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Ground Area (ground + area)
Kinds of Ground Area Selected AbstractsWater use characteristics of cacao and Gliricidia trees in an agroforest in Central Sulawesi, IndonesiaECOHYDROLOGY, Issue 4 2009Michael Köhler Abstract Water use characteristics of cacao (Theobroma cacao) and Gliricidia sepium shade trees were studied in an agroforest on Sulawesi, Indonesia. The objectives were: (1) to identify environmental and tree structural factors controlling water use, (2) to analyse the effect of shade tree cover on cacao water use and (3) to estimate stand level transpiration. Sap flux density was measured in up to 18 trees per species and described with a Jarvis-type model. Model parameters suggested a 49% higher maximum sap flux density in cacao than in Gliricidia and species differences in the response to vapour pressure deficit and radiation. Tree water use was positively related to tree diameter in both species, but this relationship tended to differ between species. In cacao trees maximal tree water use increased with decreasing canopy gap fraction above the trees (R2adj = 0·39, p = 0·04). This was paralleled by an increase of cacao stem diameter and leaf area with decreasing gap fraction. Maximum water use rate per unit crown area of cacao was 13% higher than that of Gliricidia. At the stand level the average transpiration rate was estimated at 1·5 mm day,1 per unit ground area, 70% of which was contributed to by cacao. We conclude that, in the given stand, species differed substantially in water use characteristics, while estimated stand transpiration is in line with findings from other studies for cacao stands. Shade trees may enhance stand transpiration through own water use and additionally by increasing water use rates of cacao trees. Copyright © 2009 John Wiley & Sons, Ltd. [source] Transpiration and stomatal conductance across a steep climate gradient in the southern Rocky MountainsECOHYDROLOGY, Issue 3 2008Nate G. McDowell Abstract Transpiration (E) is regulated over short time periods by stomatal conductance (Gs) and over multi-year periods by tree- and stand-structural factors such as leaf area, height and density, with upper limits ultimately set by climate. We tested the hypothesis that tree structure, stand structure and Gs together regulate E per ground area (Eg) within climatic limits using three sites located across a steep climatic gradient: a low-elevation Juniperus woodland, a mid-elevation Pinus forest and a high-elevation Picea forest. We measured leaf area : sapwood area ratio (Al : As), height and ecosystem sapwood area : ground area ratio (As : Ag) to assess long-term structural adjustments, tree-ring carbon isotope ratios (,13C) to assess seasonal gas exchange, and whole-tree E and Gs to assess short-term regulation. We used a hydraulic model based on Darcy's law to interpret the interactive regulation of Gs and Eg. Common allometric dependencies were found only in the relationship of sapwood area to diameter for pine and spruce; there were strong site differences for allometric relationships of sapwood area to basal area, Al : As and As : Ag. On a sapwood area basis, E decreased with increasing elevation, but this pattern was reversed when E was scaled to the crown using Al : As. Eg was controlled largely by As : Ag, and both Eg and Gs declined from high- to low-elevation sites. Observation-model comparisons of Eg, Gs and ,13C were strongest using the hydraulic model parameterized with precipitation, vapour pressure deficit, Al : As, height, and As : Ag, supporting the concept that climate, Gs, tree- and stand-structure interact to regulate Eg. Copyright © 2008 John Wiley & Sons, Ltd. [source] The contribution of bryophytes to the carbon exchange for a temperate rainforestGLOBAL CHANGE BIOLOGY, Issue 8 2003Evan H. DeLucia Abstract Bryophytes blanket the floor of temperate rainforests in New Zealand and may influence a number of important ecosystem processes, including carbon cycling. Their contribution to forest floor carbon exchange was determined in a mature, undisturbed podocarp-broadleaved forest in New Zealand, dominated by 100,400-year-old rimu (Dacrydium cupressimum) trees. Eight species of mosses and 13 species of liverworts contributed to the 62% cover of the diverse forest floor community. The bryophyte community developed a relatively thin (depth <30 mm), but dense, canopy that experienced elevated CO2 partial pressures (median 46.6 Pa immediately below the bryophyte canopy) relative to the surrounding air (median 37.6 Pa at 100 mm above the canopy). Light-saturated rates of net CO2 exchange from 14 microcosms collected from the forest floor were highly variable; the maximum rate of net uptake (bryophyte photosynthesis , whole-plant respiration) per