Feedbacks between vegetation and disturbance processes promote long-term persistence of forest-grassland mosaics in south Brazil

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Cotton yield and fiber quality affected by row spacing and shading at different growth stages

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Crop, Native Vegetation, and Biofuels: Response of White- Tailed Deer to Changing Management Priorities

The expansion of the cellulosic biofuels industry throughout the United States has broad-scale implications for wildlife management on public and private lands. Knowledge is limited on the effects of reverting agriculture to native grass, and vice versa, on size of home range and habitat use of white-tailed deer (Odocoileus virginianus). We followed 68 radio-collared female deer from 1991 through 2004 that were residents of DeSoto National Wildlife Refuge (DNWR) in eastern Nebraska, USA. The refuge was undergoing conversion of vegetation out of row-crop agriculture and into native grass, forest, and emergent aquatic vegetation. Habitat in DNWR consisted of 30% crop in 1991 but removing crops to establish native grass and wetland habitat at DNWR resulted in a 44% reduction in crops by 2004. A decrease in the amount of crops on DNWR contributed to a decline in mean size of annual home range from 400 ha in 1991 to 200 ha in 2005 but percentage of crops in home ranges increased from 21% to 29%. Mean overlap for individuals was 77% between consecutive annual home ranges across 8 years, regardless of crop availability. Conversion of crop to native habitat will not likely result in home range abandonment but may impact disease transmission by increasing rates of contact between deer social groups that occupy adjacent areas. Future research on condition indices or changes in population parameters (e.g., recruitment) could be incorporated into the study design to assess impacts of habitat conversion for biofuel production.

Surface ecophysiological behavior across vegetation and moisture gradients in tropical South America

Surface ecophysiology at five sites in tropical South America across vegetation and moisture gradients is investigated. From the moist northwest (Manaus) to the relatively dry southeast (Pé de Gigante, state of São Paulo) simulated seasonal cycles of latent and sensible heat, and carbon flux produced with the Simple Biosphere Model (SiB3) are confronted with observational data. In the northwest, abundant moisture is available, suggesting that the ecosystem is light-limited. In these wettest regions, Bowen ratio is consistently low, with little or no annual cycle. Carbon flux shows little or no annual cycle as well; efflux and uptake are determined by high-frequency variability in light and moisture availability. Moving downgradient in annual precipitation amount, dry season length is more clearly defined. In these regions, a dry season sink of carbon is observed and simulated. This sink is the result of the combination of increased photosynthetic production due to higher light levels, and decreased respiratory efflux due to soil drying. The differential response time of photosynthetic and respiratory processes produce observed annual cycles of net carbon flux. In drier regions, moisture and carbon fluxes are in-phase; there is carbon uptake during seasonal rains and efflux during the dry season. At the driest site, there is also a large annual cycle in latent and sensible heat flux.

Emissions of volatile organic compounds from tropical savanna vegetation and biomass burning

This dissertation focuses on characterizing the emissions of volatile organic compounds (VOCs) from grasses and young trees, and the burning of biomass mainly from Africa and Indonesia. The measurements were performed with a proton-transfer-reaction mass spectrometer (PTR-MS). The biogenic emissions of tropical savanna vegetation were studied in Calabozo (Venezuela). Two field campaigns were carried out, the first during the wet season (1999) and the second during the dry season (2000). Three grass species were studied: T. plumosus, H. rufa and A. canescens, and the tree species B. crassifolia, C. americana and C. vitifolium. The emission rates were determined with a dynamic plant enclosure system. In general, the emissions increased exponentially with increasing temperature and solar radiation. Therefore, the emission rates showed high variability. Consequently, the data were normalized to a standard temperature of 30°C, and standard emission rates thus determined allowed for interspecific and seasonal comparisons. The range of average daytime (10:00-16:00) emission rates of total VOCs measured from green (mature and young) grasses was between 510-960 ngC/g/h. Methanol was the primary emission (140-360 ngC/g/h), followed by acetaldehyde, butene and butanol and acetone with emission rates between 70-200 ngC/g/h. The emissions of propene and methyl ethyl ketone (MEK) were <80 ngC/g/h, and those of isoprene and C5-alcohols were between 10-130 ngC/g/h. The oxygenated species represented 70-75% of the total. The emission of VOCs was found to vary by up to a factor of three between plants of the same species, and by up to a factor of two between the different species. The annual source of methanol from savanna grasses worldwide estimated in this work was 3 to 4.4 TgC, which could represent up to 12% of the current estimated global emission from terrestrial vegetation. Two of the studied tree species, were isoprene emitters, and isoprene was also their primary emission (which accounted for 70-94% of the total carbon emitted) followed by methanol and butene + butanol. The daytime average emission rate of isoprene measured in the wet season was 27 mgC/g/h for B. crassifolia, and 123 mgC/g/h for C. vitifolium. The daytime emissions of methanol and butene + butanol were between 0.3 and 2 mgC/g/h. The total sum of VOCs emission measured during the day in the wet season was between 30 and 130 mgC/g/h. In the dry season, in contrast, the methanol emissions from C. vitifolium saplings –whose leaves were still developing– were an order of magnitude higher than in the wet season (15 mgC/g/h). The isoprene emission from B. crassifolia in the dry season was comparable to the emission in the wet season, whereas isoprene emission from C. vitifolium was about a factor of three lower (~43 mgC/g/h). Biogenic emission inventories show that isoprenoids are the most prominent and best-studied compounds. The standard emission rates of isoprene and monoterpenes of the measured savanna trees were in the lower end of the range found in the literature. The emission of other biogenic VOCs has been sparsely investigated, but in general, the standard emissions from trees studied here were within the range observed in previous investigations. The biomass burning study comprised the measurement of VOCs and other trace-gas emissions of 44 fires from 15 different fuel types, primarily from Africa and Indonesia, in a combustion laboratory. The average sum of emissions (excluding CO2, CO and NO) from African fuels was ~18 g(VOC)/kg. Six of the ten most important emissions were oxygenated VOCs. Acetic acid was the major emission, followed by methanol and formaldehyde. The emission of methane was of the same order as the methanol emission (~5 g/kg), and that of nitrogen-containing compounds was ~1 g/kg. An estimate of the VOC source from biomass burning of savannas and grasslands worldwide suggests that the sum of emissions is about 56 Tg/yr, of which 34 Tg correspond to oxygenated VOCs, 14 Tg to unsaturated and aromatic compounds, 5 Tg to methane and 3 Tg to N-compounds. The estimated emissions of CO, CO2 and NO are 216, 5117 and 9.4 Tg/yr, respectively. The emission factors reported here for Indonesian fuels are the first results of laboratory fires using Indonesian fuels. Acetic acid was the highest organic emission, followed by acetol, a compound not previously reported in smoke, methane, mass 97 (tentatively identified as furfural, dimethylfuran and ethylfuran), and methanol. The sum of total emissions of Indonesian fuels was 91 g/kg, which is 5 times higher than the emissions from African fuels. The results of this study reinforces the importance of oxygenated compounds. Due to the vast area covered by tropical savannas worldwide, the biogenic and biomass burning emission of methanol and other oxygenated compounds may be important for the regional and even global tropospheric chemistry.

