Toward Carbon Certificate in Vietnam: Net Ecosystem Production and Basic Income for the Local Community

Abstract

In recent years, ecologists have focused on estimating Net Ecosystem Production (NEP) to understand the role of forests against increasing concentrations of CO₂ in the atmosphere, a major concern in researches and debates on global warming. This is due to the fact that NEP of a forest is the amount of carbon accumulated in a unit of area and time. This chapter discusses NEP in tropical broad-leaved forests of the Copia Natural Reserve , northwest Vietnam and the need for a carbon certificate to support the local community. Based on field research in northwest Vietnam , this chapter proposes a modified and easily applicable method for estimating NEP. Research results indicate that one hectare of secondary broad-leaved forest in Vietnam can accumulate 6.57 Mg C y⁻¹, more than twice that of old-growth forest at 2.57 Mg C y⁻¹. Research suggests that NEP is higher than some other forests around the world. We suggest that a price should minimally sustain the livelihood of forest protectors, at around 10 US$/ton carbon , a price much higher than current government payments of 10 US$ ha y⁻¹, regardless of carbon accumulation. This chapter asserts the importance of issuing forest carbon certificate to forest protectors so that local communities can raise their bargaining power to improve their income while at the same time, protect the natural forests sustainably.

Appendices

Appendix: Methodologies

Data Collection

One plot of 30 m × 30 m was established in old-growth forest and another plot of the same size was established in 35-year-old secondary forest for NEP estimation. In each plot, all stems with DBH (diameter at breast height) ≥ 5 cm were measured and identified to species level in March 2014 and April 2015 for ΔM estimation. In each 30 m × 30 m plot, fifteen plots of 1 m × 1 m each were established in March 2014 on a forest surface floor by removing all materials for litterfall collection. Litter was collected three times in July, December 2014, and April 2015. Sequence soil cores were collected in March 2014 and on the same dates of litter collection. On each date, 30 soil cores were collected using stainless steel tube of 36 mm in diameter (inner diameter of 34 mm), and coring to a depth of 21 cm. 15 litter bags were buried in March 2014 and collected in July 2014. Another 15 bags were buried in July 2014 and were collected in December. Finally, 15 litter bags were buried in December 2014 and were collected in April 2015. Then, γ_ij (decomposition ratio) was estimated for corresponding intervals (March−July 2014, July−December 2014, December 2014−April 2015). Fine root production was then estimated by continuous inflow method in Eq. 4.6.

Five close chambers (see Fig. 4.8c) were set up in each 30 m × 30 m plot for soil respiration (R_s) measurement. R_s was measured on the same dates as collecting litterfall and sequence soil core sampling. Measuring CO₂ concentration in ppm in chambers was conducted continuously through days including the night. Temperature and moisture inside chambers were also measured parallel with R_s. Through CO₂ concentration in chamber, it was converted to mass of carbon .

Fig. 4.8

Litter trap (a), soil core sampling (b), and measuring soil respiration (c)

Estimation Methodology

Net ecosystem production (NEP) or rate of carbon accumulation in a forest ecosystem is simply estimated in Eq. 4.1 (O’Connell et al. 2003).

$${\text{NEP}} = {\text{NPP}} - {\text{R}}_{\text{s}} ,$$

(4.1)

where NPP is net primary production and R_s is heterotrophic respiration (soil respiration) .

NPP Estimation

There are four compartments included in NPP following Eq. 4.2.

$${\text{NPP }} = \Delta {\text{M}} + \Delta {\text{Cr}} + {\text{Lf}} + {\text{Pr}} ,$$

(4.2)

where △M is aboveground biomass increment, △Cr is coarse root increment, Lf is aboveground litterfall, and Pr is fine root production.

