Increasing Tree Size Research Articles

Precommercial thinning increases growth of overstory aspen and understory balsam fir in a boreal mixedwood stand

We applied four precommercial thinning (PCT) intensities (unthinned control, 2.5, 3.0, and 3.5m residual spacings) to aspen (Populus tremuloides Michx.) stems, while preserving understory balsam fir (Abies balsamea (L.) Mill.) in an even-aged stratified boreal mixedwood stand. We evaluated treatment influence on aspen and balsam fir growth, and regeneration dynamics over a 10-year period. Compared to the unthinned control, PCT increased relative diameter increment of aspen saplings by 66–85% and relative basal area increment by 234–326%. Increases were similar among PCT treatments. Understory balsam fir regeneration ⩾1m in height at time of thinning strongly benefited from PCT, with increases in height and crown width growth two to three times higher than in the control. The establishment of balsam fir regeneration, however, was not favored by PCT compared to the control. Our results show PCT increased tree size of individual aspen while promoting understory balsam fir growth in this type of stratified mixture. This approach should therefore be useful in limiting hardwood conversion in the boreal mixedwood forest at an early stage in stand development. Developing silvicultural approaches such as this one would be in line with the concept of ecosystem-based forest management.

Municipal Solid Waste Compost Benefits on Short Rotation Woody Crops

The effects of municipal solid waste compost (MSWC) on the productivity of potential short rotation woody crops (SRWC) were evaluated in two genetics x silviculture studies in Florida. In the 2002 study cottonwood Populus deltoides (PD), Eucalyptus grandis (EG), and E. amplifolia (EA) were planted in single rows with four cultural treatments: irrigation (I), MSWC, I+MSWC, and a control (no I and MSWC). The 2004 study extended the evaluation to PD, EG, and EA planted in a double row configuration and cypress Taxodium distichum (TD) progenies planted in single rows with three cultural treatments: I, I+MSWC, I + Fertilizer (F). MSWC and I each increased tree size in the 2002 study, although survival was affected by inconsistent I on this sandy site. In the 2004 study, I+MSWC also increased tree size (some PD clones were 4.6 m tall in 8 months) compared to I alone but had lower survival; however, PD was less vigorous in the I+F culture that resulted in the fastest growing EA and EG. MSWC appears to be an effective soil amendment for PD, EG, EA, and TD grown as SRWCs in Florida for mulchwood, energywood, pulpwood, windbreaks, lumber, and/or environmental services such as dendroremediation, mined land reclamation, and CO2 mitigation.

Uromycladium tepperianum (a gall-forming rust fungus) causes a sustained epidemic on the weed Acacia saligna in South Africa

Uromycladium tepperianum, a gall inducing rust fungus native to Australasia, was introduced into South Africa as a biological control agent in 1987. Incidence and severity of infection has been monitored from 1991 to 2010 at permanent sites. After release, disease incidence increased rapidly and it has stayed at (or just under) 100% on plants ≥5 cm stem diameter since. Incidence on smaller plants has decreased then increased rapidly following years of fires with mass regeneration from the soil-stored seed bank, or following years of high recruitment in the absence of fire. The maximum severity on mature trees is approximately 2000 galls per tree, with severity increasing exponentially with increasing tree size. Severity of infection on all tree size classes has shown a decreasing trend over the last 10 years, coinciding with a decrease in host tree density. It is concluded that infection is host density dependent.

Fire Reinforces Structure of Pondcypress (Taxodium distichum var. imbricarium) Domes in a Wetland Landscape

Fire periodically affects wetland forests, particularly in landscapes with extensive fire-prone uplands. Rare occurrence and difficulty of access have limited efforts to understand impacts of wildfires fires in wetlands. Following a 2009 wildfire, we measured tree mortality and structural changes in wetland forest patches. Centers of these circular landscape features experienced lower fire severity, although no continuous patch-size or edge effect was evident. Initial survival of the dominant tree, pondcypress (Taxodium distichum var. imbricarium), was high (>99%), but within one year of the fire approximately 23% of trees died. Delayed mortality was correlated with fire severity, but unrelated to other hypothesized factors such as patch size or edge distance. Tree diameter and soil elevation were important predictors of mortality, with smaller trees and those in areas with lower elevation more likely to die following severe fire. Depressional cypress forests typically exhibit increasing tree size towards their interiors, and differential mortality patterns were related to edge distance. These patterns result in the exaggeration of a dome-shaped profile. Our observations quantify roles of fire and hydrology in determining cypress mortality in these swamps, and imply the existence of feedbacks that maintain the characteristic shape of cypress domes.