Effects of flooding on coastal vegetation and salt marshes

This thesis examines the effects of flooding on coastal and salt marsh vegetation. I conducted a field experiment in Bellocchio Lagoon to test the effects of different inundation periods (Level 1 = 0.468 or 11.23 hours; Level 2 = 0.351 or 8.42 hours; Level 3 = 0.263 or 6.312 hours; Level 4 = 0.155 or 3.72 hours; Level 5 = 0.082 or 1.963 hours; Level 6 = 0.04 or 0.96 hours) on the growth responses and survival of the salt marsh grass Spartina maritima in summer 2011 and 2012. S. maritima grew better at intermediate inundation times (0,351 hours; 0,263 hours, 0,115 hours; 0,082 hours), while growth and survival were reduced at greater inundation periods (0,468 hours). The differences between the 2011 and 2012 experiment were mainly related to differences in the initial number of shoots (1 and 5, respectively in 2011 and 2012). In the 2011 experiment a significant lower number of plants was present in the levels 1 and 6, the rhizomes reached the max pick in level 4, weights was major in level 4, spike length reached the pick in level 3 while leaf length in level 2. In the 2012 experiment the plants in level 6 all died, the rhizomes were more present in level 3, weights was major in level 3, spike length reached the pick in level 3, as well as leaf length. I also conducted a laboratory experiment which was designed to test the effects of 5 different inundation periods (0 control, 8, 24, 48, 96 hours) on the survival of three coastal vegetation species Agrostis stolonifera, Trifolium repens and Hippopae rhamnoides in summer 2012. The same laboratory experiment was repeated in the Netherlands. In Italy, H. rhamnoides showed a great survival in the controls, a variable performance in the other treatments and a clear decrease in treatment 4. Conversely T. repens and A. stolonifera only survive in the control. In the Netherlands experiment there was a greater variability responses for each species, still at the end of the experiment survival was significantly smaller in treatment 4 (96 h of seawater inundation) for all the three species. The results suggest that increased flooding can affect negatively the survival of both saltmarsh and coastal plants, limiting root system extension and leaf growth. Flooding effect could lead to further decline and fragmentation of the saltmarshes and coastal vegetation, thereby reducing recovery (and thus resilience) of these systems once disturbed. These effects could be amplified by interactions with other co-occurring human impacts in these systems, and it is therefore necessary to identify management options that increase the resilience of these systems.

Vegetation and Acidification

In this chapter, the impact of watershed acidification treatments on WS3 at the Fernow Experimental Forest (FEF) and at WS9 on vegetation is presented and summarized in a comprehensive way for the first time. WS7 is used as a vegetative reference basin for WS3, while untreated plots within WS9 are used as a vegetative reference for WS9. Bioindicators of acidification impacts that will be considered include several measures of tree and stand growth rates, foliar chemistry, bolewood chemistry, and herbaceous species composition and diversity. These studies enhance our understanding of the inter-relationships of changes in soil conditions caused by the acidification treatment and the condition of forest vegetation.