Terrestrial ecosystems have continued to provide the critical service of slowing the atmospheric CO2 growth rate. Terrestrial net primary productivity (NPP) is thought to be a major contributing factor to this trend. Yet our ability to estimate NPP at the regional scale remains limited due to large uncertainties in the response of NPP to multiple interacting climate factors and uncertainties in the driver data sets needed to estimate NPP. In this study, we introduced an improved NPP algorithm that used local driver data sets and parameters in China. We found that bias decreased by 30% for gross primary production (GPP) and 17% for NPP compared with the widely used global GPP and NPP products, respectively. From 2000 to 2012, a pixel-level analysis of our improved NPP for the region of China showed an overall decreasing NPP trend of 4.65TgCa(-1). Reductions in NPP were largest for the southern forests of China (-5.38TgCa(-1)), whereas minor increases in NPP were found for North China (0.65TgCa(-1)). Surprisingly, reductions in NPP were largely due to decreases in solar radiation (82%), rather than the more commonly expected effects of drought (18%). This was because for southern China, the interannual variability of NPP was more sensitive to solar radiation (R-2 in 0.29-0.59) relative to precipitation (R-2<0.13). These findings update our previous knowledge of carbon uptake responses to climate change in terrestrial ecosystems of China and highlight the importance of shortwave radiation in driving vegetation productivity for the region, especially for tropical forests.

abstract: Climate change will result not only in changes in the mean state of climate but also on changes in variability. However, most studies of the impact of climate change on ecosystems have focused on the effect of changes in the central tendency. The broadest objective of this thesis was to assess the effects of increased interannual precipitation variation on ecosystem functioning in grasslands. In order to address this objective, I used a combination of field experimentation and data synthesis. Precipitation manipulations on the field experiments were carried out using an automated rainfall manipulation system developed as part of this dissertation. Aboveground net primary production responses were monitored during five years. Increased precipitation coefficient of variation decreased primary production regardless of the effect of precipitation amount. Perennial-grass productivity significantly decreased while shrub productivity increased as a result of enhanced precipitation variance. Most interesting is that the effect of precipitation variability increased through time highlighting the existence of temporal lags in ecosystem response. Further, I investigated the effect of precipitation variation on functional diversity on the same experiment and found a positive response of diversity to increased interannual precipitation variance. Functional evenness showed a similar response resulting from large changes in plant-functional type relative abundance including decreased grass and increased shrub cover while functional richness showed non-significant response. Increased functional diversity ameliorated the direct negative effects of precipitation variation on ecosystem ANPP but did not control ecosystem stability where indirect effects through the dominant plant-functional type determined ecosystem stability. Analyses of 80 long-term data sets, where I aggregated annual productivity and precipitation data into five-year temporal windows, showed that precipitation variance had a significant effect on aboveground net primary production that is modulated by mean precipitation. Productivity increased with precipitation variation at sites where mean annual precipitation is less than 339 mm but decreased at sites where precipitation is higher than 339 mm. Mechanisms proposed to explain patterns include: differential ANPP response to precipitation among sites, contrasting legacy effects and soil water distribution. Finally, increased precipitation variance may impact global grasslands affecting plant-functional types in different ways that may lead to state changes, increased erosion and decreased stability that can in turn limit the services provided by these valuable ecosystems. / Dissertation/Thesis / Doctoral Dissertation Biology 2014

In addition to causing an increase in mean temperatures, climate change is also altering precipitation regimes across the globe. General circulation models project both latitude-dependent changes in precipitation mean and increases in precipitation variability. These changes in water availability will impact terrestrial primary productivity, the fixation of carbon dioxide into organic matter by plants. In my thesis, I addressed the following three questions: 1.) What will be the relative effect of changes in the mean and standard deviation of annual precipitation on mean annual primary production? 2.) Which ecosystems will be the most sensitive to changes in precipitation? 3.) Will increases in production variability be disproportionately greater than increases in precipitation variability? I gathered 58 time series of annual precipitation and aboveground net primary production (ANPP) from long-term ecological study sites across the globe. I quantified the sensitivity of ANPP at each site to changes in precipitation mean and variance. My results indicated that mean ANPP is about 40 times more sensitive to changes in precipitation mean than to changes in precipitation variance. I showed that semi-arid ecosystems such as shortgrass steppe in Colorado or typical steppe in Inner Mongolia may be the most sensitive to changes in precipitation mean. At these sites and several others, a 1% change in mean precipitation may result in a change in ANPP that is greater than 1%. To address how increases in interannual precipitation variability will impact the variability of ANPP, I perturbed the variability of observed precipitation time series and evaluated the impact of this perturbation on predicted ANPP variability. I found that different assumptions about the precipitation-ANPP relationship had different implications for how increases in precipitation variability will impact ANPP variability. Increases in ANPP variability were always directly proportional to increases in precipitation variability when ANPP was modeled as a simple linear or a lagged function of precipitation. However, when ANPP was modeled as a nonlinear, saturating function of precipitation, increases in ANPP variability were disproportionately low compared to increases in precipitation variability during wet years but disproportionately high during dry years. My thesis addresses an existing research gap regarding the long-term impact of increases in interannual precipitation variability on key ecosystem functioning. I showed that increases in precipitation variability will have negligible impacts on ANPP mean and have disproportionately large impacts on ANPP variability only when ANPP is a concave down, nonlinear function of precipitation. My work also demonstrates the importance of the precipitation-ANPP relationship in determining the magnitude of impacts to ANPP caused by changes in precipitation. Finally, my thesis highlights the potential for considerable changes in ANPP variability due to increases in precipitation variability.

