Effects of grazing and cultivation on forest plant communities in Mount Elgon National Park, Uganda

Plant communities in the montane forest of Mount Elgon National Park were studied in order to assess the impact of grazing and cultivation on species composition. Present and former land uses, tree, shrub and herb species, soil properties and the percentage cover and height of trees, shrubs and herbs were determined in 40 plots. An indirect ordination of these plots showed that species composition was primarily determined by successional stage and agricultural disturbance. In forest plots (ordinated separately) where the widest range of former and current grazing intensities had occurred, evidence of grazing history, soil phosphorus and vegetation height correlated negatively with the strongest ordination axis. Least grazed forest plots had fewer tree seedlings and saplings than more intensively grazed plots. This may be due to the increase in Mimulopsis alpina (Acanthaceae) in less grazed forest where tree regeneration might otherwise be more advanced. Tree seedlings and saplings were uncommon in the forest, rarely exceeding 30cm in height and there was no tree understorey. Although grazing is important for preserving species diversity in Mount Elgon National Park through the maintenance of species-rich grasslands, long-term effects on montane forest communities must be considered in future park management.     

Contrasting Cloud Forest Restoration Potential Between Plantations of Different Exotic Tree Species

The role of exotic tree plantations for biodiversity conservation is contested. Such plantations nevertheless offer various ecosystem service benefits, which include carbon storage and facilitation of indigenous tree species regeneration. To assess forest restoration potential in tropical exotic tree plantations, we assessed native cloud forest tree regeneration in 166 plots in ca. 50‐year‐old plantations of five timber species that are widely used in tropical plantations (Pinus patula, Eucalyptus saligna, Cupressus lusitanica, Grevillea robusta and Acacia mearnsii). Differences in species abundance, diversity and composition were compared among plantations, and between plantations and disturbed and undisturbed indigenous Afromontane cloud forest (southeast Kenya) relicts after controlling for environmental variation between plots (i.e. altitude, distance to indigenous forest, soil depth, slope, aspect) and for environmental and stand structural variation (i.e. dominant tree height and basal area). Regenerating trees were mostly early‐successional species. Indigenous tree species regeneration was significantly higher in Grevillea plantations, where the seedling community also included late‐successional tree species. Regeneration under Eucalyptus was particularly poor. Acacia had a strong invasive nature, reducing its potential role and usefulness in indigenous forest restoration. Our study underlined that exotic tree plantations have differential effects on native tree species regeneration, with high potential for Grevillea plantations and low potential for invasive exotic species.     

Disturbance Level Determines the Regeneration of Commercial Tree Species in the Eastern Amazon

The effects of reduced‐impact logging (RIL) on the regeneration of commercial tree species were investigated, as long‐term timber yields depend partly on the availability of seedlings in a managed forest. On four occasions during a 20‐month period in the Tapajós National Forest (Eastern Amazon, Brazil), seven commercial tree species were assessed as follows: the long‐lived pioneers Bagassa guianensis and Jacaranda copaia; the partially shade‐tolerant Hymenaea courbaril, Dipteryx odorata, and Carapa guianensis; and the totally shade‐tolerant Symphonia globulifera and Manilkara huberi. In 2439 10 × 10 m plots, all individuals < 20 cm diameter at breast height (dbh) were assessed over three intervals, before, during, and after the forest being logged. Before logging, the density of seedlings and saplings of the seven species did not change. Logged trees were spatially aggregated, with 9.2 percent of the plots being heavily impacted by logging. After logging, the recruitment rate increased more than the mortality rate, so that post‐harvesting densities of seedlings and saplings increased. The increase in density was concentrated in logged plots with more disturbances. It is concluded that post‐harvesting heterogeneity of micro‐environments created by RIL may be an important component to be taken into account for sustainable forest management and conservation of commercial species.     

