Biogeographical contrasts to assess local and regional patterns of invasion: a case study with two reciprocally introduced exotic maple trees

Quantitative comparisons of distribution and abundance of exotic species in their native and non‐native ranges represent a first step when studying invaders. However, this approach is rarely applied 2 particularly to tree species. Using biogeographical contrasts coupled with regional dispersal surveys, we assessed whether two exotic maple tree species, Acer negundo and Acer platanoides, can be classified as invasive in the non‐native regions surveyed. We also examined the importance of biogeography in determining the degree of invasion by exotic species using this reciprocal approach. Local‐scale surveys were conducted in a total of 34 forests to compare density, relative abundance, age structure of native and introduced populations, and whether the two introduced maple species negatively affected native tree species density. Regional‐scale surveys of a total of 136 forests were then conducted to assess distribution in the introduced regions. Introduced populations of A. negundo were denser than populations measured in their native range and negatively related to native tree species density. Age structure did not differ between regions for this species. At the regional scale, this species has invaded most of the riparian corridors sampled in France. Conversely, the density of A. platanoides introduced populations was similar to that of native populations and was not related to native tree species density. Although seedling recruitment was higher away than at home, this species has invaded only 9% of the forests sampled in southern Ontario, Canada. Although reported invasive, these two exotic maple species differed in their relative demographic parameters and regional spread. Acer negundo is currently invasive in southern France while A. platanoides is not aggressively invasive in southern Ontario. Importantly, this study effectively demonstrates that biogeography through structured contrasts provide a direct means to infer invasion of exotic species.     

Herbivores limit the population size of big‐leaf mahogany trees in an Amazonian forest

The Janzen–Connell hypothesis proposes that specialized herbivores maintain high numbers of tree species in tropical forests by restricting adult recruitment so that host populations remain at low densities. We tested this prediction for the large timber tree species, Swietenia macrophylla, whose seeds and seedlings are preyed upon by small mammals and a host‐specific moth caterpillar Steniscadia poliophaea, respectively. At a primary forest site, experimental seed additions to gaps – canopy‐disturbed areas that enhance seedling growth into saplings – over three years revealed lower survival and seedling recruitment closer to conspecific trees and in higher basal area neighborhoods, as well as reduced subsequent seedling survival and height growth. When we included these Janzen–Connell effects in a spatially explicit individual‐based population model, the caterpillar's impact was critical to limiting Swietenia's adult tree density, with a > 10‐fold reduction estimated at 300 years. Our research demonstrates the crucial but oft‐ignored linkage between Janzen–Connell effects on offspring and population‐level consequences for a long‐lived, potentially dominant tree species.     

Testing for Janzen–Connell Effects in a West African Montane Forest

The Janzen–Connell hypothesis proposes that density dependent seed and seedling mortality, combined with increasing seed and seedling survival away from the parent tree, together promote regular spacing of species and thus α diversity. This hypothesis has rarely been tested in tropical Africa, and rarely in montane forests anywhere. We tested this hypothesis using a combination of field experiments and observations in the most floristically diverse dry submontane forest in Nigeria. We investigated distance effects on seedling herbivory, seedling survival and seedling height growth. We found a significant decrease in herbivory with distance from conspecific adult trees for all three species of experimentally planted seedlings (Entandrophragma angolense, Deinbollia pinnata and Sterculia setigera), and also for naturally occurring seedlings of Pouteria altissima but not of Newtonia buchananii or Isolona pleurocarpa. The relative density of large seedlings/saplings of P. altissima, N. buchananii and I. pleurocarpa increased significantly at greater distance from conspecific adult trees; however, we found no significant distance effect on survival or height growth over 3 mo for all three experimentally planted species. Taken together, our results are some of the first to show that Janzen–Connell effects occur on the African continent and in particular montane tropical forest and suggest that such effects may be pantropical.     