京都大学 / 0048 / 新制・課程博士 / 博士(農学) / 甲第21163号 / 農博第2289号 / 新制||農||1060(附属図書館) / 学位論文||H30||N5137(農学部図書室) / 京都大学大学院農学研究科森林科学専攻 / (主査)教授 大澤 晃, 教授 北島 薫, 教授 神﨑 護 / 学位規則第4条第1項該当 / Doctor of Agricultural Science / Kyoto University / DGAM

abstract: Aboveground net primary production (ANPP) is an important ecosystem process that, in drylands, is most frequently limited by water availability. Water availability for plants is in part controlled by the water holding capacity of soils. Available water holding capacity (AWHC) of soils is strongly influenced by soil texture and depth. This study drew upon localized rain gauge data and four data-sets of cover-line and biomass data to estimate ANPP and to determine annual precipitation (PPT). I measured soil depth to caliche and texture by layer of 112 plots across the four landscape units for which estimation of ANPP were available. A pedotransfer function was used to estimate AWHC from soil depth increments to depth of caliche measurements and texture analysis. These data were analyzed using simple and multivariate regression to test the effect of annual precipitation and available water holding capacity on aboveground net primary production. Soil texture remained constant among all plots (sandy loam) and depth to caliche varied from 15.16 cm to 189 cm. AWHC and the interaction term (PPT*AWHC) were insignificant (p=0.142, p=0.838) and annual PPT accounted for 18.4% of the variation in ANPP. The y-intercept was significantly different for ANPP ~ annual PPT when considering AWHC values either above or below 3 cm. Shrub ANPP was insensitive to precipitation regardless of AWHC (R2=-0.012, R2=0.014). Results from this study indicate that a model incorporating annual PPT and AWHC may not serve as a good predictor for ANPP at a site level where there is little variation in soil texture. / Dissertation/Thesis / Masters Thesis Sustainability 2019

No description available.

In the southwest United States, the current prolonged warm drought is similar to the predicted future climate change scenarios for the region. This study aimed to determine patterns in vegetation response to the early 21st century drought across multiple biomes. We hypothesized that different biomes (forests, shrublands, and grasslands) would have different relative sensitivities to both climate drivers (precipitation and temperature) and legacy effects (previous-year's productivity). We tested this hypothesis at eight Ameriflux sites in various Southwest biomes using NASA Moderate-resolution Imaging Spectroradiometer Enhanced Vegetation Index (EVI) from 2001 to 2013. All sites experienced prolonged dry conditions during the study period. The impact of combined precipitation and temperature on Southwest ecosystems at both annual and sub-annual timescales was tested using Standardized Precipitation Evapotranspiration Index (SPEI). All biomes studied had critical sub-annual climate periods during which precipitation and temperature influenced production. In forests, annual peak greenness (EVImax) was best predicted by 9-month SPEI calculated in July (i.e., January-July). In shrublands and grasslands, EVImax was best predicted by SPEI in July through September, with little effect of the previous year's EVImax. Daily gross ecosystem production (GEP) derived from flux tower data yielded further insights into the complex interplay between precipitation and temperature. In forests, GEP was driven by cool-season precipitation and constrained by warm-season maximum temperature. GEP in both shrublands and grasslands was driven by summer precipitation and constrained by high daily summer maximum temperatures. In grasslands, there was a negative relationship between temperature and GEP in July, but no relationship in August and September. Consideration of sub-annual climate conditions and the inclusion of the effect of temperature on the water balance allowed us to generalize the functional responses of vegetation to predicted future climate conditions. We conclude that across biomes, drought conditions during critical sub-annual climate periods could have a strong negative impact on vegetation production in the southwestern United States.

