Small-diameter Trees Research Articles

Development of crop trees after different thinning methods in mixed Norway spruce (Picea abies L.) and Birch (Betula spp.) forests in Southern Sweden

In Northern Europe, novel thinning methods of small diameter trees are being tested to promote early competition release in young tree-dense forests at a low cost. These methods involve harvesting the whole above-ground tree biomass in 1 – 2 m wide strips between extraction racks (i.e. strip roads). Before recommending such methods to practical forestry, we need to know how the growth of remaining stand and individual trees perform at different stages of stand rotation to avoid compromising future forest production and the overall economy. Therefore, we analysed data from three Norway spruce dominated experimental sites in Southern Sweden with conventional selective biomass thinning (BT) versus geometrical BT in strips, where trees between extraction racks are cut in 1 – 2 m wide, ca. 10 m long strips (i.e. boom-corridor thinning) including unthinned reference treatment. To assess the thinning effect on the remaining stand, we analysed data from the remaining trees five to six years after thinning. We compared stand properties such as standing volume, diameter, height, basal area, volume increment, basal area increment and damages for different cohorts of the remaining trees. We found that BT in 1 – 2 m wide strips do not affect the growth and yield of the most important crop trees (i.e. the 500-largest crop trees and the next 400-largest crop trees) and to some extent protect the remaining stand from damages. Although not statistically significant, we observed that for the cohort of the 500-largest crop trees, the proportions of new damages were lower in unthinned treatment (4.8 %), and strict BT in 1 – 2 m wide strips (1.7 % and 5.8 % respectively) than in conventional BT (14.4 %) and semi-selective BT in 1 m wide strips (7.9 %). A similar pattern was seen for the next 400-largest crop trees. Thus, these short-term results suggests that BT in narrow strips of 1 – 2 m can be used in young tree-dense forests in Southern Sweden without compromising the development of the remaining crop trees. However, more long-term research on a broader geographical scale is required before we can fully recommend these novel-thinning methods to forest owners across the Northern Europe on a large scale.

Genetic variation of English yew (Taxus baccata L.) in the Bavarian Forest National Park, Germany

AbstractTaxus baccata L. is a highly valuable species with wide distribution but scattered and locally rare occurrence. Human intervention, including forest management practices and fragmentation, can significantly impact the species’ genetic diversity, structure, and dynamics. In this study, we investigated these factors within T. baccata populations in the Bavarian Forest National Park (NP) in Germany and their implications for conservation. We used 13 EST-SSRs to assess the genetic diversity and structure of the population. Our analysis revealed a scarcity of small-diameter trees, indicating limited natural regeneration over time. However, conservation efforts, like selectively removing competitor species and using protective fencing, have improved growth conditions and promoted seedling emergence. The NP’s natural zone has no active management, which is confined to the development and management zones. Genetic diversity assessments revealed high genetic diversity (He: 0.612 and 0.614 for seedlings and adults, respectively) compared to other studies in Taxus baccata, dispelling concerns of significant inbreeding and showcasing a stable genetic structure. However, significant spatial clustering of related individuals (family structures) in both cohorts and low effective population size in the progeny hints at restricted gene flow, necessitating conservation efforts prioritizing safeguarding and promoting natural regeneration in development and management zones. Limited natural regeneration and the recent decrease in effective population size in the NP populations indicate habitat fragmentation and human interventions. Effective population size estimates emphasize the need for diverse conservation strategies. Conservation efforts should prioritize protecting natural regeneration and enhancing gene flow by actively promoting European yew, e.g., by shelterwood cutting, to ensure the long-term viability of T. baccata in the region outside the NP.

