Individual study: Establishment and growth of stakes of two tree species, Bursera simaruba and Gliricidia sepium, at three deforested sites in Pico Bonito National Park, Honduras
Zahawi R. A. (2005) Establishment and growth of living fence species: an overlooked tool for the restoration of degraded areas in the tropics. Restoration Ecology, 13, 92-102
In the tropics there are numerous tree species which can establish vegetatively and could potentially be used in forest restoration projects. However, often little is known about a particular species establishment ability. This study evaluated the establishment ability and cover development of a number of 'living fence' tree species in three separate field trials in Honduras, central America. This study evaluated two such species, Bursera simaruba and Gliricidia sepium, over 2 years to assess their ability to establish vegetatively and develop cover at three deforested sites.
Study area: The study was carried out between March 2000 and June 2002 in Pico Bonito National Park, a 100,000 ha mountainous park on the north coast of Honduras. Approximately 80% is a core zone of undisturbed forest. However, the surrounding buffer zone is heavily deforested and populated with numerous villages. In March 2000 three sites (elevation 100–400 m) were chosen within the northern buffer zone:
1) Playitas (PLY) - an abandoned pasture that was initially cleared and burned approximately 25 years ago and seeded with the exotic aggressive forage grasses Urochloa brizantha and Pennisetum purpureum.
2) San Francisco (SFR) - a ridge that was originally native pine forest prior to deforestation more than 30 years ago, since dominated by the bracken Pteridium aquilinum, and maintained in a state of arrested succession through repeated fires.
3) Centro Universitario Regional Litoral Atlántida (CRL) - an abandoned pasture dominated by a variety of native grasses and forbs, and a few early successional shrubs.
Gliricidia & Bursera stake planting: This study investigated successional processes in patches created by planting stakes of the two study species in monoculture and in a grid format, as compared to the surrounding pasture and 2° forest. Between April and June 2000, at each site, vegetation was cleared using machetes to create four blocks, each 20 m wide x 100 m long. Four replicates of each of three patch sizes (4 m² (5 stakes), 16 m² (13 stakes), and 64 m² (41 stakes)) were created for each species at each site. All blocks were fenced to prevent accidental cattle incursion. All stakes were planted within 1–3 days of harvesting. Prior to planting, stake bases were cut at a 45° angle, as this was considered to improve rooting. If present, lateral branches were removed. A hole was made with a stick and stakes planted approximately 15–20 cm deep. Due to the scale of the study, planting time differed among sites. PLY was planted between 26 and 29 April; SFR, 24 and 25 May; and CRL, 9 and 10 June 2000. In April 2001 a fire consumed two of the four blocks at CRL. The site was subsequently cleared and replanted using the same two species between 8 and 11 May 2001 (n = 118 stakes/species).
Stake establishment & survival: Stake establishment and survival were recorded biweekly. Stakes that died were replaced in two phases during the first year: immediately after the setup of the experiment in June–August 2000 (first replanting phase) and at the onset of the dry season in February–March 2001 (second replanting phase). A determination of whether planting season had an effect on stake establishment and survival could then be made.
Stake dbh was measured after the dry season planting in May 2001. Percent cover was visually estimated biweekly using a series of cover classes (0–5, 5–10, 10–25, 25–50, 50–75, 75–95, and 95–100%).
Postfire replanting: During the postfire replanting phase at CRL in May 2001 it was found that the below ground portions of G.sepium stakes had not died and were resprouting in some cases but unfortunately, most had been uprooted. A subsample of this original population was saved (n = 23/118). Their dead aboveground portion was cut at ground level in May 2001, and data were collected bimonthly on survival and height for the remainder of the study. Postfire survival of B.simaruba stakes was negligible.
Soil measurements: Soil moisture and soil texture measurements were undertaken for each site.
Survival of Gliricidia and Bursera: Survival for G.sepium was high (>90%) at all three sites. It was lowest at CRL, the last site planted (June 2000). The CRL fire in April 2001, and the subsequent replanting of the two burned blocks, made it possible to test the effect of pre- and postfire planting survival. Replanted patches (planted early May 2001) had significantly greater survival for the remainder of the study as compared to pre-fire islands (planted mid-June 2000). Survival in the two unburned blocks at CRL continued to decline.
Survival for B.simaruba was low at all sites (averaging 30–50%). Stakes planted in the dry season had significantly higher survival than those planted in the wet season at PLY but not at SFR. Stakes replanted following the CRL fire had extremely poor survival.
Influence of dbh: Stake survival was influenced by dbh. A comparison of stakes that were alive and dead at the end of the study showed that B.simaruba stakes surviving through June 2002 had higher initial dbh values compared to stakes that died. Significance of initial dbh on G.sepium stake survival was found at PLY only. The lack of significance at other sites was probably due to high overall survival and little variation in initial dbh among stakes.
Cover: Cover developed more rapidly in G.sepium patches and was consistently lower for B.simaruba. A seasonal pattern in crown cover was present for G.sepium, being leafless from December to March coinciding with the end of the wet season. Following the CRL fire and replanting in early May 2001, cover development of G.sepium improved. Despite being a year younger, replanted blocks developed a much greater canopy cover than the two unburned blocks. Of the original G.sepium stakes remaining after the fire (those not uprooted), 78% survived and resprouted. At the end of the study average resprout height was 170 ± 48 cm. Postfire survival of original B.simaruba stakes was negligible.
Flowering and fruiting: G.sepium stakes flowered twice during the study (January to February) when stakes were leafless. Almost all at PLY and SFR flowered, whereas flowering at CRL was partial. Successful fruit development in the first year did not occur. In the second year, at PLY and SFR developed numerous fruit pods with viable seeds (with some germinating in the patches). B.simaruba stakes did not flower during the study.
Soils: Soil moisture differed among sites and between wet and dry seasons. PLY had greater percent soil moisture for both seasons (44.3 ± 9.5 wet, 20.8 ± 5.1 dry), CRL values were intermediate (34.7 ± 9.6 wet, 16.9 ± 5.8 dry), SFR had the lowest values (18.4 ± 5.5 wet, 10.9 ± 3.9 dry). Soil texture was similar for PLY and CRL and both were classified as loam soils. SFR comprised a sandy loam, the higher proportion of sand and low amount of clay here explaining the consistently lower soil moisture.
Conclusions: Establishment for G.sepium was nearly 100% at all sites, whereas B.simaruba ranged from 30–50%. G.sepium stakes developed more rapidly and attained greater cover than B.simaruba. Dry season planting may increase the establishment success of both species.
Note: If using or referring to this published study, please read and quote the original paper. The original paper can be viewed at: http://www.blackwell-synergy.com/journal.asp?ref=1061-2971