Establishment and growth of living fence species: an overlooked tool for the restoration of degraded areas in the tropics

Summary

Study 1

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 vis stake planting. This study evaluated the establishment ability and cover development of a number of proposed ‘living fence’ tree species in three separate field trials in Honduras, central America. The study focused on the evaluation of 11 species for their ability to establish in a garden experiment.

Study area: The study was carried out between March 2000 and June 2002 in Pico Bonito National Park (100,000 ha) in northern Honduras. Approximately 80% is a core zone of undisturbed forest, with a surrounding buffer zone heavily deforested and populated with numerous villages.

Stake planting: In March 2000 in the northern buffer zone, an abandoned pasture dominated by native grasses, forbs and shrubs, was selected to undertake stake-planting trials. The study was undertaken to quantify stake establishment and survival of 11 tree species thought to establish vegetatively. Establishment was defined as when stakes first sprouted. All stakes were cut and planted in 1 week at the onset of the dry season (n = 30 stakes/species) in rows 1.5 m apart, in a 15 × 45 m grid. Within each row, one stake of each species was randomly assigned a location. Prior to planting, stake bases were cut at a 45° angle (this was considered to improve rooting). If present, lateral branches were removed. A hole was made with a suppoting stick and stake planted approximately 15–20 cm deep. Dbh was measured at planting, stake establishment and survival were monitored for 5 months.

Establishment success: The 11 species differed greatly in rapidity of establishment and overall survival. Four species (Gliricidia sepium, Erythrina berteroana, Jatropha curcas and Erythrina fusca) had rapid establishment and high survival in the first month (70-94%) with most of these subsequently surviving for the 5-month duration of the study. Bursera simaruba had high initial establishment success (around 90%) but survival decreased over time (to 60% after 5-months). 20% of Spathodea campanulata stakes had established by the third month but overall establishment success was less than 10% at 5 months. Spondias mombin (20% survival) and Dendropanax arboreus (10% survival) took 3-5 months to establish. No Salix humboldtiana survived beyond the first month. Lonchocarpus lasiotropis and Dalbergia glomerata stakes all died soonafter planting.

Conclusions: Of the stakes of 11 tree species planted at the onset of the dry season, Gliricidia sepium, Erythrina berteroana and Jatropha curcas had high establishment success and overall survival. Erythrina fusca also proved successful (establishment and subsequent survival of over 80% by the end of the 5-month study period); Bursera simaruba was lower (60% establishing). The remaining six species had poor establishment success and survival. The authors indicate however, that some might benefit from wet season planting.

Study 2

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.

 

Study 3

In the tropics there are numerous tree species which can establish vegetatively and which could potentially be used in forest restoration projects. However, often little is known about a particular species establishment ability. This study examined whether greater initial stake height and diameter increased the establishment success and crown development of Gliricidia sepium stakes trials in Honduras, central America, where this species is a common constituent of 'living fences.

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 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 originally native pine forest prior to deforestation more than 30 years ago, since dominated by 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 sepium planting & size classes: The study was undertaken at each of the sites to quantify the effect of initial stake height and dbh on survival, crown development and biomass of G.sepium. Treatments were initial stake height (50 and 200 cm) and dbh (1.5–3, 3–4.5, 4.5–6 cm). Planting time differed among sites. PLY was planted in the wet season in mid-July 2001, SFR and CRL at the onset of the dry season in early February 2002. Prior to planting, sites were cleared with machetes. Stakes were planted 1.5 m apart in a complete random factorial design forming a 8 × 11 m grid (n = 8/treatment, n = 48 total/site). Survival and crown diameter data were collected monthly. At the end of the study(June 2002), all growth since planting was harvested, dried, and then weighed to estimate above ground biomass production for each stake size class.

Gliricidia sepium survival & growth: Stake establishment and survival was 100% at both SFR and CRL. Initial stake height and diameter affected survival at PLY. Shorter stakes and those with smaller dbh had significantly lower survival values as compared to larger stakes.

Cover: Final cover values differed significantly with respect to diameter and height. Larger diameter stakes had greater cover development than smaller stakes, and tall stakes had greater cover development than short ones. Larger diameter stakes had greater biomass production than smaller stakes, and tall stakes had greater biomass production than short stakes.

Conclusions: Greater initial stake height and diameter at breast height each resulted in greater crown development for G.sepium.

 

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