Closed-canopy Areas Research Articles

Soil Fungal Function Centralization Enhances the Decomposition of Fine Roots at Canopy Gap Borders

Canopy gaps can result in abiotic heterogeneities and diverse niches from gap borders to centers, potentially affecting fine root decompositions mediated by soil fungal communities. Despite extensive discussions on the relationship between soil fungi and fine root decomposition, the mechanism by which gap locations regulate fine root decomposition through the soil fungal community remains elusive. Here, we conducted an in situ field decomposition experiment of Chinese Toon (Toona senensis) fine roots in a low-efficiency weeping cypress (Cupressus funebris) plantation forest across three microhabitats: gap centers, gap borders, and closed canopy areas. Soil fungal communities were determined using internal transcribed spacer (ITS) sequencing after two years of field incubation. Results showed that soil properties and nutrient content in residual roots varied across the three microhabitats, with the gap borders exhibiting the highest decomposition rates. While fungal α-diversity remained relatively consistent, taxonomic compositions differed significantly. Decomposition rates did not show significant correlations with soil properties, observed fungal ASVs, or overall community composition. However, they positively correlated with the relative abundance of saprotrophic Sordariomycetes, which in turn positively correlated with soil total nitrogen (with a highest correlation), peaking at the gap borders. Overall community variations were primarily driven by soil temperature and magnesium content in residual roots. Further analysis revealed high fungal community similarities and low dispersal limitations between the gap borders and closed canopy areas, with more phylogenetically clustered communities at the borders. These results demonstrate that the gap borders possess a high decomposition rate, likely due to the centralization of functions driven by soil fungi such as saprotrophs existing in the “microbial seed bank” or migrating from closed canopy areas. These findings highlight the key role of soil fungi, especially saprotrophic fungi, in fine root decomposition at the gap borders, stressing the importance of soil fungi-driven mechanisms in nutrient cycling, and also informing sustainable forest management practices.

Circadian (re)colonisation dynamics of macroinvertebrates in an isolated karst spring.

Freshwater ecosystems, especially springs, are highly sensitive to environmental changes. They are also excellent natural laboratories because of their stable conditions, reducing the number of variables to be considered in field studies. We examined the composition, dynamics and colonisation patterns of macroinvertebrates with respect to canopy coverage and time of day in which available areas are actively colonised. We used artificial substrates that mimicked the natural habitat structure at an isolated karst spring and recovered exposed substrates every 12 h. Physico-chemical parameters of water did not differ significantly regardless of canopy cover. The most numerous representatives and the pioneering champions were larvae of Baetidae (Ephemeroptera) and Chironomidae (Diptera). Simuliidae were also among the most successful pioneering species. Most observed groups more actively colonised substrates in the closed canopy area. Oligochaeta and Gammarus fossarum were more numerous on substrates in the open canopy area. Individuals of all analysed groups showed day-night migration patterns and were more active at night. Coleoptera (Elmis sp.) were the poorest (re)colonisers among the analysed taxa.

Evaluation of UAS LiDAR data for tree segmentation and diameter estimation in boreal forests using trunk- and crown-based methods

Very high point density laser scanning data from unmanned aerial systems (UAS) can be used to segment the trunks of individual trees. Such segmentation (e.g., individual trunk segmentation (ITS)) is useful, for example, in the estimation of diameter at breast height (DBH), which in turn is needed for the estimation of other tree and stand attributes, such as stem volume and diameter of the basal area median tree (DGM). In this paper, we assess the estimation of DBH directly from UAS LiDAR data in open and closed canopy conditions that represent the range of operational conditions encountered in boreal forests in Finland. We also compare trunk-based DBH estimates to corresponding estimates from individual tree crown segmentation (ITC) and fuse the results from the trunk- and crown-based estimates. The results showed that trunk segmentation performed slightly better than ITC in open canopy areas, whereas ITC performed better in closed canopy areas. The DBH prediction error was smaller for ITS (3.0 cm) than ITC (3.9 cm) when considering the trees that were recognized by both methods. We also conclude that a hybrid method, where both segmented tree trunks and tree crowns are fused, considerably increases the number of correctly segmented trees but does not decrease the prediction error associated with DGM compared to using either ITC or ITS individually.

