Characterising wide spatial variation in population size structure of a keystone African savanna tree

Helm, C.V.; Witkowski, E.T.F.

doi:10.1016/j.foreco.2011.09.024

Cited by 65 publications

(62 citation statements)

References 34 publications

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“…Effective management actions are those that result in increased recruitment and survival of recruits and adults (Muller 2002). The distribution of size classes in reserves is an important consideration when determining the viability of these large tree populations (Helm and Witkowski 2012). With recruitment rates being linked to the production of fruit, it is important that trees which are producing large amounts of fruit are preserved in reserves to ensure that sustainable recruitment rates are taking place (Emanuel et al 2005, Helm et al 2011.…”

Section: Discussionmentioning

confidence: 99%

“…Both species have been shown to be experiencing losses of individuals in large height classes within protected areas in which elephant are present (Moncrieff et al 2008, Helm et al 2009, Shannon et al 2011. Focusing management strategies and actions on areas which are conducive to the growth of large trees of each species will be important to maintain populations of each species in reserves (Helm and Witkowski 2012). Such actions comprise activities such as increased seed dispersal by human agents, or by removing seed predators or reducing browser numbers in order to control the effects of herbivores on vegetation (Lombard et al 2001).…”

Section: Discussionmentioning

confidence: 99%

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Using Maximum Entropy modeling to predict the potential distributions of large trees for conservation planning

et al. 2012

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Citation: Smith, A., B. Page, K. Duffy, and R. Slotow. 2012. Using Maximum Entropy modeling to predict the potential distributions of large trees for conservation planning. Ecosphere 3(6):56. http://dx.doi.org/10.1890/ES12-00053.1Abstract. Large trees, as keystone structures, are functionally important in savanna ecosystems, and low recruitment and slow growth makes their conservation important. Understanding factors influencing their distribution is essential for mitigation of excessive mortality, for example from management fires or large herbivores. We recorded the locations of large trees in Hluhluwe-Imfolozi Park (HiP) using GPS to record trees along 43 km of 10 m-wide transects. Maximum entropy modeling (MaxEnt) uses niche modeling to predict the distribution of a species from the probability of finding it within raster squares, based on environmental variables and recorded locations. MaxEnt is typically applied at a regional spatial scale, and here we assessed its usefulness when predicting the distribution of species at a small (local) scale. HiP has variable topography, heterogeneous soils, and a strong rainfall gradient, resulting in a wide variety of habitat types. We used locations of 179 Acacia nigrescens and 106 Sclerocarya birrea (large trees ! 5m), and raster environmental layers for: aspect, elevation, geology, annual rainfall, slope, soil and vegetation. A. nigrescens was largely restricted to the Imfolozi section, while S. birrea had a wider distribution across the reserve. Understanding the interaction of environmental variables dictating tree distribution may facilitate habitat restoration, and will assist planning decisions for persistence of large trees within reserves, including options to reduce fire frequency or herbivore impacts. Though the AUC (Area Under the Curve) values used to test model predictions were high for both species, the ground truthing test data showed that distribution for A. nigrescens was more accurate than that for S. birrea, highlighting the need for independent test data to assess model accuracy. We emphasize that MaxEnt can be used at finer spatial scales than those typically used for species occurrence, but models must be tested using spatially independent test data.

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Using Maximum Entropy modeling to predict the potential distributions of large trees for conservation planning

et al. 2012

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“…Based on the assessment of diameter class distributions, the population structure patterns of the woody species recorded from Island Safari, Shorobe and Xobe were categorized into two groups. In the first group, the number of individuals decreased with the increasing diameter class, resulting in an inverted J-shaped population, an indication of stable population structure or healthy regeneration status (Teketay 1997a;Alelign et al, 2007;Tesfaye et al, 2010;Zegeye et al, 2011;Helm & Witkowski, 2012;El-Sheikh, 2013). This pattern was exhibited by about 29%, 20% and 15% of the woody species recorded at Island Safari, Shorobe and Xobe, respectively.…”

Section: Hyphaene Petersianamentioning

confidence: 96%

Stand Structure, Diversity and Regeneration Status of Woody Species in Open and Exclosed Dry Woodland Sites around <i>Molapo</i> Farming Areas of the Okavango Delta, Northeastern Botswana