Forest regeneration following ungulate removal in a montane Hawaiian wet forest

Most Hawaiian forests lack resiliency following disturbance due to the presence of non‐native and invasive plant and animal species. The montane wet forest within Hakalau Forest National Wildlife Refuge on Hawai'i island has a long history of ungulate disturbance but portions of the refuge were fenced and most ungulates excluded by the early 1990s. We examined patterns of regeneration within two 100 ha study sites in this forest following the removal of ungulates and in the absence of invasive woody tree species to determine, in part, if passive restoration techniques can be successful under these conditions. We characterized growth, mortality, and basal area (BA) changes for approximately 7,100 marked individuals of all native tree species present in two surveys over a 17–18‐year period within two hundred 30 m diameter forest plots. Considerable recruitment within plots of new trees of all species significantly changed size class distributions and erased deficits in small‐sized trees observed during the first survey, particularly for the codominant canopy tree, koa (Acacia koa). Overall, growth of established dominant 'ōhi'a trees (Metrosideros polymorpha) and recruitment of mid‐canopy trees contributed to increases in BA while high levels of mortality for large A. koa trees contributed to decreased BA. This resulted in a slight increase in BA between the two surveys (+1.9%). This study demonstrates that fencing and ungulate removal may have rescued the A. koa population by facilitating the first real pulse in recruitment in over a century, and that passive restoration can be a successful management strategy in this forest.     

The Vanishing De Brazza's Monkey (Cercopithecus neglectus Schlegel) in Kenya

We conducted a trail survey of De Brazza's monkey (Cercopithecus neglectus) on Mt. Elgon and the Cherangani Hills between October 1994 and February 1995. The objectives were to assess the status and distribution of the species and its habitats and to formulate recommendations on its conservation. We counted a total of 49 monkeys: 3 groups and 6 lone individuals near Kimothon River (Mt. Elgon) and 4 groups and 6 lone individuals at Kapolet Forest Reserve and its environs (Cherangani Hills). The mean group size is 6.6. Wanton habitat destruction was evident in all the forest habitats. The species now inhabits unprotected remnant strips of riverine forest. Furthermore, the Kapolet Forest Reserve offers little or no protection to De Brazza's monkeys or their habitat. Translocation of the monkeys from unprotected areas to a protected habitat is recommended as an urgent conservation measure to save the De Brazza's population in Mt. Elgon and the Cherangani areas of Kenya.     

Canopy disturbance and gap partitioning promote the persistence of a pioneer tree population in a near‐climax temperate forest of the Qinling Mountains,China

An unresolved question of temperate forests is how pioneer tree species persist in mature forests. In order to understand the responsible mechanisms, we investigated a near‐climax mixed temperate forest dominated by Betula albosinensis in the Qinling Mountains of China. Through establishing four 50 m × 50 m plots, we examined the canopy disturbance characteristics and its effects on tree recruitments. We further test the intra‐ and interspecific effects on the recruitment of B. albosinensis. The obtained data demonstrated canopy disturbance was frequent but most small‐sized. The canopy gaps are caused mainly by adult B. albosinensis by snapping. The regeneration of coexistent tree species shows a distinct preference for gap size. B. albosinensis were clumped at the juvenile stage and small scales. B. albosinensis juveniles were positively associated with B. utilis juveniles and negatively associated with the conspecific and B. utilis large trees. In addition, B. albosinensis juveniles showed negative associations with contemporary other tree species. Our results suggested that canopy disturbance caused by canopy trees and gap partitioning among the coexistent tree species are important for the persistence of the mixed forest. As a main gapmaker, B. albosinensis appear to develop a self‐perpetuating life‐history trait and allow them to persist.     

Fire disturbance and forest structure in an old‐growth Pinus ponderosa forest,southern Cascades,USA

Questions: Did fire regimes in old‐growth Pinus ponderosa forest change with Euro‐American settlement compared to the pre‐settlement period? Do tree age structures exhibit a pattern of continuous regeneration or is regeneration episodic and related to fire disturbance or fire‐free periods? Are the forests compositionally stable? Do trees have a clumped spatial pattern and are clumps even‐ or mixed‐age? How might information from this old‐growth forest inform current restoration and management practices? Location: A 235‐ha old‐growth forest in the Ishi Wilderness, southern Cascade Mountains, California. Methods: Age, size, and spatial pattern of trees were quantified in seven stands. Fire history was reconstructed using fire scar dendrochronology. The influence of fire on stand structure was assessed by comparing fire history with age, size, and spatial structure of trees and identifying and measuring trees killed by two recent fires. Results: Species composition in plots was similar but density and basal area of tree populations varied. Age structure for P. ponderosa and Quercus kelloggii showed periods of episodic recruitment that varied among plots. Fire disturbance was frequent before 1905, with a median period between fires of 12 years. Fire frequency declined after 1905 but two recent fires (1990, 1994) killed 36% and 41% of mostly smaller diameter P. ponderosa and Q. kelloggii. Clusters of similar age trees occurred at scales of 28‐1018 m² but patches were not even‐aged. Interactions between tree regeneration and fire promoted development of uneven age groups of trees. Conclusions: Fire disturbance strongly influenced density, basal area, and spatial structure of tree populations. Fire exclusion over the last 100 years has caused compositional and structural changes. Two recent fires, however, thinned stands and created gaps favorable for Q. kelloggii and P. ponderosa regeneration. The effects of infrequent 20th century fire indicate that a low fire frequency can restore and sustain structural characteristics resembling those of the pre‐fire suppression period forest.     

