Population Ecology of Some Keystone Tree Species in the Jebel Marra Region of Darfur

Population ecology of some keystone tree species in the Jebel Marra region of Darfur

Ahmad K. Hegazy, Hasnaa A. Hosni, Hanan F. Kabiel, El-Shafie M. Badawi, Mona H. Emam & Lesley Lovett-Doust

Rendiconti Lincei. Scienze Fisiche e Naturali SCIENZE FISICHE E NATURALI

ISSN 2037-4631 Volume 29 Number 3

Rend. Fis. Acc. Lincei (2018) 29:659-673 DOI 10.1007/s12210-018-0701-z

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Rendiconti Lincei. Scienze Fisiche e Naturali (2018) 29:659–673 https://doi.org/10.1007/s12210-018-0701-z

Population ecology of some keystone tree species in the Jebel Marra region of Darfur

Ahmad K. Hegazy1 · Hasnaa A. Hosni1 · Hanan F. Kabiel1 · El‑Shafe M. Badawi2 · Mona H. Emam1 · Lesley Lovett‑Doust3

Received: 17 December 2017 / Accepted: 16 April 2018 / Published online: 26 April 2018 © Accademia Nazionale dei Lincei 2018

Abstract Populations of Albizia amara, Acacia senegal, Anogeissus leiocarpus, and Balanites aegyptiaca were monitored in fve habitats in the Jebel Marra region: clay plains, sand plains, wadis, northern slopes, and southern slopes of the Jebel Marra (mountain) region. The plains and wadi habitat types had been regularly disturbed because of cycles of shifting cultivation. When land was prepared for cultivation, seedlings and juvenile plants were removed, leaving only larger adult plants, and, therefore, unstable tree populations, lacking juveniles, and growing in fallow lands. A. amara and A. senegal were more abundant than A. leiocarpus and B. aegyptiaca. The healthiest populations, with more juvenile recruits, were found in the grazing lands at higher elevations. However, A. amara and A. senegal showed stable size structure in both grazing and fallow lands. In general, in the four study species, we see a decline in growth and reproduction (with growth measured as tree height and number of branches, and reproduction assessed in terms of number of fruits per tree and dry weight of seeds) along a progression from fallow lands to the grazing lands, and, separately, from lower to higher altitudes. The resilience potential of each species in the fallow lands indicated two distinct population resilience strategies: (1) we saw faster rebound in the case of A. amara and A. senegal and (2) slow recovery from disturbance in the case of A. leiocarpus and B. aegyptiaca which showed low juvenile recruitment in fallow lands.

Keywords Land-use strategy · Semiarid savanna · Demography · Altitude · Functional traits · Population age structure · Juvenile recruitment · Population resilience · Sudan

1 Introduction

* Ahmad K. Hegazy [email protected] Darfur is in the western region of Sudan; with the isolated Hasnaa A. Hosni massif of Jebel Marra (Jebel being the Arabic term for [email protected] mountain) in the center. It represents a transitional Sahe- Hanan F. Kabiel lian zone between the Sahara and the Sahelian and tropical [email protected] savanna where the arid Sahara in the northern part of the El‑Shafe M. Badawi state merges gradually to the Sahelian woodland savanna [email protected] in the south (Ahmed 1982; Wilson 2012). The Jebel Marra Mona H. Emam region lies near the geographic center of the African conti- [email protected] nent, being more than 1600 km from the sea and sitting more Lesley Lovett‑Doust than 2000 m above the surrounding land in Central Darfur [email protected] (Gindy 1984). The mountain is a stratovolcanic complex reaching more than 3000 m above sea level; this moder- 1 Department of Botany and Microbiology, Faculty of Science, ates the climate relative to the surrounding Sahel (Gindy Cairo University, Giza, Egypt 1984; Miehe 1986; Babikir 1988). The rainy season in Jebel 2 Department of Botany, Faculty of Science, Alfasher Marra is from June to September, and surface runof fows University, Darfur, Sudan into three main watersheds around the mountain: the Wadi 3 Department of Biology and Chemistry, Nipissing University, Elku, Wadi Ibra, and Wadi Azum drainage basins (Elsiddig North Bay, ON, Canada

