Current Forest Structure Research Articles

Fire and Forest Management in Montane Forests of the Northwestern States and California, USA

We reviewed forest management in the mountainous regions of several northwestern states and California in the United States and how it has impacted current issues facing these forests. We focused on the large-scale activities like fire suppression and logging which resulted in landscape level changes. We divided the region into two main forests types; wet, like the forests in the Pacific Northwest, and dry, like the forests in the Sierra Nevada and Cascade ranges. In the wet forests, the history of intensive logging shaped the current forest structure, while fire suppression played a more major role in the dry forests. Next, we looked at how historical management has influenced new forest management challenges, like catastrophic fires, decreased heterogeneity, and climate change. We then synthesized what current management actions are performed to address these issues, like thinning to reduce fuels or improve structural heterogeneity, and restoration after large-scale disturbances. Lastly, we touch on some major policies that have influenced changes in management. We note a trend towards ecosystem management that considers a forest’s historical disturbance regime. With expected climate induced changes in fire frequency, it is suggested that fuel treatments be implemented in dry forests to ensure an understory fire regime is restored in these forest systems. With respect to wet forests in this region, it is suggested that there is still a place for stand-replacing fire regimes. However, these forests will require structural changes incorporating heterogeneity to improve their resiliency and health.

Stand basal area and solar radiation amplify white spruce climate sensitivity in interior Alaska: Evidence from carbon isotopes and tree rings.

The negative growth response of North American boreal forest trees to warm summers is well documented and the constraint of competition on tree growth widely reported, but the potential interaction between climate and competition in the boreal forest is not well studied. Because competition may amplify or mute tree climate-growth responses, understanding the role current forest structure plays in tree growth responses to climate is critical in assessing and managing future forest productivity in a warming climate. Using white spruce tree ring and carbon isotope data from a long-term vegetation monitoring program in Denali National Park and Preserve, we investigated the hypotheses that (a) competition and site moisture characteristics mediate white spruce radial growth response to climate and (b) moisture limitation is the mechanism for reduced growth. We further examined the impact of large reproductive events (mast years) on white spruce radial growth and stomatal regulation. We found that competition and site moisture characteristics mediated white spruce climate-growth response. The negative radial growth response to warm and dry early- to mid-summer and dry late summer conditions intensified in high competition stands and in areas receiving high potential solar radiation. Discrimination against 13 C was reduced in warm, dry summers and further diminished on south-facing hillslopes and in high competition stands, but was unaffected by climate in open floodplain stands, supporting the hypothesis that competition for moisture limits growth. Finally, during mast years, we found a shift in current year's carbon resources from radial growth to reproduction, reduced 13 C discrimination, and increased intrinsic water-use efficiency. Our findings highlight the importance of temporally variable and confounded factors, such as forest structure and climate, on the observed climate-growth response of white spruce. Thus, white spruce growth trends and productivity in a warming climate will likely depend on landscape position and current forest structure.

Sharp Savanna-forest Transitions in the Midwest Followed Environmental Gradients but are Absent from the Modern Landscape

Historically, closed eastern forests transitioned into open savannas and prairies in the U.S. Midwest, but this transition is poorly understood. To investigate the eastern boundary of the prairie-forest ecotone, we conducted a case study of historic and modern vegetation patterns of the Yellow River watershed in northwest Indiana. Historic vegetation came from the Public Land Survey notes collected in the early 1800s, whereas modern vegetation came from the Forest Inventory Analysis and USGS National Land Cover Database. We mapped vegetation data using GIS to reconstruct the region's past and current forest composition and structure. We also mapped climate, topography, and soil composition across the watershed to investigate the relationship between historic vegetation and environmental gradients. We found a sharp transition in the presettlement forest structure and composition, with dense deciduous forests in the eastern portion of our study area and open oak savannas in the west. The savanna ecosystem dominated in sandy well-drained soils and was at a slightly lower elevation than the adjacent closed forest. Modest environmental changes accompanied major vegetation changes in the past, which might suggest fire and hydrological patterns helped maintain the sharp ecotone. By contrast the modern forest shows no difference in tree density and composition across the watershed, which is consistent with major land use and hydrology changes in the watershed since settlement. On the modern landscape, land that was historically closed forest now has higher agricultural productivity compared to land that was historically savanna, whereas the historic savanna currently supports more mesic forest. These results suggest the environmental gradient continues to subtly shape the landscape. Though land use change has largely removed the closed mixed hardwood forests and oak savannas from this area, a better understanding of the historic vegetation and the conditions that supported it can help inform land management and restoration, as well as reveal ecological processes that drive vegetation transitions.