Aboveground Biomass Increment

△M is estimated in the following manner. Diameter at breast height (DBH) of all living stems is measured at time t_i and t_j (t_j > t_i). Then, aboveground biomass increment is estimated in Eq. 4.3 (Clark et al. 2001).

$$\Delta {\text{M}} = \mathop \sum \limits_{{{\text{stem }}1}}^{\text{stem n}} {\text{AGB}}_{{{\text{stem a }}_{\text{in tj}} }} - {\text{AGB}}_{{{\text{stem a }}_{\text{in ti}} }} + \mathop \sum \limits_{{{\text{stem }}1}}^{\text{stem m}} {\text{AGB }}_{{{\text{ingrowth stem b }}_{\text{in tj}} }} - {\text{AGB}}_{{ {\text{ingrowth stem b }}_{{{\text{at DBH}} = 5 {\text{cm}}}} }}$$

(4.3)

Aboveground biomass (AGB; kg dry weight) of each stem is estimated based on allometry. Generally, a site-specific allometry results in more accurate AGB estimation than non-site-specific one. However, destructive sampling a number of trees is required and it is costly for allometry establishment, worldwide allometry is usually accepted in application following Eq. 4.4 (Chave et al. 2005).

$${\text{AGB}} = {\rm{\rho *}}\exp \left[ {\begin{array}{*{20}c} { - 1.499 + \,2.148\ln \left( {DBH} \right) + } \\ {0.207\left( {\ln \left( {DBH} \right)} \right)^{2} -\, 0.0281\left( {\ln \left( {DBH} \right)} \right)^{3} } \\ \end{array} } \right] ,$$

(4.4)

where ρ is wood-specific gravity, and DBH is diameter at breast height in cm.

Coarse Root Increment

△Cr is estimated based on relationship between coarse root biomass (CRB) and AGB (Mokany et al. 2006) following Eq. 4.5.

$${\text{CRB}} = 0.489{\text{AGB}}^{ \wedge 0.890}$$

(4.5)

Equation 5 is a worldwide equation, therefore, it can be applied to any tropical forests. If we know AGB at time t_j and t_i through its DBH, respectively, then △Cr = CRB_j – CRB_i.

Aboveground Litterfall

Lf (including all falling materials as leaves, branches, productive organs, etc.) is estimated by litter trap technique (see Fig. 4.8a). Litter traps made by cloth of circle or square shape are widely used. They are set up generally 1 m from surface ground and litterfall is collected periodically. For much research in developing countries, as local people usually disturb litter traps by collecting cloth, plots of square shape (1 m × 1 m) established on forest surface floor by removing all living and dead materials are usually used for reducing cost and disturbance. The shape of litter traps, materials used, and collected intervals vary by case. There are no specific requirements.

Fine Root Production

There are several methods for estimating fine root production (e.g., Osawa and Aizawa 2012; Metcalfe et al. 2007; Majdi et al. 2005; Bernier and Robitaille 2004; Hendricks and Pregitzer 1993; Raich and Nadelhoffer 1989; Fairlay and Alexander 1985), all having advantages and disadvantages. Continuous inflow method (Osawa and Aizawa 2012) is introduced, since it is a new method, results in a highly accurate estimation, and uses rather simple techniques as sequence soil core sampling and litter bag techniques.

Pr (fine root production) is estimated in Eq. 4.6.

$$Pr = \left( {B_{j} - B_{i} } \right) + \left( {N_{j} - N_{i} } \right) + \left[ { - \left( {N_{j} - N_{i} } \right) - \left( {\left( {N_{j} - N_{i} } \right)/\gamma_{ij} + N_{i} } \right)*\ln \left( {1 - \gamma_{ij} } \right)} \right] ,$$

(4.6)

where B_i and B_j are mass of living fine roots (biomass) at time t_i and t_j, respectively (t_j > t_i), N_i and N_j are mass of dead fine roots (necromass) at time t_i and t_j, respectively, and γ_ij is decomposition ratio of dead fine roots between t_i and t_j. Sequential soil core sampling was used for B_i, B_j, N_i, and N_j, while litter bag technique was used for γ_ij.