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2007; CBD 2009). The study area lies on the western slopes sheep, cattle and camels, where the number and types of ani- in the watershed of wadi Azum, which in turn drains into mals signify the herder’s wealth (UNEP 2013a). As the area the endorheic basin of Lake Chad. Mesic woody species are under cultivation expanded, pastoralists were forced to shift found on these western slopes, in contrast to the more xeric into more marginal areas, increasing the liklihood of overgraz- species found on the northern and eastern slopes that are ing and soil degradation (Glover 2005). subjected to drying northeasterly winds (Lebon and Rob- The third major land-use pattern in the region is that of ertson 1961; Ahmed 1983). The vegetation is classifed as “fallow land”—areas that were formerly cultivated but that “Acacia Wooded Grassland and Bush Land”; historically, it have been abandoned either because of the high costs of was home to populations of lion and greater kudu (Tragela- cultivation (Babikir 1988), or as a direct result of regional phus strepsiceros), a woodland antelope (CBD 2009). The conficts. The Jebel Marra region of Central Darfur was one soil in the area is considered highly fertile; however, it is of the most difcult areas in which to provide humanitarian subjected to overgrazing year-round, and wildfres occur assistance during recent and ongoing civil conficts (UNO- sporadically in the dry season, from September to February CHA 2015). Such abandoned areas are now being used for (Awok et al. 2013; FAO 2015). grazing, and the natural vegetation is re-establishing there. Three land-use strategies were recognized in the region: The human impact (cutting and overgrazing) is very evident upland areas used for rough pasture, land used for agricul- in these areas that had previously experienced a diferent ture (either year-round, or opportunistically when there is pattern of disturbance involving partial clearing of natural sufcient moisture), and former farmland that is lying fallow vegetation for cultivation, rather than intense herbivory. (abandoned either due to regional conficts, or due to the high Disturbance in the fallow lands is seen in terms of selec- costs of cultivation), but that is being heavily grazed. First, tive uprooting of seedlings and juveniles of tree species and rough grazing land consisting of the natural savanna vegeta- clearing of wild grasses, followed by preparation of the land tion, such areas are typically on slopes at higher elevations, for cultivation. There was a clear diference in the vigor of i.e., marginal areas that are far from villages, with no evidence trees in the grazing lands compared to those in a fallow- of tillage, that are used as rough pasture (Ahmed 2004). The cultivation rotation. Trees in the fallow lands showed more second land-use strategy is that of cultivated land located in vigorous growth, even though they were being subjected to the plains (with sandy or clay soils) and wadis (ephemeral disturbance, whereas those in the exclusively grazed lands wadis, where cultivation requires terracing of the slope). This grew poorly. version of the agricultural strategy is more “opportunist” and The present study was designed to investigate: (1) Popula- is seen near water courses (ephemeral wadis) where cultivation tion size, and age composition in each of the three environ- is carried out by “smallholders” in the “ofseason” in patches ments, for each of the four species of trees; (2) the vegetative where the water table is high, and close to the soil surface and reproductive traits of the four tree species in contrasting (Ahmed 2004). The savanna vegetation has been modifed by habitat types; and (3) Population resilience (potential for cutting small trees and clearing grasses to allow rain-fed cul- natural regeneration and maintenance of the tree populations tivation; this of course disturbs the populations of the four tree over time), for each of the four study species, in all three species. This “agro-forestry” rotation land-use system occurs environments. around villages, where adult trees remaining within feld crops It is noted that there is some confounding of altitude and are protected and harvested by farmers, while seedlings and land use, in that the upland pastures are found on the North- juveniles are removed (Miehe 1986). The most common cul- and South-facing slopes, whereas the grazed fallow lands tivated crop in the area is pearl millet, Pennisetum glaucum are found in sandy and clay plains and wadi habitat types. In (L.)R. Br., which is grown mainly for human consumption addition, before the fallow lands were abandoned, and their as a staple of the local diet, and is used in many traditional soils may have received some nutrient enrichment as well as dishes in Western Sudan (Vogel and Graham 1979; Ishaq and mixing of the soil layers (from tillage) with resulting shifts Meseka 2014). Other lands adjacent to the study area, within in the relative abundance of fungi and bacteria in the soil the Jebel Marra region, indeed all over Darfur, are cultivated microbial community. occasionally to produce several cash crops: orange, mango, guava, Bambara groundnut, wheat, sesame, chewing tobacco, dried hibiscus petals, dried tomatoes, dried okra, onions, pota- 2 Materials and methods toes, the extremely hot pepper ‘Dingaba’, and watermelon seeds (Ahmed 2004; CBD 2009; UNEP 2013b). Despite the 2.1 Study species expansion of cultivation in Sudan, pastoral rangelands (natural savanna grasslands and their associated shrubs and trees) Four tree species, frequently occurring in the region, were still occupy a greater area than those used for rain-fed agricul- selected for the study; two deciduous leguminous species ture (UNEP 2013a). Livestock producers keep herds of goats, Albizia amara (Roxb) Boiv. In addition, Acacia senegal (L.)

