Analysis of woody plants dimensions on the affected and restricted land management practices in Sudan Vegetation Zone, Adamawa State, Nigeria

Human activities have transformed the vegetal environment into affected and restricted areas with varied woodland dimensions. The aim of the study is to identify the difference in distributions, heights, girths and bole lengths of native woody plants on continuous cultivation, fallow and reserve lands of Hong Local Government Area in 2018. Data on woody plants distributions, heights, girths and bole lengths were generated from the field using quadrat samples and measuring tape. Stratified sampling technique was adopted to cover the study area while purposively sampling method was adopted to establish the sample quadrats on the three dissimilar land management practices adopted. Variance was used to analyze the data while ‘F’ distribution at 0.05% confidence limit was used to test for the significance. From the result, there are 181 woody plant stands observed on the 12 sample plots (1800m 2 ). The woodland distributions vary from 17, 13 and 1 on fallow, reserve and continuous cultivation lands on 100m 2 . The tallest (11.37m) woodlands are on continuous cultivation land followed by the reserve (10.20m) while the shortest (2.58m) is on fallow land. The girths vary from 1.89m, 1.03m and 0.23m on continuous cultivation, reserve and fallow lands respectively. The stems are 4.34m, 2.53m and 0.80m for reserve, continuous cultivation and fallow lands. For significant increase in tree distributions farmers should preserve seedlings during annual clearing and clean weeding as well adopt longer fallow period. The result implies with increase in human activities such as arable farming and wood harvesting lead to decrease in plant distribution and vice versa. Keywords: Land management practices, Native woodlands, Savanna region, woodland dimensions

Environment provides resources and sits for human survival. Therefore, components of the environment have never remained static in form, but changes do occur that led to concern over disappearing of vegetation cover (Environmental Agency, 2007). Increase in human population manifested by competitive landuse causes land scarcity, conversion of wild lands to agricultural and built-up areas in the local environment (Kanianska, 2016). Landuse practices such as arable farming is one of the major causes of changes in woodland distribution. The over use of the reserve lands for arable farming especially the expansion of fragmented farmlands in many parts of sub-Sahara Africa under the demographic pressure have led to devegetation (Neba, 2009). Shifting cultivation is the major system of arable farming practiced by peasant communities in Asia, Africa and Latin America since the Neolithic period (13,000 to 3,000 BC) which affects woodlands adversely due to forward and backward clearance (Karthic et al., 2009).
Result of study indicate that the adoption of slash-andburn, rotational bush fallow, continuous cultivation and clean weeding as management techniques for exotic plants causes reduction in species diversity, crowdedness, regeneration, and sizes of native plants on the affected areas (Freeman et al., 2014;Mazzott et al., 2013;Jamala et al., 2012). Pantami et al., (2010) maintained that bush fires depending on severity, temperature and frequency deplete vegetation cover through destruction of susceptible stands, reduce the height and girth of woody plants by burning the apical meristem and bark. Studies revealed that sunlight, temperature, soil fertility and moisture determine sizes of woody plants (British Trust for Ornithology, 2019;Field Study Council, 2009).
Results of studies on importance of woody plants dimensions like bole length, girth, height and distribution are important by protecting the Earth's surface from erosion and soil desiccation (Zang, 2016;Houser, 2012;Lutz et al., 2012). Therefore, estimation of woody plants distribution, girth and height is essential in monitoring tree quality, and management of vegetation cover (Mweresa et al., 2017).
Results of studies especially those of Mazzotti et al., (2013);Freeman et al., (2014) are important by observing that vegetation cover is degrading due to increase in human activities such as arable farming, wood harvesting and bush burning. However, these studies did not significantly carry out micro-scale study on the Sudan vegetation characterized by sparse woodland covers neither embarked on assessment of woody plant characteristics that are affected adversely by arable farming nor restricted their studies to comparative analysis of indigenous woody plants distributions, heights, girths and bole length on the affected and restricted land management practices adapted in Hong Local Government Area, Adamawa State, Nigeria.
In Hong Local Government Area, exotic species such as guinea corn, groundnuts, beans and maize are important by providing food materials and commodity of trade. However, the continuous and substantial cultivation of these crops significantly affects indigenous woody plants distributions, heights, girths and bole lengths unfavorably. Furthermore, result of field observation revealed that farmlands on fallow and continuous cultivation contrast significantly from reserve land in woodlands dimensions.
It is from the above perspectives the study was embarked upon to identify the distributions, heights, girths and bole lengths of indigenous woodlands on continuous cultivation, fallow and reserve land management practices. The objectives include: to identify the land management practices adapted in the study area; to determine distributions, heights, girths and bole lengths of indigenous woody plants; and to highlight the possible causes of difference in woodland dimensions in the area.
The scope covers Hong Local Government Area of Adamawa State, Nigeria. The focus is to identify indigenous woody plants distributions, heights, girths and bole lengths on farmlands under continuous cultivation, fallow and reserve lands in 2018 with a view to highlight the difference. The study is significant by identifying woodlands dimensions on the adopted land management practices. Monitoring dimensions of native woody plants community enable researchers and policy makers to precisely understand the impacts of arable farming on woodland degradation (Ansari et al., 2016). The study is restricted to native woodlands because they form the fundamental environmental resource base of the area that is observably degrading. The study excludes exotic species of woodlands because they are managed and form insignificant part of the environmental resource base of the populace. Woody plant within this study applies to trees, shrubs and herbs that have hard material beneath their bark which is the main supporting tissues (Beaulieu, 2019).
Geographic Background to the Study Area: Hong Local Government Area lies approximately between latitudes 09 0 57'26.079" to 10 0 34'7.517"N and between longitudes 12 0 29'54.298" to 13 0 06'30.705"E (Nigeria: Administrative Division, 2016). It is located in Adamawa State, Nigeria. It has an approximate landmass of 2,486km 2 . The mean annual rainfall varies between 700 to 1000mm. The dry season is usually experienced from the months of November to April of the following year while the wet season is from May to October every year. The mean daily temperature is between 36 0 to 41 0 C of the dry season to about 20 0 to 25 0 C during the wet season (Online Nigeria, 2017). The low rainfall and high temperature implies that increase in woodland dimension is restricted to the rainy season when moisture is available to plants. Relief and landform of the area is generally undulating with highlands ranging from about 426m to 1158m above mean sea level (Garkida,Nigeria,Sheet 155). Because of the hilly and hard soils woodlands are short and sparsely distributed. The vegetation lies within the Sudan zone characterized by short and scattered woody plants (Makinwa, 2018

