Woody plant species enumeration in abandoned farmlands within Omuigwe Agrarian Community in Aluu, Rivers State, Nigeria

This study was conducted to enumerate woody plant species in abandoned farmlands of different ages in Omuigwe community, ALUU, Rivers State, with a view to ascertaining the impact of different fallow periods on woody species composition and diversity. Four fallow farmlands: FL1 (1 year old), FL2 (3 years old), FL3 (5 years old) and FL4 (7 years old), were purposively chosen for the study. Tree enumeration was carried out using five 20 m x 20 m quadrats randomly distributed on each fallow land. All woody species found in the quadrats were identified to species level, and the number of individuals counted and recorded for each fallow period. Woody species diversity was measured using Simpson (1-D) and Shannon-Wienner (H') indices while similarity in woody species between fallow lands was computed using Sorensen’s index. Total height and diameter of the woody species were measured using a pole graduated in metres and a caliper respectively. Woody species that contribute to livelihoods in the community were identified through oral interviews with twenty randomly selected Heads of households in the community. A total of twenty-five species belonging to nineteen families were identified as contributing to livelihoods in the community. This information was used to ascertain the number of the key livelihood species among the woody species in the fallow farmlands. Populations of woody species in fallow farmlands among the species identified as contributing to livelihoods in the community were low (20%, 20%, 29% and 20% in FL1, FL2, FL3 and FL4, respectively). Total woody species population decreased with an increase in the age of fallow land while woody species diversity was slightly higher in FL3 (1-D = 0.86; H' =2. 21) than in FL1 (1-D = 0.85; H' = 2.11), FL2 (1-D = 0.84; H' = 2.10) and FL4 (1-D = 0.82; H' = 2.10). Woody species diameter and height showed an increasing trend with increase in fallow period with some species and varied significantly (p < 0.05) amongst fallow farmlands in some cases. Similarity in woody species composition between sites was generally low (below 50% except between FL2 and FL3 where a similarity of 50% was recorded). Woody species diversity and the populations of woody species contributing to rural livelihoods decreased after a fallow period of five years. Integrated land use system like agroforestry is suggested for effective regeneration and conservation of woody species in the community especially those that contribute to rural livelihoods.Keywords: Shifting cultivation, fallow period, woody species, rural livelihood, regeneratio

Below- and above-ground tree species diversity in natural forest and monoculture tree plantations at Omo Biosphere Reserve, Nigeria

The conversion of natural forests to monoculture tree plantations (MTPs) has been known to reduce above-ground tree diversity. However, information is lacking on the impact of MTPs on below-ground tree species diversity. This study evaluated below- and above-ground tree species diversity in a Strict Nature Reserve (SNR), a monoculture plantation of an indigenous tree species – Nauclea diderrichii (Nd), and four MTPs of exotic species – Gmelina arborea (Ga), Tectona grandis (Tg), Pinus caribaea (Pc) and Theobroma cacao (Tc) within Omo Biosphere Reserve in South-western Nigeria. Below-ground tree species was ascertained by evaluating the soil seed banks from the natural forest and the monoculture plantations using the seedling emergence method while tree species enumeration aboveground was done using the quadrat method. Below- and above-ground tree species diversity was higher in the SNR than in the MTPs and higher in the MTP of indigenous species (Nd) than in those of the exotic species. Below-ground tree species diversity was zero in both the SNR and MTPs below 0-5 cm soil depth. Similarity in tree species composition was also higher between the SNR and the indigenous species (Nd) plantation. The negative impact of natural forest conversion to MTPs on below- and above-ground tree species diversity was found to be lower in the indigenous species (Nd) plantation than in the exotic species (Ga, Tg, Pc & Tc) plantations. Consequently, plantation forestry may consider native species for biodiversity restoration.Keywords: Forest conversion, species origin, regeneration potential, tree diversit

Effect of sowing depth on the germination and early seedling growth of Dialium guineense Willd

