Complex Forest Research Articles

Stand structural complexity of mixed old-growth and adjacent selection forests in the Dinaric Mountains of Bosnia and Herzegovina

Research results on the structure of European OGF are often contradictory; while some researchers stress equilibrium structures, others suggest that this rarely happens due to biomass accumulation. If the former were the case, then there would be a fairly strong argument that OGF should serve as natural references for selection management. At the same time, mountain mixed selection forests are in many regions considered to be the most “natural” type of MF, and thus to a large extent similar to corresponding OGF. However, because there are few old-growth forests (OGF) left in Europe, comparisons between OGF and selection-managed forests (MF) are rare. Since nature-based silviculture should follow natural processes and not exclude any species from its natural range, in this study we compared two mixed OGF and neighboring MF (Piceo-Abieti-Fagetum illyricum) in the Dinaric Mountains of Bosnia and Herzegovina. The MF were managed by the single-tree selection system for almost a century. The results indicated that this management approach yielded a statistically significant difference in tree species composition and presence of large-diameter trees. The cumulative diameter distributions, however, were similar in OGF and MF as both exhibited the shapes that are considered to provide demographic equilibrium. On the species level, though, this was the case only for beech. Species occurrence matrices indicated significant dominance of young European beech (Fagus sylvatica L.) trees over silver fir (Abies alba Mill.) and Norway spruce (Picea abies L. Karst) in OGF. Nevertheless, based on the results from MF, the study highlights the crucial role of silvicultural measures that may potentially provide targeted long-term coexistence of the studied broadleaved and coniferous tree species.

Analysis of forest structural complexity using airborne LiDAR data and aerial photography in a mixed conifer–broadleaf forest in northern Japan

Determining forest structural complexity, i.e., a measure of the number of different attributes of a forest and the relative abundance of each attribute, is important for forest management and conservation. In this study, we examined the structural complexity of mixed conifer–broadleaf forests by integrating multiple forest structural attributes derived from airborne LiDAR data and aerial photography. We sampled 76 plots from an unmanaged mixed conifer–broadleaf forest reserve in northern Japan. Plot-level metrics were computed for all plots using both field and remote sensing data to assess their ability to capture the vertical and horizontal variations of forest structure. A multivariate set of forest structural attributes that included three LiDAR metrics (95th percentile canopy height, canopy density and surface area ratio) and one image metric (proportion of broadleaf cover), was used to classify forest structure into structural complexity classes. Our results revealed significant correlation between field and remote sensing metrics, indicating that these two sets of measurements captured similar patterns of structure in mixed conifer–broadleaf forests. Further, cluster analysis identified six forest structural complexity classes including two low-complexity classes and four high-complexity classes that were distributed in different elevation ranges. In this study, we could reliably analyze the structural complexity of mixed conifer–broadleaf forests using a simple and easy to calculate set of forest structural attributes derived from airborne LiDAR data and high-resolution aerial photography. This study provides a good example of the use of airborne LiDAR data sets for wider purposes in forest ecology as well as in forest management.

Disturbance-mediated heterogeneity drives pollinator diversity in boreal managed forest ecosystems.

Intensive forest management, together with fire suppression, have decreased structural complexity and altered dynamics of boreal forests profoundly. Such management threatens forest biodiversity and can reduce the provision of ecosystem services. Although the importance of ecosystem services is widely acknowledged, conservation strategies are hindered by poor knowledge about diversity patterns of service provider species as well as on mechanisms affecting these assemblages at different spatial and temporal scales. In this study, we assessed the effect of disturbance management on forest pollinator communities. To do so, we used a large-scale ecological experiment conducted in the year 2000, where forest complexity was manipulated with different harvest regimes and prescribed fire. Results were consistent with a positive response of pollinators to increasing habitat heterogeneity driven by past disturbances. Harvested sites harbored a diverse pollinator community, and showed higher spatial and temporal turnover in species richness. Conversely, old-growth forest communities were a nested subset of harvested sites and contained half of their total diversity. Variation in community composition (β diversity) was primarily affected by species temporal turnover. Throughout the season, β diversity was controlled by fire and harvesting legacies, which provide environmental heterogeneity in the form of flowering and nesting resources over space and time. Conservation strategies may undervalue ecosystem services in dynamic, naturally disturbance-driven, landscapes when relying solely on undisturbed forests areas. However, maintaining natural dynamics in early successional forests, by emulating natural disturbances at harvesting, hold promise for the conservation of both biodiversity and ecosystem services in boreal forests.

