Genetic diversity of Kenyan Prosopis populations based on random amplified polymorphic DNA markers

Several Prosopis species and provenances were introduced in Kenya, either as a single event or repeatedly. To date, naturally established Prosopis populations are described as pure species depending on site, despite the aforementioned introduction of several species within some sites. To determine whether naturally established stands consist of a single or mixture of species, six populations from Bamburi, Bura, Isiolo, Marigat, Taveta and Turkwel were compared for relatedness with reference to Prosopis chilensis, Prosopis juliflora and Prosopis pallida using random amplified polymorphic DNA markers. Cluster analysis based on Nei’s genetic distance clustered Kenyan populations as follows: Marigat, Bura and Isiolo with P. juliflora, Bamburi with P. pallida and Taveta with P. chilensis, whereas the Turkwel population is likely to be a hybrid between P. chileneis and P. juliflora. Four populations had private markers, revealing germplasm uniqueness. Expected heterozygosity tended to be larger for Kenyan populations (ranging from 0.091 to 0.191) than in the three reference (ranging from 0.065 to 0.144). For the six Kenyan populations and two P. juliflora provenances from the Middle East, molecular variation was larger within populations than between population. Higher molecular variance among populations is attributed to their geographical separation and the low variation within populations is due to gene flow between individuals within a population. Overall, this study shows that (1) the Kenyan Prosopis populations are genetically isolated, (2) multiple introductions enhanced genetic diversity within sites and (3) P. juliflora and its hybrid are the most aggressive invaders.Key words: Prosopis chilensis, Prosopis juliflora, Prosopis pallida, multiple introductions, genetic diversity

Ecology, growth and management of black locust (Robinia pseudoacacia L.), a non‑native species integrated into European forests

Black locust (Robinia pseudoacacia L.), a species native to the eastern North America, was introduced to Europe probably in 1601 and currently extends over 2.3 × 106 ha. It has become naturalized in all sub-Mediterranean and temperate regions rivaling Populus spp. as the second most planted broadleaved tree species worldwide after Eucalyptus spp. This wide-spreading planting is because black locust is an important multipurpose species, producing wood, fodder, and a source of honey as well as bio-oil and biomass. It is also important for carbon sequestration, soil stabilization and re-vegetation of landfills, mining areas and wastelands, in biotherapy and landscaping. In Europe, black locust is drought tolerant so grows in areas with annual precipitation as low as 500–550 mm. It tolerates dry, nutrient poor soils but grows best on deep, nutrient-rich, well-drained soils. It is a fast-growing tree and the height, diameter and volume growth peak before the age of 20. It mostly regenerates vegetatively by root suckers under a simple coppice system, which is considered the most cost-effective management system. It also regenerates, but less frequently, by stool sprouts. Its early silviculture in production forests includes release cutting to promote root suckers rather than stool shoots, and cleaning-respacing to remove low-quality stems, reduce the number of shoots per stool, and adjust spacing between root suckers. In addition, early, moderate and frequent thinning as well as limited pruning are carried out focusing on crop trees. The species is regarded as invasive in several European countries and its range here is expected to expand under predicted climate changes

Complexity of Forest Management: Exploring Perceptions of Dutch Forest Managers

Challenges of contemporary forest management are frequently referred to as complex. This article empirically studies complexity in forest management decision-making. In contrast to what is often assumed in the literature, this article starts by assuming that complexity does not just consist of an external descriptive element, but also depends on how decision-makers perceive the system at hand. This “perceived complexity” determines decision-making. We used a straightforward interpretation of perceived complexity using two criteria: the number of factors considered and the uncertainty perceived about these factors. The results show that Dutch forest managers generally consider forest management decision-making to be complicated (many factors to consider) rather than complex (many uncertain factors to consider). Differences in sources of complexity confirm the individual character of perceived complexity. The factors perceived to be most relevant for decision-making (the forest itself, the organization’s objective, the cost of management, public opinion, national policies and laws, and new scientific insights and ideas) are generally seen as rather certain, although “complexity reduction” may play a role that can adversely affect the quality of decision-making. Additional use of more open-ended, forward-looking methods, such as qualitative foresight tools, might enable addressing uncertainty and complexity, and thereby enhance decision-making in forest management to prepare for increasing complexity in the future

Seedling leaf physiological traits: (a) stomatal conductance (g_s), (b) midday leaf water potential (ψ_mid) of plants from which water was withheld and plants that received daily watering for 9 weeks in 5% of full sunlight (black bars) and 20% of full sunlight (grey bars).