Experimental infection of small-diameter trees with chaga (Inonotus obliquus) in a postagrogenous birch forest

In Plyussky district of the Pskov region, an experiment was carried out to infect birch trees with the Chaga pathogen Inonotus obliquus in an 18-year-old postagrogenic birch forest. After 10 years of the experiment, sterile bodies of Chaga were found on six out of ten trees, swelling of the bark was found in one tree, and one tree died from Phellinus nigricans. Infected trees continued to grow at a rate no different from the rest of the forest. Sterile growths were mainly located above the inoculation site. The study showed that the production of Chaga raw materials can be considered as an additional form of forest management in the Non-Black Earth Region of Russia.

Effects of topography and stand spatial structure on the diameter at breast height growth of major pioneer tree species of natural broad-leaved mixed forests in Zhejiang Province, China.

Based on the continuous inventory data of forest resources in Zhejiang Province in 2019 and 2021, we used statistical methods such as polynomial regression to analyze the impacts of topography and forest spatial structure on average annual diameter at breast height (DBH) growth of main pioneer tree species in natural broad-leaved mixed forests. The results showed that DBH of Schima superba, Quercus glauca, Quercus fabri, Lithocarpus glaber, Castanopsis eyrei, and Castanopsis sclerophylla were between 5-50.8, 5-41.5, 5-50.8, 5-43.9, 5-55.5, and 5-46.1 cm, respectively. We classified all the trees into three classes based on DBH: small (6-12 cm), medium (12-14 cm), and large (>26 cm). The average annual DBH growth of S. superba and Q. glauca was the highest on semi-shady slope and shady slope, with increases of 2.9%-15.7% and 1.1%-41.2%, respectively. The average annual DBH growth of large-diameter S. superba, L. glaber, C. eyrei and C. sclerophylla decreased with the increase of slope, with a maximum decrease of 27.0% for S. superba, with no significant difference among small- and medium-diameter trees as a whole. The slope position did not affect the annual DBH growth of small-diameter trees, while that of medium- and large-diameter S. superba, Q. glauca, and large-diameter Q. fabri, L. glaber decreased with the change of slope position from downhill, mesoslope, uphill to ridge, with a maximum decrease of 28.1% for L. glabe, and the major-diameter C. eyrei was on the contrary. Appropriate increase in the mingling was beneficial to the average annual DBH growth of medium- and large-diameter trees. Moderate mixing was suitable for S. superba, while low degree mixing and moderate mixing was suitable for Q. glauca, Q. fabri and L. glaber, and intensive mixing was suitable for C. eyrei and C. sclerophylla. No significant difference was observed for minor-diameter trees under the mingling. The neighborhood comparison only had a significant effect on the average annual DBH growth of large-diameter Q. glauca, Q. fabri, and L. glaber, which was significantly higher under subdominance-moderation than moderation-inferiority. The average annual DBH growth in the study area was mainly affected by aspect and mixing degree.

Constraints and opportunities in harvesting woody biomass: perspectives of foresters and loggers in the Northeastern United States

ABSTRACT Extensive forest resources make the Northeastern United States a promising source of woody biomass. Managing overstocked stands, common to the region, has been a major challenge due to a significant proportion of the harvest being low-value products. There are also various socio-economic and ecological factors that constrain the harvest decision. The objectives of the study were to compare and identify the key components, circumstances, and constraints related to the harvesting of small-diameter trees (SDT), regionally; to test if the responses varied between different job and experience categories; and to understand the perspectives of foresters and loggers to improve the current constraints. An online survey with 270 inputs from foresters and loggers in the Northeastern United States showed that, on average, 24% of the total harvest residue comprised small-diameter trees. The strongest agreement was on utilizing woody biomass for bioenergy and institutional heat energy. The primary reason for harvesting woody biomass was to satisfy the landowner’s objectives and for maintaining aesthetic value. The major constraints in woody biomass harvesting were the lack of markets and higher trucking distance. Respondent recommendations strongly emphasized the need for new and improved markets, infrastructure, and increased support from government.

