Impact of changing soil moisture distribution on net ecosystem productivity of a boreal aspen forest during and following drought

Krishnan, P.; Black, T. Andrew; Grant, N.J.; Barr, Alan G.; Hogg, Edward H.; Jassal, Rachhpal S.; Morgenstern, K.

doi:10.1016/j.agrformet.2006.07.002

Cited by 186 publications

(147 citation statements)

References 66 publications

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“…Mao et al (2002) derived values for α in a subtropical region of Florida (USA) over sawgrass and cattail communities interspersed with open water areas of between 1.12 and 0.90. Most available literature regarding suitable α values is, however, derived from studies in subarctic regions (Eaton et al, 2001), arid areas (Bidlake, 2000), over lakes (Rosenberry et al, 2007) or boreal aspen forest (Krishnan et al, 2006). The Priestley-Taylor α is site-specific and these estimates from the Mfabeni Mire for southern African vegetation and climatic conditions are valuable.…”

Section: Discussionmentioning

confidence: 99%

Measurement and modelling of evaporation from a coastal wetland in Maputaland, South Africa

Clulow

Everson

Mengistu

et al. 2012

Hydrol. Earth Syst. Sci.

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Abstract. The surface renewal (SR) method was used to determine the long-term (12 months) total evaporation (ET) from the Mfabeni Mire with calibration using eddy covariance during two window periods of approximately one week each. The SR method was found to be inexpensive, reliable and with low power requirements for unattended operation.Despite maximum ET rates of up to 6.0 mm day −1 , the average summer (October to March) ET was lower (3.2 mm day −1 ) due to early morning cloud cover that persisted until nearly midday at times. This reduced the daily available energy, and the ET was lower than expected despite the available water and high average wind speeds. In winter (May to September), there was less cloud cover but the average ET was only 1.8 mm day −1 due to plant senescence. In general ET was suppressed by the inflow of humid air (low vapour pressure deficit) and the comparatively low leaf area index of the wetland vegetation. The accumulated ET over 12 months was 900 mm. Daily ET estimates were compared to the Priestley-Taylor model results and a calibration α = 1.0 (R 2 = 0.96) was obtained for the site. A monthly crop factor (K c ) was determined for the standardised FAO-56 Penman-Monteith. However, K c was variable in some months and should be used with caution for daily ET modelling.These results represent not only some of the first longterm measurements of ET from a wetland in southern Africa, but also one of the few studies of actual ET in a subtropical peatland in the Southern Hemisphere. The study provides wetland ecologists and hydrologists with guidelines for the use of two internationally applied models for the estimation of wetland ET within a coastal, subtropical environment and shows that wetlands are not necessarily high water users.

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Section: Discussionmentioning

confidence: 99%

Measurement and modelling of evaporation from a coastal wetland in Maputaland, South Africa

Clulow

Everson

Mengistu

et al. 2012

Hydrol. Earth Syst. Sci.

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“…The sign of the correlation coefficient depends on the relationships between climatic and biotic drivers (Ricciuto et al, 2008;Krishnan et al, 2006;Tjoelker et al, 2001). The relative contributions of these relationships determine the ultimate correlation between BE and CE in an ecosystem.…”

Section: Biotic Responses Of C Cycling To Climatic Variationsmentioning

confidence: 99%

Biotic and climatic controls on interannual variability in carbon fluxes across terrestrial ecosystems

Shao

Zhou

Luo

et al. 2015

Agricultural and Forest Meteorology

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a b s t r a c tInterannual variability (IAV, represented by standard deviation) in net ecosystem exchange of CO 2 (NEE) is mainly driven by climatic drivers and biotic variations (i.e., the changes in photosynthetic and respiratory responses to climate), the effects of which are referred to as climatic (CE) and biotic effects (BE), respectively. Evaluating the relative contributions of CE and BE to the IAV in carbon (C) fluxes and understanding their controlling mechanisms are critical in projecting ecosystem changes in the future climate. In this study, we applied statistical methods with flux data from 65 sites located in the Northern Hemisphere to address this issue. Our results showed that the relative contribution of BE (CnBE) and CE (CnCE) to the IAV in NEE was 57% ± 14% and 43% ± 14%, respectively. The discrepancy in the CnBE among sites could be largely explained by water balance index (WBI). Across water-stressed ecosystems, the CnBE decreased with increasing aridity (slope = 0.18% mm −1 ). In addition, the CnBE tended to increase and the uncertainty reduced as timespan of available data increased from 5 to 15 years. Inter-site variation of the IAV in NEE mainly resulted from the IAV in BE (72%) compared to that in CE (37%). Interestingly, positive correlations between BE and CE occurred in grasslands and dry ecosystems (r > 0.45, P < 0.05) but not in other ecosystems. These results highlighted the importance of BE in determining the IAV in NEE and the ability of ecosystems to regulate C fluxes under climate change might decline when the ecosystems experience more severe water stress in the future.

