Tree Regeneration Research Articles

Initial succession after wildfire in dry boreal forests of northwestern North America

Wildfires in the boreal forest of North America are generally stand renewing, with the initial phase of recovery often governing the vegetation trajectory for decades. Here, we investigated post-fire vegetation changes in dry boreal forests of the Northwest Territories, Canada, during the first 5 years following the unusually severe 2014 wildfire season. We sampled post-fire tree regeneration and the understory plant community at 1, 3, and 5 years post-fire across different stand types within fires that burned in 2014. Post-fire trajectories of tree recruitment, understory cover by plant functional types, and plant diversity varied widely among sampled stands, as well as among years post-fire. Tree seedling density reached relative equilibrium by 3-years post-fire, whereas trends in understory plant cover and understory species assemblages suggested an ongoing change that will extend beyond 5 years of observation. In almost half of sampled stands, the composition of recruited trees differed from that of the pre-fire stand, suggesting a change in tree species dominance. An analysis of regional climate revealed a significant, albeit spatially variable, warming and drying trend that will further accelerate forest stand transformation through both climate drivers of plant community composition and indirectly through increasing fire activity. While the 2014 wildfires enhanced the structural and compositional heterogeneity of the region, they also triggered vegetation changes that are likely to be persistent. As such, this study exemplifies the speed and variability that characterizes post-fire stand development in a strongly moisture-limited part of North America.

A forested wetland at a climate-induced tipping-point: 17-year demographic evidence of widespread tree recruitment failure

Regeneration and survival of forested wetlands are affected by environmental variables related to the hydrologic regime. Climate change, specifically alterations to precipitation patterns, may have outsized effects on these forests. In Tennessee, USA, precipitation has increased by 15% since 1960. The goal of our research was to assess the evidence for whether this change in precipitation patterns resulted in shorter growing seasons and recruitment failure in common canopy trees for a forest wetland. In 2001 and 2018, the density of Quercus lyrata (overcup oak), Liquidambar styraciflua (sweetgum), Quercus phellos (willow oak), and Betula nigra (river birch) seedling, sapling and adult density were mapped in an area of 2.3 ha within a seasonally flooded karst depression. Overall, the percentage of the growing season experiencing inundation was 26% greater in the deep than in shallow areas between 2001 and 2018. Saplings and small adults of all four species were restricted to shallow areas, and their abundance has declined substantially. Overcup oak and sweetgum individuals that were recruited into the adult life history stage were repelled from the deep zone. Overcup oak and sweetgum adults experienced lower mortality across the 2.3-ha study area (11% and 26%, respectively) relative to willow oak (56%) and river birch (64%) over the 17-year study. Growing-season inundation showed no relation to mortality in adult sweetgum and willow oak, a positive relation to mortality among adult river birch across size classes and among small adult overcup oak, and an inverse relation to mortality among large adult overcup oak. In shallow regions, overcup oak and sweetgum adults had greater basal area increment relative to the intermediate and deep regions of the pond. Results of hydrologic modeling for the study area, based on rainfall and temperature records covering 1855–2019, show ponding durations after 1970 considerably longer than the historical baseline, across ponding-depth classes. Our results strongly suggest that climate change is a driving factor suppressing tree regeneration since 1970 in this seasonally flooded karst depression.

Logging legacies in a plant biodiversity hotspot: Altered distribution and abundance patterns of the shrub layer in the southern Appalachians

