Leaf Dispersal Research Articles

An agent-based model of the foraging ascomycete hypothesis

Abstract Most trees host hundreds of species of fungi asymptomatically in their internal tissues, known collectively as fungal endophytes. The Foraging Ascomycete (FA) hypothesis proposed that some fungal endophytes inhabit the internal leaf tissue of forest trees in order to enhance dispersal to substrates on the forest floor, by using leaves as vectors and as refugia during periods of environmental stress. This dispersal strategy has recently been termed viaphytism and is now thought to apply to fungal groups beyond ascomycetes. Viaphytism implies that many fungi may be in continuous and cyclical flux between life stages as endophytes in the forest canopy and as wood-decomposing fungi on the forest floor. This cycle may represent a very common and previously-ignored process in the ecology of forests, with implications for forest health. The ecological consequences of the viaphyte lifestyle are complex, so we constructed an agent-based model to explore it. Our model is intended to serve as both an explicit conceptual explanation of viaphytism, and as an exploration of the conditions in which a strategy of endophytism accompanied by leaf dispersal may be advantageous for fungi. In a scenario of a viaphytic fungal species on a model forest landscape, without fungal competitors, viaphytism is predicted to be a plausible alternative to dispersal to substrates by spores alone, allowing the fungus to persist reliably in the landscape. In a scenario that allows competition from aggressively dispersed non-viaphytic fungi, the model predicts some competitive benefits to fungal dispersal via leaves. However, these benefits are conditional, requiring sufficient retention through time of endophyte infections by host trees, and sufficient host trees in the landscape. In the model, loss of these fungal populations can result from increased local disturbances of forest canopy, and deforestation.

Modelling leaf dispersal and nutrient return in tree species mixtures

Litter fall and the associated nutrient return are a significant supply of resources in forest ecosystems. In mixed stands both litter quantity and quality can change under different species compositions. Spatial heterogeneity inherent in mixed stands, defined by stand structure and the present species, will affect the litter composition around a tree of interest. Therefore spatially explicit information will be needed to determine how neighbourhood characteristics in a mixed stand have an effect on litter composition and nutrient return. Using a leaf dispersal model, we determined litter production and leaf shedding parameters of four different tree species. Results from this model indicated that the proportion of litter that originated from the neighbourhood was 86% and 77% at the local tree level for oak and beech respectively. Using this information we found that the presence of accompanying species birch or hornbeam had beneficial effects on local return of N, P, Ca, Mg and Mn. Return of K was optimal with only beech trees in the neighbourhood. These results could give an indication on how to use stand establishment, structure and management to optimize nutrient return.

Studies on the Phenology of African Breadfruit (Treculia africana Decne) in South Eastern Nigeria

Studies on the phenology of African breadfruit (Treculia africana Decne) Moraceae was carried out monthly for three years (2012 - 2014) in five Southeastern States of Nigeria in two seasons, dry and wet. The study covered five towns across the States namely: Isulabor (Abia), Agulu (Anambra), Ezzamgbo (Ebonyi), Nenwe (Enugu) and Mbato (Imo State). The species was investigated to provide information on the species periods and pattern of leaf exchange, leaf dispersal, flowering, fruit formation, maturity and dropping. The species is semi-deciduous and fruits throughout the year with two fruiting periods (heavy and lean) which alternated each other. The reproductive and vegetative phenophases overlapped each other. The observations were consistent in all the location. Early October showed various degrees of vegetative growth; bud flush, leaf formation, maturity and leaf abscission, which spilled into November thus starting the dry season phenophases. In dry season, light flowering, fruit formation and maturity stretched from November to late March, while fruit dropping lasted from February to March. April as in October also showed various degrees of vegetative growth which spilling into May in the wet season. In the wet season, heavy period of flowering was from May to June, fruit formation, maturity, ripening and dropping began from July to September. These periods were shorter in the wet season than that of the dry season. T. africana had highest fruit dropping (heavy periods) in the wet season, alternated with lean periods in dry season. Therefore, the species is an indigenous Nigerian food crop that can mitigate seasonal food scarcity throughout the year.

Comparative characteristics of Puccinia recondita Rob. ex Desm. syn.: Puccinia triticina Erikss. Virulence in the Middle Volga region

According to a study conducted in 2011–2012, Puccinia recondita populations from Ulyanovsk and Bezenchuk share one geographic range of leaf rust variety formation and dispersal. At the same time, a significant similarity between the structures of the Middle Volga population and of populations from the North Caucasus and Northwestern Russia was shown. Clones virulent to Lr 9 and Lr 41 were absent from all the examined regions. Virulence genes plr19, plr24, plr28, plr29, and plr47 are characterized by low frequencies.

