Allometric Equations for Estimating Silk Oak (Grevillea robusta) Biomass in Agricultural Landscapes of Maragua Subcounty, Kenya

Omamo Augustine Owate,Mwangi James Kinyanjui,Mugo Joseph Mware

doi:10.1155/2018/6495271

Omamo Augustine Owate, Mwangi James Kinyanjui + Show 1 more

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https://doi.org/10.1155/2018/6495271

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Abstract

Grevillea robusta is widely interplanted with crops in Maragua subcounty, a practice that enhances biomass quantities in farmlands. However, quick tools for estimating biomass of such trees are lacking resulting in undervaluation of the farm product. This study sought to develop allometric equations for estimating tree biomass using diameter at breast height (DBH) and tree height as predictor variables. Tree biomass was computed using thirty-three (33) trees randomly selected from 12 one hectare plots established in each of the four agroecological zones (AEZs). DBH of all Grevillea robusta trees per plot was measured and three trees were selected for destructive sampling to cover the variety of tree sizes. Regression analysis was used to develop equations relating DBH/tree height to biomass based on linear, exponential, power, and polynomial functions. The polynomial and the power equations had the highest R2, lowest SEE, and MRE values, while DBH was the most suitable parameter for estimating tree biomass. The tree stem, branches, foliage, and roots biomass comprised 56.89%, 14.11%, 6.67%, and 22.32% of the total tree biomass, respectively. The mean tree biomass density (12.430±1.84 ton ha−1) showed no significant difference (p=0.09) across AEZs implying no difference in G. robusta agroforestry stocks across the AEZ. The allometric equations will support marketing of tree products by farmers and therefore better conservation and management of the tree resource.

Highlights

Trees in agricultural ecosystems offset pressure on forest resources in conventional forests and play a major role in sustaining the productivity of agricultural and forested landscapes
A total of 1,090 trees were measured for diameter at breast height (DBH) in the twelve (12) plots 222 in agroecological zones (AEZs) 1, 308 in AEZ2, 292 in AEZ 3, and 268 in AEZ 4
The values for DBH ranged from 1cm to 39.5cm with a mean of 11.08 cm in AEZ1, 11.51 cm in AEZ 2, 10.07 cm in AEZ 2, and 12.14 cm in AEZ 4

Summary

Introduction

Trees in agricultural ecosystems offset pressure on forest resources in conventional forests and play a major role in sustaining the productivity of agricultural and forested landscapes They are a source of livelihood for the rural communities providing wood and nonwood products like resin, honey, medicine, vegetables, among others and are important in conservation of biological diversity, water, and soil conservation [1]. REDD+ requires countries to establish measurement, reporting, and verification (MRV) methods [4] This may consists of inventory of forests/trees in sampled plots and application of appropriate allometric equations to estimate biomass [2]. Biomass estimates eventually are converted into carbon and carbon dioxide (CO2) equivalents

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