Factors affecting species richness of tree regeneration in mixed‐wood stands of central Maine

Question: Two questions about within‐stand spatial variability are addressed in this paper. How does species richness of tree regeneration respond to small‐scale ecological gradients, and what effect does natural Abies balsamea abundance have on the species richness of other tree regeneration? Location: A long‐term, gap‐silviculture experiment, Acadian mixed‐wood forest, Maine, USA. Methods: Eight stands treated with and without gap harvesting were sampled to capture sub‐stand heterogeneity of understorey tree regeneration concurrently with patterning of local stand conditions. Spatial and non‐spatial models were developed to test the relationships between two response variables [species richness of small (height ≥0.1 m, but <0.75 m) and large (height ≥0.75 m, but <1.4 m) regeneration] and five explanatory variables (depth to water table, percentage canopy transmittance, A. balsamea regeneration density, and overstorey basal area and species richness). Results: Despite high unexplained variance for all models, consistent associations among variables were found. Negative associations were found between: (1) the species richness of small regeneration and A. balsamea regeneration density and (2) the species richness of large regeneration and overstorey basal area. Positive associations were found between: (1) the species richness of small regeneration and both overstorey basal area and species richness and (2) the species richness of small and large regeneration and canopy transmittance. Conclusions: Promoting tree species diversity in Acadian mixed‐wood stands may not be achievable through the use of gap‐harvesting alone if the density of understorey Abies balsamea is not reduced either naturally or through silvicultural intervention.     

A casualty of climate change? Loss of freshwater forest islands on Florida's Gulf Coast

Sea level rise elicits short‐ and long‐term changes in coastal plant communities by altering the physical conditions that affect ecosystem processes and species distributions. While the effects of sea level rise on salt marshes and mangroves are well studied, we focus on its effects on coastal islands of freshwater forest in Florida's Big Bend region, extending a dataset initiated in 1992. In 2014–2015, we evaluated tree survival, regeneration, and understory composition in 13 previously established plots located along a tidal creek; 10 plots are on forest islands surrounded by salt marsh, and three are in continuous forest. Earlier studies found that salt stress from increased tidal flooding prevented tree regeneration in frequently flooded forest islands. Between 1992 and 2014, tidal flooding of forest islands increased by 22%–117%, corresponding with declines in tree species richness, regeneration, and survival of the dominant tree species, Sabal palmetto (cabbage palm) and Juniperus virginiana (southern red cedar). Rates of S. palmetto and J. virginiana mortality increased nonlinearly over time on the six most frequently flooded islands, while salt marsh herbs and shrubs replaced forest understory vegetation along a tidal flooding gradient. Frequencies of tidal flooding, rates of tree mortality, and understory composition in continuous forest stands remained relatively stable, but tree regeneration substantially declined. Long‐term trends identified in this study demonstrate the effect of sea level rise on spatial and temporal community reassembly trajectories that are dynamically re‐shaping the unique coastal landscape of the Big Bend.     

High and dry: post‐fire tree seedling establishment in subalpine forests decreases with post‐fire drought and large stand‐replacing burn patches