Structural Attributes of Old-Growth and Partially Harvested Northern White-Cedar Stands in Northeastern North America

Forestry practitioners often need to identify old-growth stands because of their high conservation value. To identify the structural and compositional characteristics potentially unique to old-growth northern white-cedar (Thuja occidentalis L.) stands, we compared 16 old-growth stands and 17 partially harvested stands in Maine, USA and New Brunswick, Canada. Potential old-growth predictors included common structural metrics such as basal area (BA), quadratic mean diameter (QMD), large tree (≥40 cm diameter at breast height) density, and volumes of coarse woody debris (CWD), along with six structural indices. Using generalized linear mixed-models, we identified two significant structural predictors that differentiate old-growth from partially harvested stands when used in combination: Volume of advanced-decay CWD and live tree QMD. None of the structural indices were useful in distinguishing between old-growth and partially harvested stands, nor did the two types differ with respect to tree species composition. Our results demonstrate that two metrics easily derived from standard inventory data—decayed CWD volume and QMD—effectively characterize the old-growth white-cedar stands sampled in this study. Taken together, these results can improve management decision making for white-cedar, particularly in the context of certification, while also shedding light on the effects of past partial harvesting on current forest structure.

Encroachment Dynamics of Juniperus virginiana L. and Mesic Hardwood Species into Cross Timbers Forests of North-Central Oklahoma, USA

Cross Timbers forests, typically dominated by Quercus stellata Wangenh. and Q. marilandica Muenchh., are the transition zone between eastern deciduous forest and prairie in the southern Great Plains. Fire exclusion beginning in the mid-1900s has led to increasing stand density and encroachment of fire-intolerant Juniperus virginiana L. and mesic hardwood. We measured current forest structure and tree ages of 25 stands (130 plots) in north-central Oklahoma to characterize the extent and dynamics of encroachment. The respective basal area and stand density of the overstory (diameter at breast height; dbh > 10 cm) were 19.0 m2 ha−1 and 407 trees ha−1 with Q. stellata comprising 43% of basal area and 42% of stand density. Quercus marilandica represented only 3% of basal area and 4% of overstory density. Juniperus virginiana represented 7% of basal area and 14% of stand density while mesic hardwoods, e.g., Celtis spp., Ulmus spp., Carya spp., 33% of basal area and stand density. The sapling layer was dominated by mesic hardwoods (68%) and J. virginiana (25%) while the seedling layer was dominated by mesic hardwoods (74%). The majority of Quercus recruited into the overstory between 1910–1970, while recruitment of J. virginiana and mesic hardwoods began more recently (post 1950s). Growth rate, based on the relationship between age and dbh, was faster for mesic hardwoods than for J. virginiana and Q. stellata. These results indicate that removal of recurrent surface fire as a disturbance agent has significantly altered forest composition in the Cross Timbers region by allowing encroachment of J. virginiana and fire-intolerant, mesic hardwoods. This increases wildfire risk because J. virginiana is very flammable and will alter how these forests respond to future drought and other disturbance events.