Regeneration from seed in herbaceous understorey of ancient woodlands of temperate Europe.

European ancient woodlands are subject to land use change, and the distribution of herbaceous understorey species may be threatened because of their poor ability to colonize isolated forest patches. The regeneration niche can determine the species assembly of a community, and seed germination traits may be important descriptors of this niche. We analysed ecological records for 208 herbaceous species regarded as indicators of ancient woodlands in Europe and, where possible, collated data on seed germination traits, reviewed plant regeneration strategies and measured seed internal morphology traits. The relationship between plant regeneration strategies and ecological requirements was explored for 57 species using ordination and classification analysis. Three regeneration strategies were identified. Species growing in closed-canopy areas tend to have morphological seed dormancy, often requiring darkness and low temperatures for germination, and their shoots emerge in early spring, thus avoiding the competition for light from canopy species. These species are separated into two groups: autumn and late winter germinators. The third strategy is defined by open-forest plants with a preference for gaps, forest edges and riparian forests. They tend to have physiological seed dormancy and germinate in light and at higher temperatures, so their seedlings emerge in spring or summer. Seed germination traits are fundamental to which species are good or poor colonizers of the temperate forest understorey and could provide a finer explanation than adult plant traits of species distribution patterns. Seed dormancy type, temperature stratification and light requirements for seed germination are important drivers of forest floor colonization patterns and should be taken in account when planning successful ecological recovery of temperate woodland understories.

Soil type, vegetation cover and temperature determinants of the diversity and structure of dung beetle assemblages in a South African open woodland and closed canopy mosaic

AbstractRegional biogeographical patterns result from a complex combination across habitat, climate and environmental variables. Biotic and abiotic variables strongly influence the diversity and spatial distribution patterns. However, very few studies analyse the close interaction and effect of environmental variables on diversity at fine spatiotemporal scales. In this study, we evaluated the influence of soil type, vegetation cover and temperature on species diversity and functional structure of dung beetle assemblages. Dung beetle species were sampled using pitfall traps baited with cattle dung from sandy and clay soils in open woodland and closed canopy areas in Mkhuze Game Reserve, KwaZulu‐Natal, South Africa. We performed a PERMANOVA, a PERMDISP and an NMDS to analyse differences in species composition between soil and vegetation cover types. To test the effect of environmental variables on species richness and abundance, we performed a generalised least squares model. Lastly, we searched for nodes using a bipartite analysis to evaluate network’s potential modularity. We collected 1439 specimens comprising 27 species and 13 genera. Species composition differed between environmental variables. Soil type was the most important driver for changes in dung beetle species composition. Species richness and abundance were influenced by the interaction between soil type and vegetation cover. The combination of microenvironmental preferences potentially influenced the dung beetle assemblage diversity and functional structure. Combining all these preferences may act as a dilution mechanism of interspecific competition in saturated habitat conditions, reducing the number of species that potentially interact and generating a modular network structure of the assemblage.

Stream Temperature and Environment Relationships in a Semiarid Riparian Corridor

This study examined the relationship between stream temperature and environmental variables in a semiarid riparian corridor in northcentral Oregon, USA. The relationships between riparian vegetation cover, subsurface flow temperature, and stream temperature were characterized along an 800 m reach. Multiple stream temperature sensors were located along the reach, in open and closed canopy areas, with riparian vegetation cover ranging from 4% to 95%. A support vector regression (SVR) model was developed to assess the relationship between environmental characteristics and stream temperature at the larger valley scale. At the reach scale, results show that air temperature was highly correlated with stream temperature (Pearson’s r = 0.97), and no significant (p < 0.05) differences in stream temperature levels were found among sensor locations, irrespective of percent vegetation cover. Channel subsurface temperature levels from an intermittent flow tributary were generally cooler than those in the perennial stream in the summer and warmer during winter months, indicating that the tributary may have a localized moderating effect on stream temperature. At the valley scale, results from the SVR model showed that air temperature, followed by streamflow, was the strongest variable influencing stream temperature. Also, riparian area land cover showed little effect on stream temperature along the entire riparian corridor. This research indicates that air temperature, subsurface flow, and streamflow are important variables affecting the stream temperature variability observed in the study area.

