The Effects of Rehabilitation Treatments on Landscape Function Within a Softwood Plantation After Fire: Implications for Catchment Management

There is global interest in enhancing the ecosystem services provided by landscapes and catchments dominated by plantation (monoculture) forestry. Partial reversion of plantations to locally native species (reforestation) is one option. However, the ecological outcomes of this kind of plantation reversion are poorly known. The partial reforestation of a pine plantation (Pinus radiata D. Don 1836) in the Australian Capital Territory with native species following a wildfire provides a rare case study of the environmental consequences of such a reversion. We estimated changes in landscape functionality by measuring indices of water infiltration, nutrient cycling, and soil surface stability across five landscape-scale treatments after the 2003 Lower Cotter Catchment bushfire: (1) natural regeneration of a native forest burned in 2003, (2) burned pine plantation replanted to pines, (3) burned plantation replanted to native trees and shrubs, (4) burned plantation allowed to naturally regenerate, and (5) forest roads rehabilitated by planting native trees and shrubs. At 14 years after the fire, we found that the regenerating native forest had the highest indices of water infiltration, nutrient cycling, and soil surface stability. The burned pine plantation that was replanted to pines in 2005 had indices of functionality that were higher than the burned plantation areas that were either allowed to naturally regenerate to native eucalypt forest or were planted with native forest species. These two types of native forest rehabilitation treatments had only minor differences in functionality. The rehabilitated closed roads were the least functional. We found that a pine plantation at the closed canopy stage can supply regulating services of water infiltration, nutrient cycling, and soil surface stability comparable to a native forest at a similar stage postfire; however, a significant limitation of the plantation was its low ecosystem resilience. It required massive soil disturbance to replant postfire and long-term maintenance of an extensive unpaved road network. The active or passive rehabilitation of native forest is justified to improve the natural resilience to wildfire. However, this rehabilitation of a native forest following use as a pine plantation is a multidecade process in this relatively low-rainfall environment. Study Implications The 2003 Canberra bushfire destroyed the entire pine plantation at Lower Cotter Catchment, a water catchment in Australian Capital Territory, but also provided an opportunity to examine and quantify changes in ecosystem functions with different restoration treatments. Landscape Function Analysis, including three indices (water infiltration, nutrient cycling, and soil surface stability), was used in this study. Findings suggest that both native eucalyptus forests and pine plantations recovered to relatively high levels of functionality within just 15 years after the bushfire, compared with all other restoration treatments, but plantations of Pinus radiata are not resilient to wildfire from a commercial perspective. These results help to justify the controversial decision to restore the majority of the catchment with native species in 2005. However, long-term monitoring is needed to determine how long it will take for the replanted and natural regeneration treatments to approach the functionality of the native forest.

Carbon Accumulation and Partitioning Above and Belowground under Coppiced and Replanted Eucalypt Plantations

The extent to which the C sink strength of eucalypt plantations can be affected by coppicing or replanting remains unclear. To address this issue, we evaluated variations in C stocks under coppiced or replanted eucalypt stands formed by clones or seedlings. For each field assessment (0 [T0], 2.5, 3.5, 4.5, 5.5 and 7.0 years [at harvest]), tree biomass, litterfall, and soil C stocks (0–120 cm depth) were determined. At harvest, debarked stemwood productivity was similar under coppice or replanting, about 50.0 Mg C ha–1. Generally, coppiced stands favored subsoil C storage (40–100 cm), whereas replanted stands favored soil C accrual in topsoil (0–20 cm), depending on the genetic material. Relative to T0, soil C increased about 2.14, 1.91, and 1.84 Mg C ha–1 yr–1 under coppice, replanting with seedlings and clones, respectively. Coarse root biomass under these stands were about 17.3, 13.4, and 9.5 Mg C ha–1, respectively, equivalent to 50% of total harvest residues. Hence, inputs from coarse roots could represent a large contribution to soil C over multiple rotations under coppiced or replanted stands. Otherwise, short-term C losses can be high where stumps and coarse roots are harvested, especially following successive coppice cycles. Study Implications: Our findings have important implications for forest managers growing eucalypt plantations aiming to maximize C accumulation. Both coppiced and replanted stands can fix up to 50 Mg C ha−1 only in debarked stemwood over 7 years, with a comparatively higher C storage in coarse roots under coppice. Despite the increasing demand for forest residues in bioenergy production, harvesting stumps and coarse roots should be avoided, especially upon replanting eucalypt stands after successive coppice cycles.