Die Rotbuche (Fagus sylvatica L.) ist die bestimmende Baumart der potentiell natürlichen Vegetation in den Wäldern Mittel- und Westeuropas die ökonomisch bedeutsamste Laubbaumart Deutschlands. Obwohl diese spät-sukzessionelle Baumart über eine hohe physiologische Toleranz gegenüber einem weiten Spektrum klimatischer Wuchsbedingungen verfügt, wird die Buche gegenüber anderen temperaten Laubbaumarten als relativ trockensensitiv eingeschätzt. Da im Zuge des globalen Klimawandels mit einer Verschlechterung der klimatischen Wasserbilanz und mit einer Zunahme sommerlicher Trockenperioden gerechnet wird, wird die zukünftige Rolle der Rotbuche in der europäischen Forstwirtschaft derzeit intensiv diskutiert. Diese Studie hatte zum Ziel, hydrologische und klimatische Einflüsse auf die Produktivität und die Vitalität der Rotbuche zu untersuchen. Hierdurch sollen grundlegende Mechanismen der Trockenstressantwort bei dieser trocken-sensitiven Art identifiziert, und Rückschlüsse auf zukünftige Klimaantworten von Buchenbeständen ermöglicht werden. Zu diesem Zweck wurde die ober- und unterirdische Biomasseproduktion von 12 Buchenaltbeständen im Norddeutschen Tiefland entlang eines natürlichen Niederschlagsgradienten (543-816 mm a-1) auf einheitlichem geologischen Substrat ermittelt. Um den zusätzlichen Einfluss der Wasserspeicherkapazität der Böden zu berücksichtigen, wurden Paare von Buchenbeständen untersucht, die unter nahezu identischen klimatischen Bedingungen, jedoch auf Böden unterschiedlicher Textur (sandige versus lehmig-sandige Böden) stockten. Einflüsse der Wasserverfügbarkeit und klimatischer Variationen auf das Wachstum wurden untersucht unter Berücksichtigung (i) der gesamten ober- und unterirdischen Biomasseproduktion, (ii) der Dynamik von Ressourcen-Allokation und Kohlenstoff-Partitionierung, sowie (iii) der Morphologie wasseraufnehmender und -abgebender Oberflächen. Unerwarteterweise zeigte sich die gesamte Produktivität von Buchen-Altbeständen nur geringfügig von Veränderungen der hydrologischen Regime entlang des Gradienten beeinflusst. Trotz deutlicher Unterschiede in der jährlichen Wasserverfügbarkeit nahmen die oberirdische und die gesamte Biomasseproduktion auf den trockeneren Flächen des Transektes nicht ab. Allerdings führten ausgeprägte früh-sommerliche Wasserdefizite (in den Monaten Juni und Juli) zu deutlichen Einbußen der oberirdischen Biomasseproduktion, und insbesondere der Stammholzproduktion. Entlang des untersuchten Gradienten konnte eine ausgeprägte, kontinuierliche Verschiebung der Allokationsmuster festgestellt werden: Mit abnehmender Wasserverfügbarkeit nahm die Feinwurzelproduktion zu und das Verhältnis von oberirdischer:unterirdischer Biomasseproduktion ab. Anders als oberirdische Komponenten zeigte die Feinwurzelproduktion eine hohe Sensibilität gegenüber Unterschieden hinsichtlich hydrologischer Regime. In Übereinstimmung mit der Optimalitätstheorie der pflanzlichen Ressourcennutzung konnte dieses Allokationsverhalten in sowohl in Reaktion auf veränderte Niederschläge, als auch in Antwort auf auch veränderte Wasserspeicherkapazitäten beobachtet werden. Allokative Anpassungsmechanismen an Wassermangel wurden im Feinwurzelbereich zusätzlich durch morphologische Plastizität (Zunahme im Verhältnis von Oberfläche: Biomasse) und durch Regulierung der räumlichen Verteilung (zunehmende Konzentrierung von Feinwurzeln in der organischen Auflage) komplementiert. Im Gegensatz zu diesen komplexen unterirdischen Trockenheits-Antworten konnten keinerlei Anpassungen der Blattmorphologie an veränderte hydrologische Bedingungen festgestellt werden. Neben Reaktionen auf Wasserverfügbarkeit wurde die Fruchtbildung als zweiter wesentlicher Einfluss auf das Allokationsverhalten der Buche erkannt. Eine deutliche Ressourcen-Allokation zu Gunsten der Fruchtentwicklung beeinträchtigte maßgeblich das oberirdische vegetative Wachstum, insbesondere den Stammholzzuwachs. Auf Grund einer hohen Attraktionsstärke der Früchte gegenüber C und N führte zunehmende Fruktifizierung auch zu einer Gewichts- (und Größen-) Abnahme der Einzelblätter und somit zu reduzierter Bildung von Blattmasse und Bestandesblattfläche (LAI). Neben dieser Abnahme an assimilierender Blattoberfläche führte auch eine deutliche Senkung der Blatt-Stickstoffgehalte in Folge der reproduktiven Ressourcenwidmung mutmaßlich zu einer Verschlechterung der C-Bilanz, sowohl im Mast- als auch im Folgejahr. Eine Analyse klimatischer Einflussfaktoren auf das Mastverhalten legt nahe, dass die Blütenbildung der Buche durch Überschreitung eines Schwellenwertes der Kohlenstoffassimilation im Frühsommer (Juni-Juli) induziert wird. Sofern diese Schlüsse zutreffen, unterliegt das zeitliche Muster der Fruktifikations-Antwort auf Witterungsauslöser einer Rückkopplungskontrolle durch pflanzliche Stickstoff-Dynamik. Vor dem Hintergrund anhaltend erhöhter Stickstoffdepositionen ergäbe sich aus diesem Mechanismus eine zusätzliche Belastung für das zukünftige vegetative Wachstum der Buche. Es ist anzunehmen, dass die in dieser Studie belegte hohe allokative Plastizität in Altbäumen Fagus sylvatica dazu befähigt, ihre hohe Konkurrenzkraft in einem breiten Spektrum hydrologischer Regime zu entfalten. Darüber hinaus werden die hier dargestellten Mechanismen einer langfristigen Trockenheitsanpassung mutmaßlich zu einer gesteigerten Resistenz und Resilienz von Buchen-Altbeständen gegenüber Ereignissen extremer Sommertrockenheit beitragen.

