Variability Of Throughfall Research Articles

Variability and temporal stability of throughfall along a hillslope

Tree species composition, tree size, and microclimate can vary along hillslopes in forest ecosystems. This will affect the amount of throughfall (TF) that reaches the ground. However, few studies have focused on the effects of topography on the spatio-temporal variability of throughfall. We therefore, measured throughfall on a steep hillslope roughly 110 m long covered by European beech trees (Fagus sylvatica) in the Re della Pietra experimental catchment, Tuscany Apennines, Central Italy. Although the trees all have a similar age, the basal area, Plant Area Index (PAI), and canopy cover are higher on the lower part of the hillslope than the upper part of the hillslope. We installed 49 throughfall collectors in two 144 m2 square grids: one on the lower hillslope and one on the upper hillslope. In addition, we installed 29 collectors on a transect connecting the lower and upper grid. Throughfall was measured from all collectors at an approximately monthly interval and compared with gross precipitation (GP) measured in a nearby open area. The overall a TF/GP ratio for the 61 manual measurements during the period from July 2020 to September 2023 study period was 70 ± 3.4 %. It was higher for the growing season (71 ± 4.0 %) characterised by higher rainfall intensities than the dormant season (69 ± 2.7 %). TF/GP was lower for the lower grid than the upper grid (61 ± 5.1 vs 73 ± 6.0 % of GP, respectively). The differences between the measurements at the lower and upper grid were significant for almost all measurement days and reflect the differences in tree size and stand density. Temporal stability analysis indicated a high persistence of the spatial TF pattern for both grids, especially in the dormant season. The higher temporal stability for in the upper grid seems to be related to the lower variability in tree size. Although these results need to be confirmed by larger-scale studies at different hillslopes, they suggest that topographic differences in stand characteristics should be taken into account when determining the water balance for forested catchments.

Quantification of enrichment processes in throughfall and stemflow in a mixed temperate forest

AbstractForest ecosystems depend on throughfall and stemflow fluxes for both water and nutrient input. Spatial and temporal variability of throughfall and stemflow fluxes are large and differ between tree species. The nutrient fluxes that accompany throughfall and stemflow are affected by climate, precipitation intensity, the seasonality of dry deposition, and canopy exchange processes. The interdependence of these factors makes it challenging to quantify changes in throughfall and stemflow amounts as well as their nutrient content. Here, we provide observation‐based evidence from 3.5 years of data collection with 222 rainfall events, of the seasonal variability of throughfall and stemflow magnitude and ion concentrations under a beech (Fagus silvatica) and spruce (Picea abies) tree. Interception and canopy cover were seasonally variable, average annual interception was 53% below beech, 61% below spruce and 68% below young spruce canopies. Further, we assess seasonality of ionic nutrients such as NH4 and NO3 as well as Mg, Ca and K and their dependence on both dry deposition and canopy exchange. Throughfall and stemflow were enriched compared to precipitation, with large differences between ions and different months. Antecedent precipitation was a main control on throughfall and stemflow enrichment. We developed a conceptual model of the potential drivers of throughfall and stemflow enrichment based on our observations. While NH4 and NO3 enrichment are likely dominated by dry deposition and dew and fog accumulation, Mg, Ca and K were additionally affected by canopy exchange. Observation based studies such as this one are needed to understand precipitation and nutrient partitioning across forests, which enables the prediction of how changes in climate and forest composition will affect local hydrology and nutrient inputs into forest ecosystems.

