Abstract
Conservation of
biodiversity and mitigation of global warming are two major
environmental challenges today. In this context, the relationship
between biodiversity (especially plant diversity) and soil carbon (C)
sequestration (as a means of mitigating global warming) has become a
subject of considerable scientific interest. This relationship was
tested for homegardens (HG), a popular and sustainable agroforestry
system in the tropics, in Thrissur district, Kerala, India. The major
objectives were to examine how tree density and plant-stand
characteristics of homegardens affect soil C sequestration. Soil samples
were collected at four depths (0–20, 20–50, 50–80, 80–100 cm) from HG
of varying sizes and age classes, and their total C content determined.
Tree density and plant-stand characteristics such as species richness
(Margalef Index) and diversity (Shannon Index) of the HG were also
determined. Results indicated that the soil C stock was directly related
to plant diversity of HG. Homegardens with higher, compared to those
with lower, number of plant species, as well as higher species richness
and tree density had higher soil carbon, especially in the top 50 cm of
soil. Overall, within 1 m profile, soil C content ranged from 101.5 to
127.4 Mg ha−1. Smaller-sized HG
(<0.4 ha) that had higher tree density and plant-species density had
more soil C per unit area (119.3 Mg ha−1) of land than larger-sized ones (>0.4 ha) (108.2 Mg ha−1).
Soil C content, especially below 50 cm, was higher in older gardens.
The enhanced soil-C storage in species-rich homegardens could have
relevance and applications in broader ecological contexts.
Kumar, B.M., Nair, P.K.R., 2004. The enigma of tropical homegardens. Agroforestry Systems 61-62, 135-152.
Abstract
Tropical homegardens,
one of the oldest forms of managed land-use systems, are considered to
be an epitome of sustainability. Although these multispecies production
systems have fascinated many and provided sustenance to millions, they
have received relatively little scientific attention. The objective of
this review is to summarize the current state of knowledge on
homegardens with a view to using it as a basis for improving the
homegardens as well as similar agroforestry systems. Description and
inventory of local systems dominated the ‘research’ efforts on
homegardens during the past 25 or more years. The main attributes that
have been identified as contributing to the sustainability of these
systems are biophysical advantages such as efficient nutrient cycling
offered by multispecies composition, conservation of bio-cultural
diversity, product diversification as well as nonmarket values of
products and services, and social and cultural values including the
opportunity for gender equality in managing the systems. With increasing
emphasis on industrial models of agricultural development,
fragmentation of land holdings due to demographic pressures, and, to
some extent, the neglect – or, lack of appreciation – of traditional
values, questions have been raised about the future of homegardens, but
such concerns seem to be unfounded. Quite to the contrary, it is
increasingly being recognized that understanding the scientific
principles of these multispecies systems will have much to offer in the
development of sustainable agroecosystems. Research on economic
valuation of the tangible as well as intangible products and services,
principles and mechanisms of resource sharing in mixed plant
communities, and realistic valuation and appreciation of hitherto
unrecognised benefits such as carbon sequestration will provide a sound
basis for formulating appropriate policies for better realization and
exploitation of the benefits of homegardens.
Kumar, B.M., 2011. Species richness and aboveground carbon stocks in the homegardens of central Kerala, India. Agriculture, Ecosystems & Environment 140, 430-440.
Abstract
P. Saikia, B.I. Choudhury and M.L. Khan (2012) Floristic composition and plant utilization pattern in homegardens of Upper Assam, India. Tropical Ecology 53(1): 105-118
Saha, S., Ramachandran Nair, P.K., Nair, V., Mohan Kumar, B., 2010. Carbon storage in relation to soil size-fractions under tropical tree-based land-use systems. Plant Soil 328, 433-446.
Abstract
Kumar, B.M., 2011. Species richness and aboveground carbon stocks in the homegardens of central Kerala, India. Agriculture, Ecosystems & Environment 140, 430-440.
Abstract
Tropical
homegardens with high agrobiodiversity have high potential for carbon
(C) sequestration, especially under changing environments. Floristic
diversity, richness, and aboveground C stocks and how size of
homegardens influence agrobiodiversity and C sequestration potential
were assessed in the Kerala homegardens. A total of 839 homegardens in
28 panchayaths (lowest unit of local self-government) of
Thrissur, Palakkad, and Malappuram districts were surveyed through a
stratified random process. Information was gathered on holding size,
floristic composition, plant height, and girth at breast height (GBH) of
all trees and shrubs (>20 cm GBH). Aboveground C stocks of trees
were computed using allometric relationships, assuming C as 50% of
biomass. The homegardens were also classified into small (<0.4 ha),
medium (0.4–1.2 ha), and large (>1.2 ha). In total, 473 species were
recorded, of which 208 were trees (>20 cm GBH), 86 shrubs, and 179
herbs. Simpson's floristic diversity index (0.64, 0.41, and 0.46 for a
subset of small, medium, and large homegardens, respectively), species
richness, and tree density (per hectare) were highest for small-sized
holdings. Large-sized homegardens, however, had more stems per garden.
