Long-term Effects Of Thinning Research Articles

Thinning and prescribed burning increase shade-tolerant conifer regeneration in a fire excluded mixed-conifer forest

Fire exclusion and past management have altered the composition, structure, and function of frequent-fire forests throughout western North America. In mixed-conifer forests of the California Sierra Nevada, fire exclusion has exacerbated the effects of drought and endemic bark beetles, resulting in extensive mortality of fire-adapted pine species. Thinning and prescribed fire are widely used in these forests to reduce fuels, moderate fire behavior, and restore ecosystems. Tree regeneration influences future forest composition and structure, and therefore future resilience to disturbances, but long-term effects of thinning and prescribed burning on tree regeneration after prolonged fire exclusion are poorly understood. We measured tree regeneration one year prior to, and periodically for 16 years following thinning and prescribed burning in a mixed-conifer forest in the Sierra Nevada, California, USA. We asked three questions. How did the composition and density of tree regeneration change after thinning and prescribed burning? Did pretreatment vegetation types influence conifer regeneration density after treatments? Did planting after overstory thinning increase regeneration density of native pine species?Sixteen years after treatments, combined natural regeneration of shade-tolerant white fir (Abies concolor) and incense-cedar (Calocedrus decurrens) averaged 2,032 trees per hectare (tph) after understory thinning, and 7,745 tph after understory thinning combined with prescribed burning, increases of 37 % and 146 % from pretreatment densities. In contrast, combined natural regeneration of white fir and incense-cedar averaged 497 tph after overstory thinning, 780 tph after overstory thinning with prescribed burning, 113 tph after prescribed burning alone, and 807 tph in untreated controls, all of which were declines from pretreatment densities. Natural regeneration of white fir and incense-cedar was consistently an order of magnitude greater than Jeffrey pine (Pinus jeffreyi) and sugar pine (Pinus lambertiana), whose combined densities 16 years after treatments averaged 37 tph across treatments and did not significantly respond to thinning and/or prescribed burning. Natural conifer regeneration after treatments varied by pre-treatment vegetation type (closed canopy, Ceanothus cordulatus shrub dominated, and open sparse), with large increases of natural regeneration after understory thinning in closed canopy and Ceanothus shrub vegetation types. Planting increased sugar pine regeneration density after overstory thinning, marginally increased Jeffrey pine regeneration after overstory thinning combined with prescribed burning, and increased white fir regeneration after overstory thinning with and without burning. No treatments reduced white fir and incense-cedar natural regeneration while simultaneously increasing natural pine regeneration, suggesting new thinning, burning, and planting approaches may be required to meet regeneration restoration objectives.

The long-term effects of thinning on soil respiration vary with season in subalpine spruce plantations

Thinning is a principal silvicultural practice in temperate plantations with potential impacts on soil respiration (Rs). However, most of the existing measurements of Rs dynamics after thinning have been performed during the growing season, while those in the nongrowing season have been seldom determined, even though recent evidence demonstrates that the nongrowing season Rs occupied a considerable proportion of the annual carbon (C) budgets in temperate forests. Here, we investigated the long-term (17 years) impacts of thinning on Rs in middle-aged subalpine spruce plantations in northwestern China. We found that thinning significantly (p < 0.001) increased Rs from 3.00 to 4.18 μmol m−2 s−1 in the growing season while significantly (p < 0.001) decreasing Rs from 1.05 to 0.90 μmol m−2 s−1 in the nongrowing season; additionally, thinning had no significant (p = 0.0989) effect on the Q10 value (temperature sensitivity of Rs) in the growing season, with values ranging from 2.10 to 2.44, while it significantly (p < 0.01) increased the Q10 value from 2.91 to 3.48 in the nongrowing season. In the growing season, increased nitrate nitrogen due to elevated soil moisture (SM) played a fundamental role in stimulating Rs by improving microbial biomass (MB) and fine root biomass, and increased soil temperature (ST) also contributed to the increases in MB and Rs. However, these variables and pathways were not applicable in the nongrowing season, when decreased dissolved organic C induced by decreased ST explained most of the decline in MB and Rs. Our results revealed that the long-term effects of thinning on the nongrowing season Rs were completely different from those in the growing seasons in subalpine spruce plantations. Furthermore, the greatly increased Q10 value in the nongrowing season indicated that a substantial increase in Rs can be expected in subalpine forests after thinning due to nongrowing season warming at high altitudes.