Seed dispersal of the non-native invasive tree <Emphasis Type="Italic">Ailanthus altissima</Emphasis> into contrasting environments

Ailanthus altissima has a long history of invasion in urban areas and is currently spreading into suburban and rural areas in the eastern U.S. The objectives of our study were to (1) determine whether A. altissima seed dispersal distance differed between populations on the edges of open fields and intact deciduous forest, and (2) determine whether dispersal differed for north and south winds. We also assessed the relationship between seed characteristics and distance from source populations in fields and forests, and whether seeds disperse at different rates throughout the dispersal season. Using two fields, two intact forest stands, and one partially harvested stand, we sampled the seed rain at 10 m intervals 100 m into each site from October to April 2002–2003. We compared seed density in field and intact forests using a three-way ANOVA with distance from source, wind direction, and environmental structure as independent variables. To assess the accuracy of common empirical dispersal models, mean seed density data at each site were fitted with alternative regression models. We found that mean seed dispersal distance depended on environmental structure and wind direction, a result driven in large part by dispersal at a single site where seed density did not decline with distance. The two alternative regression models fit each site’s dispersal curve equally well. More seeds were dispersed early than in mid- or late-season. Large, heavy seeds traveled as far as small light seeds. Turbulent winds appear to be necessary for seed release, as indicated by a wind tunnel experiment. A. altissima is able to disperse long distances into fields and into mature forests, and can reach canopy gaps and other suitable habitats at least 100 m from the forest edge. It is an effective disperser and can spread rapidly in fragmented landscapes where edges and other high light environments occur. These conditions are increasingly common throughout the eastern U.S. and in other temperate regions worldwide.     

Differences in nitrogen use strategies between native and exotic tree species: predicting impacts on invaded ecosystems

Background and aim

Exotic plant species can alter the nitrogen cycle in invaded ecosystems. We assess the differences in nitrogen use strategies and litter production and dynamics among three native riparian trees (Fraxinus angustifolia, Populus alba and Ulmus minor) and three co-occurring exotics (Ailanthus altissima, Robinia pseudoacacia and Ulmus pumila), currently spreading throughout river banks in inner Spain. We aim to predict the ecological consequences of a replacement of the natives by the exotics.

Methods

We compared the leaf lifespan, nitrogen resorption efficiency in leaves, nitrogen mean residence time, amount and timing of litter production and amount of nitrogen returned to soils between these native and exotic species.

Results

We found differences among species in all the variables measured, but not between native or exotic origins. Species were ranked from the most to the least conservative nitrogen use strategy as follows: U. pumila was the most conservative species, followed by the three natives (with an intermediate strategy), A. altissima and finally by the nitrogen-fixer R. pseudoacacia. The studied exotic species would produce contrasting impacts on the nitrogen cycle upon invasion.

Conclusions

On the basis of our results, we predict little impacts on the nitrogen cycle if U. pumila dominates the landscape. Despite being nitrogen-fixer R. pseudocacia would not increase soil nitrogen availability in the study area due to its low litter production and litter decomposition rates. In contrast, we predict an increase in nitrogen availability of soils upon A. altissima invasion, as this species produces a high amount of nitrogen rich and labile litter. This study offers a striking example of the contingencies involved in predicting the ecosystem impacts of exotic plant invasion.     

Invertebrate Seed Predators are not all the Same: Seed Predation by Bruchine and Scolytine Beetles Affects Palm Recruitment in Different Ways

Because most invertebrate seed predators are host‐specific, they are usually expected to produce Janzen–Connell patterns. This expectation was fulfilled for Astrocaryum but not for Allagoptera, depending on the effects of bruchine and scolytine predators on the seeds of these palms. Thus, the mere existence of invertebrate predation is not sufficient for generating Janzen–Connell; what matters is seed mortality, which varies between predators and between plant species for the same predator.     

Analysis of interactions between the invasive tree-of-heaven (<Emphasis Type="Italic">Ailanthus altissima</Emphasis>) and the native black locust (<Emphasis Type="Italic">Robinia pseudoacacia</Emphasis>)

Invasive exotic plants can persist and successfully spread within ecosystems and negatively affect the recruitment of native species. The exotic invasive Ailanthus altissima and the native Robinia pseudoacacia are frequently found in disturbed sites and exhibit similar growth and reproductive characteristics, yet each has distinct functional roles such as allelopathy and nitrogen fixation, respectively. A four-month full additive series in the greenhouse was used to analyze the intraspecific and interspecific interference between these two species. In the greenhouse experiment, the inverse of the mean total biomass (g) response per plant for each species was regressed on the density of each species and revealed that the performance of the plants was significantly reduced by interspecific interference and not by intraspecific interference (p < 0.05). Other biomass traits such as root dry weight, shoot dry weight, stem dry weight, and leaf dry weight were also negatively affected by interspecific interference. Competition indices such as Relative Yield Total and Relative Crowding Coefficient suggested that A. altissima was the better competitor in mixed plantings. Ailanthus altissima consistently produced a larger above ground and below ground relative yield while R. pseudoacacia generated a larger aboveground relative yield in high density mixed species pots.     

