Increasing Tree Density Research Articles

LATERAL BRANCH INDUCTION AT NURSERY WITH GROWTH REGULATORS IN ‘MAXI GALA’ APPLE TREES GRAFTED ON FOUR ROOTSTOCKS

ABSTRACT Apple production in Southern Brazil has been increasing along the past decade, and part of this was due to the introduction of more adapted dwarfing rootstocks and consequently increased tree density in the orchards. Looking for obtaining early beariness, the use of branched nursery trees is one of the most important steps. The objective of this experiment was to determine the effects of plant the growth regulators Benzyladenine (BA), Benzyladenine + Gibberellic acid4+7, Thidiazuron, and Cyclanilide + Ethephon on the induction of lateral branches of ‘Maxi Gala’ apple trees at nursery, grafted on the rootstocks G.202, G.213, M.9, and Marubakaido with M.9 interstem. The growth regulators Benzyladenine (BA), and Benzyladenine + Gibberellic acid4+7 are the most effective on improving tree’s architecture and on increasing the number of spurs, for all scion-rootstock combinations tested. Plant growth regulators at elevated doses strongly interrupt apical dominance and stimulate an elevated number of lateral branches with narrower crotch angles.

Stand-level windthrow patterns and long-term dynamics of surviving trees in natural secondary stands after a stand-replacing windthrow event

Abstract We examined typhoon windthrow patterns in stand-scale permanent plots within three natural forests and the long-term dynamics of surviving trees in two of these plots. The aim was to verify whether pre-disturbance composition and structure affected windthrow damage and stand recovery. The stands, which were in Hokkaido, the northernmost main island of Japan, differed in pre-disturbance composition (coniferous, mixed and broadleaved stands) and structure, and the basal area losses by the windthrow event were 81–93 per cent. Tree mortality was significantly related to tree size (diameter at breast height) and species. The windthrow patterns differed among the three stands; and, windthrow severity was affected by the pre-disturbance composition and structure. The mortality of trees that survived the windthrow event was ~60 per cent in the two plots. The surviving trees comprised a majority of the canopy layer in the secondary stands. The relative basal area of surviving trees decreased rapidly with increasing tree density in the stand initiation stage but differed between plots. Consequently, the pre-disturbance composition and structure influenced windthrow severity, stand recovery and secondary succession in the recovered stands.

Ommatissus lybicus Infestation in Relation to Spatial Characteristics of Date Palm Plantations in Oman

The agricultural ecosystem and its interaction with the outside environment plays a major role in the population of herbivores. The infestation of the Dubas bug, Ommatissus lybicus, has shown a spatial and temporal variation among different date palm plantations in Oman. This study focused on the relationship of infestation with date palm cultivation environments. The infestation and some selected environmental factors were evaluated in 20 locations for four consecutive infestation seasons over two years. Ordinary least squares (OLS) regression was used to identify the significant factors and the global relationship. Geographically weighted regression (GWR) was used to determine the spatial relationship. The results showed that GWR had better prediction than OLS. The model explained 61% of the infestation variation in the studied locations. The most significant coefficient was the tree planting pattern, the trees planted in uneven rows and columns (irregular pattern) had a positive effect; the infestation increased as the irregularity increased due to an increase in tree density. This reduced the interaction of harsh outside weather with the date palm plantation microclimate. The proportion of side growing area had a negative effect on insect population; as the percentage of side growing area increased as the infestation decreased, assuming the side growing crops hosted natural enemies. The study concluded that the variation of spatial and temporal infestation was primarily due to the variation of the cultural practices and spatial environment of the date palm plantations.

