Simple dynamics in non-monotone Kolmogorov systems

In this paper we analyse the global dynamical behaviour of some classical models in the plane. Informally speaking we prove that the folkloric criteria based on the relative positions of the nullclines for Lotka–Volterra systems are also valid in a wide class of discrete systems. The method of proof consists of dividing the plane into suitable positively invariant regions and applying the theory of translation arcs in a subtle manner. Our approach allows us to extend several results of the theory of monotone systems to nonmonotone systems. Applications in models with weak Allee effect, population models for pioneer-climax species, and predator–prey systems are given.

STRUCTURAL ATTRIBUTES, DIVERSITY AND MANAGEMENT OF SOME VAN PANCHAYAT FOREST STANDS OF GARHWAL HIMALAYA

Oak (Quercus oblongata) is an important component of mid-altitude ecosystem of the Central Himalaya which are exposed to over-exploitation making conditions favourable for the invasion by light-demanding conifers such as chirpine (Pinus roxburghii). The present study provides information on woody vegetation structure, composition, regeneration and management of four broadleaved forest stands of Garhwal Himalaya managed by Village Panchayat. Quercus oblongata was the most important and dominant species in all the stands. Although dominance was shared by a number of species, no single species was found to complete with this climax species. The presence of Alnus nepalensis (a nitrogen-fixing species) depicts the poor nitrogen status of these forest stands. High density values and low basal cover suggest that these community forest stands are younger than the natural oak reserve forests of the Central Himalaya. The richness index shows that the seedling strata are ecologically richer than the tree, sapling and/or shrub strata. High richness in the seedling strata is attributed to the low magnitude of biotic interferences in these communities based conserved forest stands. The regeneration potential of Quercus oblongata is much higher than the natural oak forests of Central Himalaya managed by the forest department. This supports the view that moderate disturbance regimes are more conducive to satisfactory regeneration of this species. Since the management of these forest stands is looked after by the Village Panchayat, they are introducing some conifers for their vested interests. This may add an additional competition of the broadleaved climax species with conifers as has been witnessed in most of the broadleaved oak forests of this altitudinal range.

Structure, composition and diversity of restored forest ecosystems on mine-spoils in South-Western Ghana

In response to national policy obligations, many mining companies in Ghana have restored/reclaimed degraded mined out sites through revegetation. The area extent of such restored areas is unknown and there is also paucity of data on success of restoration, species diversity and compositional dynamics of such restored landscapes, particularly using mixed species. This study assessed stand structure, diversity and composition dynamics of sites restored with mixed species and models species abundance distribution on these sites. Three reclaimed and one control site (adjacent natural forest) were inventoried using 27, 30 x 30 m plots on the Hwini-Butre and Benso concession of the Golden Star Wassa Limited. Overall 3057 (per 24 plots) and 150 (per 3 plots) individual trees were recorded in the overstorey of the reclaimed and control sites, respectively. In all, 31 species in 13 families occurred on the reclaimed site while 61 species in 29 families occurred on the control. Species richness, abundance and diversity were significantly lower in the reclaimed sites than the control in the overstorey (p≤0.018), mid-storey (p ≤ 0.032), and understorey (p≤ 0.031). Species composition of the reclaimed and control sites were mostly dissimilar in the overstorey, midstorey, and understorey. However, the midstorey and overstorey of the reclaimed sites showed high similarity in composition (Jaccard’s index = 0.817). Pioneer and shade-tolerant species were most dominant in the understorey of the control while only shade-tolerant species (mostly herbs and grasses) dominated the reclaimed sites. Species abundance distribution of both reclaimed and control sites followed the geometric series model, indicating that both sites are disturbed but at different intensities. It is concluded that reclamation with mixed species does not necessarily lead to rapid restoration of indigenous climax species on mine spoils. Nonetheless, it may lead to accomplishments of short-term goals of stabilizing and protecting landscapes while conditioning the sites for colonisation of the climax species.

Soil forming role of birch in the Ore Mts.

Large areas were deforested as a consequence of the immission calamity in the Czech Republic in the last decades. As a part of restoration activities, preparatory species were utilized, both planted and sown, to cover forest soils, to prevent soil erosion and to regenerate forest microclimate, necessary for reintroduction of target, climax species. Birch (especially Betula pendula Roth.) was among the mostly common preparatory species. Presented paper documents the effects of birch in the case of its cultivation on an intact soil. In this case, birch was documented as a species suitable in a short-time perspective, improving soil characteristics and forming effective shelter against increased humus mineralization.

Impending Regeneration Failure of the IUCN Vulnerable Borneo Ironwood (Eusideroxylon zwageri)

The regeneration of many climax species in tropical forest critically depends on adequate seed dispersal and seedling establishment. Here, we report the decreased abundance and increased spatial aggregation of younger trees of the Borneo ironwood ( Eusideroxylon zwageri) in a protected forest in Sabah Malaysia. We observed a high level of seedling herbivory with strong density dependence, likely exacerbated by local aggregation and contributing to the progressively shrinking size distribution. We also note the largely undocumented selective herbivory by sambar deer on E. zwageri seedlings. This study highlights the combined impact of altered megafauna community on a tree population through interlinked ecological processes and the need for targeted conservation intervention for this iconic tropical tree species.

Edge effect on the spatial distribution of trees in an Araucaria Rainforest fragment in Brazil

The objective of this research was to evaluate which species in the Brazilian Araucaria forest have its spatial distribution influenced by edge effects. We performed annual forest inventories inside two one-hectare plots, divided in 10 rectangular subplots, delimited by every 10 meters of edge distance. Each tree with at least 10 cm at DBH was identified to species level, and their allometric measurements and geographical coordinates were recorded considering the categories living, recruitment and mortality. We analyzed the correlation between the abundance of each species in each subplot and its distance by the Spearman's Correlation Coefficient and a Generalized Additive Model (GAM) with a Poisson distribution. We analyzed the distribution of some species and the ecological groups using a Kernel density model. We observed numerous pioneers and early secondary species with relationship with the edge distance, usually concentrated close to the edges. The late secondary/climax species are more evenly distributed in the plots, despite of some species, as Eugenia uniflora, are negatively affected by the edge. From these results, it is observed that some light demanding species can be favored to live close to the edges, even if some shadow tolerant species can inhabit this region as well.

Impending Regeneration Failure of the Iucn Vulnerable Borneo Ironwood (Eusideroxylon Zwageri)

The regeneration of many climax species in tropical forest critically depends on adequate seed dispersal and seedling establishment. Here we report the decreased abundance and increased spatial aggregation of younger trees of the Borneo ironwood (Eusideroxylon zwageri) in a protected forest in Sabah Malaysia. We observed a high level of seedling herbivory with strong density dependence, likely exacerbated by local aggregation and contributing to the progressively shrinking size-distribution. We also note the largely undocumented selective herbivory by sambar deer on E. zwageri seedlings. This study highlights the combined impact of altered megafauna community on a tree population through interlinked ecological processes and the need for targeted conservation intervention for this iconic tropical tree species.