This is the peer reviewed version of the following article: Uebel, K., Wilson, K. A. and Shoo,

L. P. 2017. Assisted natural regeneration accelerates recovery of highly disturbed rainforest.

Ecological Management and Restoration. 18:231–238., which has been published in final

form at http://doi.org/10.1111/emr.12277. This article may be used for non-commercial

purposes in accordance with Wiley Terms and Conditions for Use of Self-Archived Versions.

Assisted natural regeneration accelerates recovery of

highly disturbed rainforest

Konrad Uebel*, Kerrie A. Wilson and Luke P. Shoo

Konrad Uebel is a PhD student, Kerrie Wilson is a Professor and Luke Shoo is Research

Fellow at the School of Biological Sciences, The University of Queensland (St Lucia, Qld

4072, Australia. Tel: +61 490 478658; Email: konrad.uebel@uq.net.au or

l.shoo@uq.edu.au). This research was conducted as part of the Australian Government’s

Linkage program.

K. Uebel, School of Biological Sciences, The University of Queensland, St Lucia, Qld 4072,

Australia. Email: konrad.uebel@uq.net.au or l.shoo@uq.edu.au Phone: +61 490 478658

Acknowledgements

This research was conducted with the support of funding from the Australian Government’s

Linkage program. We thank personnel at the Natural Areas Management Unit of the City of

Gold Coast for supporting access to sites and generously providing data on restoration

activities. In particular, Darren Roche, Zoe White, Clay Taylor and Rob Booth provided

advice and support on the project and invaluable assistance in the field. Thanks also to Joanne

Edes and Samantha Reynolds who assisted with field work.

2

Summary

Large areas of rainforests in Australia and other tropical regions have been extensively

cleared since the mid 19th

century. As abandoned agro-pastoral land becomes increasingly

prominent, there is an ongoing need to identify cost effective approaches to reinstate forest on

these landscapes. Assisted regeneration is a potentially lower cost restoration approach which

aims to accelerate forest recovery by removing barriers to natural regeneration. However,

despite being widely used its ecological benefits are poorly quantified, particularly on long

cleared and grazed land. This study quantified the benefits of assisted regeneration on

previously cleared land in a subtropical rainforest ecosystem within eastern Australia. Three

different site types were used (grazed, grazing excluded and grazing excluded plus assisted

regeneration) to compare forest recovery up to ten years after grazing was relieved with and

without four to six years of assisted regeneration. Assisted regeneration sites showed a three-

fold increase in canopy cover, four-fold increase in native tree and shrub species richness and

over 40 times greater native stem density compared to non-assisted regeneration sites.

Stimulation of native recruitment appears dependent on the simultaneous removal of multiple

barriers to regeneration, with the exclusion of grazing alone insufficient. This demonstrates

the additional ecological benefits arising from investment in assisted regeneration. It offers

considerable promise as a cost-effective tool for accelerating and improving re-instatement of

forest on retired agro-pastoral land in the humid subtropics.

Keywords: assisted regeneration, native recruitment, forest recovery, canopy cover, agro-

pastoral land

3

Introduction

Since the early 19th

century deforestation of tropical forests and other biomes has occurred at

an alarming rate with more than one-third of ecosystems converted for human use (Suding

2011; Paul et al. 2010). Socio-economic shifts (e.g. urbanization) and agro-economic

marginality have contributed to the abandonment of considerable areas of agro-pastoral land,

but residual vegetation remains fragmented with ongoing potential for biodiversity loss

(Sobanski & Marques 2014; Sloan et al. 2015). Ecological restoration is an increasingly

important tool used to mitigate human damage and achieve a diverse range of conservation

outcomes (McBride et al. 2010). Globally over 150 million ha of disturbed and degraded land

has been targeted to be restored by 2020 (Menz et al. 2013).

