Understory Research Articles

Ecosystem carbon stocks of Estonian premature and mature managed forests: effects of site conditions and overstorey tree species

The crucial role of forests in terrestrial carbon (C) balance is well acknowledged, but nationwide C assessments still show some uncertainties. We estimated the effect of forest site type on various ecosystem C pools in premature- and mature-aged forests of hemiboreal Estonia. Furthermore, the effects of soil physico-chemical properties and the tree species on soil organic carbon (SOC) stocks were analysed. The weighted mean SOC stock of Estonian forests was 77 Mg C ha−1 in humipedon layer and 118 Mg C ha−1 in solum. The mean ecosystem C stock of Estonian forests was 174 (confidence range: 141 to 214) Mg C ha−1, from which 111 Mg C ha−1 was distributed in the solum layer, 61 Mg C ha−1 in the overstorey tree layer, 0.5 Mg C ha−1 in the understorey tree layer and 1.7 Mg C ha−1 in the ground vegetation. Forest site type had a significant (p < 0.001) effect on all analysed C stocks. The variation of SOC stocks in the humipedon (R2 = 0.71) and in the solum (R2 = 0.79) was explained by the thickness of the layer, the total nitrogen stock, base saturation, hydrolytic acidity, soil trophic and moisture conditions. The higher quantity of deciduous tree species in a stand composition was in a positive correlation with the SOC stock in the humipedon of fertile site types. The accuracy of nationwide assessments of forest C reporting can be improved by using a site-specific approach, considering deeper soil layers and incorporating other structural forest layers.

&lt;b&gt;Leaf architecture and symmetry of understory tree species of an Araucaria forest

Shade plants of ombrophilous forests are subjected to light-limiting conditions and need to invest in architectural structures associated with leaf symmetry to increase light capture. This study investigated the leaf architecture of six Araucaria forest tree species with distinct symmetry: Cupania vernalis, Casearia sylvestris, Schinus terebinthifolius, Piper gaudichaudianum, Roupala brasiliensis and Cedrela fissilis . We hypothesized that symmetry, associated with other traits, minimizes self-shading. Asymmetry index, petiole length, total leaf area, leaf angle, internode length and stem diameter were measured. The asymmetry index did not indicate a clear distinction between asymmetric and symmetric leaves. Leaves classified as asymmetric had higher values for the asymmetry index in the median and basal regions of the leaf, while symmetrical leaves had higher values in the apical region. The results also indicated an adjustment among structural leaf traits that facilitated a three-dimensional organization that produced an advantageous arrangement for light capture, which seems to be a response to selective pressure by the heterogeneous light conditions of the ombrophilous forest understory.

Identifying regrowth forests with advanced mature forest values

In this study, we examined the associations between field-assessed floristic and structural habitat values for mature forest and GIS-derived variables to assess whether high conservation value forests could be predicted for strategic reservation at a landscape scale. We investigated the Eucalyptus regnans forests of the Victorian Central Highlands in south-eastern Australia, where several extensive wildfires in the last century have left little mature forest. We assessed the extent to which the floristic composition and a suite of habitat-related structural variables could be explained by two forest inventory GIS variables (percentage senescence and site productivity) and whether explanatory capacity improved from inclusion of additional environmental variables (climate, soils, topography, structure and spatial location). Results showed that the floristic composition was weakly related to productivity, but not to percentage senescence. Four habitat-related structural variables were positively related to percentage senescence (density of old-growth eucalypts, the quadratic mean diameter (QMD) of both live and dead eucalypts, and the maximum eucalypt form class (a proxy for tree hollows)) while the volume of CWD had a marginally significant positive relationship. Three structural variables were related to productivity (the maximum eucalypt form class, the QMD of dead understorey trees and of dead eucalypts). However, in all cases the explanatory power of percentage senescence and productivity was weak (proportion of deviance explained by the models <0.3). Inclusion of the other environmental variables did not substantially improve explanatory power in any case. Our results suggest that there is a high degree of stochasticity driving floristic and structural composition within these forests, making the detection of most mature forest values difficult without site visits. There may be some limited capacity for the presence of senescent trees visible in aerial photographs to highlight stands more likely to contain habitat trees, but there was no relationship with floristic maturity. Our results also suggest that more productive sites do not have substantially greater habitat values, indicating that the current timber harvesting approach of prioritising the harvest of stands on more productive sites is unlikely to have negative consequences for biodiversity.