Forest floor properties across sharp compositional boundaries separating trembling aspen and jack pine stands in the southern boreal forest

Jack pine and trembling aspen are two early-seral boreal tree species with contrasting nutrient cycling strategies. Both species may form adjacent mono-specific stands separated by sharp compositional boundaries. We hypothesized that such boundaries result in wider functional ecotones. Spatial transitions in humus forms, forest floor chemistry and microbial communities were assessed across 32 m long transects set perpendicular to sharp compositional boundaries separating four jack pine and aspen stands. Split moving window analysis (SMWA) and moving window regression analysis (MWRA) were used to locate functional boundaries and ecotones. We found a gradual transition from moder (aspen) to mor (jack pine) humus spanning 16 m across the compositional boundary. An abrupt increase in forest floor water content at 3 m within jack pine stands was possibly due to aspen roots foraging for water beyond the boundary. The functional boundary and associated ecotone for forest floor pH, C:N ratio, Mg and ammonification were skewed toward jack pine stands, likely the result of aspen leaf dispersal. Low nitrification rates throughout jack pine stands and up to 11 m into aspen stands suggested that jack pine roots might extend far within aspen stands and produce metabolites that suppress nitrification. SMWA performed on the multivariate dataset of microbial fatty acids (FAs) revealed three distinct forest floor microbial communities that were skewed toward jack pine stands. Pine-type communities were associated to fungal FAs, pine-type and transition-type communities to non-fungal eukaryotic FAs, and aspen-type communities to bacterial FAs. Taken collectively, our data delimit a 24 m wide functional ecotone straddling sharp compositional boundaries separating trembling aspen and jack pine stands. We conclude that the functional diversity of boreal landscapes, where adjacent mono-specific stands are prevalent, is related to the patchiness of the landscape.

Improvements in anisotropic models of single tree effects in Cartesian coordinates

For anisotropic density functions of e.g. fruit or leaf dispersal, most mathematical research is only done in polar coordinates. However, in software solutions aiming to derive inverse models for real world dispersal data, Cartesian coordinates may be preferred for several reasons. Thus, we introduce an anisotropic model in Cartesian coordinates following the approach in Wälder et al. (2009) with the von Mises approach. By introducing a correction factor, we thereby consider the fundamental attribute, that the integral over a density function with respect to the Cartesian coordinates has to be equal 1. It may have been overlooked so far that guaranteeing for this attribute needs different approaches whether working in polar or Cartesian coordinates. One result is that our approach can be used also for other anisotropic models rather than models from the von Mises approach.

Seasonal variation in leaf-litter input and leaf dispersal distances to streams: the effect of converting broadleaf riparian zones to conifer plantations in central Japan

Sugi (Cryptomeria japonica D. Don) is one of the most important evergreen coniferous plantation species in Japan. Much of the riparian forest that was originally dominated by deciduous broadleaf trees has been converted into sugi plantations. The present study investigated the seasonality of leaf-litter input and leaf dispersal to streams to assess the effects of converting riparian forest to sugi plantations. The seasonality of leaf-litter input was assessed at three streams in Nagoya University Forest. At one stream dominated by deciduous broadleaf trees, input was limited to autumn. At two streams in a sugi plantation, input was prolonged from autumn to early spring, and was dominated by sugi needles from winter to early spring. These results suggest that sugi plantations alter the seasonality of leaf-litter input from riparian forests and affect stream ecosystems. Leaf dispersal was assessed by considering the relationship between leaf dispersal distance from three forest layers to the stream and leaf-litter input into two streams. The maximum leaf dispersal distance was 26–28 m for deciduous broadleaf trees from mid-October to November and 10–12 m for sugi needles from December to April. Leaf dispersal distance depended on the tree species. Four species of deciduous broadleaf tree showed greater leaf dispersal than that of sugi. The mean weight of individual sugi needles was higher than that of the broadleaf trees’ leaves, and dispersal depended on strong winds in winter and early spring. Although the leaf dispersal distance from the understory was within 2–4 m, it could be a significant source of leaf-litter input to streams.

MODELING LEAF DISPERSAL IN MIXED HARDWOOD FORESTS USING A BALLISTIC APPROACH

In mixed-species stands, modeling leaf litter dispersal is important to predict the physical and chemical characteristics of the forest floor, which plays a major role in nutrient cycling and in plant population dynamics. In this study, a spatially explicit model of leaf litterfall was developed and compared with two other models. These three models were calibrated for a mixed forest of oak and beech using litterfall data from mapped forest plots. All models assumed that an allometric equation described individual leaf litter production, but they strongly differed in the modeling of the probability density of leaf shedding with distance from source trees. Two models used a negative exponential function to account for leaf dispersal with distance, and this function was allowed to vary according to wind direction in one of them. In contrast, our approach was based on a simple ballistic equation considering release height, wind speed, wind direction, and leaf fall velocity; the distributions of wind speeds and wind directions were modeled according to a Weibull and a Von Mises distribution, respectively. Using an independent validation data set, all three models provided predictions well correlated to measurements (r > 0.83); however, the two models with a direction-dependent component were slightly more accurate. In addition, parameter estimates of the ballistic model were in close agreement with a foliar litter production equation derived from the literature for beech and with wind characteristics measured during leaf litterfall for both species. Because of its mechanistic background, such a spatially explicit model might be incorporated as a litterfall module in larger models (nutrient cycling, plant population dynamics) or used to determine the manner in which patch size in mixed-species stands influences litter mixture.