Impact of invasion of Acer platanoides on canopy structure and understory seedling growth in a hardwood forest in North America

Invasion by exotic plant species is known to affect native communities and ecosystems, but the mechanisms of the impacts are much less understood. In a field study, we examined the effects of a tree invader, Acer platanoides (Norway maple, NM), on canopy structure and seedling growth in the understory of a North American deciduous forest. The experimental site contains a monospecific patch of A. platanoides and a mixed patch of A. platanoides with its native congener, A. rubrum (red maple, RM). In the study, we examined canopy characteristics of three types of trees in the forests, i.e., RM trees in the mixed forest, NM trees in the mixed forest, and NM trees in its monospecific patch. Height growth and biomass production of RM and NM seedlings under intact canopies and newly created gaps of the three types of trees were followed for two growing seasons. We found that removal of half of the canopy from focal trees increased canopy openness and light transmission to the forest floor, but to a greater extent under NM trees than under RM trees. Seedlings of these two Acer species varied greatly in biomass production under canopies of the same type of trees and in their responses to canopy opening. For example, seedlings of the exotic NM grown under the native RM trees in the mixed forests increased biomass production by 102.4% compared to NM seedlings grown under conspecific trees. The native RM seedlings grown under NM trees, however, reduced biomass production by 23.5% compared to those grown under conspecific trees. It was also observed that RM was much more responsive in biomass production to canopy opening than NM. For instance, total seedling biomass increased by 632.2% in RM, but by only 134.6% in NM in response to the newly created gaps. In addition, we found that NM seedlings allocated a greater portion of biomass below-ground as canopy openness increased, whereas the same trend was not observed in RM seedlings. Our results thus demonstrated that invasion of NM significantly altered canopy structure and community dynamics in the hardwood forest. Because the exotic NM seedlings are able to grow well under the native RM trees, but not vice versa, NM will likely expand its distribution in the forests and make it an ever increasingly serious tree invader in its non-native habitats, including North America.     

Plant density can increase invertebrate postdispersal seed predation in an experimental grassland community

Janzen–Connell effects are negative effects on the survival of a plant's progeny at high conspecific densities or close to its conspecifics. Although the role of Janzen–Connell effects on the maintenance of plant diversity was frequently studied, only few studies targeted Janzen–Connell effects via postdispersal seed predation in temperate grassland systems. We examined effects of conspecific density (abundance of conspecific adult plants) on postdispersal seed predation by invertebrates of three grassland species (Centaurea jacea, Geranium pratense, and Knautia arvensis) in experimental plant communities. Additionally, we examined the impact of plant species richness and different seed predator communities on total and relative seed predation (= seed predation of one plant species relative to others). We offered seeds in an exclusion experiment, where treatments allowed access for (1) arthropods and slugs, (2) arthropods only, (3) small arthropods only, and (4) slugs only. Treatments were placed in plots covering a gradient of abundance of conspecific adults at different levels of plant species richness (1, 2, 3, 4, 8 species). Two of the plant species (C. jacea and K. arvensis) experienced higher rates of seed predation and relative predation with increasing abundance of conspecific adults. For C. jacea, this effect was mitigated with increasing plant species richness. Differences in seed predator communities shifted seed predation between the plant species and changed the magnitude of seed predation of one plant species relative to the others. We exemplify density‐dependent increase in seed predation via invertebrates in grassland communities shaping both the total magnitude of species‐specific seed predation and seed predation of one species relative to others. Further differences in seed predator groups shift the magnitude of seed predation between different plant species. This highlights the importance of invertebrate seed predation to structure grasslands via density‐dependent effects and differing preferences of consumer groups.     

Responses of exotic plant species to fires in Pinus ponderosa forests in northern Arizona

Abstract. Changes in disturbance due to fire regime in southwestern Pinus ponderosa forests over the last century have led to dense forests that are threatened by widespread fire. It has been shown in other studies that a pulse of native, early‐seral opportunistic species typically follow such disturbance events. With the growing importance of exotic plants in local flora, however, these exotics often fill this opportunistic role in recovery. We report the effects of fire severity on exotic plant species following three widespread fires of 1996 in northern Arizona P. ponderosa forests. Species richness and abundance of all vascular plant species, including exotics, were higher in burned than nearby unburned areas. Exotic species were far more important, in terms of cover, where fire severity was highest. Species present after wildfires include those of the pre‐disturbed forest and new species that could not be predicted from above‐ground flora of nearby unburned forests.     