More ways than one: Mixed-severity disturbance regimes foster structural complexity via multiple developmental pathways

Abstract Mixed-severity disturbance regimes are prevalent in temperate forests worldwide, but key uncertainties remain regarding the variability of disturbance-mediated structural development pathways. This study investigates the influence of disturbance history on current structure in primary, unmanaged Norway spruce (Picea abies) forests throughout the Carpathian Mountains of central and eastern Europe, where windstorms and native bark beetle outbreaks are the dominant natural disturbances. We inventoried forest structure on 453 plots (0.1 ha) spanning a large geographical gradient (>1,000 km), coring 15–25 canopy trees per plot for disturbance history reconstruction (tree core total n = 11,309). Our specific objectives were to: (1) classify sub-hectare-scale disturbance history based on disturbance timing and severity; (2) classify current forest structure based on tree size distributions (live, dead, standing, downed); (3) characterize structural development pathways as revealed by the association between disturbance history and current forest structural complexity. We used hierarchical cluster analysis for the first two objectives and indicator analysis for the third. The disturbance-based cluster analysis yielded six groups associated with three levels of disturbance severity (low, moderate, and high canopy loss) and two levels of timing (old, recent) over the past 200 years. The structure-based cluster analysis yielded three groups along a gradient of increasing structural complexity. A large majority of plots exhibited relatively high (53%) or very high (26%) structural complexity, indicated by abundant large live trees, standing and downed dead trees, and spruce regeneration. Consistent with conventional models of structural development, some disturbance history groups were associated with specific structural complexity groups, particularly low-severity/recent (very high complexity) and high-severity/recent (moderate complexity) disturbances. In other cases, however, the distribution of plots among disturbance history and structural complexity groups indicated either divergent or convergent pathways. For example, multiple disturbance history groups were significantly associated with the high complexity group, demonstrating structural convergence. These results illustrate that complex forest structure – including features nominally associated with old-growth – can be associated as much with disturbance severity as it is with conventional notions of forest age. Because wind and bark beetles are natural disturbance processes that can induce relatively high levels of tree mortality while simultaneously contributing to structural complexity and heterogeneity, we suggest that forest management plans allow for the stochastic occurrence of disturbance and variable post-disturbance development trajectories. Such applications are especially appropriate in conservation areas where biodiversity and forest resilience are management objectives, particularly given projections of increasing disturbance activity under global change.

Land-use history as a major driver for long-term forest dynamics in the Sierra de Guadarrama National Park (central Spain) during the last millennia: implications for forest conservation and management

In the Mediterranean Basin, long-lasting human activities have largely resulted in forest degradation or destruction. Consequently, conservation efforts aimed at preserving and restoring Mediterranean forests often lack well-defined targets when using current forest composition and structure as a reference. In the Iberian mountains, the still widespread Pinus sylvestris and Quercus pyrenaica woodlands have been heavily impacted by land-use. To assess future developments and as a baseline for planning, forest managers are interested in understanding the origins of present ecosystems to disclose effects on forest composition that may influence future vegetation trajectories. Quantification of land-use change is particularly interesting to understand vegetation responses. Here we use three well-dated multi-proxy palaeoecological sequences from the Guadarrama Mountains (central Spain) to quantitatively reconstruct changes occurred in P. sylvestris forests and the P. sylvestris-Q. pyrenaica ecotone at multi-decadal to millennial timescales, and assess the driving factors. Our results show millennial stability of P. sylvestris forests under varying fire and climate conditions, with few transient declines caused by the combined effects of fire and grazing. The high value of pine timber in the past would account for long-lasting pine forest preservation and partly for the degradation of native riparian vegetation (mostly composed of Betula and Corylus). Pine forests further spread after planned forest management started at 1890CE. In contrast, intensive coppicing and grazing caused Q. pyrenaica decline some centuries ago (ca. 1500–1650CE), with unprecedented grazing during the last decades seriously compromising today's oak regeneration. Thus, land-use history played a major role in determining vegetation changes. Finally, we must highlight that the involvement of forest managers in this work has guaranteed a practical use of palaeoecological data in conservation and management practice.