Altered disturbance regimes in forest ecosystems can lead to the formation of dense, persistent understory vegetation composed of a small number of dominant species. This understory layer often limits tree seedling recruitment, decreases biodiversity, and can alter forest ecosystem structure and functioning. In the southern Appalachians – one of the most biodiverse regions in North America – pervasive logging in the 19th and early 20th centuries may have contributed to the formation of a dense understory shrub layer that suppresses plant diversity and tree recruitment, but the evidence for this idea has been mixed. To help clarify this issue, we tested whether (a) the two dominant understory shrub taxa (Kalmia latifolia and evergreen Rhododendron species) were more common or more abundant in areas with a history of intense logging than in areas undisturbed by logging, and (b) the relationships between the understory shrub layer and environmental gradients that drive regional biodiversity and plant distributions in the Southern Appalachians (e.g., climate, soils) differ in logged versus undisturbed areas. We used publicly available, extensive, and spatially explicit data on vegetation, climate, topography, soils, solar radiation, and logging history in Great Smoky Mountains National Park to build beta and binomial regression models of shrub frequency and cover as a function of logging history and environmental variables. Contrary to our expectation and speculations in the literature, we found that the dominant shrub taxa were more common (frequent) in areas with no logging history. However, we also found that logging history effects on shrub abundance (cover) varied along environmental gradients. For example, in topographically shaded landscape positions evergreen Rhododendron thickets exhibited greater cover in logged areas than in areas with no logging history. On the other hand, Rhododendron thickets exhibited lower cover in logged areas than in areas with no logging history at low elevations. Thus, conservation planning and forest management in topographically complex regions need to consider both landscape context (e.g., elevation, landscape position) and past logging as important interacting drivers that either facilitate or suppress local formation of dense shrub understories that can ultimately impact tree regeneration patterns, biodiversity, and ecosystem functioning.

Stand development stages and recruitment patterns influence fine-scale spatial genetic structure in two Patagonian Nothofagus species

Key messageNothofagus alpina (Poepp. et Endl.) Oerst. and Nothofagus obliqua (Mirb.) Oerst forests have strong fine-scale spatial genetic structures. The intensity of genetic structure patterns differed according to species, stand development stages, life stages, and spatial arrangement of regeneration groups. This data becomes useful for forest management as it provides an understanding of how populations evolve as well as of the consequences of disturbances and enables the establishment of sampling strategies.ContextThe understanding of fine-scale spatial genetic structure in natural populations is useful for forest management. Although Nothofagus alpina (Poepp. et Endl.) Oerst. and N. obliqua (Mirb.) are important species of the Patagonian forest, little is known about the genetic structure of their populations.AimsThe main objectives were to investigate the differences in fine-scale spatial genetic structure among mature tree populations of both species considering two stands at different development stages. Genetic structure was also evaluated among life stages and spatial distribution groups of regeneration within the old-growth stand.MethodsGenetic structure was examined by microsatellite DNA analysis of regeneration and mature tree populations of both species (around 1300 individuals). Gene dispersal distance was additionally estimated.ResultsIn both stands and species, strong fine-scale spatial genetic structure and short dispersal distance were found. This pattern was stronger in the early successional forest, in N. obliqua populations, in earlier life stages, and in scattered regeneration.ConclusionStand development stages and recruitment patterns influence the fine-scale spatial genetic structure of both Nothofagus species. However, the genetic structure also differs between species.

Influence of site conditions and land management on Quercus suber L. population dynamics in the southern Iberian Peninsula

During recent decades, tree mortality and dieback have been reported in forest ecosystems across global biomes. Although numerous forest species, including those of the genus Quercus, have been affected by hotter and drier conditions in the Mediterranean Basin during the last decades, there is scarce information regarding the interactive role of past management and climate across large areas of south-western Europe. Here, we examined the influence of several climatic factors (mean annual temperature, annual precipitation) over the last 3 decades, latitude, land management and site conditions on the cork oak (Quercus suber L.) population dynamics given their high ecological and economic relevance. We sampled 20 plots across contrasting environmental conditions in SW Iberian Peninsula with different land property (public vs. private) to characterize cork oak tree size, stand density, mortality ratio and regeneration. We observed widespread effects of latitude (8.9% at northern vs. 15.6% at southern plots) and land property (6.9% in private properties vs. 13.9% in public ones) on tree mortality. Tree density and basal area differed with latitude, with higher values (307.2 trees ha-1 and 38.4 m2 ha-1, respectively) at northern populations. In addition, the more intense cork-focused productive management resulted in higher tree sizes in private (mean DBH = 47.3 cm) than in public (mean DBH = 37.8 cm) plots. Tree regeneration was higher in northern forests (94.9 ± 25.2 vs. 26.0 ± 6.1 saplings ha-1 for the southern location), being this difference more pronounced in public plots. These findings highlight the importance of sustainable forest management in public and private forests for further reduction of mortality processes, as well as for enhancing the regeneration aimed to the conservation of cork oak under forecasted drier conditions of these economically invaluable Mediterranean forests.