Soil drivers of local-scale tree growth in a lowland tropical forest.

Soil nutrients influence the distribution of tree species in lowland tropical forests, but their effect on productivity, especially at local scales, remains unclear. We used tree census, canopy occupancy, and soil data from the Barro Colorado Island (BCI; Panama) 50-ha forest dynamics plot to investigate the influence of soil nutrients and potential toxins on aboveground tree productivity. Growth was calculated as the increase in diameter of 150,000 individual stems ≥1cm diameter at breast height, representing 207 species. The effects of soil variables and other strong predictors of growth (e.g., light) were estimated using hierarchical, linear, mixed-effects models. Growth was weakly positively associated with phosphorus (P), particularly for understory tree species that are typically considered to be limited by light. In contrast, growth was strongly negatively related to manganese (Mn) and aluminum (Al), although the latter effect was confounded by strong correlations between Al and other soil variables. The negative response to increasing Mn (and Al) suggests a toxicity effect due to solubilization and uptake of amorphous pools of metal oxides in the soil. These results show that Plimits tropical tree growth at local scale on BCI, but that toxic metals represent an even greater constraint on productivity.

Taxonomic Revision of Garcinia Section Garcinia (Clusiaceae)

Species of Garcinia sect. Garcinia are typically understorey trees in rain forest and are distributed from eastern India to Malesia. A taxonomic revision of Garcinia section Garcinia (Clusiaceae) has resulted in the recognition of 13 species, two of which have three varieties each. Several species are excluded from Garcinia section Garcinia, reported as insufficiently known, or reduced to synonymy. Five species, G. acuticosta, G. discoidea, G. exigua, G. ochracea and G. sangudsangud, and two varieties, G. diospyrifolia var. minor and G. mangostana var. borneensis, are newly described. Morphological characters that are important for sectional delimitation are terminally attached inflorescences of simple cymes, stamen bundles 4 or 4-angled, and fruits with a smooth surface. Species limits are defined on the basis of a combination of characters of the male flower (i.e. shape of stamens, presence of pistillode), type of fruit, and characters of the leaf (shape and size, venation pattern and glandular lines).

Time shifts in height and diameter growth allocation in understory European beech (Fagus sylvatica L.) following canopy release

In understory trees, height–diameter allocation is subject several constraints: maximal height growth is limited, height growth is never null and, in terms of time dependency, diameter growth always precedes height growth. Understory trees experience a succession of canopy opening and closure events during their lifetime. Preferential allocation of their biomass to height or diameter growth is part of the acclimation process to their immediate environment. In this study, we investigated annual height and diameter increments in Fagus sylvatica understory trees submitted to canopy release. Annual height and diameter increments were obtained from retrospective stem analysis from the top of the tree to the stump on 39 understory trees. The relationship between height and diameter increments was investigated and temporal correlations among successive annual height and diameter increments were analyzed. An asymptotic relationship between annual height and diameter increment indicates that stem height growth was limited in understory trees. The intercept significantly differed from zero suggesting that height growth never stopped even when diameter growth was null. Following canopy release events, immediate diameter growth increase was observed while the height growth response was delayed, resulting in a time shift in the growth allocation strategy. Strong and asymmetric temporal correlations between annual height and diameter increments were observed: past annual diameter growth was positively correlated to present height growth. In understory trees, tree height is the main factor determining their potential growth since it determines their access to above-canopy light. However, the precedence of diameter growth over height growth suggests that tree growth is driven by diameter instead of height. This apparent discrepancy may be explained by the fact that, under closed canopy conditions, stem allometry reaches a functional threshold that forces tree to grow in diameter before growing in height.