Caribou Conservation: Restoring Trees on Seismic Lines in Alberta, Canada

Seismic lines are narrow linear (~3–8 m wide) forest clearings that are used for petroleum exploration in Alberta’s boreal forest. Many seismic lines have experienced poor tree regeneration since initial disturbance, with most failures occurring in treed peatlands that are used by the threatened woodland caribou (Rangifer tarandus caribou). Extensive networks of seismic lines, which often reach densities of 40 km/km2, are thought to have contributed to declines in caribou. The reforestation of seismic lines is therefore a focus of conservation. Methods to reforest seismic lines are expensive (averaging $12,500 per km) with uncertainty of which seismic lines need which treatments, if any, resulting in inefficiencies in restoration actions. Here, we monitored the effectiveness of treatments on seismic lines as compared to untreated seismic lines and adjacent undisturbed reference stands for treed peatlands in northeast Alberta, Canada. Mechanical site preparation (mounding and ripping) increased tree density when compared to untreated lines, despite averaging 3.8-years since treatment (vs. 22 years since disturbance for untreated). Specifically, treated lines had, on average, 12,290 regenerating tree stems/ha, which is 1.6-times more than untreated lines (7680 stems/ha) and 1.5-times more than the adjacent undisturbed forest (8240 stems/ha). Using only mechanical site preparation, treated seismic lines consistently have more regenerating trees across all four ecosites, although the higher amounts of stems that were observed on treated poor fens are not significant when compared to untreated or adjacent undisturbed reference stands.

Landscaping of Residential Estates as a Mitigation Measure to Reduce Carbon Dioxide and Temperature Levels in Inner Ibadan City, Nigeria

This study assessed the spatial distribution of carbon dioxide emanation in selected residential estates and the impact of landscaping in reducing their levels in Ibadan metropolis. The study was carried out in high, medium and low commercial activity areas characterized by population density and traffic congestion within Ibadan city. CO<SUB>2</SUB> concentrations and temperature were measured at 4 hourly interval from 9am to 5pm for a period of seven consecutive days while numbers of trees/plants (biomass density) were counted, at 21 different points from seven areas each with high, medium and low commercial activities. Measurements were carried out with the aid of calibrated portable gas meters. The means CO<SUB>2</SUB> (ppm) were 542±95, 415±11 and 376±14 at 1.00 pm in the high, medium and low commercial activity areas respectively. CO<SUB>2</SUB> concentrations were generally higher than IPCC value, but highest in the afternoon. Temperature values were generally higher in the afternoon in high and medium commercial activity areas, but lower in the low commercial activity zones. Significantly, density of trees in low commercial activity areas (234.3±6.7) was higher compared to those in medium (22.8±0.5) and high (24.2±0.7) activity areas respectively. An inverse correlation was observed between CO<SUB>2</SUB> concentration and the density of trees (r=-0.456; p=0.038). The spatial distribution of CO<SUB>2</SUB> concentration in relation to landscaping revealed that CO<SUB>2</SUB> concentration reduces northward away from the urban core areas where there were fewer trees. The areas with low commercial activities had large numbers of trees while temperature and CO<SUB>2</SUB> flux were lower in these areas. Temperature and density of trees contribute significantly in explaining the CO<SUB>2</SUB> concentration (p=0.015). CO<SUB>2</SUB> concentrations and temperature were high in high commercial activities areas in Ibadan metropolis, few or no trees were observed in those areas. Increase in density of trees could be attributed to decrease in the CO<SUB>2</SUB> concentration. Hence, tree planting needs to be encouraged in the urban core of Ibadan metropolis to reduce air pollution.

Bird community responses to changes in vegetation caused by increasing large mammal populations in the Serengeti woodlands

Context The increase in density of large tree species, Vachellia robusta and V. tortilis, in the Serengeti Ecosystem of Tanzania has resulted in a decline of small tree species Senegalia senegal, V. hockii, Commiphora spp. This change has occurred since the late 1970s, a consequence of an increase in wildebeest following the extirpation of rinderpest, which reduced the dry grass fuel for fires, resulting in low fire frequencies. Change in tree species raises the question of whether there are indirect consequences for the avifauna that depend on the large trees for food and nesting. Aims To determine how an increase in large mammals could influence diversity and distribution of avifauna communities in the Serengeti ecosystem woodlands. Methods Data used to estimate changes in density of large and small trees were measured by Point Centre Quarter (PCQ). Bird species were recorded in 19 small-tree sites and 18 large-tree sites in the Serengeti National Park. Richness of bird guilds was calculated in the two habitat complexes (small and large trees), and the ‘rarefaction’ method was used to assess the difference in richness in habitats of the study area. Mean abundance for each species was calculated over the total number of sites for each habitat and compared using the Wilcoxon Rank Sum test to examine how the abundance of avifauna changes with each habitat type. Key results There was an increase in the density of large trees in some areas in which they have replaced the original small trees. Such changes have resulted in greater richness of hole nesters and bark feeders, and a greater abundance of large-hole nesters and gleaner bird species. Conclusions Because the increase in tree density was caused by an increase in large mammals, we conclude that this increasing mammal population is indirectly increasing richness and abundance of birds using the trees. Implications Understanding the influence of large mammal populations on bird distributions has important conservation implications because the Serengeti ecosystem is classified as an important, endemic bird area.