Spatial variability of throughfall in heavily fogged old-growth Fagus orientalis forests is controlled by fog precipitation and stand structural characteristics

Ecological impacts of the spatial heterogeneity of throughfall (TF) in forest ecosystems are recognized in ecohydrology. The objective of this study was to evaluate the spatial variability of TF and to quantify the effects of forest cover, fog, and gross rainfall (GR) characteristics on TF. Data were collected from May 2016 to November 2017 on an event basis in an intact, old-growth oriental beech (Fagus orientalis L.) stand in northern Iran. Over the measurement time period, 22 rainfall events were observed (total rain = 648 mm). Because the region experienced considerable fog, TF was greater than 100% of GR in 14 rainfall events with negative interception loss (total = -24.1 mm), causing low interception values, and 8 rainfall events were found with positive I (total = 25.5 mm). The low TF spatial variability and increasing TF depth observed in this study were related to increases in rainfall depth and intensity. TF was significantly and positively correlated with LAI and significantly and negatively correlated with canopy openness for rainfall events of more than 50 mm. The high amount of TF depth highlighted the role of LAI to enhance fog interception and the role of fog precipitation to increase TF in the study site. Spatial continuity at an effective range of 3-8 m was observed by variogram analyses. The increasing spatial continuity of TF with increasing GR observed in this study, along with the larger effective range for GR >50 mm and correspondingly similar LAI range, suggest an effect of LAI on the spatial patterning of TF for larger GR. Therefore, this heavily fogged ecosystem received considerable TF due to fog interception, and higher LAI increased TF for larger rainfall events. Our findings can optimize forest management practices by accounting for the effect of Fagus orientalis trees on the local hydrological processes of the Hyrcanian mountain forests.

Exotic tropical pine forest impacts on rainfall interception: Canopy, understory, and litter

Tropical forests have experienced rapid deforestation due to demand from agriculture, timber, and urbanisation. Throughout the Caribbean, planting resilient, fast growing exotic pine trees such as Pinus Caribaea or Pinus Oorcarpa have been used to reforest many degraded landscapes. However, little is understood on how these exotic pine forests alter hydrological processes and water resource availability. We examined the rainfall interception dynamics between an exotic pine and contiguous native secondary forest in Trinidad. Canopy, understory, and litter interception were quantified and examined along with throughfall variability, rainfall characteristics and canopy cover. Our results indicate that over a one-year period, the exotic pine forest intercepts 30% more of the incoming precipitation than the native forest, reducing the rainfall reaching the forest floor. The pine forest had a lower canopy cover but still had a higher storage capacity of 4.3 mm, leading to a higher annual interception of 29%. The native forest had a lower storage capacity of 2.6 mm and a lower annual interception of 24%. Understory vegetation played a critical role in the interception process in the pine forest storing an additional 29% of incoming rainfall increasing the total vegetative interception in the pine forest to 58% (763 mm). These findings point to the creation of drier conditions within pine forest and the need to re-examine the use of pine trees as a reforestation tool. This study highlights the importance of understory vegetation interception and stresses the need for more research on understory-precipitation interactions.

Complementary effects of tree species on canopy rainfall partitioning: New insights for ecological restoration in Andean ecosystems

Vegetation affects local water balance partitioning via effects on incoming precipitation, local radiation balance and soil hydrological properties. The extent of these effects is related to plant functional traits, such that forest composition plays an important role in its hydrological function. Therefore, the selection of species in forest restoration processes is key to recovering ecological (including hydrological) function. However, most restoration projects often do not include functional criteria for species selection, and even less frequently they include ecohydrological functions, although many projects are intended to recover hydrological regulation. We explored the association between plant functional traits and ecohydrological function, indicated by precipitation partitioning in the canopy into stemflow and throughfall, in an 8-year watershed restoration project in the Central Andes of Colombia. We monitored stemflow and throughfall (both mean and variability) on planted individuals from ten native tree species for almost two years and measured functional traits that describe tree crowns and are associated with rainfall partitioning. We found that stemflow and throughfall behavior is generally inverse and differ among species, with the highest variability in mean stemflow and coefficient of variation of throughfall. Furthermore, our results show that stemflow and throughfall are significantly associated with tree crown functional traits (R2 = 0.74 for crown area and R2 = 0.62 for crown density × volume). Besides, the studied species are organized in a variation space of ecohydrological processes and crown functional traits (first two principal components from PCA explain 71.7% of data variability). They are organized from wider/less dense crowns in Alnus acuminata to smaller/denser crowns in Quercus humboldtii, which significantly influenced the temporal variability of stemflow and throughfall, respectively. Other species are located intermittently along this variation space. From a multivariate perspective, our species were differentiated into four discrete groups based on similar functional traits and, therefore, with similar effects on ecohydrological processes. This suggests a complementary effect of different species on the ecosystem hydrological functions, thus highlighting the importance of considering diversity on ecosystem management and ecological restoration for the recovery of ecosystem integrity.