unit ground area at saturating irradiance was 1.9 ,mol m,2 s,1 and in one microcosm, the net rate of CO2 exchange was negative (respiration). CO2 exchange for all microcosms was strongly dependent on water content. The average water content in the microcosms ranged from 1375% when fully saturated to 250% when air-dried. Reduction in water content across this range resulted in an average decrease of 85% in net CO2 uptake per unit ground area. The results from the microcosms were used in a model to estimate annual carbon exchange for the forest floor. This model incorporated hourly variability in average irradiance reaching the forest floor, water content of the bryophyte layer, and air and soil temperature. The annual net carbon uptake by forest floor bryophytes was 103 g m,2, compared to annual carbon efflux from the forest floor (bryophyte and soil respiration) of ,1010 g m,2. To put this in perspective of the magnitude of the components of CO2 exchange for the forest floor, the bryophyte layer reclaimed an amount of CO2 equivalent to only about 10% of forest floor respiration (bryophyte plus soil) or ,11% of soil respiration. The contribution of forest floor bryophytes to productivity in this temperate rainforest was much smaller than in boreal forests, possibly because of differences in species composition and environmental limitations to photosynthesis. Because of their close dependence on water table depth, the contribution of the bryophyte community to ecosystem CO2 exchange may be highly responsive to rapid changes in climate. [source] Seasonal and habitat differences affect the impact of food and predation on herbivores: a comparison between gaps and understory of a tropical forestOIKOS, Issue 1 2007Lora A. Richards Herbivore populations are influenced by a combination of food availability and predator pressure, the relative contribution of which is hypothesized to vary across a productivity gradient. In tropical forests, treefall gaps are pockets of high productivity in the otherwise less productive forest understory. Thus, we hypothesize that higher light availability in gaps will increase plant resources, thereby decreasing resource limitation of herbivores relative to the understory. As a result, predators should regulate herbivore populations in gaps, whereas food should limit herbivores in the understory. We quantified potential food availability and compared arthropod herbivore and predator densities in large forest light gaps and in the intact understory in Panama. Plants, young leaves, herbivores and predators were significantly more abundant per ground area in gaps than in the understory. This pattern was similar when we focused on seven gap specialist plant species and 15 shade-tolerant species growing in gaps and understory. Consistent with the hypothesis, herbivory rates were higher in gaps than the understory. Per capita predation rates on artificial caterpillars indicated higher predation pressure in gaps in both the dry and late wet seasons. These diverse lines of evidence all suggest that herbivores experience higher predator pressure in gaps and more food limitation in the understory. [source] Can improvement in photosynthesis increase crop yields?PLANT CELL & ENVIRONMENT, Issue 3 2006STEPHEN P. LONG ABSTRACT The yield potential (Yp) of a grain crop is the seed mass per unit ground area obtained under optimum growing conditions without weeds, pests and diseases. It is determined by the product of the available light energy and by the genetically determined properties: efficiency of light capture (,i), the efficiency of conversion of the intercepted light into biomass (,c) and the proportion of biomass partitioned into grain (,). Plant breeding brings , and ,i close to their theoretical maxima, leaving ,c, primarily determined by photosynthesis, as the only remaining major prospect for improving Yp. Leaf photosynthetic rate, however, is poorly correlated with yield when different genotypes of a crop species are compared. This led to the viewpoint that improvement of leaf photosynthesis has little value for improving Yp. By contrast, the many recent experiments that compare the growth of a genotype in current and future projected elevated [CO2] environments show that increase in leaf photosynthesis is closely associated with similar increases in yield. Are there opportunities to achieve similar increases by genetic manipulation? Six potential routes of increasing ,c by improving photosynthetic efficiency were explored, ranging from altered canopy architecture to improved regeneration of the acceptor molecule for CO2. Collectively, these changes could improve ,c and, therefore, Yp by c. 50%. Because some changes could be achieved by transgenic technology, the time of the development of commercial