Historical and current forest conditions in the range of the Northern Spotted Owl in south central Oregon, USA

Restoration to increase resilience to current and projected drought and fire in historically open-canopy forests in fire-prone environments may be constrained by concern for species that favor dense forest conditions. To assist the recovery of a threatened species, the Northern Spotted Owl (NSO), in dry forest environments, the US Fish & Wildlife Service (USFWS) recommends embedding NSO conservation and recovery in restoration efforts that enable ecosystem recovery from past management actions and increase resilience to changing climate. In this study, we assessed changes between historical and current (1) forest structure and composition and (2) extent of NSO nesting and roosting (NR) or foraging (F) forest cover on 39,000ha at the eastern edge of the current designation of the range of the NSO. Historical records depict a predominantly open-canopy landscape dominated by large ponderosa pine. Current conditions include more than a 600% increase in trees 15–53cmdbh, substantial decline in trees ⩾81cmdbh, loss of the widespread distribution of trees ⩾53cmdbh, and loss of the dominance of ponderosa pine on mixed conifer sites. NSO habitat assessment involves a suite of attributes including: landscape context; species composition; canopy cover; basal area; average tree diameter; diameter diversity; and abundance of large trees, snags, canopy layers, coarse woody debris, and mistletoe. We tested for the presence of forest that met USFWS threshold values for two of these variables, canopy cover and basal area. Historically none of the area met the 60% canopy cover threshold for NR or F forest cover and almost none meets it currently. However, several NSO nesting pairs and individual birds have been observed in the study area over the last 20years, and studies in other frequent-fire forests show that canopy cover as low as 50% may be functional for NSO. To assess the implications of lower threshold values, we tested for NR or F forest cover presence at half the recommended thresholds, considerably below published estimates. Only five percent of the area exceeded 30% canopy cover historically; much of the current forest exceeds it today. Increase in canopy cover comes at the expense of increasing vulnerability to fire and drought and loss of historical functions and processes. Conflicting objectives of forest restoration and maintenance of spotted owl habitat on this site – isolated habitat in the dry margin of the range of the NSO – raises questions about how to achieve forest restoration in altered landscapes where existing, novel conditions favor at-risk species.

Individual-tree- and stand-based development following natural disturbance in a heterogeneously structured forest: A LiDAR-based approach

Large-scale severe natural disturbance events drive spatial and temporal patterns of forests by altering forest structure, composition, and functions. In the Bavarian Forest National Park in Germany, windthrow events led to large disturbances caused by the European bark beetle (Ips typographus L.). Until recently, it was assumed that at the initial stage of regeneration, trees tend to form a homogeneous stand structure, whereas structural heterogeneity is an attribute of later developmental stages. Yet recent studies provide evidence that under certain conditions structural heterogeneity can arise much earlier in stand development. Here we combined LiDAR data and forest growth modeling based on individual trees to develop a workflow for studying forest development in post-disturbed areas in the upper montane regions of the national park. The current forest structure was derived from LiDAR data of individually detected trees and a set of forest structural attributes were derived. The results served as input to simulate tree development spatio-temporally for a period of 80years. Several spatial statistics, including landscape and spatial point pattern metrics, were calculated to assess the structural heterogeneity. The results showed that naturally regenerating forests on post-disturbed sites reveal structural heterogeneity already at the early-seral stage. Moreover, a significant portion of the eventual old-growth structural heterogeneity might already be determined in the early successional stages. Our workflow highlights the use of multi-sensor aerial remote sensing to provide detailed structural information useful for the investigation of early-phase forest dynamics.

Changes of forest cover and disturbance regimes in the mountain forests of the Alps