Effect of canopy gap size on soil respiration in a mixed broadleaved-Korean pine forest: Evidence from biotic and abiotic factors

Understanding the effects of forest structure, the frequency and size of canopy gaps is pivotal for precisely modelling forest soil carbon budgets. We aimed to determine the differences in soil respiration between closed canopy areas and canopy gaps with various sizes and how soil respiration is affected by biotic and abiotic factors, e.g., soil nutrients, soil microbial biomass and community composition, enzyme activities and fine root biomass. Soil respiration and these environmental factors were measured in eleven tree fall gaps (separated into small, medium and large with sizes ranging from 20 m2 to 450 m2) and three control plots in a mixed broadleaved-Korean pine forest during the growing season. Our results showed that soil respiration was similar between the control and small canopy gaps, while it was 17–49% lower in the medium and large canopy gaps compared to that of the control. There was a significant parabolic relationship between soil respiration and soil moisture, and the optimum moisture was approximately 40%. Fine root biomass and soil enzyme activities showed positive effects on soil respiration across different levels of canopy gaps. Furthermore, soil respiration was significantly declined with increasing soil microbial diversity (OTUs of bacteria). Our findings demonstrate that canopy gap has significant impact on soil CO2 emission in a temperate mixed forest, however, further studies concerning other forest ecosystem types and larger scale are warranted.

Vertical and horizontal vegetation cover synergistically shape prey behaviour

An animal's perception of predation risk varies across a heterogeneous landscape. Animals rely on indirect cues in the environment, including availability of protective cover, openness of sightlines and distance to refuge to evaluate potential predation risk. Interactions between the indirect cues that influence an animal's perception of predation risk are poorly understood, especially for prey at risk of avian and terrestrial predation. We conducted a giving-up density (GUD) study to examine how interactions between terrestrial predator presence, ceiling (canopy) cover, wall (shrub/grass) cover and distance to nearest tree influence fox squirrel, Sciurus niger, risk perception. The GUD indicates an animal's perceived predation risk, such that increased GUD (decreased foraging) corresponds to greater perceived risk. We found that fox squirrels perceived cues of predation risk in response to a synergistic interaction between ceiling and wall cover. In open canopy areas, fox squirrels increased GUD where there was also increased wall cover. However, fox squirrels reduced GUD in closed canopy areas where there was also increased wall cover. We attribute the differential effects of wall cover depending on ceiling cover to the effectiveness of open sightlines in decreasing predation risk from avian or terrestrial predators. Our study shows that the effect of vegetation structure on prey risk perception and antipredator behaviour depends on the relative risk posed by avian and terrestrial predators that use different hunting strategies.

Natural regeneration of oriental beech (Fagus orientalis Lipsky) trees in canopy gaps and under closed canopy in a forest in northern Iran

For developing nature-based silvicultural practices in a beech forest to promote, abundance, height, vitality, and preferred growth form, regenerated trees growing in gaps were compared with those under closed canopies. A systematic 50 × 50 m grid was plotted in a beech stand in the Kheyrud Experimental Forest for selecting trees to measure variables in gaps and under closed canopies. Abundance and mean height of regenerated beech trees were significantly higher in closed canopies than in canopy gaps. Beech seedlings with excurrent growth were significantly taller within regeneration patches under closed canopy. Moreover, regenerated trees with high vitality were more abundant in closed canopy areas than in gaps. Thus, beech regeneration should improve under closed canopies; hence, gaps in a near natural forest should be created only after adequate regeneration and appropriate growth under the parent tree in a closed canopy area is ensured. The results of this research have profound implications for the sustainable management of the forest and for ensuring sustainable beech regeneration. The presence of a closed canopy cover likely will reduce potential stresses on oriental beech regeneration.