California black oak responses to fire severity and native conifer encroachment in the Klamath Mountains

Fire exclusion in forests across the western United States has resulted in widespread vegetation change, often with notable increases in density and cover of fire-sensitive species. In California oak woodlands, encroachment by the more shade-tolerant native Douglas-fir (Pseudotsuga menziesii) is particularly common, and results in the piercing and eventual overtopping of crowns of shade-intolerant trees. We investigated canopy competition, paired tree ages, and post-fire effects in a recently burned, encroached California black oak (Quercus kelloggii) woodland. Pre-fire woodland overstory was heavily dominated by Douglas-fir, which commonly pierced and overtopped California black oak crowns. Trees that pierced overstory oak crowns were younger (mean difference=43.6years, p<0.001) than their paired oaks. Fire effects were variable, leaving some areas unchanged and others with complete above-ground stem mortality. Although above-ground stem-kill was often high for California black oak, the majority (82%) re-sprouted from the root collar. Logistic modeling revealed a significant relationship between California black oak mortality and neighboring Douglas-fir height and plot heat load index. The probability of California black oak mortality increased as neighboring Douglas-fir height increased and decreased with increasing heat load index. Probability of mortality for Douglas-fir decreased with increasing tree size, while the probability of California black oak top-kill was much higher than that for 20–30cmdbh Douglas-fir across a continuous measure of char height. Results indicate that competitive pressure from encroaching trees may compromise California black oak’s ability to survive fire while resilience of encroaching Douglas-fir improves with greater size. Caution should be taken when planning and implementing restoration activities in California black oak woodlands to minimize loss of compromised, remnant oaks while still achieving adequate removal of encroaching conifers.

Leaf area and light use efficiency patterns of Norway spruce under different thinning regimes and age classes

Silviculture focuses on establishing forest stand conditions that improve the stand increment. Knowledge about the efficiency of an individual tree is essential to be able to establish stand structures that increase tree resource use efficiency and stand level production. Efficiency is often expressed as stem growth per unit leaf area (leaf area efficiency), or per unit of light absorbed (light use efficiency). We tested the hypotheses that: (1) volume increment relates more closely with crown light absorption than leaf area, since one unit of leaf area can receive different amounts of light due to competition with neighboring trees and self-shading, (2) dominant trees use light more efficiently than suppressed trees and (3) thinning increases the efficiency of light use by residual trees, partially accounting for commonly observed increases in post-thinning growth. We investigated eight even-aged Norway spruce (Picea abies (L.) Karst.) stands at Bärnkopf, Austria, spanning three age classes (mature, immature and pole-stage) and two thinning regimes (thinned and unthinned). Individual leaf area was calculated with allometric equations and absorbed photosynthetically active radiation was estimated for each tree using the three-dimensional crown model Maestra. Absorbed photosynthetically active radiation was only a slightly better predictor of volume increment than leaf area. Light use efficiency increased with increasing tree size in all stands, supporting the second hypothesis. At a given tree size, trees from the unthinned plots were more efficient, however, due to generally larger tree sizes in the thinned stands, an average tree from the thinned treatment was superior (not congruent in all plots, thus only partly supporting the third hypothesis).

Effect of thinning, pruning and nitrogen fertiliser application on transpiration, photosynthesis and water-use efficiency in a young Eucalyptus nitens plantation