Natural durability of 8 tropical species suitable for structural roundwood: laboratory screening tests for resistance to fungi and termites

Knowledge of the wood properties of tropical tree species is still relatively limited, so timber extraction focuses on a few abundant, large-diameter species. Very little is known about small-diameter trees, although they could be used directly as roundwood for construction. The aim of this study was to determine the natural durability of 8 candidate species for use as structural roundwood in French Guiana: Goupia glabra, Licania alba, Hymenopus heteromorphus, Lecythis persistens, Oxandra asbeckii, Pouteria bangii, Simarouba amara, Tachigali melinonii and Virola surinamensis. Samples of their wood were exposed to white rot (European and tropical), brown rot (European), and European subterranean termites (using non-choice and multi-choice tests) in laboratory conditions and subjected to screening tests adapted from European standards. Only two species were classified as durable against both fungi and termites: L. alba and P. bangii, which means they can be used without treatment as building material in tropical or temperate climates. The other species tested were classified (1) as durable but with notable differences observed in their resistance to fungi and termites respectively (G. glabra, L. persistens, O. asbeckii), (2) moderately durable (H. heteromorphus), (3) low durability to sensitive (T. melinonii, S. amara, V. surinamensis), meaning actual European standards would not let use these last species in outdoor structures without protection, despite their use by local population in traditional building. However, they could be used for building purposes with appropriate protection systems (including wood protection). The results we obtained for resistance to wood decay provide essential information to assess the potential of these eight tree species in French Guiana’s construction sector.

Carbon and biomass models for five Sierra Nevada mixed conifer species

Data from tree cores and disks were used to develop biomass and carbon mass taper models for five major Sierra Nevada conifer species. These taper models were used to predict masses of tree boles, tree bole portions, branch, and foliage using carbon fraction data for oven-dried and living tissues. Taper models developed using core data were well modeled to disk data with R2 values ranging from 0.98 to 0.99 by inclusion of a calibration parameter. The fit of the final models suggests our approach can be used to include large diameter trees that cannot be cut down in biomass data collection efforts that otherwise would only sample smaller diameter trees. Our results show that biomass-weighted living carbon estimates at the whole tree level ranged from 2.8% to 9% higher than estimation methods using the standard carbon fraction of 0.5 depending on the tree species. Our approach addresses the need to account for variation in carbon fraction and wood density throughout trees, as well as demonstrating a data collection and modeling approach to include large old growth trees that cannot be destructively sampled.

Opportunities and challenges of woody biomass harvesting practices in the Southeastern region of the United States

ABSTRACT The Southern US has the potential to make a significant contribution to the global bioenergy market by producing woody biomass feedstock. Despite extensive research on the technical and economic aspects of biomass production in the Southeastern region, most studies didn’t incorporate the social aspects of forest stakeholders. This study aimed to understand the perceptions of forest stakeholders toward biomass production, consumption, and overall biomass market conditions. We conducted online surveys of biomass producers and consumers using Qualtrics software and found that, on average, 30% of the total harvested volume was made up of small-diameter trees. The main reasons for harvesting biomass were improving the aesthetic value of the site, increasing total revenue, and diversifying the business. Trucking distance with an average haul distance of 84–140 km (one-way), limited local markets, equipment availability, machine and labor costs, and production costs were ranked as biomass producers’ five major challenges. If there were more profitable options with better logistics, shorter transportation distances, and lower production costs, most of the producers (strongly agree = 56%, agree = 34%) would be willing to harvest more biomass. As for consumers, 80% of pellet producers, 33% of heat combustion plants, and only 14% of power combustion plants intend to expand biomass consumption over the next five years. Moreover, stakeholders’ occupation type, tract size, length of ownership, years of consuming biomass, and consumption rate affect biomass production and consumption decisions.

