0675-B3

Assessment of 10 year old reforested plots in an abandoned paddock in the edge of Tropical Rainforest, North Queensland, and Australia

S. K. Florentine ^1,2 , & M. E. Westbrooke ¹

Abstract

The lag time for natural recruitment of tropical rainforest species in abandoned pastureland is a very long; therefore artificial restoration techniques have been employed to accelerate natural recruitment. The objectives of this study were to investigate the (i) success/failure of 397 forest seedlings belonging to 15 different species from 11 families planted approximately 9 years ago and (ii) influence of artificial seedling on enhancing natural recruitment during this period. The study was conducted as a completely randomised block design involving five treatments in the wet tropical rainforest region of Australia. In treatment 1, only 63% of 63 Omalanthus novo-guineesis seedlings planted survived compared with 71% of 33 seedlings and 95% of 44 seedlings of Omalanthus novo-guineesis and Alphitonia petriei, respectively. Highest natural recruitment 239 occurred in treatment 2, where Omalanthus novo-guineesis seedlings were planted with 8 primary promoter species, followed by 99 in treatment 4, 36 in treatment 3, 10 in treatment 1 and 13 in control. In treatment 2 and 4, 50% and 74 % of seedlings were naturally recruited Acacia sp. The canopy cover in treatment 4 was 84% where the species diversity was high compared with 72, 39 and 12% canopy cover in treatment 3, 2 and 1 respectively suggesting canopy cover increased with increasing species diversity. Weed cover decreased with increasing species diversity and is confirmed by a negative association between the two. The results show that seedling species diversity in artificial planting had larger influence on the success of artificial restoration than the number of seedlings planted. The influence of artificial seedling on natural recruitment seems to be slow.

Introduction

Approximately 50% of 36, 000 sq. km of the pristine tropical rainforest in Far North Queensland, Australia, has been logged for grazing and other agricultural activities. During the last 3 to 4 decades some of the grazed pastureland have been abandoned due to low productivity and have been left for natural reforestation. In general, natural reforestation in abandoned pastureland land is a very slow process (Aide et al. 1995, Chapman & Chapman 1996). Natural recruitment in deforested and abandoned land is depend on previous land use pattern (Uhl et al. 1988, Aide & Cavelier 1994), soil seed bank depletion due to repeated burning (Nepstad et al. 1991), and the non-attraction of frugivours, which bring native tropical rainforest species seeds to these area (Duncan and Chapman 1999). Though natural recruitment occurred in few instances, the subsequent survival and growth were poor due to changes in microenvironment (Brown and Lugo 1994). Therefore, artificial recruitment in deforested and abandoned lands has been proposed to accelerate reforestation (Lugo 1992, Aide et al. 1995). In the artificial recruitment approach different species and those exhibiting different ecological characteristic features capable of creating suitable microclimate (by producing quick canopy closure) and as a `bait ' in attracting faunal community, which may enhance soil seed bank density in the rehabilitated areas have been suggested as the best approach (Goosem and Tucker 1995). The objectives of this study were to investigate the (i) success/failure of 397-forest seedling belonging to 15 different species from 11 families planted approximately 9 ago and (ii) influence of artificial seeding on enhancing natural recruitment during this period.

Methods

Study Site

The study site is located on the Centre for Rainforest Studies (CRS) property which in encompass 62.5 ha, on the Atherton Tableland, North Queensland, Australia (17 15' 19" S, 145 30' 59" E). The elevation is _780m above the sea level and mean annual rainfall of 1700mm most of it received during December to May. This paddock was clear felled _ 60 years ago for beef cattle. The paddock is located on the North West boundary of the CRS property. Since 1970's this paddock was abandoned, no natural recruitment has not occurred and number of weeds species have been invaded, mainly Imperata cylindrica, Melinis minutiflora, and Panicum maximum. The soil is mainly grantic and the pH range from 6.5 to 7.0.

Experimental design and species used

The study area was divided into 10 plots of equal size of 17m, by 11m. Between each plot 5 m buffer zone was created to reduced inter plot interference. In each plot, 63 tropical rainforest seedlings from single or combination of species were planted, except plot 4 A and B only 62. Two control plots were laid out. Plot 1a and 1b contain 63 Omalanthus novo-guineesis (frame work species method - using only single species) (Table 1).

Table 1: Number of species used and restoration technique followed for this study.