Interactions between thinning, pruning and fertiliser application in forestry are rarely examined, even though these treatments are often applied simultaneously in practice. Understanding these interactions can facilitate the design of regimes to best exploit such silvicultural interventions. The effects of these treatments on stand transpiration ( E), photosynthesis and water-use efficiency (AGB-WUE, defined as the above-ground biomass production per unit transpiration) were measured in a Eucalyptus nitens plantation in south-eastern Australia. Two levels of each treatment were applied at age 3.2 years and transpiration was measured between ages 5.3 and 6.3 years. Treatments were: unthinned, or thinned from ca. 900 to 300 trees ha −1; unpruned, or 50% of the live crown length pruned of the 300 largest-diameter potential sawlog crop trees ha −1; and nil, or 300 kg ha −1 N fertiliser. There were no significant treatment interactions on growth, E or AGB-WUE. Thinning and pruning reduced E by 45% and 12%, respectively, and fertiliser application increased E by 21%. Transpiration was linearly related to stand leaf area, which explained more than 90% of the variation across treatments. Thinning and pruning also increased AGB-WUE by 23% and 21%, respectively, while fertiliser application had no significant effect. There was a small increase in AGB-WUE with increasing tree size, such that in unthinned stands the largest 50% of trees were 7% more efficient than the smallest 50% of trees. Thinning increased AGB-WUE by increasing the light available to the lower canopy and pruning increased AGB-WUE by removing the least efficient lower canopy foliage and increasing the efficiency of the remaining foliage. All treatments also modified the hydraulic architecture of the trees by changing leaf area to sapwood area ratios and radial sap flux density profiles. This study shows how silvicultural treatments can be used to modify stand transpiration and AGB-WUE of E. nitens plantations, potentially reducing their drought susceptibility while making more efficient use of the sites water resources.

Biomass structure and allometry of Abies nephrolepis (Maxim) in Northeast China

Above- and below-ground tree biomass structure and allometric relationships of Abies nephrolepis (Maxim) were assessed in an old secondary forest dominated by A. nephrolepis, Pinus koraiensis, Quercus mongolica, Tilia amurensis, Fraxinus mandshurica and Acer mono in northeast China. Based on the breast-height diameter (D), a total of 21 sample trees were divided into three tree size classes: the small trees (1 cm ≤ D &lt; 10 cm), the medium trees (10 cm ≤ D &lt; 20 cm) and the big trees (D ≥ 20 cm). The greatest amount of live branch biomass was located in the middle and bottom layers of the crown, while the largest foliage biomass was found in the middle layer in each tree size category. The relative contribution of canopy biomass components (live branches and foliage) decreased with increasing tree size, while that of coarse root biomass remained almost constant. The relationship between above- and belowground biomass was linear. D and tree height (H) decreased with increasing competition intensity. The small trees had lower average crown ratio and higher average height-to-diameter ratio than those of the medium and big trees. The big trees had higher average stem to foliage mass ratio than those of the small and medium trees. Crown ratio, height-to-diameter ratio and stem to foliage mass ratio were not correlated with competition intensity in the same tree size class. Root to shoot mass ratio was almost constant among tree sizes. Allometric equations based on D gave higher correlations compared to those with other stem diameters: at tree base, at 30-cm height and at crown base.

Short-term effects of prescribed burning on radial growth of Douglas-fir trees in south central British Columbia

Radial increment of Douglas-fir (Pseudotsuga menziesii var. glauca (Beissn.) Franco) trees in uncut and partially cut and grazed and ungrazed dry cool Interior Douglas-fir forests near Isobel Lake in southern central British Columbia was measured for 2-year periods before and after prescribed burning in burned and unburned (control) areas. Parameters thought to influence the effects of prescribed burning on tree growth – characteristics of the tree and its immediate environment, adjacent surface and ladder fuels, and fire effects – were also measured. Burning caused a decrease in tree radial growth. The proportional change in radial tree growth was not related to degree of cutting or the presence of cattle grazing, but was negatively correlated with preburn radial growth, tree size, and also with some fire effect variables, particularly char height, suggesting that an increasing proportional decline in radial growth was associated with increasing tree size and with increasing fire severity. Soil nutrient (N, S, P, K, Mg or Ca) level was not a significant determinant of tree growth. The best prediction model could only explain 23% of the variation in the change in radial growth. Our results show that the effects of fire on Douglas-fir radial growth are complex and difficult to predict with the variables measured.