MATERIALS AND METHODS
Types of data required for the study include distributions, heights, girths and bole lengths of native woodlands. The metric for distribution is total number of stands on sample quadrat of 100m 2 (Purcell et al., 2016). Data on distributions, heights, girths and bole lengths are compared to determine the magnitude of difference in dimension between woodlands on affected and restricted land management practices. Data on distributions, heights, girths and bole lengths were generated from the field by direct measurements. Instruments used to generate the data are measuring tape to determine height, girth, bole length of woodland stand and size of the sample quadrats; and plastic netting (nylon) ropes to construct the sample quadrats.
Sample quadrats were adopted to demarcate the study plots within which distributions, heights, girths and bole lengths of woody plant were detected (Minnesota Project, 2012). Vodopich (2010) observed that a sample square quadrat is the most widely used method to demarcate study plots within which to measure numbers of woody plants in a terrestrial community. The uniform size (100m 2 ) and shape (square) of the sample quadrats were adopted because the plots are ideal for observing woody plant stands in Sudan vegetation zone characterized by sparse woody plant, but small enough to count all indigenous woodlands in a reasonable time.
The height of each standing woody plant was determined from the ground level at the base to the highest apical meristem, the girth at the base while the bole length from the ground surface to the first branching point of the trunk. Furthermore, a clinometer was used to determine the height of woody plants (American Forest Measuring Guidelines, 2013; Offwell Woodland and Wildlife Trust, 2010; Private Native Forestry Code of Practice Guideline, 2007). However, where because of the clinometer's limitation to generate data on a single tree height on the reserve land due inadequate bare space to view the apex and distance (base line) between the observer to the base of the tree, supplementary method using measuring tape; and a pole considerably long, thin, straight and strong were adopted (Gandapa, 2015). The process includes: first, by climbing the tall tree up to a convenient bole to come closer to the apex; second, the pole on which a measuring tape was nailed at the tip was directed to the person at the bole that raised the pole to reach the remaining height of the tree; third, the height of the tree was determined on the ground surface at the base in metres (Gandapa, 2015). To cover the study area stratified sampling technique was adopted. The area (2486km 2 ) was divided into six (6) sections that served as a guide to locate the twelve (12) sample quadrats as shown on Figure I. From each sub section, farmland on continuous cultivation, fallow and reserve lands were identified. On each one (1) sample quadrat was established purposively to avoid bare lands devoid of woodland stand. Woodland heights, girths and bole lengths of all stands were measured while the crowdedness was recorded.