Vegetation regeneration in a sustainably harvested mangrove forest in West Papua, Indonesia

Bintuni Bay, located in the south of the Bird’s Head Peninsula of West Papua, Indonesia, contains one of the largest mangrove forests in the world, growing in a variety of environmental conditions and geomorphologies. In the southern area of the bay, 82,120ha of mangrove forest are actively undergoing a management regime conducted by PT. Bintuni Utama Murni Wood Industries (PT. BUMWI). Operations are focused upon woodchip production; however, sustainable forest management is also a priority as the area is Forest Stewardship Council® (FSC®) certified. Currently, PT BUMWI is approaching the completion of a 25-year rotation (with stands ranging from 0 to 25years) which presents a good time to examine and evaluate current management practices and their effects on the forest concession. Part of a successful regeneration of a forest stand is attaining the range of ecological integrity and ecosystem functions similar to baseline forests. Forest structure and complexity, along with biodiversity at the stand level could function as regeneration criteria to evaluate the success of a sustainable forest management program. The objective of the study was to observe if the forest structure and biodiversity in secondary stands, considered as proxies for ecological integrity, would regenerate to similar levels within the 25years as baseline forests. Post-harvest forest regeneration was evaluated in different aged secondary forest stands by measuring biomass, species composition and forest structure in circular plots along transects. Nonlinear regression was used to determine and predict different forest structure dynamics (sapling and stem densities, tree height, DBH), diversity and volumes throughout and beyond the 25-year rotation period. Dynamics in species composition and diversity of tree species was observed. Results suggest that the forest structure in secondary stands follows a natural regeneration dynamic over the rotation period but had not yet attained the same structure and composition as baseline forests at 25years. Furthermore, growth models suggest that the harvest rotation may need to be extended to 30–40years for secondary stands to attain similar ranges of forest structure, compositions and volumes to that of baseline forests. These observations will help future forest management of the concession as the company strives to manage secondary forests to keep the same ecosystem functions and high volumes observed in baseline forests.

Influence of Anthropogenic Disturbances on Stand Structural Complexity in Andean Temperate Forests: Implications for Managing Key Habitat for Biodiversity.

Forest attributes and their abundances define the stand structural complexity available as habitat for faunal biodiversity; however, intensive anthropogenic disturbances have the potential to degrade and simplify forest stands. In this paper we develop an index of stand structural complexity and show how anthropogenic disturbances, namely fire, logging, livestock, and their combined presence, affect stand structural complexity in a southern Global Biodiversity Hotspot. From 2011 to 2013, we measured forest structural attributes as well as the presence of anthropogenic disturbances in 505 plots in the Andean zone of the La Araucanía Region, Chile. In each plot, understory density, coarse woody debris, number of snags, tree diameter at breast height, and litter depth were measured, along with signs of the presence of anthropogenic disturbances. Ninety-five percent of the plots showed signs of anthropogenic disturbance (N = 475), with the combined presence of fire, logging, and livestock being the most common disturbance (N = 222; 44% of plots). The lowest values for the index were measured in plots combining fire, logging, and livestock. Undisturbed plots and plots with the presence of relatively old fires (> 70 years) showed the highest values for the index of stand structural complexity. Our results suggest that secondary forests < 70-year post-fire event, with the presence of habitat legacies (e.g. snags and CWD), can reach a structural complexity as high as undisturbed plots. Temperate forests should be managed to retain structural attributes, including understory density (7.2 ± 2.5 # contacts), volume of CWD (22.4 ± 25.8 m3/ha), snag density (94.4 ± 71.0 stems/ha), stand basal area (61.2 ± 31.4 m2/ha), and litter depth (7.5 ± 2.7 cm). Achieving these values will increase forest structural complexity, likely benefiting a range of faunal species in South American temperate forests.

