Long-Term Trends in Forest Net Primary Productivity: Cascade Mountains, Washington

Abstract. Peatlands are a major terrestrial carbon store and a persistent natural carbon sink during the Holocene, but there is considerable uncertainty over the fate of peatland carbon in a changing climate. It is generally assumed that higher temperatures will increase peat decay, causing a positive feedback to climate warming and contributing to the global positive carbon cycle feedback. Here we use a new extensive database of peat profiles across northern high latitudes to examine spatial and temporal patterns of carbon accumulation over the past millennium. Opposite to expectations, our results indicate a small negative carbon cycle feedback from past changes in the long-term accumulation rates of northern peatlands. Total carbon accumulated over the last 1000 yr is linearly related to contemporary growing season length and photosynthetically active radiation, suggesting that variability in net primary productivity is more important than decomposition in determining long-term carbon accumulation. Furthermore, northern peatland carbon sequestration rate declined over the climate transition from the Medieval Climate Anomaly (MCA) to the Little Ice Age (LIA), probably because of lower LIA temperatures combined with increased cloudiness suppressing net primary productivity. Other factors including changing moisture status, peatland distribution, fire, nitrogen deposition, permafrost thaw and methane emissions will also influence future peatland carbon cycle feedbacks, but our data suggest that the carbon sequestration rate could increase over many areas of northern peatlands in a warmer future.

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Soil processes dominate the long-term response of forest net primary productivity to increased temperature and atmospheric CO2 concentration

Canadian Journal of Forest Research ◽

10.1139/x00-026 ◽

2000 ◽

Vol 30 (6) ◽

pp. 873-888 ◽

Cited By ~ 16

Author(s):

Belinda E Medlyn ◽

Ross E McMurtrie ◽

Roderick C Dewar ◽

Mark P Jeffreys

Keyword(s):

Time Scales ◽

Primary Productivity ◽

Net Primary Productivity ◽

N Uptake ◽

Forest Growth ◽

Equilibrium Analysis ◽

Soil Processes ◽

Growth Responses ◽

Term Response

Predicting the responses of forest growth to elevated temperature (T) and atmospheric CO2 concentration ([CO2]) on decadal time scales presents a formidable challenge because of the many interacting processes involved. A key uncertainty concerns the relative importance of plant and soil processes to the overall long-term response. In this study, the plant-soil model G'DAY was used to simulate forest growth responses to T and [CO2] on different time scales for forests in cool and warm climates. An equilibrium-based graphical analysis was used to distinguish the roles played by plant and soil processes in determining the response. Doubled [CO2] caused a large initial increase (~20%) in net primary productivity (NPP), but this did not persist in the long term. By contrast, a 2°C increase in T caused a persistent long-term increase in NPP of approximately 10-15%. These responses were similar at cool and warm sites. The equilibrium analysis indicated that soil processes dominated the long-term responses predicted by the model. In particular, the predicted long-term increase in NPP under elevated T reflected an increase in predicted N mineralization and plant N uptake, assuming that a constant fraction of mineralized N is taken up by plants. The analysis highlights key uncertainties for future research.

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Response of plant community structure and primary productivity to experimental drought and flooding in an Alaskan fen

Canadian Journal of Forest Research ◽

10.1139/cjfr-2014-0100 ◽

2015 ◽

Vol 45 (2) ◽

pp. 185-193 ◽

Cited By ~ 23

Author(s):

Amber C. Churchill ◽

Merritt R. Turetsky ◽

A. David McGuire ◽

Teresa N. Hollingsworth

Keyword(s):

Plant Species ◽

Water Table ◽

Primary Productivity ◽

Net Primary Productivity ◽

Species Abundance ◽

Total Biomass ◽

Climate Control ◽

Green Area ◽

Northern Peatlands

Northern peatlands represent a long-term net sink for atmospheric CO2, but these ecosystems can shift from net carbon (C) sinks to sources based on changing climate and environmental conditions. In particular, changes in water availability associated with climate control peatland vegetation and carbon uptake processes. We examined the influence of changing hydrology on plant species abundance and ecosystem primary production in an Alaskan fen by manipulating the water table in field treatments to mimic either sustained flooding (raised water table) or drought (lowered water table) conditions for 6 years. We found that water table treatments altered plant species abundance by increasing sedge and grass cover in the raised water table treatment and reducing moss cover while increasing vascular green area in the lowered water table treatment. Gross primary productivity was lower in the lowered treatment than in the other plots, although there were no differences in total biomass or vascular net primary productivity among the treatments. Overall, our results indicate that vegetation abundance was more sensitive to variation in water table than total biomass and vascular biomass accrual. Finally, in our experimental peatland, drought had stronger consequences for change in vegetation abundance and ecosystem function than sustained flooding.

