Oak/Douglas-fir/sheep: A three-crop silvopastoral system

A small scale agroforestry study which was begun in 1952 was revisited in 1985 to evaluate the long-term influence of site preparation and grazing on tree growth and survival in a Douglas-fir (Pseudotsuga menziesii)-white oak (Quercus garryana)-sheep silvopastoral system. In 1952–1953, two-year-old Douglas-fir seedlings were planted at the rate of 2500 trees/ha under three levels of site preparation: (1) no treatment, (2) oak thinned by 50%, and (3) oak clearcut. From 1954 to 1960, yearling ewes grazed one-half of each of the three thinning treatments for 3–4 weeks each spring. The conifers have been undisturbed since grazing was discontinued in 1960. Survival of planted conifers averaged 64% in 1985 and did not vary among either site preparation or grazing treatments. From 1964 to 1985, trees on the thinned and clearcut plantations grew an average of 1060 and 990 cm in height, respectively, compared to 900 cm on the unthinned plantation. Diameter at breast height (dbh) averaged 3.8 and 5.6 cm greater on thinned or clearcut plantations, respectively, than on the unthinned control by 1985 (p < 0.05). Conifers on grazed plantations had increased height and dbh growth during the first 12 years of plantation life, averaging 63 cm taller (p < 0.10) and 0.7 cm greater in dbh (p < 0.05) than the ungrazed plots by 1964. By 1985 the difference in height (122 cm) and dbh (1.0 cm) between grazed and ungrazed plantations was not statistically significant. These data suggest that although site preparation can positively influence conifer growth, total clearfelling is no better than thinning oaks. Furthermore, proper grazing can increase height and dbh growth of the conifers during and immediately after the grazing years.     

Oak/Douglas-fir/sheep: A three-crop silvopastoral system

A small scale agroforestry study which was begun in 1952 was revisited in 1985 to evaluate the long-term influence of site preparation and grazing on tree growth and survival in a Douglas-fir (Pseudotsuga menziesii)-white oak (Quercus garryana)-sheep silvopastoral system. In 1952–1953, two-year-old Douglas-fir seedlings were planted at the rate of 2500 trees/ha under three levels of site preparation: (1) no treatment, (2) oak thinned by 50%, and (3) oak clearcut. From 1954 to 1960, yearling ewes grazed one-half of each of the three thinning treatments for 3–4 weeks each spring. The conifers have been undisturbed since grazing was discontinued in 1960. Survival of planted conifers averaged 64% in 1985 and did not vary among either site preparation or grazing treatments. From 1964 to 1985, trees on the thinned and clearcut plantations grew an average of 1060 and 990 cm in height, respectively, compared to 900 cm on the unthinned plantation. Diameter at breast height (dbh) averaged 3.8 and 5.6 cm greater on thinned or clearcut plantations, respectively, than on the unthinned control by 1985 (p < 0.05). Conifers on grazed plantations had increased height and dbh growth during the first 12 years of plantation life, averaging 63 cm taller (p < 0.10) and 0.7 cm greater in dbh (p < 0.05) than the ungrazed plots by 1964. By 1985 the difference in height (122 cm) and dbh (1.0 cm) between grazed and ungrazed plantations was not statistically significant. These data suggest that although site preparation can positively influence conifer growth, total clearfelling is no better than thinning oaks. Furthermore, proper grazing can increase height and dbh growth of the conifers during and immediately after the grazing years.     

Development of beeted seedlings in three Picea abies (L) karst. stands

Development in height, diameter and basal area was studied for beeted and for originally planted Norway spruce (Picea abies (L.) Karst.) seedlings. The study was carried out as a survey in three unthinned stands in southern Sweden. Beeted seedlings were separated from those originally planted by differences observed in the number of annual rings at stump height. In all stands height and diameter were smaller and growth rates in height and basal area were lower for beeted than for originally planted seedlings. The lower growth rates for beeted seedlings may be explained as effects of inter‐tree competition. The oldest stand was thinned at the time of inventory. 40% of the thinned trees were beeted representing 18% of the thinned volume.     