A major impediment to landscape-level restoration is financial cost (Parrotta et al. 1997) and

so there is a need to identify cost-effective restoration techniques. Restoration interventions

can vary along a spectrum from passive to active (Holl & Aide 2011). A highly passive

approach is focused on natural or unassisted regeneration and is usually considered on

degraded land in which recovery is likely within a set time-frame (Van Andel & Aronson

2006). Highly active approaches include planting or seeding to reintroduce native species or

restoring the topography of terrestrial and wetland systems (Perrow & Davy 2002; Van Andel

& Aronson 2006). This can yield rapid benefits but is often expensive (Catteral & Harrison

2006) and the scalability of such methods over large areas is often questioned (Prach &

Hobbs 2008; Clewell & McDonald 2009). More appropriate for this site is a third,

intermediate, strategy between natural regeneration and active reconstruction. This strategy is

commonly termed assisted regeneration (Standards Reference Group SERA 2017) . This

approach aims to accelerate natural regeneration by removing barriers to it, which typically

include competition from non-native plants and recurring disturbances such as grazing,

harvesting and fire (Shono et al. 2007). Assisted regeneration is potentially more cost

effective than active approaches because planting and seeding costs are eliminated (Ganz &

Durst 2003). In Australia assisted regeneration is typically used in the context of bush or

rainforest regeneration in which grazing is alleviated and herbicide control of non-native

plants carried out (e.g. Woodford 2000; Harden et al. 2004).

4

However, despite an obvious demand for lower cost interventions and the widespread

application of assisted regeneration within a range of degraded land types globally, there have

been relatively few studies quantifying its actual benefit (but see Caradang et al. 2007).

Furthermore there is a paucity of studies on the applicability of assisted regeneration on long

cleared and grazed land in Australia such as retired agro-pastoral land, although the effect of

distance from extant vegetation on natural recovery has long been understood (McClanahan

1986, Cairns 1991, Dosch et al. 2007). These information gaps can impede effective

decision-making regarding the appropriate choice of restoration approaches that differ in cost,

labour resources and recovery rates (Shoo et al. in press). Additionally, restoration of retired

agro-pastoral land remains a key challenge, notorious for its variable rate of natural recovery

and optimal restoration approaches of such areas are not yet completely understood (Shoo &

Catterall 2013). Currently lacking is a quantitative understanding of the extent to which

removing grazing (often a first step) and the subsequent application of assisted regeneration

influences the rate of forest recovery under different contexts (e.g. vegetation quality, weed

species). This represents a fertile area of applied research that can provide useful information

about contexts where assisted regeneration management strategies might be most applicable.

This study aims to compare the potential of two levels of management intervention to restore

structure and recruitment of the tree and shrub community on retired agro-pastoral land: 1)

exclusion from grazing; and 2) exclusion from grazing plus the application of assisted

regeneration (in the form of herbicide treatment of non-native vegetation). Native recruitment

and canopy cover were used to measure the degree of vegetation recovery that occurred ten

years after grazing was relieved with and without an additional four to six years of assisted

regeneration.

Methods

Study Area

The study was conducted within the Numinbah Conservation Area, Numinbah Valley, in

southeast Queensland, Australia (28.0167° S, 153.4000° E). Numinbah Valley represents an

important linkage between two areas of World Heritage listed Gondwana Rainforests of

Australia on the Springbrook and Beechmont plateaus (GCCC 2009b). Settlement of the area

in the 1870s was first associated with timber getting and later dairy, beef production and

banana plantations (Hall et al. 1988).

5

Experimental Design

The experimental design consisted of three site types that were differentiated based on

presence of ongoing disturbance (i.e. grazing) and level of restoration intervention. These

were: grazed-only, ungrazed-only and ungrazed plus assisted regeneration. All sites were

previously subtropical rainforest historically cleared and subjected to grazing; but grazing

was relieved in 2005 (ten years prior to study) from ungrazed-only and ungrazed-plus

assisted regeneration sites. Ungrazed plus assisted regeneration sites also received assisted

regeneration treatment in the four to six years prior to evaluation. Assisted regeneration

consisted of systematic control of non-native plant species to encourage regeneration of

native species using a range of techniques: cut, scrape and paint with herbicide in close

proximity to native plants; over-spraying herbicide after isolating infestations; spot spraying

herbicide when germination or reshooting occurred; and, manual removal on steep banks and

near sensitive plants (D. Roche pers. comm.). Non-native species were continually supressed

to ensure native species germinated and grew to a point where most vegetation gaps had been

filled with native species.

Five replicate sites were established for each of the three site types (see Fig. 1 for an

overview of sites), all within the same pre-clear regional ecosystem classified as complex

notophyll vine forest on Cainozoic igneous rocks, with an elevation < 600m (RE 12.8.3). A

combination of historical aerial photography, spatial maps of pre-clearing and current

vegetation and spatial mapping of annual restoration work by the local government authority,

along with pre-existing site-level photo-point monitoring data (for three ungrazed assisted

regeneration sites) were used to select and retrospectively characterise the baseline conditions

of all sites (see Supplementary Material A).