Neelo¹,

Teketay²,

Kashe³

et al. 2015

OJF

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Stand structure, diversity and regeneration status of woody species were investigated in open and exclosed dry woodland sites in Island Safari, Shorobe and Xobe, northeastern Botswana. A total of 105, 111 and 130 quadrats, measuring 20 × 20 m each, were laid down along parallel line transects in the three sites, respectively, to collect data. A total of 47 species, representing 16 families and 24 genera, were recorded in the study sites. Of these, 33 species representing 13 families and 20 genera, 41 species representing 15 families and 23 genera and 27 species representing 10 families and 14 genera were encountered in Island Safari, Shorobe and Xobe, respectively. The most diverse family was Fabaceae followed by Combretaceae and Tiliaceae at all the three sites. The most diverse genus was Acacia, followed by Combretum and Grewia. The diversity of woody species in the study sites were 2.18, 2.15 and 1. sii and A. luederitzii in Xobe. The alarming result was the fact that 71%, 80% and 85% of the woody species recorded in Island Safari, Shorobe and Xobe, respectively, exhibited hampered regeneration and, thus, unhealthy population structures. Therefore, there is an urgent need to address the observed unhealthy population structures of the woody species through investigation of the major causes of their hampered regeneration, and also designing measures that will facilitate natural and artificial regeneration of these species at the three study sites.

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“…In the absence of long-term demographic data on population trends, the use of diameter class distributions of woody species from a single survey has been shown to be a potential and reliable tool to reveal status of population structures and regeneration of woody species as well as predict responses of the species to disturbance and resultant changes in population structure [15,18,34,42,45]. A population size structure is simultaneously the outcome of past demographic events and an indicator of its demographic future [21,47].…”

Section: Population Structure Of Selected Treesmentioning

confidence: 99%

Distribution, Abundance and Population Status of Four Indigenous Threatened Tree Species in the Arba Minch Natural Forest, Southern Ethiopia

Robi¹,

Edris²

2017

IJNREM

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Abstract:The study on distribution, abundance and population structure of four indigenous threatened tree species in the Arba Minch natural forest, southern Ethiopia. The objective of this study was to assess the use of this species by local communities and its current population structure and status in its natural habitat in southern Ethiopia where it is poorly known. The study approach was categorized in to three; market survey, informant interview and species population inventory in the surrounding natural habitat. Market survey was mainly focused on market observation to estimate the amount of fruits, charcoal, timber, firewood and pole sold in the market. Informant interview was focused on the uses of the species and its availability in the surrounding forest fragments. The adult tree species abundance and regeneration status in the existing forest was estimated. The result indicates that the species are used source of food, charcoal production, timber production, house constriction, fuel-wood and farm implement. Local communities supplement their livelihood by selling wild collected ripe fruit, charcoal, timber, fuel-wood of these species for income. These species are locally very useful plant that needs attention for future research that benefits communities. Current over harvesting of mature tree influenced the regeneration of the species. If this unsustainable harvesting by local people continues, the capacity of the species to maintain its wild population is significantly reduced. Therefore, management and conservation strategies that incorporate this factor is required.

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Characterising wide spatial variation in population size structure of a keystone African savanna tree

Cited by 65 publications

References 34 publications

Using Maximum Entropy modeling to predict the potential distributions of large trees for conservation planning

Using Maximum Entropy modeling to predict the potential distributions of large trees for conservation planning

Stand Structure, Diversity and Regeneration Status of Woody Species in Open and Exclosed Dry Woodland Sites around <i>Molapo</i> Farming Areas of the Okavango Delta, Northeastern Botswana

Distribution, Abundance and Population Status of Four Indigenous Threatened Tree Species in the Arba Minch Natural Forest, Southern Ethiopia

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Characterising wide spatial variation in population size structure of a keystone African savanna tree

Cited by 65 publications

References 34 publications

Using Maximum Entropy modeling to predict the potential distributions of large trees for conservation planning

Using Maximum Entropy modeling to predict the potential distributions of large trees for conservation planning

Stand Structure, Diversity and Regeneration Status of Woody Species in Open and Exclosed Dry Woodland Sites around &lt;i&gt;Molapo&lt;/i&gt; Farming Areas of the Okavango Delta, Northeastern Botswana

Distribution, Abundance and Population Status of Four Indigenous Threatened Tree Species in the Arba Minch Natural Forest, Southern Ethiopia

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Stand Structure, Diversity and Regeneration Status of Woody Species in Open and Exclosed Dry Woodland Sites around <i>Molapo</i> Farming Areas of the Okavango Delta, Northeastern Botswana