Influence of conventional and chemical thinning on stand structure and diversity of plant and mammal communities in young lodgepole pine forest

Silvicultural practices that provide a wide variety of vegetative composition and structure (habitats) in young stands should help manage for biological diversity across forested landscapes. This study was designed to test the hypotheses that: (i) abundance and diversity of stand structure attributes (species diversity and structural diversity of herb, shrub and tree layers) and forest floor small mammal communities, and (ii) relative habitat use by large herbivores, will increase from unthinned to conventionally thinned to chemically thinned stands of young lodgepole pine (Pinus contorta) forest. Replicate study areas were located near Summerland, Kelowna and Williams Lake in south-central British Columbia, Canada. Each study area had three treatments: a conventionally thinned, a chemically thinned and an unthinned stand. Pre-commercial thinning was conducted in 1993. Coniferous stand structure and understory vegetation were measured prior to thinning in 1993 and 5 years later in 1998. Small mammal populations were sampled intensively from 1993 to 1998. Relative habitat use by large herbivores was sampled in 1998.

Our results indicate that chemical thinning of young lodgepole pine stands produced an aggregated pattern of crop trees compared with stands subjected to conventional thinning. Diameter growth of crop trees in the chemically thinned stands was similar to that in the conventionally thinned, but also to that in unthinned stands. Although horizontal stratification (aggregates of trees) was enhanced, vertical stratification (structural diversity of vegetation) was less in the chemically than conventionally thinned stands. Abundance and diversity of understory vegetation and small mammal communities were generally unaffected by stand thinning in these particular installations. Relative habitat use by mule deer (Odocoileus hemionus) occurred in a gradient from highest in the conventionally thinned stand to lowest in the unthinned stand. Habitat use by snowshoe hares (Lepus americanus) tended to have the opposite trend. Moose (Alces alces) exhibited no difference in habitat use among stands. Thus, although there were few differences among treatment stands, chemical thinning could be used to develop an aggregated pattern of crop trees in pre-commercially thinned stands to maintain habitat for herbivores such as snowshoe hares and mule deer. Understory plant and forest floor small mammal communities would be maintained in these stands as well.     

Should unthinned oak stands of advanced age (≥ 60 yr) be thinned?

ABSTRACT

Oaks (Quercus sp.) account for nearly one-third of the sawtimber harvest in Wisconsin. As trees age, their ability to respond to thinning is reduced; therefore, the objective of this study was to determine whether thinning previously unthinned oak stands of advanced age (≥ 60 yr) would achieve biological, financial, and operational objectives. During 2014, we conducted an inventory of 25 oak stands in northern Wisconsin. Fifteen received their first thinning 8–14 yr ago at ages 60–78 yr and 10 had never been thinned. Stand-level volume growth, logging costs, and net present values were estimated for each site. The age and site index of the thinned and unthinned sites were not significantly different (p > .10). Thinned and unthinned sites grew comparable net volumes per ha (5.09 and 5.90 m³, respectively); however, because this growth was concentrated on fewer trees, the trees on the thinned sites responded vigorously to thinning. As age at first thinning increased, growth response was reduced (p = .067); however, thinning still increased the growth of residual trees. Thinned sites had higher net present values compared to unthinned sites (p < .01) and logging costs were 10.6% lower (p = 0.06). Overall, for stands between 60 and 78 years old, thinning was beneficial financially, operationally, and biologically.     