6

Fig. 1. Aerial photograph (2011) showing the location of survey sites within the Numinbah

Conservation Area. UT = Ungrazed Assisted Regeneration sites (N=5), UC = Ungrazed-only

sites (N=5), GC = Grazed-only sites (N=5). Red line indicates the approximate position of

the fence-line used to exclude grazing; white line, unpaved access road; green shading, pre-

clear extent of regional ecosystem code 12.8.3 (complex notophyll vine forest on Cainozoic

igneous rock).

In practice, potential confounding factors may mask a treatment’s effect and can inhibit a

proper evaluation of conservation interventions (Ferraro & Pattanayak 2006). In forest

recovery several factors, such as surrounding landscape, intrinsic resilience of the ecosystem,

land use history and existing cover of trees and shrubs are known to potentially influence the

rate of vegetation recovery (Holl 2007; Shono et al. 2007). Effort was made to standardise

several potentially confounding factors (see Supplementary Material A for site selection

criteria and descriptions of site types). For example, we specifically quantified and accounted

for differences in initial cover of trees and shrubs by incorporating as a covariate in

subsequent analyses (see below) and all selected sites were within close proximity (maximum

distance 120 m) to remnant forest, although treatments were not specifically blocked for

distance.

7

Field Methods

On-ground vegetation surveys were undertaken to quantify measures of vegetation

development with a focus on canopy cover and native tree and shrub recruitment. Site centre

points were located in the field using GPS and 50m transects were delineated at bearings

previously established during site selection. Canopy cover was visually estimated as the

percentage cover of trees and shrubs > 2m (native and non-native) above ground level in each

of three 10m x 10m quadrats (centred at 5m, 25m and 45m along the transect).

Recruitment was evaluated by counting all live free-standing stems of trees and shrubs > 1m

within 2.5 m either side of the transect (total area surveyed = 50m x 5m per site = 0.025 ha).

All stems were identified to a species level and tallied by dbh class (<2.5cm, 2.5-5cm and 5-

10cm). It was not considered necessary to extend the sampling protocol to accommodate

large trees (of dbh > 10cm) as they were not part of this recruitment-focussed study. Instead,

large trees were considered to represent relictual or regrowth ‘paddock’ trees (as opposed to

evidence of recent recruitment). One to two paddock trees were recorded in a subset of sites

within each of the site types (2, 2 and 3 sites in grazed-only, ungrazed-only and ungrazed plus

assisted regeneration respectively).

Species belonging to other life-forms, including grasses, herbs and ferns (both typically

clumped) and vines were recorded where present within any of the three quadrats.

Data Analysis

Individual observations were classified by life-form (tree/shrub, herb, vine, fern, grass/sedge),

origin (native or non-native) and height (>1m or <1m). Although count data for three dbh

classes (<2.5cm, 2.5cm-5cm, 5-10cm) were recorded separately, for the purpose of this

analysis, these were grouped to a single dbh class (i.e. dbh <10cm).

Sites were replicates in statistical analyses (five replicates for each site type). Data for

attributes that were subsampled within sites were pooled at the site level (i.e. canopy cover).

Analysis of covariance (ANCOVA) was used to test for differences in vegetation attributes

(stem density and species richness of recruited trees and shrubs) between site types (three-

level factor) after accounting for variation in initial (2005) canopy cover.

8

Species richness and stem density analyses were repeated for all individuals, native

individuals only and non-native individuals only. Prior to analysis, homogeneity of variances

was evaluated using Bartlett’s test. Subsequently, stem density was log transformed to satisfy

the assumption of homogeneity of variance and all analyses were performed on transformed

data. Pair-wise comparisons amongst site types were performed using Tukey’s honest

significant differences method (TukeyHSD function in R) at 95% confidence levels.

Rarefaction was also used (Chao et al. 2014) to compare species richness–abundance

relationships (details in Supplementary Material B).

Finally, dissimilarity in floristic composition of trees and shrubs (<10cm dbh) among site

types was estimated using the Bray-Curtis index (based on whether species were shared

between site pairs) and visualised using non-metric multi-dimensional scaling ordination via

the metaMDS function in the R package vegan (Oksanen et al. 2013; Clarke & Ainsworth

1993). We used PerMANOVA to test for compositional differences among the three site

types via the ‘adonis’ function in the R package vegan.