Diversity and structural complexity of mangrove forest along Puerto Princesa Bay, Palawan Island, Philippines

Abstract The paper describes the diversity and structural complexity of mangrove forest along Puerto Princesa Bay, Palawan Island, Philippines. Occurrence of 28 mangrove species and 11 floral associates were found, which identifies the entire bay as one of the most diverse mangrove forests in the country. Of the six coastal barangays surveyed, San Pedro had the highest diversity index, H′ = 0.912 while Sta Monica had the lowest, H′ = 0.349. Mangrove stands are structurally simple with two types of vegetation, fringe and riverine that further constitute five distinct mangrove zones named according to dominating species, Rhizophora - Sonneratia ; Rhizophora-Sonneratia-Lumnitzera ; Rhizophora-Lumnitzera-Xylocarpus ; Rhizophora-Xylocarpus ; and Rhizophora-Avicennia . Commonality among these zones is obvious as revealed in Bray-Curtis cluster analysis. Structural features differed across zones. Trees of larger dbh, 104.5 cm and higher species richness, a total of 15 species, were found in zone 1 while those that comprised the highest basal area, 438 m −2 ha −1 and density, 8100 ha −1 from zones 2 and 4, respectively. Zones 1 and 4 are fringing mangrove forests. Degrees of perturbations greatly depend on human access to mangrove areas. Garbage dumping, occasional cutting of trees, soil erosion, and encroachment of human settlers were identified as potential threats to mangrove forest along the bay.

Interactions between white-tailed deer density and the composition of forest understories in the northern United States

Forest understories across the northern United States (US) are a complex of tree seedlings, endemic forbs, herbs, shrubs, and introduced plant species within a forest structure defined by tree and forest floor attributes. The substantial increase in white-tailed deer (Odocoileus virginianus Zimmerman) populations over the past decades has resulted in heavy browse pressure in many of these forests. To gain an objective assessment of the role of deer in forested ecosystems, a region-wide forest inventory across the northern US was examined in concert with white-tailed deer density information compiled at broad scales. Results indicate that deer density may be an additional driver of tree seedling abundance when analyzed along with stand attributes such as aboveground biomass, relative density, and stand age. Tree seedling abundance generally decreased as deer density increased above 5.8deerkm2 for all forest type groups with the exception of oak-dominated forests. Findings indicate that introduced plant species, of which 393 were recorded in this study, increased in areas with higher deer density. The abundance of white-tailed deer is just as important as forest stand and site attributes in the development of forest understories. Given the complexity of forest and land use dynamics across the northern US, this study provides directions for future research as more data linking forest-dependent wildlife and forest dynamics at regional and national scales become available.

Can Retention Harvest Maintain Natural Structural Complexity? A Comparison of Post-Harvest and Post-Fire Residual Patches in Boreal Forest

Variable retention harvest promotes biodiversity conservation in managed boreal forests by ensuring forest continuity and structural complexity. However, do post-harvest and post-fire patches maintain the same structural complexity? This study compares post-harvest and post-fire residual patches and proposes retention modalities that can maintain the same structural complexity as in natural forests, here considering both continuous forest stands and post-fire residual patches. In boreal black spruce forests, 41 post-fire residual patches, and 45 post-harvest retention patches of varying size and ages (exposure time to disturbed matrix) and 37 continuous forest stands were classified into six diameter structure types. Types 1 (inverted-J) and 2 (trunked-unimodal) characterized stands dominated by small trees. The abundance of small trees decreased and the abundance of large trees increased from Type 1 to Type 6. Type 6 had the most irregular structure with a wide range of diameters. This study indicates that: (1) old post-harvest residual retentions maintained the range of structural complexity found in natural stands; (2) Types 1 and 2 were generally associated with young post-fire patches and post-harvest retention clumps; (3) the structure of residual patches containing only small trees was usually younger (in terms of the age of the original forest from which residual patches were formed) than those with larger trees. To avoid the risk of simplifying the structure, retention patches should be intentionally oriented towards Types 3–6, dominated by intermediate and large trees.

Logging impacts on avian species richness and composition differ across latitudes and foraging and breeding habitat preferences

Understanding the causes underlying changes in species diversity is a fundamental pursuit of ecology. Animal species richness and composition often change with decreased forest structural complexity associated with logging. Yet differences in latitude and forest type may strongly influence how species diversity responds to logging. We performed a meta-analysis of logging effects on local species richness and composition of birds across the world and assessed responses by different guilds (nesting strata, foraging strata, diet, and body size). This approach allowed identification of species attributes that might underlie responses to this anthropogenic disturbance. We only examined studies that allowed forests to regrow naturally following logging, and accounted for logging intensity, spatial extent, successional regrowth after logging, and the change in species composition expected due to random assembly from regional species pools. Selective logging in the tropics and clearcut logging in temperate latitudes caused loss of species from nearly all forest strata (ground to canopy), leading to substantial declines in species richness (up to 27% of species). Few species were lost or gained following any intensity of logging in lower-latitude temperate forests, but the relative abundances of these species changed substantially. Selective logging at higher-temperate latitudes generally replaced late-successional specialists with early-successional specialists, leading to no net changes in species richness but large changes in species composition. Removing less basal area during logging mitigated the loss of avian species from all forests and, in some cases, increased diversity in temperate forests. This meta-analysis provides insights into the important role of habitat specialization in determining differential responses of animal communities to logging across tropical and temperate latitudes.