The global carbon (C) balance is vulnerable to disturbances that alter terrestrial C uptake and loss. Moderate disturbances that kill or defoliate only a subset of canopy trees such as insect defoliation, drought, and age-related senescence are increasing in extent and frequency; yet, little is known about the effect of moderate disturbance on forest production and the mechanisms sustaining or supporting the recovery of the C cycle across a range of moderate disturbance severities. We used a broad plot-scale gradient of upper canopy tree mortality within a large manipulation of forest disturbance to: 1) quantify how aboveground wood net primary production (ANPPw) responds to a range of moderate disturbance severities and; 2) identify the primary mechanisms supporting ANPPw resistance or resilience following moderate disturbance. We found that ANPPw was highly resistant to moderate disturbance, with production levels sustained following the senescence of 9 to > 60 % of the upper canopy tree basal area. As upper canopy gap fraction increased with rising disturbance severity, greater light availability to the subcanopy enhanced leaf-level C uptake and the growth of this formerly light-limited canopy stratum, compensating for upper canopy production losses. As a result, whole-ecosystem production efficiency (ANPPw/LAI) increased at high levels of disturbance severity and leaf area loss. These findings provide a mechanistic explanation for sustained ANPPw across the disturbance gradient, in which the physiological and growth enhancement of undisturbed vegetation was proportional to the level of disturbance severity. Our results have important ecological and management implications, showing that moderate disturbances may minimally alter ecosystem functions such as C storage.

Temperate forests are complex ecosystems that sequester carbon (C) in biomass. C storage is related to ecosystem-scale forest structure, changing over succession, disturbance, and with community composition. We quantified ecosystem biological and physical structure in two forest chronosequences varying in disturbance intensity, and three late successional functional types to examine how multiple structural expressions relate to ecosystem C cycling. We quantified C cycling as wood net primary production (NPP), ecosystem structure as Simpson’s Index, and physical structure as leaf quantity (LAI) and arrangement (rugosity), examining how wood NPP-structure relates to light distribution and use-efficiency. Relationships between structural attributes of biodiversity, LAI, and rugosity differed. Development of rugosity was conserved regardless of disturbance and composition, suggesting optimization of vegetation arrangement over succession. LAI and rugosity showed significant positive productivity trends over succession, particularly within deciduous broadleaf forests, suggesting these measures of structure contain complementary, not redundant, information related to C cycling.