Effect of variation in winter rainfall and anthropogenic disturbances on regeneration of trees in (Van-Panchayt) community forests Uttarakhand, India

Effect of variation in winter rainfall and anthropogenic disturbances on regeneration of trees in (Van-Panchayt) community forests Uttarakhand, India

Forest regeneration within Earth system models: current process representations and ways forward.

Earth system models must predict forest responses to global change in order to simulate future global climate, hydrology, and ecosystem dynamics. These models are increasingly adopting vegetation demographic approaches that explicitly represent tree growth, mortality, and recruitment, enabling advances in the projection of forest vulnerability and resilience, as well as evaluation with field data. To date, simulation of regeneration processes has received far less attention than simulation of processes that affect growth and mortality, in spite of their critical role maintaining forest structure, facilitating turnover in forest composition over space and time, enabling recovery from disturbance, and regulating climate-driven range shifts. Our critical review of regeneration process representations within current Earth system vegetation demographic models reveals the need to improve parameter values and algorithms for reproductive allocation, dispersal, seed survival and germination, environmental filtering in the seedling layer, and tree regeneration strategies adapted to wind, fire, and anthropogenic disturbance regimes. These improvements require synthesis of existing data, specific field data-collection protocols, and novel model algorithms compatible with global-scale simulations. Vegetation demographic models offer the opportunity to more fully integrate ecological understanding into Earth system prediction; regeneration processes need to be a critical part of the effort.

Responses of a shallow temperate lake ecosystem to major late-Holocene terrestrial vegetation shifts

Major terrestrial vegetation shifts (MTVSs) resulting from either human activities or natural processes can exert substantial pressure on lakes mainly through impacts on catchment biogeochemical cycles and groundwater circulation. To better understand the links between terrestrial vegetation dynamics and lake ecosystem structure and functions over long temporal scales, in this study, we reconstructed the responses of shallow Lake Spore (N Poland) to major late-Holocene vegetation shifts. We combined newly acquired data from pollen and spores, Cladocera, TOC/N, δ13C, and δ15N analyses of bulk organic matter with the already published results from sediment dating and analyses of several biotic and geochemical proxies. Statistical analysis of the abundance data for all the major terrestrial pollen taxa and reconstruction of vegetation openness derived from the REVEALS model indicated five MTVSs, each followed by a change in the lake environment. Changes in Lake Spore trophic status at MTVS1 (~2.82 kyr BP) and MTVS2 (~2.17 kyr BP) were attributed to the reorganization of the catchment’s nutrient cycling associated with a decline (MTVS1) and subsequent regeneration (MTVS2) of deciduous tree stands in the area. A distinct drop in the CaCO3 content of the lake sediments that started at MTVS4 (~0.57 kyr BP) likely occurred due to the substantial depletion of the water calcium pool following an abrupt transition from a tree-dominated to an herb-dominated landscape. Our record also suggested slight lake acidification following a spread of Pinus sylvestris at MTVS1 (~2.82 kyr BP) and MTVS3 (~1.10 kyr BP) and a lake level rise concurrent with the sharp increase in landscape openness at MTVS4 (~0.57 kyr BP).

Stasis in forest regeneration following deer exclusion and understory gap creation: A 10-year experiment.