The effects of cultivar and training system on vegetative growth of mango (Mangifera indica) orchards in Far North Queensland

Understanding how and why canopy structural growth imposes productivity limitations is critical to managing high yielding, regular bearing mango (Mangifera indica) orchards. This study aimed to see how vegetative and reproductive growth responds to canopy management including bending. To investigate the relationship between shoot architecture, flowering and fruiting we measured structural, functional and temporal patterns of branching and flowering at the tree, scaffold and growth unit levels. Mango architectural analysis found strong varietal effects on vegetative growth, while increasing tree density led to increasing flowering across the orchard area. Single leader medium density trees had a significantly higher mean flower count (m-3 canopy volume tree-1) compared to the conventional training systems, and there was no significant difference between the densities within the conventional system. Limb bending of a parent in the single leader training systems led to an increase in the length of children growth units (bent = 16.07 cm, unbent = 12.05 cm). This paper outlines briefly the techniques used to collect architecture data and summarises the first year of vegetative and reproductive growth in each of the management scenarios.

Trees and Crime in Bogota, Colombia: Is the link an ecosystem disservice or service?

There is a perception that increased forest cover and density in urban contexts is associated with increased criminality. But, this complex relationship between urban vegetation, crime, ecosystem services (ES) and disservices (ED), has been little studied in low and middle income countries. This study’s aim was to statistically determine if specific structural and socioeconomic characteristics of urban treescapes were related to crime occurrence, considered an ED, in a major Latin American city. We used spatial and statistical analyses of a public tree inventory, homicide occurrence, and available geospatial data to analyze if urban treescape, demographic, and socioeconomic variables were related to the incidence of homicides in Neotropical Bogota, Colombia. First, a generalized linear model indicated that fewer homicides occurred in public treescapes with taller trees and higher tree density. In contrast, the amount of overall green space and average tree basal area were not significant predictors of homicide occurrence. Second, a geographically weighted regression model indicated that the inclusion of tree basal area rendered tree height insignificant, and that higher basal areas were associated with fewer homicides. Thus, both models indicated that increased tree density and size were actually associated with lower homicide occurrences. The amount of public green areas was however, not significantly related to homicide occurrence. Results indicate that in general, Bogota´s treescapes provided overall net ES as opposed to ED in terms of crime. Findings could be used to develop land use policies and management practices that increase the overall provision and demand for ES from urban forests.

Remarkable increase in tree density and fuelwood production in the croplands of northern Nigeria

This paper examines trends in woody vegetation and tree species composition in the Sudan zone of West Africa, using the Kano region of northern Nigeria as a case study. The study compares data on tree density, fuelwood production and tree species composition from fieldwork conducted in 1981 and 2016, as well as on several dates of aerial and satellite images since the 1960s. Recent satellite-based reports of greening in arid West Africa as a response to recovery from droughts in the 1970s and 1980s, are examined to explain the observed trends. Tree densities in the goods and services hinterland of Kano city have at least doubled since the drought period, and no decline, rather a slight increase was observed during the drought decades. This contradicts reports of woody vegetation trends from the more arid and less densely populated Sahel zone, which generally observed decline during the drought years and current recovery to pre-drought levels. The remarkable increase in tree numbers in Kano region is accompanied by increasing fuelwood production as suggested by greater concentration by farmers on tree species highly valued for fuel, at the expense of other traditional species. The main driver of such trends is thought to be rapid population growth in the context of a remaining dependence on wood as fuel by both urban and rural populations in Nigeria. Climate is thought to play only a minor role in explaining the trends. These observations confirm trends in fuelwood production observed in Kano region more than three decades previously, and indicate a somewhat Boserupian response to Malthusian-type pressures on available resources. Nevertheless, a return to rainfall levels of the drought decades combined with climate change predictions of increasing temperatures in dryland Africa, may have serious consequences for rural households if energy sources are not diversified.

