1,721,062 research outputs found
Drone‐based photogrammetry‐derived crown metrics for predicting tree and oil palm water use
No full textChanges in leaf area index by tropical forest transformation to plantations increase below-canopy surface temperatures
No full textClimate change affects life in tropical landscapes by increasing temperatures, among other impacts. In addition, land transformation from forest to other land cover types typically increases temperatures of surfaces exposed to direct solar radiation. In rural areas, however, many organisms including humans live sheltered below canopies, but little is known about below-canopy surface temperatures. We assessed canopy leaf area index (LAI) and below-canopy surface temperatures in a landscape of rural lowland Sumatra, Indonesia. In this region, land-use trajectories in the past decades led from forest to monocultural plantations. We found that LAI varied more than 10-fold, with the highest values observed in forest and low values in rubber and oil palm plantations. Below-canopy surface temperatures increased significantly with decreasing LAI. A decrease in LAI by one unit (m2 leaf area per m2 ground area) increased ground surface temperature by 0.95 °C (confidence interval: 1.07–0.83 °C) around noon. Likewise, the temperatures measured on peoples’ cap or hijab surfaces under the canopy was strongly affected. For a light-brown hijab, the average noon surface temperature increased by 4.0 °C from forest to oil palm. Thus, in addition to climate warming, land transformation and associated declines in canopy LAI significantly increased below-canopy surface temperatures. Strategies for mitigating such potentially adverse temperature effects may include the integration of more and densely foliated trees into landscapes
Jurnal Manajemen Hutan Tropika Vol.6 No.1,Th. 2000
No full textPengaruh variabilitas sifat-sifat hidrolika tanah terhadap aliran air pada lereng berhutan dianalisis dengan menggunakan persamaan dua dimensi Richard secara numerik. Model fungsi-fungsi konduktivitas hidrolika dan retensi air digunakan model lognormal (Kosugi, 1996). Variabilitas sifat-sifat hidrolika tanah dievaluasi dengan menggunakan teori penyekalaan (scaling theory) (Hendrayanto, et al., 2000). Hasil penelitian menunjukkan bahwa penggunaan nilai rata-rata sifat hidrolika tanah cenderung memberikan nilai dugaan aliran air yang lebih rendah (under estimate). Pola penyebaraan faktor penyekala (scaling factor) mempengaruhi debit maksimum dan kurva resesi hidrograf. Makin besar faktor penyekala ke arah hilir lereng, debit maksimum makin lebih besar dan kurva resesi hidrograf makin curam, dan sebaliknya
The Effect of Variability in Soil Hydraulic Properties on Water Flow in A Forested Hill Slope
Full text linkPengaruh variabilitas sifat-sifat hidrolika tanah terhadap aliran air pada lereng berhutan dianalisis dengan menggunakan persamaan dua dimensi Richard secara numerik. Model fungsi-fungsi konduktivitas hidrolika dan retensi air digunakan model lognormal (Kosugi, 1996). Variabilitas sifat-sifat hidrolika tanah dievaluasi dengan menggunakan teori penyekalaan (scaling theory) (Hendrayanto, et al., 2000). Hasil penelitian menunjukkan bahwa penggunaan nilai rata-rata sifat hidrolika tanah cenderung memberikan nilai dugaan aliran air yang lebih rendah (under estimate). Pola penyebaraan faktor penyekala (scaling factor) mempengaruhi debit maksimum dan kurva resesi hidrograf. Makin besar faktor penyekala ke arah hilir lereng, debit maksimum makin lebih besar dan kurva resesi hidrograf makin curam, dan sebaliknya
Multi-Level Temporal Variation of Sap Flux Densities in Oil Palm
No full textOil palms (Elaeis guineensis Jacq.) are increasingly cultivated throughout the humid tropics and are reported to have high transpiration rates. A potential contribution of stem water storage to transpiration has been discussed in previous studies. We assessed the water-use characteristics of oil palms at different horizontal and vertical positions in the plant by using three sap flux techniques, i.e., thermal dissipation probes, the heat ratio method and heat field deformation sensors. In a radial profile of the stem, sap flux densities were low at the outer margin, increased to 2.5 cm under the bark and remained relatively high to the innermost measured depth at 7.5 cm. In a vertical profile of the stem and with further sensors in leaf petioles, we found only small time lags in sap flux densities. Time lags along the flow path are often used for analyzing the contribution of water storage to transpiration. Thus, the small observed time differences in our study would leave only little room for the contribution of water storage to transpiration. However, water storage might still contribute to transpiration in ways that are not detected by time lag analysis. Such mechanisms may be explored in future studies
Cacao trees under different shade tree shelter: effects on water use