Natural disturbances, such as avalanches, snow breakage, insect outbreaks, windthrow or fires shape mountain forests globally. However, in many regions over the past centuries human activities have strongly influenced forest dynamics, especially following natural disturbances, thus limiting our understanding of natural ecological processes, particularly in densely-settled regions. In this contribution we briefly review the current understanding of changes in forest cover, forest structure, and disturbance regimes in the mountain forests across the European Alps over the past millennia. We also quantify changes in forest cover across the entire Alps based on inventory data over the past century. Finally, using the Swiss Alps as an example, we analyze in-depth changes in forest cover and forest structure and their effect on patterns of fire and wind disturbances, based on digital historic maps from 1880, modern forest cover maps, inventory data on current forest structure, topographical data, and spatially explicit data on disturbances. This multifaceted approach presents a long-term and detailed picture of the dynamics of mountain forest ecosystems in the Alps. During pre-industrial times, natural disturbances were reduced by fire suppression and land-use, which included extraction of large amounts of biomass that decreased total forest cover. More recently, forest cover has increased again across the entire Alps (on average +4% per decade over the past 25–115years). Live tree volume (+10% per decade) and dead tree volume (mean +59% per decade) have increased over the last 15–40yearsin all regions for which data were available. In the Swiss Alps secondary forests that established after 1880 constitute approximately 43% of the forest cover. Compared to forests established previously, post-1880 forests are situated primarily on steep slopes (>30°), have lower biomass, a more aggregated forest structure (primarily stem-exclusion stage), and have been more strongly affected by fires, but less affected by wind disturbance in the 20th century. More broadly, an increase in growing stock and expanding forest areas since the mid-19th century have - along with climatic changes - contributed to an increasing frequency and size of disturbances in the Alps. Although many areas remain intensively managed, the extent, structure, and dynamics of the forests of the Alps reflect natural drivers more strongly today than at any time in the past millennium.

The historical disturbance regime of mountain Norway spruce forests in the Western Carpathians and its influence on current forest structure and composition

In order to gauge ongoing and future changes to disturbance regimes, it is necessary to establish a solid baseline of historic disturbance patterns against which to evaluate these changes. Further, understanding how forest structure and composition respond to variation in past disturbances may provide insight into future resilience to climate-driven alterations of disturbance regimes.We established 184 plots (mostly 1000m2) in 14 primary mountain Norway spruce forests in the Western Carpathians. On each plot we surveyed live and dead trees and regeneration, and cored around 25 canopy trees. Disturbance history was reconstructed by examining individual tree growth trends. The study plots were further aggregated into five groups based on disturbance history (severity and timing) to evaluate and explain its influence on forest structure.These ecosystems are characterized by a mixed severity disturbance regime with high spatiotemporal variability in severity and frequency. However, periods of synchrony in disturbance activity were also found. Specifically, a peak of canopy disturbance was found for the mid-19th century across the region (about 60% of trees established), with the most important periods of disturbance in the 1820s and from the 1840s to the 1870s. Current stand size and age structure were strongly influenced by past disturbance activity. In contrast, past disturbances did not have a significant effect on current tree density, the amount of coarse woody debris, and regeneration. High mean densities of regeneration with height >50cm (about 1400 individuals per ha) were observed.Extensive high severity disturbances have recently affected Central European forests, spurring a discussion about the causes and consequences. We found some evidence that forests in the Western Carpathians were predisposed to recent severe disturbance events as a result of synchronized past disturbance activity, which partly homogenized size and age structure and made recent stands more vulnerable to bark beetle outbreak. Our data suggest that these events are still part of the range of natural variability. The finding that regeneration density and volume of coarse woody debris were not influenced by past disturbance illustrates that vastly different past disturbance histories are not likely to change the future trajectories of these forests. These ecosystems currently have high ecological resilience to disturbance. In conclusion, we suggest that management should recognize disturbances as a natural part of ecosystem dynamics in the mountain forests of Central Europe, account for their stochastic occurrence in management planning, and mimic their patterns to foster biodiversity in forest landscapes.

Assessing post-storm forest dynamics in the pyrenees using high-resolution LIDAR data and aerial photographs

We evaluated how historical storm events have shaped the current forest landscape in three Pyrenean subalpine forests (NE Spain). For this purpose we related forest damage estimations obtained from multi-temporal aerial photographic comparisons to the current forest typology generated from airborne LiDAR data, and we examined the role of past natural disturbance on the current spatial distribution of forest structural types. We found six forest structural types in the landscape: early regeneration (T1 and T2), young even-aged stands (T3), uneven-aged stands (T4) and adult stands (T5 and T6). All of the types were related to the timing and severity of past storms, with early-regeneration structures being found in areas markedly affected in recent times, and adult stands predominating in those areas that had suffered lowest damage levels within the study period. In general, landscapes where high or medium levels of damage were recurrent also presented higher levels of spatial heterogeneity, whereas the opposite pattern was found in the less markedly affected landscape, characterized by the presence of large regular patches. Our results show the critical role that storm regimes in terms of timing and severity of past storms can play in shaping current forest structure and future dynamics in subalpine forests. The knowledge gained could be used to help define alternative forest management strategies oriented toward the enhancement of landscape heterogeneity as a measure to face future environmental uncertainty.