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Willd., and the two evergreen species Anogeissus leiocar- a.s.l., 4 = 1050–1150 m a.s.l., and 5 > 1150 m a.s.l. The pus (DC.) Guill. & Perr., often called the “African Birch” climate in the three study areas is comparable with a and Balanites aegyptiaca (L.) Delile., sometimes called the mean temperature of 23–26 °C and total annual rainfall of “desert date, or “soap berry tree”. Both are members of the 520–690 mm (Zalingei Metrological Station). The period of Rosids, and can grow vegetatively by re-sprouting from the summer rain extends from June to September. old stems after being subjected to wood cutting, heavy graz- At each site, the occurrence of each of the four study ing or fre (Adams 1967; Viswanatahan 1986; Hall 1992). In species was recorded to calculate the frequency of each spe- contrast, re-growth from cut stems has not been reported in cies. Non-destructive measurements were made of the study the two leguminous species. populations in terms of vegetative traits (height and number of branches) and reproductive traits were also assessed 2.2 Study area and habitat types (number of fruits and dry mass of 50 seeds). The relative abundance of each of the study species was estimated in The study area is in the western part of the center of Darfur each habitat types and altitudinal zone. For each population, state, within the Jebel Marra region, to the West of the dor- the size distribution and the mean values of the vegetative mant Marra volcano (Fig. 1 and Table 1). The area drains (number of branches and tree height) and reproductive traits into Lake Chad in the republic of Chad towards the west (number of fruits and weight of dry seeds) were determined. of Darfur. Ephemeral wadis (valleys or water courses) are Tree volume was calculated using the following equa- frequent; they collect water from the period of summer rain, tion, representing the volume of an ellipsoid (π/6(R1R2R3)), and dissect the area forming patches of alluvial deposits where R1 is the tree height, and R2 and R 3 are the major (Worrall 1957). and minor diameters of the crown (www.onlineconversio Habitat types in the area were classifed in terms of topog- n.com/object_volume_190 ellipsoid.htm). Trees were raphy, soil texture and aspect (direction they were facing), then classifed into fve sizes according to their volume: into: (1) lowland habitat types with higher water availability, A = < 5 m3, B = 5–20 m3, C = 20–50 m3, D = 50–100 m3, including the sand plains, clay plains and wadis (valleys) and E = 100–150 m3, and F => 150 m3. The linear regression (2) highland habitats represented by the northern and south- of the size distribution (number of individuals in each size ern slopes of the Jebel Marra region (cf. El-Sheikh et al. class) in diferent habitat types and elevation classes was 2013). The plains and wadis included some of the contrast- used to infer and compare the status of the populations, fol- ing “fallow” and “farmed” use patterns, while the slopes rep- lowing Sop et al. (2011). A more negative slope indicates resent the rough grazing land-use strategy. The fallow land a healthier and more stable population as more individu- was subjected to periodic disturbance through the clearing of als are in the smaller size classes, with decreasing numbers small trees and grasses for cultivation followed by abandon- in progressively larger size classes. This pattern refects an ment of the land to be used for grazing. In contrast, the lands expanding population where the presence of many juve- used continuously as rough pasture contain open natural veg- niles will allow for continuous recruitment to reproductive etation for grazing that has not been subjected to systematic cohorts, and persistence of the population. In contrast, a pos- agricultural activities, tillage, or selective clearing. itive slope, and even or variable frequencies of size classes The sand plains in the region are red sands, or “Goz”. suggests an unstable and potentially declining population as These are thick dune-like accumulations that represent deep, juvenile recruitment is low. wind-blown materials from the Nubian Series to the north, where the grains are of uniform size. The clay plains, in 2.3 Statistical analysis contrast, are alluvium deposits formed from weathered rocks washed by rain down to the plains (Worrall 1957). During The effects of habitat type, altitudinal zone, and the rainy periods, the wadis receive runof which remains for a interaction between these factors in terms of efects on few days in the small runnels and for a few months in the population structure (size distribution) was tested using main wadis at lower altitudes, where most of the agriculture a generalized linear model with normal distribution. This is practiced. The plains (both sand- and clay plains) experi- was done separately for each of the study species, and ence the most extensive land use and anthropogenic efects. for the pooled data for all the species studied. Similarly, A total of 47 sites, with fve 100 m2 plots each, were the efect of the habitat type and altitudinal zone and the selected in three study regions: Nerttiti, Zalingei, and Wadi interaction between these factors was tested for vegeta- Saleh (Fig. 1 and Table 1). The fve habitat types recognized tive and reproductive traits. A normal distribution model were: clay plains (CP), sand plains (SP), wadis (W), North- was used for the analysis of plant height and seed mass, facing slopes (NS), and South-facing slopes (SS). Study while a Poisson distribution with a log-link function was sites were also assigned to one of the fve elevation classes: used to analyze the number of branches and number of 1 = 750–850 m a.s.l., 2 = 850–950 m a.s.l., 3 = 950–1050 m fruits per tree. Habitat types are nested within the two