Midcanopy growth following thinning in young-growth conifer forests on the Olympic Peninsula western Washington

Midcanopy layers are essential structures in “old-growth” forests on the Olympic Peninsula. Little is known about which stand and tree factors influence the ability of midcanopy trees in young-growth forests to respond to release; however, this information is important to managers interested in accelerating development of late-successional structural characteristics. We examined basal area growth response of midcanopy trees following variable-density thinning in an effort to determine the effect of thinning and local environment on the release of western hemlock (Tsuga heterophylla (Raf.) Sarg.) and western redcedar (Thuja plicata ex. D. Don) on the Olympic Peninsula in western Washington. Release was measured as the difference between average annual basal area growth over the 5-year prior to thinning and the 3-to-6 year period following thinning. Results indicate that while growth rates were similar prior to thinning (5.4 cm² year⁻¹in both thinned and unthinned patches) midcanopy trees retained in a uniformly thinned matrix grew significantly more (8.0 cm² year⁻¹) than those in unthinned patches (5.4 cm² year⁻¹) for western hemlock and for western redcedar. Crown fullness and crown crowding affected the release of western hemlock in the thinned matrix. Initial tree size, relative age, local crowding and measures of crown size and vigor affected the release of western redcedar in the thinned matrix. Our results indicate that midcanopy western hemlock and western redcedar retain the ability to respond rapidly with increased growth when overstory competition is reduced and the magnitude of response is related to neighborhood variables (intracohort competition, overstory competition, and tree vigor), thus suggest that variable-density thinning can be an effective tool to create variability in the growth of midcanopy trees in young-growth stands. We expect that this rapid response will produce even greater variability over time.     

Effects of thinning intensity on species diversity and timber production in a conifer (Cryptomeria japonica) plantation in Japan

In conifer plantations, enhancement of species diversity has become an important management goal. Although thinning is a useful method to enhance diversity, determining optimum thinning intensities may be rather complicated because of potential trade-offs among a broad array of management goals (e.g., recovery of biodiversity, increasing individual tree sizes, increasing net primary production, saving management costs). To evaluate the optimum thinning intensity by analyzing these relationships, we conducted a thinning experiment with three different thinning intensities—unthinned, 33% thinned, and 67% thinned—in a Cryptomeria japonica plantation in 2003, and investigated the number, diameter at breast height (DBH), and diversity of hardwoods (height?>?1.5?m) in 2008, and the growth of conifers over five?years. In hardwoods, the number of individuals, number of species, mean DBH, and total basal area were greatest in the 67% thinned treatment, irrespective of successional status. However, Shannon’s diversity index did not differ among the three treatments due to a disproportionate increase with thinning intensity in the abundance of a mid-successional species, Cornus controversa. Diameter growth of conifers was also highest in the 67% thinned and lowest in the unthinned treatment, whereas the reverse was true for stand volume increment. These results suggest that intensive thinning is a reliable method to convert conifer plantations into conifer–hardwood mixed forests at canopy level much more quickly and consistently than weak thinning, although primary production is to some extent reduced. If forest managers prefer sustainable timber production of conifers rather than full recovery of diversity, weak thinning may be suitable.     

Effects of thinning on plant species diversity and composition of understory herbs in a larch plantation

The effects of thinning on plant species diversity and composition of understory herbs in a larch plantation were investigated. The relationships between plant species diversity and composition of understory herbs and light conditions were established. Twenty-five 1 m × 1 m plots and fifteen 13 m × 1 m transects were set up in unthinned and thinned stands, respectively. All the transects in the thinned stands were set across the thinned rows and unthinned rows, and each of them was divided into nine 1 m × 1 m sub-plots. The herb diversity and light conditions were observed in each plot and sub-plot. The results show that there was a significant difference in herb diversity between the thinned and unthinned stands. All biodiversity indices except for evenness index in the thinned stand were higher than those of the unthinned stand, i.e., the herb diversity increased after thinning. According to the changes in herb densities and whether one species could be found in a stand or not before and after thinning, all herb species were classed into three types: positive, neutral and negative species, which referred to a species newly appeared and having an obviously increased density after thinning, with no obvious changes in its appearance and density after thinning, and disappeared and having an obviously decreased density after thinning, respectively. Many new species were found in the thinned stand like Corydalis pallida, Prenanthes tatarinowii, Vicia unijuga and Sonchus brachyotus etc. However, most species found in both the thinned and unthinned stands were negative species. In all nine subplots, only 11 and 10 species were found in spring and in autumn respectively, accounting for 17.74% and 15.15% of all the species in the thinned stand, respectively. All biodiversity indices were the highest in the center sub-plots and most of them tended to reduce from middle to side sub-plots. There was a close correlation between most of the three types of species and light conditions which was similar to each other in the thinned and unthinned stands. __________ Translated from Chinese Journal of Ecology, 2006, 25(10): 1201–1207 [译自: 生态学杂志]     

