Late-successional Tree Research Articles

Ecosystem development in short-term postglacial chronosequences: N and P limitation in glacier forelands from Santa Inés Island, Magellan Strait

Glacier foreland moraines provide an ideal model to examine the patterns of ecosystem development and the evolution of nitrogen and phosphorous limitation over successional time. In this paper, we focus on a 400-year soil chronosequence in the glacier forelands of Santa Ines Island in the Magellan Strait, southern Chile by examining forest development on phosphorus (P)-poor substrates in a uniquely unpolluted region of the world. Results show a steady increase in tree basal area and a humped trend in tree species richness over four centuries of stand development. The increase in basal area suggests that the late successional tree species were more efficient nutrient users than earlier successional ones. Total contents of carbon (C) and nitrogen (N) in soils increased during the chronosequence, reaching an asymptote in late succession. The net increases in soil C : N, C : P and N : P ratios observed over successional time suggest that nutrient limitation is maximal in 400-year-old substrates. Foliar C : N and C : P ratios also increased over time to reach an asymptote in old-growth stages, following soil stoichiometric relationships; however the foliar N-to-P ratio remained constant throughout the chronosequence. Biological N fixation was greater in early postglacial succession, associated with the presence of the symbiotic N-fixer Gunnera magellanica. Declining trends of δ15N in surface soils through the 400-year chronosequence are evidence of decreasing N losses in old-growth forests. In synthesis, glacier foreland chronosequences at this high South American latitude provide evidence for increasing efficiency of N and P use in the ecosystem, with the replacement of shade-intolerant pioneers by more efficient, shade-tolerant tree species. This pattern of ecosystem development produces a constant foliar N : P ratio, regardless of variation in soil N-to-P ratio over four centuries.

The scientific value of the largest remaining old-growth red pine forests in North America

Old growth red pine forests (Pinus resinosa) cover less than 1% of their original range in North America and are essential for maintaining biodiversity at stand and landscape scales. Despite this, the largest remaining old-growth red pine forest in the world, the Wolf Lake Forest Reserve, is currently threatened by mining claims in Northern Ontario and has been receiving considerable media and public attention in recent months. We provide a timely review of how large old growth red pine forests maintain biodiversity at several taxonomic levels (with a focus on trees and plants) through heterogeneous partitioning of limiting resources such as light and nitrogen, formation of complex habitats through increased accumulation of coarse woody debris, and the maintenance of natural disturbance-driven succession. These processes shape the overstory community, allowing for the regeneration of pines, coexistence of early-mid successional shade intolerant species and cross-ecotonal establishment of late successional tree species in response to regional warming over the past three decades. Using Wolf Lake as a case study, we review legislation and policy complexities around this issue and provide scientific arguments for the preservation of this forest. We invoke recent insights into the ecological role of refugia, the development of criteria for assessing endangered ecosystems, and the challenges of conservation in the face of climate change and disturbance regimes. These forests are ecologically important and provide a scientifically irreplaceable system for assessing baseline ecosystem function, processes and services. As the largest remaining old-growth red pine forest in the world, Wolf Lake Forest Reserve deserves intensive study, monitoring and full protection from future development.

Interspecific vs intraspecific patterns in leaf nitrogen of forest trees across nitrogen availability gradients

Leaf nitrogen content (δ) coordinates with total canopy N and leaf area index (LAI) to maximize whole-crown carbon (C) gain, but the constraints and contributions of within-species plasticity to this phenomenon are poorly understood. Here, we introduce a game theoretic, physiologically based community model of height-structured competition between late-successional tree species. Species are constrained by an increasing, but saturating, relationship between photosynthesis and leaf N per unit leaf area. Higher saturating rates carry higher fixed costs. For a given whole-crown N content, a C gain-maximizing compromise exists between δ and LAI. With greater whole-crown N, both δ and LAI increase within species. However, a shift in community composition caused by reduced understory light at high soil N availability (which competitively favors species with low leaf costs and consequent low optimal δ) counteracts the within-species response, such that community-level δ changes little with soil N availability. These model predictions provide a new explanation for the changes in leaf N per mass observed in data from three dominant broadleaf species in temperate deciduous forests of New England. Attempts to understand large-scale patterns in vegetation often omit competitive interactions and intraspecific plasticity, but here both are essential to an understanding of ecosystem-level patterns.