Recent Trends in Large Hardwoods in the Pacific Northwest, USA

Forest densification, wildfires, and disease can reduce the growth and survival of hardwood trees that are important for biological and cultural diversity within the Pacific Northwest of USA. Large, full-crowned hardwoods that produce fruit and that form large cavities used by wildlife were sustained by frequent, low-severity fires prior to Euro-American colonization. Shifts in fire regimes and other threats could be causing declines in, large hardwood trees. To better understand whether and where such declines might be occurring, we evaluated recent trends in Forest Inventory and Analysis (FIA) data from 1991–2016 in California and southern Oregon. We included plots that lay within areas of frequent fire regimes during pre-colonial times and potential forest habitats for fisher, a rare mammal that depends on large live hardwoods. We analyzed changes in basal area for eight hardwood species, both overall and within size classes, over three time periods within ecoregions, and in public and private land ownerships. We found the basal area to generally be stable or increasing for these species. However, data for California black oak suggested a slight decline in basal area overall, and among both very large trees and understory trees; that decline was associated with fire mortality on national forest lands. In addition, mature trees with full crowns appeared to sharply decline across all species. Many trends were not statistically significant due to high variation, especially since more precise data from remeasured trees were only available for the two most recent time periods. Continued analysis of these indicators using remeasured trees will help to evaluate whether conservation efforts are sustaining large, full-crowned trees and their associated benefits.

Hurricane disturbances, tree diversity, and succession in North Carolina Piedmont forests, USA

Windthrow plays a critical role in maintaining species diversity in temperate forests. Do large-scale strong wind events (i.e., tropical cyclones, including hurricanes, typhoons and severe cyclonic storms) increase tree diversity in severely damaged forest areas? Do hurricanes (tropical cyclones that occurs in the Atlantic Ocean and northeastern Pacific Ocean) lead to altered relative abundance of shade-tolerant and shade-intolerant species? Did historic hurricanes alter the succession trajectory of the damaged forests? We used nearly 70-year tree demographic data to assess the effects of two major hurricanes on woody species diversity in Piedmont forests, North Carolina, USA. Species richness (S) and Shannon–Wiener’s diversity index (H′) were used to evaluate the changes in tree diversity. The changes in composition were assessed with Nonmetric Multidimensional Scaling. The pre-hurricane successional phase can strongly influence both the damage severity and subsequent responses. Although there is often an immediate drop in diversity following a hurricane, understory tree diversity quickly increases to levels that exceed those prior to the disturbance. This leads to an increase in diversity in stands that were substantially damaged. Hurricanes significantly decrease the dominance of shade-intolerant canopy species while increasing pre-established, more shade-tolerant species. We conclude that large, and infrequent hurricanes help to maintain local tree diversity, but also accelerate the increase in dominance of understory species such as red maple and beech.

Exploring the Inclusion of Small Regenerating Trees to Improve Above-Ground Forest Biomass Estimation Using Geospatial Data

Research on the contribution of understory components to the total above ground biomass (AGB) has to date received very little attention because most prior biomass estimation studies have ignored small regenerating trees beneath the main canopy with the assumption that their contribution to biomass is generally negligible. Only a few biomass studies have emphasized a considerable contribution to biomass of understory components in forest ecosystems. However, this study of native, tropical, deciduous forest biomass in the Central Highlands of Vietnam was able to explore the contribution of small regenerating trees to total biomass by exploiting a large field inventory of hundreds to thousands of individually-counted small regenerating trees per hectare. Thus, this study investigated the influence of small regenerating tree biomass on models of the relationship between total AGB and remote sensing data. These analyses were trained with and without topographic variables derived from ASTER-GDEM. Our results demonstrate that the inclusion of small regenerating understory trees (R2 = 0.42, NRMSE or %RMSE = 30.5%) provides a quantifiable improvement in total estimated AGB compared to using only large woody canopy trees (R2 = 0.21, NRMSE or %RMSE = 36.6%) when correlating field-based biomass measurements with optical image-derived variables. All analyses show that the inclusion of terrain factors made an important contribution to biomass modeling. This study suggests that for young, open forests where there are many small regenerating trees, the contribution of understory biomass should be taken into consideration to improve total AGB estimation.