Data collection

Tree height and diameter data were taken during July 2001. Tree height was taken with tree pole and diameter was taken (trees > 2 m in height, diameter was taken at 1.3 m dbh, trees < than 2 meters in height, diameter was taken at 30 cm from the soil surface) with digital caliper. Within each plot all the seedlings recruited was located, tagged with numbered metal tag and identified. To estimate the canopy cover, at 4 m interval belt transects that ran east west direction across plots. Each transects comprised one side of a continuous series of 1 x 1m ² plots. Within each of these plots, the percentage of weeds, and crown cover was estimated using the Braun-Blanquet cover scale.

Result

Survival rate

Out of the 126 O. novo-guineesis (primary promoter) were planted in treatment 1 only 78 or 61% survived after 9 years compared with 33 (71%) out of 46 in treatment 2. On the other hand 42 (91%) out of 46 of the A. petriei (primary promoter) survived in treatment 3.

In treatments 2 and 3, not single one of the (n = 10) P. tropicum (primary promoter) seedlings survived. In treatment 2, 100% of (n = 10) A. acidula, E. angustifolius, and C. triplinervis (primary promoters) seedlings were found survived. Similarly, in treatment 3, 100% of (n = 10) A. acidula, T. sericocarpa and C. triplinervis (primary promoters) seedlings were also found survived. In treatment 2, 40% of (n = 4) E. falcate, G. acutifolia (primary promoters) seedlings, 60% (n = 6) of C. alphandii and 80% of (n = 8) T. sericocarpa seedlings were found survived.

In treatment 3, 30% of (n = 3) Guioa acutifolia, 60% (n = 6) of E. falcate, 90% (n = 9) of E. angustifolius and 10% (n = 1) C. alphandii seedlings were found alive.

In treatment 4, seven middle phase canopy species were selected (n = 6 from each species); from those all the 6 seedlings from A. robusta, B. acerifolus and M. elleryana were survied. Similarly 100% primary promoters (n = 4) such as E. angustifolius, T. sericocarpa, A. acidula and A. petriei seedlings and mature phase species C. hypospodia and C. laubatii (n = 6) seedlings were survived. However not single one of the C. triplinervis and P. tropicum (primary promoter species) and two mature phase species P. turnerana and Syzygium wesa survived. From rest of the middle phase species, 66% (n = 4) F. bourjotiana and S. cochinchinensis and 83% (n = 5) C. sublimis and F. pimenteliana survived. From primary promoters: 75% (n = 3) of O. novo-guineesis G. acutifolia, 25% (n = 1) E. falcate and 50% (n = 2) of C. alphandii seedlings were found alive. Similarly, from rest of the mature phase species 83% (n = 5) of Toona ciliata, 66% (n = 4) of A. peralatum and 16% (n = 1) S. papyraceum seedlings were found alive.

Seedling recruitment

Natural seedling recruitment varied noticeably between treatments. A total 397 seedlings were naturally recruited from 11 different families in the 9 yea old reforested site (Table 2). The seedling density m ^-2 varied between treatments. Density of seedling recruitment in the control plot 0.03 seedlings m ^-2 , compared to 0.63, 0.10 and 0.27 seedlings m ^-2 in treatment 2, 3 and 4 respectively. The highest number of seedling recruitment was recorded in treatment 2 where O. novo-guineesis and 8 primary promoters were planted to gather. In treatment 2, highest number of seedlings from Acacia sp. and P. elegans both, contributed 36% and 21% respectively. Similarly, 13% and 74% Acacia sp. Seedling were recruited in treatment 3 and 4 respectively. Even without Acacia sp. the density m ^-2 was found highest (0.31 m ^-2 ) in the treatment 2 than others treatments.