Forest fragmentation does not matter to invasions by Hovenia dulcis

Testing whether biological invasions can be facilitated by habitat fragmentation can provide important insights for the study of invasion ecology. Hovenia dulcis is considered an aggressive non-native species in subtropical Atlantic forest ecosystems and following the assumptions of invasion ecology we hypothesized it would occur mainly in smaller forest remnants, which are more susceptible to edge effects compared to larger ones. In this study, we verified the relationships between H. dulcis invasion on forest remnants and the current habitat fragmentation and tested whether both occurrence and abundance of this species are driven by landscape and habitat variables. We selected 30 forest fragments in initial, middle or late successional stages and verified the occurrence and abundance of trees and saplings of H. dulcis. We evaluated spatial autocorrelation and the influence of landscape and habitat metrics on occurrence and abundance of such species and the influence of fruiting trees (adults) on the abundance of non-adult individuals. We found that H. dulcis distribution was not related to geographic distance among remnants. The occurrence of adult H. dulcis was directly associated to closed-canopy areas and remnant shape and, contrary our initial hypothesis, not related to remnant size. The occurrence of adult trees increased H. dulcis regeneration leading to higher sapling abundance. High abundance of H. dulcis saplings close to adult trees pointed out the successful colonization of recently invaded Atlantic forest remnants. We showed that this invasive tree species successfully invades closed-canopy forest fragments, which highlight undisturbed subtropical Atlantic forest habitats are as susceptible to biological invasions as disturbed ones.

Regeneration of Abies pinsapo within gaps created by Heterobasidion annosum-induced tree mortality in southern Spain

We explored the effects of tree-fall gaps caused by Heterobasidion annosum-induced tree death on the regeneration of the relict Abies pinsapo in southern Spain. We analyzed the structure and regeneration of A. pinsapo in 44 circular closed-canopy plots and 11 gaps (mean size 75 m2) located in H. annosum infection foci. We measured adult density, basal area, and height of all tree species with a diameter at breast height greater than 7.5 cm and quantified regeneration abundance. Diameter structures were analyzed using Weibull functions. A. pinsapo comprised 49-81% of total adult tree density (358-1418 trees ha-1) and total basal area (15.70-39.22 m2 ha-1). Density of A. pinsapo juveniles ranged from 129 to 416 individuals ha-1, while that of juveniles of other tree species such as Quercus ilex was much lower. A. pinsapo saplings and seedlings were more abundant within gaps than in closed-canopy sites. A. pinsapo regeneration was related to the tree species composition of the stands adjacent to gaps. The main potential species replacing A. pinsapo in H. annosum-induced gaps were, in decreasing order of importance, Quercus ilex, Q. faginea, and Juniperus oxycedrus. The current stand structure and gap-infilling processes suggest that A. pinsapo regenerates adequately within H. annosum-induced gaps. However, the relative proportion of other coexisting tree species within H. annosum-related gaps will increase substantially over time as compared with closed-canopy areas.

Impact of Seed Predation by Mice on Wild Lupine in and near Oak Savannas

Wild blue lupine (Lupinus perennis) in the Oak Openings Region of Northwest Ohio is an important nitrogen fixer and serves as an essential food source for the federally endangered Karner Blue butterfly (Lycaeides melissa samuelis). In order to examine potential factors that might be affecting mice predation on wild blue lupine seeds in oak savannas, we used seed trays placed in the open or on the forested edge to estimate seed predation rate. We recorded management histories, performed vegetation surveys, and used GIS to find spatial variables related to prescribed burning and edge to assess how they affect seed predation. Our major findings were that seed removal by mice for the summer averaged across sites was 22%, seed removal varied significantly across time (P < 0.05), and was more likely in areas with increased crypto-biotic crust (P < 0.0001). Seed predation rates increased under more prescribed burns over the last 10 y (P = 0.034) and 19 years (P = 0.0001). This leads us to support current management practices of a rotation of prescribed burning in open to partially closed canopy areas to create a balance between promoting lupine growth and minimal seed predation.

