Climate-smart forestry through innovative wood products and commercial afforestation and reforestation on marginal land.

Afforestation and reforestation (AR) on marginal land are nature-based solutions to climate change. There is a gap in understanding the climate mitigation potential of protection and commercial AR with different combinations of forest plantation management and wood utilization pathways. Here, we fill the gap using a dynamic, multiscale life cycle assessment to estimate one-century greenhouse gas (GHG) mitigation delivered by (both traditional and innovative) commercial and protection AR with different planting density and thinning regimes on marginal land in the southeastern United States. We found that innovative commercial AR generally mitigates more GHGs across 100 y (3.73 to 4.15 Giga tonnes of CO2 equivalent (Gt CO2e)) through cross-laminated timber (CLT) and biochar than protection AR (3.35 to 3.69 Gt CO2e) and commercial AR with traditional lumber production (3.17 to 3.51 Gt CO2e), especially in moderately cooler and dryer regions in this study with higher forest carbon yield, soil clay content, and CLT substitution. In a shorter timeframe (≤50 y), protection AR is likely to deliver higher GHG mitigation. On average, for the same wood product, low-density plantations without thinning and high-density plantations with thinning mitigate more life cycle GHGs and result in higher carbon stock than that of low-density with thinning plantations. Commercial AR increases the carbon stock of standing plantations, wood products, and biochar, but the increases have uneven spatial distributions. Georgia (0.38 Gt C), Alabama (0.28 Gt C), and North Carolina (0.13 Gt C) have the largest carbon stock increases that can be prioritized for innovative commercial AR projects on marginal land.

Legacy forest structure increases bird diversity and abundance in aging young forests.

Many studies have demonstrated the importance of early-successional forest habitat for breeding bird abundance, composition, and diversity. However, very few studies directly link measures of bird diversity, composition and abundance to measures of forest composition, and structure and their dynamic change over early succession. This study examines the relationships between breeding bird community composition and forest structure in regenerating broadleaf forests of southern New England, USA, separating the influences of ecological succession from retained stand structure. We conducted bird point counts and vegetation surveys across a chronosequence of forest stands that originated between 2 and 24 years previously in shelterwood timber harvests, a silvicultural method of regenerating oak-mixed broadleaf forests. We distinguish between vegetation variables that relate to condition of forest regeneration and those that reflect legacy stand structure. Using principal components analyses, we confirmed the distinction between regeneration and legacy vegetation variables. We ran regression analysis to test for relationships between bird community variables, including nesting and foraging functional guild abundances, and vegetation variables. We confirmed these relationships with hierarchical partitioning. Our results demonstrate that regenerating and legacy vegetation correlate with bird community variables across stand phases and that the strength with which they drive bird community composition changes with forest succession. While measures of regeneration condition explain bird abundance and diversity variables during late initiation, legacy stand structure explains them during stem exclusion. Canopy cover, ground-story diversity, and canopy structure diversity are the most powerful and consistent explanatory variables. Our results suggest that leaving varied legacy stand structure to promote habitat heterogeneity in shelterwood harvests contributes to greater bird community diversity. Interestingly, this is particularly important during the structurally depauperate phase of stem exclusion of young regenerating forests.

Fragmentation reduces community-wide taxonomic and functional diversity of dispersed tree seeds in the Central Amazon.