Individual biomass factors for beech, oak and pine in Slovakia: a comparative study in young naturally regenerated stands

Biomass conversion and expansion factors (BCEF) which convert tree stem volume to whole tree biomass and biomass allocation patterns in young trees were studied in order to estimate tree and stand biomass in naturally regenerated forests. European beech (Fagus sylvatica L.), Sessile oak (Quercus petraea (Mattuschka) Liebl.) and Scots pine (Pinus sylvestris L.) stands were compared. Seven forest stands of each species were chosen to cover their natural distribution in Slovakia. Species-specific BCEF are presented, generally showing a steep decrease in all species in the smallest trees, with the only exception in the case of branch BCEF in beech which grows with increasing tree size. The values of BCEF for all tree compartments stabilise in all species once trees reach about 60–70-mm diameter at base. As they grow larger, all species increase their allocation to stem and branches, while decreasing the relative growth of roots and foliage. There are, however, clear differences between species and also between broadleaves and conifers in biomass allocation. This research shows that species-specific coefficients must be used if we are to reduce uncertainties in estimates of carbon stock changes by afforestation and reforestation activities.

Quasi-tree mobility management for internet connectivity of mobile ad hoc networks

The location of mobile nodes must be managed to enable Internet connectivity of mobile ad hoc networks. Node mobility can be managed efficiently using a tree topology in which a mobile node registers with an Internet gateway along a tree path without using flooding. However, a node that loses connectivity to its parent has to find and connect to a new parent through a join-handshaking process. This tends to increase control overhead and impose some delay on on-going communication. Furthermore, the node may join its descendant because of the synchronization delay in updating topology change, creating a loop that significantly increases control overhead. We improve these problems by maintaining a quasi-tree topology in which a node maintains multiple parents. We also present a technique for detection and resolution of loops. The simulation results show that the quasi-tree mobility management approach far outperforms the traditional approaches and is highly robust against the significant increases in tree size and node mobility.

Spatial pattern of central African rainforests can be predicted from average tree size

When considering all trees irrespective of their species, natural tropical rain forests typically exhibit spatial patterns that range from random to regular. The regularity is often interpreted as a footprint of tree competition. Using 23 permanent sample plots totalling 61 ha in the rain forests of central Africa, we characterized their spatial patterns and modelled those that exhibited regularity by a Strauss point process. This Strauss process is obtained as a Markov point process whose interaction function is an exponential function of a competition index commonly used in forestry. The parameter of this Strauss process characterizes the strength of competition. The 23 plots in central Africa differed in tree density and basal area, and could be discriminated depending on the type of spatial patterns: plots having a large basal area with respect to their density had a non regular pattern, whereas those having a small basal area with respect to their density had a regular pattern. For those plots that exhibited regularity, average tree size could be used to predict the strength of competition. The parameter of the Strauss process was significantly related to the average size by a linear relationship, such that competition decreases as average tree size increases. This relationship extrapolated to a null value of the Strauss parameter when average tree size reaches 32 cm in diameter. This relationship between average tree size and spatial pattern is a testable feature for future studies on the relationship between competition and spatial pattern in natural forests.

Spatial pattern formation and relative importance of intra‐ and interspecific competition in codominant tree species, Podocarpus nagi and Neolitsea aciculata

AbstractSpatial patterns, their changes due to mortality, and intra‐ and interspecific competition of two codominant tree species, Podocarpus nagi and Neolitsea aciculata, were analyzed at Mt. Mikasa, Nara City, Japan. Podocarpus nagi has a higher shade tolerance but a narrower seed dispersal range than N. aciculata. We inferred the mechanisms of spatial pattern formation and coexistence of the two species. Podocarpus nagi and N. aciculata trees were clumped and showed a spatial repulsion from each other. Patches dominated by either P. nagi or N. aciculata were formed. Podocarpus nagi trees were less clumped with increasing tree size, although no significant change in spatial patterns due to mortality was detected. A patch formation of the P. nagi population seemed to be induced by the narrow seed dispersal range. On the other hand, N. aciculata trees were more clumped and more repulsive from P. nagi trees with increasing tree size. The distribution of N. aciculata trees shifted to more clumped than expected from the random mortality over the research period. Post‐dispersal mortality due to competitive exclusion by P. nagi affected the patch formation of the N. aciculata population. The relative importance of intraspecific competition to interspecific competition on the relative growth rate increased with increasing tree size. The shift corresponded to an increasing spatial repulsion between the two species. The patch formation of P. nagi population may create the spatial refuge of N. aciculata from P. nagi and may enable avoidance of interspecific competition and the coexistence of the two species.