Chronically elevated ungulate browse pressure in temperate forests worldwide often generates ecological legacies characterized by low plant diversity and contributes to the formation of dense, nearly monodominant, and highly recalcitrant layers of understory vegetation. Once established, these recalcitrant layers combined with continued browsing may jointly constrain tree establishment and diversity so completely that understory recovery may be unattainable without mitigating browse pressure, the recalcitrant layer, or both. Here, we investigate the independent and synergistic effects of both white-tailed deer (Odocoileus virginianus) browsing and hay-scented fern (Dennstaedtia punctilobula) competition on tree regeneration in a 10-year experiment. Specifically, we examine how tree seedling establishment, growth, and composition are filtered by fern cover versus fern removal (gaps), browser presence versus absence (exclosures), and their combined effects during 10 years at three hardwood forest sites in Pennsylvania, USA. Fern gaps enhanced establishment for multiple tree species, increasing seedling density and diversity, particularly in the first 3 years post-treatment, and enhancing richness (≤1 species) over the course of the experiment. Excluding deer for a decade increased the height growth of other regeneration and altered species composition, but had no effect on diversity, richness, and density. Notably, we observed higher Prunus serotina seedling densities outside exclosures, possibly due to greater secondary dispersal. We argue that browsing legacies in second growth forests established at the turn of the last century created two conditions inimical to diverse forest regeneration: an overstory dominated by two species, P. serotina and Acer rubrum (86% of basal area), and a dense recalcitrant understory layer dominated by a native fern. The first condition limits propagule supply, the second strongly filters seedling establishment, and both create impoverished forest understories composed of few individuals and species. In undisturbed forest understories, the inertia toward impoverishment was sustained across the decade even where browsing was eliminated. Consequently, stand replacing disturbances (whether natural or anthropogenic) that disrupt the understory layer and reinitiate succession may be necessary to propel forests out of their current stasis and down a pathway leading to greater diversity.

Sapling Stocking Targets for Multiple Management Goals in Northern Hardwood Forests: How Do Stands Measure Up?

Abstract Well-stocked natural tree regeneration is critical to sustainable management of northern hardwood forests (NHF) by selection silviculture, but explicit goals and stocking criteria for sapling recruit size classes are lacking. For stems 0–2 in. (0–5.1 cm), we define 171 and 691 stems ac−1 (422.5 and 1,707.5 ha−1) as lower and upper full stocking thresholds for basic NHF management goals (wood and biomass productivity) and overabundant/pest–pathogen-challenged species. We define component stocking targets as 15% of full stocking targets for six additional wildlife (e.g., nut producers) and resilience (e.g., pest–pathogen) goals and individual species representation. Applying our system to 141 managed stands in Michigan, USA, we found several areas of concern. At low threshold, 33% of stands were understocked for biomass and wood goals, whereas 67% were fully stocked with overabundant/pest–pathogen-challenged species. Among goals, component stocking (low threshold) was as low as 5% (nut producers), with more than half the stands component stocked for ≤ 2 goals and ≤ 2 individual species. Stocking varied geographically and decreased with increasing site quality, overstory basal area, and deer use. Study Implications The stocking goals and density criteria we developed can help managers objectively identify areas where current silvicultural practices are ineffective and need modification. Our system is based on an interactive platform that can be readily modified to accommodate new information and management goals. Several management suggestions emerged from applying our system to selection-managed NHF stands in Michigan. First, highest quality sites have the greatest stocking challenges. Stocking outcomes could likely be improved via more intense overstory harvests and mitigation of deer impacts. Second, most stands meeting stocking goals are vulnerable to future changes in climate and pest–pathogen outbreaks, given stocking is often dominated by a small subset of candidate species. Planting, including the incorporation of assisted migration species candidates could help ameliorate this problem, as species could be evaluated based on their contribution to multiple component stocking goals.