Effects of five tree-selection strategies when thinning spruce (Picea abies) stands: a case study in a field trail in southern Sweden

The aim of this study was to show the effects of five tree-selection strategies when thinning on quality and growth properties of Norway spruce stands, and their potential for improving quality in the stands. The five strategies were thinning to retain high-quality (HQ) and low-quality (LQ) trees, thinning from above (A) and below (B) and thinning to obtain an even distribution of residual trees (S). The study was conducted in two planted stands close to rotation age, located in southern Sweden, which had been thinned twice since the establishment of the thinning experiment. In the two quality-based treatments trees were selected for harvest on the basis of the following growth and quality traits: tree class, vitality, dbh, height, straightness, branch diameter and quality defects. The quality traits were found to be largely independent of tree size, thus the selection strategies based solely on dbh (A and B) did not improve quality within the stands. Thinning targeting HQ traits promoted the retention and growth of HQ trees, and improved overall quality of the stands compared to the other treatments. HQ thinning increased the share of straight trees by 15%, on average. Significant proportions of stem crooks and quality defects detected before the first thinning were invisible 21 years after it. All thinned stands had higher proportions of naturally pruned trees than unthinned stands. The selection method had no influence on periodic annual increment after thinning.     

Canopy density in stands of Picea abies and Pinus sylvestris after different thinning methods

Altogether 82 plots (261 estimations) of Picea abies (L.) Karst, and 193 plots (360 estimations) of Pinus sylvestris (L.) stands were estimated by a vertical tube. The “crown free projection”, CFP, of stands thinned in three methods with different thinning grades was measured: unthinned, heavily and very heavily thinned, heavily thinned delayed first thinning, extra heavily thinned and thinned from the top. Basal area (m²ha^?1) density (stems ha^?1) and diameter sum (m ha^?1) were plotted against CFP. Basal area was the best practical measure of stand in this study. Generally Scots pine stands have higher CFP and the curves are steeper than in Norway spruce stands. Depending on the grade of thinning, heavily and very heavily thinned spruce stands, delayed first thinning included, have CFP values of 10–15% and stands thinned from the top, 20–40%, compared with 30–80% and 30–60% respectively in pine stands. Extra heavily thinned stands have the highest CFP, 20–80% in spruce and 50–90% in pine stands. The CFP levels after thinning are too high in pine stands for avoidance of sucker and sprout production of aspen and birch. In dense Norway spruce stands thinned from the top or heavily and very heavily thinned, the CFP values are low enough (≤30%) to diminish the production of suckers.     

Corrigendum to: Growth of white spruce underplanted beneath spaced and unspaced aspen stands in northeastern B.C.—10 year results

Establishing white spruce (Picea glauca (Moench) Voss) by planting it under established aspen (Populus tremuloides Michx.), stands has substantial potential as a technique for regenerating boreal mixedwood stands. The presence of an aspen overstory serves to ameliorate frost and winter injury problems and suppresses understory vegetation that may compete with white spruce. In this study we examine the growth of white spruce during the first 10 years after being planted underneath a 39-year-old stand of trembling aspen following thinning and fertilization. Results indicate successful establishment and reasonable growth rates of white spruce planted under thinned and unthinned aspen stands, even with aspen basal area of 51 m² ha⁻¹. Thinning of overstory aspen to 1000 or 2000 stems ha⁻¹ did not increase light reaching seedlings, but did result in improvements in light above the shrub layer and in diameter and height growth of the underplanted seedlings. However, these increases in growth of underplanted spruce may not justify the expense of thinnings. Fertilization of these stands prior to planting had no effect on spruce growth. Growth of spruce underplanted at this site near Fort Nelson was similar to that at two other stands near Dawson Creek, B.C.     