Results

Structural attributes of vegetation

Aerial photography – temporal change in cover (both native and non-native trees and shrubs)

In 2005 (the baseline year of this study), all sites had similar mean tree and shrub vegetation

cover (15.13% for grazed-only sites, 17.13% for ungrazed-only and 15.66% for ungrazed

assisted regeneration sites, F = 0.058, P < 0.944, Fig. 2). Ungrazed assisted regeneration sites

showed the largest overall temporal gain in cover (reaching approximately 40% by year 8)

and was particularly pronounced after year 4 when sites had commenced assisted

regeneration. Cover at ungrazed-only sites exhibited a similar upturn (slightly over 10%) but

this occurred later (i.e. between years 6 and 8) and accumulated cover by year 8 was a more

modest at 30.5%. There was limited evidence of change at grazed-only sites where cover only

increased by 5% over the 8 year time-span of aerial photography, reaching 20.1% (Fig. 2)

9

Fig. 2. Comparison of the estimated percentage cover of trees and shrubs > 2m (both native

and non-native) between site types over 10 years (2005, 2009, 2011 and 2013 - all assessed

by aerial photographs; and, 2015 - assessed in the field). Thin lines and open circles indicate

mean of individual estimated site tree and shrub cover from three quadrats; bold lines, mean

tree and shrub estimated cover across sites within each site type. Vertical arrows indicate

onset of exclusion from grazing and horizontal arrow represents period of assisted

regeneration.

Field Assessment

Mean canopy cover of native and non-native trees and shrubs (with height > 2m) differed

among site types (F = 11.72, P = 0.002) and was highest at ungrazed assisted regeneration

sites (51.4%) followed by ungrazed-only and grazed-only sites (17.7% and 16.3%,

respectively) (Fig. 2). Pairwise analyses showed signficant differences between ungrazed

assisted regeneration and other site types (both P < 0.004). Though differences in methods

prevent a direct comparison, the field-assessed mean canopy cover also appeared to represent

a continued increase in tree and shrub cover from the aerial photo-assessed estimates (Fig. 2).

In contrast, tree and shrub cover at both ungrazed-only and grazed-only site types actually

decreased from year 8 mean values (Fig. 2). All grazed-only sites had considerable grass

coverage (native and non-native were not distinguished) with a mean of almost 80%,

principally Broad-leaved Paspalum (Paspalum mandiocanum). Ungrazed-only sites also had

moderate grass cover with a mean of 39%, albeit with high variance. In contrast, all ungrazed

assisted regeneration sites had very low grass cover (a mean of less than 1%).

Stem density

The survey obtained 713 records of tree and shrub stems (< 10cm dbh and > 1m in height).

The vast majority (73.3%) of all stems were associated with ungrazed assisted regeneration

sites of which 98% were native. Ungrazed-only sites comprised only 14.7% of counted tree

10

and shrub stems and most were non-native (92.7%). Grazed-only sites contributed 7.8% of

stems of which 78.8% were non-native.

There were differences between site types in total, native and non-native stem density with no

obvious effect of initial canopy cover (Table 1, Fig. 3). Pair-wise analyses revealed that:

native stem density was greater in ungrazed assisted regeneration than other site types (both P

< 0.006); non-native stem density was lower in ungrazed assisted regeneration than ungrazed-

only (P = 0.040); and, total stem density was greater in ungrazed assisted regeneration than

grazed-only (P = 0.009).

Fig. 3. Comparison of total, native and non-native stem density of trees and shrubs (< 10cm

dbh and >1m in height) between site types. Open circles indicate site estimates; lines, mean

estimate across sites within each site type.

Floristic diversity and composition

A total of 124 species were identified across all sites and comprised 72 trees and shrubs

(58.1%), 27 herbaceous plants (21.8%), 6 grasses or sedges (4.8%), 10 vines (8.1%) and 9

ferns (7.3%). Most species of trees and shrubs, vines, ferns and grasses or sedges were

classified as native (90.2%, 70%, 100% and 66.7%, respectively) but the percentage of native

species was considerably lower for herbaceous plants (25.9%).

11

Table 1: The effect of site-type on vegetation attributes, using ANCOVA with initial canopy cover as

a covariate.