Regeneration and growth of tree seedlings and saplings in created gaps of different sizes in a subtropical secondary forest in southern China

Gap-based silvicultural systems are of particular interest in secondary forest management because gaps are associated with regeneration and tree species diversity. However, whether using a range of gap sizes to influence tree regeneration is effective remains unclear. In this study, gaps of different sizes were created to determine their effects on tree regeneration and growth in a secondary Pinus massoniana Lamb. forest in Hunan Province, China. A robustly designed experiment was used with over nine years of repeated measurements. Seedling densities were highest in small gaps, and seedling diversity increased with increasing gap size. Sapling densities and diversity were highest in medium gaps. Within medium and large gaps, saplings were heterogeneously distributed along gradients from opening to closed forest canopy, suggesting gap partitioning of saplings. Emergence rates of three dominant species (Pinus massoniana Lamb, Schima superba Gardn. et Champ., and Cyclobalanopsis glauca (Thunb.) Oerst.) were roughly equal in medium gaps. Regeneration of P. massoniana and C. glauca was spatially diverse as gap sized increased. However, there was little evidence of S. superba divergence within and among gaps, which indicated differential tolerance to shade. A nonlinear mixed-effects model was used to detect effects of microenvironmental variables on diameter–biomass relations. The model suggested that gaps combined with solar radiation, soil moisture, and soil temperature had various effects on sapling biomass accumulation. For saplings with the same basal diameter, estimated average aboveground biomass of S. superba and C. glauca was highest in medium gaps, whereas that of P. massoniana was highest in large gaps. The study suggests that tree regeneration and growth requirements are often not met with a single gap size alone. In practice, a single tree/group selection with medium gaps hybrid approach may be required in subtropical secondary forests to increase regeneration and ecosystem resilience, while also considering other factors such as microenvironmental variables, shade tolerance, and others.

Changes within a South Carolina Coastal Wetland Forest in the Face of Rising Sea Level

Rising sea levels and increasing salinity are impacting coastal forests of the Southern U.S. Forest productivity and composition was studied from 2014 to 2020 in paired plots (20 × 25-m) along a porewater salinity gradient (0, 0.8, 2.6, 4.6 PSU). Aboveground net primary productivity was estimated by summing annual litterfall and woody growth. In addition, voucher specimens for each vascular plant species were collected. Productivity differed in forest communities across the salinity gradient averaging 1081, 777, 694, and 613 g m−2 yr−1 in fresh, low-salt, mid-salt, Freshwater forest communities and high-salt sites, respectively. The vascular flora consisted of 144 species within 121 genera and 57 families. Although salinity in Strawberry Swamp is currently declining, it hasn’t reached levels low enough to reverse the loss of forested wetlands. With projections of continuing sea level rise and increasing salinity intrusions, tree regeneration and growth will continue to decline as the forest transitions into marsh.

Nurse species facilitate persistence of dry forests in agricultural landscapes in Uruguay

AbstractQuestionsPark forests are shaped by extensive cattle ranching in the transition between natural riverine forests and open grasslands. The underlying mechanisms driving tree regeneration have not been studied, however, they determine biodiversity, sustainability and multifunctionality of these ecosystems. We explored patterns of tree regeneration by analyzing nurse–beneficiary interactions and tree community composition.LocationPark forests within the departments of Rio Negro, Paysandú, Artigas and Tacuarembó, República Oriental del Uruguay, South America.MethodsWe established 205 (1 × 1 m2) paired plots in open microhabitat and under the tree canopy to evaluate the patterns of tree regeneration. To assess tree community composition and diversity we carried out forest inventories within one‐hectare plots of ten park forests.ResultsScattered trees in park forests had a positive effect on tree regeneration density, whereas, dense grass coverage had a negative effect. Regeneration density increased and grass cover reduced under the canopy of nurse trees. Regeneration beneficiaries were mainly bird dispersed species with different life strategies. Tree communities varied between forest types and spatially closer forests were more similar.ConclusionsOur study outlines the importance of park forest trees to the promotion of forest regeneration and recovery in grazed forests. Our results found a positive interaction effect between nurse trees and saplings, based on our results we suggested possible facilitation mechanisms including the provision of shade, reduction of grass competition and the attraction of seed dispersers.