Linking Seasonal Variability in Throughfall and Stemflow Dissolved Organic Carbon to Canopy Phenology in an Evergreen Broad-Leaved Subtropical Forest in Central Japan

Linking Seasonal Variability in Throughfall and Stemflow Dissolved Organic Carbon to Canopy Phenology in an Evergreen Broad-Leaved Subtropical Forest in Central Japan

Large broad-leaved canopy of banana (Musa nana Lour.) induces dramatically high spatial–temporal variability of throughfall

Abstract Throughfall (TF) is an important water input of rainfall redistribution into floor, and its spatial–temporal variability under some species' canopies has been documented to evaluate effect on splash erosion. However, the understanding of TF variability under large broad-leaved canopy remains insufficient. In this study, the spatial heterogeneity, temporal stability and drop size of TF were quantified using variogram fitting, normalised ranking and filter paper staining, respectively, under banana (Musa nana Lour.) canopy comprising long and wide leaves. Results indicated TF pattern showed strong spatial correlation at a range of 3–5 m. High spatial variability of TF was found, which was affected by rainfall event size and was accompanied by great canopy disturbance. TF plots revealed high time variability, which was mainly controlled by unstable banana canopy structure. TF drop size from leaf dripping points varied in 3–10 mm and showed significant differences (p < 0.05) among five kinds of leaf shapes, implying that concave and broken banana leaves were involved in the variability of TF drop size. Overall, results demonstrate the spatial–temporal variability of TF is dramatically induced by banana canopy with broad leaves, which may result in non-uniform soil water content and splash erosion under the canopy.

Spatial Variability and Optimal Number of Rain Gauges for Sampling Throughfall under Single Oak Trees during the Leafless Period

This study examined the spatial variability of throughfall (Tf) and its implications for sampling throughfall during the leafless period of oak trees. To do this, we measured Tf under five single Brant’s oak trees (Quercus brantii var. Persica), in the Zagros region of Iran, spanning a six-month-long study period. Overall, the Tf amounted to 85.7% of gross rainfall. The spatial coefficient of variation (CV) for rainstorm total Tf volumes was 25%, on average, and it decreased as the magnitude of rainfall increased. During the leafless period, Tf was spatially autocorrelated over distances of 1 to 3.5 m, indicating the benefits of sampling with relatively elongated troughs. Our findings highlight the great variability of Tf under the canopies of Brant’s oaks during their leafless period. We may also conclude that the 29 Tf collectors used in the present study were sufficient to robustly estimate tree-scale Tf values within a 10% error of the mean at the 95% confidence level. Given that a ±10% uncertainty in Tf is associated with a ±100% uncertainty in interception loss, this underscores the challenges in its measurement at the individual tree level in the leafless season. These results are valuable for determining the number and placement of Tf collectors, and their expected level of confidence, when measuring tree-level Tf of scattered oak trees and those in forest stands.