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A long-term and comprehensive assessment of the urbanization-induced impacts on vegetation net primary productivity

The Science of The Total Environment ◽

10.1016/j.scitotenv.2019.02.361 ◽

2019 ◽

Vol 669 ◽

pp. 342-352 ◽

Cited By ~ 17

Author(s):

Xiaobin Guan ◽

Huanfeng Shen ◽

Xinghua Li ◽

Wenxia Gan ◽

Liangpei Zhang

Keyword(s):

Primary Productivity ◽

Net Primary Productivity ◽

Comprehensive Assessment

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Using net primary productivity and water use efficiency for assessing the degree of land degradation and rehabilitation in the Northeast Asia dryland region

10.5194/egusphere-egu2020-6351 ◽

2020 ◽

Author(s):

Sinkyu Kang ◽

Wenping Kang

Keyword(s):

Species Composition ◽

Water Use Efficiency ◽

Water Use ◽

Land Degradation ◽

Primary Productivity ◽

Net Primary Productivity ◽

Northeast Asia ◽

Term Trend ◽

Use Efficiency

<p>Changes in vegetation productivity and species composition have been used as conventional indicators of land degradation and rehabilitation assessments. The two biophysical parameters vary nonlinearly during land change process with various time lags, which provide, as a whole, a useful framework to diagnose degree of land degradation and rehabilitation. In this study, the net primary productivity (NPP) and water use efficiency (WUE), which are the proxies of vegetation productivity and ecophysiological properties related to species composition, were combined to develop an eco-physiological framework to assess the degree of land degradation in the Northeast-Asia dryland regions (NADR) from 1982 to 2012. Results from long-term trends analysis showed early, middle or late degradation stages occurred in northern grassland and central barren or sparsely vegetated regions, respectively, while the rehabilitation prevailed in eastern croplands and forest, southern, and western grassland. In contrast, short-term trend analysis illustrated the recent rehabilitation in mideastern Mongolia and Loess Plateau, which was unseen in long-term trend analysis. The spatial patterns and temporal changes of land degradation and rehabilitation could be explained partly by either or both natural and anthropogenic factors. Longterm drying and warming might induce land degradation in northern and central NADR, respectively, while the recovery projects and wetting conditions after 2000s promoted the land rehabilitation in Loess Plateau and mid-eastern Mongolia. Here, our NPP&#8211;WUE framework may contribute further conceptual development and rapid assessments on land degradation and rehabilitation in wide geographic regions.</p>

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Effects of stand age on net primary productivity of boreal black spruce forests in Ontario, Canada

Canadian Journal of Forest Research ◽

10.1139/x01-165 ◽

2002 ◽

Vol 32 (5) ◽

pp. 833-842 ◽

Cited By ~ 69

Author(s):

Wenjun Chen ◽

Jing M Chen ◽

David T Price ◽

Josef Cihlar

Keyword(s):

Primary Productivity ◽

Net Primary Productivity ◽

Fine Root ◽

Black Spruce ◽

Practical Method ◽

Root Turnover ◽

Stand Age ◽

New Techniques ◽

Fine Root Turnover

Quantification of the effects of stand age on its net primary productivity (NPP) is critical for estimating forest NPP and carbon budget at regional to global scales. This paper reports a practical method for quantifying ageNPP relationships using existing normal yield tables, biomass equations, and measurements of fine-root turnover and litterfall. Applying this method, we developed mean ageNPP relationships for black spruce (Picea mariana (Mill.) BSP) stands in Ontario. We define "mean ageNPP relationship", as the changes in NPP that occur with age under long-term mean environmental conditions. These relationships indicate that NPP at more productive sites culminates to a higher value and at an earlier age and also declines more rapidly thereafter. A further component analysis indicates that the decrease in biomass growth of woody tissues is the main contributor to the decline with age. Finally, error assessment suggests that the uncertainty in NPP estimates can be substantially reduced with a better quantification of fine-root turnover and litterfall, which are the two dominant NPP components, particularly in the later stages of stand development. With new techniques now available, more accurate measurement of these components is possible, and thus strongly recommended.

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