Growth of white spruce underplanted beneath spaced and unspaced aspen stands in northeastern B.C.—10 year results

Establishing white spruce (Picea glauca (Moench) Voss) by planting it under established aspen (Populus tremuloides Michx.), stands has substantial potential as a technique for regenerating boreal mixedwood stands. The presence of an aspen overstory serves to ameliorate frost and winter injury problems and suppresses understory vegetation that may compete with white spruce. In this study we examine the growth of white spruce during the first 10 years after being planted underneath a 39 year-old stand of trembling aspen following thinning and fertilization. Results indicate successful establishment and reasonable growth rates of white spruce planted under thinned and unthinned aspen stands, even with aspen basal area of 51 m² ha⁻¹. Thinning of overstory aspen to 1000 or 2000 stems ha⁻¹ did not increase light reaching seedlings, but did result in improvements in light above the shrub layer and in diameter and height growth of the underplanted seedlings. However, these increases in growth of underplanted spruce may not justify the expense of thinnings. Fertilization of these stands prior to planting had no effect on spruce growth. Growth of spruce underplanted at this site near Fort Nelson was similar to that at two other stands near Dawson Creek, B.C.     

Initial Response of Understory Vegetation to Three Alternative Thinning Treatments

This study compares initial understory vegetation response among three thinning treatments and a control in 30- to 50-year-old even-aged Pseudotsuga menziesii (Mirbel) Franco (Douglas-fir) stands. It was conducted on four sites on the western slope of the central Oregon Cascades. Treatments included a control (no thinning), a light thinning, and two treatments designed to encourage development of understory vegetation: a light thinning with gap creation and a heavy thinning. Vegetation response was measured during the first post-treatment growing season and 5–7 years later. At a treatment-scale, vegetation structure and composition differed between thinned and unthinned stands but varied little among thinning treatments. Thinnings resulted in initial declines of bryophytes, tall shrubs, and low shrubs followed by subsequent recovery and growth. Herbs displayed little initial response, but a release of early-seral species was evident in thinned stands by 5–7 years posttreatment. The addition of gaps resulted in differentiation of plant composition across the gradient from gap center to the thinned forest matrix, but this was only statistically detectable at a within-treatment scale. The causal mechanisms driving initial post-thinning response are discussed to better understand long-term implications and potential roles of thinning in managing for understory vegetation.     

Commercial thinning that maintained species diversity of a mixed black spruce–jack pine stand enhanced productivity

Commercial thinning enables forest managers to meet timber production objectives. Thinning reduces tree density to alleviate competition for resources and favour growth of selected tree species. However, in doing so, thinning can homogenize the composition of mixed-species forests and raise biodiversity issues. There is increasing evidence that species richness can lead to higher productivity through a complementarity effect. Hence, thinning that would maintain species diversity of mixed-species forests could enhance stand productivity and help forest managers to reconcile timber production objectives and biodiversity issues. The objective of this study was to compare post-thinning stand production, experimentally over 10 years, in mixed and monospecific stands of black spruce (Picea mariana [Mill.] B.S.P.) and jack pine (Pinus banksiana Lamb.). The post-thinning stand production curve of the mixed stand converged toward that of the unthinned mixed stand while the production curves of the thinned and unthinned monospecific stands remained parallel. The convergent productivity of the mixed stand could be explained by a positive interaction between effects of thinning and niche complementarity. We propose that thinning that maintains species diversity of mixed stands could help forest managers who are implementing ecosystem management to reconcile timber production objectives with biodiversity issues.     