Restoration of tropical forests requires more than just planting trees, a lot more…

AbstractForest restoration is an important tool for combating climate change and protecting biodiversity. In this issue of Applied Vegetation Science, Garcia et al. show that alone, planting trees is insufficient for fully restoring rain forest complexity. This study highlights the need for longer‐term restoration plans, including enrichment plantings that speed the recovery of non‐tree forest components once planted trees have established.

Spatial patterns of saproxylic beetles in a relic silver fir forest (Central Italy), relationships with forest structure and biodiversity indicators

The conservation of biological diversity is one of the main goals for managing forests in an ecologically sustainable way. Presence and abundance of microhabitats, such as tree cavities or bark pockets, can be conveniently used as indicators to evaluate the effectiveness of sustainable forest management measures. In Mediterranean forest ecosystems, the relationships between stand-structure attributes and species-diversity indicators are still poorly studied.We described the structural attributes, deadwood characteristics and microhabitat occurrence in a silver fir forest of Central Apennines (Italy), which has not been submitted to silvicultural interventions for several decades. We assessed linkages between these characteristics and the abundance, distribution and diversity of saproxylic beetle fauna. A systematic aligned sampling method was conduced on 240ha, examining 50 plots of 530m2 each. Saproxylic beetles were sampled using window flight traps and emergence traps in relation to abundance and species richness at the plot level, but also on decaying deadwood. The heterogeneity in types and frequencies of microhabitats, and the link between structural attributes associated with stand complexity and saproxylic species, were also analysed. With the aim of describing the complex saproxylic ecological network, beetle species were classified according to the type of interactions with wood and other insects fauna, but also in relation to the trophic guilds. Linear regressions were conducted for highlighting metric variability and relationships between parameters, while geostatistical analyses were used to describe the spatial variability of structural features and the spatial pattern of beetle distributions.Results of linear regression and geostatistical analysis showed how the saproxylic beetle community is influenced by the amount, type and stage of decay of deadwood, but also by the forest structural complexity and the occurrence of microhabitats. Gap dynamics and natural disturbances had effects on deadwood amounts and microhabitat abundance, which was significantly higher than in managed and structurally simplified forest stands. Most of the entomological variables (namely, Families, Species, Total individuals, Saproxylic individuals, Staphylinidae, Elateridae, Nothodes parvulus, Curculionidae, Ernoporus fagi, Phyllobius emery) were clumped, highlighting the existence of aggregation areas in the sampled forest. In several cases the insect distribution was linked to the spatial pattern of forest attributes, particularly deadwood components.

Effects of small changes in riparian forest complexity on aquatic insect bioindicators in Brazilian subtropical streams

Riparian forests have positive effects on water quality and biodiversity. However, most studies have only tested the effects of distinct vegetation types or streams with and without forests, despite the fact that riparian forests differ in degrees of complexity. The aim of the present study was to test whether riparian forest complexity affected the composition and abundance of the Ephemeroptera, Plecoptera and Trichoptera (EPT) taxa across a small environmental gradient. We also measured whether EPT genera or feeding groups responded to changes in riparian forest complexity. The study was conducted in two protection areas (i.e. Lagoa do Peri Municipal Park, PERI; and the Permanent Protection Area of Ratones, RAT) of Santa Catarina Island, Brazil. Primary production increased in streams with lower canopy percentage, and EPT assemblages differed among streams with different riparian forest complexity. In RAT, the water quality and forest variables affected EPT composition; however, in PERI, only water quality variables were important. Indicator species analysis based on genera suggested Kempnyia (Plecoptera) and Zelusia (Ephemeroptera) to be indicative of streams with greater forest complexity, whereas Farrodes (Ephemeroptera) was significant in streams of intermediate riparian forest complexity; however, no one functional group dominated. The results of the present study show that small changes in riparian forest complexity influence the composition of EPT insects in subtropical streams.

