Impacts of elevated atmospheric CO2 on forest trees and forest ecosystems: knowledge gaps

Abstract

Atmospheric CO 2 is rising rapidly, and options for slowing the CO 2 rise are politically charged as they largely require reductions in industrial CO 2 emissions for most developed countries. As forests cover some 43% of the Earth's surface, account for some 70% of terrestrial net primary production (NPP), and are being bartered for carbon mitigation, it is critically important that we continue to reduce the uncertainties about the impacts of elevated atmospheric CO 2 on forest tree growth, productivity, and forest ecosystem function. In this paper, I review knowledge gaps and research needs on the effects of elevated atmospheric CO 2 on forest above-and below-ground growth and productivity, carbon sequestration, nutrient cycling, water relations, wood quality, phenology, community dynamics and biodiversity, antioxidants and stress tolerance, interactions with air pollutants, heterotrophic interactions, and ecosystem functioning. Finally, I discuss research needs regarding modeling of the impacts of elevated atmospheric CO 2 on forests.Even though there has been a tremendous amount of research done with elevated CO 2 and forest trees, it remains difficult to predict future forest growth and productivity under elevated atmospheric CO 2 . Likewise, it is not easy to predict how forest ecosystem processes will respond to enriched CO 2 . The more we study the impacts of increasing CO 2 , the more we realize that tree and forest responses are yet largely uncertain due to differences in responsiveness by species, genotype, and functional group, and the complex interactions of elevated atmospheric CO 2 with soil fertility, drought, pests, and co-occurring atmospheric pollutants such as nitrogen deposition and O 3 . Furthermore, it is impossible to predict ecosystem-level responses based on short-term studies of young trees grown without interacting stresses and in small spaces without the element of competition. Long-term studies using free-air CO 2 enrichment (FACE) technologies or forest stands around natural CO 2 vents are needed to increase the knowledge base on forest ecosystem responses to elevated atmospheric CO 2 . In addition, new experimental protocols need to continue to be developed that will allow for mature trees to be examined in natural ecosystems. These studies should be closely linked to modeling efforts so that the inference capacity from these expensive and long-term studies can be maximized. D

Environmental Pollution

“…Significant treatment interactions and effects on branch architecture involving the main effect of CO 2 and O 3 with genotype, are a probable result of post-canopy closure light-competition in the control, þCO 2 , and þCO 2 þ O 3 treatments reducing the growth-enhancement effects of CO 2 , and differing genotypic tolerance to O 3 . Canopy closure at the site has been described as having occurred circa 2003(Kostiainen et al, 2008. This is generally consistent with the observations of site conditions by the authors, with the caveat that closure was visibly less advanced in the þO 3 plots in 2007, where significantly more light was able to penetrate to the understory (unpublished data).…”

“…Aspen clone 216 was alternated with birch and maple in the AB and AM communities, respectively. A selection of aspen clones (8L, 42E, 216, 259, and 271) representing a wide range of O 3 sensitivity (8L ¼ tolerant; 216 and 271 ¼ somewhat tolerant; 42E ¼ relatively sensitive; 259 ¼ sensitive [Karnosky, 2003]) comparable to that which exists in natural populations were randomized within the AA communities; clone 259 has since died out. Fumigation treatments are applied in the manner of the Brookhaven National Laboratory's design .…”

“…Atmospheric concentrations of gases, including CO 2 and O 3 , have been increasing since the Industrial Revolution Pitts, 1997, 2000;Fowler et al, 1999;IPCC, 2001) and evapotranspiration (ET) could be significantly impacted by changes in forest tree physiology and growth. Elevated atmospheric CO 2 has been shown to increase plant growth, leaf area index and water use efficiency, while increases in tropospheric O 3 have been shown to decrease plant growth, leaf area display, and stomatal control (Karnosky, 2003;Karnosky et al, 2005;McLaughlin et al, 2007a;Wittig et al, 2007) as well as to directly affect plant water balance (Panek, 2004;McLaughlin et al, 2007a,b). The antagonistic effects of elevated CO 2 and O 3 on plant growth may offset one another (Allen, 1990;Dickson et al, 1998;Volin et al, 1998;Loats and Rebbeck, 1999;Karnosky et al, 1999), although such offsets have not been consistently observed (Barnes et al, 1995;Kull et al, 1996).…”

Effects of Elevated CO2Concentration on Leaf Phenology of Quercus acutissima

“…이러한 생물계절현상 변화에 대한 연구 는 생산성 및 동해피해 발생과 연계되기 때문에 봄의 개엽과 가을의 낙엽 또는 동아 형성 시기에 대한 것 이 주를 이루고 있다 (Chen et al, 1999;Karnosky, 2003). 아한대 지역에서의 이른 개엽은 생육기간의 연 장으로 탄소흡수의 증대를 기대할 수 있지만 (Beuker, 1994;Chen et al, 1999), 생육시기 초기의 잎과 줄 기 조직은 성숙한 조직에 비하여 민감하기 때문에 이 른 개엽은 늦서리에 의한 피해 가능성이 높아지게 된 다 (Murray et al, 1989;Taschler et al, 2004).…”

“…이산화탄소 농도 증가에 의한 봄철 수목의 동아 파 열은 빠르게 나타나거나 (Karnosky, 2003), 지연되거나 (Murray et al, 1994;Repo et al, 1996), 변동이 없는 (Norby et al, 2003;Badeck et al, 2004) 등 다양 한 양상으로 나타났고, 가을의 동아 형성 시기도 빨라 지거나 (Mousseau and Enoch, 1989;Murray et al, 1994), 지연되어 나타났다. 이러한 수목의 생물계절학적 현상은 토양의 양료 상황 과 (Koike, 1995;Murray et al, 1994), 개체 또는 종자 산지의 차이에 의한 유전적 특성의 영향으로 다르게 나타나기도 하였다 (Murray et al, 1994).…”