Twenty-Five Years after Stand Thinning and Repeated Fertilization in Lodgepole Pine Forest: Implications for Tree Growth, Stand Structure, and Carbon Sequestration

Abstract

Silvicultural practices such as pre-commercial thinning (PCT) and repeated fertilization have been used successfully around the world to increase forest biomass for conventional wood products, biofuels, and carbon sequestration. Two complementary studies were designed to test the hypotheses (H) that large-scale PCT and PCT with repeated fertilization of young (13-17 years old) lodgepole pine (Pinus contorta var. latifolia) stands, at 25 years after the onset of treatments, would enhance (H 1 ) productivity and structural features (diameter and height growth, crown volume and dimensions) of crop trees; (H 2 ) merchantable volume of crop trees, (H 3 ) abundance of understory conifer, herb and shrub layers, and (H 4 ) carbon storage (sequestration) of all layers. Results are from two studies in south-central British Columbia, Canada. The PCT study had three densities: 500, 1000, and 2000 stems/ha, an unthinned, and old-growth stand replicated at three areas. The PCT-FERT study had four densities: 250, 500, 1000, and 2000 stems/ha with and without a repeated fertilization treatment, and an unthinned-unfertilized stand, replicated at two areas. Heavily thinned (≤1000 stems/ha) and fertilized stands generally had larger mean diameters and crown dimensions than lightly thinned or unfertilized stands, whereas mean heights of crop trees remained relatively unaffected, and hence partial support for H 1 . Despite differences in stand density (4-and 8-fold) of original crop trees, ingress of intermediate crop trees over the 25 years changed density dramatically. There was no support for H 2 , as mean merchantable volume of total crop trees was similar across stand densities owing to ingress, and was also similar in fertilized and unfertilized stands. In stands thinned to ≤500 trees/ha, there is an anticipated increase in crop tree density of 2.2 to 4.3 times over 25 years compared with the original post-thinning densities. Mean abundance of understory conifers was generally similar among stands owing to successional development towards canopy closure, whereas herbs and shrubs persisted only in canopy gaps in heavily thinned stands, thereby providing no support for H 3 . Mean carbon storage was similar across densities in both studies with ingress contributing a considerable amount to carbon sequestration at the lower densities. Fertilization increased (1.4 times) mean carbon storage significantly among total crop trees, total conifers, and the grand total of all layers, thereby providing partial support for H 4 . Thus, much of the potential above-ground carbon storage lost by thinning was restored in the heavily thinned stands at 25 years post-treatment.Forests 2020, 11, 337 2 of 23Forests 2020, 11, 337 3 of 23 Materials and Methods Experimental Design and Study AreasData from two separate long-term studies with 25-year datasets in naturally regenerated post-harvest lodgepole pine stands were used to test our study hypotheses: (1) PCT only (1988PCT only ( -2013 and (2) PCT with fertilization (PCT+FERT) . The PCT study was lo...

Pinus contorta Douglas ex Loudon and climate change: A literature review of opportunities, challenges, and risks in European forests

“…(Little 1979;Lotan, Critchfield 1990). This pine species has been widely planted, primarily for commercial purposes, and its exotic distribution includes Sweden, Iceland, the United Kingdom, Ireland, Russia, Central Europe, the Baltics, New Zealand, Turkey, Argentina, and Chile (Krajina et al 1982;Watt 1987;Elfving et al 2001;Ledgard 2001;Peña et al 2008;Kuznetsova et al 2009;Fedorkov, Turkin 2010;Juntunen 2010;Langdon et al 2010;Jansons et al 2013;Sullivan et al 2020).…”

“…Lodgepole pine (Pinus contorta Douglas ex Loudon) is a fast-growing conifer tree species native to western North America (Farjon, Filer 2013). It has a very broad ecological valence and is planted extensively in North and South America, Europe, and New Zealand due to its considerable silvicul-tural timber production value and for erosion control on forest lands (Svoboda 1976;Ledgard 2001;Richardson, Rejmánek 2004;Sullivan et al 2020). Because of its climate and air-pollution resistance and pioneer character, it is often used in the reforestation of air-polluted areas and in the reforesta-https://doi.org/10.17221/101/2022-JFS tion of reclamation areas after coal mining, etc.…”

“…It is particularly remarkable in forestry use due to its resistance to abiotic and biotic factors (drought, to name one) and also for its pioneer nature in colonizing anthropogenically disrupted areas (Dimitrovský 2000). The resistance of some Pinus contorta populations to air pollution is the result of long-term evolutionary adaptation (Begon et al 1990) in their natural ranges where volcanic activity had been abundant (Lotan et al 1985;Lotan, Critchfield 1990;Kaňák 2001;Sullivan et al 2020).…”

Acceleration of Forest Structural Development for Large Trees and Mammals: Restoration in Decades or Centuries?

“…Our premise in forest restoration rests on the assumption that if accelerated development of mature/old-growth forest attributes that include large diameters and crowns of crop trees, understory conifers, vegetation, and ingress are a goal, then stands need to be thinned to <1000 stems/ha, and likely to <500 stems/ha [29,33,34]. Fertilization may also be added either as a single or repeated application.…”

Application of Innovative Silvicultural Treatments in Pine Forests

“…Concerning pine forests and provisioning services, Zhao et al [1] in China used 57 plots in a Pinus tabuliformis plantation to investigate the direct and indirect influences of site conditions, population structure, and population stability on the productivity of the plantation. The effect of silvicultural treatments and fertilization on provisioning and regulating services are investigated by Sullivan et al [2] in Pinus contorta var. latifolia natural forest in Canada.…”