Aim Climate warming and increased wildfire activity are hypothesized to catalyse biogeographical shifts, reducing the resilience of fire‐prone forests world‐wide. Two key mechanisms underpinning hypotheses are: (1) reduced seed availability in large stand‐replacing burn patches, and (2) reduced seedling establishment/survival after post‐fire drought. We tested for regional evidence consistent with these mechanisms in an extensive fire‐prone forest biome by assessing post‐fire tree seedling establishment, a key indicator of forest resilience. Location Subalpine forests, US Rocky Mountains. Methods We analysed post‐fire tree seedling establishment from 184 field plots where stand‐replacing forest fires were followed by varying post‐fire climate conditions. Generalized linear mixed models tested how establishment rates varied with post‐fire drought severity and distance to seed source (among other relevant factors) for tree species with contrasting post‐fire regeneration adaptations. Results Total post‐fire tree seedling establishment (all species combined) declined sharply with greater post‐fire drought severity and with greater distance to seed sources (i.e. the interior of burn patches). Effects varied among key species groups. For conifers that dominate present‐day subalpine forests (Picea engelmannii, Abies lasiocarpa), post‐fire seedling establishment declined sharply with both factors. One exception was serotinous Pinus contorta, which did not vary with either factor. For montane species expected to move upslope under future climate change (Larix occidentalis, Pseudotsuga menziesii, Populus tremuloides) and upper treeline species (Pinus albicaulis), establishment was unrelated to either factor. Greater post‐fire tree seedling establishment on cooler/wetter aspects suggested local topographic refugia during post‐fire droughts. Main conclusions If future drought and wildfire patterns manifest as expected, post‐fire tree seedling establishment of species that currently characterize subalpine forests could be substantially reduced. Compensatory increases from lower montane and upper treeline species may partially offset these reductions, but our data suggest important near‐ to mid‐term shifts in the composition and structure of high‐elevation forests under continued climate warming and increased wildfire activity.     

人为干扰对川西碧峰峡山矾次生林群落结构和物种多样性的影响

为探讨人为干扰对川西碧峰峡山矾(Symplocos sumuntia)次生林群落结构和物种多样性的影响,对其群落结构、物种组成和物种多样性特征进行了研究。结果表明,在总面积为7200 m~2的12块样地中共记录到维管束植物151种,隶属于58科98属,以樟科(Lauraceae)、山矾科(Symplocaceae)、蔷薇科(Rosaceae)等为主。单因素方差分析表明,不同强度人为干扰对山矾次生林群落径级、高度级结构影响的差异不显著(P0.05),群落乔木层径级为单峰型结构,高度级结构分布呈倒“J”型,群落天然更新能力强。受不同人为强度干扰的山矾次生林群落各层次物种组成和优势种数量不同,乔木层优势种数量差异显著,且轻度干扰中度干扰重度干扰;灌木层和草本层中,中度干扰的优势种数量最多,轻度干扰次之,重度干扰的最少。总体上看,人为干扰对山矾次生林群落乔木层、草本层物种多样性水平具有负面影响,群落Shannon-Wiener多样性指数(H)、Simpson优势度指数(H′)、物种丰富度指数(S)和均匀度指数(J_(sw))随人为干扰强度的增加而降低,物种多样性水平呈下降趋势;中度干扰下灌木层的物种多样性有增加的趋势。总体上物种多样性指数表现出灌木层乔木层草本层的规律。     

Double jeopardy: bark harvest for malaria treatment and poor regeneration threaten tree population in a tropical forest of Uganda

Several forest plants known to supply medicine are under pressure worldwide. We carried out a study of four tree species (Warburgia ugandensis Sprague, Fleroya rubrostipulata (K.Schum.) Y.F.Deng, Syzygium guineense DC. and Zanthoxylum chalybeum Engl.) that are highly demanded for malaria treatment. The study was undertaken between 2006 and 2009 in the Sango Bay Forest Reserve, southern Uganda. The aim was to determine the conservation status of trees targeted for malaria treatment. We assessed the level of damage inflicted on trees during harvesting of medicinal parts and determined the population density of target species in the forest. We used 95 plots established along nineteen transects. Survival of the most preferred species, F. rubrostipulata, is of particular concern as its population suffered from a combination of extensive damage due to poor methods of harvesting and poor regeneration. The density of trees with diameter ≥5 cm differed between species and sites, demonstrating different recruitment and survival strategies. Management of Protected Areas should augment strategies to monitor the legal and illegal harvest of medicinal plants, by adopting low impact harvesting methods, and designating the temporal and spatial patterns of harvesting. This might reduce tree damage and mortality.     