Spatial Variability of Throughfall in a Larch (Larix gmelinii) Forest in Great Kingan Mountain, Northeastern China

Larix gmelinii forest is one of the dominant forest types in boreal forest and plays a unique eco-hydrological role in the terrestrial ecosystem. However, the throughfall variability in boreal forest ecosystems, which plays a crucial role in regulating hydrology, remains unclear. Here, we investigated the spatial variability and temporal stability of throughfall within a Larix gmelinii forest in the full leaf stage in Great Kingan Mountain, Northeast China, and the effects of rainfall properties and canopy structure on throughfall variability were systematically evaluated. The results indicate that throughfall represented 81.26% of the gross rainfall in the forest. The throughfall CV (coefficient of variation of throughfall) had a significant and negative correlation with the rainfall amount, rainfall intensity, rainfall duration, and distance from the nearest trunk, whereas it increased with increasing canopy thickness and LAI (leaf area index). The correlation analysis suggested that the throughfall variability was mainly affected by the rainfall amount (R2 = 0.7714) and canopy thickness (R2 = 0.7087). The temporal stability analysis indicated that the spatial distribution of the throughfall was temporally stable. Our findings will facilitate a better understanding of the spatiotemporal heterogeneity of throughfall and help the accurate assessment of throughfall and soil water within boreal forests.

Temporal variability of throughfall as a function of the canopy development stage: from seasonal to intra-event scale

ABSTRACT The interception process impacts rainfall magnitude and intensity under the canopy. In this study, the effect of plant interception on throughfall characteristics was assessed in the deciduous Caatinga vegetation, at different canopy development stages and for temporal scales ranging from seasonal to the intra-event scale. Throughfall and stemflow percentages were slightly higher at the onset of the rainy season, when leaf area density is low, with resulting lower interception losses. However, there was no statistical difference among the variables at the seasonal scale. At the intra-event scale, average and maximum throughfall intensity at different time intervals showed statistical difference between the stages of canopy development. Regardless of leaf area density and rainfall depth, vegetation is able to retain all the water up to 2 min in the beginning of each rainfall event with accumulated rainfall smaller than 0.6 mm. Furthermore, the Caatinga vegetation attenuates the rainfall intensity by 30–40%.

Horizontal variability of soil water content, evaporation and throughfall in corn row

AbstractHorizontal variability of soil water content (θ), soil surface water evaporation (E), and throughfall (TF) at the row scale have great influence on agricultural production, hydrological simulation and sampling strategy. The objective of the present study was to assess the horizontal variability and the most representative measurement position of θ, E, and TF at the corn (Zea mays L.) row scale in a field experiment. Five measurement positions of P0, P15, P30, P45 and P60 were at 0, 15, 30, 45 and 60 cm from the corn row line, respectively. The horizontal variability of θ mainly existed in 0–15 cm soil layer (P = 0.031). The coefficient of variation (CV) of the θ of 0–15, 30, and 50 cm ranged from 7.0–25.1%, 4.1–10.2%, and 5.3–11.4%, respectively. The CV of the E and TF ranged from 9.9–27.2% and 20.4–35.6%, respectively. The P15 or P45 was regarded as the most representative measurement position for measuring the θ of 0–15, 30, and 50 cm, with a probability of 51.0–58.8%, 43.1–43.1%, and 54.9–60.8%, respectively, and that for TF was 93.9–84.8%. The probability of P15 as the most representative measurement position to determine E was 61.1%. Therefore, horizontal variability of θ, E, and TF in a row‐planted crop field could not be ignored. The P15 was the most representative measurement position of θ, E, and TF in such an experimental condition.

Spatial and Temporal Variability of Throughfall among Oak and Co-Occurring Non-Oak Tree Species in an Upland Hardwood Forest