Interacting effects of warming and drought on regeneration and early growth of Acer pseudoplatanus and A. platanoides

Climate change is acting on several aspects of plant life cycles, including the sexual reproductive stage, which is considered amongst the most sensitive life‐cycle phases. In temperate forests, it is expected that climate change will lead to a compositional change in community structure due to changes in the dominance of currently more abundant forest tree species. Increasing our understanding of the effects of climate change on currently secondary tree species recruitment is therefore important to better understand and forecast population and community dynamics in forests. Here, we analyse the interactive effects of rising temperatures and soil moisture reduction on germination, seedling survival and early growth of two important secondary European tree species, Acer pseudoplatanus and A. platanoides. Additionally, we analyse the effect of the temperature experienced by the mother tree during seed production by collecting seeds of both species along a 2200‐km long latitudinal gradient. For most of the responses, A. platanoides showed higher sensitivity to the treatments applied, and especially to its joint manipulation, which for some variables resulted in additive effects while for others only partial compensation. In both species, germination and survival decreased with rising temperatures and/or soil moisture reduction while early growth decreased with declining soil moisture content. We conclude that although A. platanoides germination and survival were more affected after the applied treatments, its initial higher germination and larger seedlings might allow this species to be relatively more successful than A. pseudoplatanus in the face of climate change.     

The incidence of exotic species following clearfelling of Eucalyptus regnans forest in the Central Highlands,Victoria

Abstract Invasion by exotic species following clearfelling of Eucalyptus regnans F. Muell. (Mountain Ash) forest was examined in the Toolangi State Forest in the Central Highlands of Victoria. Coupes ranging in age from < 1- to 10-years-old and the spar-stage forests (1939 bushfire regrowth) adjacent to each of these coupes and a mature, 250-year-old forest were surveyed. The dispersal and establishment of weeds was facilitated by clearfelling. An influx of seeds of exotic species was detected in recently felled coupes but not in the adjacent, unlogged forests. Vehicles and frequently disturbed areas, such as roadside verges, are likely sources of the seeds of exotic species. The soil seed bank of younger coupes had a greater number and percentage of seeds of exotics than the 10-year-old coupes and the spar-stage and mature forests. Exotic species were a minor component (< 1% vegetation cover) in the more recently logged coupes and were not present in 10-year-old coupes and the spar-stage and mature forests. These particular exotic species did not persist in the dense regeneration nor exist in the older forests because the weeds were ruderal species (light-demanding, short-lived and short-statured plants). The degree of influence that these particular exotic species have on the regeneration and survival of native species in E. regnans forests is almost negligible. However, the current management practices may need to be addressed to prevent a more threatening exotic species from establishing in these coupes and forests.     

Neighborhood‐contingent indirect interactions between native and exotic plants: multiple shared pollinators mediate reproductive success during invasions

Native and exotic plants can influence one another's fecundity through their influence on shared pollinators. Specifically, invasion may alter abundance and composition of local floral resources, affecting pollinator visitation and ultimately causing seedset of natives in more‐invaded and less‐invaded floral neighborhoods to differ. Such pollinator‐mediated effects of exotic plants on natives are common, but native and exotic plants often share multiple pollinators, which may differ in their responses to altered floral neighborhoods. We quantified pollinator‐mediated interactions between three common forbs of western Washington prairies (native Microseris laciniata and Eriophyllum lanatum and European Hypochaeris radicata) in three floral neighborhoods: 1) high native and low exotic floral density, 2) high exotic floral density and low native density, and 3) experimentally manipulated low exotic floral density. Pollinator visitation rates varied by floral neighborhood, plant species identity, and their interaction for all three plant species. Similarly, pollinator functional groups (eusocial bees, solitary bees, and syrphid flies) contributed differing proportions of total visitation to each species depending upon neighborhood context. Consequently, in exotic neighborhoods H. radicata competed with native M. laciniata, reducing seed set, while simultaneously facilitating visitation and seed set for native E. lanatum. Seed set of H. radicata was also highest in exotic neighborhoods (with high densities of conspecifics), raising the possibility of a positive feedback between exotic abundance and success. Our results suggest that the outcome of indirect interactions between native and exotic plants depends on the density and the composition of the floral neighborhood and of the pollinator fauna, and on context‐dependent pollinator foraging.     