This study was carried out to determine the effect of different sowing depths on seed germination and seedling growth performance of Dialium guineense. The experiment was laid out in a Completely Randomized Design (CRD) with 5 treatments: 0, 3, 6, 9 and 12 cm sowing depths. Fifteen viable seeds were sown into 15 polypots filled with bulked forest topsoil for each treatment and this gave rise to a total of 75 seeds sown for the 5 treatments. Observation on germination was made and recorded daily for a period of 30 days after sowing (DAS). Inception of plumule emergence was observed and germination percentage calculated for each of the sowing depths (treatments). Evaluation of early seedling growth was based on height, collar diameter and leaf number. Observation on seedling growth performance commenced one month after sowing (MAS) and continued bi-weekly thereafter up to 12 weeks after sowing (WAS). Plumule emergence was earliest at 0 cm sowing depth (10 DAS) and latest at the 12 cm sowing depth (16 DAS). Germination percentage was highest (80.00%) at 3 and 6 cm sowing depths and lowest (13.33%) at 0 cm sowing depth. Highest mean seedling height and collar diameter were observed at 3cm sowing depth while the lowest mean seedling height was observed at 12 cm sowing depth at all growth stages (4, 6, 8, 10, and 12 WAS). Highest mean leaf number was observed in 3 and 6 cm sowing depths at 4 and 6 WAS and in 3 cm sowing at 8 to 12 WAS while lowest mean leaf number was observed in 12 cm sowing depth at 4 to 12 WAS. Mean seedling height did not vary significantly (p>0.05) among 3, 6 and 9 cm sowing depths at all stages of growth. Collar diameter did not vary significantly (p>0.05) among 3, 6 and 9 cm sowing depths at 4 WAS, among all the treatments, at 6 and 8 WAS, and among 6, 9 and 12 cm sowing depths at 10 and 12 WAS. Seedling growth generally decreased with increase in sowing depth. It is recommended that seeds of D. guineense should be sown at shallow depths (from 3 to 6 cm) since best germination and seedling growth were observed at the two depths.Keywords: Dialium guineense, sowing depths, germination, early seedling growt

Comparative evaluation of growth performance and soil quality of two age sequences of Gmelina arborea plantation in University of Port Harcourt, Nigeria

This study was conducted in 2019 to compare the growth performance and soil quality of two agesequences of Gmelina arborea plantation within the premises of the University of Port Harcourt, Nigeria. Data were collected from two stands of G. arborea established in 2011 and 2015. Growth performance was evaluated based on tree growth variables and above-ground carbon stored. Tree growth variables estimated were total height (TH), diameter at breast height (DBH), crown height (CH), crown diameter (CD) and merchantable height (MH). Topsoil (0 – 30 cm) samples collected from the two sites were analyzed for particle size distribution, organic carbon (OC), total nitrogen (TN), available phosphorus (Av.P), exchangeable bases (Mg, Ca, K and Na), exchangeable acidity (Al+ H+), effective cation exchange capacity (ECEC), base saturation (BS), pH, Manganese (Mn), Iron (Fe), Copper (Cu) and Zinc (Zn). The above-ground biomass (AGB) and carbon stock (CS) were also determined. T-test was used to test for significant difference in the measured parameters between the two age-sequences of G. arborea. Higher values for TH, DBH, CS and MH were recorded for the older stand although the differences between the two age-sequences were not significantly different (p ≥ 0.05). The AGB and CS per hectare were higher for the older than the younger G. arborea stand (302.27 m3 ha-1 and 151.52 m3 ha-1, respectively). Higher values for silt, clay, Ca, Mg, Al+ H+, ECEC, BS, Mn, Fe and Zn were also recorded for the older stand. However, the observed differences were only significant (p < 0.05) for clay, pH, Av.P, Mn and Fe. The study revealed that although soil properties, tree growth as well as carbon sequestration capacity of G. arborea stand improved/increased with age, the differences were mainly not statistically significant (p ≥ 0.05) between the two (eight and four years) age-sequences. Keywords: Gmelina arborea, age sequence, soil quality, carbon sequestratio