3 results
Anthropogenic hillslope terraces and swidden agriculture in Jiuzhaigou National Park, northern Sichuan, China
- Amanda Henck, James Taylor, Hongliang Lu, Yongxian Li, Qingxia Yang, Barbara Grub, Sara Jo Breslow, Alicia Robbins, Andrea Elliott, Tom Hinckley, Julie Combs, Lauren Urgenson, Sarah Widder, Xinxin Hu, Ziyu Ma, Yaowu Yuan, Daijun Jian, Xun Liao, Ya Tang
-
- Journal:
- Quaternary Research / Volume 73 / Issue 2 / March 2010
- Published online by Cambridge University Press:
- 20 January 2017, pp. 201-207
-
- Article
- Export citation
-
Small, irregular terraces on hillslopes, or terracettes, are common landscape features throughout west central China. Despite their prevalence, there is limited understanding of the nature of these topographic features, the processes that form them, and the role humans played in their formation. We used an interdisciplinary approach to investigate the geology, ecology, and cultural history of terracette development within Jiuzhaigou National Park, Sichuan Province, China. Terracettes occur on south facing, 20° slopes at 2500 m elevation, which appears to coincide with places people historically preferred to build villages. Ethnographic interviews suggest that traditional swidden agricultural cycles removed tree roots, causing the loess sediments to lose cohesion, slump, and the terrace risers to retreat uphill over time. This evidence is supported by landslide debris at terracette faces. Archaeological analysis of terracette sites reveal remains of rammed spread soil structures, bones, stone tools, and ceramics dating from at least 2200 years before present within a distinct paleosol layer. Radiocarbon and optically stimulated luminescence dating of terracette sediments ranged in age from between 1500 and 2000 14C yr BP and between 16 and 0.30"ka, respectively. These multiple lines of evidence indicate a long history of human habitation within Jiuzhaigou National Park and taken together, suggest strong links between terracette formation and human-landuse interactions.
Leaf injury characteristics of grassland species exposed to ozone in relation to soil moisture condition and vapour pressure deficit
- P. BUNGENER, G. R. BALLS, S. NUSSBAUM, M. GEISSMANN, A. GRUB, J. FUHRER
-
- Journal:
- The New Phytologist / Volume 142 / Issue 2 / May 1999
- Published online by Cambridge University Press:
- 01 May 1999, pp. 271-282
- Print publication:
- May 1999
-
- Article
- Export citation
-
A range of plant species typical of semi-natural grasslands were tested for their sensitivity to short-term ozone injury under normal and reduced irrigation, and in relationship to air vapour pressure deficit. Potted specimens of 24 herbs, legumes and grasses were exposed during two seasons to four O3 treatments in open-top chambers. The ozone treatments were: (a) charcoal-filtered air; (b) charcoal-filtered air plus ozone to match ambient levels; (c) charcoal-filtered air plus O3 to ambient levels 1.5 and (d) charcoal-filtered air with ozone added to twice ambient levels during selected episodes of 7–13 d. During these ozone episodes, half of the plants in each ozone treatment received reduced irrigation (dry treatment) while the rest was kept under full irrigation (wet treatment). Type and date of first occurrence of leaf injury were noted during individual growth periods. Plants were harvested three times per year, and the percentage of injured leaves was recorded. Depending on species, injury symptoms were expressed as flecking (O3-specific injury), leaf yellowing or anthocyanin formation. Carum carvi and most species of the Fabaceae family (Onobrychis sativa, Trifolium repens, Trifolium pratense) were found to be most responsive to O3, injury occurring after only a few days of exposure in treatment (b). An episodic reduction in irrigation tended to reduce the expression of O3-specific symptoms, but only in species for which a reduction in soil moisture potential and an associated reduction in stomatal conductance during the dry episodes were observed. In other species, the protection from O3 injury seemed to be of little importance. Using artificial neural networks the injury response of nine species was analysed in relation to Species, stomatal conductance, ozone as AOT40 (accumulated exposure above a threshold of 0.04 ppm for periods with global radiation [ges ]50 W m−2 (Fuhrer et al., 1997)), mean relative growth rate, air vapour pressure deficit and global radiation. In the model with all factors, Species was most important, and when Species was omitted, stomatal conductance was the most important determinant for leaf injury to occur, whereas mean relative growth rate was less important. With no plant-related factors included, air vapour pressure deficit and AOT40 were of highest importance. Only in eight species was a positive relationship found between these two factors during the five days before the onset of injury, indicating increasing protection from ozone with increasing air vapour pressure deficit in some but not all species. These data show that across a range of grassland species, leaf injury caused by elevated levels of ozone is most likely to occur in species with high stomatal conductance and that protection from ozone during dry periods is species-specific and depends on a reduction in stomatal conductance due to a decrease in soil moisture potential. Protection under increased vapour pressure deficit can occur in some but not all species, depending on the relationship between stomatal conductance and air vapour pressure deficit.