Scaling relationships among twig size, leaf size and leafing intensity in a successional series of subtropical forests

Scaling relationships among twig size, leaf size and leafing intensity fundamentally influence the twig-leaf deployment pattern, a property that affects the architecture and functioning of plants. However, our understanding of how these relationships change within a species or between species as a function of forest succession is unclear. We determined log-log scaling relationships between twig cross-sectional area (twig size) and each of total and individual leaf area, and leafing intensity (the number of leaves per twig volume) for 78 woody species along a successional series in subtropical evergreen forests in eastern China. The series included four stages: secondary shrub (S1), young (S2), sub-climax (S3) and climax evergreen broadleaved forests (S4). The scaling slopes in each of the three relationships did not differ among the four stages. The y-intercept did not shift among the successional stages in the relationship between twig cross-sectional area and total leaf area; however, the y-intercept was greatest in S4, intermediate in S3 and lowest in S2 and S1 for the relationship between twig size and individual leaf area, while the opposite pattern was found for the twig size-leafing intensity relationship. This indicates that late successional trees have few but large leaves while early successional trees have more small leaves per unit twig size. For the relationship between twig cross-sectional area and total leaf area, there was no difference in the regression slope between recurrent (appear in more than one stages) and non-recurrent species (appear in only one stage) for each of the S1-S2, S2-S3 and S3-S4 pairs. A significant difference in the y-intercept was found in the S2-S3 pair only. In the relationship between twig cross-sectional area and individual leaf area, the regression slope between recurrent and non-recurrent species was homogeneous in the S1-S2 and S3-S4 pairs, but heterogeneous in the S2-S3 pair. We conclude that forest succession caused the shift in the intercept, but did not affect scaling slopes for relationships among twig size, leaf size and leaf intensity. For recurrent species, the invariant scaling slope in the twig-leaf size relationship between adjacent pairs of successional stages may be related to their phenotypic plasticity by adjusting their twig and leaf deployment strategy to similar to what the non-recurrent species display.

Monthly stem increment in relation to climatic variables during 7 years in an East African rainforest

Monthly stem increment of 766 trees was assessed for 7 years in Kakamega Forest, Kenya and related to monthly climatic variables. Mean stem increment of all tree individuals correlated negatively with maximum temperature but not with mean and minimum temperatures. For the precipitation variables sum of precipitation and number of rainy days we found positive correlations. Stem increment of the trees in the early-, mid-, and late-successional groups correlated positively with the number of rainy days. For late-successional trees increment correlated negatively with mean and maximum temperature and positively with all other precipitation variables. For mid-successional trees we found a negative correlation with mean temperature. In addition, the stem increment of most species related positively to precipitation variables and negatively to mean and maximum temperature. In view of the expected increasing temperatures and fewer but heavier rain events, our results suggest that climate change will lead to a reduction in stem increment. The results appertaining to the successional groups imply that early and mid-successional species are better equipped to perform well under the expected future climatic conditions than the late-successional species. This could reduce the role of this East African forest as a carbon store. As the responses to climatic variables were highly group- and species-specific it is likely that climate change will result in a species composition shift, presumably in favour of drought-resistant and heat-tolerating species.

Can a fast-growing early-successional tree (Ochroma pyramidale, Malvaceae) accelerate forest succession?

Abstract:Species-specific traits of trees affect ecosystem dynamics, defining forest structure and understorey development. Ochroma pyramidale is a fast-growing tree species, with life-history traits that include low wood density, short-lived large leaves and a narrow open thin crown. We evaluated forest succession in O. pyramidale-dominated secondary forests, diverse secondary forests, both 10–15 y since abandonment, and rain forests by comparing height, density and basal area of all trees (> 5 cm dbh). Furthermore, we compared species richness of understorey trees and shrubs, and basal area and density of trees of early- and late-successional species (< 5 cm dbh) between forest types. We found that tree basal area (mean ± SD: 32 ± 0.9 m2 ha−1) and height (12.4 ± 1.8 m) of canopy trees were higher, and density (1450 ± 339 ha−1) lower in O. pyramidale forests than in diverse forests, and more similar to rain forest. Understorey shrub diversity and tree seedling density and diversity were lower in O. pyramidale forests than in diverse forests, but these forest types had a similar density of early- and late-successional trees. Canopy openness (> 15%) and leaf litter (> 10 cm) were both highest in O. pyramidale forests, which positively affected density of understorey trees and shrubs and negatively affected density of late-successional trees. In conclusion, O. pyramidale forests presented structural features similar to those of rain forest, but this constrained the establishment of understorey tree species, especially late-successional species, decreasing successional development.