Predicting mortality for five California conifers following wildfire

Fire injury was characterized and survival monitored for 5677 trees >25 cm DBH from five wildfires in California that occurred between 2000 and 2004. Logistic regression models for predicting the probability of mortality 5-years after fire were developed for incense cedar ( Calocedrus decurrens (Torr.) Florin), white fir ( Abies concolor (Gord. & Glend.) Lindl. ex Hildebr.), sugar pine ( Pinus lambertiana Douglas), Jeffrey pine ( P. jeffreyi Balf.), and ponderosa pine ( P. ponderosa C. Lawson). Differences in crown injury variables were also compared for Jeffrey and ponderosa pine. Most mortality (70–88% depending on species) occurred within 2 years post-wildfire and had stabilized by year 3. Crown length and crown volume injury variables predicted tree mortality equally well; however, the variables were not interchangeable. Crown injury and cambium kill rating was significant in predicting mortality in all models. DBH was only a significant predictor of mortality for white fir and the combined ponderosa and Jeffrey pine models developed from the McNally Fire; these models all predicted increasing mortality with increasing tree size. Red turpentine beetle ( Dendroctonus valens) was a significant predictor variable for sugar pine, ponderosa pine, and Jeffrey pine; ambrosia beetle ( Trypodendron and Gnathotrichus spp.) was a significant predictor variable for white fir. The mortality models and post-fire tree survival characteristics provide improved prediction of 5-year post-wildfire tree mortality for several California conifers. The models confirm the overall importance of crown injury in predicting post-fire mortality compared to other injury variables for all species. Additional variables such as cambium kill, bark beetles, and tree size improved model accuracies, but likely not enough to justify the added expense of data collection.

Separating the effects of tree size and meristem maturation on shoot development of grafted scions of red spruce (Picea rubens Sarg.)

In order to separate the effects of size and meristem maturation on age-related changes in shoot growth behaviour, a reciprocal grafting experiment was conducted involving juvenile (J), mid-age (MA) and old-growth (OG) red spruce (Picea rubens Sarg.) trees as both scion donors and rootstock. The effects of rootstock and scion age on vegetative growth, foliar morphology and reproductive development were assessed over 7 years after grafting. Vegetative growth potential declines with meristem maturation, but the high growth potential of J meristems on J rootstock cannot be expressed when J scions are grafted on MA and OG rootstock. Branch density decreases with meristem maturation. The tendency for high J branch density is expressed across all rootstock ages, but is minimally expressed on MA rootstock where elongation of terminal shoots is significantly greater than on OG rootstock. Both needle width and leaf mass area increase with meristem maturation and increasing tree size. Reproductive competence is mainly a function of meristem maturity, and rootstock had little effect on strobilus development, although the more fecund rootstocks did promote some flowering on J scions. Developmental decline in height growth does not appear to be a function of decreased meristem vigour, but reduced terminal long shoot elongation and decreased apical control in OG trees will reduce height growth.

Spatial distribution and biomass of root nodules in a naturally regenerated stand of Alnus hirsuta (Turcz.) var. sibirica

To estimate nodule biomass of Alnus hirsuta var. sibirica, an N2-fixing tree species, we examined the distribution pattern and size structure of nodules in a 17 to 18 year old stand naturally regenerated after disturbance by road construction in Japan. Nodules were harvested within 1 m from the outer edge of stems of plants with different sizes on four occasions from June to October. The diameter of the subtending root at the base of each nodule and nodule dry weight were measured in 20 cm increments outwards from the base of each stem. Horizontal distribution of nodules around each tree varied greatly among tree diameters at 1.3 m (dbh) within the even-aged stand. In particular, smaller individuals had a concentrated distribution of nodules close to the stem. Nodule abundance occurred further from the stems with increasing tree size. Nodule biomass within 1 m from the outer edge of individual stems increased with tree size ([nodule biomass] = 0.442 [dbh]2.01, R2 = 0.747, P < 0.05). By using the relationship, nodule biomasses were estimated to be 84.1 kg ha−1. These results suggest that it is necessary to take into account tree size and patterns of tree distribution in nodule biomass estimates.