Influences of fern and vine coverage on the above-ground biomass recovery in a Bornean logged-over degraded secondary forest

ABSTRACT Tropical secondary forests are widespread in the anthropogenically modified landscapes. Because tropical secondary forests were known to show a steady rate of above-ground biomass (AGB) recovery, they were expected to play a crucial role in carbon sequestration. However, in a preliminary survey of logged-over forests in Borneo, some patches covered with ferns and vines do not seem to recover steadily despite the fact that several decades have passed since the last logging. The presence and abundance of fern/vine thickets may affect the AGB recovery, but few studies have investigated the effects of the thickets. We established a total of seventeen 20-m radius circular plots in logged-over forests, Sabah, Malaysia, with a varying degree of fern/vine coverage, and tested the hypothesis that the greater fern/vine coverage would retard the AGB recovery. The net AGB accumulation rate from 2014 to 2019 was lower in the forests with a higher fern/vine coverage. Our lower bound of the accumulation rate was much lower than the previously reported rates elsewhere. The number of newly recruited and small-diameter trees was lower, and the mortality of remnant trees was higher with increasing fern/vine coverage. The growth rate of the extant pioneer trees, which are expected to significantly contribute to the initial build-up phase of the secondary succession, was inhibited when ferns and vines covered the canopy. Our study suggests that the secondary succession is arrested and the recoverability of forest stands is lower than formerly predicted when they are covered by thick ferns and vines.

Forest structure, tree species diversity and distribution status for wildlife habitat in ukpon river forest reserve, cross river state, Nigeria

For effective conservation management, it is crucial to comprehend the diversity, abundance, and distribution of the forest as wildlife habitat. The fundamental composition of the forest is significantly influenced by the ecological features of the sites, species diversity, and rate of tree species regeneration. This finding aimed to assess the diversity, abundance, and distribution of tree species as suitable habitat for wildlife species and for sustainable forest management, climate change mitigation, and environmental resilience. The study was conducted in dry season (between 5th September, 2021 and April, 2022). Purposive sampling techniques and systematic line transects were used for data collection and plot delineation. There were laid 8 transects, each 1000 meters long and 500 meters apart. Descriptive statistics such as mean, frequencies, and percentages were used to analyze the data. Correlation analyses and diversity indices were carried out using the R programming software. In the study area, 68 tree species from 34 families were found. Meliacea (6 trees per ha), Caesalpiniceae, and Moracea (5 trees per ha) were the three most common tree species in the study area. Melicia excelsa showed the highest relative frequency (2.256%) and (2.241%). The species Bialonella toxisperma had the highest relative dominance (4.970%). In Melicia excelsa, IVI recorded the highest value (4.970%). The tallest tree and Dbh (Diameter at Breast Height) measured 80.5 cm and 68.3m). The Margelef index was 36.10, the Shannon Wiener index was 5.058, and species richness was 68. However, the high proportion of smaller-diameter trees in the forest reserve implies that, it is strong and healthy. Since natural areas play a critical role in slowing down climate change, strict oversight of these areas should be strongly encouraged.

Above ground biomass after 39 years logging in Kintap Research Forest, South Kalimantan

Land degradation causes the fragmentation of forest areas. The fragmentation can be in the form of a decrease in species diversity and carbon storage in an area including logged-over areas. This study aims to obtain stand abundance, basal area, and potential of above ground biomass that can be used in estimating natural recovery in logged-over areas. Stand measurements were carried out in 3 different areas with the distance of the plot from the road as a differentiating factor. The measurement parameters include tree species, diameter, and tree height with the smallest diameter being 10 cm. Making plots at each location covering an area of 1 ha with an observation sub-plot measuring 20 m x 20 m (400 m2). Estimation of carbon storage used the allometric model compiled by Brown, Ketterings, and Basuki. The results showed that the biomass potential reached 190 tones/hectares – 290 tones/hectares. This potential is mostly contributed by trees with a diameter of more than 20 cm. Trees with a diameter of 20 cm accounted for more than 50% of the total biomass. This condition indicates that silvicultural technique in the form of maintaining the remaining stands after felling are very necessary for accelerating the growth of small-diameter trees so that natural succession can occur more quickly.