Forest seedling community response to understorey filtering by tree ferns

AbstractQuestionsLarge pteridophytes frequently co‐occur with conifers and angiosperms in the understorey of temperate broad‐leaved podocarp forests but interactions between them are poorly understood. We evaluated the impact of tree ferns on the regeneration niche of vascular woody species to determine whether tree ferns function as biotic filters and influence seedling occurrence. We asked the following questions: (i) do understorey tree ferns influence the woody seedling bank, and (ii) which potential mechanisms drive any such influence?LocationAuckland and Waikato regions, northern New Zealand.MethodsWe measured woody seedlings in 164 1‐m2 plots in northern New Zealand temperate broad‐leaved podocarp forest and used multivariate analyses and modelling to assess the relative contributions of abiotic and biotic effects on community composition and seedling abundance. We manipulated the environments beneath 160 tree fern individuals by removing fronds and/or macro‐litter in a balanced factorial design, and recorded the response of the seedling community over 1 year. We then assessed the relative influences of shading and litter depth on the seedling community response.ResultsDistance to the nearest tree fern was the best predictor of understorey seedling abundance; seedling abundance decreased beneath tree ferns. There was no strong evidence, however, that tree ferns influence seedling community composition; although the palm Rhopalostylis sapida, was consistently present away from tree fern micro‐sites. Removal of tree fern shading and macro‐litter both influenced the local seedling community; conifers responded positively, and most consistently to frond removal. Frond‐shading and deep litter reduced seedling species richness and seedling abundance.ConclusionsTree ferns influence the woody seedling bank in temperate broad‐leaved podocarp forest through increased shading and macro‐litter accumulation, both of which reduce the abundance of angiosperm and conifer seedlings. A tree fern‐dominated understorey is likely to reduce conifer establishment and may limit direct competition among woody plants by reducing densities and regeneration opportunities immediately beneath tree fern canopies.

Characterization and Conservation Status of Evergreen Rainforest Understory: Case of Campo Ma'an National Park (Cameroon)

The Campo Ma'an National Park is located in the evergreen rainforest area rich in biological diversity. This biological diversity remains poorly known, especially those of the understory. The objective of the present study is to characterize undersotory tree and to determine their IUCN conservation status. To know the floristic diversity of understory (5 cm ≤ dbh <10 cm) of this forest, a tree inventory using the plots method of 25 m x 25 m, in which 36 plots were placed out on 6 transects of 4 km each. The IUCN Red List was used to determine the status of inventoried species. The result showed a total richness of 256 species belonging to 148 genera and 50 families for the entire site has been identified. The Shannon diversity index is 4.90 and 4.02 for Old secondary forest (OSF) and Secondary forest (SFO), respectively. The floristic background belongs to the field of Guinean-Congolese endemism, with 6 endemic species in Cameroon. The conservation status analysis shows that 22 species are listed as endangered in the red list of the International Union for the Conservation of Nature. This study provides a base for reflection on the integration of understory trees species in inventories and in the development of conservation strategies.

Northern red oak regeneration: 25-year results of cutting and prescribed fire in Michigan oak and pine stands

Overstory and understory treatments were established in natural oak stands and red pine plantations in Michigan in 1991 to test the hypotheses that (1) oak seedling survival and growth would be greater in pine than oak stands and (2) removal of competitors would enhance oak seedling performance. Late spring prescribed fires were implemented in 2002 and 2008 to investigate their effectiveness in controlling understory red maple. Performance of planted northern red oaks has been monitored since 1991 and the abundance of naturally regenerating oak and red maple seedlings and sprouts in different size classes has been documented since 2001. A subset of oaks has been protected against deer browsing since planting. Results suggest partial competitor removal enhances oak seedling and sprout performance, whereas complete removal increases mortality from browsing and frost. Increases in red maple abundance and decreases in oak abundance were documented after the prescribed fires in 2015. Greater growth and survival of planted oaks was observed in the pine stands, provided they were protected from browsing. Based on these results, the most viable management scenario for maximizing survival and growth of oak seedlings and sprouts in the study region would include protecting oak seedlings from deer in 25% canopy cover shelterwoods in pine plantations. Opportunities exist for developing systems involving alternating rotations and mixtures of oak and pine.