Attribute df Total stem

density*

Native stem

density*

Non-native

stem density*

Total species

richness

Native

species

richness

Non-native

species

richness

Source F P F P F P F P F P F P

Covariate (initial

canopy cover)

1 0.46 0.513 2.18 0.170 0.03 0.872 2.19 0.170 4.76 0.054 0.02 0.901

Site type (n=3) 2 5.93 0.020 11.17 0.002 4.64 0.038 16.67 <0.00

1

53.34 <0.00

1

2.69 0.114

Initial canopy

cover x site type

2 0.529 0.605 0.86 0.454 2.88 0.103 1.08 0.376 1.97 0.190 0.39 0.686

Residuals 10

*All analyses of stem density were performed using log transformed data

Species richness

Total and native tree and shrub species richness (< 10cm dbh and > 1m in height) differed

strongly between site types (Table 1, Fig. 4). Pair-wise analyses indicated that site-level

differences were between ungrazed assisted regeneration sites and other site types (in all

cases P < 0.001), coinciding with a 3-6 times greater species richness at ungrazed assisted

regeneration sites (Fig. 4). Non-native species richness, in contrast, was comparatively much

lower and did not differ between site types (Table 1, Fig. 4). Rarefied species richness

showed that ungrazed assisted regeneration sites consistently had higher native tree and shrub

species richness values for a given number of stems than both grazed-only and ungrazed-only

sites indicating that species richness accumulated more rapidly in these sites (Fig. S3).

Fig. 4. Comparison of total, native and non-native species richness of trees and shrubs (<

10cm dbh and >1m in height) between site types. Open circles indicate site estimates; lines,

mean estimate across sites within each site type.

12

Composition

Bray-Curtis dissimilarity analysis with PerMANOVA testing showed that the floristic

composition of trees and shrubs (< 10cm dbh and >1m in height) differed strongly between

site types. Ungrazed assisted regeneration sites were separated from all other sites while

there was considerable overlap (similarity) between grazed-only and ungrazed-only sites (Fig.

5).

Fig. 5. Non-metric multi-dimensional scaling ordination plots (based on Bray-Curtis

dissimilarity) of the composition of native and non-native trees and shrubs (<10 cm dbh)

between site types. Closed circles = grazed; open circles = ungrazed; open triangles =

ungrazed plus assisted regeneration.

Discussion

Efforts were made to control for non-treatment factors that could potentially confound

vegetation recovery. However, ungrazed assisted regeneration sites were, on average, 30m

closer to remnant forest than both grazed and ungrazed sites. This greater proximity may

have facilitated greater seed dispersal (Dosch et al. 2007) and explained some of the

increased native recruitment seen in these sites.

However we consider the size of the differences cannot be explained by distance effects and

suggest that the results demonstrate that additional investment in assisted regeneration can

13

considerably accelerate early forest recovery on retired pasture, well above what might be

expected from simply removing disturbance alone (i.e. exclusion of grazing). Ungrazed

assisted regeneration sites had approximately three times more canopy cover, four times

greater native tree and shrub richness and over 40 times greater native stem density than

grazed-only and ungrazed-only sites, indicating a clear ecological benefit over simply

relieving grazing (ungrazed-only sites) or taking no restoration action at all (grazed-only

sites). Additionally, the attributes of high grass cover and density of non-native shrubs that

were characteristic of grazed-only and ungrazed-only sites, respectively, were not evident at

ungrazed assisted regeneration sites. Differences between site types are considered in more

detail below, along with possible underlying mechanisms and implications for future

management decisions on similar degraded land.

Status quo – ongoing grazing

Sites that experienced ongoing grazing (grazed-only sites) showed limited evidence of

development in forest attributes. Canopy cover remained very low, was coupled with

extensive cover of pasture grasses (mostly non-native Broad-leaved Paspalum) and there was

very little evidence of native tree and shrub recruitment. Whilst stocking levels were

relatively low the presence of cattle can be expected to have contributed to seedling mortality,

both directly (through consumption or trampling of seedlings) and indirectly (through

compaction of soil and a subsequent reduction in infiltration rates) (Gageler et al. 2014,

Posada et al. 2000). Grass cover has been cited as a principal limiting factor affecting native

tree seedling survival and growth (Holl 1999, Hooper et al. 2005) and, given the extensive

grass cover of grazed-only sites, this was likely also an important barrier.

A modest benefit of relieving grazing

There was little additional benefit evident from relieving grazing. Canopy cover remained

similarly low at ungrazed-only sites with limited evidence of native tree or shrub recruitment.

Cover of pasture grass was moderately reduced at some sites but remained high at other sites.