The Amazon harbors one of the most diverse tree floras on earth, and most species depend on mutualists for pollination and seed dispersal. This makes them susceptible to reproductive decline in fragmented forest because many of these mutualists suffer area-related extinction in fragments. It remains unknown, however, whether this highly biodiverse tree flora will reproduce and ultimately persist in fragmented forest. We conducted a 2-yr study of seed fall in an experimentally fragmented, highly diverse Central Amazonian forest. We determined the effect of fragment size (1, 10, 100 ha and continuous forest control) on the density, species richness, functional diversity and functional composition of seeds separated into two data sets: dispersed tree seeds, and undispersed tree seeds. Our results show a 3× reduction in the density of undispersed, non-pioneer tree seeds in fragments of all sizes, indicating reduced seed production of the non-pioneer tree community. The density of dispersed tree seeds was reduced by 6× in fragments of all sizes, while species richness was reduced by 6× in 1-ha fragments and by 3× in 10- and 100-ha fragments compared to intact forest. This provides evidence of reduced community-wide seed dispersal, which became more pronounced with declining fragment size. The functional diversity (FRic) of dispersed tree seeds was reduced 9.6× in small fragments, and significant shifts in the functional composition for 8 of the 10 reproductive and ecological traits studied were identified, suggesting compromised ecosystem functioning. These functional compositional shifts provide evidence for disrupted mutualistic processes in fragments, which include loss of pollination by bees, especially small eusocial (meliponid) bees, and loss of dispersal by primates and large birds, which reduced the frequency of large-seeded tree species. Fragments also lost rare and mature-forest species, and collectively these changes suggest that future tree communities in fragmented Amazonian landscapes will retain a taxonomically and functionally impoverished species pool with a biased functional composition unless efforts are undertaken to conserve dispersal by large frugivores and pollination by meliponid bees.

Two salamander species respond differently to timber harvests in a managed New England forest.

BACKGROUND: Managing forests for timber while protecting wildlife habitat is of increasing concern. Amphibians may be particularly sensitive to forest management practices due to their unique biology; however, it is not clear how different species respond to timber harvest practices-particularly over longer time scales. METHODS: Here we report on the differential responses of two salamander species-the eastern red-backed salamander (Plethodon cinereus Green) and the eastern newt (Notophthalmus viridescens Rafinesque)-to forest harvesting, by examining communities across a 25-year chronosequence of regenerating shelterwood harvests. RESULTS: Populations of both species were lowest immediately after harvest, but increased at substantially different rates. Red-backed salamander populations were highest in 20-25 year-old shelterwoods-significantly higher than in mature, unharvested, control (100-120 year old) stands. Eastern newt populations, however, were greatest in unharvested control stands and still had not recovered to population levels found in mature stands in the 25 years since harvest. Red-backed salamander abundances were strongly tied to stand age as well as abundance of decayed coarse woody debris, suggesting that timber harvests influence some wildlife species by affecting a suite of interacting habitat variables that change over time. In contrast, newt abundances were not directly related to stand age but were more related to downed wood and vegetation characteristics. Our results highlight markedly variable responses by two common salamander species to forest harvesting-species with markedly different life histories and reproductive patterns-and that time since harvest may be useful in predicting abundance.

Influence of dry season on Quercus suber L. leaf traits in the Iberian Peninsula.

PREMISE: Water deficit and drought conditions are increasing in intensity, frequency, and duration in the Iberian Peninsula. We observed natural variation in leaf traits across the range of Quercus suber L. (cork oak), an ecologically important species within this region. Stomatal traits (e.g., pore length, maximum aperture) and carbon isotope composition (δ13 C) provide an opportunity to examine the integrative effects of drought and dry-season intensity on leaf development, maximum stomatal conductance, and adaptation to precipitation regimes. METHODS: Gross leaf traits (e.g., area, thickness), stomatal traits (e.g., pore length, size, aperture), and carbon isotope discrimination were measured in Q. suber leaves, and maximum stomatal conductance to water vapor (gwmax ) was calculated. Trees were sampled from nine natural populations across a climate gradient in the Iberian Peninsula, including trees from two genetic lineages. Linear mixed models compared total water deficit to leaf traits, accounting for tree and site as random effects. RESULTS: Quercus suber gross leaf morphology remained consistent across the climate gradient, but increasing water deficit was correlated with smaller stomata at the leaf level and low δ13 C at the tree level. No traits were significantly different between the two genetic lineages. CONCLUSIONS: While there were no significant differences in gross leaf morphology across the climate gradient or between the genetic lineages, stomatal traits and δ13 C responded to climate, suggesting that Q. suber can inhabit a range of environments in the Iberian Peninsula via micro-adjustments of the trait that controls water loss into the atmosphere.