<p>Bars are means and error bars are standard errors of the means.</p

Performance of Ghanaian tree seedlings in terms of (a) survival and (b) relative biomass growth rate (RGR) in response to drought and shade.

<p>Shade treatments consisted of low light (5% of full sunlight, black bars) and high light (20% of full sunlight, grey bars). The water treatment consisted of a wet treatment (plants continuously watered for nine weeks) and dry treatment (water was withheld from seedlings for nine weeks). Means and standard error of the means are shown. Bars accompanied by a different letter are significantly different at P < 0.05 (ANOVA, Post hoc LSD test). n = 10 species.</p

List of ten tree species, their family, natural distribution and light requirements for regeneration (species guild).

<p>NPLD = non-pioneer light demander. Species guild and preference for a different forest type is based on [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0121004#pone.0121004.ref049" target="_blank">49</a>–<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0121004#pone.0121004.ref051" target="_blank">51</a>]. Average dry seed mass is based on [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0121004#pone.0121004.ref052" target="_blank">52</a>–<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0121004#pone.0121004.ref058" target="_blank">58</a>].</p><p>List of ten tree species, their family, natural distribution and light requirements for regeneration (species guild).</p

The Effects of Drought and Shade on the Performance, Morphology and Physiology of Ghanaian Tree Species

<div><p>In tropical forests light and water availability are the most important factors for seedling growth and survival but an increasing frequency of drought may affect tree regeneration. One central question is whether drought and shade have interactive effects on seedling growth and survival. Here, we present results of a greenhouse experiment, in which seedlings of 10 Ghanaian tree species were exposed to combinations of strong seasonal drought (continuous watering versus withholding water for nine weeks) and shade (5% irradiance versus 20% irradiance). We evaluated the effects of drought and shade on seedling survival and growth and plasticity of 11 underlying traits related to biomass allocation, morphology and physiology. Seedling survival under dry conditions was higher in shade than in high light, thus providing support for the “<i>facilitation hypothesis</i>” that shade enhances plant performance through improved microclimatic conditions, and rejecting the <i>trade-off hypothesis</i> that drought should have stronger impact in shade because of reduced root investment. Shaded plants had low biomass fraction in roots, in line with the <i>trade-off hypothesis</i>, but they compensated for this with a higher specific root length (i.e., root length per unit root mass), resulting in a similar root length per plant mass and, hence, similar water uptake capacity as high-light plants. The majority (60%) of traits studied responded independently to drought and shade, indicating that within species shade- and drought tolerances are not in trade-off, but largely uncoupled. When individual species responses were analysed, then for most of the traits only one to three species showed significant interactive effects between drought and shade. The uncoupled response of most species to drought and shade should provide ample opportunity for niche differentiation and species coexistence under a range of water and light conditions. Overall our greenhouse results suggest that, in the absence of root competition shaded tropical forest tree seedlings may be able to survive prolonged drought.</p></div

Relationship between survival under stressful conditions (drought and high light) and (a) mean plasticity of nine traits, (b) Leaf mass fraction (LMF) plasticity.

<p>Relationship between relative growth rate under optimal conditions (continuous watering and 20% of full sunlight) and (c) mean plasticity and (d) root mass fraction plasticity. Plasticity for each trait was calculated as maximum minus minimum mean trait values divided by maximum mean trait values across four treatment combinations. For each species, mean plasticity was calculated as the average plasticity of 9 traits. Regression line and coefficient of determination are shown. Ns = not significant, * = p ≤ 0.05, ** = p ≤ 0.01, n = 10 species.</p

A Three- way ANCOVA of species (S, df = 9), water (W, df = 1) and light (L, df = 1) as main factors and relative growth rate, biomass allocation, morphological and leaf physiological traits as dependent variables.

<p>Plant dry mass was included in the ANOVA as a covariate for all variables but RGR, and beta is the regression coefficient of the slope. F-value, significance levels and R² of the model are shown.</p><p>*:p ≤ 0.05</p><p>**: p ≤ 0.01</p><p>***: p ≤ 0.001</p><p>ND = not determined. Leaf mass fraction, stem mass fraction and root mass fraction were arcsine transformed and all other traits were log₁₀ transformed prior to analysis.</p><p>A Three- way ANCOVA of species (S, df = 9), water (W, df = 1) and light (L, df = 1) as main factors and relative growth rate, biomass allocation, morphological and leaf physiological traits as dependent variables.</p