Tropical forest responses to increasing atmospheric CO2: current knowledge and opportunities for future research

Abstract

Abstract. Elevated atmospheric CO 2 concentrations (c a ) will undoubtedly affect the metabolism of tropical forests worldwide; however, critical aspects of how tropical forests will respond remain largely unknown. Here, we review the current state of knowledge about physiological and ecological responses, with the aim of providing a framework that can help to guide future experimental research. Modelling studies have indicated that elevated c a can potentially stimulate photosynthesis more in the tropics than at higher latitudes, because suppression of photorespiration by elevated c a increases with temperature. However, canopy leaves in tropical forests could also potentially reach a high temperature threshold under elevated c a that will moderate the rise in photosynthesis. Belowground responses, including fine root production, nutrient foraging and soil organic matter processing, will be especially important to the integrated ecosystem response to elevated c a .Water use efficiency will increase as c a rises, potentially impacting upon soil moisture status and nutrient availability. Recruitment may be differentially altered for some functional groups, potentially decreasing ecosystem carbon storage. Whole-forest CO 2 enrichment experiments are urgently needed to test predictions of tropical forest functioning under elevated c a . Smaller scale experiments in the understorey and in gaps would also be informative, and could provide stepping stones towards stand-scale manipulations.

Minimizing Risks of Invasive Alien Plant Species in Tropical Production Forest Management

“…Tropical forests supply an estimated 9% of the global demand for timber and wood products [2,3], and the production and processing of these makes a significant contribution to incomes and employment in many tropical countries. However, current global concerns for tropical forests focus largely on carbon-they account for about half the total biomass carbon in the terrestrial biosphere and a third of global terrestrial carbon fluxes [4]-and biodiversity-they are believed to support more than half of global terrestrial biodiversity [5].…”

Amazon Forest Ecosystem Responses to Elevated Atmospheric CO2 and Alterations in Nutrient Availability: Filling the Gaps with Model-Experiment Integration

“…Recent studies indicate that tropical C storage may be strongly determined by the hyperdominance (Fauset et al, 2015) and functional composition of tropical tree communities in association with different life-history strategies of tropical trees (Fauset et al, 2012). A CO 2 induced shift to shorter average tree life span could favor fast-growing tree species that invest in low-cost tissue, which could increase the turnover of C and thus decrease the C storage at the landscape scale (Phillips et al, 2009;Fauset et al, 2012;Cernusak et al, 2013). In accordance, simulations of nonrandom species loss for fast-growing species with low wood density increased C storage by 10%, whereas the loss of high statured slow-growing species decreased C stocks by over 30% (Bunker, 2005).…”

“…Efforts to quantify the response of aboveground carbon storage derived from forest inventory plots concluded that such events have the potential to reverse a multi-decadal biomass C sink across Amazonia (Phillips et al, 2009). However, to date predicted responses of the Amazon forest to projected global climate changes (mainly precipitation and temperature) remain largely speculative due to a lack of direct experimental evidence Davidson et al, 2012;Cernusak et al, 2013). As a surrogate, ecosystem models that include the mechanistic representation of key ecosystem processes, such as photosynthesis, respiration, growth, and C allocation, have been used for projections of ecosystem responses to changes in climate, atmospheric CO 2 and nutrient availability (e.g., Goll et al, 2012;Huntingford et al, 2013;Joetzjer et al, 2014;Smith et al, 2014;Yang et al, 2014).…”

“…Therefore most ecosystem models incorporating the Farquhar scheme (Long, 1991;Drake et al, 1997;Hickler et al, 2008Hickler et al, , 2015Cernusak et al, 2013) suggest that eCO 2 increases rates of leaf-level photosynthesis (Lloyd and Farquhar, 1996) based on the following simplified relationship:…”

“…Ecosystem scale experiments subjecting mature forests to eCO 2 and nutrient addition in the tropics, and in particular the Amazon forest, are crucial for filling major gaps in our understanding of expected global change effects Cernusak et al, 2013;Norby et al, 2016). Two major endeavors are currently underway in Amazonia; the first free-air carbon enrichment experiment in a mature tropical old-growth forest (AmazonFACE; Lapola and Norby, 2014), as well as the first large-scale factorial nutrient addition experiment (AFEX; Amazon fertilization experiment).…”