Estimation of Airborne Lidar-Derived Tropical Forest Canopy Height Using Landsat Time Series in Cambodia

In this study, we test and demonstrate the utility of disturbance and recovery information derived from annual Landsat time series to predict current forest vertical structure (as compared to the more common approaches, that consider a sample of airborne Lidar and single-date Landsat derived variables). Mean Canopy Height (MCH) was estimated separately using single date, time series, and the combination of single date and time series variables in multiple regression and random forest (RF) models. The combination of single date and time series variables, which integrate disturbance history over the entire time series, overall provided better MCH prediction than using either of the two sets of variables separately. In general, the RF models resulted in improved performance in all estimates over those using multiple regression. The lowest validation error was obtained using Landsat time series variables in a RF model (R2 = 0.75 and RMSE = 2.81 m). Combining single date and time series data was more effective when the RF model was used (opposed to multiple regression). The RMSE for RF mean canopy height prediction was reduced by 13.5% when combining the two sets of variables as compared to the 3.6% RMSE decline presented by multiple regression. This study demonstrates the value of airborne Lidar and long term Landsat observations to generate estimates of forest canopy height using the random forest algorithm.

Land use legacy effects on structure and composition of subtropical dry forests in St. Croix, U.S. Virgin Islands

Tropical dry forests are subject to intense human pressure and land change, including conversion to agricultural crops, pasture or agroforestry, and urban encroachment. Decades, and even centuries, of conversion, expansion, regrowth, and changing land-use practices can result in a mosaic of secondary growth patches with different land-use histories. Whereas post-agricultural landscapes may appear as contiguous areas of forest regeneration, the successional trajectory of forest patches from historic land cover to their current state may differ substantially, with consequences for species composition and ecosystem structure and function. We examined the effect of different land-use histories on current forest structure, biomass, and composition in subtropical dry forests in St. Croix, U.S. Virgin Islands. We sampled three types of secondary forests that followed different regeneration pathways after centuries of sugarcane agriculture: 40-year old secondary forests that naturally regenerated after sugarcane abandonment, 40-year old secondary forests that were reforested with timber plantations before management ceased and they were overtaken by natural succession, and 10-year old secondary forests that were intensive pasture prior to recent forest regeneration. Secondary forests that naturally regenerated after sugarcane had similar structural characteristics, in terms of basal area, stem density, aboveground biomass, and species diversity compared to secondary forests of the same age that were former plantations. Species composition, however, remained distinct. Compositional differences between the two types of 40-year old secondary forests could be partially attributed to plantation species, specifically Swietenia mahagoni, whereas naturally regenerated forests were dominated by common secondary forest species, such as Melicoccus bijugatus and Cordia alba. The effects of hurricane damage helped to explain structural similarity and compositional dissimilarity between naturally regenerated secondary forests and former plantations. Forest age had a significant effect on forest structure and composition. Differences between 10-year old and both types of 40-year old secondary forests were driven by a dominance of the nitrogen-fixing species Leucaena leucocephala, which rapidly established in 10-year old secondary forests and resulted in greater stem density and lower basal area, biomass, and species richness. Our results show that land-use history plays an important role in shaping species composition, especially in post-agricultural tropical dry forests. Although forests with differing land-use histories may structurally resemble one another within decades of abandonment, species composition may remain distinct for much longer. Understanding the legacy of human land use is important for dry forests that have a long history of disturbance and for predicting their response to future environmental change.