cultivars could be considerably less than by conventional breeding and potentially, within 10,15 years. [source] Scaling-up from leaf to canopy-aggregate properties in sclerophyll shrub speciesAUSTRAL ECOLOGY, Issue 3 2006CASSIA READ Abstract: Plant species vary widely in their average leaf lifespan (LL) and specific leaf area (SLA, leaf area per dry mass). The negative LL,SLA relationship commonly seen among species represents an important evolutionary trade-off, with higher SLA indicating greater potential for fast growth (higher rate of return on a given investment), but longer LL indicating a longer duration of the revenue stream from that investment. We investigated how these leaf-economic traits related to aggregate properties of the plant crown. Across 14 Australian sclerophyll shrub species, those with long LL accumulated more leaf mass and leaf area per unit ground area. Light attenuation through their canopies was more severe. Leaf accumulation and light attenuation were more weakly related to SLA than to LL. The greater accumulation of foliage in species with longer LL and lower SLA may counterbalance their generally lower photosynthetic rates and light-capture areas per gram of leaf. [source] The role of vegetation patterns in structuring runoff and sediment fluxes in drylandsEARTH SURFACE PROCESSES AND LANDFORMS, Issue 2 2005Juan Puigdefábregas Abstract The dynamics of vegetation-driven spatial heterogeneity (VDSH) and its function in structuring runoff and sediment fluxes have received increased attention from both geomorphological and ecological perspectives, particularly in arid regions with sparse vegetation cover. This paper reviews the recent findings in this area obtained from field evidence and numerical simulation experiments, and outlines their implications for soil erosion assessment. VDSH is often observed at two scales, individual plant clumps and stands of clumps. At the patch scale, the local outcomes of vegetated patches on soil erodibility and hydraulic soil properties are well established. They involve greater water storage capacity as well as increased organic carbon and nutrient inputs. These effects operate together with an enhanced capacity for the interception of water and windborne resources, and an increased biological activity that accelerates breakdown of plant litter and nutrient turnover rates. This suite of relationships, which often involve positive feedback mechanisms, creates vegetated patches that are increasingly different from nearby bare ground areas. By this way a mosaic builds up with bare ground and vegetated patches coupled together, respectively, as sources and sinks of water, sediments and nutrients. At the stand scale within-storm temporal variability of rainfall intensity controls reinfiltration of overland flow and its decay with slope length. At moderate rainfall intensity, this factor interacts with the spatial structure of VDSH and the mechanism of overland flow generation. Reinfiltration is greater in small-grained VDSH and topsoil saturation excess overland flow. Available information shows that VDSH structures of sources and sinks of water and sediments evolve dynamically with hillslope fluxes and tune their spatial configurations to them. Rainfall simulation experiments in large plots show that coarsening VDSH leads to significantly greater erosion rates even under heavy rainfall intensity because of the flow concentration and its velocity increase. Copyright © 2005 John Wiley & Sons, Ltd. [source] Soil properties and perceived disturbance of grasslands subjected to mechanized military training: evaluation of an indexLAND DEGRADATION AND DEVELOPMENT, Issue 3 2007D. P. Althoff Abstract Mechanized maneuver training impacts the landscape by creating depressions, compacting soils, producing bare ground areas, transporting seeds of invasive plants, and crushing vegetation. We measured 3 physical, 13 chemical, and 2 biological soil properties and used a disturbance index (DI) based on perceptions of soil conditions on a military installation to assess the condition of 100,×,100,m plots (1 ha): 10 in 2002 and 10 in 2004. Potential DI scores range from 0 (no appreciable evidence of disturbance) to 1 (>95 per cent of the plot disturbed). Bulk density, porosity (%), and water content (%),all at 5·1,10·0,cm depth, and nematode family richness (NFR) were significantly, negatively correlated (Spearman coefficients, rs) with the DI of both years. The strong negative correlation (rs,=,,0·69 in 2002, ,0·79 in 2004) of NFR with the DI appears to reflect the status of nematode diversity and, therefore, may serve as a useful, inexpensive approach to rapidly assessing grasslands subjected to mechanized military training. Copyright © 2007 John Wiley & Sons, Ltd. [source] | |||||||||||||