Canopy throughfall comprises the largest portion of net precipitation that is delivered to the forest floor. This water flux is highly variable across space and time and is influenced by species composition, canopy foliage, stand structure, and storm meteorological characteristics. In upland forests throughout the central hardwoods region of the Eastern United States, a compositional shift is occurring from oak-hickory to more mesic, shade-tolerant species such as red maple, sweetgum, and winged elm. To better understand the impacts of this shift on throughfall flux and the hydrologic budget, we monitored throughfall for one year in Northern Mississippi under the crowns of midstory and overstory oak (post oak and southern red oak) and non-oak species (hickory, red maple, and winged elm). In general, oak had more throughfall than co-occurring non-oak species in both canopy levels. In the overstory during the leaf-off canopy phase, white oak had relatively higher throughfall partitioning (standardized z-score = 0.54) compared to all other species (z-score = −0.02) (p = 0.004), while in the leaf-on canopy phase, red maple had relatively lower throughfall (z-score = −0.36) partitioning compared to all other species (z-score = 0.11). In the midstory, red maple was the only species to exhibit a difference in throughfall between canopy phases, with much lower throughfall in the leaf-off compared to the leaf-on canopy phase (z-score = −0.30 vs. 0.202, p = 0.039). Additionally, throughfall under oak crowns was less variable than under non-oak crowns. These results provide evidence that the spatial and temporal distribution of throughfall inputs under oak crowns are different than non-oak species, likely due to differences in crown architecture (i.e., depth and density). As oak dominance diminishes in these forests, it is possible that the portion of rainfall diverted to throughfall may decrease as well. The net impacts to watershed hydrology are still unknown, but these results provide one mechanism by which the distribution of water resources may be affected.

Spatial-temporal variability of throughfall in a subtropical deciduous forest from the hilly regions of eastern China

Throughfall variability plays a crucial role in regulating hydrological and biogeochemical processes in forest ecosystems. However, throughfall variability and its potential influencing factors remain unclear in the subtropical deciduous forest because of its complex canopy and meteorological conditions. Here, the spatial variability and temporal stability of throughfall were investigated from October 2016 to December 2017 within a deciduous forest in the subtropical hilly regions of eastern China, and the effects of meteorological variables and distance from nearest tree trunk on throughfall variability were systematically evaluated. Throughfall variability during the leafed period was slightly higher than that during the leafless period inferred from the coefficient of variation of throughfall amounts (CVTF), with 13.2%–40.9% and 18.7%–31.9%, respectively. The multiple regression model analysis suggested that the controlling factors of throughfall variability were different in studied periods: Maximum 10-min rainfall intensity, wind speed and air temperature were the dominant influencing factors on throughfall variability during the leafed period, with the relative contribution ratio (RCR) of 25.9%, 18.7% and 8.9%, respectively. By contrast, throughfall variability was affected mainly by the mean rainfall intensity (RCR=40.8%) during the leafless period. The temporal stability plots and geostatistical analysis indicated that spatial patterns of throughfall were stable and similar among rainfall events. Our findings highlight the important role of various meteorological factors in throughfall variability and are expected to contribute to the accurate assessment of throughfall, soil water and runoff within the subtropical forests.

Shrub tundra ecohydrology: rainfall interception is a major component of the water balance

As shrubs expand across the Arctic, they alter all cycles in the Earth system, including the water cycle. However, the coupling of shrubs with the water cycle during summer remains poorly understood. Rainfall interception, a major cause of divergent hydrological responses between vegetated and non-vegetated environments, is particularly poorly constrained. We quantified shrub rainfall interception and redistribution in birch and alder in the Western Canadian Arctic using networks of throughfall and stemflow gauges. We find that rainfall interception losses are a major component of the water budget, as effective rainfall was reduced by 15%–30% in the birches. Underneath alders, effective rainfall was almost as large or larger than gross rainfall, but they also left a rain shadow. The spatial variability in throughfall was substantial underneath both shrub species. Stemflow was a small but non-negligible component, as the alders concentrated ∼15% of rainfall to their few vertical stems, compared to the ∼8% the birches funnelled along their numerous, predominantly skewed stems. The substantial small-scale variability in effective rainfall may create islands in which conditions for certain biogeochemical processes are particularly favourable. On larger scales, rainfall interception reduces the water yield and thus the runoff received by downstream ecosystems such as lakes. The interception losses are predicted to increase with shrub density in a way that also depends on climatic conditions, with large losses in many coastal environments. The extent to which shrub expansion leads to drier Arctic ecosystems is, however, unclear because of the complex interplay between many ecohydrological processes. Shrub rainfall interception is one major, previously overlooked piece of this puzzle.