Mangrove tree growth is size-dependent across a large-scale salinity gradient

Salinity-influenced ecosystems are projected to face a tree to stand level growth reduction as a response to climate change. Although large and mature trees play a central role in defining carbon dynamics and site conditions, their eco-physiological and functional responses to increasing salinity remain poorly understood. Therefore, we test our hypotheses, i.e., large-diameter trees are predominantly contributing to above-ground biomass (AGB) stocks, whilst small-diameter trees are mainly contributing to AGB growth or gain (biomass changes over time) in higher salinity areas of the Sundarbans mangrove forest, Bangladesh. It can further be expressed by a growth dominance coefficient (GDC) that turns negative (a negative GDC indicates small trees proportionately contribute more to growth) in high-salinity areas while remaining positive in lower-salinity areas. We also hypothesized that species and structural diversity positively influence AGB stocks and gain. To test our hypotheses, we employed data from 60 permanent sample plots installed in the Sundarbans mangrove forest to estimate size-dependent functions by examining tree size, diversity, and growth dominance patterns to salinity gradients. Trees in higher salinity areas showed negative or reverse growth dominance patterns, indicating large trees contributed less to forest growth, which means smaller trees were disproportionately responsible for growth within the stand. Across the salinity zones, large-diameter (>20 cm in diameter at breast height, DBH) trees contributed primarily to AGB stocks, while small-diameter (<20 cm in DBH) trees contributed more to forest growth. We observed species diversity had no significant influence, whilst vertical diversity (height diversity) had a significant positive influence on AGB stocks and gain. Forest functioning (e.g., biomass accumulation rate) is more asymmetric (higher growth of small trees vs. low growth of large trees) in poor sites (i.e., high salinity), as poor site quality favors small trees to grow but not the large-diameter trees, which indicates large trees are more sensitive to high salinity as they lose growth. Our results indicate the size-dependent tree functions also depend on biotic and abiotic factors in mangroves. Increased structural diversity and removing mature trees to allow small trees to grow may benefit mangrove forest functioning (biomass stocks and growth), but species diversity may not.

Condition of pine and larch forests adjacent to the reservoir within the Sayano-Shushensky Nature Reserve

Forests cover 60% of the Sayano-Shushensky Nature Reserve, 48% of which are larch and pine stands. The purpose of the research was to assess condition of Larix sibirica Ledeb. and Pinus sylvestris L. forests adjacent to the reservoir within the reserve. We conducted forest pathological inspection (for each species on four research plots), an integral assessment of the stands condition, macroscopic diagnostics and disease manifestations indicators estimation and studied model trees affected by xylophagous insects. Studied stands ranged from sustainable to ones with disturbed sustainability and their health status ranged from healthy to varying degrees of weakening. One of the main factors weakening forest stands were ground fires, leading to increased mortality of small-diameter trees that are less resistant to heat stress (most typical of P. sylvestris). Medium and large diameter trees post-fire mortality in L. sibirica forest stands was due to the Zeiraphera griseana feeding, and in relatively flat coastal areas due to repeating flooding. The presence of groups of trees dying from the top down were observed in pine forests growing on thin soils most likely due to an imbalance between the amount of required and available soil moisture. Diseases were not common and did not have a significant impact on the forest stands. Potentially harmful are the following diseases: in larch forests - European larch canker (pathogen - Lachnellula willkommii), in pine forests - Scots pine blister rust (pathogen - Cronartium pini). Xylophagous insects (dominated by Ips acuminatus) had an increased abundance and fed on dying trees in pine forests weakened after fires.