Average aboveground standing stocks of C ranged from 16 to 36 Mg ha−1,
with small homegardens having higher C stocks on unit area basis than
large- and medium-sized ones. Implicit in this is the potential for C
sequestration and agrobiodiversity conservation, especially by small
homegardens.
Kumar, B.M., Nair, P.K.R., Saha, S., Stein, T., Andreu, M., 2011. The Socioeconomic Context of Carbon Sequestration in Agroforestry: A Case Study from Homegardens of Kerala, India. In: Kumar, B.M., Nair, P.K.R. (Eds.), Carbon Sequestration Potential of Agroforestry Systems. Springer Netherlands, pp. 281-298.
Abstract
Kumar, B.M., Nair, P.K.R., Saha, S., Stein, T., Andreu, M., 2011. The Socioeconomic Context of Carbon Sequestration in Agroforestry: A Case Study from Homegardens of Kerala, India. In: Kumar, B.M., Nair, P.K.R. (Eds.), Carbon Sequestration Potential of Agroforestry Systems. Springer Netherlands, pp. 281-298.
Abstract
While the biological
and ecological role of agroforestry (AF) on climate change mitigation
has received considerable research attention lately, the role of
socio-psychological factors in this context has been left largely
unexplored. Socio-psychological variables such as culture, demography,
economy, and social values play important roles in farmers’ decision
making with the land management, which in turn influence the ability of
AF systems to sequester carbon (C). This chapter presents a case study
from Thrissur, Kerala, India, which examined how different
socio-psychological factors influence soil C sequestration through land
management decisions in tropical homegardens (HGs), a popular
agroforestry system in the tropics. This study used the Theory of
Planned Behavior (TPB) as the theoretical framework to understand
homegarden owners’ perceptions on the adoption of five land management
practices (i.e., tillage, tree planting, plant residue incorporation,
manure usage, and fertilizer applications), which are known to impact C
sequestration. Data collected using focus group and household interviews
were analyzed by regression statistics. Results indicated that farmers’
decision making processes were most influenced by factors such as
ancestors and education, followed by peers, financial condition, and
economic importance of the AF land holding. The results of this case
study will not only benefit researchers and extension practitioners, but
can also contribute to the policy platform to recognize the role of
socio-psychological factors in agricultural decision making.
P. Saikia, B.I. Choudhury and M.L. Khan (2012) Floristic composition and plant utilization pattern in homegardens of Upper Assam, India. Tropical Ecology 53(1): 105-118
Abstract
Homegardens
of Upper Assam, northeastern India are diverse and species-rich. We conducted
vegetation survey of 80 homegardens in 17 villages of Golaghat and Jorhat districts
of Upper Assam. Structure, diversity and plant uses were analyzed. Altogether,
294 plant species representing 217 genera and 92 families were encountered. Of
these, 260 species were economically important and were categorized into seven
use categories. The remaining 34 species were weeds and grasses. Aquilaria
malaccensis Lam., an endangered and red listed species of India, was the most
dominant tree (1,414 trees ha-1). This species contributes significantly to the
economy of the region. Principal Component Analysis (PCA) using frequency data
showed two groups for each of the tree, shrub and herb layers. The high
floristic diversity and presence of many rare/endangered species in the
homegardens reflect the ways how owners utilize and conserve plant diversity.
However, genetic diversity of such rare species of forest origin could be
affected in managed ecosystems due to limited gene flow, inbreeding and selection
pressure. Therefore, studies on genetic diversity of rare/endangered species in
homegardens are required so that potential of homegardens for their
conservation can be assessed.Saha, S., Ramachandran Nair, P.K., Nair, V., Mohan Kumar, B., 2010. Carbon storage in relation to soil size-fractions under tropical tree-based land-use systems. Plant Soil 328, 433-446.
Abstract
The extent of carbon
(C) sequestration in soils under agroforestry systems in relation to
soil types (fraction sizes) and vegetation structure remains largely
unexplored. This study examined soil C storage, an indicator of C
sequestration potential, in homegardens (HGs), natural forest, and
single-species stands of coconut (Cocos nucifera), rice (Oryza sativa)-paddy, and rubber (Hevea brasiliensis),
in Thrissur district, Kerala, India. Soil samples collected from four
depth zones up to 1 m were fractionated to three size classes (250 –
2000 µm, 53 – 250 µm, < 53 µm) and their total C content determined.
Total C stock (Mg ha−1) was highest in
forests (176.6), followed by managed tree-based systems, and lowest in
rice-paddy field (55.6). The results show storage of higher amounts of C
in the < 53 µm fraction, the most stable form of C in soil, up to
one- meter depth, in land-use systems with high stand density of trees
such as forests and small-sized HG. Although the results do not allow
comparison of changes in soil C stock in different land-use systems,
they show higher C storage in soils under tree-based land-use systems
compared with the treeless (rice-paddy) system, especially in lower soil
depths, suggesting the higher soil C sequestration potential of
tree-based systems, and thereby their role in reducing atmospheric
concentration of carbon dioxide.