Evaluating the uncertainty of Landsat-derived vegetation indices in quantifying forest fuel treatments using bi-temporal LiDAR data

Forest ecosystems in the American west have long been influenced by timber harvests and fire suppression, and recently through treatments that reduce fuel for fire management. Precisely quantifying the structural changes to forests caused by fuel treatments is an essential step to evaluate their impacts. Satellite imagery-derived vegetation indices, such as the normalized difference vegetation index (NDVI), have been widely used to map forest dynamics. However, uncertainties in using these vegetation indices to quantify forest structural changes have not been thoroughly studied, mainly due to the lack of wall-to-wall validation data. In this study we generated forest structural changes in aboveground biomass (AGB) and canopy cover as a result of fuel treatments using bi-temporal airborne light detection and ranging (LiDAR) data and field measurements in a mixed coniferous forest of northern Sierra Nevada, California, USA. These LiDAR-derived forest structural measures were used to evaluate the uncertainties of using Landsat-derived vegetation indices to quantify treatments. Our results confirmed that vegetation indices can accurately map the extents of forest disturbance and canopy cover changes caused by fuel treatments, but the accuracy in quantifying AGB changes varied by the pre-treatment forest densities and treatment intensity. Changes in vegetation indices had relatively weaker correlations (coefficient of determination < 0.45) to biomass changes in forests with sparse (AGB < 100 Mg/ha) or dense biomass (AGB > 700 Mg/ha), than in forests with moderate-density (AGB between 100 Mg/ha and 700 Mg/ha) before the disturbances. Moreover, understory treatments (canopy height < 10 m) were poorly indicated by changes in satellite-derived vegetation indices. Our results suggest that when relating vegetation indices to AGB changes, researchers and managers should be cautious about their uncertainties in extremely dense or sparse forests, particularly when treatments mainly removed small trees or understory fuels.

Understory vegetation plays the key role in sustaining soil microbial biomass and extracellular enzyme activities

Abstract. While we know that understory vegetation affects the soil microbial biomass and extracellular enzyme activities in subtropical Chinese fir (Cunninghamia lanceolata) forests, we are less certain about the degree of its influence. We determined the degree to which the soil abiotic and biotic properties, such as PLFAs and extracellular enzyme activities, were controlled by understory vegetation. We established a paired treatment in a subtropical Chinese fir plantation, which comprised one plot from which the understory vegetation and litter were removed (None) and another from which the litter was removed but the understory vegetation was left intact (Understory). We evaluated how the understory vegetation influenced the soil abiotic properties, the bacterial, fungal, and actinobacterial PLFAs, and the activities of five hydrolases and two oxidative enzymes. The dissolved organic carbon (DOC), particulate organic carbon, soil organic carbon, ammonia nitrogen (NH4+–N), and total nitrogen contents and soil moisture were 18 %, 25 %, 12 %, 34 %, 8 %, and 4 % lower in the None treatments than in the Understory treatments, respectively (P&lt;0.05). Soil bacterial, fungal, and total PLFAs, and the potential activities of β-1,4-glucosidase (βG), β-1,4-N-acetylglucosaminidase, phenol oxidase, and peroxidase, were as much as 24 % lower in None treatments than in Understory treatments (P&lt;0.05). The specific activities of C-acquiring enzymes were as much as 41 % higher (P&lt;0.05), and the ratio of C- to N-acquiring enzymes was also higher in the None treatments than in the Understory treatments. This suggests that in the absence of understory vegetation microbes invested more in C acquisition than N acquisition because the carbon (C) inputs were less labile. The negative relationship between DOC and AP shows that DOC is consumed when P-acquiring enzymes are produced. The positive correlation between NH4+–N and βG suggested the increased availability of N promoted the decomposition of C. More extracellular enzymes that degrade soil organic matter are produced when there is understory vegetation, which leads to losses of soil C. On the other hand, the soil C sink is maintained by increased inputs of C. We can therefore conclude that understory vegetation contributes to C sequestration in Chinese fir forests and suggest that understory should be maintained to sustain soil quality in subtropical Chinese fir plantations.