Differences in fine root traits between early and late-successional tree species in a Chinese subtropical forest

The aim of this study was to compare fine root (≤2 mm diameter) traits (i.e. biomass distribution and architecture) of three tree species (Alniphyllum fortunei, Liquidambar formosana and Cyclobalanopsis glauca) growing in a mixed-species stand in a subtropical forest. Fine root samples were collected using soil cores. The collected samples were scanned with the Win-RHIZO system to analyse architectural parameters and were then ovendried to determine dry mass. Fine roots of the three species were mainly distributed in the top 15 cm of soil and decreased with soil depth across all horizontal distances. C. glauca had the highest fine root biomass at 15‐ 30 cm depth at 1.0 m from the tree trunk. The specific fine root area (SRA) and the length (SRL) were the highest for C. glauca, followed by L. formosana and A. fortunei. These species use different soil exploitation strategies. The early-successional species (A. fortunei and L. formosana) increase their fine root biomass and length throughhighcarboninvestment,whereaslate-successionalspecies(C.glauca)increasenutrientuptakeefficiency viachangesinfinerootmorphologyandhigherSRAandSRLvalues.Insecondarybroadleavedforestmanagement and mixed plantation establishment, root trait differences among tree species and their effects on belowground competition and species coexistence should be considered.

Testing Broadcast Seeding Methods to Restore Urban Forests in the Presence of Seed Predators

AbstractForest restoration in urban areas often occurs in isolation from remnant forest, limiting the chances for recolonization by native species. Plants with bird‐dispersed seeds can be particularly vulnerable to dispersal limitation and regeneration can be further impeded by non‐native seed predators. We used a factorial experiment to investigate broadcast seeding as a method to reintroduce trees with large seeds and fleshy fruits into early successional forests. We assessed rates of seed and fruit loss, germination and seedling establishment in three seed treatments: (1) caging to exclude introduced mammalian seed predators; (2) removal of fleshy fruit pericarp; and (3) placing seeds in nutritionally enriched clay balls. Across all species (Beilschmiedia tawa, Elaeocarpus dentatus, and Litsea calicaris) seeds and fruits accessible to mammalian predators suffered significantly greater loss (58%) than those protected by cages (4%). However, seed and fruit loss in the presence of predators was reduced to only 35% across all species by the treatment combining the removal of fruit flesh and clay ball application to seeds. Establishment of B. tawa seedlings after 1 year was significantly enhanced by the clay ball treatment (12% of seeds sown vs. 6% without clay balls). Very low establishment rates were recorded for E. dentatus and L. calicaris. Broadcast seeding was found to be a viable method of improving regeneration of large‐seeded late successional trees and may be a cost‐effective alternative to planting saplings. Seedling establishment can be improved with fruit flesh removal and clay ball treatments, especially in the presence of mammalian seed predators.

Dead wood in clearcuts of semi-natural forests in Estonia: site-type variation, degradation, and the influences of tree retention and slash harvest

Semi-natural forests, which naturally regenerate after timber harvesting, provide distinct opportunities for dead wood (DW) management for biodiversity. We described DW pool and sources of its variation during the first decade after final felling in Estonia, hemiboreal Europe. Depending on forest type, the mean post-harvest volumes of above-ground DW ranged from 70 to 119 m3 ha−1. Final felling generally did not reduce downed coarse woody debris (CWD) because many sawn logs were left on-site, and soil scarification was rarely used. However, subsequent decay of downed CWD appears to be accelerated due to the increased ground contact of logs, so that even the relatively small inputs from live retention trees observed (5 m3 ha−1 per decade) can be ecologically significant. While final felling greatly reduced snag abundance, the mortality of retained live trees generally balanced their later losses. The volumes of downed fine woody debris in conventional cutover sites were roughly double that of pre-harvest forests. Slash harvest caused an approximately twofold reduction in downed DW and resulted in CWD volumes that were below mature-forest levels. The results indicate that the habitat quality of cutovers critically depends both on the retention and on the post-harvest management of biological legacies. In Estonia, the necessary improvements include more careful retention of snags in final felling, selecting larger retention trees, focusing slash harvest on the fine debris of common tree species, and providing snags of late-successional tree species.