Fig. I: Sample Quadrats Location
Generated data on woodland distributions, heights, girths and bole lengths on the three (3) land management practices were analyzed by comparison to highlight the magnitude of differences. Likewise, variance was adopted to determine the magnitude of difference between the three (3) sects of woodland numbers generated on continuous cultivation, fallow and reserve land management practices. This is to test the assumption that there exist significant differences in woodland distributions on continuous cultivation, fallow and reserve lands. 'F' distribution at 0.05% confidence limit was used to test for the significance.

RESULTS AND DISCUSSION
There are 181 woody plant stands observed on the 18 sample quadrats (1800m 2 ). The distributions varied from 99, 79 and 3 on fallow, reserve and continuous cultivation lands respectively. Fallow and reserve lands are less varied (17 and 13) on 100m 2 than the continuous cultivation land with 1 (one). There is insignificant difference in height between those on continuous cultivation (11.37m) and reserve lands (10.20m) than fallow land (2.58m). Likewise plants on continuous cultivation and reserve lands are more uniform in girth (1.89 and 1.03m) than fallow land (0.23m). There is significant dissimilarity in bole length between plants on reserve, continuous cultivation and fallow lands with 4.34m, 2.53m and 0.80m accordingly.
For emphasis the results on identified variations in woodland distributions, heights, girths and bole lengths are discussed below.  From Table 1, the average distributions on 100m 2 shows 17, 13 and 1 on fallow, reserve and continuous cultivation lands accordingly. The reason for the occurrence of highest (17) distribution of woodlands on fallow lands could be attributed to loose soil structure due to cultivation that took place before abandoned that favour regeneration of seedlings, and lack of significantly matured tree stands that could smother the seedlings. Likewise, the higher (13) distribution on the reserve land may be due to occurrence of significantly matured tree stands that are better adapted to the environment and deny new invading species from survival because of their inability to compete positively for sunlight, space and air. Furthermore, there could be selective harvesting of certain species. The least (1) distribution occur on farmlands under continuous cultivation. This is because of the repeated annual clearing and clean weeding, and mechanical plowing that uproot seedlings and cut off lateral roots of trees. Moreover, some of the preserved species like Cordia abyssinica and Acacia nilotica later dry up due to excessive harvesting of the bark and roots for medicinal purpose. The result implies fallow and reserve land management practices should be adopted to conserve tree distributions because they retain more woody plant stands.
Comparing the results of the computed 'F' value (-2.45) to the Table 'F' value (2.48) at 0.05% confidence limit the result falls within the accepted region. The assumption that there is a significant difference between the distributions of woody plants among continuous cropping, reserve and fallow lands is not statistically accepted. Fallow and reserve lands are less varied (17 and 13) and more uniform in woody plant distributions than the continuous cropping land all still in 1 (one) on 100m 2 . The insignificant difference (4) in woody plant distributions on fallow and reserve lands could be due to wood harvesting for poles, hafts and fuelwood from matured trees on the reserve, and environmental factors such as rock types. Likewise, the significant difference (16) between fallow and continuous cropping lands is due to annual clearing and clean weeding at the detriment of distributions on continuous cropping lands. The result implies with decrease in arable farming and wood harvesting leads to increase in woody plant distributions and vice versa. Table 1, the height of woodlands in the area varied from 11.37, 10.20 and 2.58m on continuous cultivation, reserve and fallow lands respectively. The reason for the occurrence of tallest (11.37m) woodlands on land under continuous cultivation could be attributed to their location on area devoid of bush fires which aid their growth in height. The woodlands on the reserve lands are equally tall (10.20m) due to crowdedness with average of 13 stands on 100m 2 . Therefore, the density encourages competitive growth in height to access the sunlight while the shortness (7.78m) revealed by some stands is attributed to inadequate access to sunlight, air and space induced by the taller (10.20m) stands. Furthermore, woodlands on fallow lands form the shortest (2.58m) category because they are not stable and newly invaded the abandoned farmland that is exhausted in soil nutrients required by plants. From the results, the average height of woodlands in the area varies from less than 2.38 to about 13.007m.

Girth of Woody Plants:
Results on woody plants girth revealed 1.89m, 1.03m and 0.23m on continuous cultivation, reserve and fallow lands accordingly as shown on Table 1. The reasons for the occurrence of the broadest (1.89m) girth of trees on continuous cultivation land than those on fallow (0.23m) and reserve lands (1.03m) remains they are not affected by the adverse effects of occasional bush fire which dehydrate tissues and burn the bark; they have additional sources of nutrients from the fertilizer and manure that are applied to crops such as groundnuts and guinea corn; and they are sparsely distributed with a single stand on 100m 2 as shown on Table 1. These conditions aid their growth in thickness more than woody plants on the reserve (13) and fallow (17)