Butterfly behavioural responses to natural Bornean tropical rain-forest canopy gaps

Abstract:Natural tree canopy gaps allow sunlight to penetrate to the forest floor, a major environmental component and resource for many tropical rain-forest species. We compare here how butterflies use sunny areas created by the natural gaps in canopies in comparison with adjacent closed-canopy areas. We chose butterflies as our focal organisms as they are taxonomically tractable and mobile, yet habitat sensitive. Previous studies have shown that butterfly diversity in tropical forests responds to varying degrees of canopy openness. Here we assess butterfly behavioural responses to gaps and equivalent sized closed-canopy patches. Butterfly occupancy time and behaviour were simultaneously observed 61 times in gaps and 61 times in equivalent sized closed-canopy patches across four sites in a tropical rain forest in northern Borneo. Out of the 20 most frequently recorded species, 12 were more frequently recorded or spent more time in gaps, four occurred more frequently in closed-canopy areas, and four showed no significant differences. Overall agonistic, basking, patrolling and resting were more common in gaps compared with the closed canopy. Many butterfly species have complex behavioural requirements for both gaps and closed canopies, with some species using these different areas for different behaviours. Each butterfly species had particular habitat requirements, and needed both canopy gaps and closed canopy areas for ecological and behavioural reasons, emphasizing the need for natural light heterogeneity within these systems.

Recruitment and Growth of Old World Climbing Fern in Hurricane-Caused Canopy Gaps

Abstract Following 2 y of severe hurricanes in 2004 and 2005, we examined the role of canopy gaps in promoting recruitment and growth of the exotic fern, Old World climbing fern Lygodium microphyllum (hereafter Lygodium), on tree islands of the Arthur R. Marshall Loxahatchee National Wildlife Refuge, Florida. We selected 12 sample tree islands, on which we placed three 1-m2 plots in a hurricane-caused canopy gap and three plots in an adjacent closed canopy area. Spore traps were placed in canopy gaps and closed canopy areas to quantify the number of spores reaching the forest floor on each island. In addition, in each plot occurrence and growth of Lygodium was measured across four height classes (recruitment class, understory, midstory, and canopy). We predicted that recruitment and growth of Lygodium would be higher in canopy gaps than in closed canopy areas. After 3 y of biannual monitoring, a significantly greater number of spores were foundin canopy gaps (4,804 spores·m2·d) than in closed canopy areas (4,288 spores·m2·d). Furthermore, we observed significantly greater recruitment and growth in canopy gaps compared with closed canopy areas in the recruitment class only. Presence of recruitment-class Lygodium in canopy gaps increased from four to five treatment areas and decreased from 1 to 0 treatment areas in closed canopy areas. These results suggest differences in recruitment and growth of Lygodium between canopy gaps and closed canopy areas on tree islands after severe hurricanes. However, despite the large number of spores in both canopy gaps and closed canopy areas, recruitment and growth were much lower than expected, with only two treatment areas having an average percent cover greater than 10% in any height class. If conducted within several years after a hurricane, focused monitoring efforts on hurricane-impacted tree islands may allow managers to detect and treat new infestations before they are able to overrun tree islands.

Relative abundance of amphibians in forest canopy gaps of natural origin vs. timber harvest origin

Small-scale canopy gaps created by logging may retain adequate habitat structure to maintain amphibian abundance. We used pitfalls with drift fences to measure relative abundance of amphibians in 44 harvested gaps, 19 natural treefall gaps, and 36 closed-canopy forest plots. Metamorphs had relatively lower capture rates in large harvest gaps for Ambystoma maculatum, Lithobates catesbeianus, L. clamitans, and L. sylvaticus but we did not detect statistically significant (p &lt; 0.1) differences among gap types for Lithobates palustris metamorphs. L. clamitans juveniles and L. sylvaticus juveniles and adults had relatively lower capture rates in large harvest gaps. For juvenile-adult A. maculatum, we caught relatively fewer individuals in all gap types than in closed-canopy areas. Some groups with overall lower capture rates (immature Plethodon cinereus, juvenile L. palustris) had mixed differences among gap types, and Notophthalmus viridescens (efts) and adult P. cinereus showed no differences among gap types. One species, L. clamitans, was captured more often at gap edges than gap centers. These results suggest that harvest gaps, especially small gaps, provided habitat similar to natural gaps for some, but not all, amphibian species or life-stages.