Chemical content and seasonal variation of throughfall and litterflow under individual trees in the Hyrcanian forests of Iran

ABSTRACTWe assessed the effect of seasons and the tree species velvet maple (Acer velutinum Boiss), Hainbuche hornbeam (Carpinus betulus L.) and chestnut-leaved oak (Quercus castanefolia C. A. Mey.; Fagaceae) on nutrient fluxes (Na+, K+ and Ca2+) in throughfall (TF) and litter flow (LF) from January 2012 to February 2013. Potassium (K+) and calcium (Ca2+) in total TF and LF over the measurement period significantly differed between 3 the species (p < 0.05). Maple and oak trees had significantly higher fluxes of K+ and Ca2+ in their TF, respectively. The average quantity of nutrients in LF was significantly higher in the leafy season than in the leafless season for all cations except for Na+. Under velvet maple trees, the average flux of nutrients (Na+, K+, and Ca2+) in TF was significantly higher than LF. Lastly, leaching of potassium (K+) and calcium (Ca2+) in LF during the measurement period was significantly lower than TF under the hornbeam trees. Our results suggest that different tree species may impact the nutrient availability and possibly the sustainability of Hyrcanian forests. Further research is needed to determine how managing different species will affect the long-term nutrient status of these forests.

Spatial variation in throughfall, soil, and plant water isotopes in a temperate forest

AbstractStudies of stable isotopes of water in the environment have been fundamental to advancing our understanding of how water moves through the soil–plant–atmosphere continuum; however, much of this research focuses on how water isotopes vary in time, rather than in space. We examined the spatial variation in the δ18O and δ2H of throughfall and bulk soil water, as well as branch xylem and bulk leaf water of Picea abies (Norway spruce) and Fagus sylvatica (beech), in a 1‐ha forest plot in the northern Alps of Switzerland. Means and ranges of water isotope ratios varied considerably among throughfall, soil, and xylem samples. Soil water isotope ratios were often poorly explained by soil characteristics and often not predictable from proximal samples. Branch xylem water isotope values varied less than either soil water or bulk leaf water. The isotopic range observed within an individual tree crown was often similar to that observed among different crowns. As a result of the heterogeneity in isotope ratios, inferences about the depth of plant root water uptake drawn from a two end‐member mixing model were highly sensitive to the soil sampling location. Our results clearly demonstrate that studies using water isotopes to infer root water uptake must explicitly consider how to characterize soil water, incorporating measures of both vertical and lateral variations. By accounting for this spatial variation and the processes that shape it, we can improve the application of water isotopes to studies of plant ecophysiology, ecohydrology, soil hydrology, and palaeoclimatology.

How does a rubber plantation affect the spatial variability and temporal stability of throughfall?

Abstract In Xishuangbanna, southwest China, the large-scale monoculture rubber plantation replaced the primary tropical forest, which changed the regional hydrology processes and biogeochemical cycles. As throughfall was an important component of the forest ecosystem water input, we researched the spatial variability and temporal stability of throughfall in the rubber plantation. We recorded 30 rainfall events by using 90 rain gauges during 2015–2016. We found a highly significant linear relationship between rainfall and throughfall, and a strong power correlation between the peak 30 min rainfall intensity and throughfall. The coefficient of variation for throughfall was significant and negatively correlated with rainfall and rainfall intensity. We also observed that throughfall had a strong spatial autocorrelation that would decrease during heavy rainfall events. The results indicate that the leaf area index did not have a significant relationship with throughfall. However, the lateral translocation of the throughfall in the canopy significantly affected the spatial distribution of the throughfall. Generally, the lower throughfall positions were close to the nearest rubber trunk, and the higher throughfall positions were mostly below the slope. This study contributes to the knowledge of the spatiotemporal heterogeneity of throughfall and helps elucidate the interception processes in the rubber plantation.