A new approach to evaluate forest structure restoration needs across Oregon and Washington, USA

Widespread habitat degradation and uncharacteristic fire, insect, and disease outbreaks in forests across the western United States have led to highly publicized calls to increase the pace and scale of forest restoration. Despite these calls, we frequently lack a comprehensive understanding of forest restoration needs. In this study we demonstrate a new approach for evaluating where, how much, and what types of restoration are needed to move present day landscape scale forest structure towards a Natural Range of Variability (NRV) across eastern Washington, eastern Oregon, and southwestern Oregon. Our approach builds on the conceptual framework of the LANDFIRE and Fire Regime Condition Class programs. Washington–Oregon specific datasets are used to assess the need for changes to current forest structure resulting from disturbance and/or succession at watershed and regional scales.Across our analysis region we found that changes in current structure would be needed on an estimated 4.7million+ ha (40% of all coniferous forests) in order to restore forest structure approximating NRV at the landscape scale. Both the overall level and the type of restoration need varied greatly between forested biophysical settings. Regional restoration needs were dominated by the estimated 3.8+ million ha in need of thinning and/or low severity fire in forests that were historically maintained by frequent low or mixed severity fire (historical Fire Regime Group I and III biophysical settings). However, disturbance alone cannot restore NRV forest structure. We found that time to transition into later development structural classes through successional processes was required on approximately 3.2million ha (over 25% of all coniferous forests). On an estimated 2.3million ha we identified that disturbance followed by succession was required to restore NRV forest structure.The results of this study are intended to facilitate the ability of local land managers to incorporate regional scale, multi-ownership context into local forest management and restoration. Meeting the region-wide restoration needs identified in this study will require a substantial increase in the pace and scale of restoration treatments and coordination amongst governments, agencies, and landowners.

Past human population history affects current forest landscape structure of Vodlozero National Park, Northwest Russia

The information about location and size of past human settlements can give new insights into the analysis of landscape structures. Vodlozero National Park (NP) is one the largest strictly protected areas in Northwestern Europe. We mapped the location of historic villages, which were abandoned in 1958, and studied the effect of past human activity in the forest landscape in two different scales using forest survey data. We assessed the possible change in age, volume and tree species composition from the edge of open fields up to the distance of 5 km from villages. We made a larger landscape analysis using a grid of forest stands covering the whole northern part of the NP. The past human activity was clearly visible in the present forest landscape. Distance from villages affected age, volume and tree species composition of the forest stands. This effect was the strongest within the first two kilometers from the villages. At the level of whole northern NP, the proportion of spruce markedly increased after approximately 15 km from the nearest old village. The changes in the forests surrounding the villages were most likely the result of the intensive use of wood for different commodities needed in households and farming, in addition to short rotation slash and burn agriculture. If the occurrence of forest fires was more frequent closer to villages than in more remote areas, it can well explain the observed pattern in the abundance of spruce in the larger landscape that is less tolerant to fire than pine.

Disturbance legacies and climate jointly drive tree growth and mortality in an intensively studied boreal forest

Most North American forests are at some stage of post-disturbance regrowth, subject to a changing climate, and exhibit growth and mortality patterns that may not be closely coupled to annual environmental conditions. Distinguishing the possibly interacting effects of these processes is necessary to put short-term studies in a longer term context, and particularly important for the carbon-dense, fire-prone boreal forest. The goals of this study were to combine dendrochronological sampling, inventory records, and machine-learning algorithms to understand how tree growth and death have changed at one highly studied site (Northern Old Black Spruce, NOBS) in the central Canadian boreal forest. Over the 1999-2012 inventory period, mean tree diameter increased even as stand density and basal area declined significantly. Tree mortality averaged 1.4 ± 0.6% yr-(1), with most mortality occurring in medium-sized trees; new recruitment was minimal. There have been at least two, and probably three, significant influxes of new trees since stand initiation, but none in recent decades. A combined tree ring chronology constructed from sampling in 2001, 2004, and 2012 showed several periods of extreme growth depression, with increased mortality lagging depressed growth by ~5 years. Higher minimum and maximum air temperatures exerted a negative influence on tree growth, while precipitation and climate moisture index had a positive effect; both current- and previous-year data exerted significant effects. Models based on these variables explained 23-44% of the ring-width variability. We suggest that past climate extremes led to significant mortality still visible in the current forest structure, with decadal dynamics superimposed on slower patterns of fire and succession. These results have significant implications for our understanding of previous work at NOBS, the carbon sequestration capability of old-growth stands in a disturbance-prone landscape, and the sustainable management of regional forests in a changing climate.