Sources and interpretation of channel complexity in forested subalpine streams of the Southern Rocky Mountains

AbstractWe evaluate correlations between stream geomorphic complexity and characteristics of the adjacent riparian forest, valley geometry, and land use history in forested subalpine streams of the Colorado Front Range. Measures of geomorphic complexity focus on cross‐sectional, planform, and instream wood piece and logjam variables. We categorize adjacent riparian forests as old‐growth unmanaged forest (OU), younger unmanaged forest (YU), and younger managed forest (YM), and valley geometry as laterally confined, partly confined, or unconfined. Significant differences in geomorphic stream complexity between OU, YU, and YM result primarily from differences in wood pieces and logjams, and these differences correlate strongly with pool volume and organic matter storage. Significant differences in planform and cross‐sectional complexity correlate more strongly with valley geometry, but do not explain as much of the observed variability in complexity between streams as do the wood variables. Unconfined OU streams have the largest wood loads and the greatest complexity, whereas legacy effects of logging, tie‐drives, and channel simplification create lower complexity in YM streams, even relative to YU streams flowing through similarly aged forest. We find that management history of riparian forests exerts the strongest control on reduced functional stream channel complexity, regardless of riparian forest stand age.

Salt marsh‐mangrove ecotones: using structural gradients to investigate the effects of woody plant encroachment on plant–soil interactions and ecosystem carbon pools

Summary Changing winter climate extremes are expected to result in the poleward migration of mangrove forests at the expense of salt marshes. Although mangroves and marshes are both highly valued ecosystems, the ecological implications of mangrove expansion have not been fully investigated. Here, we examined the effects of mangrove expansion on below‐ground properties related to peat development and carbon storage. We investigated plant–soil interactions in marshes and across mangrove forest structural gradients in three locations in the northern Gulf of Mexico (USA). We compared our results to those from terrestrial grasslands where the effects of woody plant encroachment are often influenced by rainfall and plant traits. Abiotic conditions at our study locations differed, particularly in terms of physicochemical properties related to precipitation. Marsh species composition, marsh above‐ground biomass, and mangrove forest structural complexity also varied across these locations. Marshes in the driest location (Central Texas) had higher salinities and were dominated by low biomass succulent plants and lower soil carbon pools. Marshes in the wetter, less saline locations (Louisiana and North Florida) contained high biomass grasses and higher soil carbon pools. At all locations, above‐ground biomass and above‐ground carbon pools were higher in mangroves than marshes; however, below‐ground soil carbon pools were only higher in mangroves than marshes in the driest location. In the wetter locations, the linkages between mangrove forest structure and soil properties were minimal or not significant. However, in the driest location, there was a significant increase in soil properties related to peat development and carbon storage with increased mangrove forest structural development. Synthesis: Our results indicate that the ecological implications of woody plant encroachment in tidal saline wetlands are dependent upon precipitation controls of plant–soil interactions. Although the above‐ground effects of mangrove expansion are consistently large, below‐ground influences of mangrove expansion appear to be greatest along low‐rainfall coasts where salinities are high and marshes being replaced are carbon poor and dominated by succulent plants. Collectively, these findings complement those from terrestrial ecosystems and reinforce the importance of considering rainfall and plant–soil interactions within predictions of the ecological effects of woody plant encroachment.

Frequent severe natural disturbances and non-equilibrium landscape dynamics shaped the mountain spruce forest in central Europe