Demographic drivers of successional changes in phylogenetic structure across life‐history stages in plant communities

To gain insight into the ecological processes driving community reassembly in disturbed ecosystems, we assessed the phylogenetic dispersion of early‐ and late‐successional tree species occurring in lowland forests of northeastern Costa Rica. Early‐successional species were more closely related than expected by chance, whereas late‐successional species tended to be less closely related than expected by chance. Then, we evaluated temporal changes in the phylogenetic structure of seedling and tree assemblages in four 1‐ha plots of secondary forests in this region. We found an increase in the phylogenetic evenness among tree individuals over time in all secondary tree assemblages, indicating that relatedness among tree individuals decreases as succession unfolds. This pattern was jointly promoted by recruitment and mortality processes, suggesting that increasing evenness was caused by the replacement of individuals of early‐successional species from closely related lineages by late‐successional species belonging to a wider diversity of lineages. Based on species occurrence, however, tree community reassembly did not show any significant phylogenetic trend over time. These results suggest that shifts in species abundance over succession have a greater impact on the phylogenetic structure of the community than the turnover of species. Seedling assemblages showed higher phylogenetic evenness than tree assemblages, suggesting that propagule colonization is an important process driving phylogenetic changes in species composition throughout succession. Overall, our findings showed that the phylogenetic structure of these successional communities varies at two temporal scales. At short timescales, decreased dominance by early‐successional species over succession leads to increased evenness among tree individuals. At longer timescales, colonization processes result in increased phylogenetic evenness in seedling communities compared to tree communities, forecasting increasing phylogenetic evenness among adult individuals at late‐successional stages.

Does selective logging affect the leaf structure of a late successional species?

The anatomical characteristics of both sun and shade leaves of Alseis pickelii were investigated in order to evaluate the consequences of selective logging (in seasonally dry Atlantic Forest) on the leaf structure of this species. Fully expanded sun and shade leaves were collected in two distinct stands of tabuleiro forest; a stand of recently logged forest and an unlogged stand. Only leaves from the unlogged stand revealed significantly different magnitudes of response to light regimes, producing leaves with structural characteristics associated with different levels of irradiance. The sun leaves from this stand had a thicker adaxial surface, mesophyll, palisade and spongy parenchyma, a secondary cell wall of fibers and a lower leaf area compared with the shade leaves. However, in the logged stand, the leaf cuticles of sun and shade leaves showed no significant differences, although the leaf area of the sun leaves was higher than the shade leaves. According to these data, we concluded that the unlogged stand produced typical "sun" and "shade" leaves. In contrast, leaves from the logged stand showed a lower variation of types, where neither typical "sun" nor typical "shade" leaves were produced, suggesting lower leaf plasticity of this late successional tree in this area.

Responses of Transplanted Native Tree Species to Invasive Alien Grass Removals in an Abandoned Cattle Pasture in the Lacandon Region, Mexico

We tested the early performance of 16 native early-, mid-, and late-successional tree species in response to four intensities of grass removal in an abandoned cattle pasture dominated by the introduced, invasive African grass, Cynodon plectostachyus, within the Lacandon rainforest region, southeast Mexico. The increase in grass removals significantly improved the performance of many species, especially of early- and mid-successional species, while performance of late-successional species was relatively poor and did not differ significantly among treatments. Good site preparation and at least one additional grass removal four months after seedling transplant were found to be essential; additional grass removals led to improved significantly performance of saplings in most cases. In order to evaluate the potential of transplanting tree seedlings successfully in abandoned tropical pastures, we developed a “planting risk index”, combining field performance measurements and plantation cost estimations. Our results showed a great potential for establishing restoration plantings with many early- and mid-successional species. Although planting risk of late-successional species was considered high, certain species showed some possibilities of acclimation after 18 months and should be considered in future plantation arrangements in view of their long-term contributions to biodiversity maintenance and also to human welfare through delivery of ecosystem services. Conducting a planting risk analysis can help avoid failure of restoration strategies involving simultaneous planting of early-, mid-, and late-successional tree species. This in turn will improve cost-effectiveness of initial interventions in large-scale, long-term restoration programs.