Response of the Soil Microbial Community to the Long-Term Effects of Thinning and its Key Roles in Tree Growth in a Natural Secondary Forest in Northeast China

Response of the Soil Microbial Community to the Long-Term Effects of Thinning and its Key Roles in Tree Growth in a Natural Secondary Forest in Northeast China

Long-term effects of thinning and mixing on stand spatial structure: a case study of Chinese fir plantations

The regular planting and periodic harvesting of a single tree species are features of plantations, which are associated with a reduction of biodiversity. Such plantations are strongly encouraged to be converted into mixed forests. However, the spatial structure dynamics of plantations during the conversion process are poorly understood. In subtropical regions, thinned forest of Chinese fir (Cunninghamia lanceolata [Lamb.] Hook.) and mixed forest of Chinese fir and Michelia macclurei Dandy are considered two ideal modes of plantation management. In this study, we analyzed the spatial structure dynamics of two forest stands and their six main tree populations over a rotation of 27 years, using spatial point analyses. We found that Chinese fir and M. macclurei had a regular distribution pattern (scale, r = 0-1 m) in the early stages of planting (1993), and Chinese fir maintained this pattern after experiencing self-thinning and selective cutting. In addition, non-planted tree species (i.e., natural regeneration of late-seral species, NRLSS) displayed significantly intraspecific clumping, which resulted in the distribution patterns of the forest stands changing from regular to aggregated (r = 0-5.5, 1-20 m), and the species distribution of mixed forest changed from random to clumped (r = 0-20 m). Moreover, during the management period (1993-2018), individuals were significantly differentiated in terms of size, and some small trees in the thinned forest were aggregated together. For the NRLSS, the diameter at breast height was randomly distributed (r = 0-20 m). Furthermore, Chinese fir and M. macclurei were separated at r = 0-1 m in the planting stage, but any pair of the six main populations in the thinned forest and mixed forest were randomly correlated over a rotation. Finally, the nearest neighbor distance of the stands became shorter after conversion, while the values for Chinese fir increased. After 25 years, the mixed plantation and the thinned plantation had a complex spatial structure. They develop towards natural forests and could be used as a template for future plantation management.

The long-term effects of thinning and mixing on species and structural diversity of Chinese fir plantations

Plantations are playing an increasingly important role in providing forest products and improving the ecological environment, but they also face many challenges, such as low biodiversity, severe pest and disease problems, reduced productivity, and diminished soil fertility. Reasonable management strategies are vital for their sustainability. In this study, we took a Chinese fir (Cunninghamia lanceolata (Lamb.) Hook.) plantation as an example to demonstrate the effects of thinning and mixing on the species diversity and structural diversity of plantations at the stand level over a rotation period (1993–2018). An intermediate thinning (26% of plant abundance) was conducted in a Chinese fir pure plantation in mid-age (2008), and a mixed forest stand of Chinese fir and Michelia macclurei Dandy was established directly. Thinning and mixing greatly increased the species diversity at the stand level, enhanced the mixture, transformed the pattern from regular to random distribution, and made the size differentiation of trees random. Thinning and mixing also greatly improved the mixture and dominance of Chinese fir. M. macclurei had an obvious advantage in tree size and maintained a high mixture proportion. Moreover, the diameter classes of the stands were bimodal. Chinese fir and M. macclurei showed a unimodal distribution of diameter, but other later-coming species with a larger number of individuals displayed a typical reverse J-shaped distribution. Our results suggest that both thinning and mixed planting may promote species diversity and structure over a long timescale, but thinning achieves these characteristics earlier because thinning directly manipulates structure in a way that accelerates stand development.

Long-term effects of thinning and woody control on longleaf pine plantation development, understory abundance, and tree damage from an ice storm

Longleaf pine (Pinus palustris) plantations have been established across the southeastern United States as the first step in restoring the declining savanna ecosystem, yet their long-term stability and development to open canopied woodlands may depend on early density and vegetation management treatments. Commercial thinning (CT) was applied in 2012 (year 18) to a long-term study of longleaf pine community restoration at the Savannah River Site near Aiken, SC to increase abundance of herb species. Although precommercial thinning (PCT) and woody vegetation control increased herb species cover during the first five years of the study, measurements from years 17 to 22 indicated a continuing decline in their cover since year 9 despite application of CT in year 18. Herb species richness, however, increased from 21 to 43 species per 100 m2 area during the last six years of the study, likely a result of disturbances associated with CT and an ice storm in year 20. Application of PCT in 1994, when the plantations were 8–11 years old, reduced their susceptibility to stem bending and breakage from the ice storm, which occurred 20 years later in 2014. Measured 5 months before the storm, pine height: dbh ratio (HD) averaged 78 and 90 for trees growing with and without PCT, respectively, and stem breakage (% of trees) from the ice storm increased linearly (r2 = 0.53) with HD. Pine mortality from the combined effects of glaze ice and wind differed with (28%) versus without (45%) PCT, indicating that long-term stability of longleaf pine plantations depends on early density management.