Intraspecific host preferences of mopane moths (Imbrasia belina) in mopane (Colophospermum mopane) woodland

Colophospermum mopane trees are a common larval food plant of the mopane moth (Imbrasia belina),which commonly reaches outbreak proportions. Our study investigated factors determining host tree choice by ovipositing mopane moths within a single host species (C. mopane). Tree size was the primary determinant of oviposition at both the habitat (tall riverine-, medium height woodland- and short-shrub mopane) and individual tree scale, with an increase in the number of egg masses with increasing tree size (estimated by height and canopy volume). Preference for larger trees was only evident at the habitat scale, however, as individual trees were utilized as expected according to the availability of their canopy size class. More detailed tree characteristics, such as leaf size, shoot size, stem number and even leaf chemistry (protein:tannin ratio and total polyphenols) had no influence on host choice. Host choice was based on the most obvious measure of resource abundance, namely tree size, as expected for an outbreak species, since resource availability rather than nutritional quality is likely to be the primary determinant of larval survival.

Intraspecific Host Preferences of Mopane Moths (Imbrasia belina) in Mopane (Colophospermum mopane) Woodland

Colophospermum mopane trees are a common larval food plant of the mopane moth (Imbrasia belina), which commonly reaches outbreak proportions. Our study investigated factors determining host tree choice by ovipositing mopane moths within a single host species (C. mopane). Tree size was the primary determinant of oviposition at both the habitat (tall riverine-, medium height woodland- and short-shrub mopane) and individual tree scale, with an increase in the number of egg masses with increasing tree size (estimated by height and canopy volume). Preference for larger trees was only evident at the habitat scale, however, as individual trees were utilized as expected according to the availability of their canopy size class. More detailed tree characteristics, such as leaf size, shoot size, stem number and even leaf chemistry (protein:tannin ratio and total polyphenols) had no influence on host choice. Host choice was based on the most obvious measure of resource abundance, namely tree size, as expected for an outbreak species, since resource availability rather than nutritional quality is likely to be the primary determinant of larval survival.

Hydraulic adjustment of Scots pine across Europe

* The variability of branch-level hydraulic properties was assessed across 12 Scots pine populations covering a wide range of environmental conditions, including some of the southernmost populations of the species. The aims were to relate this variability to differences in climate, and to study the potential tradeoffs between traits. * Traits measured included wood density, radial growth, xylem anatomy, sapwood- and leaf-specific hydraulic conductivity (K(S) and K(L)), vulnerability to embolism, leaf-to-sapwood area ratio (A(L) : A(S)), needle carbon isotope discrimination (Delta13C) and nitrogen content, and specific leaf area. * Between-population variability was high for most of the hydraulic traits studied, but it was directly associated with climate dryness (defined as a combination of atmospheric moisture demand and availability) only for A(L) : A(S), K(L) and Delta13C. Shoot radial growth and A(L) : A(S) declined with stand development, which is consistent with a strategy to avoid exceedingly low water potentials as tree size increases. In addition, we did not find evidence at the intraspecific level of some associations between hydraulic traits that have been commonly reported across species. * The adjustment of Scots pine's hydraulic system to local climatic conditions occurred primarily through modifications of A(L) : A(S) and direct stomatal control, whereas intraspecific variation in vulnerability to embolism and leaf physiology appears to be limited.

Size‐dependent mortality in a Neotropical savanna tree: the role of height‐related adjustments in hydraulic architecture and carbon allocation

Size-related changes in hydraulic architecture, carbon allocation and gas exchange of Sclerolobium paniculatum (Leguminosae), a dominant tree species in Neotropical savannas of central Brazil (Cerrado), were investigated to assess their potential role in the dieback of tall individuals. Trees greater than approximately 6-m-tall exhibited more branch damage, larger numbers of dead individuals, higher wood density, greater leaf mass per area, lower leaf area to sapwood area ratio (LA/SA), lower stomatal conductance and lower net CO(2) assimilation than small trees. Stem-specific hydraulic conductivity decreased, while leaf-specific hydraulic conductivity remained nearly constant, with increasing tree size because of lower LA/SA in larger trees. Leaves were substantially more vulnerable to embolism than stems. Large trees had lower maximum leaf hydraulic conductance (K(leaf)) than small trees and all tree sizes exhibited lower K(leaf) at midday than at dawn. These size-related adjustments in hydraulic architecture and carbon allocation apparently incurred a large physiological cost: large trees received a lower return in carbon gain from their investment in stem and leaf biomass compared with small trees. Additionally, large trees may experience more severe water deficits in dry years due to lower capacity for buffering the effects of hydraulic path-length and soil water deficits.