Potential increases in natural disturbance rates could offset forest management impacts on ecosystem carbon stocks

Forested ecosystems contain the majority of the world’s terrestrial carbon, and forest management has implications for regional and global carbon cycling. Carbon stored in forests changes with stand age and is affected by natural disturbance and timber harvesting. We examined how harvesting and disturbance interact to influence forest carbon stocks over the Superior National Forest, in northern Minnesota. Forest inventory data from the USDA Forest Service, Forest Inventory and Analysis program were used to characterize current forest age structure and quantify the relationship between age and carbon stocks for eight forest types. Using these findings, we simulated the impact of alternative management scenarios and natural disturbance rates on forest-wide terrestrial carbon stocks over a 100-year horizon. Under low natural mortality, forest-wide total ecosystem carbon stocks increased when 0% or 40% of planned harvests were implemented; however, the majority of forest-wide carbon stocks decreased with greater harvest levels and elevated disturbance rates. Our results suggest that natural disturbance has the potential to exert stronger influence on forest carbon stocks than timber harvesting activities and that maintaining carbon stocks over the long-term may prove difficult if disturbance frequency increases in response to climate change.

Structure and regeneration capacity of a urban forest fragment

Understanding the plant communities affected by human activities related to urbanization is an important tool to conserve these. In this way, this study on an urban forest fragment aimed to evaluate, through a phytosociological study and investigation of the germination of the seed bank, the current forest structure, the successional strata, and the regenerative capacity of the remnant. Three different stages comprised this research, the first with a floristic survey of the entire forest remnant, then the phytosociological study of the canopy (PAP above 10 cm) and regeneration strata (PAP 5-10 cm), and at last, the study on the seed bank. The phytosociological survey of the canopy stratum presented 1,368 individuals, with 41 species distributed into 24 families. The stratum of natural regeneration had 665 individuals, being 38 species distributed into 24 familie s. The seed bank was made up by only 8 native species, and 3 exotic species. The floristic diversity of the seed bank in all samples was low due to few species provide seeds to the soil. In addition, the strata and the seed bank had a low similarity, confirming thus the fragility and the need for preservationist attitudes.

Dendroecological reconstruction of the disturbance dynamics and human legacy in an old-growth hardwood forest in Korea

The rapidly maturing forests of Korea are now in need of new management objectives to meet the increasing national demands for various ecosystem services. To properly tackle these new challenges, it is critical that we understand the historical disturbance regime that shaped the current forest structure and composition. In this study, we investigated the disturbance history of an old-growth hardwood forest on Jumbong Mountain, Korea, a designated UNESCO biosphere reserve. We used dendroecological analysis to reconstruct disturbance events of various intensities, collected historical records and interviewed long-time residents to evaluate influences from historical human activities. The results suggest that a shift in the disturbance regime occurred during the early 1900s. Prior to the 1900s, most disturbances (67%) were minor to moderate in intensity, which enabled the occasional establishment and growth release of the shade-tolerant Acer pseudo-sieboldianum and Carpinus cordata. Starting from the 1910s, widespread and intensive disturbance events dramatically increased, and continued until the 1960s, represented by strong pulse of establishment (e.g., 60% of all establishments between the 1930s and 1950s) across all major species regardless of their shade tolerance. Increased disturbances during this period coincided with similar increase in slash-and-burn farming activities, triggered by the collapse of the peasant class during the Japanese colonial era. Since the 1970s, disturbance was practically non-existent because of the successful slash-and-burn farming regulation and fire suppression policy. Results suggest that the current composition and structure of the study stand and other mature natural hardwood forests in Korea, especially those characterized by the dominance of Quercus mongolica, strongly reflect the history of both natural disturbance regimes and human legacy, and will likely continue to last into the future.