Tree recruitment at the treeline across the Continental Divide in the Northern Rocky Mountains, USA: the role of spring snow and autumn climate

ABSTRACTBackground: Topoclimate can influence tree establishment within treeline ecotones. Yet much less is known about how regional topography, such as the Continental Divide, Rocky Mountains, mediates the role of climate in governing treeline dynamics.Aims: To utilise the Continental Divide to test whether contrasts in growing-season moisture regimes to the west (summer-dry) and east (summer-wet) impact the spatio-temporal patterns of tree establishment and rates of treeline advance in the Northern Rocky Mountains.Methods: We sampled trees at sites on north- and south-facing slopes, west and east of the Continental Divide. We used dendroecological techniques to reconstruct patterns of tree establishment. Age-structure data were quantitatively compared with climate to evaluate possible mechanistic linkages.Results: Across all sites, 96% of trees established after 1950. There was a treeline advance (range = 39–140 m) accompanied by increases in tree density. Significantly more trees established during wet springs on both sides of the Divide.Conclusions: Overall, snow duration in spring and autumn temperatures appear to influence patterns of tree recruitment at the treeline. Continued warming will likely amplify the role of autumn climate in regulating tree establishment throughout treeline ecotones in the Northern Rocky Mountains, particularly west of the Divide where summer-dry conditions persist.

Effects of stand density on understory species diversity and soil physicochemical properties of Pinus massoniana plantation

We analyzed understory species diversity, soil physicochemical traits and their relationships in the 25-year-old non-commercial Pinus massoniana plantations with five different stand densities, i.e., 1057, 1136, 1231, 1383 and 1515 trees·hm-2, in Wenfeng Mountain, Xinjin District, Sichuan Province, China. The results showed that a total of 110 species were found, belonging to 57 families and 98 genera. With the increase of tree density, the understory species showed a succession pattern from positive to moderate to shady. Different densities had significant effects on the contents of total potassium and organic matter in the soils. With the increase ofdensity, the contents of organic matter and total potassium in understory vegetation first increased and then decreased. The trends of the relationship between both diversity and soil physiochemical characteristics and tree density were similar. Both of them increased with the increase of density, with the maximum value presented at the density of 1136 trees·hm-2. The concentrations of total phosphorus, available potassium, total potassium and total nitrogen was closely related to plant diversity index. The results suggested that the density at 1136 trees·hm-2 would be more beneficial to improve the stability of species diversity and soil fertility of P. massoniana non-commercial plantations in Wenfeng Mountain.

Photosynthetic responses of understory savanna plants: Implications for plant persistence in savannas under tree encroachment

Savannas are ecosystems where plants are expected to have leaf-level adaptations conferring tolerance to high irradiances, which characterizes this type of open canopy vegetation. The neotropical savannas of Brazil (Cerrado) harbour a large diversity of heliophilous herbaceous species, which are threatened by the current invasion of those open canopy habitats by forest trees, increasing tree density and canopy cover, thereby strongly reducing light availability. In this study, we measured leaf pigment concentrations, specific leaf area and light response curves of photosynthesis to determine whether herbaceous species of open savanna habitats were less tolerant to shade than the ones that were more characteristic of forested savanna. Relative to species of forested savannas, herbaceous species of open savannas had heavier leaves with higher concentration of carotenoids. They also achieved higher photosynthetic rates, reaching light compensation and saturation at higher irradiances. Based on measurements of light compensation points and of prevailing irradiances in forested savannas, leaves of most herbaceous species of more open savannas would be strongly light-limited in sites with a dense woody layer. In summary, we provide evidence that forest tree encroachment of savannas would select for leaf trait combinations in the understory vegetation that would favor shade tolerance and, depending on the degree of leaf acclimatization to shade of individual species, could strongly constrain persistence of the current understory vegetation.