Keragaman Permudaan Pohon di Area Sumber Air Blok Seda, Taman Nasional Gunung Ciremai

Water availability in Mount Ciremai National Parks (MCNP) is influenced by sustainability of the vegetation. Therefore, tree regeneration around the water springs area needs to be investigated to maintain the sustainability of water springs ecosystem in the future. The purpose of this study was to analyzed and identify natural seedlings of tree regeneration around the water springs area Seda Block MCNP. The collections of vegetation and abiotic data was carried out on 9 sample plots measuring 3 m × 3 m which is purposively placed around water springs. Result show that vegetation in water springs dominate by seedlings Ficus sp., Ficus hemsleyana, and Trevesia sundaica. Shannon-Weiner diversity index in this location was moderate, but evenness and dominance index classified as high and low, respectively. Overall, seedling of trees dominated by orthodox seed-type and shade tolerant plant. The vegetation in this study dominated by plants categorized least concern (LC) based on IUCN red list. Microclimatic of study site affects 58.89% on abundance and distribution of tree seedlings. Therefore, the springs are in the Seda Block MCNP needs to be conserved and maintain its natural vegetation.
 Keywords: Mount Ciremai National Park, eco-hydrology, canonical correspondent analysis, conservation

Effects of wildfire and soil compaction on recovery of narrow linear disturbances in upland mesic boreal forests

Energy exploration has led to fragmentation of habitats worldwide. In boreal forests of Alberta, Canada narrow clear-cut linear disturbances (3–14 m wide) called seismic lines are often the largest local source of forest fragmentation. Many lines have failed to recover decades after their creation leading to changes in forest dynamics and biodiversity. In some cases, these linear features function as habitat and/or corridors for species, while being detrimental in other species, most notably the threatened woodland caribou (Rangifer tarandus caribou). Recently, industry and government have focused on reforestation of these lines using silvicultural treatments and tree planting. However, these applications are expensive (> $12,500/km) and do not account for wildfires that can destroy restoration investments (planted trees), yet also initiate early seral conditions that favor natural recovery. Here, we examined soil compaction (bulk density) and tree regeneration density in burnt and unburnt seismic lines within mesic upland forest types and compared these to adjacent (paired) forest controls. Bulk density on seismic lines increased by 34% compared to undisturbed adjacent forests, but was not severe enough to impede regeneration. Despite increases in compaction, regeneration density was 19% higher on lines than in adjacent forests. Specifically, regeneration density averaged 19,622 stems/ha in burnt lines, 11,870 stems/ha in unburnt lines, 16,739 stems/ha in adjacent burnt forest, and 6,934 stems/ha in adjacent unburnt forest where regeneration rates are expected to be lower. We suggest that leave-for-natural recovery (passive restoration) of seismic lines can be expected post-fire in mesic upland forests with even the majority of unburnt seismic lines recovering to densities above the 5,000 stems/ha guidelines. Active restoration treatments using intensive silviculture treatments should therefore only be considered where recovery is not observed or wildfire likely.

Ten-year Douglas-fir regeneration and stand productivity differ among contrasting silvicultural regimes in western Washington, USA