Assessment of spatial discordance of primary and effective seed dispersal of European beech (Fagus sylvatica L.) by ecological and genetic methods

Spatial discordance between primary and effective dispersal in plant populations indicates that postdispersal processes erase the seed rain signal in recruitment patterns. Five different models were used to test the spatial concordance of the primary and effective dispersal patterns in a European beech (Fagus sylvatica) population from central Spain. An ecological method was based on classical inverse modelling (SSS), using the number of seed/seedlings as input data. Genetic models were based on direct kernel fitting of mother‐to‐offspring distances estimated by a parentage analysis or were spatially explicit models based on the genotype frequencies of offspring (competing sources model and Moran‐Clark's Model). A fully integrated mixed model was based on inverse modelling, but used the number of genotypes as input data (gene shadow model). The potential sources of error and limitations of each seed dispersal estimation method are discussed. The mean dispersal distances for seeds and saplings estimated with these five methods were higher than those obtained by previous estimations for European beech forests. All the methods show strong discordance between primary and effective dispersal kernel parameters, and for dispersal directionality. While seed rain was released mostly under the canopy, saplings were established far from mother trees. This discordant pattern may be the result of the action of secondary dispersal by animals or density‐dependent effects; that is, the Janzen‐Connell effect.     

Density‐dependent pre‐dispersal seed predation and fruit set in a tropical tree

Negative density‐dependent demographic processes operating at post‐dispersal seed, seedling, and juvenile stages are the dominant explanation for the coexistence of high numbers of tree species in tropical forests. At adult stages, the effect of pollinators and pre‐dispersal fruit predators are often dependent on the density or abundance of flowers and fruit in the canopy, but each have opposite effects on individual realized reproduction. We studied the effect of density on total and mature fruit set and pre‐dispersal predation rates within individual tree canopies in a common canopy tree species, Jacaranda copaia in a 50‐ha forest census plot in central Panama. We sampled all reproductive sized trees in the plot (n = 188) across three years and estimated fruit set and predation rates. Population‐wide pre‐dispersal seed predation averaged between 6–37% across years. Using linear mixed effects models, we found that increased density and fecundity of conspecific neighbours increased focal tree fruit set, but also the rate of pre‐dispersal predation. An interaction between individual and neighbourhood fruit production predicted lower predation rates at high individual and neighbourhood fecundities, which suggests predator satiation at high fruit abundance levels. However, the rate at which fruit set increased with conspecific neighbour fruit production was greater than the rate at which fruit were lost to predation, resulting in an overall positive effect of neighbour density on mature fruit production in focal trees. Our results run counter to the expectation of a uniformly negative effect of density across all life stages in tropical trees and suggest further exploration of the role of spatial clumping, pollen dispersal limitation, and predation at pre‐dispersal adult stages in maintenance of species diversity in plant communities.     

Edge Effects on Species Composition and Exotic Species Abundance in the North Carolina Piedmont

Edges between forest and non-forest habitats often have significant effects on forest microclimate and resource availability, with corresponding effects on species composition and abundance. Exotic species are often increased in abundance near forest edges. This increase in abundance could be either because of the increase in resource availability near edges, or because of increased dispersal into forest edges. We measured species composition and a set of geospatial variables on transects at 66 edges in the North Carolina Piedmont in an attempt to distinguish between these two factors. Mantel tests show that species composition is significantly different in forest edges than in the forest interior, but that this effect only penetrates about 5 m into the forest. Indicator species analysis finds several species that are indicative of edge communities, including trumpet vine (Campsis radicans), two drought-tolerant oak species (Quercus stellata and Q. falcata), a serviceberry (Amelanchier arboreum), and a common exotic species, tree-of-heaven (Ailanthus altissima). Poisson regression techniques showed that in both the seedling and tree strata of the forest, exotic species increased in abundance on flat sites with a high potential seed source. Mapping predicted exotic species abundance onto the landscape. We find that large-scale variation in exotic species abundance is due mostly to variation in potential seed sources, while small-scale variation relates more to edaphic factors. Our results stress that both dispersal and environmental filters are important for determining exotic species abundance, but potentially the filters operate at different spatial scales.     

