Tracking Changes to Urban Trees over 100 Years in Ithaca, NY, USA

Municipally managed urban trees provide environmental, social, and economic benefits. Continued provision of these benefits depends on the health and sustainability of these trees, which depends in turn on tree managers having the type of information usually found in a tree inventory. The city of Ithaca, New York, USA possesses 7 inventories of its street and park trees dating back to 1902. This paper uses the data contained in these inventories to assess the health and sustainability of the city’s street and park tree populations. Attention is given to the structure of these populations with emphasis placed on species and genera diversity and DBH size class distributions. Prior to 1987, the city’s municipal tree population was dominated by a few species, such as Norway maple (Acer platanoides), and genera such as maples (Acer) and elms (Ulmus), and the DBH size class distribution was skewed unsustainably towards older trees. From 1987 onwards, new plantings have significantly increased species and genera diversity, and the DBH size class distribution suggests sufficient younger trees to account for tree mortality and removals. These changes did not occur quickly due to the persistent legacy effect of past planting preferences and practices, but required a consistent effort by municipal tree managers over many years. As a result, based on an analysis of the most recent tree inventory conducted in 2019, the city’s street and park trees and the benefits they provide look to be on a more sustainable footing, although challenges still remain.

Size fractionation, chemotaxonomic groups and bio-optical properties of phytoplankton along a transect from the Mediterranean Sea to the SW Atlantic Ocean

The relationships between the structure of the phytoplankton community and the bio-optical properties of surface waters were studied during the TransPEGASO cruise along a transect across the Atlantic Ocean that covered seven biogeographical provinces, from the Alborán Sea (SW Mediterranean) to the Patagonian Shelf. We characterized the composition of the phytoplankton community by means of high-performance liquid chromatography and CHEMTAX pigment analyses applied to whole water and two filtration size classes (< 3 and ≥ 3 μm), flow cytometric determinations and microscopic observations. Additionally, the study was complemented by measurements of the absorption of particulate matter and coloured dissolved organic matter (CDOM). The size class distribution of the chlorophyll a (Chl a) obtained from the size-fractionated filtration (SFF) was compared with that resulting from the diagnostic pigment algorithms (VU) developed by Vidussi et al. (2001) and Uitz et al. (2006), and the total Chl a–based expressions (HI) of Hirata et al. (2011). The seven provinces crossed by the transect could be divided into an oligotrophic group with Chl a < 0.25 mg m-3 comprising the tropical and subtropical Atlantic (including the Canary Current Coastal Province), and a eutrophic group (Chl a > 0.5 mg m-3) with a single Mediterranean (MEDI) sample and those from the southwestern Atlantic Shelf (SWAS). According to CHEMTAX, the most important taxa in the tropical and subtropical Atlantic were Prochlorococcus, haptophytes and Synechoccoccus, while the MEDI and SWAS were dominated by diatoms and haptophytes. Both the VU and HI algorithms, which are based on pigment composition or Chl a concentration, predicted for SWAS a high proportion of nano- and microphytoplankton, while the SFF indicated dominance of the < 3 μm size class. In addition, the CHEMTAX results indicated a high average diatom contribution in this province. However, at several SWAS stations with relatively high values of diatom Chl a estimated by CHEMTAX, the microscopic observations found only small concentrations of nano- or microplankton-sized cells. This discrepancy appeared to be due to the presence, confirmed by scanning electron microscopy, of picoplankton-sized cells of the diatom Minidiscus sp. and of Parmales (a group sharing the pigment composition with the diatoms). These findings caution against a routine assignment of diatom pigments to the microplankton size class. The total non-water absorption in the water column was dominated by CDOM. The average contribution of phytoplankton absorption for the different provinces ranged from 19.3% in the MEDI to 45.7% in the SWAS and 47% in the western tropical Atlantic (WTRA). The Chl a–specific phytoplankton absorption [aph*(443), m2 mg-1] was lower in the MEDI and SWAS than in the oligotrophic provinces. aph*(443) was negatively correlated with the first principal component derived from a principal component analysis based on the concentration of the main pigments and was not correlated with indicators of phytoplankton community size structure such as the proportion of Chl a in the < 3 μm class or a size index derived from the VU size class distribution. These findings indicate that the variability observed in aph*(443) was mainly related to differences in pigment composition and possibly to photoacclimation processes, and that any package effects due to cell size were probably masked by other factors, an outcome that may be related to the relatively small influence of size within the narrow range of Chl a concentrations (all ≤ 2.4 mg m-3) considered in our study.