Predicting the Spatial Distribution of Leaf Litterfall in a Mixed Deciduous Forest

Abstract An accurate prediction of the spatial distribution of litterfall can improve insight in the interaction between the canopy layer and forest floor characteristics, which is a key feature in forest nutrient cycling. Attempts to model the spatial variability of litterfall have been made across forest types, but the reported models have not yet been compared. We predicted the spatial distribution of leaf litterfall for the same mixed hardwood stand using inverse distance interpolation, ordinary kriging, single and multiple regressions based on plot basal area, and three individual-tree models. Models were calibrated using litterfall data (n = 67) of white birch (Betula pendula Roth), pedunculate oak (Quercus robur L.), and northern red oak (Quercus rubra L.). Model performance was compared using an independent validation data set (n = 37). Interpolation techniques did not reliably estimate spatial patterns of leaf litterfall (r < 0.60, n = 37). However, models incorporating tree data, such as linear regressions and individual-tree models, successfully reproduced the observed spatial litterfall heterogeneity of each species (r > 0.80). No model was able to predict the variability of the total leaf litterfall of the three species. We conclude that, for an intimately mixed forest stand, a model that simulates leaf dispersal of individual trees is likely to be the best choice for predicting the spatial distribution of leaf litterfall. FOR. SCI. 50(6):836–847.

A model of wind-influenced leaf litterfall in a mixed hardwood forest

Litterfall is an important ecological process in forest ecosystem functioning. Some attempts have been made to develop spatially explicit models of litterfall, but wind influence has never been included. Therefore, we studied the effect of wind on litterfall in an intimately mixed birch-oak forest using tree diameter and position as input data. After testing a litterfall model that assumed isotropic leaf dispersal, an anisotropic dispersal module was developed to account for wind influence. Using leaf fall data of 104 litter traps, isotropic and anisotropic models were optimized for silver birch (Betula pendula Roth), pedunculate oak (Quercus robur L.), and red oak (Quercus rubra L.) and model quality was compared. The anisotropic leaf litterfall model proved to be relevant because (i) the estimated litterfall directions corresponded very well to prevailing wind directions during leaf fall and (ii) including directionality significantly increased the goodness of fit of the models for both oak species but not for birch. Consequently, prevailing wind directions during leaf fall affected leaf dispersal in a broad-leaved deciduous forest. Insight into the spatial variability of the litter layer in forest ecosystems can benefit from the improved understanding of small-scale litterfall processes.

Development of leaf rust (Peridiopsora mori) and dispersal of urediniospores in mulberry (Morus spp.)

Studies were conducted on the effect of pruning time, host age, urediniospore release and weather parameters on the incidence and intensity of mulberry leaf rust (Peridiopsora mori). Rust severity significantly increased with increasing shoot age, irrespective of pruning time. Maximum disease severity was observed in plants pruned during the third week of October, and minimum severity in plants pruned during last week of November. Apparent infection rate was higher in younger shoots. Infection rate was higher in plants pruned during the last week of November. Urediniospore release was influenced by prevailing climatic conditions. A higher rate of spore release was noticed during sunny days. Maximum spore release was found between 12.00 h and 14.00 h. Spore release was positively correlated with temperature and negatively correlated with relative humidity. Rust severity (34.97%) was higher in January and least (1.03%) during May. Rust severity was negatively correlated with both temperature and rainfall. An exponential model was developed for the prediction of rust severity which was accurate up to 96.60%.

Effect of thinning and nitrogen fertilization on diameter growth of pole-size sugar maple

Diameter growth of pole-size sugar maple crop trees was increased significantly by commercial thinning but not by fertilization treatments applied 3 years after or 3 years before thinning. DBH growth was strongly related to initial DBH both before and after release. Neither urea nor ammonium nitrate increased growth. Fertilizing individual crop trees on medium and better sites is not likely to increase growth significantly because of dilution by large nutrient pools in these soils, uptake by competing trees and understory vegetation, and distribution of absorbed nutrients by leaf dispersal. Commercial thinning removed the small and defective stems, increased diameter growth of residual crop trees by 40%, and provided stand conditions favorable for development of high value sawlogs.

Leaf dispersal in a pole-size maple stand

The horizontal distribution of leaf fall was determined for one nonthinned, and two previously released pole-size sugar maple (Acersaccharum Marsh.) trees. Leaf dispersal showed a general north–south pattern reflecting the prevailing winds; most leaves were within 100 ft (30.5 m) of the sample trees. Only about 5% of the total number of leaves remained on the estimated major rooting area. Consequently, fertilizing individual maple trees is likely to have limited long-term value because nutrients contained in the leaves will be distributed throughout the stand.