Constrained Spectral Clustering of Individual Trees in Dense Forest Using Terrestrial Laser Scanning Data

The present study introduces an advanced method for 3D segmentation of terrestrial laser scanning data into single tree clusters. It intentionally tackled difficult forest situations with dense and structured tree formations, which inventory practitioners are often faced with. The strongly interlocking tree crowns of different sizes and in different layers characterized the test conditions of close to nature forest plots. Volumetric 3D images of the plots were derived from the original point cloud data. A clustering method with automatically derived priors focused on the segmentation of these images by global optimization. Therefore, each image was segmented as a whole and partitioned into individual tree objects using a combination of state-of-the-art techniques. Multiple steps were combined in a workflow that included a morphological detection of the tree stems, the construction of a similarity graph from the image data, the computation of the eigenspectrum which was weighted with the tree stem priors and the final labelling of the transformed data points in a Markov Random Field framework. The detected trees were verified by number and position which allowed for comparison with other studies. Additionally, for a subset of the data, we provided a detailed verification of the three-dimensional extent of the complete trees. The detection rate by number and position was 97.40% for major trees with a stem diameter at breast height (DBH) ≥ 12 cm and 84.62% for regeneration trees with a DBH &lt; 12 cm. The three-dimensional extent of the detected trees resulted in an average producer’s accuracy of 93.66% and a user’s accuracy of 94.06%. Overall, these numbers confirm the capacity of the method for accurate segmentation of strongly layered and understory trees. Future studies could test the method on wider areas with large scale data and different forest types in order to determine its general transferability.

Fragmentation and matrix contrast favor understory plants through negative cascading effects on a strong competitor palm.

Understanding the patterns and processes driving biodiversity maintenance in fragmented tropical forests is urgently needed for conservation planning, especially in species-rich forest reserves. Of particular concern are the effects that habitat modifications at the landscape scale may have on forest regeneration and ecosystem functioning: a topic that has received limited attention. Here, we assessed the effects of landscape structure (i.e., forest cover, open area matrices, forest fragmentation, and mean inter-patch isolation distance) on understory plant assemblages in the Los Tuxtlas Biosphere Reserve, Mexico. Previous studies suggest that the demographic burst of the strong competitor palm Astrocaryum mexicanum in the core area of this reserve limits plant recruitment and imperils biodiversity conservation within this protected area. Yet, the local and landscape predictors of this palm, and its impact on tree recruitment at a regional scale are unknown. Thus, we used structural equationmodeling to assess the direct and cascading effects of landscape structure on stem and species density in the understory of 20 forest sites distributed across this biodiversity hotspot. Indirect paths included the effect of landscape structure on tree basal area (a proxy of local disturbance), and the effects of these variables on A. mexicanum. Density of A. mexicanum mainly increased with decreasing both fragmentation and open areas in the matrix (matrix contrast, hereafter), and such an increase in palm density negatively affected stem and species density in the understory. The negative direct effect of matrix contrast on stem density was overridden by the indirect positive effects (i.e., through negative cascading effects on A. mexicanum), resulting in a weak effect of matrix contrast on stem density. These findings suggest that dispersal limitation and negative edge effects in more fragmented landscapes dominated by open areas prevent the proliferation of this palm species, enhancing the diversity and abundance of understory trees. This "positive" news adds to an increasing line of evidence suggesting that fragmentation may have some positive effects on biodiversity, in this case by preventing the proliferation of species that can jeopardize biodiversity conservation within tropical reserves.

Ecological characteristics of floodplain forest reference sites in the Upper Mississippi River System

Historical and present day disturbances have contributed to long-term changes in the extent, composition, and structure of Upper Mississippi River System (UMRS) floodplain forests. Loss of forest habitat, low tree species diversity, a lack of successful regeneration in many areas, and continued declines in forest health over time are serious threats to this ecosystem. Floodplain forest restoration has therefore gained importance as a management goal throughout the UMRS. A key component of the restoration process is assessing the ecological characteristics of remnant, high quality reference sites to identify appropriate targets for forest restoration efforts. In this study, fourteen reference sites were located and established along a ∼1140 km longitudinal stretch of the Upper Mississippi River, lower Illinois River, lower Big Muddy River, and lower Cache River watershed. Biological and abiotic data were sampled from 1000 m2 permanent plots located at each study site. Overstory floodplain forest communities were generally dominated by silver maple (Acer saccharinum) and a variable combination of green ash (Fraxinus pennsylvanica), American elm (Ulmus americana), cottonwood (Populus deltoides), pin oak (Quercus palustris), and hackberry (Celtis occidentalis). Common understory trees capable of overstory recruitment included silver maple, green ash, American elm, and hackberry. Overstory species richness and diversity were generally high, but species richness and diversity in the understory layer were much lower, a trend that was most pronounced in the northernmost sites. In addition, the scarcity of mast producing and/or shade intolerant species in the understory was evident throughout the study, even at sites where they were present in the overstory. Herbaceous communities were notably variable between study sites. Despite the latitudinal gradient, ordination of the floodplain forest communities revealed substantial compositional overlap between sites. However, patterns in the ordination were significantly correlated with local variability in canopy cover, elevation, soil texture, and several hydrologic parameters. Species richness and diversity generally increased from north to south. Results suggest that regional differences and local characteristics such as microtopographic features should be considered when selecting target restoration conditions and evaluating the suitability of individual species for specific restoration projects.