PARTITIONING OF RAINFALL IN EXPERIMENTAL PLANTATIONS OF Eucalyptus urophylla AND Pinus elliottii

In a period of 36 months, the partitioning of rainfall was studied in plantations of 30-year-old Eucalyptus urophylla and Pinus elliottii cultivated in flat drainage lysimeters. Gross precipitation was measured with one rain gauge installed in an open area located near the plantations; throughfall was determined by the arithmetic mean of five rain gauges located under the canopy of each species; stemflow was obtained with polyurethane foam collars connected to plastic containers installed on four trees of each species. The mean proportions of throughfall, stemflow and interception in relation to gross rainfall for eucalyptus were 89.0%, 5.4% and 5.6%, respectively, and for pine, they were 79.8%, 1.0 % and 19.2%, respectively. The interannual variation in the percentages of interception for the two species had an amplitude of approximately 6%. There was marked variation in the proportion of stemflow depending on the season for eucalyptus, averaging 8.7% between April and September and 4.6% from October to March. There was a large number of events with negative interception for eucalyptus. One of the likely causes of the negative interception was capture of fog water by the canopy. Linear regressions estimated that rainfall amounts were responsible for approximately 99% and 70% of the variation in throughfall and stemflow, respectively, in the two plantations.

Shade trees and tree pruning alter throughfall and microclimate in cocoa (Theobroma cacao L.) production systems

Shade trees in agroforestry systems protect the understory cocoa from climate extremes. Shade tree pruning manages microclimatic conditions in favor of cocoa production while tree diversity is maintained. Adaptation of pruning has to consider seasonal changes in temperature and precipitation to protect the understory cocoa. Structural characteristics of tree stands such as species diversity, tree density, and stratification can affect throughfall and microclimate. Pruning changes the canopy and may therefore modulate internal conditions. The aim of this study is to assess the environmental growing conditions of cocoa trees. We monitored canopy openness and the impact of stand structure on throughfall and microclimate in three cocoa production systems (monoculture, agroforestry, and successional agroforestry) and a natural regrowth in a long-term trial in Bolivia from 2013 to 2015. We further focused on the effect of annual shade tree and cocoa pruning on these variables to evaluate the potential impact of this activity. Agroforestry systems buffered extreme climate events like temperature fluctuations compared to monocultures but reduced light and throughfall drastically. Spatial variability of throughfall and transmitted light were low under a high and closed shade tree canopy. Shade tree pruning resulted in higher canopy openness, light transmittance, and throughfall, while the buffer function of the agroforestry systems concerning temperature and humidity fluctuations was reduced. Differences between cocoa production systems regarding throughfall and microclimate were overlain by pruning activities. Cocoa agroforestry systems are temporal dynamic systems. Pruning timing and intensity is pivotal for balancing light and water availability under seasonally varying environmental conditions to conserve micro-environments for cocoa production with less exposure to unfavorable climate.

Spatial Patterns and Temporal Stability of Throughfall in a Mature Douglas-fir Forest

Forest plays a key role in spatial distribution of rainfall and nutrients at fine spatial scales. Areas of localized rainfall and nutrient input at the soil surface may have a large effect on several hydrological and biogeochemical processes. In this paper, a Douglas-fir stand was revisited to evaluate the changes in the throughfall spatial distribution and its temporal stability due to forest growth and thinning. We used 32 funnel-type collectors distributed in a random stratified array within a 0.2 ha plot to measure throughfall amounts from February to November 2015. The throughfall variability was much lower as compared to the values reported ~25 years ago in the same site. We further assessed the spatial patterns of throughfall in spring and summer. We detected a spatial correlation length of 12 m and 8 m for spring and summer, respectively, which are higher than the values reported for other mature Douglas-fir forests in similar climatic conditions. Temporal stability plots confirmed that detected spatial patterns were stable in time.