However, the most prominent difference between grazed and ungrazed sites was the greater

stem density of the non-native shrub Lantana (Lantana camara). Lantana is known to

negatively impact the diversity and abundance of native species (Gooden et al. 2009, Sanders

et al. 2003) and suppress native recruitment (Litton et al. 2006), especially in heavily infested

areas (Fensham et al. 1994) and this appears a likely factor in low recruitment in ungrazed-

only sites.

14

Despite these negative effects, the presence of Lantana may provide benefits to forest

recovery not afforded by grass cover. As a flowering shrub, it significantly increases

vegetation structure (compared to grasses) and so might be expected to attract seed-dispersing

birds, ultimately accelerating (relative to grazed-only sites) the re-establishment of dispersal

and seedbanks. As soil seed banks were not evaluated in this study, this can only be

speculated upon, although it can be said that if any such effect existed it, did not translate to

greater density of seedlings.

Additional benefit of assisted regeneration

In contrast, the results of the study suggest assisted regeneration facilitates successful native

tree and shrub recruitment and can significantly accelerate the rate of forest recovery relative

to grazed-only and ungrazed-only sites. Ungrazed assisted regeneration sites were

characterised by much higher canopy cover (despite staged removal of non-native Tobacco

Bush, Solanum mauritianum), greater native tree and shrub stem density, species richness and

a shift in floristic composition toward a community dominated by native species, along with

much lower grass cover. This indicates that many of the initial barriers to forest regeneration

(i.e. competition with non-natives, seed dispersal limitation, seed germination and seedling

survival) have been at least partially alleviated.

Recovery of reference forest attributes

After 10 years of exclusion from grazing with four to six years of assisted regeneration,

ungrazed assisted regeneration sites had reached about two-thirds of canopy cover expected

for reference forest (i.e. closed ~80% canopy cover) and native tree and shrub density was

comparable to previous measurements of intact rainforest (i.e. over 3000 stems per hectare)

(Kanowski et al. 2003; Shoo et al. 2015). A comparative assessment of species richness is

more problematic with only young stems counted and inconsistencies in the size of area

sampled among studies. However, the average of almost 12 native tree and shrub species at

ungrazed assisted regeneration sites appears to be three to four times lower than species

richness measurements of south-eastern subtropical rainforest communities (Laidlaw et al.

2011).

Stark differences also remained in the representation of species expected from reference

forest. Of the 12 characteristic species listed for this regional ecosystem, only two were

15

present in ungrazed assisted regeneration sites with stems over 1m (and a dbh < 2.5cm);

Native Olive (Olea paniculata) and Rose Marara (Pseudoweinmannia lachnocarpa),

although when all stems (or seedlings) below 1m were taken into account three more of these

species were present: White Bollygum (Neolitsea dealbata), Blackbean (Castanospermum

australe) and Native Tamarind (Diploglottis australis).

Implications for management

The partial but incomplete canopy cover of ungrazed assisted regeneration suggests several

important conditions have not yet been reached. Reformation of the canopy has been shown

to be an important milestone in forest recovery, allowing for the microclimate on the forest

floor to stabilize, in turn improving conditions for the germination and survival of shade-

loving rainforest species (Harden et al. 2004). The canopy gaps of ungrazed assisted

regeneration sites provide sunlight for opportunistic grasses and herbs and increase the

likelihood of these in the seed bank (Paul et al. 2010). A strong negative relationship in

canopy cover of the upper story and lantana density in dry rainforest (Fensham et al. 1994)

also suggests the possibility of Lantana re-establishment. This demonstrates a maintenance

phase has not yet been achieved and that ungrazed assisted regeneration sites require ongoing

assisted regeneration (such as spot-spraying of newly germinating and re-sprouting non-

natives).

Conclusions

A varied array of factors can influence recovery and a notable design limitation was the

greater proximity to remnant forest of ungrazed assisted regeneration. Despite this, there is

strong support for the applicability of assisted regeneration on retired agro-pastoral land, with

a trajectory of accelerated recovery clearly evident and recovery of some forest attributes

appearing achievable relatively quickly (within ten years). Importantly, the exclusion of

grazing alone does not appear to facilitate successful recruitment of native trees and shrubs in

the short-term, supporting assertions that it is necessary to simultaneously remove multiple

barriers to promote forest recovery (Shoo & Catterall 2013). Together, assisted regeneration

shows considerable promise as a cost-effective tool for improving the ecological value of

retired agro-pastoral land and secondary forest in the humid subtropics.

16

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