Effects of thinning level and site productivity on age-related changes in stand volume growth can be explained by a single rescaled growth curve

In this study, I developed a nonlinear mixed-effects model based on the Richards curve that describes the effects of thinning and site productivity on stand volume growth. I fitted the model to data from 29 long-term experimental monitoring plots in Japanese cedar (Cryptomeria japonica D. Don) plantations in northeastern Japan. Simulations using the model on high-productivity sites and at moderate thinning intensities indicated that net yields after ca. 80 years were lower in unthinned stands than in thinned stands; in other cases, such as at younger ages and at sites with low and average productivities, net yields were similar for each thinning intensity (including no thinning). These results could be attributed to the fact that the net current annual increment in stand volume (CAI_net) in the thinned stands exceeded that of the unthinned stands after a certain age (the “inversion” age) and to the negative correlation between site productivity and the inversion age. In addition, I found that a single rescaled growth curve was capable of describing the growth in stand volume at sites with different thinning histories and site productivities. This rescaled curve simply and clearly explained the effects of thinning and site productivity on stand volume growth. The existence of a single curve suggests that the positive effect of thinning on stand volume growth does not depend on site productivity, but it will require patient measurements over longer periods to reveal a positive effect at sites with low productivity.     

Effects of overstorey retention on ash regeneration and bramble growth during conversion of a pine plantation to native broadleaved woodland

Conversion of monoculture plantations to mixed stands with greater diversity is an important aim of sustainable forest management, and in Britain, this is concentrated on the restoration of native broadleaved woodland on ancient woodland sites that were planted with conifers. Current British guidelines for this restoration have rarely been examined, and this study is the first to test their value for natural regeneration. The survival and growth of naturally regenerating ash (Fraxinus excelsior L.) seedlings was observed in thinned, selectively felled and clearfelled plots within a c. 40-year-old stand of Corsican pine (Pinus nigra Arnold ssp. laricio Maire). After felling in 2001, the ground flora in all treatments became dominated by bramble (Rubus fruticosus L. agg.) and its cover 5 years after felling was 75–95?% at a height of 0.9–1.2?m. During the study, seedling numbers declined 80–90?%. Although bramble had some adverse effects, seedling survival was unaffected by felling treatment. Seedling growth varied between treatments with those in the clearfell being tallest. Mean height of seedlings was always less than that of bramble, but by 2006 65?% of quadrats in the clearfelled plots had well-established individuals taller than the bramble compared with 35?% in the thinned plots. Models that described the relationships between seedling growth, basal area and bramble were complex, but results clearly indicate that maintaining canopy cover during restoration is probably an ineffective method of suppressing bramble on sites where it grows well. Results do not support the current British advice on conversion, but this may reflect the characteristics of pine canopies and the maintenance of canopy cover during conversion may be appropriate in stands of species, which cast more shade.     

Wind and snow damage in a thinning and fertilization experiment in Picea abies in southern Sweden

Changes in susceptibility to wind and snow damage due to thinningand fertilization were examined in even aged Norway spruce (Piceaabies (L.) Karst.) stands in southern Sweden. The stands arepart of a nationwide experiment to investigate growth and yieldfollowing different thinning and fertilization regimes establishedbetween 1966 and 1983. The material used in this study included16 replications of seven treatments. The treatments were: threelevels of thinning from below (20–70 per cent); 20 percent thinning from above; thinning from below in combinationwith N and NP fertilization (thinning percentage 25–28per cent); and unthinned control. The stands have been censusedtwice for damage during an average period of 12 years. The degree of wind and snow induced damage varied between 9and 20 per cent of the basal area increment produced duringthe observation period. For treatments with high basal arearemoval, the highest relative number of trees damaged by windoccured during the first period after thinning. The denseststands (i.e. unthinned controls and stands thinned from above)showed a high proportion of snow damage throughout the observationperiod. The block effect was in general more significant thanthe effect of treatments on damage level. When analysing theinfluence of the block effect (i.e. of site and stand characteristics)on damage level, wind damage was best predicted by stand basalarea left after thinning and stand age, while snow damage wasbest predicted by latitude, altitude, site index, and standage. On average the tested site and stand characteristics explained17 per cent of the variation in wind damage and 36 per centin snow damage.     