Forest response to chronic hurricane disturbance in coastal New England

Question: Hurricanes and cyclones cause a wide range of damage to coastal forests worldwide. Most of these storms are not catastrophic in ecological terms, but forest responses to storms of moderate intensities are poorly understood. In regions with a high frequency of moderate hurricanes, how does variation in disturbance intensity affect the magnitude of ecological responses? Location: Naushon Island, Massachusetts, USA. Methods: We use historical records and dendroecological methods to characterize establishment and growth of Fagus grandifolia, Quercus alba, and Quercus velutina in response to seven non‐catastrophic hurricanes of varying intensity, and a major logging event, relative to baseline conditions, over the past 150 years. Our aim was to document variation in the magnitude of responses to known disturbance events of varying intensity, and to determine whether tree growth after moderate hurricanes differs from growth during periods of no disturbance. Results: Forest harvesting in 1824‐1827 had a strong impact on forest composition and growth. Since then, the study region has been characterized by little harvesting but frequent hurricanes. However, only one of the seven storms examined caused substantial increases in growth and new establishment for the dominant species; most moderate disturbances had minimal impact on growth and regeneration dynamics. We also document highly variable responses among species to individual storms, including substantial growth decreases that may not be detected by standard analytical approaches. Conclusions: Our results caution against the use of simple metrics such as wind speed to predict forest response to specific hurricanes, and highlight the importance of individual disturbance events in controlling long‐term forest dynamics, even in regions characterized by high disturbance frequency. In addition, we show that standard approaches to reconstructing disturbance history based on increases in radial growth and pulses of tree establishment are likely to underestimate the frequency of moderate disturbances.     

Diverging diversity patterns of vascular plants and geometrid moths during forest regeneration on Mt Kilimanjaro, Tanzania

Aim This study investigates diversity patterns of vascular plants and plant‐feeding geometrid moths during montane rain forest regeneration in relation to the biogeographical and historical conditions of Mt Kilimanjaro. Location Investigations were undertaken on the south‐western slopes of Mt Kilimanjaro at altitudes between 2075 and 2265 m. Methods Thirteen plots were selected for this study. Four of these were situated in the middle of large clearings (> 1000 m²), three in secondary forest, two in mature forest remnants surrounded by secondary forest and four plots within continuous closed mature forest. Vascular plant species were recorded in an area of 20 × 20 m². Geometrid moths were attracted using lamps placed inside reflective gauze cylinders. Results Ninety‐three species of vascular plants were recorded on the plots. Plant diversity increased in the course of forest regeneration from clearings and secondary forest to mature forest remnants and mature forest. This increase was visible in all vegetation strata as well as in the species number of Dicotyledoneae. The diversity of geometrid moths conversely decreased from early to late successional stages. A total of 2276 Geometridae representing 114 morphospecies were included in the study. Local values of Fisher's α varied from 10.3 to 18.3 on clearings and in secondary forest, whereas they remained below 8.0 in mature forest and mature forest remnants. There was a significant negative correlation between the diversity of Geometridae and the number of dicots, and of plant species in the shrub layer. Main conclusions Contrary to an expected positive correlation between the diversity of vascular plants and herbivorous geometrid moths, diversity patterns of these two groups are strongly diverging due to biogeographical and ecological factors differently affecting the two groups. The increase in plant diversity can chiefly be explained with an increase in epiphyte diversity which is related to the occurrence of suitable habitats in extensive moss layers on huge Ocotea usambarensis (Engl.) trees in the mature forest. The low diversity of geometrid moths in these forests may be connected to the isolation and relatively young age of the montane rain forests on Mt Kilimanjaro. Hence only a small number of moth species adapted to the cool and perhumid conditions within moist mature forest have so far immigrated into these habitats, and time was insufficient for the evolution of many new species.     

Without management interventions,endemic wet‐sclerophyll forest is transitioning to rainforest in World Heritage listed K’gari (Fraser Island), Australia

Wet‐sclerophyll forests are unique ecosystems that can transition to dry‐sclerophyll forests or to rainforests. Understanding of the dynamics of these forests for conservation is limited. We evaluated the long‐term succession of wet‐sclerophyll forest on World Heritage listed K'gari (Fraser Island)—the world's largest sand island. We recorded the presence and growth of tree species in three 0.4 hectare plots that had been subjected to selective logging, fire, and cyclone disturbance over 65 years, from 1952 to 2017. Irrespective of disturbance regimes, which varied between plots, rainforest trees recruited at much faster rates than the dominant wet‐sclerophyll forest trees, narrowly endemic species Syncarpia hillii and more common Lophostemon confertus. Syncarpia hillii did not recruit at the plot with the least disturbance and recruited only in low numbers at plots with more prominent disturbance regimes in the ≥10 cm at breast height size. Lophostemon confertus recruited at all plots but in much lower numbers than rainforest trees. Only five L. confertus were detected in the smallest size class (<10 cm diameter) in the 2017 survey. Overall, we find evidence that more pronounced disturbance regimes than those that have occurred over the past 65 years may be required to conserve this wet‐sclerophyll forest, as without intervention, transition to rainforest is a likely trajectory. Fire and other management tools should therefore be explored, in collaboration with Indigenous landowners, to ensure conservation of this wet‐sclerophyll forest.     