Mapping Tree Density in Forests of the Southwestern USA Using Landsat 8 Data

The increase of tree density in forests of the American Southwest promotes extreme fire events, understory biodiversity losses, and degraded habitat conditions for many wildlife species. To ameliorate these changes, managers and scientists have begun planning treatments aimed at reducing fuels and increasing understory biodiversity. However, spatial variability in tree density across the landscape is not well-characterized, and if better known, could greatly influence planning efforts. We used reflectance values from individual Landsat 8 bands (bands 2, 3, 4, 5, 6, and 7) and calculated vegetation indices (difference vegetation index, simple ratios, and normalized vegetation indices) to estimate tree density in an area planned for treatment in the Jemez Mountains, New Mexico, characterized by multiple vegetation types and a complex topography. Because different vegetation types have different spectral signatures, we derived models with multiple predictor variables for each vegetation type, rather than using a single model for the entire project area, and compared the model-derived values to values collected from on-the-ground transects. Among conifer-dominated areas (73% of the project area), the best models (as determined by corrected Akaike Information Criteria (AICc)) included Landsat bands 2, 3, 4, and 7 along with simple ratios, normalized vegetation indices, and the difference vegetation index (R2 values for ponderosa: 0.47, piñon-juniper: 0.52, and spruce-fir: 0.66). On the other hand, in aspen-dominated areas (9% of the project area), the best model included individual bands 4 and 2, simple ratio, and normalized vegetation index (R2 value: 0.97). Most areas dominated by ponderosa, pinyon-juniper, or spruce-fir had more than 100 trees per hectare. About 54% of the study area has medium to high density of trees (100–1000 trees/hectare), and a small fraction (4.5%) of the area has very high density (&gt;1000 trees/hectare). Our results provide a better understanding of tree density for identifying areas in need of treatment and planning for more effective treatment. Our analysis also provides an integrated method of estimating tree density across complex landscapes that could be useful for further restoration planning.

Competition amplifies drought stress in forests across broad climatic and compositional gradients

AbstractForests around the world are experiencing increasingly severe droughts and elevated competitive intensity due to increased tree density. However, the influence of interactions between drought and competition on forest growth remains poorly understood. Using a unique dataset of stand‐scale dendrochronology sampled from 6405 trees, we quantified how annual growth of entire tree populations responds to drought and competition in eight, long‐term (multi‐decadal), experiments with replicated levels of density (e.g., competitive intensity) arrayed across a broad climatic and compositional gradient. Forest growth (cumulative individual tree growth within a stand) declined during drought, especially during more severe drought in drier climates. Forest growth declines were exacerbated by high density at all sites but one, particularly during periods of more severe drought. Surprisingly, the influence of forest density was persistent overall, but these density impacts were greater in the humid sites than in more arid sites. Significant density impacts occurred during periods of more extreme drought, and during warmer temperatures in the semi‐arid sites but during periods of cooler temperatures in the humid sites. Because competition has a consistent influence over growth response to drought, maintaining forests at lower density may enhance resilience to drought in all climates.

The effect of the shortage of gravel sediment in midstream river channels on riparian vegetation cover

AbstractThe vegetation cover in the steep, gravelly reaches of rivers was originally low. However, significant vegetation colonization can currently be observed in these riparian areas, and understanding the cause of this colonization is important for management. The objective of this study was to assess the effect of sediment deposition and erosion on vegetation colonization in gravel bed rivers. The delay in colonization by herbs and trees after sediment deposition or erosion was investigated using aerial photos of 6 Japanese rivers. A field study was conducted before and after a large flood at depositional and erosional locations. The colonization of vegetation after flushing was substantially delayed at sites where gravels were deposited compared with that at erosional sites, and it was faster in sandy reaches compared with gravelly reaches. Little tree colonization was observed at the depositional sites of gravelly sediments, whereas at erosional sites, new shoots sprouted from the collapsed live trees in the following spring, achieving a rapid increase in tree density. The nutrient and moisture contents of the sediment were significantly higher at the erosional sites. Gravels are deposited after washing and being segregated from fine sediment during floods. This coarse‐sediment layer is low in moisture and nutrients compared with the erosional sites, at which the underlying sediments are exposed by flooding. However, moisture and nutrients are the primary requirements for vegetation colonization. Therefore, the reduction in gravelly sediments due to gravel mining, river regulation, and modification of river basins can have a substantial effect on vegetation colonization.