Shade tolerance of <Emphasis Type="Italic">Ailanthus altissima</Emphasis> revisited: novel insights from southern Switzerland

The tree of heaven (Ailanthus altissima (Mill.) Swingle) is considered to be an early-successional, gap-obligate pioneer species with vigorous height growth, low shade tolerance, early fecundity and large seed production. It is a highly invasive species in many temperate and Mediterranean ecosystems outside its natural range, especially after disturbance. Due to its low shade tolerance, the potential of A. altissima to colonise undisturbed forests is thought to be low. In this study we analysed the potential of juvenile A. altissima to grow and survive in sweet chestnut (Castanea sativa Mill.) forests in southern Switzerland. We used hemispherical photography to assess the light conditions of 204 individuals of A. altissima (31 % generative, 69 % vegetative) aged between 1 and 7 years (median: 3 years) in six sites. Generative (seed-borne) and vegetative (clonal ramet) offspring of A. altissima are able to grow in light conditions well below the requirements of shade-intolerant tree species such as European larch (Larix decidua Mill.) and Scots pine (Pinus sylvestris L.). The relatively low light conditions found to be sufficient for the growth and survival of generative regeneration of A. altissima suggest a higher shade tolerance for this species than previously stated, at least for early regeneration. Consequently, the colonisation frontier of A. altissima should be intensively monitored in both forest openings but also in closed canopy forests in the vicinity of seed-bearing A. altissima.     

A highly resolved food web for insect seed predators in a species‐rich tropical forest

The top‐down and indirect effects of insects on plant communities depend on patterns of host use, which are often poorly documented, particularly in species‐rich tropical forests. At Barro Colorado Island, Panama, we compiled the first food web quantifying trophic interactions between the majority of co‐occurring woody plant species and their internally feeding insect seed predators. Our study is based on more than 200 000 fruits representing 478 plant species, associated with 369 insect species. Insect host‐specificity was remarkably high: only 20% of seed predator species were associated with more than one plant species, while each tree species experienced seed predation from a median of two insect species. Phylogeny, but not plant traits, explained patterns of seed predator attack. These data suggest that seed predators are unlikely to mediate indirect interactions such as apparent competition between plant species, but are consistent with their proposed contribution to maintaining plant diversity via the Janzen–Connell mechanism.     

Fitness dynamics within a poplar hybrid zone: II. Impact of exotic sex on native poplars in an urban jungle

Trees bearing novel or exotic gene components are poised to contribute to the bioeconomy for a variety of purposes such as bioenergy production, phytoremediation, and carbon sequestration within the forestry sector, but sustainable release of trees with novel traits in large‐scale plantations requires the quantification of risks posed to native tree populations. Over the last century, exotic hybrid poplars produced through artificial crosses were planted throughout eastern Canada as ornamentals or windbreaks and these exotics provide a proxy by which to examine the fitness of exotic poplar traits within the natural environment to assess risk of exotic gene escape, establishment, and spread into native gene pools. We assessed postzygotic fitness traits of native and exotic poplars within a naturally regenerated stand in eastern Canada (Quebec City, QC). Pure natives (P. balsamifera and P. deltoides spp. deltoides), native hybrids (P. deltoides × P. balsamifera), and exotic hybrids (trees bearing Populus nigra and P. maximowiczii genetic components) were screened for reproductive biomass, yield, seed germination, and fungal disease susceptibility. Exotic hybrids expressed fitness traits intermediate to pure species and were not significantly different from native hybrids. They formed fully viable seed and backcrossed predominantly with P. balsamifera. These data show that exotic hybrids were not unfit and were capable of establishing and competing within the native stand. Future research will seek to examine the impact of exotic gene regions on associated biotic communities to fully quantify the risk exotic poplars pose to native poplar forests.     

Wood preference of spalting fungi in urban hardwood species

Five fungal species representing the three major spalting categories were inoculated onto wood of five different urban tree species with low to moderate economic value. Sugar maple (Acer saccharum) was also inoculated to serve as a control. Test samples were evaluated both internally and externally for spalting. The tested fungi had significant preferences for different wood species, and the preferences appeared to be related to sucrose availability. Specifically, zone line producing fungi preferred American elm (Ulmus americana), while Arthrographis cuboidea (pink stain) preferred tree-of-heaven (Ailanthus altissima). Wood species preference was also significant by decay class, with decay fungi preferring American elm, silver maple (Acer saccharinium), and horse chestnut (Aesculus hippocastanum). Staining fungi showed a preference for tree-of-heaven, while both decay classes readily colonized sugar maple and Norway maple (Acer platanoides).