Forest and urban trees are of great importance for the environmental quality. It is well known that forests, urban trees and grass lands play critical roles in providing oxygen to the population and reduce carbon dioxide accumulation, maintaining high quality of clean air. Moreover, forests play critical roles in water quality, it is documented that forest streams and groundwater is of good quality compared to water from other land uses [1] - [7] . Forest ecology is an imported element in the ecosystem in Palestine. The population has special interests in forest and agricultural areas. Nevertheless, forest area in West Bank, Jerusalem and Gaza Strip decreased from 320 km² in 1970 to 100 km² in 2008 [8] . However, Ministry of Agriculture took initiative steps to protect these vulnerable areas through developing forest protecting act. Due to this initiative, the protected natural area reached to 60 Km². Moreover, further initiative was taken for greening the urban areas through planting forest trees in the main and sub-main roads. So far, there is a growing need for forest protection, development and management in Palestine. Moreover, residues of forest leaves and woods can friendly be converted to charcoal [9] . Urban trees and forest have critical role in reducing air or noise pollution, decreasing soil erosion and improving water quality. Moreover, they provide habitat for wildlife and become recreation areas for the local population. So far atmospheric pollution and human activities exposing urban trees and forest with pests or disease infestation result in reduction of tree growth. Sustainable management of forests and urban trees maintain high environmental quality and healthy forest. So far poor management of forests and urban trees may lead to losing tree population, diversity, health status and productivity. Tree population, age and biodiversity are important elements in the forest that determine its productivity growth, and health status [10] . It is well known in the literature that forest structure is categorized into four groups such as canopy trees, dominant trees, co-dominant trees, intermediate trees and suppressed trees.

Moreover, forest and urban areas may be exposed to a negative impact such as dumping chemical wastes and/or waste water [11] [12] , overuse of wood trees, acid rain and so on. Several attempts have been made to measuring negative impact on forest; these include life cycle assessment, material flow analysis, environmental management accounting and phytotoxicity due to pesticides application [13] - [18] . In addition forest degradation in Palestine may occur due to population increase and urbanization of agricultural land whereas in other countries forest degradation may occur due to anthropogenic activities [19] [20] , or intensification of agriculture and expansion of mixed-crop livestock systems into former grazing land and other natural areas [21] [22] [23] . These processes may lead to a decline in the ecological stability of these systems [24] [25] . Management of forests requires background information on the forest structure, tree distribution, abundance, relative density and biodiversity. However, several attempts [26] - [32] have been made to estimate population, biodiversity, productivity and total biomass of many forests around the globe. These studies consumed longer time, large efforts and the estimation did not cover many properties of the forest. This study describes a field statistical protocol that can easy be applied for accurately determining forest structure, biodiversity, population and health status. The idea stands behind the field protocol based on the distribution of randomized block design in the forest, selection of surveying plots and testing the protocol in different locations.

The presented results in Table 1 clearly show the application of the statistical method for determination the RD and population (P) of each tree type assuming nearly homogenized distribution of each tree type in the forest.

Tree type 1 had the highest RD among all followed by tree type 4, tree type 2, tree type 5. It can be concluded that tree type 1 is the dominant type in the forest followed by tree type 5, co-dominant type, type 3 is suppressed group whereas group 3 and 6 can be considered the forest floor. The data in Table 2 clearly show theoretical calculation of unhomogenized distribution of tree types (type 2, 3 and 6) as reported in bold in the table. These values were removed from calculating the average and RD. Accordingly revised average and RD values were obtained. Consequently, the values of corrected average (CA), corrected relative density (CRD) and corrected population (CP) are higher than original ones (A, RD⁰ and P⁰). These data indicate the validation of the applied method for determination of forest structure and biodiversity. These results agree with recent [22] - [27] and previous reports [44] [45] who used weed index to survey weed population under field conditions.

In this paper we provided an easy applied field protocol for estimating tree abundance, population, relative density, biodiversity and health status. The protocol based on theoretical and practical field survey. The strong point of the protocol is that it is flexible in determining the average and the standard deviation and make homogenization in case of high variation in the survey plots as in Table 1 and Table 2. Moreover, the protocol enabled corrections to avoid extreme values to be in the actual mode of estimation. In addition, the protocol enabled the determination of biodiversity of forest at end point and its health status (Table 4). The weak point of the protocol is that it cannot be applied for forest was exposed to disasters or ecological imbalance. Furthermore, the paper provided several possibilities of using the protocol in estimating the tree abundance, biodiversity, total population, and health status.