Heavy and frequent thinning promotes drought adaptation in Pinus sylvestris forests.

Droughts and their negative effects on forest ecosystems are projected to increase under climate change for many regions. It has been suggested that intensive thinning could reduce drought impacts on established forests in the short-term. Most previous studies on the effect of thinning on drought impacts, however, have been confined to single forest sites. It is therefore still unclear how general and persisting the benefits of thinning are. This study assesses the potential of thinning to increase drought tolerance of the wide spread Scots pine (Pinus sylvestris) in Central Europe. We hypothesized (1)thatincreasing thinning intensity benefits the maintenance of radial growth of crop trees during drought (resistance) and its recovery following drought, (2) that those benefits to growth decrease with time elapsed since the last thinning and with stand age, and (3) that they may depend on drought severity as well as water limitations in pre- and post-drought periods. To test these hypotheses, we assessed the effects of thinning regime, stand age, and drought severity on radial growth of 129 Scots pine trees during and after drought events in four long-term thinning experiments in Germany. We found that thinning improved the recovery of radial growth following drought and to a lesser extent the growth resistance during a drought event. Growth recovery following drought was highest after the first thinning intervention and in recently and heavily thinned stands. With time since the last thinning, however, this effect decreased and could even become negative when compared to unthinned stands. Further, thinning helped to avoid an age-related decline in growth resistance (and recovery) following drought. The recovery following drought, but not the resistance during drought, was related to water limitations in the drought period. This is the first study that analyzed drought-related radial growth in trees of one species across several stands of different age. The interaction between thinning intensity and time since the last thinning underline the importance to distinguish between short- and long-term effects of thinning. According to our analysis, only thinning regimes, with relatively heavy and frequent thinning interventions would increase drought tolerance in pine stands.

Effect of thinning on wood density and tracheid properties of Scots pine on drained peatland stands

The properties of wood and wood tracheids from trees growing in peatland stands are still insufficiently known. The long-term effects of thinning on wood and tracheid properties of Scots pine (Pinus sylvestris L.) were investigated in two thinning experiments on peatland sites in central Finland. The two sites were ditched for the first time in 1958 and 1973, and thinning experiments were established in 1987 and 1993, respectively. Thinning increased the basal area increment of the remaining trees by 20 per cent. No differences between the trees that were growing on the thinned plots and those that were growing on the unthinned control plots were found in the latewood proportion, wood density, tracheid diameter, cell wall thickness and tracheid length. Moreover, the wood and tracheid properties did not differ markedly from those of corresponding material originating from mineral soil sites. The results confirm the previous results on mineral soils, which showed that an increasing availability of resources primarily increases the rate of tracheid production but has no major effects on wood and tracheid properties.

Long-term effects of thinning on growth and yield of an upland black spruce stand

Knowledge of the long-term effects of silviculture treatments is crucial to forest management. The long-term effects of thinning, a common and widely used silviculture treatment, is little documented for upland black spruce ( Picea mariana (Mill.) Britton, Sterns &amp; Poggenb.) stands. We revisited a partial cutting experiment installed in 1961 in a 65-year-old unmanaged upland black spruce stand. The aim was to document the long-term effects of thinning on tree and stand growth and to complete previously published results of the first 15 years of response to thinning by determining its influence in terms of merchantable volume. Free thinning was applied following three intensities: 0%, 25%, and 50% of total basal area removal. The retrospective analysis of growth rings showed that the response over the first 15 years was less significant when determined in net merchantable volume instead of net total volume. Heavily thinned plots, nonetheless, showed a net stand merchantable volume increment 33% greater than that of the unthinned plots. In the longer term, a spruce budworm ( Choristoneura fumiferana Clemens) outbreak affected the site; nevertheless, the heavily thinned plots maintained a superior tree growth rate and did not show senescence mortality like the other plots, allowing stand volume to catch up to that of the unthinned plots after 33 years. Results suggested that thinning upland black spruce stands may be useful in mitigating reductions in volume production associated with growing stands to longer rotations as called for by certain ecosystem-based management approaches.