Tree species richness and the logging of natural forests: A meta-analysis

Forests cover much of the earth’s surface and are regularly logged. Well established ecological theory predicts, and the results of extensive silvicultural studies demonstrate the role of disturbance in maintaining species richness in forests; however, logging and other human initiated disturbance is often credited with the degradation of forest ecosystems throughout the world. Presented here are the results of a meta-analysis of 19 published studies investigating 25 distinct paired human-disturbed and primary forests in the tropical and temperate biomes. Regardless of whether studies were grouped across biomes or considered independently, the current literature indicates a significant reduction in tree species richness following logging. While the reasons for this reduction in richness are as diverse as the forests considered here, some common themes are clear. Although logging may increase the richness of early successional tree species, it also tends to reduce the richness of late successional trees. This occurs both through the altering biotic and abiotic processes regulating resource availability and through size-class and species based selection biases common in logging. Logging also makes primary forests more accessible, setting the stage for a chronic human disturbance cycle.

Photosynthesis, photoprotection, and growth of shade-tolerant tropical tree seedlings under full sunlight

High solar radiation in the tropics is known to cause transient reduction in photosystem II (PSII) efficiency and CO(2) assimilation in sun-exposed leaves, but little is known how these responses affect the actual growth performance of tropical plants. The present study addresses this question. Seedlings of five woody neotropical forest species were cultivated under full sunlight and shaded conditions. In full sunlight, strong photoinhibition of PSII at midday was documented for the late-successional tree species Ormosia macrocalyx and Tetragastris panamensis and the understory/forest gap species, Piper reticulatum. In leaves of O. macrocalyx, PSII inhibition was accompanied by substantial midday depression of net CO(2) assimilation. Leaves of all species had increased pools of violaxanthin-cycle pigments. Other features of photoacclimation, such as increased Chl a/b ratio and contents of lutein, β-carotene and tocopherol varied. High light caused strong increase of tocopherol in leaves of T. panamensis and another late-successional species, Virola surinamensis. O. macrocalyx had low contents of tocopherol and UV-absorbing substances. Under full sunlight, biomass accumulation was not reduced in seedlings of T. panamensis, P. reticulatum, and V. surinamensis, but O. macrocalyx exhibited substantial growth inhibition. In the highly shade-tolerant understory species Psychotria marginata, full sunlight caused strongly reduced growth of most individuals. However, some plants showed relatively high growth rates under full sun approaching those of seedlings at 40% ambient irradiance. It is concluded that shade-tolerant tropical tree seedlings can achieve efficient photoacclimation and high growth rates in full sunlight.

Successional stages of primary temperate rainforests of Chiloé Island, Chile

Understanding forest succession is required when designing management strategies, analyzing forest functioning, and forecasting the effects of changes in disturbance regime of forests. However, assigning a certain successional stage to forests in nature is challenging, especially when long-lived tree species dominate succession. Temperate rainforests commonly harbor emergent pioneer trees with long lifespans (>500 years) and may persist even when forest have reached stability in tree species composition (compositional equilibrium) and stability in structure (e.g. biomass). Thus, it is difficult to locate stands along a successional trajectory. Here, we propose a method for identifying the successional stages of forests using a dynamic forest model that estimate the time taken for a forest to reach the late successional stage, i.e. when forests have reached stability. Using this method, we examined the successional stages of 13 old, unmanaged stands of temperate rainforests located on Chiloé Island (Chile, 42°S). We parameterized the model for 17 tree species using field data and a comprehensive literature search. The model predicted varied successional pathways for reproducing the observed structural variability of studied forests stands. Model results suggest that forests in this region can take 490–850 years to reach the late successional stage. We found 6 out of the 13 studied forests represent a transient successional stage. Forest stands in the late successional stage commonly contained pioneer species with basal area <20 m2/ha. According to our simulations, pioneers can persist until the late successional stage because of their long lifespans and the occurrence of small canopy openings (<1.6 ha) produced by windstorms. Above-ground biomass in the studied forests (estimated at 539 t/ha, average among stands) tended to decrease as forests approach the late successional stage because large pioneers are replaced by smaller late-successional trees. These results can assist in the classification of natural forest according to their successional stages as well as in developing management and conservation strategies of primary forests in this region.