Assessing the Economic Viability of the Mechanized Removal of Understory Beech during a Shelterwood Harvest

Beech bark disease is a pathogenic complex that has been spreading throughout the American beech’s range since the 1800s. A litany of negative consequences have manifested from the infestation of this disease, many of which deteriorate the ecological functions of forestland. This case study sought to analyze the cost structure for removing a recalcitrant beech understory via mechanized shelterwood harvesting. High-resolution data regarding the day-to-day operation of harvesting equipment was collected using daily production journals. Interviews were conducted with the logging company owner and maintenance supervisor to gather additional information required to calculate machine costs, overhead, job specific costs, and trucking costs. The yield from this harvest was 527 metric tonnes of sawtimber and 4,893 tonnes of clean chips. The total harvesting cost equated to $4,651/ha, with the cost attributed to removing beech at $204/ha. Despite the additional cost of beech removal, the logger generated a total profit of $5,965 and a return on investment of 7.5%, allowing us to conclude that mechanized harvesting can be a viable beech removal strategy given the forest stocking and market conditions that are in place. Study Implications This study breaks down the various costs associated with cutting, skidding, landing, and transporting wood products from a mechanized harvesting operation designed to remediate the effects of beech bark disease. The beech remediation harvest was economically viable for both the landowner and the logger because the timber sale included some valuable hardwood sawtimber, and the harvest system was capable of generating clean chips for a pulp mill with the low-grade hardwood. Furthermore, the landowner’s willingness to accept lower sawtimber stumpage revenues allowed the logger to make a profit and return-on-investment on the job. Had the timber sale been limited to only hardwood pulpwood or fuel chips, the operation would not have been economically viable without the landowner paying for the operation, which, based on our analysis, would be approximately $200/ha.

Single-Step Genomic Analysis Increases the Accuracy of Within-Family Selection in a Clonally Replicated Population of Pinus taeda L.

The use of genomic markers in forest tree breeding is expected to improve the response to selection, especially within family. To evaluate the potential improvements from genotyping, we analyzed a large Pinus taeda L. clonal population (1,831 cloned individuals) tested in multiple environments. Of the total, 723 clones from five full-sib families were genotyped using 10,337 single-nucleotide polymorphism markers. Single-step models with genomic and pedigree-based relationships produced similar heritability estimates. Breeding value predictions were greatly improved with inclusion of genomic relationships, even when clonal replication was abundant. The improvement was limited to genotyped individuals and attributable to accounting for the Mendelian sampling effect. Reducing clonal replication by omitting data indicated that genotyping improved breeding values similar to clonal replication. Genomic selection predictive ability (masking phenotypes) was greater for stem straightness (0.68) than for growth traits (0.41 to 0.44). Predictive ability for a new full-sibling family was poorer than when full-sibling relationships were present between model training and validation sets. Species that are difficult to propagate clonally can use genotyping to improve within-family selection. Clonal testing combined with genotyping can produce breeding value accuracies adequate to graft selections directly into deployment orchards without progeny testing. Study Implications Genomic markers can improve the reliability of breeding values, resulting in a more confident ranking of individuals within families. For genotyped individuals, the improvements were comparable to clonal testing. Breeding programs for species that are difficult to propagate clonally should consider genotyping to replace or supplement clonal testing as a means to improve within-family selection. For genomic prediction of breeding values without phenotypes (genomic selection), a robust genetic relationship between model training and validation sets is required. The single-step model allows genotyping a subset of the population and is a straightforward extension of well-established methods.

Spatial and Temporal Patterns in Carbon and Nitrogen Inputs by Net Precipitation in Atlantic Forest, Brazil