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Fig. 1 Map of the study area, see Table 1 for locations, elevations, and habitat types of the study sites. Note: the sites are numbered according to their increasing elevation above sea level major land-use categories as follows: sandy plains, clay altitudes, north-facing slopes were predominantly at 900 m plains and wadis fall in the fallow/cultivated rotation, and above, the sandy plains and clay plains were below and the North-facing and South-facing slopes (NS, SS) 900 m, and wadis occurred at intermediate altitudes, from are the steeper lands used only for rough grazing. Note 887 to 938 m above sea level. that while South-facing slopes are found at a variety of

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Table 1 Location, habitat type, Site number Location Habitat type Elv. class Elevation and altitude of the study sites (ma.s.l.)

1 11.55°N 23.36°E (Segergerah) CP 1 752 2 11.57°N 23.5°E (Segergerah) CP 1 755 3 11.64°N 23.57°E (Segergerah) CP 1 756 4 11.55°N 23.78°E (Brango) SP 1 757 5 11.71°E 23.63°E (Segergerah) CP 1 758 6 11.58°E 23.65°N (Brango) SP 1 761 7 11.92°E 23.52°N (Angeria) SP 1 766 8 11.82°E 23.42°E (Angeria) SP 1 775 9 11.73°E 23.36°E (Angeria) SP 1 791 10 11.65°E 23.37°E (Jebel Karto) SS 1 825 11 12.81°E 23.27°E (Gerei) CP 1 829 12 12.86°E 23.28°E (JebelGerei) SS 1 845 13 12.75°E 23.30°E (Gerei) CP 2 859 14 12.91°E 23.31°E (JebelGerei) SS 2 873 15 12.66°E 23.57°E (Abundoboba) W 2 887 16 12.97°E 23.54°E (Garash) CP 2 897 17 12.92°E 23.48°E (WadiAreeba) W 2 897 18 11.72°E 23.47°E (Jebel Karto) SS 2 897 19 12.63°E 23.58°E (Abundoboba) W 2 902 20 12.96°E 23.48°E (Garash) W 2 904 21 12.95°E 23.22°E (JebelGerei) SS 2 906 22 12.6°E 23.58°E (Abundoboba) W 2 911 23 12.86°E 23.53°E (Sermi) W 2 924 24 12.64°E 23.31°E (Jebel Ban Jadeed) NS 2 924 25 12.99°E 23.46°E (Jebel Karadito) SS 2 935 26 12.83°E 23.48°E (Sermi) W 2 938 27 12.5°E 23.42°E (Jebel Ban Jadeed) NS 2 940 28 12.59°E 23.52°E (Jebel Ban Jadeed) NS 2 940 29 12.6°E 23.47°E (Jebel Ban Jadeed) NS 2 946 30 13.02°E 23.44°E (Jebel Karadito) NS 2 950 31 12.54°E 23.43°E (Jebel Ban Jadeed) NS 2 950 32 12.61°E 23.36°E (Jebel Ban Jadeed) NS 3 962 33 12.83°E 23.55°E (Jebel Sermi) NS 3 964 34 12.61°E 23.43°E (Jebel Ban Jadeed) NS 3 966 35 13.05°E 23.5°E (Jebel Karadito) SS 3 974 36 12.79°E 23.58°E (Jebel Sermi) NS 3 1009 37 12.74°E 23.6°E (Jebel Sermi) SS 4 1069 38 12.7°E 23.62°E (Jebel Sermi) SS 4 1084 39 3.04°E 23.93°E (Jebel Nerttiti) SS 4 1096 40 12.88°E 23.61°E (Jebel Sermi) NS 4 1109 41 12.78°E 23.72°E (Jebel Sermi) SS 4 1112 42 12.95°E 23.22°E (Jebel Nerttiti) SS 5 1207 43 12.87°E 23.95°E (Jebel Nerttiti) NS 5 1230 44 12.91°E 23.94°E (Jebel Nerttiti) NS 5 1244 45 12.95°E 23.93°E (Jebel Nerttiti) NS 5 1249 46 12.97°E 23.84°E (Jebel Nerttiti) NS 5 1255 47 12.99°E 23.96°E (Jebel Nerttiti) NS 5 1265