Disturbances shape forest structure and composition, but the temporal dynamics of disturbance patterns, their influence on dynamics of forest structural complexity, and the potential impacts of ongoing climate changes are not fully understood. We addressed these issues by focusing on (1) long-term, landscape level retrospective analysis of disturbance dynamics of mountain Norway spruce (Picea abies) forest; (2) testing for the prevailing disturbance agent; and (3) the detection of disturbance drivers, particularly site conditions, using a dendrochronological approach.We had a unique opportunity to sample a large area of natural forest (in otherwise altered region) in Bohemian Forest, that was recently affected by extensive and severe wind and bark beetle disturbances raising management concerns. Tree-ring series of a minimum of 35 trees on each of the 26 study plots were analysed for signals of past disturbances that were indicated either by release from suppression (rapid growth increase) or rapid early growth rate (gap origin).A broad range of disturbance severities were detected across the landscape, but severe disturbances (>50% trees responded), with a short rotation period of 174years, best characterize the area. Reconstructed disturbances were associated with historically documented windstorms and bark beetle outbreaks. They were distributed across the landscape and affected its large portions with spatially variable severity. Over the last five centuries, disturbances peaked in the 1820s, but were rare after 1880. This non-equilibrium dynamics resulted into mature landscape structure at the end of 20th century and contributed to the large extent of disturbances in the last two decades. Disturbances were more frequent on wind-exposed locations such as mountain ridges and flatter terrain.Frequent disturbances did not allow the forest to develop into an old-growth phase; rather disturbance events of variable severities created structures important for biodiversity and could also preserve key early-seral phases in the landscape. We anticipate that potential future increase of disturbance intensities will not lead to comparable regime shifts in forests shaped by high-severity disturbances that kill largely mature trees (e.g., wind and bark beetle), because such disturbances are followed by resistant forest structure. Conservation areas should be large enough to allow for a wide range of disturbances. Emphasizing ecological functions needs understanding of biological legacies of natural disturbances and managers could partly rely on natural events to restore natural features into cultivated forests.

Influence of fire regime and other habitat factors on a eucalypt forest bird community in south-eastern Australia in the 1980s

We investigated bird habitat relationships in extensive eucalypt forest in the Blue Mountains, New South Wales, in 1986–87, assessing the importance of fire regime variables compared with other habitat variables. Our study sites encompassed a wide range of postfire ages, fire frequencies and fire severity, but we found no major bird community differences corresponding to differences in fire regime. The more common forest bird species appeared well adapted to fire regime variation in the 1980s. Tree canopy height was a far greater influence, with more species and more birds in taller forests (interpreted as a result of higher soil fertility leading to higher productivity of bird foods and greater structural complexity in taller forests). Other trends were fewer birds where there was a rainforest understorey under the eucalypts (reflecting the general scarcity of rainforest birds in the Blue Mountains), and more birds where nectar-rich flowers were more abundant (reflecting the abundance of nectarivorous birds in the Blue Mountains, especially over winter). The climate has changed since the 1980s and fires threaten to become much more severe, extensive and frequent. How these changes will impact on forest birds, and what management responses are required, is a critical area for further study.

Spatiotemporal fire dynamics in mixed‐conifer and aspen forests in the San Juan Mountains of southwestern Colorado, USA

Mixed‐severity fire regimes may be the most extensive yet poorly understood fire regimes of western North America. Understanding their long‐term spatiotemporal dynamics is central to debates regarding altered fire regimes and the need for restoration in the context of changing climate and nearly a century of active fire suppression. However, the complexity of fire patterns and forest stand and landscape structures characteristic of mixed‐severity regimes poses a substantial challenge to understanding their long‐term dynamics. In this study, we develop analysis methods aimed at understanding the fire‐driven forest dynamics of mixed‐severity systems and apply them in the San Juan Mountains of southwestern Colorado. We sampled fire scars, stand structure, and &gt;4300 tree ages across two 1340‐ha landscapes (Williams Creek and Squaretop Mountain) that span the environmental gradient of montane mixed‐conifer and aspen forests. New approaches were applied to identify pulses of tree recruitment, evaluate climate and fire as potential drivers of synchronous recruitment pulses, and combine fire scar and recruitment data to reconstruct fires. The reconstructions provided detailed fire history for each stand, which in turn was used to develop a fire‐severity metric, compare fire frequency and severity by forest type, and develop a simulation procedure to evaluate the degree to which tree regeneration depended on fire by species within each forest type.Twenty fires were reconstructed since 1685 at Williams Creek and 13 fires since 1748 at Squaretop Mountain. Patterns of fire severity varied within each fire and over successive events, including high‐severity patches of hundreds of hectares in both study areas. Dry mixed‐conifer forests experienced relatively short fire intervals (mean 21 years) and low fire severity, and regeneration of the main conifer species was largely dependent on open conditions sustained over successive fires. Moist mixed‐conifer forests experienced longer fire intervals (mean 32 years) and a broader range of severities, and fire‐caused canopy openings were important for initiating pulses of tree recruitment. Most (83%) aspen stands included two or more post‐fire cohorts. The methods presented here can be adapted to other mixed‐severity systems to better understand their long‐term spatial and temporal dynamics and develop restoration priorities.