Sward structural characteristics and herbage accumulation of Piatã palisade grass (Brachiaria brizantha) in a crop–livestock–forest integration area

The aim of this study was to evaluate the effects of shading on structural characteristics and herbage accumulation of palisade grass (Brachiaria brizantha cv. Piatã), in a crop–livestock–forest integration area. Three shade regimes were evaluated: no shade (NS), moderate shade (MS, 338 trees ha–1), and intense shade (IS, 714 trees ha–1). The effects of shade regime on soil-water content and nitrogen nutrition index were also evaluated. Grazing management was established based on sward light interception targets (95% LI pre-gazing). The MS and IS regimes were divided into two shade strips (central and lateral) in order to describe the variation in light availability within the paddocks. Two methods for taking the reference readings of LI were tested in IS paddocks: LI reading inside (under the tree canopy) and outside (under full sunlight) the experimental area. Increased tree density reduced photosynthetically active radiation on lateral and central shade strips by 37% and 12% for MS, and 52% and 50% for IS, respectively. For NS, MS, IS (outside) and IS (inside), grazing intervals were 23, 26, 28 and 35 days, pre-grazing heights corresponded to 33, 35, 43 and 52 cm, and pre-grazing herbage mass to 5.37, 4.44, 2.96 and 3.23 t ha–1, respectively. Leaf percentage remained relatively stable across shade regimes, but stem percentage was greater and dead material percentage was smaller for IS than for NS and MS. Soil water content was lower near the trees, especially during the dry season. Relative to NS, herbage accumulation decreased by 39% and 68% for MS and IS, respectively. Under natural shade, small variations in light availability affect sward structure and herbage production. The use of the 95% LI target developed under full sunlight conditions is not suitable for use under trees, emphasising the need to generate specific grazing-management targets for pastures cultivated under trees.

Can low‐severity fire reverse compositional change in montane forests of the Sierra Nevada, California, USA?

AbstractThroughout the Sierra Nevada, nearly a century of fire suppression has altered the tree species composition, forest structure, and fire regimes that were previously characteristic of montane forests. Species composition is fundamentally important because species differ in their tolerances to fire and environmental stressors, and these differences dictate future forest structure and influence fire regime attributes. In some lower montane stands, shade‐tolerant, fire‐sensitive species have driven a threefold increase in tree density that may intensify the risk of high‐severity fire. In upper montane forests, which were historically characterized by longer fire return intervals, the effects of fire exclusion are both less apparent and less studied. Although land managers have been reintroducing fire to lower and upper montane forests for &gt;4 decades, the potentially restorative effects of these actions on species composition remain largely unassessed. We used tree diameter and species data from 51 recently burned and 46 unburned plots located throughout lower and upper montane forests in Yosemite National Park and Sequoia &amp; Kings Canyon National Parks to examine the effects of low‐ to moderate‐severity (hereafter, lower‐severity) fire on the demography of seven prevalent tree species. The density of Abies concolor &lt;30 cm diameter at breast height (dbh) was significantly lower in burned plots than unburned plots; densities of A. concolor 30–45 cm dbh, A. magnifica &lt;30 cm dbh, and Calocedrus decurrens &lt;15 cm dbh were lower in burned plots than unburned plots at a marginal level of significance. These diameter thresholds represent the maximum size at which each species is likely to experience significant mortality from lower‐severity fire. We overlaid these thresholds on historical and contemporary diameter distributions to show that: (1) lower‐severity fire has reduced mean tree density to historical levels for A. concolor but not for C. decurrens, and (2) variability in tree density among plots that burned at lower severity exceeded the range of tree densities reported in historical data sets. High proportions of shade‐tolerant species in some postfire stands may increase the prevalence of shade‐tolerant species in the future, a potential concern for managers who seek to minimize ladder fuels and promote forest structure that is less prone to high‐severity fire.