Canopy cover

Significant difference (P < 0.001) was found in canopy cover between treatments. Treatment 1a and b, where frame work method using single species (O. novo-guineesis) showed, very low canopy cover, but canopy cover has increased in treatment 2 where O. novo-guineesis seedlings were planted with primary promoters species. However, in treatment 3 canopy cover has increased when same 8 primary promoters species were planted with A. petriei seedlings. Maximum canopy cover was found in the treatment 4 but no significance difference between treatment 3 and 4

Discussion

In this experiment, two major types of restoration techniques have been followed and wider variety of fast growing, fruit and flower producing trees have also been incorporated. Single species (frame work method - treatment 1), combination of pioneers species (frame work method - treatment 2and 3) or incorporated several successional species (maximum species diversity methods treatment 4) (Goosem and Tucker, 1995). Different restoration techniques had marginal effects on natural seedling recruitment, except in treatment 2 where significantly highest numbers of seedling were found recruited. Not much difference was detected between control plots and treatment 1 single species (O. novo-guineesis) framework method. However, total number of seedlings recruited framework method using O. novo-guineesis with 8 primary promoters (treatment 2) showed 239 seedlings have recruited. However, 50, 36 and 74 % of those recruited seedlings in treatment 2 3 and 4 respectively, are from Acacia sp. As Hopkins and Graham (1984) found that, common nomads or early secondary tree species: Polyscias sp. Acacia north qu. Sp. and A. petriei dominate in the abandoned to 30 years of regrowth forests. Our study also indicates that Polyscias sp. Acacia north qu. sp. and A. ptriei have germinated in restored sites. In our experiment significant numbers of Acacia north qu. species recruited possibly because ≈ 10 to 15 m distance from east, west and south sides experiment plots are surrounded by ≈ 40-year-old Acacia north. qu. Species. It is surprising to note that no Acacia seedling recruited in the control and treatment 1. This may be due to high weed cover present in both control and treatment 1 plots. This also indicates that, in an abandoned paddock, fast growing pioneer species like Acacia will also be struggling to recruit.

Seeds dispersing into a reforested sites are very important enhance the reforestation and this will speed up the recovery process. Aide and Cavelier (1994) found only few seeds disperse more than 10 m from the forest edge and seedling numbers declined to nearly zero within 20 m from the forest edge. Study conducted in Puerto Rico, out of 35 species produced fruits in the surrounding forest, only five species detected in the seed rain or seed bank at distance > 4 m from the forest edge (Cubina and Aide 2001). Another study showed that animal facilitated seed rain decreased with increasing distance from the forest edge, with most seed rain within only 30 m from the forest edge (Charles-Dominique 1986). Lack of seed movement from the tropical rainforest to abandoned pasturelands or reforested lands is depending on several reasons. Most of the tropical rainforest trees and shrubs are depend on animals. However, considerable numbers of animals such as frugivorous, and bats avoid large open areas, where, they could be easily targeted by predators (Howe and Smallwood 1982). Several studies have showed that frugivours birds visiting degraded pasture from forest remained with in 80m of the forest (da Silva et al. 1996). That why, in most restoration programs, species selection is important, significant number of fast growing and fruit and flower producing trees may help to bring sed dispersal agents into the reforested lands. Lack of seedling recruitment in our experimental site possibly due to some of aforementioned reasons. In addition poor seedling recruitment in 9-year-old reforested plots can also be attributed to the following factors. Prolonged use of pastural activity has depleted soil nutrients, fostering establishment of fast growing grass species, seasonal drought, lack of soil nutrients, soil compaction and lack of mycorrhizae (Richards 1996, Cubina and Aide 2001).

In conclusion, without any restoration, abandoned pasture will not develop into forest. To accelerate the recover process, artificial tree planting using fast growing native tropical rainforest species has widely been practiced in the tropics. As previously been reported, seedling recruitments under reforested sites will take considerable amount of time. Further work on soil seed bank species composition and avifauna utilization study on the reforested plots may provide further information about the effectiveness of the restoration in an abandoned paddock.

Acknowledgements

We would like to thank, Tony Cummings, Barry Thurling and Nigel Tucker are thanked for initial set up of this project. This research was funded by School for Field Studies, Beverly, USA.

References

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Figure 3: Mean canopy cover under different planting regimes. C = Control, T1 = Treatment 1, T2 = treatment 2, T3 = treatment 3 and T4 = treatment 4.

Table 2: Seedling species found natural recruitment in reforested plots. C = Control, 1a+b= treatment 1, 2a+b=treatment 2, 3a+b= treatment, 3 and 4a+b= treatment 4

¹ School for Field Studies, Centre for Rainforest studies, Yungaburra QLD 4872. Australia.
² Corresponding author: School of Science, University of Ballarat, PO Box 663, Victoria 3350, Australia. Tel. + 61 3 5327 9231, Fax + 61 3 5327 9240, Email: [email protected]