Understanding both carbon and nitrogen temporal and spatial inputs by rainfall in tropical forests is critical for proper forest conservation and management and might ultimately elucidate how climate change might affect nutrient dynamics in forest ecosystems. This study aimed to quantify the net precipitation contribution to the Atlantic Forest’s total carbon (C) and total nitrogen (N), identifying potential differences between these inputs regarding temporal (seasonal and monthly) and spatial scales. Rainfall samples were collected before and after interacting with the forest canopy from May 2018 to April 2019. The rainfall was enriched after crossing the forest canopy. Significant differences were found for gross rainfall and net precipitation between annual carbon (104.13 kg ha−1 and 193.18 kg ha−1) and nitrogen (16.81 kg ha−1 and 36.95 kg ha−1) inputs, respectively. Moreover, there was seasonal variability in the C and N inputs with 75% occurring in the wet season. Overall, the spatial patterns revealed that the same locations had the highest inputs regardless of the analyzed period. The forest-rainfall interactions provide constant C and N inputs, especially in the wet season, and are fundamental for the maintenance of ecological processes. Study Implications The hydrological and nutrient cycles are tied together. There was significant nutrient enrichment after rainfall interacts with the forest canopy. Rainfall seasonality and canopy deciduousness and heterogeneity drive the temporal and spatial variabilities of carbon and nitrogen. The wet season represented an average of 75% of the total annual carbon and nitrogen contribution, via net precipitation. Such findings enhance our understanding of nutrient deposition, leaching, and absorption processes by canopies and the importance of the tropical forest in the hydrological and nutrient cycle. This knowledge might serve as a guide to improve management practices and justify conservation initiatives.

Carbon and Nitrogen Dynamics in Mexican Management Forest: Simulation of Biomass Harvesting and C and N Amendments

Sustainable silvicultural management requires the maintenance of long-term ecosystem processes. We used the CENTURY model to simulate the impact of wood extraction and organic amendments on aboveground biomass, carbon (C) storage, and the availability of nitrogen (N) in the two dominant silvicultural methods in Mexico: the silvicultural development method (SDM) and irregular forest management (IFM). The values of the mean absolute percentage error for the SDM and IFM were 2.1% and 3.3% for C in aboveground biomass, 5.7% and 5.0% for soil organic carbon (SOC), and 14.9% and 21.6% for N, respectively. Simulation for the SDM (1967–2068) suggested a reduction of ~7% in C in soil, microbial biomass, and litter, 9% in aboveground biomass C, and ~20% in the mineral N available. For IFM, the simulation (2009–2019) suggested a reduction of 14% in the accumulation of aboveground biomass and 13% in the mineral N available. Simulation of the adoption of management practices suggested that N mineral availability would increase by 2%–3% without drastically reducing the SOC, improving aboveground biomass production by ~7%, in each management system. Study Implications In Mexico, current silvicultural management is causing alterations in the biological and chemical processes of the soil, but the future impacts on the production of forest wood and loss of fertility cannot be estimated by direct measurements. We simulated two silvicultural management alternatives with two rotation cycles and measured the response in terms of SOC, nitrogen availability, and aboveground biomass. The model shows that improving forest residue management by adding organic amendments to the soil would counteract changes in soil microbial activity, nitrogen availability, SOC, and aboveground biomass in the future. Managers should consider this information to reorient current crop residue management to achieve the objectives and the sustainability of forest management in Mexican temperate forests.

Implementation of Forestry Best Management Practices and Sediment Delivery in Three Regions of North Carolina and Virginia

Forestry best management practices (BMPs) were created in response to the Clean Water Act of 1972 to protect water quality from nonpoint source pollutants such as sediment. The objectives of this study were to quantify the relationship between BMP implementation and sediment delivery on 58 recently harvested sites across three physiographic regions and five forest operational features. BMP implementation rates, erosion rates, sediment delivery ratios, and sediment masses were calculated at 183 silt fences functioning as sediment traps adjacent to streams in Virginia and North Carolina. Major access system features, including stream crossings, skid trails, and haul roads, typically delivered the greatest sediment mass to streams and had the highest sediment delivery ratios on a per feature basis. When accounting for sediment mass delivered and area in each feature, harvest area accounted for approximately 70% of sediment delivered to streams for all regions. Most features had proportionally higher erosion rates than sediment masses collected at silt fences, indicating that most erosion generated by forest operations is being trapped by either harvest areas or streamside management zones. For most features and regions, as BMP implementation increased, erosion rates and the sediment masses delivered to streams decreased. Study Implications Forestry best management practices (BMPs) are designed to mitigate the amount of sediment entering streams and affecting other aquatic features as a result of forest operations. In this study, a significant inverse relationship between BMP implementation and the amount of sediment delivered to streams was found, indicating that increasing levels of BMP implementation reduces sediment delivery. Most of the erosion caused by forest operations is being trapped before it is delivered to streams. This research highlights the importance of leaving streamside management zones along streams and minimizing the extent of bare soil and area in temporary and permanent roads.