Habitat types are: CP clay plain, SP sand plain, W wadi Bed, NS north-facing slope, SS south-facing slope. Note that the fallow land-use pattern is represented by the plains and wadis, i.e., the SP, CP, and W habitat types, while the upland grazing land-use pattern is represented by the site on the slopes, i.e., the NS and SS habitat types. Elevation classes are: 1 = 750–850 m a.s.l., 2 = 850–950 m a.s.l., 3 = 950–1050 m a.s.l., 4 = 1050–1150 m a.s.l. and 5 = > 1150 m a.s.l

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3 Results (a) 1300 Minimum )

. Maximum l

3.1 Species distribution . 1200 s Mean . a 1100 m (

The elevation ranges of the various habitat types are shown n 1000 o i t

a 900

in Fig. 2a. The NS and SS occupied the widest range of v e l altitudes as compared to the other habitat types: from 924 to E 800 1265 m a.s.l. for North-facing slopes (NS) and from 825 to 700 1207 for the South-facing slopes (SS). The Wadi (W) habitat SP CP WNSSS type was found between 887 and 938 m a.s.l. followed by the (b) Sandy Plains (SP) habitat type at a lower and narrower alti- 100 SP CP W NS SS tudinal range: from 757 to 791 m a.s.l. The Clay Plains (CP)

) 80 %

habitat type occupied a wider range from 752 to 897 m a.s.l. ( y

c 60

Overall, across the study habitats and altitudinal belts, n e

A. amara u the most abundant species were the two legumes, q 40 e r and A. senegal. The other two species, A. leiocarpus and F B. aegyptiaca, were less abundant (Fig. 2b, c). The Sandy 20 Plains were the areas, where A. amara was most abundant; 0 there it was found in all sites, while it was of lower, but ALAM ACSE ANLE BAAE consistent abundance in the other habitat types (at a frequency of 40–60% frequency). In the Clay Plains, A. senegal (c) was less abundant than it was in other habitat types, where 80 Class 1 Class 2 Class 3 Class 4 Class 5 it consistently occurred at a frequency ≥ 50% (Fig. 2b). In ) 60 % contrast, A. leiocarpus and B. aegyptiaca were more abun- ( y c dant (40–60%) in SP and CP sites, but were only at 20–40% n 40 e u in the other habitat types (Fig. 2b). Albizia amara is more q e

