THIS POST IS A PRESENTATION OF PUBLISHED RESEARCH ON THE OBSERVATION THAT TREE GROWTH IS ACCELERTING AND THE ATTRIBUTION OF THE ACCELERATION TO RISING ATMOSPHERIC CO2 CONCENTRATION WITH THE IMPLICATION THAT RISING ATMOSPHERIC CO2 IS SELF CORRECTING BY WAY OF THE HIGHER VEGETATION DRAWDOWN OF ATMOSPHERIC CO2 AT HIGHER ATMOSPHERIC CO2 LEVELS.

CITATION:

ABSTRACT

Many forest ecosystems have experienced recent declines in productivity; however, in some alpine regions, tree growth and forest expansion are increasing at marked rates. Dendrochronological analyses at the upper limit of alpine forests in the Tibetan Plateau show a steady increase in tree growth since the early 1900s, which intensified during the 1930s and 1960s, and have reached unprecedented levels since 1760. This recent growth acceleration was observed in small/young and large/old trees and coincided with the establishment of trees outside the forest range, reflecting a connection between the physiological performance of dominant species and shifts in forest distribution. Measurements of stable isotopes (carbon, oxygen, and nitrogen) in tree rings indicate that tree growth has been stimulated by the synergistic effect of rising atmospheric CO2 and a warming-induced increase in water and nutrient availability from thawing permafrost. These findings illustrate the importance of considering soil-plant-atmosphere interactions to understand current and anticipate future changes in productivity and distribution of forest ecosystems.

SUPPORTING PAPERS

Koutavas, Athanasios. “Late 20th century growth acceleration in greek firs (Abies cephalonica) from Cephalonia Island, Greece: A CO2 fertilization effect?.” Dendrochronologia 26.1 (2008): 13-19. ABSTRACT; Abies cephalonica or greek fir is indigenous to the island of Cephalonia in the Ionian Sea, which gives the species its name. Here I report ring-width variations from eight trees growing between 1300 and 1600 m elevation on the southern slopes of Mt. Ainos on this island, indicating strong acceleration of growth over the second half of the 20th century. The sustained increase in growth since 1990 in particular is unprecedented over the full length of the dataset (1840–2005 AD). These trends bear no relationship to regional temperature or precipitation variations and therefore are unlikely to be climatically induced. Disturbance effects from human activities are also unlikely as the study site lies in a remote forest area with difficult access. A plausible alternative hypothesis is that the enhanced growth reflects a fertilization effect due to rising CO2 in the global atmosphere. Based on the timing of individual tree responses, it is further hypothesized that the crossing of a CO2 threshold was responsible for the enhanced growth, and that this threshold may be age dependent (decreasing with age). A more systematic sampling of the Mt. Ainos firs is needed to further test this hypothesis. If interpreted correctly the results imply that CO2 fertilization may already be an important factor in tree growth at this location.

Frank, David, Ulf Büntgen, and Jan Esper. “Comment on “Late 20th century growth acceleration in Greek firs (Abies cephalonica) from Cephalonica Island, Greece: a CO2 fertilization effect?”.” Dendrochronologia 27.3 (2009): 223-227. ABSTRACT:

In the recent article ‘‘Late 20th century growth acceleration in Greek firs (Abies cephalonica) from Cephalonia Island, Greece: A CO2 fertilization effect?’’ (Dendrochronologia 26(2008) 13–19) by Koutavas, a dataset of radial stem growth increment was presented. Eight individual trees, after detrending to remove the biological age trend, show a growth increase that is hypothesized to be related to CO2 fertilization. Such a conclusion, if correct, would be of great relevance towards understanding the impact of anthropogenic emissions on forest productivity, with consequences on the global carbon cycle, ecosystem functioning, land– atmosphere interactions, and climate model experiments. However, as suggested by the author, these results reflect a preliminary assessment of CO2 fertilization effects on tree growth. Here in, we expand upon known challenges in growth attribution, and bring attention to subtle though important methodological considerations, in using such tree-ring data to make conclusions about CO2 impacts on radial tree growth. These issues are: (i) few data, (ii) non-systematic consideration of environmental forcing factors and, (iii) end-effects in detrending. We suggest that these three factors reduce support for the conclusion that the Greek fir data from Cephalonia Island contain CO2 fertilization signals. {translation: maybe it’s not really CO2 fertilizaation after all but something else that we don’t yet understand.

Sullivan, Thomas P., and Druscilla S. Sullivan. “Acceleration of old-growth structural attributes in lodgepole pine forest: Tree growth and stand structure 25 years after thinning.” Forest Ecology and Management 365 (2016): 96-106. ABSTRACT: Acceleration of forest succession to develop late-seral structural characteristics in younger stands may be achieved by silvicultural practices such as pre-commercial thinning (PCT). Young second-growth stands of lodgepole pine (Pinus contorta) range across several million ha of the inland Pacific Northwest of North America and respond positively to various stand treatments. Objectives of this project were that large-scale stand thinning to a wide range of densities, at a 25-year period after PCT, would enhance: (1) productivity and structural features (diameter and height growth, and crown volume and dimensions of crop trees; (2) merchantable volume of crop trees; and (3) development of old-growth structural attributes. Three stands thinned to densities of ∼500 (low), ∼1000 (medium), and ∼2000 (high) stems/ha at age 17 years, with an unthinned young pine and old-growth pine stand for comparison, were located near Penticton in south-central British Columbia. Lodgepole pine grew faster in mean diameter (cm) in the low- (13.89) than either of the medium- (10.2) or high-density (9.2) stands, but mean height growth increment (8.8–9.7 m) was similar over the 25-year period since PCT. Mean diameter was 2.2 times greater in the low-density stand than unthinned stand. The medium- and high-density stands also tended to have large diameters (1.7–1.9 times that of the unthinned stand) and crowns, but still with mean heights 5–6 m less than trees in the pine component of the old-growth stand. Mean merchantable stand volume (m3/ha) was 1.7–1.9 times higher in the medium- (231) and high-density (257) stands than low-density (137) stand, and comparable to the old-growth pine (225). Mean crown volume (m3) of crop trees was substantially greater in the low- (88) than in the medium- (27) and high-density (31), unthinned (4), or old-growth stands (4 pine only). Mean structural diversity of five layers of coniferous trees was highest in the low- and medium-density stands, with declining diversity from the high-density to unthinned to old-growth stands. In terms of old-growth structural attributes, large dominant trees with substantial crowns, multi-layered canopies of conifers, some canopy gaps, and understory patchiness of herbs and shrubs appeared in the heavily thinned (⩽1000 stems/ha) stands at 25 years post-thinning. These stands were 42 years old at this re-measurement, and hence were not considered “old-growth” but the heavily thinned stands seemed to have some old-growth structural attributes. Silvicultural trade-off of stand volume gain vs. old-growth attributes may be necessary for low-density stands.

THE VIEW FROM THE GUARDIAN

TRANSLATION: YES THERE IS CO2 FERTILIZATION BUT THAT IS BAD NEWS BECAUSE ACCELERATED GROWTH ALSO ACCELRATES DEATH.

SUMMARY AND CONCLUSION: THERE APPEARS TO BE SIGNIFICANT EVIDENCE THAT THE COMBINATION OF RISING ATMOSPHERIC CO2 AND WARMING IS ACCELERATING FOREST GROWTH AND THAT THIS SELF CORRECTING NATURE OF NATURE MAY NOT HAVE BEEN GIVEN DUE CONSIDERATION IN THE EVALUATION OF THE IMPACT OF FOSSIL FUEL EMISSIONS.