Unearthing the hidden world of roots: Root biomass and architecture differ among species within the same guild.

The potential benefits of planting trees have generated significant interest with respect to sequestering carbon and restoring other forest based ecosystem services. Reliable estimates of carbon stocks are pivotal for understanding the global carbon balance and for promoting initiatives to mitigate CO2 emissions through forest management. There are numerous studies employing allometric regression models that convert inventory into aboveground biomass (AGB) and carbon (C). Yet the majority of allometric regression models do not consider the root system nor do these equations provide detail on the architecture and shape of different species. The root system is a vital piece toward understanding the hidden form and function roots play in carbon accumulation, nutrient and plant water uptake, and groundwater infiltration. Work that estimates C in forests as well as models that are used to better understand the hydrologic function of trees need better characterization of tree roots. We harvested 40 trees of six different species, including their roots down to 2 mm in diameter and created species-specific and multi-species models to calculate aboveground (AGB), coarse root belowground biomass (BGB), and total biomass (TB). We also explore the relationship between crown structure and root structure. We found that BGB contributes ~27.6% of a tree's TB, lateral roots extend over 1.25 times the distance of crown extent, root allocation patterns varied among species, and that AGB is a strong predictor of TB. These findings highlight the potential importance of including the root system in C estimates and lend important insights into the function roots play in water cycling.

A hyperspectral image can predict tropical tree growth rates in single-species stands.

Remote sensing is increasingly needed to meet the critical demand for estimates of forest structure and composition at landscape to continental scales. Hyperspectral images can detect tree canopy properties, including species identity, leaf chemistry and disease. Tree growth rates are related to these measurable canopy properties but whether growth can be directly predicted from hyperspectral data remains unknown. We used a single hyperspectral image and light detection and ranging-derived elevation to predict growth rates for 20 tropical tree species planted in experimental plots. We asked whether a consistent relationship between spectral data and growth rates exists across all species and which spectral regions, associated with different canopy chemical and structural properties, are important for predicting growth rates. We found that a linear combination of narrowband indices and elevation is correlated with standardized growth rates across all 20 tree species (R2  = 53.70%). Although wavelengths from the entire visible-to-shortwave infrared spectrum were involved in our analysis, results point to relatively greater importance of visible and near-infrared regions for relating canopy reflectance to tree growth data. Overall, we demonstrate the potential for hyperspectral data to quantify tree demography over a much larger area than possible with field-based methods in forest inventory plots.

Changing gears during succession: shifting functional strategies in young tropical secondary forests.

Adaptations to resource availability strongly shape patterns of community composition along successional gradients in environmental conditions. In the present study, we examined the extent to which variation in functional composition explains shifts in trait-based functional strategies in young tropical secondary forests during the most dynamic stage of succession (0-20 years). Functional composition of two size classes in 51 secondary forest plots was determined using community-weighted means of seven functional traits, which were intensively measured on 55 woody plant species (n = 875-1,761 individuals). Along the successional gradient in forest structure, there was a significant and consistent shift in functional strategies from resource acquisition to resource conservation. Leaf toughness and adult plant size increased significantly, while net photosynthetic capacity (A(mass)) decreased significantly during succession. Shifts in functional strategies within size classes for A(mass) and wood density also support the hypothesis that changes in functional composition are shaped by environmental conditions along successional gradients. In general, 'hard' functional traits, e.g., A(mass) and leaf toughness, linked to different facets of plant performance exhibited greater sensitivity to successional changes in forest structure than 'soft' traits, such as leaf mass area and leaf dry matter content. Our results also suggested that stochastic processes related to previous land-use history, dispersal limitation, and abiotic factors explained variation in functional composition beyond that attributed to deterministic shifts in functional strategies. Further data on seed dispersal vectors and distance and landscape configuration are needed to improve current mechanistic models of succession in tropical secondary forests.