Characterizing Stand and Biomass Tables from Diameter Distribution Models: A Case Study for Mixed-Hardwood Forests in Eastern Tennessee, USA

Accurately assessing forest structure and productivity is critical to making timely management decisions and monitoring plant communities. This study aims to evaluate the prediction accuracy of site-level stand and biomass tables from the diameter distribution models. The efficacy of the single Weibull function and two finite mixture models was compared for six species groups on three mixed-hardwood sites in eastern Tennessee, USA. To evaluate model performance, two types of stand/biomass tables were generated. The first type was constructed from all species on a given site (site-specific), whereas the second type was built for a single species from all sites (species-specific). Results indicate that both types of stand and biomass tables were consistently well quantified by the two-component mixture model in terms of goodness of fit, parsimony and robustness. The two-component mixture model better characterized the complex, multimodal diameter distributions than the single Weibull model, which underpredicted the upper portion of the distributions. The three-component model tends to overfit the data, which results in lower prediction accuracy. Among the three models examined, the two-Weibull mixture model is suggested to construct site-level stand/biomass tables, which provides more reliable and accurate predictions to assess forest structure and product class. Study Implications Compared to pine monocultures, diameter distribution models for upland mixed-hardwood forests in the Southeastern United States have not been widely explored. Mixed-hardwood forests not only supply high-quality timber for domestic and international uses, but also provide various ecosystem services and essential habitats for wildlife. The finite mixture model has been proposed for characterizing the irregular forms of diameter distribution curves, but the reliability of this method has not been explicitly examined for a wide variety of species. This study provided insights for natural resources managers to select appropriate models when modeling stand and biomass tables for mixed-hardwood forests.

Strip Clearcutting Drives Vegetation Diversity and Composition in the Moso Bamboo Forests

Strip clearcutting of Moso bamboo forests in southern China has seen increasing interest as a way of reducing harvesting costs. Previous research has shown that cutting influences the overstory structure and drives changes in the microclimate and soil properties. However, the effects of strip cutting on understory vegetation diversity and composition remain unclear. To better understand the influence of cutting on the understory vegetation, this study compares sites under natural restoration after cut and uncut sites in the Moso bamboo forest. We selected plots that were cut in 2019 (C19) and 2017 (C17), as well as unharvested plots as controls (CK). The results showed that strip clearcutting increased the understory vegetation richness and diversity, and a significant difference (A = 0.23, P = 0.001) existed in the composition of the vegetation between the three treatments. Furthermore, the decrease of soil total phosphorus and total potassium content resulted in the difference in undergrowth vegetation distribution and composition between the uncut plots and the cut plots. Our results suggest that strip clearcutting may not be harmful to biodiversity on a local scale in the Moso bamboo forest. Study Implications: This study demonstrates that strip clearcutting, which is an economically important harvesting method for bamboo, had significant effects on understory vegetation composition and diversity, and understory vegetation has not returned to preharvest levels after two years. The understory vegetation was affected by soil nutrient content and light conditions in the forest. We believe our research has made a significant contribution to the literature because bamboo is commercially important and its sustainable management is needed by many industries. This study highlights the impact of strip cutting on understory vegetation. The retention of understory vegetation characteristics is critical for the sustainable management of these forests, and this study not only demonstrates the dynamics of cut plots recovery but also increases our knowledge of this important species.

Plasticity as a Link Between Spatially Explicit, Distance-Independent, and Whole-Stand Forest Growth Models

Models at various levels of resolution are commonly used for both forest management and ecological research. They all have comparative advantages and disadvantages, making desirable a better understanding of the relationships between various approaches. Accounting for crown and root morphological plasticity in the limit where equilibrium among neighbors is reached (perfect plasticity) transforms spatial models into nonspatial, distance-independent versions. The links between spatial and nonspatial models obtained through a perfect plasticity assumption are more realistic than ignoring spatial structure by a mean field approximation. This article also reviews the connection between distance-independent models and size distributions and how distributions evolve over time and relate to whole-stand descriptions. In addition, some ways in which stand-level knowledge feeds back into detailed individual-tree formulations are demonstrated. This presentation is intended to be accessible to nonspecialists. Study Implications Introducing plasticity improves the representation of physio-ecological processes in spatial modelling. Plasticity explains in part the practical success of distance-independent models. The nature of size distributions and their relationship to individual-tree and whole-stand models are discussed. A size distribution is a one-variable distribution; joint distributions for two or more trees depend on the distances between them unless spatial structure is negligible. Limitations of current individual-tree models and questions for future research are discussed.