Spatial Distribution Of Throughfall Research Articles

Interception loss, throughfall and stemflow by Larrea divaricata: The role of rainfall characteristics and plant morphological attributes

AbstractRainfall partitioning into interception loss, throughfall and stemflow affects the amount and the spatial heterogeneity of water entering into the soil at the patch scale, strongly controlling net primary productivity of drylands. In this paper, we explored rainfall partitioning and its biophysical controls in Larrea divaricata (jarilla), one of the most abundant shrubs in the Dry Chaco rangelands (Argentina). On average, interception loss, throughfall and stemflow accounted for 9.4, 78.6 and 12.0% of total rainfall, respectively. Interception loss proportion decreased with the increment of rainfall event size and intensity, whereas throughfall proportion showed the opposite pattern. Stemflow proportion increased with the increment of rainfall event size but presented different relations with rainfall event intensity. The increment of rainfall event intensity increased the stemflow in small events (<20 mm), but decreased it in large events (>20 mm). Stemflow increased in plants with higher angles of insertion of stems (measured at 50 and 100 cm from soil surface; p < .05 and p < .01, respectively), but decreased in plants with larger canopy areas (p = .01). Spatial distribution of throughfall (coefficient of variation) decreased with the increment of rainfall event size and intensity. L. divaricata presented more stemflow generation and fewer interception losses than other similar woody species. Our findings help to understand the key role of vegetation canopy affecting the amount of water entering into the soil in drylands.

Spatial variability of throughfall in a stand of Scots pine (Pinus sylvestris L.) with deciduous admixture as influenced by canopy cover and stem distance

Summary Vegetation cover affects the amount of precipitation, its chemical composition and its spatial distribution, and this may have implications for the distribution of water, nutrients and contaminants in the subsurface soil layer. The aim of this study was a detailed diagnosis of the spatio-temporal variability in the amount of throughfall (TF) and its chemical components in a 72-year-old pine stand with an admixture of oak and birch. The spatio-temporal variability in the amount of TF water and the concentrations and deposition of the TF components were studied. The components that are exchanged in canopy (H + , K, Mg, Mn, DOC, NH 4 + ) were more variable than the components whose TF deposition is the sum of wet and dry (including gas) deposition and which undergo little exchange in the canopy (Na, Cl, NO 3 − , SO 4 2− ). The spatial distribution was temporally stable, especially during the leafed period. This study also investigated the effect of the selected pine stand characteristics on the spatial distribution of throughfall and its chemical components; the characteristics included leaf area index (LAI), the proportion of the canopy covered by deciduous species and pine crowns, and the distance from the nearest tree trunk. The LAI measured during the leafed and leafless periods had the greatest effect on the spatial distribution of TF deposition. No relationship was found between the spatial distribution of the amount of TF water and (i) the LAI; (ii) the canopy cover of broadleaf species or pines; or (iii) the distance from the trunks.

Experimental Study on Spatial Distribution of Throughfall Under a Japanese Cypress Tree

ヒノキにおける樹冠通過雨の空間分布特性を明らかにするため，大型降雨実験施設において室内実験を行った．施設内に樹高11 mのヒノキを植栽し，グリッド状に配置した120個の測定容器により10分間の雨量を測定した．降雨強度（雨滴の運動エネルギー）・枝下高をそれぞれ変化させ，測器間隔の差異・樹木の無い状態での人工降雨を含めて11パターンの測定を行った．樹冠通過雨量は，与えた降雨よりも測点ごとのばらつきが大きく，その範囲は与えた降雨の40-484 ％であった．ばらつきの範囲は，降雨強度の大きさによって異なった．樹幹から遠ざかるほど雨量が増加し樹冠縁に沿って雨量が多くなる傾向が見られ，特に雨滴エネルギーが小さい降雨の場合に明瞭であった．雨量の多い集中滴下点は樹幹近くに多く存在することが確認された．また，枝の切り落としの前後で雨量が大きく変化した地点が，いずれも切り落とした枝の近辺に存在した．以上より，樹冠通過雨の空間分布特性について，幹からの距離及び最下層に位置する枝の配置により整理されうることが示された．

Rainfall interception and spatial distribution of throughfall in a pine forest planted in an arid zone

Summary Afforestation in arid zones is of increasing importance as it is one of the favored approaches to combat desertification. Rainfall interception by the canopy plays an important role in determining the amount of rainfall reaching the forest floor. The throughfall patterns of coniferous forests planted in arid zones have hitherto not been well documented. The research site in which the measurements were carried out was located within a mature pine forest ( Pinus halepensis, Mill) planted in an arid zone (average annual precipitation: 280 mm and annual class-A evaporation pan: 2500 mm). Measurements of precipitation, throughfall, stemflow, soil water content and transpiration were recorded during three years. Canopy cover was estimated from the analysis of hemispherical photographs obtained during the winter. The spatially averaged throughfall, obtained for each event from 20 rainfall gauges installed below the canopy was linearly correlated with gross rainfall and independent of rainfall intensity. We found that the spatial distribution of the throughfall on the forest floor was highly heterogeneous. A fairly consistent distribution of throughfall was evident with some gauges steadily showing a higher percentage of throughfall than others. However, we could not find any relation between the degree of canopy openness (or any other quantifiable canopy characteristic) and the relative throughfall. The spatial pattern of throughfall was however found to be significant when assessed by means of the “K-means Clustering” analysis. The spatial distribution of water in the soil as measured 48 h after rainfall events with a neutron gauge was not correlated to the distribution of throughfall when each of the measuring points was assessed individually. The average throughfall was however well correlated to the average increase in the soil water content and indicates that there is some degree of horizontal water movement (overland or below ground) within the plot. The results presented suggest that point measurements are not the correct tool for water balances of sparse canopy forests and that even for small plots horizontal sampling is of the essence. The practical implication of this study is that it shows that for this particular site a very large fraction of the rainfall reaches the ground and is thus available for plant and/or tree development, a key issue in an area with a rainless period of at least six months during which high pan evaporation rates prevail.

Throughfall and throughfall spatial variability in Madrean oak forest communities of northeastern Mexico

Point throughfall data were generated in two representative red oak stands of a small Madrean watershed in northeastern Mexico during the 2000 and the 2001 wet seasons. Cumulative gross precipitation for 18 selected events was 392.9 mm, while the mean cumulative point throughfall flux from 38-fixed gauges was 331.0±9.0 mm (84.2±2.3%). The influence of canopy and understory cover fraction, vegetation area index (VAI), distance to nearest tree bole, as well as the basal area and height of that tree may have on point throughfall depth were evaluated. No significant ( α=0.05) relationship between point throughfall and these stand characteristics could be established for gross precipitation inputs >5 mm. However, excluding events in which occult precipitation was thought to contribute to throughfall generation, the spatial distribution of throughfall was found to be a function of at least one of these factors during each of the gross precipitation inputs <5 mm. For gross precipitation events >5 mm point throughfall for all but one event did not significantly deviate from the normal distribution, suggesting that stand-scale throughfall fluxes associated with these relatively larger events may be estimated from a random array of gauges. An average of 9 (range=3–14) and 34 (range=11–54) gauges would have been required to estimate mean event throughfall input to the red oak forest floor to within ±10 and ±5% at the 95% confidence level, respectively, for gross precipitation events >5 mm.