Presence Of Woody Species Research Articles

Thus far but no further: predatory mites do not migrate effectively into strawberry plantations

Enhancing the performance of predatory mites is often regarded as the best biological control approach towards the spider mite Tetranychus urticae, the main pest of strawberry plantations. Optimizing the colonization of plantations by predators from adjacent areas such as field margins is seen as an important component of conservation biocontrol. We have investigated the factors contributing to enhancing the numbers of predatory mites (Acari: Phytoseidae), such as management of the field margins, vegetation composition and the effect of the presence of woody species. We also tested the penetration of the phytoseiids from the field margins into the crop. In a study carried out in 14 open-field extensively managed strawberry plantations in Poland we found phytoseiids to be abundant in field margins; 14 taxa were discovered. However, only two species Amblyseius andersoni and Euseius finlandicus dispersed a modest distance into the crop. We found that the diversity and densities of the predatory mites were enhanced somewhat by the management type of the field margins; especially the spontaneous vegetation favoured the presence of phytoseiids. However, despite the predatory mites being rather retained in the field margins also significant reduction in numbers of their prey T. urticae was recorded over the course of the year. The low penetration of predatory mites into the main part of the field, indicates that conservation biological control measures in the field margin might not be sufficient on their own to enhance the impact of predatory mites within the main part of the fields.

Environmental factors interact with spatial processes to determine herbaceous species richness in woody field margins

The species richness of hedges in an agricultural landscape may be determined by the environment and by the spatial processes which occur in that landscape. Here, we divided the environmental predictors into three groups: site conditions, hedge stand and landscape structure. We determined their independent and joint effects on the richness of four guilds of herbaceous species in 92 hedge stands in a north-Mediterranean intensive agricultural landscape. The fine—(at 550 m) spatial patterns of the key environmental predictors and the pure spatial effects on species richness were measured using a computation of the principal coordinates of a matrix of geographical neighbours integrated into a variation partitioning. The total explained variation of species richness among hedgerows was highest for wetland herbs (62 %), with increasing rates for rare plants (33 %), forest herbs (43 %) and arable weeds (47 %). 43–11 % of that variation was spatially structured and mostly explained by some of the key environmental predictors, such as proportion of a given landuse, presence of woody species and dead trees. This indicates that complex relationships between herbaceous species distribution and spatial processes exist in woody field margins and much of that is related to key factors which are spatially structured, both at fine or broad-scales, with implications for management and landuse planning.

Post-fire regeneration in a Mediterranean pine forest with historically low fire frequency

Abstract Species of Mediterranean vegetation are known to regenerate directly after fire. The phenomenon of autosuccession (direct regeneration) has been found to be often combined with an increase of species richness during the first years after fire due to the high abundance of short-lived herbaceous plants facilitated by plentiful nutrients and light. The high degree of vegetation resilience, which is expressed in terms of autosuccession, has been explained by the selective pressure of fire in historic times. According to existing palaeoecological data, however, the Pinus halepensis forests in the Ricote Mountains (Province of Murcia, SE Spain) did not experience substantial fire impact before the presence of man nor are they especially fire-prone today. Therefore, we studied post-fire regeneration to find out if direct succession is present or if species from pre-fire vegetation are absent during the post-fire regeneration stages. Patterns of succession were deduced from observations made in sample plots on sites of a known regeneration age as well as in adjacent unburnt areas. The results of the vegetation analyses, including a Detrended Correspondence Analysis, indicate that Pinus halepensis forest regeneration after fire resembles autosuccession. As regards the presence of woody species, there is a high percentage similarity on north (83%) and south (70%) facing slopes during the first year after fire vs. reference areas which is due, for example, to direct regeneration of the resprouting Quercus coccifera or seeders like Pinus halepensis or Fumana laevipes . However, if herbaceous species are included in the comparison, the similarity on north-facing sites decreases (to 53%) with the presence of additional species, mainly ruderals like Anagallis arvensis or Reseda phyteuma , and even woody species on the burnt plots. This effect indicates “enhanced autosuccession”, which was not found on south-facing sites where overall species richness was very high irrespective of the impact of fire. Locally we found limited regeneration of some species, for example Pinus halepensis at high altitudes (1000 m), even 22 years after fire. As we assume that historical fires did not play an important role in the area and direct succession is present nevertheless, our results support the theory that autosuccession is not a process restricted to fire-prone areas. Fire has been only one of several selective forces since human settlement that probably led to a set of species pre-adapted against recurrent disturbance.