In addition, the presented field protocol revealed accurate estimation of trees after inclusion of corrections (Table 2) and shows that removal of extreme values for calculation provides accurate and actual population of tree type in the forest. Furthermore, the field protocol was successfully tested on weed estimation

in Gaza for a small agricultural area (1 Km²) data not shown. In this test, two weed populations (Cyperus rotundus and Setaria viridis) were estimated by the model and by manual sorting method [11] [25] [37] [40] [44] . There has been about 11% difference between the two methods of estimation. A traceable investigation of errors found that Cyperus rotundus weed was counted as Setaria viridis in many cases due to similarity of plant feature (see Figure 2).

Correcting this minor mistake in the test, reduced the difference from 11% to 7% between the two method of estimation. This test validates our field protocol for estimating forest tree population and relative density. More support to our field protocol comes from estimating urban trees in two main roads in Gaza Strip (Salah Eddin Street 45 km long; Omer Al-Mukhtar Street 5 km long). The protocol found 17% difference between actual number in trees in the data base of Municipality of Gaza and those existing in the street. Traceability test of the street found about 5 km long of the street free from trees due to road construction and repair. Application of the correction in our field protocol (Table 2) reduced the difference from 17% to 6%, confirming the accuracy of our field protocol. The test with Omer Al-Mukhtar street shows 7% difference which is in the acceptable range of field difference [46] [47] . Further support to our field protocol came from testing the field protocol in a protected area (Wadi Gaza) (Figure 3) and found differences less that 5% in the planted trees such as fruit trees (olive trees, grapes, palm) but we found 19% differences in weed population in the Wadi and in urban trees (Figure 4). Traceable investigation found differences in soil types which was stand behind the differences in weed population [48] [49] . Additional support to the protocol comes for practical testing the productivity in agricultural land cultivated with cabbage (Figure 5). So far, the presented results clearly show practical application of field protocol for determining forest tree population relative density and biodiversity. These data agree with previous reports [46] [47] who used weed index to estimate the abundance of weeds in herbicides treated field plots. Further support to our method come from Ref. [48] and Ref. [49] who estimated the field phyto-toxicity of pesticides using plant biomass and heights. Moreover, several authors [50] [51] [52] [53] [54] successfully used the statistical methods to determine distribution and abundance of different pollutants in all components of ecosystem. Further supports to our method can be obtained from different studies [55] - [60] who used statistical methods to differentiate the growth of cyanobacterial mats under stress factors. The weakness of the field protocol is that it can produce large differences in estimating weeds or planted trees in urban areas, or in fields with different soil type or in area with different climate conditions such as a coastal zone area

and desert land. For instance, if we estimated the population of salt plants (Mesembryanthemum acinaciforme) in the coastal area, the abundance of the salt plant will be very close to the sea shore and become very rare far away from the shore due to the decline of salt concentration. Moreover, estimating the population of desert plants in a coastal area will not be homogenized due to growth conditions. Under these conditions, the field protocol may be validated if the area can be subdivided to a small scale and deal with each scale as a separate unit in applying the protocol.

The field protocol provides accurate results that can easily match the data obtained by manual investigation. The protocol can easily be applied for multi scale environment. It is also valid for large scale forests where trees are normally grown without any man-made interference and not exposed to fire or a disaster. So far, the protocol can easily be applied for estimating productivity, health status and maturity of fruits of agricultural lands. Moreover, it is a useful tool in investigating percentage of seed germination in large scale agricultural land, testing herbicidal activity and maturity of fruits in large field scale, to evaluate sugar production in citrus fruit. The weak point of protocol is that it may not provide accurate results in a small scale forest where trees are exposed to grazing of animal infestation. The method can save time and efforts and cost of evaluation.

Special thanks to the Alexander von Humboldt foundation for a Research Fellowship at Leipzig University and BAM institute Germany 2016. I would also like to thank my students at faculty of science for helping me during the field work.

This study was not funded by any organization.

Author declares that he has no conflict of interest.

The study complies with the international ethics issues.

El-Nahhal, Y. (2017) A New Field Protocol for Determination of Forest Structure, Biodiversity and Heath Status by Means of GPS Tools: A Case Study from Gaza Forest. Open Journal of Ecology, 7, 69-83. http://dx.doi.org/10.4236/oje.2017.71006