Large-diameter trees and deadwood correspond with belowground ectomycorrhizal fungal richness

BackgroundLarge-diameter trees have an outsized influence on aboveground forest dynamics, composition, and structure. Although their influence on aboveground processes is well studied, their role in shaping belowground fungal communities is largely unknown. We sought to test if (i) fungal community spatial structure matched aboveground forest structure; (ii) fungal functional guilds exhibited differential associations to aboveground trees, snags, and deadwood; and (iii) that large-diameter trees and snags have a larger influence on fungal community richness than smaller-diameter trees. We used MiSeq sequencing of fungal communities collected from soils in a spatially intensive survey in a portion of Cedar Breaks National Monument, Utah, USA. We used random forest models to explore the spatial structure of fungal communities as they relate to explicitly mapped trees and deadwood distributed across 1.15 ha of a 15.32-ha mapped subalpine forest.ResultsWe found 6,177 fungal amplicon sequence variants across 117 sequenced samples. Tree diameter, deadwood presence, and tree species identity explained more than twice as much variation (38.7% vs. 10.4%) for ectomycorrhizal composition and diversity than for the total or saprotrophic fungal communities. Species identity and distance to the nearest large-diameter tree (≥ 40.2 cm) were better predictors of fungal richness than were the identity and distance to the nearest tree. Soil nutrients, topography, and tree species differentially influenced the composition and diversity of each fungal guild. Locally rare tree species had an outsized influence on fungal community richness.ConclusionsThese results highlight that fungal guilds are differentially associated with the location, size, and species of aboveground trees. Large-diameter trees are implicated as drivers of belowground fungal diversity, particularly for ectomycorrhizal fungi.

Private forest owner willingness to mobilise wood from dense, small-diameter tree stands

Forests are a source of renewable biomass, and their utilisation will play a vital role in the transition towards a climate-neutral economy. Small-diameter tree management could contribute to this transition via providing renewable biomass for sustainable uses and fostering tree growth towards long-lifecycle bioproducts. The utilisation of small-diameter trees in the EU is still low since new technologies and work models are required to make the operations economically profitable, environmentally sound, and socially attractive. The supply of biomass from small-diameter tree stands is dependent on forest owners with diverse perceptions on their forests and diverse ownership objectives. However, there is scarce research on forest owner perceptions on small-diameter tree management, which encompasses home consumption, self-active work, and commercial forestry services. A survey in four EU countries was designed to identify the main factors affecting the motivation of forest owners to mobilise biomass from small-diameter stands. Factor and clustering analyses were used to identify four forest owner segments: weakly-engaged traders, well-being seekers, self-active profit-seekers, and well-informed service users. The willingness to utilise biomass from small-diameter tree stands and participate in the market was shaped by forest owner knowledge of forestry, economic and socio-cultural motivations, and sensitivity to service offerings. Forest owner preferences for market participation are heterogenous, and thus different policy implementation approaches are needed and proposed.

Drivers of collapse of fire‐killed trees

AbstractLarge quantities of dead wood can be generated by disturbances such as wildfires. Dead trees created by disturbances play many critical ecological roles in forest ecosystems globally. The ability of deadwood to serve its ecological roles is contingent, in part, on the length of time trees remain standing following disturbance. Here, we briefly outline the results of a 10‐year study that aimed to quantify the rate of collapse of trees killed in a major wildfire in the wet ash forests of mainland south‐eastern Australia. We also quantified the factors associated with dead tree collapse. Our analyses revealed that 23% of 417 measured trees collapsed between 2011 and 2021. The most parsimonious model of the factors influencing tree collapse revealed a strong effect of diameter; smaller diameter trees were more likely to collapse over the 10 years of our study than larger diameter trees. In addition, trees in small and large patches were more likely to collapse than trees in contiguous forest (where there had been no logging in the surrounding area). If current rates of tree fall are maintained, then many of trees initially measured will have collapsed by 2030. Such losses of dead trees will have major negative effects on key values of ash‐type forests such as biodiversity conservation.