The role of facilitation in seedling recruitment and survival patterns, in the Strandveld Succulent Karoo, South Africa

Several studies in arid ecosystems have demonstrated that seedling establishment and survival were greater underneath the canopies of shrubs than in the open spaces between shrubs. These results led to the formulation of the hypothesis that seedling recruitment and survival were dependent on the shelter provided by shrub species (nurse-plant hypothesis). Seedling emergence and survival beneath and between the canopies of selected perennial shrub species were investigated at five localities in the Strandveld Succulent Karoo, each dominated by a different shrub species. Seedling emergence and survival were also examined at three localities dominated by annual species. In general, species richness and seedling densities were significantly higher in open areas than underneath shrubs, while seedling survival percentages did not differ significantly between microsites. Therefore, no evidence could be found to support the hypothesis that seedling recruitment and survival were facilitated by the presence of shrub species. Although most species will be able to establish in the absence of shrubs, the presence of woody species may have other advantages when restoring vegetation in mined areas.

Agroforestry as alternative land‐use production systems for the tropics

AbstractThe science of agroforestry has progressed significantly during the past three decades. This article describes and documents various prominent traditional agroforestry systems. In‐depth research on interactive processes of some agrisilvicultural systems have been undertaken and quantified. It has been found that the presence of woody species can enhance nutrient cycling, and can improve soil productivity, soil conservation and soil biotic andfaunal activities. In simultaneous systems however, their presence can also cause competition with the associated food crops. Most agroforestry systems constitute ecologically and bio‐physically sustainable land use systems. Some are highly sustainable and economically viable, in particular the highly complex and specialized types, such as the damar and rubber agroforests in Indonesia. Agroforestry systems have potential uses in stabilization of sloping lands and buffer zones around forest reserves, for recovering degraded lands, and for improving the productivity of the bush fallow system. Despite rapid progress in biophysical research, field application of the science of agroforestry is still minimal. This article examines the possibilities of exploring the multiple contributions of trees to food security, rural income generation, diversity of products and ecosystem conservation within sustainable agroforestry contexts. Research efforts in the new millennium need to focus more on practical research and also on socio‐economic and policy factors that can enhance beneficial application of the science in the near future to smallholder farmers in the tropics.

Alley cropping—soil productivity and nutrient recycling

In the past few decades there has been growing concern about the exhaustibility of non-renewable soil resources in developing countries in the tropics to meet the needs of present and future generations. Land degradation is a major problem in many parts of the tropics, including subSaharan Africa, mainly owing to overexploitation of vegetation and soil resources and adoption of inappropiate farming methods. The challenge is to increase the sustainable agricultural productivity of the land with acceptable inputs to meet increasing human needs, while maintaining the soil resource base and minimising environmental degradation. One technology that can meet this need for rainfed upland farming with low external chemical inputs is the alley cropping system. This technology integrates trees and shrubs in spatial zonal arrangements with food crops in the production system. The presence of woody species in the alley cropping production system has been shown to contribute to (1) nutrient recycling, (2) reduction in soil nutrient leaching losses, (3) stimulation of higher soil faunal activities, (4) soil erosion control, (5) soil fertility improvement and (6) sustained levels of crop production. These experiences can be utilised in developing sustainable and environmentally friendly agroforestry systems.