Woody species recruitment under monospecific plantations of pioneer trees - facilitation or inhibition?

The successional model of forest restoration is based on the facilitation process, in which the establishment of pioneer tree species favors the late successional tree species. We tested the hypothesis of facilitation through a case study, comparing tree species diversity in the understory of two Neotropical native tree species plantations, Trema micrantha (L.) Blüme (Cannabaceae) and Schinus molle L. (Anacardiaceae). Results obtained under the plantations were compared with an adjacent area under spontaneous secondary succession, analyzing the ligneous plant diversity, soil physic-chemistry and shading. Additionally, the seed rain under the two plantations was analyzed. The area of spontaneous secondary succession and the area with T. micrantha had the highest ligneous plant diversity. The understory of T. micrantha plantation had the lowest light intensity and higher late successional species abundance. In addition, T. micrantha had higher plant diversity than S. molle, which could be explained at least partially by higher diversity in the seed rain. Higher litterfall and mineral content of leaves and twigs of T. micrantha did not coincide with higher topsoil mineral content under that species. Instead, soil under S. molle had higher level of P than the soil under T. micrantha. Data suggest that a high diversity of ligneous plants could be thrived by the spontaneous succession. On the other hand, T. micrantha had promoted a higher richness and abundance of late successional species, which could be related to a more pronounced shade effect, in agreement with the facilitation conception. The lowest diversity and density of ligneous plant species under S. molle characterizes an inhibition effect. T. micrantha could be included in restoration plans assembled with other species or combined with areas without intervention, whenever the spontaneous regeneration is possible.

Soil-nutrient availability modifies the response of young pioneer and late successional trees to elevated carbon dioxide in a Brazilian tropical environment

The aim of this work was to determine the impact of three levels of [CO 2] and two levels of soil-nutrient availability on the growth and physiological responses of two tropical tree species differing in their ecological group: Croton urucurana Baillon, a pioneer (P), and also Cariniana legalis (Martius) Kuntze, a late succession (LS). We aimed to test the hypothesis that P species have stronger response to elevated [CO 2] than LS species as a result of differences in photosynthetic capacity and growth kinetics between both functional groups. Seedlings of both species were grown in open-top-chambers under high (HN) or low (LN) soil-nutrient supply and exposed to ambient (380 μmol mol −1) or elevated (570 and 760 μmol mol −1) [CO 2]. Measurements of gas exchange, chlorophyll a fluorescence, seedling biomass and allocation were made after 70 days of treatment. Results suggest that elevated [CO 2] significantly enhances the photosynthetic rates ( A) and biomass production in the seedlings of both species, but that soil-nutrient supply has the potential to modify the response of young tropical trees to elevated [CO 2]. In relation to plants grown in ambient [CO 2], the P species grown under 760 μmol mol −1 [CO 2] showed increases of 28% and 91% in A when grown in LN and HN, respectively. In P species grown under 570 μmol mol −1 [CO 2], A increased by 16% under HN, but there was no effect in LN. In LS species, the enhancement of A by effect of 760 μmol mol −1 [CO 2] was 30% and 70% in LN and HN, respectively. The exposure to 570 μmol mol −1 [CO 2] stimulated A by 31% in HN, but was no effect in LN. Reductions in stomatal conductance ( g s) and transpiration ( E), as a result of elevated [CO 2] were observed. Increasing the nutrient supply from low to high increased both the maximum rate of carboxylation ( V cmax) and maximum potential rate of electron transport ( J max). As the level of [CO 2] increased, both the V cmax and the J max were found to decrease, whereas the J max/ V cmax ratio increased. In the LS species, the maximum efficiency of PSII ( F v/ F m) was higher in the 760 μmol mol −1 [CO 2] treatment relative to other [CO 2] treatments. The results suggest that when grown under HN and the highest [CO 2], the performance of the P species C. urucurana, in terms of photosynthesis and biomass enhancement, is better than the LS species C. legalis. However, a larger biomass is allocated to roots when C. legalis seedlings were exposed to elevated [CO 2]. This response would be an important strategy for plant survival and productivity of the LS species under drought stresses conditions on tropical environments in a global-change scenario.