In the Pacific Northwestern USA, concerns regarding impacts of forest harvesting on visual quality, wildlife habitat, and carbon management have prompted evaluations of alternative silvicultural regimes for coast Douglas-fir (Pseudotsuga menziesii var. menziesii). Research was initiated in 1998 near Olympia WA USA to conduct long-term comparisons among six silvicultural regimes: clearcut (harvest all trees), two age (harvest all except 38 mature trees ha−1), patches (harvest 20% of the area in 0.6–2.0 ha tracts), groups (harvest 20% of the area in 0.1–0.5 ha tracts), thinning (reduce stand density to 45% of the biological maximum for Douglas-fir), and a non-treated control. Harvested areas in the first four regimes were planted with Douglas-fir seedlings. This report focuses on tree regeneration and stand productivity during the first decade of the study. Fifth year height of planted Douglas-fir was greater in the clearcut regime (1.8 m) than in the patches and groups regimes (1.1–1.2 m). Fifth year tree regeneration in the clearcut and two-age regimes was dominated by Douglas-fir (80–86% of seedlings), but regeneration in the patches and groups regimes was composed of a mixture of conifer and hardwood species. Ten-year periodic annual increment (PAI) in Douglas-fir ingrowth volume was greater in the clearcut regime (1.4 m3 ha−1 yr−1) than in the control (0.1 m3 ha−1 yr−1), whereas ingrowth volume PAI of other conifer species was greater in the two-age regime (0.4 m3 ha−1 yr−1) than in the control (0.0 m3 ha−1 yr−1). Tree regeneration responses indicated increasing abundance of shade tolerant species in the non-clearcut regimes, especially western hemlock (Tsuga heterophylla). Fifth year cover of the vine, California blackberry (Rubus ursinus), in the clearcut regime (21%) was over four times that in the control (5%). Ground disturbance in the clearcut regime reduced 5th-year height of the shrubs, salal (Gaultheria shallon) and red huckleberry (Vaccinium parvifolium), by 40–50% compared to the control. Ten-year volume PAI of Douglas-fir was linearly related to post-harvest stand basal area (r2 = 0.94), and the relationship did not vary significantly among the three replicate sites. During the first decade of the study, Douglas-fir regeneration and stand productivity differed among silvicultural regimes because of post-harvest variation in stand edge competition, species composition of tree seedlings and ingrowth, and residual stand density.

Nucleation by isolated emergent native trees can push back the shade-intolerant invader Broussonetia papyrifera (L.) L'Hér. ex Vent.

The facilitatory role that isolated trees play in the regeneration of degraded areas that are not under the cover of invasive exotic plants is well recognized. In contrast, the influence of isolated trees in restoring sites invaded by exotic plants has hardly been studied. Such studies are needed because conditions that favor native tree regeneration under isolated trees, such as microclimate amelioration, increased nutrient levels, and facilitated dispersal, may also be favorable to certain species of exotic plants. Using transects, we studied species richness, abundance and resilience (as indicated by re-sprouting) of trees regenerating underneath the crowns of 15 isolated native trees that are emergent over a near continuous canopy of paper mulberry Broussonetia papyrifera in a degraded area of Mabira Forest, Uganda. Data collected beneath emergent tree crowns were matched by control data from the area immediately beyond the crowns. Native tree species abundance and richness were significantly higher beneath than beyond crowns; while the opposite was true of the density of B. papyrifera seedlings and saplings. Species richness was significantly higher beneath than beyond crowns for late-, but not early-succession trees. Polynomial regressions of species richness and abundance showed that B. papyrifera abundance increased significantly from stem bases to crown edges and leveled-off beyond crowns; while the density of native tree species was constant from stem bases to crown edges and decreased thereafter. Native tree species richness peaked at crown edges. The proportion of re-sprouts assigned to cutting of native tree species was significantly higher beyond than beneath crowns. We attribute the higher abundances and species richness of native species underneath crowns to both facilitation by isolated trees and the apparent shade-intolerance of B. papyrifera. Significantly higher levels of re-sprouting by native tree species could be an indication that the regeneration underneath crowns is less resilient to disturbance than that beyond, or that less resilient species occur beneath crowns. Overall, the results suggest that in sites invaded by mulberry, isolated trees have potential to accelerate recovery of native tree species while suppressing mulberry. Peaking of species richness at crown edges is not a commonly reported finding for isolated trees and needs to be further investigated.

Lessons learned from a long‐term irrigation experiment in a dry Scots pine forest: Impacts on traits and functioning