Interactive effects of introduced herbivores and post‐flowering die‐off of bamboos in Patagonian Nothofagus forests

Question: In November 2000, Chusquea culeou, a bamboo species dominating Andean forest understories in southern Argentina and Chile, massively flowered and died over a north‐south distance of ca. 120 km. Because bamboo is the major forage for large herbivores in these forests, we examined the interactive influences of the bamboo die‐off and herbivory by introduced cattle on understory and tree regeneration. Location: Lanín National Park, Argentina. Methods: Permanent plots, in and outside livestock exclosures, were installed in a Nothofagus dombeyi forest in patches of flowered and non‐flowered C. culeou. Plots were monitored over four years for changes in understory composition and tree seedling densities and heights. Results: After the C. culeou die‐off, new establishment of N. dombeyi was low, both with and without herbivory. Livestock alone directly increased N. dombeyi seedling mortality through physical damage. However, tree seedling browse ratings and height growth were interactively affected by bamboo flowering and herbivory; unfenced plots in flowered bamboo patches had the shortest seedlings, highest browse ratings, and lowest tree seedling annual growth rates. Understory cover was higher where livestock were excluded, and this effect was intensified in the patches of flowered bamboo. Neither herbivory nor bamboo flowering resulted in major changes in species composition, with the exception of Alstroemeria aurea. Conclusion: Effects of livestock on N. dombeyi regeneration were contingent on flowering of C. culeou. Prior to introduction of livestock, N. dombeyi regeneration was probably successful beneath canopy gaps during windows of opportunity following bamboo die‐off, but now livestock impede tree regeneration. Herbivory during bamboo withering periods also produces more open understories, particularly affecting palatable heliophyllous herb species such as Alstroemeria aurea. The results underscore the importance of assessing herbivore impacts on tree regeneration during relatively short periods of potential tree regeneration immediately following rare bamboo flowering and die‐off.     

Chance versus determinism in canopy gap regeneration in coastal scarp forest in South Africa

Question: Is tree regeneration in canopy gaps characterized by chance or predictable establishment. Location: Coastal scarp forests, Umzimvubu district, Eastern Cape Province, South Africa. Methods: Estimation of richness of gap‐filling species across canopy gaps of different size. Data are compared with regeneration under the canopy. Probability of self‐replacement of gap forming species is calculated. Results: Forest area under natural gap phase was 7.8%, caused mostly by windthrow (54%). The abundance and average size of gaps (87.8 m²) suggests that species diversity may be maintained by gap dynamics. However, only four of 53 gap‐filler species displayed gap size specialization and these were pioneer species. An additional 13 species were more common in larger gaps but there was no gradient in composition of gap‐filler species across gap size (p= 0.61). Probabilities of self‐replacement in a gap were low (< 0.3) and common canopy species were equally abundant in gaps and the understorey. Species composition in gaps showed no pattern of variation, i.e. was unpredictable, which suggests absence of a successional sequence within tree‐fall gaps. There was also only a slight increase in species richness in gaps at intermediate levels of disturbance. Conclusions: Coastal scarp forest appears not to comprise tightly co‐evolved, niche‐differentiated tree species. Unpredictable species composition in gaps may be a chance effect of recruitment limitation of species from the species pool. Chance establishment slows competitive exclusion and may maintain tree diversity in these forests. These data suggest that current levels (≤ 3 gaps per ha) of selective tree harvesting may not cause a reduction in species richness in this forest.     