r 20 frequent in lowlands (elevation zones 1 and 2) and at high F elevations (elevation class 5) elevation at > 50%, while A. 0 senegal was more frequent at mid-elevations (zones 2–4 ALAM ACSE ANLE BAAE (Fig. 2c). Anogeissus leiocarpus occurred at > 50% fre- Species quency in elevation classes 1 and 5 and B. aegyptiaca was most frequent (around 40%) in elevation classes 1, 2, and 4, Fig. 2 a Elevational ranges for each of the study habitat types show- but was entirely absent from elevation class 5. ing the minimum, maximum, and mean altitude and b frequency (% of sites where the species was recorded) for each of the study species in diferent habitat types and c frequency of occurrence for each of the study species in each elevation class. Habitat types are: 3.2 Demography SP sand plain, CP clay plain, W wadi, NS north-facing slope, SS south-facing slope. The study species are labelled as: ALAM: Albizia amara ACSE Acacia senegal ANLE Anogeissus leiocarpus BAAE Patterns of size-class distribution showed that popula- , : , : , : Balanites aegyptiaca. Elevation classes are: 1 = 750–850 m a.s.l., tions of all four study species showed better recruitment 2 = 850–950 m a.s.l., 3 = 950–1050 m a.s.l., 4 = 1050–1150 m a.s.l., on South-facing pasture slopes (SS) than in other habitat and 5 = > 1150 m a.s.l types (Fig. 3a–e). This is also refected in the more negative slopes of the regression analyses of size distribution (Table 2). Albizia amara had the most healthy populations The most vigorous populations of A. leiocarpus were compared to the other study species, in each of the fve found on South-facing pasture slopes (SS) followed in rank habitat types (Fig. 3a, c, e, g, i and Table 2). The slope of order by: CP, SP, NS, and W (Table 2). The linear charac- the regression analysis showed that populations became terization of size distribution was not signifcant in case of progressively less vigorous in the diferent habitats in the the CP and W sites, where smaller size classes were of com- following order, from greatest to least: SS, NS, SP, and CP, parable abundance (Fig. 3a, c, e, g, i and Table 2). Positive followed by W (Table 2). Similarly, Acacia senegal had slopes, indicating low recruitment and unstable population healthier populations on South-facing slopes (SS), but for structure, were seen for Balanites aegyptiaca in the W and this species, the ranking of sites was a little diferent: SS, SP habitats. The ranking of habitat types in terms of popu- SP, NS, and W followed by CP. lation vigor and likelihood of persistence of B. aegyptiaca was: SS and NS followed by CP.

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Fig. 3 Size-class distribution Habitat Eleva on for the four study species in dif- ferent habitat types and in dif- A B C D E F A B C D E F ferent elevational ranges. Study 60 60 (f) species are labelled as: ALAM: (a) SP class1 Albizia amara, ACSE: Acacia 40 40 senegal, ANLE: Anogeissus leiocarpus, BAAE: Balanites aegyptiaca. Size class, corre- 20 20 sponding to estimated tree vol- 3 ume is classifed as: A = < 5 m , 0 0 B = 5–20 m3, C = 20–50 m3, D = 50–100 m3, E = 100–150 m3 F 3 60 (g) class 2 and = > 150 m . Habitat types 60 (b) CP are: SP sand plain, CP clay plain, W Wadi Bed, NS north- 40 40 facing slope, SS south-facing slope. Elevation classes are: 20 20 1 = 750–850 m a.s.l., 2 = 850– ) 950 m a.s.l., 3 = 950–1050 m 0 0 a.s.l., 4 = 1050–1150 m a.s.l. and 5 = > 1150 m a.s.l 60 (c) W 60 (h) class3 40 40

20 20

0 0 Contribuon (%

60 60 (d) NS (i) class4 40 40

20 20

0 0

60 (e) SS 60 (j) class 5 40 40 20 20 0 0 ALAM ACSE ANLE BAAE ALAM ACSE ANLE BAAE Species Species