Slow carbon and nutrient accumulation in trees established following fire exclusion in the southwestern United States.

Increasing tree density that followed fire exclusion after the 1880s in the southwestern United States may have also altered nutrient cycles and led to a carbon (C) sink that constitutes a significant component of the U.S. C budget. Yet, empirical data quantifying century-scale changes in C or nutrients due to fire exclusion are rare. We used tree-ring reconstructions of stand structure from five ponderosa pine-dominated sites from across northern Arizona to compare live tree C, nitrogen (N), and phosphorus (P) storage between the 1880s and 1990s. Live tree biomass in the 1990s contained up to three times more C, N, and P than in 1880s. However, the increase in C storage was smaller than values used in recent U.S. C budgets. Furthermore, trees that had established prior to the 1880s accounted for a large fraction (28-66%) of the C, N, and P stored in contemporary stands. Overall, our century-scale analysis revealed that forests of the 1880s were on a trajectory to accumulate C and nutrients in trees even in the absence of fire exclusion, either because growing conditions became more favorable after the 1880s or because forests in the 1880s included age or size cohorts poised for accelerated growth. These results may lead to a reduction in the C sink attributed to fire exclusion, and they refine our understanding of reference conditions for restoration management of fire-prone forests.

Sixty‐year post‐windthrow study of stand dynamics in two natural forests differing in pre‐disturbance composition

AbstractWe examined the dynamics of stand structure and composition over 60 years in two natural secondary forest plots in central Hokkaido, Japan, that had been severely disturbed by a stand‐replacing windthrow in 1954. We determined temporal trends in tree density, species richness, species diversity, successional composition, and stand developmental stage. One of the plots contained a coniferous stand prior to the disturbance; the second plot contained a mixed stand. Tree density and species richness increased after the windthrow, and peaked in both stands in 1991, 37 years after the windthrow. Based on the dynamics of tree density and species richness, the stand development phase of both plots remained within the stand initiation stage until 1991, and then progressed to the stem exclusion stage by 2014, 60 years after the windthrow. Based on patterns of increasing tree density by species in both plots, vegetative regeneration was presumed to have contributed abundantly to the recovery of the stand after the windthrow. Species diversity increased after the windthrow as species richness increased in both stands; diversities peaked 23 or 32 years after the windthrow and declined slightly thereafter. Although the successional composition of the pre‐disturbance coniferous stand regressed to an early stage under the influence of the windthrow, the relative importance of late‐successional species approached the pre‐disturbance value as the plot recovered. In contrast, the successional composition of the mixed conifer/hardwood plot was unaffected by the windthrow, but gradually changed to an early stage over several decades following the windthrow. The difference in successional composition between plots was likely a result of differences in pre‐disturbance stand conditions between stands. Our 60‐year permanent plot study determined stand and population dynamics, the duration of the stand initiation stage, and the interrelationships between diversity and species richness. Long‐term permanent plot studies contribute crucial data for the interpretation of forest dynamics following disturbance.

'Jones hybrid' hickory: a case study in Carya curation.

‘Jones Hybrid’ hickory is an accession in the National Collection of Genetic Resources for Pecans and Hickories for which information about origin, identity and characteristics is very incomplete. Phenotypic and genetic profiles, when examined in the context of historic literature, provide evidence that the accession in question is ‘Siers’ a cultivar of Carya × laneyi (an interspecific hybrid between C. ovata and C. cordiformis). The accession has traits that make it interesting in the pecan breeding program, with potential for both rootstock and scion development. The tall, slender tree form of ‘Jones Hybrid’ is a trait that could be valuable in commercial pecan cultivars, allowing increased tree densities and reducing the need for expensive hedging operations. Tree size reduction is a goal to be pursued in scion selection and rootstock development, with each goal requiring assessment of reproductive potential of the accession.