Состав и численность адвентивных и инвазивных кустарников и деревьев подлеска в лесопарках г. Екатеринбурга

Состав и численность адвентивных и инвазивных кустарников и деревьев подлеска в лесопарках г. Екатеринбурга

Causes of reduced leaf-level photosynthesis during strong El Niño drought in a Central Amazon forest.

Sustained drought and concomitant high temperature may reduce photosynthesis and cause tree mortality. Possible causes of reduced photosynthesis include stomatal closure and biochemical inhibition, but their relative roles are unknown in Amazon trees during strong drought events. We assessed the effects of the recent (2015) strong El Niño drought on leaf-level photosynthesis of Central Amazon trees via these two mechanisms. Through four seasons of 2015, we measured leaf gas exchange, chlorophyll a fluorescence parameters, chlorophyll concentration, and nutrient content in leaves of 57 upper canopy and understory trees of a lowland terra firme forest on well-drained infertile oxisol. Photosynthesis decreased 28% in the upper canopy and 17% in understory trees during the extreme dry season of 2015, relative to other 2015 seasons and was also lower than the climatically normal dry season of the following non-El Niño year. Photosynthesis reduction under extreme drought and high temperature in the 2015 dry season was related only to stomatal closure in both upper canopy and understory trees, and not to chlorophyll a fluorescence parameters, chlorophyll, or leaf nutrient concentration. The distinction is important because stomatal closure is a transient regulatory response that can reverse when water becomes available, whereas the other responses reflect more permanent changes or damage to the photosynthetic apparatus. Photosynthesis decrease due to stomatal closure during the 2015 extreme dry season was followed 2months later by an increase in photosynthesis as rains returned, indicating a margin of resilience to one-off extreme climatic events in Amazonian forests.

Leaf nitrogen assimilation and partitioning differ among subtropical forest plants in response to canopy addition of nitrogen treatments

Global increases in nitrogen deposition may alter forest structure and function by interfering with plant nitrogen metabolism (e.g., assimilation and partitioning) and subsequent carbon assimilation, but it is unclear how these responses to nitrogen deposition differ among species. In this study, we conducted a 2-year experiment to investigate the effects of canopy addition of nitrogen (CAN) on leaf nitrogen assimilation and partitioning in three subtropical forest plants (Castanea henryi, Ardisia quinquegona, and Blastus cochinchinensis). We hypothesized that responses of leaf nitrogen assimilation and partitioning to CAN differ among subtropical forest plants. CAN increased leaf nitrate reductase (NR) activity, and leaf nitrogen and chlorophyll contents but reduced leaf maximum photosynthetic rate (Amax), photosynthetic nitrogen use efficiency (PNUE), ribulose-1,5-bisphosphate carboxylase (Rubisco) activity, and metabolic protein content of an overstory tree species C. henryi. In an understory tree A. quinquegona, CAN increased NR activity and glutamine synthetase activity and therefore increased metabolic protein synthesis (e.g., Rubisco) in leaves. In the shrub B. cochinchinensis, CAN increased Amax, PNUE, Rubisco content, metabolic protein content, and Rubisco activity in leaves. Leaf nitrogen assimilation and partitioning results indicated that A. quinquegona and B. cochinchinensis may better acclimate to CAN than C. henryi and that the acclimation mechanism differs among the species. Results from this study suggest that long-term elevated atmospheric nitrogen deposition has contributed to the ongoing transformation of subtropical forests into communities dominated by small trees and shrubs.