The healthiest populations at lower elevations (the frst classes 1 and 3 represented the healthier populations of the and second elevation classes) were those of A. amara; A. species in the region. senegal was most vigorous at higher elevations (the third, Similarly, for A. leiocarpus, the healthiest populations, fourth, and ffth elevation classes) (Fig. 3e, f, g, h, i and with more balanced size distributions, were seen at lower Table 2). Albizia amara populations were healthier at eleva- elevations (classes 1 and 2), whereas populations at higher tion class 2 followed by elevation classes 1, 5, 4, and 3. Aca- elevations showed irregular size-class distributions. In the cia senegal showed more negative slopes (indicating more case of B. aegyptiaca, more negative slopes were seen in stable population structure) in the following order: zones 2, populations at higher elevations (altitudinal belts 3, 4, and 4, 5, 1, and 3. However, in elevation classes 2, 4, and 5, the 5), where they also showed irregular patterns of size-class negative slopes were largely due to the absence of individu- distribution. Unstable populations of B. aegyptiaca, with als in larger size classes; the pattern of size-class distribution positive slopes indicating low juvenile recruitment, were was also irregular. As a result, the populations at elevation seen at lower elevations (elevation classes 1 and 2).

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Table 2 Linear regression of Species Environmental variable Slope R2 p value Signifcance the size-class distribution for members of the study species in ALAM Habitat SP − 1.514 0.90 0.004 ** each habitat type and altitudinal CP − 0.971 0.92 0.003 ** zone W − 0.542 0.76 0.025 * NS − 2.850 0.93 0.002 ** SS − 3.428 0.96 0.001 ** Elevation 1 − 2.885 0.91 0.003 ** 2 − 3.914 0.94 0.001 ** 3 − 0.285 0.71 0.034 ** 4 − 0.457 0.91 0.003 ** 5 − 1.240 0.97 0.000 *** ACSE Habitat SP − 1.371 0.88 0.005 ** CP − 0.600 0.82 0.013 * W − 1.114 0.96 0.003 ** NS − 1.230 0.82 0.014 * SS − 3.057 0.92 0.002 ** Elevation 1 − 1.085 0.48 0.130 – 2 − 3.742 0.73 0.031 * 3 − 0.771 0.80 0.015 * 4 − 1.771 0.82 0.014 * 5 − 1.200 0.56 0.086 – ANLE Habitat SP − 0.628 0.74 0.028 * CP − 0.742 0.63 0.060 – W − 0.342 0.62 0.064 – NS − 0.514 0.87 0.007 ** SS − 1.371 0.82 0.013 * Elevation 1 − 1.828 0.75 0.026 * 2 − 0.342 0.62 0.064 – 3 − 0.371 0.85 0.009 ** 4 − 0.200 0.47 0.134 – 5 − 0.857 0.58 0.077 – BAAE Habitat SP + 0.685 0.73 0.031 * CP − 0.485 0.60 0.067 – W +0.371 0.69 0.040 * NS − 0.828 0.81 0.015 * SS − 1.457 0.91 0.003 ** Elevation 1 + 1.285 0.83 0.011 * 2 + 0.857 0.80 0.016 * 3 − 0.514 0.77 0.020 * 4 − 0.314 0.61 0.067 – 5 − 0.458 0.85 0.008 **

Signifcance of the relationship is indicated as: ***p < 0.001; **p < 0.01; *p < 0.05, and a dash (–) denotes that the relationship was not statistically signifcant Study species are labelled as: ALAM: Albizia amara, ACSE: Acacia senegal, ANLE: Anogeissus leiocarpus, BAAE: Balanites aegyptiaca. Habitat types are: SP sand plain, CP clay plain, W wadi Bed, NS north-facing slope, SS south-facing slope. Elevation classes are: 1 = 750–850 m a.s.l., 2 = 850–950 m a.s.l., 3 = 950– 1050 m a.s.l., 4 = 1050–1150 m a.s.l. and 5 = > 1150 m a.s.l