Growth response of grassland species to ozone in relation to soil moisture condition and plant strategy
- P. BUNGENER, S. NUSSBAUM, A. GRUB, J. FUHRER
-
- Journal:
- The New Phytologist / Volume 142 / Issue 2 / May 1999
- Published online by Cambridge University Press:
- 01 May 1999, pp. 283-293
- Print publication:
- May 1999
-
- Article
- Export citation
-
Plant species typical of semi-natural grasslands were tested for their sensitivity to long-term ozone effects on growth under two irrigation regimes, and the relationship between ozone sensitivity, relative growth rate, and plant strategy was analysed. Individuals of 24 grasses, herbs and legumes were grown in pots and exposed for two seasons to four levels of ozone in open-top chambers: (a) CF, charcoal-filtered air, (b) CFAA, charcoal-filtered air plus ozone to match ambient levels, (c) CF+, charcoal-filtered air plus ozone added to match 1.5 times ambient levels and (d) CF++, charcoal-filtered air with ozone added to match twice ambient levels during selected episodes of 7–13 d. During the ozone episodes, one half of the plants received reduced irrigation (dry treatment) while the rest was kept well watered (wet treatment). The effect of ozone on the relative growth rate was determined during the initial growth period during the first season. Above-ground plant dry weight was determined three times during each season, and stubble dry weight at the end of the experiment. In most species, the effect of ozone on relative growth rate was not significant, except in Centaurea jacea and Lychnis flos-cuculi for which a significant stimulation of relative growth rate was found. There was a significant negative relationship between percentage relative growth rate and relative growth rate measured in the CF treatment, indicating that in species growing faster in clean air relative growth rate tended to be more sensitive to ozone than in slower-growing species. After the first re-growth period during the first season, a significant effect of ozone on above-ground biomass was found in five species, i.e. a decrease in Chrysanthemum leucanthemum, Trifolium pratense and T. repens, and an increase in Silene dioïca. During the second season no significant ozone effect was detected, except for an increase in stubble mass in C. leucanthemum. In 10 species, the dry treatment caused a significant decrease in biomass, but in Plantago lanceolata during the first year, and in Knautia arvensis and T. repens during the second year, an ozone×irrigation interaction was observed. Exposure–response patterns in the wet treatment varied between species. In some species growth tended to be increased in charcoal-filtered air plus ozone to ambient levels, in others either a continuous increase or decrease in biomass was observed with increasing ozone. Trifolium repens showed the lowest AOT40 (ozone accumulated above a threshold of 40 ppb) corresponding to a 10% change in biomass. The comparison between exposure–response pattern between the wet and dry treatments revealed reduced, increased, or unchanged ozone sensitivity. The shift was related to plant strategy and not to the specific sensitivity to the dry treatment. The specific response to both ozone and dry treatment tended to be related to Grime's triangular classification of plant strategies, i.e. the C-S-R model. In species with a large component of C (competitor strategy), and/or R (ruderal strategy), biomass was more sensitive to both stresses, compared with species with a high component of S (stress tolerators), and ozone×drought interactions were more pronounced. The results indicate that specific relative growth rate is an important determinant for the potential sensitivity of grassland species to long-term effects of ozone, and that reduced irrigation causes no general protection from the effects of ozone on growth.