Response of ectomycorrhizal community structure to gap opening in natural and managed temperate beech-dominated forests

Data on the impact of forest management practices on ectomycorrhizal community structure remains fragmentary and mainly originates from studies in northern coniferous forests. This study focuses on a comparison of ectomycorrhizal communities between canopy gaps and closed canopy areas within natural and managed beech-dominated forests at four locations in Europe. We used high resolution rDNA techniques to identify ectomycorrhiza-forming fungi and attempted to extract potential stand-, gap-, soil-, and selected environmentally derived variables by applying multivariate analysis and ordination for pooling of ecological groups of ectomycorrhiza. A significant reduction of diversity indices, ectomycorrhizal and fine root dynamics, in gaps in comparison with closed canopy stands indicates an effect of forest management practice and the high importance of maintaining and protecting natural forest areas for conservation of soil biodiversity and forest genetic resources. The ordination analysis revealed three groups of ectomycorrhiza correlated with changing environmental conditions. The litter and soil pH, number of beech seedlings, and presence of a gap had a pronounced effect on the ectomycorrhizal community. Combined analysis of ectomycorrhiza and environmental factors using correspondence analysis provided an insight into the ecological preferences of the analysed species and confirmed that environmental factors drive ectomycorrhizal community changes.

Beetle responses to artificial gaps in an oceanic island forest: implications for invasive tree management to conserve endemic species diversity

Natural forests are often replaced by invasive alien trees on isolated oceanic islands. Adequate eradication of invasive trees should be conducted with the goal of biodiversity conservation, because islands support many endemic organisms that depend on native forests. An invasive alien tree, Bischofia javanica Blume (Euphorbiaceae), has invaded and replaced natural forests on the oceanic Ogasawara (Bonin) Islands, Japan, in the northwestern Pacific Ocean. To determine how the removal of B. javanica trees affects insect diversity, we examined flying beetles captured using Malaise traps in B. javanica forests on Hahajima. The abundance, species density, and species composition of wood-boring beetles (Coleoptera: Cerambycidae, Elateridae, Mordellidae, and Scolytidae) were compared between closed-canopy sites and gaps created by girdling B. javanica trees in alien forests during two seasons (June–July and October–November 2005). Of the collected beetles, 75.8, 87.5, 90.0, and 0.0% of cerambycid, elaterid, mordellid, and scolytid beetle species, respectively, were endemic to the Ogasawara Islands. More cerambycid, elaterid, and mordellid individuals were captured in June–July than in October–November; the number of scolytid individuals did not differ between seasons. More cerambycid, elaterid, and scolytid individuals were captured in artificial gaps than on the closed-canopy forest floor. Although fewer mordellid individuals were captured in gaps, more endemic mordellids were captured in gaps. More cerambycid and scolytid species were captured in artificial gaps than in closed-canopy areas. The positive responses of beetles to artificial gaps suggest that the removal of B. javanica increases beetle diversity and the abundance of endemic beetles.

Effect of Gaps on Species Diversity in the Naturally Regenerated Mixed Broadleaved-Korean Pine Forest of the Xiaoxing'an Mountains, China

Recognizing the ecological importance of forest gap formation for forest community structure, we examined the differences in species diversity between forest gaps and closed canopy areas for trees and shrubs in three developmental stages (seedling, sapling I, and sapling II) in a typical mixed broadleaved-Korean pine forest. We randomly placed 100 sample plots (<TEX>$2{\times}2m$</TEX> for seedling and sapling I, and <TEX>$5{\times}5m$</TEX> for sapling II) in forest gap and closed canopy areas of a 9 ha permanent sample plot for vegetation surveys of plants of each developmental stage in each habitat type. Even though the formation of forest gaps encouraged the occurrence of gap-dependent species and increased overall species diversity, there were no significant differences in species richness among the three developmental stages for both tree and shrub species (p>0.05). Comparing the two types of sites, statistical tests revealed no difference in species richness for trees, but highly significant differences (p<0.01) between forest types for shrubs for seedlings and sapling I, but not sapling II. Analysis of variance test indicated that there were no significant differences in species diversity among the three developmental stages of tree species (p>0.05) for both Simpson and Shannon indices. The variance for shrub seedlings was significantly different between forest gaps and closed canopy areas, but not for sapling I and sapling II. The analysis showed that the species diversity in forest gaps was significantly different from that of closed canopy areas for seedling and sapling I (p<0.01), but not for sapling II (p>0.05).

