by niche differentiation that may alleviate the negative effects of competition due to high niche overlap. We studied two blueberry species, Vaccinium angustifolium and V. myrtilloides often found in proximity to one another after forest harvesting to test the hypothesis that coexisting congeneric species differentiate their resource acquisition and use through variation in their functional traits (niche differentiation). Discovering the coexistence mechanisms of Vaccinium spp. that flourish after forest harvesting and fire is important from both theoretical and applied perspectives. Vaccinium spp. are dominant shrubs after forest harvesting and fire and constitute a significant food source for wildlife and health-conscious consumers and are also of cultural significance to indigenous peoples. From three post-harvest forest sites in northwestern Ontario, we measured cover of Vaccinium spp. in 81 1 × 1 m quadrats where they occurred alone and together. We then excavated 103 ramets of the two Vaccinium spp. occurring alone and together after measuring three habitat variables (organic matter depth, soil moisture and soil temperature) in the immediate surroundings of the excavated plants. We measured five functional traits: height, canopy diameter, specific leaf area, specific stem density and specific root length. Using these data, we calculated functional hypervolumes (niche space occupancy) of each species occurring alone and together. We also calculated probabilistic niche overlap between the two species as well as their reaction norms to habitat variables. We found that species hypervolumes changed in size, and the probability and degree of overlap between the two Vaccinium spp. changed when occurring alone and co-occurring. Linear regression showed no significant effect of habitat factors on traits. We detected high intraspecific variation in some traits leading to shifts in hypervolumes when they co-occurred. We conclude that at fine spatial scales (homogeneous habitats, open canopy condition) individual trait variation allows for niche complementarity promoting coexistence among these important, early succession, closely related species.