For sequential soil core sampling (see Fig. 4.8b), stainless steel tubes of 36 mm in diameter (inner diameter of 34 mm) were used to core the ground sequentially to the depth of 21 cm. Fine roots are separated by washing and sieving collected soil. Then, the fine roots were classified into dead and live roots by their color, resilience, and structural integrity (Hishi and Takeda 2005). Roots were then dried in a forced-air oven at 70°C until constant mass, and the masses of live roots and dead roots were weighed separately.

The litter bag technique is used for γ_ij. Envelope-type root litter bags made from special cloth (root-impermeable water-permeable sheet/RIWP, Toyobo Co., Osaka, Japan) were used. The RIWP has a pore size of approximate 0.6 μm, which blocks practically the ingrowth of fine roots; however, fine soil particles, water, and microorganisms can penetrate through the sheet. Dead fine roots are collected from the field, washed free of soil, and then oven dried at 70°C until constant mass. Approximate one gram of fine roots is put into a litter bag (10 cm × 10 cm). Litter bags are buried to 10–15 cm soil depth at time t_i, then, are collected at time t_j. Collected litter bags are washed, and then oven dried for remained mass. γ_ij is estimated as equaling (initial mass—remained mass)/initial mass.

Converting NPP to Carbon

To convert NPP to carbon , the dry mass containing 50% carbon was assumed (Hoen and Solberg 1994; Sarmiento et al. 2005).

Soil Respiration Measurement

Similar to other field research, we conducted soil respiration measurement. As one component to estimate NEP, soil respiration is important to be conducted well on site. Soil respiration (R_s) by microorganisms to decompose litter in soil and on forest floor is known as heterotrophic respiration. This process returns nutrients to soil for sustaining the life of plants, however, it also emits a huge amount of CO₂ to the atmosphere (Schlesinger and Andrews 2000). A closed chamber method (CC-method) using an infrared gas analyzer—IRGA (Bekku et al. 1995) has been widely used in estimating soil respiration .

Soil CO₂ efflux includes autotrophic respiration from living roots (R_a) and heterotrophic respiration (R_s) from microbes and soil fauna to decompose organic matter. For estimating NEP, R_s must be known. R_s is measured using close-chamber method (Bekku et al. 1995). To separate R_a from soil CO₂ efflux for measuring R_s, plot is made (see Fig. 4.8c) by trenching to a depth of 80 cm. This ensures no roots survive inside the plot, therefore, soil CO₂ efflux from that plot contains only R_s.

Statistical Analysis

Spatial variation in △M and △Cr was quantified as standard errors. First, a 30 m × 30 m plot was divided into four 15 m × 15 m plots. Aboveground biomass in March 2014 and April 2015 was estimated for four 15 m × 15 m plots separately. The difference of biomass between 2014 and 2015 (a one-year basis) was then calculated for four 15 m × 15 m plots separately. Mean of biomass difference and its standard error from four 15 m × 15 m plots represented △M and its standard error. The same process was applied for △Cr and its standard error. Spatial variation in Lf was quantified as a standard error and was estimated in the following manner: in each collection, the mean of Lf from 15 traps and its standard error represented values of the collected intervals. While mean and standard error from 15 traps of aboveground litterfall in all three collections were annual mean and its standard error.

For fine root production estimation, 30 cores in each collection date were randomly divided into six groups of five cores each. Means of five cores were used to estimate production, mortality, and decomposition by continuous inflow method in Eq. 4.6. The outputs were six values. Mean and its standard error of these six values were means of production, mortality, and decomposition with their standard errors.

Soil respiration was estimated as daily mean and its standard error from data of all recorded dates in July, December 2014, and April 2015.

NPP was first estimated as dry biomass (Mg ha⁻¹ y⁻¹), then was converted to carbon (Mg C ha⁻¹ y⁻¹) as equaled to 50% of dry biomass (Hoen and Solberg 1994, Sarmiento et al. 2005). Meanwhile, R_s was measured as ppm (part per million), then was also converted to carbon (Mg C ha⁻¹ y⁻¹). Finally, the difference of NPP and R_s is carbon accumulation (Mg C ha⁻¹ y⁻¹).