Land use history, hurricane disturbance, and the fate of introduced species in a subtropical wet forest in Puerto Rico

Tropical forests are suffering from increasing intensities and frequency of disturbances. As a result, non-native species accidentally introduced or intentionally planted for farming, plantations, and ornamental purposes may spread and potentially invade undisturbed native forest. It is not known if these introduced species will become invasive, as a result of recurrent natural disturbances such as hurricanes. Using data from three censuses (spanning 15 years) of a 16-ha subtropical wet forest plot, we investigated the impact of two hurricanes on populations of plant species that were planted in farms and plantations that were then abandoned and from the natural spread of species introduced into Puerto Rico in the past. The populations of four species (Citrus paradis, Mangifera indica, Musa sp., and Simarouba glauca) changed little over time. Six species (Artocarpus altilis, Calophyllum calaba, Genipa americana, Hibiscus pernambucensis, Syzygium jambos, and Swietenia macrophylla) declined between the first two censuses after Hurricane Hugo, then increased again in Census 3 after Hurricane Georges. Spathodea campanulata gradually increased from census to census, while Coffea arabica declined. These introduced species represent only a small part of the forest basal area and few show signs of increasing over time. The number of stems per plant, new recruits, and the growth rates of these introduced species were within the ranges of those for native plant species. The mortality rates over both census intervals were significantly lower for introduced species (<5% year−1) than for native ones (15% year−1). Many new recruits established after Hurricane Hugo (prior to this study) had opened the forest canopy and these high mortality rates reflect their death as the canopy recovered. Only Swietenia macrophylla and Syzygium jambos showed an increase in stem numbers in the closed canopy area of forest that had suffered limited human disturbance in the past. A future increase in frequency of disturbance may enable greater stem numbers of introduced species to establish, while lower-mortality rates compared to native species, may allow them to persist during inter-hurricane intervals. An increase in the population of introduced species, especially for those that grow into large trees, may have an impact on this tropical forest in the future.

New options for land rehabilitation and landscape ecology in Southeast Asia by “rainforestation farming”

Continental and insular Southeast Asia were originally endowed with vast areas of luxurious Tropical Evergreen Forest. Mainly since the sixties of the last century these tropical rainforests have been under a steadily increasing pressure due to intensive logging for commercial purposes and the increasing number of people depending on the given environment for more agricultural land and for fuel wood. One innovative approach to combine the necessities of rural development, safe natural resource management and biodiversity restoration was developed under the acronym “Rainforestation Farming” on the island of Leyte in the Philippines. More than 100 different local forests and fruit tree species were tested and planted in a near-to-nature planting scheme concerning species composition in a former degraded area covered by Imperata cylindri c a . The recommended planting scheme includes both sun-requiring trees and shade-loving trees, highly valuable timber trees and fruit trees. During the first year of planting, nursery grown sun-loving trees were planted at close distance of 2×2 m to quickly reach the condition of a closed canopy and therefore shading out of the grass. During the second year, shade-loving trees, coming from either the nursery or from the natural forest in the form of seedlings sitting under mother trees, were planted under the established first year pioneers. To support the protection of the remaining forest, particularly the mother trees as resource for seedlings and to spur biodiversity rehabilitation efforts through people's participation a support system with community organisers was established. Already after four years some highly endangered species like the herbivorous Flying Lemure, Gynocephalus volans, and the insectivorous nocturnal ape , Tarsius syrichta , moved back into parts of the reforested closed canopy areas of the research and model farm.