Carbon dynamics of North American boreal forest after stand replacing wildfire and clearcut logging

Boreal forest carbon (C) storage and sequestration is a critical element for global C management and is largely disturbance driven. The disturbance regime can be natural or anthropogenic with varying intensity and frequency that differ temporally and spatially the boreal forest. The objective of this review was to synthesize the literature on C dynamics of North American boreal forests after most common disturbances, stand replacing wildfire and clearcut logging. Forest ecosystem C is stored in four major pools: live biomass, dead biomass, organic soil horizons, and mineral soil. Carbon cycling among these pools is inter-related and largely determined by disturbance type and time since disturbance. Following a stand replacing disturbance, (1) live biomass increases rapidly leading to the maximal biomass stage, then stabilizes or slightly declines at old-growth or gap dynamics stage at which late-successional tree species dominate the stand; (2) dead woody material carbon generally follows a U-shaped pattern during succession; (3) forest floor carbon increases throughout stand development; and (4) mineral soil carbon appears to be more or less stable throughout stand development. Wildfire and harvesting differ in many ways, fire being more of a chemical and harvesting a mechanical disturbance. Fire consumes forest floor and small live vegetation and foliage, whereas logging removes large stems. Overall, the effects of the two disturbances on C dynamics in boreal forest are poorly understood. There is also a scarcity of literature dealing with C dynamics of plant coarse and fine roots, understory vegetation, small-sized and buried dead material, forest floor, and mineral soil.

Comparative hydraulic architecture of tropical tree species representing a range of successional stages and wood density

Plant hydraulic architecture (PHA) has been linked to water transport sufficiency, photosynthetic rates, growth form and attendant carbon allocation. Despite its influence on traits central to conferring an overall competitive advantage in a given environment, few studies have examined whether key aspects of PHA are indicative of successional stage, especially within mature individuals. While it is well established that wood density (WD) tends to be lower in early versus late successional tree species, and that WD can influence other aspects of PHA, the interaction of WD, successional stage and the consequent implications for PHA have not been sufficiently explored. Here, we studied differences in PHA at the scales of wood anatomy to whole-tree hydraulic conductance in species in early versus late successional Panamanian tropical forests. Although the trunk WD was indistinguishable between the successional groups, the branch WD was lower in the early successional species. Across all species, WD correlated negatively with vessel diameter and positively with vessel packing density. The ratio of branch:trunk vessel diameter, branch sap flux and whole-tree leaf-specific conductance scaled negatively with branch WD across species. Pioneer species showed greater sap flux in branches than in trunks and a greater leaf-specific hydraulic conductance, suggesting that pioneer species can move greater quantities of water at a given tension gradient. In combination with the greater water storage capacitance associated with lower WD, these results suggest these pioneer species can save on the carbon expenditure needed to build safer xylem and instead allow more carbon to be allocated to rapid growth.

An exotic insect and pathogen disease complex reduces aboveground tree biomass in temperate forests of eastern North America

Forests store a large portion of global carbon in tree and soil biomass. However, our understanding of the factors that may reduce rates of forest carbon accumulation is incomplete. This study examines the impact of an exotic insect and fungal pathogen disease on aboveground tree biomass in forests of eastern North America. We determine how beech bark disease (BBD) — a pervasive but nonextirpating disease — influences the growth and survival of its host tree, Fagus grandifolia Ehrh., and the effects of changes in the demography of this late-successional dominant tree species on total stand-level aboveground tree biomass. Our analyses use US Forest Service Forest Inventory and Analysis data from eastern states located along a gradient in the time since introduction of BBD. In Maine, where BBD has been present for &gt;50 years, we observed reduced growth and survival of the host tree and reduced overall stand-level aboveground tree biomass compared with states where BBD arrived more recently. Additionally, there is a negative relationship between host tree abundance and overall stand-level aboveground tree biomass. Where beech is most abundant, BBD results in substantial declines in aboveground tree biomass (e.g., 11% in Maine); where beech is less abundant, we expect more modest declines (1%–4%).