Stem Form and Taper Changes After Thinning and Nitrogen Fertilization in Picea abies and Pinus sylvestris Stands

Stem form and taper changes after thinning and thinning combined with N fertilization were studied in 23 Norway spruce [Picea abies (L.) Karst.] and 46 Scots pine (Pinus sylvestris L.) stands in Sweden observed for 5-28 yrs. Average taper was calculated for the stem section 1.3-6.0 m above ground level and as the ratio between the diameter at breast height and total tree height for periods of 5-10 yrs. At the start of the experiment, before the first thinning, the dominant height was 12-15 m. Once 65% of the basal area had been removed in a single thinning from below, the remaining trees showed a strong increase in taper compared with trees in unthinned stands. Stems in stands treated with heavily recurrent thinnings from below also increased in taper, although the increases were not always statistically significant. Trees in thinned, N-fertilized Scots pine stands in middle and northern Sweden developed a more pronounced taper compared with stems in equally thinned, unfertilized stands.     

Natural mortality in thinning and fertilisation experiments with pine and spruce in Sweden

Natural mortality in a 30-year period was examined in thinning and fertilisation experiments with 48 blocks in Scots pine (Pinus sylvstris L.) and 23 blocks in Norway spruce (Picea abies (L.) Karst.) with up to 12 different treatments. Of about 90,000 living trees at start of the experiments 18.7% were registered as dead by natural mortality in the 30-year observation period. In non-thinned stands about 20% of the volume growth disappeared by natural mortality, in thinned stands about 10%. In normally thinned pine stands (repeated thinning from below with moderate intensity) the annual mortality of the basal area at start of an average 7-year period was 0.34%. In spruce stands, on more fertile sites, the corresponding figure was about 0.6%. In an effort to model the mortality, severe damage not leading to final felling was identified in 1.7% of the observation periods. It was assumed that this part of the mortality, representing 24% of the total volume mortality, could be recovered by active thinning. The probability for severe damage increased sharply with stand top height, as shown in a logistic regression. The more sparse mortality was expressed as a function of site fertility, stand density, disturbance by thinning and form of treatment (thinned from above or below or non-thinned). The naturally dead trees were approximately of mean size in normally thinned stands while the self-thinning in non-thinned stands tended to occur amongst smaller than average trees. Diagrams were presented for basal area development and stem number reduction in the non-thinned stands.     

Cherrybark oak stump sprout survival and development five years following plantation thinning in the lower Mississippi alluvial valley,USA

Cherrybark oak (Quercus pagoda Raf.) stump sprouts were studied for 5 years in a 30-year-old plantation thinned to 70–75% stocking (light thinning) and 45–50% stocking (heavy thinning). Sprouting success, survival, number of sprouts per stump, and sprout height differed little between thinning treatments throughout the 5-year study period. Pre-harvest tree d.b.h. also had no influence on sprout survival and development. A 2-year drought reduced survival and may have influenced sprout development. Sprout clump survival dropped from 90% 1 year following thinning to 46% 3 years after thinning. Although sprout height averaged 337 cm 5 years after thinning, annual sprout growth decreased from 166 cm the first year after thinning to 33 cm in each of the last 2 growing seasons. Results indicated that bottomland hardwood regeneration evaluation models may underestimate the potential of oak stump sprouts to contribute to pre-harvest regeneration assessments. Further study in the role of stump sprouts to regenerate bottomland oak species is needed. The U.S. Government's right to retain a non-exclusive, royalty-free license in and to any copyright is acknowledged