Vachellia erioloba dynamics over 38 years in the Kalahari Gemsbok National Park, South Africa

Vachellia erioloba is a keystone tree species in the southern Kalahari. This long-term study over nearly four decades tracks two populations in different landscapes (the interior sandy duneveld versus the clayey Nossob riverbed) of a large conservation area and offers valuable data on this species under natural soil moisture conditions and with limited anthropogenic influences. In 1978, 18 trees were permanently marked in a 1 ha plot in the interior duneveld of the Kalahari Gemsbok National Park (Dankbaar site). In the Nossob riverbed all trees in a 1 ha plot were surveyed in 1979 (Grootkolk site). At both sites, tree height and stem circumference were subsequently measured at irregular intervals until 2016 in order to investigate growth rates and population structure. Of the 18 marked trees at Dankbaar, six died and three showed coppice regrowth following substantial dieback after a fire. A mean height increase of 60 mm/year was recorded and the mean height of the remaining uncoppiced trees was 6.8 m in 2016. Stem diameter growth rate per year varied widely between trees and between years with a mean value of 2.5 mm/year over the 38-year period. Growth rate calculated for three 10-year intervals varied. Using the mean growth rate derived in the current study and stem size of the dead trees, the mean age of the trees when they died was estimated. At the Grootkolk site, the position of the centroid in relation to the midpoint of the diameter class range suggests that this population is gradually becoming a mature to old population with limited recruitment. This was supported by the size class distribution curves. However, no differences between slopes or intercepts of the stem diameter size class distributions were found.Conservation implications: This study was conducted in a large conservation area, that is, a natural ecosystem excluding most of the anthropogenic threats that are present outside of the park. The study illustrated that in the duneveld the population studied was self-sustaining, with recruitment occurring and large individuals presumably dying of old age. Although fire caused a few individuals to coppice, no fire-related deaths were reported. In the Nossob riverbed, surveys started in a stand of predominantly young trees and the size class distribution at that stage already showed a lack of recruitment. This stand is ageing and will likely disappear at this site; however, new young stands are appearing at other sites in the Nossob riverbed. Under the current conditions with negligible anthropogenic influences, it therefore appears that some V. erioloba populations in the park are increasing in size while others are decreasing, but that overall the species will persist. The impact of global climate change on this species is, however, unknown.

Aspects of the population biology, life history and threats to Aloe ortholopha Christian and Milne-Redh.: A serpentine endemic from the northern Great Dyke of Zimbabwe

Background: Aloe ortholopha is a rare endemic confined to serpentine soils of the Great Dyke of Zimbabwe. Its International Union for Conservation of Nature (IUCN) status is listed as Vulnerable; however, its population biology and life history are poorly documented.Objectives: The aim of this article is to provide information on the population biology and life history of A. ortholopha through assessment of its size-class distribution, population size and density, reproductive output and fitness, and threats related to fire and mining.Method: Circumference of A. ortholopha leaf rosette was used to ascertain size-class distribution. Population size and density were determined by enumerating flowering individuals. Per-capita reproductive output was determined as mean number of flowers per plant, fruit set and mean number of seeds per fruit. Fitness was determined from seed germination capacity. Impact of fire and mining were recorded photographically.Results: Determination of size-class distribution of A. ortholopha from three study sites (southern region [SR], central region [CR] and northern region [NR]) revealed a bell-shaped curve dominated by intermediate size classes. Population size (number of flowering individuals) ranged from 36 to 66 per site. This translated to a density of 4.0–7.3 flowering plants per hectare. Per-capita reproductive output, measured as mean number of flowers per plant, was significantly different in SR and CR compared to that in the NR region. Mean number of fruits per plant did not significantly differ across the three regions. Mean seed set per plant in CR and NR was significantly different to that in the SR region. Species fitness, as determined from in vitro germination assays, showed that seeds harvested from fire-damaged capsules have the lowest cumulative germination percentage. It was also observed that leaf rosettes curled up to form a ball that protects the apical centre of plants from fire damage.Conclusion: A. ortholopha occurs in small population clusters of low density. The species has a low per-capita reproductive output characterised by production of many flowers, but with very low percentage fruit and seed set. The species has low fitness as evidenced by nominal recruitment of saplings and juveniles. Conspecific mates are frequently lost owing to fire and mining activities.