AbstractClimate change exposes ecosystems to strong and rapid changes in their environmental boundary conditions mainly due to the altered temperature and precipitation patterns. It is still poorly understood how fast interlinked ecosystem processes respond to altered environmental conditions, if these responses occur gradually or suddenly when thresholds are exceeded, and if the patterns of the responses will reach a stable state. We conducted an irrigation experiment in the Pfynwald, Switzerland from 2003–2018. A naturally dry Scots pine (Pinus sylvestris L.) forest was irrigated with amounts that doubled natural precipitation, thus releasing the forest stand from water limitation. The aim of this study was to provide a quantitative understanding on how different traits and functions of individual trees and the whole ecosystem responded to increased water availability, and how the patterns and magnitudes of these responses developed over time. We found that the response magnitude, the temporal trajectory of responses, and the length of initial lag period prior to significant response largely varied across traits. We detected rapid and stronger responses from aboveground tree traits (e.g., tree‐ring width, needle length, and crown transparency) compared to belowground tree traits (e.g., fine‐root biomass). The altered aboveground traits during the initial years of irrigation increased the water demand and trees adjusted by increasing root biomass during the later years of irrigation, resulting in an increased survival rate of Scots pine trees in irrigated plots. The irrigation also stimulated ecosystem‐level foliar decomposition rate, fungal fruit body biomass, and regeneration abundances of broadleaved tree species. However, irrigation did not promote the regeneration of Scots pine trees, which are reported to be vulnerable to extreme droughts. Our results provide extensive evidence that tree‐ and ecosystem‐level responses were pervasive across a number of traits on long‐term temporal scales. However, after reaching a peak, the magnitude of these responses either decreased or reached a new stable state, providing important insights into how resource alterations could change the system functioning and its boundary conditions.

Establishing a baseline to monitor future climate-change-effects on peripheral populations of Abies alba (Mill.) in central Apennines

Understanding tree species responses to climate change is crucial for preserving biodiversity especially in Southern Europe hot spots where Abies alba is widely spread. Three Apennine silver fir populations, Pigelleto (PIG), La Verna (LV) and Bocca Trabaria (BT), ensured gene flows in interglacial periods between the two phylogenetically different groups of northern and southern Apennines. These stands were analysed (nuclear and chloroplast SSRs) with the aim to establish a baseline for their future management in view of the expected changes. The three forests were tested for the Centre-Periphery Hypothesis (CPH) compared to forty-five Italian populations. At the same time, permanent areas were surveyed within LV and PIG on dominant (a) and dominated or natural regeneration (r) tree layers, and on age classes. In two consecutive years, spring cambial phenology activity was also weekly monitored on microcores, and critical phenology dates recorded. The stands matched CPH only partially, showing different phylogenetic history and their bridging between northern and southern groups of silver fir populations was confirmed. LV was distinct from PIG and BT. The within-population variance component was significantly high, and no narrow relatedness was observed between dominant and dominated/regeneration spatially closer trees, and genetic parameters were comparable in both layers at LV and PIG. In both stands, older age classes ensured natural regeneration. Cambium phenology was highly variable within populations, consistently to other Mediterranean conifers, and highly sensitive to local and year’s conditions and monitoring will improve population’s adaptive capacity detection. Shelterwood-system silvicultural treatments are suggested on small areas to drive the demographic and panmictic balance towards an uneven-aged more resilient structure, and iterated monitoring will help to adapt the forest management to the isotherm shift.

Debarking intensity of European bison in the Bieszczady Mountains in relation to forest habitat features

The damage to trees that is caused by ungulate species is a natural result of their presence in ecosystems. High densities of ungulates may have a negative effect on biodiversity and the regeneration and survival of trees. The aim of this study was to identify the factors that affect the probability of the occurrence of damage in forest stands as a result of the presence of European bison (Bison bonasus). We collected data on the presence of European bison in given locations in winter and spring of 2020; this data also concerned damage to trees, forest stand characteristics, and densities of other ungulates.European bison was the most important debarking agent. Within the home range of the European bison, 344 forest stands were damaged, which represented 43.5% of all stands. The most frequent damage was bark stripping, 35.9%. The most important factors in terms of bark damage were canopy cover, dominating tree species, dominating tree age, and distance to a feeder. More debarking occurred in stands with open canopies, and coniferous species were more likely to be damaged than broadleaved species. Frequency of damage in forest stands with dominating Norway spruce was higher than 0.5, whereas for forest stands with silver fir and Scots pine it was over 0.4. Other coniferous species also presented a relatively high proportion of damage (0.38). The results of our study indicate a need for rational damage-prevention measures in the ranges of other free-living wisent populations that live in managed forests.