Stand-level structural characteristics dictate hurricane resistance and resilience more than silvicultural regime in longleaf pine woodlands

Hurricanes frequently impact coastal forests throughout the southeastern United States and are expected to increase in frequency and intensity in the future. Given this projection, interest has grown in adopting forest management practices that can reduce the risk of hurricane damage by increasing stand resistance and resilience. Empirical evidence suggests that uneven-aged stands are more resistant and resilient to hurricanes than even-aged stands, due to their heterogeneous stand structure and multiple age classes. Nevertheless, opportunities to compare the impact of hurricanes on stands managed under different silvicultural regimes at the same location are uncommon. Moreover, no research has detailed how different stocking regulation methods influence hurricane risk in uneven-aged stands. An opportunity to conduct a natural experiment presented itself in 2004 when Hurricane Ivan passed 24 km west of the Escambia Experimental Forest in southern Alabama, USA. At the time of the storm, the experimental forest contained long-term experiments examining the performance of longleaf pine (Pinus palustris) managed under different silvicultural systems. Here, we report on the resistance and resilience of three even-aged stands compared to six uneven-aged stands that were managed under BDq (two stands), Volume Control Guiding Diameter Limit (VC-GDL) (two stands), and Diameter Limit Cutting (DLC) (two stands) stocking control methods.Average stand resistance (proportion of basal area remaining in 2005) was not statistically different among even-aged (0.866)and uneven-aged stands (all variants pooled) (0.858) p > 0.05). Among uneven-aged variants, resistance was highest in the VC-GDL stands (0.876) and lowest in the DLC stands (0.840). Across all stands, resistance was positively related to stand density (p = 0.03) and negatively associated with increases in quadratic mean diameter (p = 0.03) and size class diversity (p = 0.01). Post-hurricane (2005) departure indices found left shifts (shift in density towards smaller size classes) in the diameter distribution of 33 % of even-aged stands and 83 % of pooled uneven-aged stands. Among uneven-aged variants, significant left shifts in diameter distribution were greatest in stands managed with VC-GDL and lowest with BDq. Average post-hurricane resilience (post hurricane basal area recovery) was statistically similar in the pooled uneven-aged stands (0.42) and even-aged stands (0.37). Yet, stands with greater tree size class diversity demonstrated increased resilience. Regardless of management regime, stands carrying a high density of smaller diameter trees are more resistant to hurricane damage than stands managed at a lower density with a higher proportion of larger diameter trees. Moreover, while not statistically significant, our findings suggest that uneven-aged stands possess a greater potential for rapid hurricane recovery than even-aged stands. Therefore, land managers seeking to foster hurricane resistance and resilience should consider modifying stand prescriptions to carry a higher proportion of stocking in smaller size classes.

Tree survival and resprouting after wildfire in tropical dry and subhumid ecosystems of Chiquitania, Bolivia

Lack of understanding the negative and positive effects of wildfires poses a challenge to the restoration and management of tropical ecosystems. Although fire can have negative impacts on tropical forests, it is known that many tropical savanna and woodland species are adapted to fire. The objective of this study was to determine the resilience of tree species to wildfire in a seasonally dry region of eastern lowland Bolivia. The study was carried out in four tropical dry Chiquitano ecosystems (Abayoy, Cerrado, Chiquitano dry forest, and sub-humid forest), in the department of Santa Cruz, 6–18 months after wildfires occurred in July - October 2019. At 45 sampling points, in both burned and unburned areas, we established 50-m x 5-m transects to determine tree species composition, number of individuals, resprout types, survival, diameter, and height of individuals that were ≥1 cm diameter at breast height (DBH). We calculated the percentages of surviving and dead stems by resprout categories and used logistic regression to determine the probability of survival and probability of resprouting as a function of pre-burn size. In the four ecosystems, 35–71% of the individuals sampled survived (crown and basal resprouting) after fire, while an additional 18–59% of individuals had only basal resprouting. Tree mortality (no reprouts) ranged from 5 to 11%. In burned areas, larger-diameter trees had a greater probability of survival. In contrast, the smaller-diameter trees had a higher probability of resprouting from the base. In conclusion, the Chiquitano tropical dry ecosystems have a high resilience to wildfire in terms of survival and resprouting. Resprouting strategy appears to be an important survival mechanism in trees, especially small trees, and must be considered in the passive restoration of burned forests.