Short- and long-term effects of thinning and prescribed fire on carbon stocks in ponderosa pine stands in northern Arizona

Euro–American logging practices, intensive grazing, and fire suppression have increased the amount of carbon that is stored in ponderosa pine (Pinus ponderosa Dougl. Ex Laws) forests in the southwestern United States. Current stand conditions leave these forests prone to high-intensity wildfire, which releases a pulse of carbon emissions and shifts carbon storage from live trees to standing dead trees and woody debris. Thinning and prescribed burning are commonly used to reduce the risk of intense wildfire, but also reduce on-site carbon stocks and release carbon to the atmosphere. This study quantified the impact of thinning on the carbon budgets of five ponderosa pine stands in northern Arizona, including the fossil fuels consumed during logging operations. We used the pre- and post-treatment data on carbon stocks and the Fire and Fuels Extension to the Forest Vegetation Simulator (FEE–FVS) to simulate the long-term effects of intense wildfire, thinning, and repeated prescribed burning on stand carbon storage.The mean total pre-treatment carbon stock, including above-ground live and dead trees, below-ground live and dead trees, and surface fuels across five sites was 74.58Mg C ha−1 and the post-treatment mean was 50.65Mg C ha−1 in the first post-treatment year. The mean total carbon release from slash burning, fossil fuels, and logs removed was 21.92Mg C ha−1. FEE–FVS simulations showed that thinning increased the mean canopy base height, decreased the mean crown bulk density, and increased the mean crowning index, and thus reduced the risk of high-intensity wildfire at all sites. Untreated stands that incurred wildfire once within the next 100 years or once within the next 50 years had greater mean net carbon storage after 100 years compared to treated stands that experienced prescribed fire every 10 years or every 20 years. Treated stands released greater amounts of carbon overall due to repeated prescribed fires, slash burning, and 100% of harvested logs being counted as carbon emissions because they were used for short-lived products. However, after 100 years treated stands stored more carbon in live trees and less carbon in dead trees and surface fuels than untreated stands burned by intense wildfire. The long-term net carbon storage of treated stands was similar or greater than untreated wildfire-burned stands only when a distinction was made between carbon stored in live and dead trees, carbon in logs was stored in long-lived products, and energy in logging slash substituted for fossil fuels.

Long-term effects of thinning and fertilization on growth of red fir in northeastern California

To determine the impact of fertilization and thinning on growth and development of red fir (Abies magnifica A. Murr.) stands, we established an experiment in a 60-year-old stand using a 2 × 3 factorial design with nitrogen-fertilized and nonfertilized treatments and three stocking levels. Plots were established in 1976 and were measured every 5 years for 26 years. The periodic annual increment in basal area was 97%, 51%, 38%, and 33% greater in fertilized trees than in nonfertilized trees during the first, second, third, and fourth 5-year periods, respectively. After 20 years, annual basal area increment was greater in nonfertilized trees. The response of annual volume increment to fertilization was not statistically significant until the fourth period. Yet, volume increases of the fertilized plots were 25%–92% greater than those of the nonfertilized plots from 1976 to 1996. Similarly, basal area increment was greater in lightly thinned plots than in unthinned plots from the second period on, until heavy mortality during 1996–2002. Basal area increment was greater in the heavily thinned plots from the fourth period on. Results indicate that red fir can respond to fertilization and thinning quickly and that both treatments speed stand development. In addition, fertilization increases the stand's carrying capacity. Therefore, forest managers can use these silvicultural practices to improve stand growth, to reduce fire fuels, and to accelerate stand development.

Long-Term Effects of Thinning and Pruning on the Quality, Quantity, and Value of Oak Lumber

Abstract After 32 years, experimental plots established to examine thinning levels and pruning effects were harvested. Randomly selected trees in each treatment were felled and sawn into 4/4 lumber, and the lumber from each tree was tallied by grade. For black oak, the species that became largely relegated to the understory, thinning caused a significant increase in the total volume outturn with the greatest increase occurring in the lowest lumber grade (3B). For scarlet oak, the species that became primarily dominant and codominant, thinning increased the total lumber yield per tree with most of the increase accumulating in the lumber grades #1C and #2C. Pruning did not affect the quantity or quality of lumber outturn in either species. North. J. Appl. For. 5:258-260, December 1988.

Stem Form and Lumber Yield: Long-Term Effects of Thinning and Pruning

Abstract Though stem form and taper greatly affect the amount of recoverable lumber in a tree, little work has been conducted on the long-term effects of thinning and pruning on stem form and lumber yield. The work described suggests that long after treatment neither stem form nor the bf/ft3 conversion ratio is affected by thinning and/or pruning. It is apparent that all of the merchantable volume increase induced by thinning will be recovered in the sawn lumber, but pruning does not appear to be a viable method for producing more cylindrical logs and increasing the conversion ratio. North. J. Appl. For. 5:56-58, March 1988.