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“…The same study determined that ecosystem respiration rates respond more quickly to drought onset, and are more sensitive to the end of a drought period than are ecosystem photosynthesis rates. This can be attributed to the fact that respiration rates are influenced by near-surface water content in soils, whereas photosynthesis rates are influenced by soil water content deeper in the rhizosphere (Krishnan, et al, 2006). In aspen, the severity of drought stress impacts the degree to which root water flow properties are altered (Siemens and Zwiazek, 2003).…”

Section: Acute Droughtmentioning

confidence: 99%

“…The impacts of drought on aspen includes a decrease in leaf area index (LAI), which continues to be affected up to two years following the drought event (Krishnan et al, 2006). The same study suggested that ecosystem respiration rates respond more quickly to drought onset, and are more sensitive to the end of a drought period than are ecosystem photosynthesis rates.…”

Section: Introductionmentioning

confidence: 99%

Aspen mortality in the Colorado and southern Wyoming Rocky Mountains: Extent, severity, and causal factors

Dudley

Burns

Jacobi

2015

Forest Ecology and Management

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We established 573 random roadside survey plots in stands that contained at least 50% aspen cover type. From these random plots, we found average standing aspen tree mortality ranged from 3.3 to 23.7 % on the four national forests and 11% on the east side of the continental divide and 4 % on the west side. Low elevation stands had significantly less mortality (7%) vs. high elevation (8%). The roadside plot data suggests that Colorado's aspen on these four national forests overall were healthy; mortality rates iii among aspen were fairly low (~3 -8%) among all stems, and average percent live crown among adults was high (~85 -90%), in spite of nearly ubiquitous presence of disease (~97 -99%) and high incidence of insect damage (~50 -75%).We also established 98 aspen stand assessment plots with half of the plots in damaged stands, as defined by U.S.D.A. Forest Service aerial detection surveys (ADS), and half in healthy aspen stands. Damaged stands were defined as those stands with (1) thinning crowns among at least 25% of adult aspen, (2) stands with moderate (<50% of stems) levels of overstory mortality, or (3) stands with high (>50% of stems) levels of overstory mortality. Healthy aspen stands were defined as having (1) a maximum mortality rate of 5 -7% among all aspen, and/or (2) more than 75% of adult aspen with full crowns.Adult aspen in damaged stands tended to be less vigorous, based a health score index from 1 to 5, with higher scores indicating less healthy conditions (where 1=0-25% damage; 2 = 25-50% damage; 3 = >50% damage; 4 = recent dead; 5 = >5 years dead).Health scores averaged 1.7 in healthy stands, compared to 2.3 in damaged stands.Saplings in damaged stands tended to be healthier with a score of 1.7, compared to 2.2 in healthy stands. Further, there was no difference in the proportion live or total numbers of saplings per hectare between healthy and damaged stands. The prevalence of damaging organisms, such as Cytospora canker (20% in damaged, 13% in healthy), wood-boring insects (27% in damaged, 10% in healthy), and aspen bark beetles (16% in damaged, 7% in healthy) was considerably greater among damaged stands. Site conditions also influenced the prevalence of some of these damage agents: bark beetles were most common among stands at low elevations (18%, compared to 11% and 6% at moderate iv and high elevations, respectively); Cytospora canker was most common among stands on south-or west-facing aspects (20% and 19%, respectively); both aspen bark beetles and Cytospora canker were also most common among stands in the southernmost section of the survey area, the Pike-San Isabel national forest (41% and 36%). There was no difference in the severity of canker or decay fungal infection between healthy and damaged stands. Cytospora canker infestations were more severe on the Medicine Bow NF compared to the other three national forests, and Marssonina foliar blight infection appeared to be most severe on slope summits, concave sites, and sites with either no to low percent slope or moderately steep sl...

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Impact of changing soil moisture distribution on net ecosystem productivity of a boreal aspen forest during and following drought

Cited by 186 publications

References 66 publications

Measurement and modelling of evaporation from a coastal wetland in Maputaland, South Africa

Measurement and modelling of evaporation from a coastal wetland in Maputaland, South Africa

Biotic and climatic controls on interannual variability in carbon fluxes across terrestrial ecosystems

Aspen mortality in the Colorado and southern Wyoming Rocky Mountains: Extent, severity, and causal factors

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