Species Diversity, Forest Community Structure and Regeneration in Banke National Park

Banke national park, located in Banke district of western Nepal with an area of 550 sq. km was established as the tenth national park in 2010 A.D. Forest community structure, species diversity and natural regeneration were studied in the Park. A total of 1067 plots at every interval of 200m were laid by line transect method for the study. In each plot three concentric rings of radii of 10m, 5m, and 1m were laid down for the study of trees, shrubs/saplings and herbs/seedlings respectively. The park was floristically rich with a total of 113 species of trees representing 57 genera and 28 families. Similarly 85 species of shrubs including climbers and 107 species of herbs including herbaceous climbers, and grasses were recorded. The obtained results from the size class distribution of the trees resembling inverse ‘J’ shape indicated the good regenerating capability of the forest in the park. Fifty eight species of saplings and 40 species of seedlings of trees were recorded. From the quantitative study of the trees, the dominant species was Shorea robusta based on IVI (important value index) values, which was followed by Terminalia alata, Anogeissus latifolius, Mallotus philippinensis, etc. The total density stand (D) and basal area (BA) of the park were 291.48 trees/ha and 21.13 m2/ha respectively. The highest density (D) and the basal area (BA) of S. robusta was 46.07 trees /ha and 5.07m2/ha respectively. The species diversity index (H) of the tree species in BaNP was 1.32, with species evenness (J) of 0.64 and index of dominance (C) of 0.08. A total of seven forest community types were estimated in the Park. The size class distribution diagram of all trees showed right skewed (inverse J shaped) pattern indicating a good regenerating capability of the forest. The regeneration of S. robusta, T. alata and A. latifolius were higher in comparison to other tree species which was indicated by the higher seedlings and saplings density of them. S. robusta was the dominant with saplings density of 200.49 / ha and seedlings density of 27153.4 /ha.Nepal Journal of Science and Technology Vol. 16, No.1 (2015) pp. 17-30

NATURAL HISTORY AND MERISTICS OF AN ALLOPATRIC POPULATION OF RED CORNSNAKES, PANTHEROPHIS GUTTATUS (LINNAEUS, 1766) IN CENTRAL KENTUCKY, USA

Life history, morphological variation, and basic biology of Pantherophis guttatus (Linnaeus, 1766), the Red Cornsnake, are not well known, particularly for the allopatric populations in Kentucky. To address some of the information gaps for this species, we report field observations, including activity patterns, reproduction, and meristics of P. guttatus in Kentucky. In 2003 and 2004 we conducted field surveys using drift fences, artificial cover, manual searching, and driving on roads and captured 101 P. guttatus in Edmonson and Hart counties, Kentucky. We found that artificial cover was the best method of detection with 77% of snakes captured using this method. Numbers of encounters peaked in April-May and August-September suggesting bimodal activity patterns similar to other colubrid snakes. Males had signifi cantly higher subcaudal scale counts than females while females had significantly higher ventral scale counts than males. We detected more individuals in 2003 than in 2004, most likely influenced by severe drought conditions in Kentucky during 2004. Size-class distribution of snakes was skewed towards large individuals (> 70 cm SVL). The absence of individuals in juvenile size classes (30 cm -70 cm) may be an artifact of lower detection probabilities for smaller size classes, different habitat use by juveniles, or may indicate low recruitment.