Have we been successful? Monitoring horizontal forest complexity for forest restoration projects

Forest management today often seeks to restore ecological integrity and enhance human well‐being by increasing forest complexity, resilience, and functionality. However, effective and financially expedient monitoring of forest complexity is challenging. In this study, we developed a practical and inexpensive technique to measure horizontal forest complexity. This monitoring method uses intuitively understandable data (imagery) and facilitates stakeholder participation in the adaptive management process within collaborative projects. We used this technique to determine if current restoration projects are successfully achieving their spatial restoration goals. We focused on the Colorado Front Range Landscape Restoration Initiative (CFRLRI) as a representative of the typical collaborative restoration projects underway in formerly fire‐dependent dry conifer forests. The developed monitoring method is practical and cost‐effective by using free aerial imagery to map, quantify, and analyze the distribution of canopy cover pre‐ and post‐treatment. We found the CFRLRI has successfully reduced canopy cover (from 44 to 26% on average) and increased some aspects of horizontal forest complexity. The application of these monitoring techniques has allowed the CFRLRI collaborative group to objectively quantify changes to horizontal forest complexity, and has facilitated stakeholder communication about forest spatial patterns. These methods could be adapted for use by other similar forest restoration projects around the world by utilizing increasingly available satellite or aerial imagery.

Trade‐offs in juvenile growth potential vs. shade tolerance among subtropical rain forest trees on soils of contrasting fertility

Summary Plant adaptation to gradients of light availability involves a well‐studied functional trade‐off, as does adaptation to gradients of nutrient availability. However, little is known about how these two major trade‐offs interact, and thus, it remains unclear whether and how the nature of the growth–shade tolerance trade‐off differs on soils of contrasting fertility. We asked whether juvenile growth–shade tolerance trade‐offs differed in slope and elevation between tree assemblages on nutrient‐rich basalt and nutrient‐poor rhyolite soils in an Australian subtropical rain forest. We measured the growth of, and the range of light environments occupied by, juveniles (40–120 cm tall) of eight basalt specialists, six rhyolite specialists, and one generalist that was common on both substrates. In situ minimum light requirements were estimated from the 5th percentile of the distribution of naturally regenerated juveniles in relation to daily light transmittance. Stem growth was measured for 12–16 months across a wide range of light environments to estimate the light compensation point of growth of each species. Light compensation points of growth showed nearly a 1 : 1 correspondence with in situ minimum light requirements of species, indicating that whole‐plant carbon balance is a key driver of ecological success in low light. Minimum light requirements were negatively correlated with relative growth rate in low light, but correlated positively with growth in high light. Soil type had no effect on either the slope or the elevation of this trade‐off, all species aligning around a common growth–shade tolerance trade‐off, but our results do show a wider range of growth rates and shade tolerance on the nutrient‐rich basalt soil than on the nutrient‐poor rhyolite. Our results suggest that adaptation to light availability involves fundamentally similar trade‐offs on these two substrates of differing fertility. However, a wider range of growth rates and shade tolerance on the nutrient‐rich basalt soil than on the nutrient‐poor rhyolite may help to explain the higher species richness and greater structural complexity of forest stands on the former substrate.

Long‐term outcomes of forest restoration in an urban park

Creating, restoring, and sustaining forests in urban areas are complicated by habitat fragmentation, invasive species, and degraded soils. Although there is some research on the outcomes of urban reforestation plantings during the first 5 years, there is little research on longer term outcomes. Here, we compare the successional trajectories of restored and unrestored forest sites 20 years after initiating restoration. The sites are located within the Rodman's Neck area of Pelham Bay Park, in the northeast corner of the Bronx in New York City (NYC), U.S.A. Compared with unrestored sites, we saw improvements in species diversity, greater forest structure complexity, and evidence of the regeneration and retention of native tree species in restored sites. In addition, we found differences in restoration outcomes depending on the level of intervention: clearing exotic shrubs and vines and planting native trees and shrubs improved tree diversity and canopy closure to a greater extent than clearing exotics alone, and the mechanical removal of invasive plants after the native plantings further improved some measures of restoration, such as tree species diversity and native tree regeneration. The results of this study suggest that the goal of a sustainable forest ecosystem dominated by native trees and other plant species may not be achievable without continued human intervention on site. In addition, these results indicate that the restoration approach adopted by NYC's reforestation practitioners is moving the site toward a more desirable vegetative community dominated by native species.