Reduced forest vulnerability due to management on the Hualapai Nation

Tribal nations in the US have worked to uphold their long history of managing forests in ways that reduce fuels, support ecosystem functioning, and enhance Indigenous livelihoods. Forests on the Hualapai Nation at the western end of the Grand Canyon have been actively managed for decades using fire and other treatments. We collected data on tree size and age structure, forest understory characteristics, and surface fuels to explore how the legacy of forest management, historical surface fire, and recent prescribed fire, have influenced the contemporary structure of the ponderosa pine-Gambel oak forest on the Hualapai tribal lands (hereafter Hualapai forest). Current overstory tree density (range: 361.1 to 1664.0 trees ha−1) and basal area (16.0 to 29.8 m2 ha−1) place the Hualapai forest in an intermediate state among more open vs. denser southwestern forests, but additional characteristics set the Hualapai forest apart from others in the region. In particular, diameter distributions of live ponderosa pine in the Hualapai forest are dominated by mid-diameter trees (trees ∼18-33 cm dbh), while diameter distributions of live ponderosa pine on forest lands across Arizona indicate a higher number of small-diameter trees (trees <23 cm dbh) and a lower number of large-diameter trees. This finding of a relatively lower number of small-diameter trees, which serve as ladder fuels, in the Hualapai forest may indicate better protection against severe wildfire, although some individual sites might be at greater risk due to higher numbers of small live trees and snags, seedlings and saplings, along with higher levels of coarse woody debris. Beyond fire risk, the Hualapai forest is lacking in large live trees and snags that support cultural needs and sustain its ecological functioning. Current management approaches are helping support the recovery of large trees and snags. While the Hualapai forest is at risk due to its location at the lower elevational limit of ponderosa pine in the Southwest, the legacy of past management and prescribed fire has differentiated it from similar forests in the region. Continued management informed by Indigenous perspectives can best position the Hualapai forest to sustain its structure and function as climate warms as well as achieve socio-cultural and ecological outcomes most important to the people of the Hualapai Tribe.

Competition and Facilitation Co-Regulate Spatial Patterns and Coexistence in a Coniferous and Broad-Leaved Mixed Forest Community in Zhejiang, China

Plant interactions have long been the subject of intense research and debate in ecology. Competition and facilitation are known to be the basic drivers of community structure, species coexistence, and forest succession dynamics; however, there remains a lack of understanding of how spatial patterns affect these in the mixed forest community of coniferous and broad-leaved species. In the present study, we studied the roles of competition and facilitation in a mixed forest community in the Zhejiang Province, China. For this, we divided plants measured at a study site according to the size of the diameter at breast height (DBH) into three levels of saplings as follows: saplings (1 cm ≤ DBH &lt; 5 cm), juveniles (5 cm ≤ DBH &lt; 15 cm), and adults (DBH ≥ 15 cm). We used the spatial point pattern method to explore the raw number, spatial distribution, and both intra- and inter-specific correlations of coniferous and broad-leaved species at these different diameter levels. The corresponding findings were as follows. First, the DBH and structure of coniferous and broad-leaved species were similar, showing a distinct distribution in an inverted “J” shape as the number of individuals with a particular diameter declined as DBH increased. Second, when all individuals of a similar diameter range were pooled, coniferous species were clustered at all size scales; however, in this situation, broad-leaved species (evergreen and deciduous) showed a clumped distribution at small scales, and this decreased as spatial scale increased. Third, there were small, but significant positive correlations between large-diameter trees and small-diameter trees of coniferous species and between evergreen broad-leaved species at different diameter levels; however, as the scale increased, the correlation diminished. On any scale, individual deciduous broad-leaved species at different diameter ranges did not have any significant correlation. Fourth, coniferous species had a strong competitive effect on broad-leaved species, and there was a weak promoting effect between deciduous and evergreen broad-leaved species as well. In summary, different tree species occupy similar living spaces, and through competition and facilitation, regulate the spatial pattern and community stability of coniferous and broad-leaved species in mixed forest communities.