No full textWe asked how shade tree admixture affects cacao water use in agroforests. In Central Sulawesi, Indonesia, cacao and shade tree sap flux was monitored in a monoculture, in a stand with admixed Gliricidia trees and in a mixture with a multi-species tree assemblage, with both mixtures having similar canopy openness. A Jarvis type sap flux model suggested a distinct difference in sap flux response to changes in vapor pressure deficit and radiation among cacao trees in the individual cultivation systems. We argue that differences originate from stomatal control of transpiration in the monoculture and altered radiation conditions and a different degree of uncoupling of the VPD from the bulk atmosphere inside shaded stands. Probably due to high sap flux variability among trees, these differences however did not result in significantly altered average daily cacao water use rates which were 16 L day−1 in the multi-species assemblage and 22 L day−1 in the other plots. In shaded stands, water use of single cacao trees increased with decreasing canopy gap fraction in the overstory since shading enhanced vegetative growth of cacao fostering transpiration per unit ground area. Estimated transpiration rates of the cacao tree layer were further controlled by stem density and amounted to 1.2 mm day−1 in the monoculture, 2.2 mm day−1 for cacao in the cacao/Gliricidia stand, and 1.1 mm day−1 in the cacao/multi-species stand. The additional transpiration by the shade trees is estimated at 0.5 mm day−1 for the Gliricidia and 1 mm day−1 for the mixed-species cultivation system
Rainfall partitioning in relation to forest structure in differently managed montane forest stands in Central Sulawesi, Indonesia
No full textManagement activities alter the structure of many tropical forest stands which can be expected to influence the magnitude of canopy water fluxes. The objectives of this study were to determine throughfall, stemflow and rainfall interception in differently managed forest stands, and to relate the observed pattern of rainfall partitioning to stand structural characteristics. The study was conducted in a lower montane rainforest region (800–1140 m asl) in Central Sulawesi, Indonesia. Stands of four management types (natural forest, forest subject to small-diameter timber extraction, forest subject to selective logging of large-diameter timber, and cacao agroforest under trees remaining from the natural forest) were analyzed with three replicates per use type. The tree basal area decreased from the natural forest (52.5 m2 ha−1) to the agroforest (19.4 m2 ha−1) which was paralleled by a reduction in mean tree height (trees ≥ 10 cm dbh) from 21.3 to 17.5 m. The estimated leaf area index (LAI), as derived from hemispherical photos, averaged 6.2 m2 m−2 in the natural forest, 5.3 in forests with small timber extraction, 5.0 in forests with large timber extraction, and 5.3 in the agroforest. The annual gross precipitation close to our different study plots varied locally between 2437 and 3424 mm during the time of the study. Throughfall was measured on 15–17 rain days per plot with a median of 70% of gross precipitation over all the natural forest plots, 79 and 80% in forest with small and large timber extraction respectively, and 81% in the agroforest. Stemflow was less than 1% in all studied use types. Thus, rainfall interception was highest in the natural forest where 30% (median) of the gross precipitation was re-evaporated back into the atmosphere, and much lower in the three other use types (18–20%). Variability in structure and rainfall partitioning was high even within the same forest use types, thus further analysis focused on gradual changes rather than categories. In the 12 stands, LAI alone did not correlate significantly with the pattern of rainfall partitioning, the throughfall percentage increased significantly with decreasing tree height (r2 = 0.63). In a multiple linear regression with tree height and LAI as influencing factors, 81% of the variation in throughfall percentage is explained. A possible reason for this tree height-LAI-throughfall relationship is that under the conditions prevailing in our study region the canopy may not completely dry up between subsequent rainfall events. Therefore, the actual water storage at the start of a rainfall event would be below its potential. We hypothesize that tall trees increase the vertical distribution of foliage and other canopy components contributing to the canopy water storage, resulting in a higher canopy roughness and a more effective energy exchange with the atmosphere. This would consequently lead to an increased re-evaporation of intercepted water, larger available water storage and, thus, a reduced throughfall in stands with tall trees
Airborne Tree Crown Detection for Predicting Spatial Heterogeneity of Canopy Transpiration in a Tropical Rainforest
No full textTropical rainforests comprise complex 3D structures and encompass heterogeneous site conditions; their transpiration contributes to climate regulation. The objectives of our study were to test the relationship between tree water use and crown metrics and to predict spatial variability of canopy transpiration across sites. In a lowland rainforest of Sumatra, we measured tree water use with sap flux techniques and simultaneously assessed crown metrics with drone-based photogrammetry. We observed a close linear relationship between individual tree water use and crown surface area (R2 = 0.76, n = 42 trees). Uncertainties in predicting stand-level canopy transpiration were much lower using tree crown metrics than the more conventionally used stem diameter. 3D canopy segmentation analyses in combination with the tree crown–water use relationship predict substantial spatial heterogeneity in canopy transpiration. Among our eight study plots, there was a more than two-fold difference, with lower transpiration at riparian than at upland sites. In conclusion, we regard drone-based canopy segmentation and crown metrics to be very useful tools for the scaling of transpiration from tree- to stand-level. Our results indicate substantial spatial variation in crown packing and thus canopy transpiration of tropical rainforests
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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