Natural forest regeneration and ecological restoration in human‐modified tropical landscapes

In human‐modified tropical landscapes (HMLs) the conservation of biodiversity, functions and services of forest ecosystems depends on persistence of old growth forest remnants, forest regeneration in abandoned agricultural fields, and restoration of degraded lands. Understanding the impacts of agricultural land uses (ALUs) on forest regeneration is critical for biodiversity conservation in HMLs. Here, we develop a conceptual framework that considers the availability of propagules and the environment prevailing after field abandonment as two major determinants of forest regeneration in HMLs. The framework proposes that regeneration potential decreases with size, duration and severity of agricultural disturbance, reducing propagule availability and creating ill‐suited environmental conditions for regeneration. We used studies from Southern Mexico to assess this framework. First, we identify regeneration bottlenecks that trees face during transit from seed to follow‐up life stages, using demographic analysis of dominant pioneer species in recently abandoned fields. Then, we explore effects of ALUs on forest regeneration at the field and landscape scales, addressing major legacies. Finally, we integrate agricultural disturbance with landscape composition to predict attributes of successful second growth forests in HMLs, and provide indicators useful to select tree native species for active restoration. An indicator of disturbance inflicted by ALUs, based on farmers’ information, predicted better regeneration potential than measurements of soil and microclimate conditions at time of abandonment. Cover of cattle pastures in the landscape was a stronger indicator of forest regenerating attributes than cover of old growth forest remnants. To conclude, we offer recommendations to promote forest regeneration and biodiversity conservation in HMLs.     

Diversity of forest plant species at the community and landscape scales in Switzerland

Abstract

Conservation strategies increasingly refer to indicators derived from large biological data. However, such data are often unique with respect to scale and species groups considered. To compare richness patterns emerging from different inventories, we analysed forest species richness at both the landscape and the community scales in Switzerland. Numbers of forest species were displayed using nationwide distributional species data and referring to three different definitions of forest species. The best regression models on a level of four predictor variables ranged between adj. R ² = 0.50 and 0.66 and revealed environmental heterogeneity/energy, substrate (rocky outcrops) and precipitation as best explanatory variables of forest species richness at the landscape scale. A systematic sample of community data (n = 729; 30 m², 200 m², 500 m²) was examined with respect to nationwide community diversity and plot species richness. More than 50% of all plots were assigned to beech forests (Eu-Fagion, Cephalanthero-Fagion, Luzulo-Fagion and Abieti-Fagion), 14% to Norway spruce forests (Vaccinio-Piceion) and 13% to silver fir forests (Piceo-Abietion). Explanatory variables were derived from averaged indicator values per plot, and from biophysical and disturbance factors. The best models for plot species richness using four predictor variables ranged between adj. R ² = 0.31 and 0.34. Light (averaged L-indicator, tree canopy) and substrate (averaged R-indicator and pH) had the highest explanatory power at all community scales. By contrast, the influence of disturbance variables was very small, as only a small portion of plots were affected by this factor. The effects of disturbances caused by extreme events or by management would reduce the tree canopies and lead to an increase in plant species richness at the community scale. Nevertheless, such community scale processes will not change the species richness at the landscape scale. Instead, the variety of different results derived from different biological data confirms the diversity of aspects to consider. Therefore, conservation strategies should refer to value systems.     

Effects of invasive alien kahili ginger (Hedychium gardnerianum) on native plant species regeneration in a Hawaiian rainforest

Questions: Does the invasive alien Hedychium gardnerianum (1) replace native understory species, (2) suppress natural regeneration of native plant species, (3) increase the invasiveness of other non‐native plants and (4) are native forests are able to recover after removal of H. gardnerianum. Location: A mature rainforest in Hawai'i Volcanoes National Park on the island of Hawai'i (about 1200 m a.s.l.; precipitation approximately 2770 mm yr^?1). Study sites included natural plots without effects of alien plants, ginger plots with a H. gardnerianum‐dominated herb layer and cleared plots treated with herbicide to remove alien plants. Methods: Counting mature trees, saplings and seedlings of native and alien plant species. Using non‐parametric H‐tests to compare impact of H. gardnerianum on the structure of different sites. Results: Results confirmed the hypothesis that H. gardnerianum has negative effects on natural forest dynamics. Lower numbers of native tree seedlings and saplings were found on ginger‐dominated plots. Furthermore, H. gardnerianum did not show negative effects on the invasive alien tree species Psidium cattleianum. Conclusions: This study reveals that where dominance of H. gardnerianum persists, regeneration of the forest by native species will be inhibited. Furthermore, these areas might experience invasion by P. cattleianum, resulting in displacement of native canopy species in the future, leading to a change in forest structure and loss of other species dependent on natural rainforest, such as endemic birds. However, if H. gardnerianum is removed the native Hawaiian forest is likely to regenerate and regain its natural structure.