The generalized linear model showed the signifcance were signifcantly correlated with habitat. However, eleva- of species, habitat type, and elevation and their interaction tion had a less generalized efect, signifcantly afecting in shaping the population structure of the study species only the number of fruits/tree (p < 0.001 for A. amara, A. (Table 3). Overall, for all four species, growth parameters senegal and A. leiocarpus) and the number of branches/tree

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(p < 0.05, for B. aegyptiaca). Indeed, the number of fruits/ generalized linear model revealed a signifcant efect of the tree, a refection of reproductive potential, is correlated with habitat type on all measured traits of A. amara (Table 3). habitat, elevation and the interaction between these two vari- However, the number of fruits per tree was also signif- ables at a level of p < 0.001 for A. amara and A. senegal, cantly afected by elevation, and the interaction between and for A. leiocarpus, the main efects are signifcant at habitat type and elevation (Table 3). p < 0.001, and the interaction is signifcant at p < 0.01). In In the case of A. senegal, there was a significant inter- contrast, in the case of B. aegyptiaca, the number of fruits/ action between habitat type and elevation class for most tree is signifcantly afected only by habitat; there is no sig- measured traits: height, number of branches, and number nifcant elevation, or interaction efect. of fruits (Table 3). Habitat type also had a significant effect on all measured traits (Fig. 4). With reference to 3.3 Population traits habitats, the greatest average height (4.41 m) for A. senegal trees was seen in Wadis (W) and the shortest trees Albizia amara trees were tallest in the Sandy Plains (SP) (2.82 m) were seen on the South-facing upland slopes at 5.2 m; on the slopes (NS, SS), they were much shorter (SS). In terms of tree height in relation to elevation, the (3.75–3.87 m) (Fig. 4a). In terms of diferences between tallest trees, at 4.64 m, were seen at low elevations (eleva- altitudinal zones, A. amara trees averaged 4.9 m in the tion class 1) and the shortest, at 2.8 m, were found at high frst, and 3.3 m in the ffth elevation zone, respectively elevations (class 5) (Fig. 4a, b). The greatest number of (Fig. 4b). The number of branches ranged from 6 branches/ branches (8 branches/tree) was seen in the Clay Plains tree in the Sandy Plains (SP), in elevation zone 1, to 4 (CP) and Wadis (W) and at low elevations (elevation class branches/tree on the SS in elevation zones 4 and 5 (Fig. 4c, 1). In contrast, the lowest value (5 branches/tree) was d).The average number of fruits per tree was 689 in the seen on South-facing slopes (SS) (Fig. 4c, d). In terms of Sandy Plains (SP), but only 460 fruits/tree in North-facing reproductive effort (fruit production), plants in the Clay upland pastures (NS). From the perspective of altitudinal Plains (CP) produced 225 fruits/tree, and 230 fruits/tree zone, the number of fruits/tree ranged from 636 in sites in lowlands in general (elevation class 1) compared to in the lowlands (elevation class 1), to 342 fruits/tree in only 138 fruits/tree for plants growing on South-facing uplands (zone 5) (Fig. 4e, f). Similarly, the mass of 50 dry slopes (SS) and 117 at higher elevations (elevation class seeds decreased from 4.45 g in the Sandy Plains (SP) to 4) (Fig. 4e, f). Similarly, in the Clay Plains (CP), plants 3.47 g/50 seeds in the North-facing upland pastures (NS), had heavier seeds (6.79 g/50 seeds) in contrast to the and from 3.65 g/50 seeds at low elevations (elevation class lighter seeds (4.6 g/50 seeds) found on the South-facing 1) to 3.15 g/50 seeds in elevation zone 5 (Fig. 4 g, h). The Slopes (SS); in relation with elevation, plants had heavier

Table 3 Generalized linear Species Parameters Habitat Elevations Interaction model testing the signifcance of the main efects of habitat Chi Square p value Chi Square p value Chi Square p value type and altitudinal class and the interaction between them on ALAM Height (m) 25.789 0.000 1.786 0.775 0.057 0.811 the vegetative and reproductive Branches/tree 27.422 0.000 1.319 0.858 0.243 0.622 traits of each of the study Fruits/tree 123.963 0.000 40.505 0.000 23.360 0.000 species Seeds (g) 9.730 0.045 2.758 0.599 0.114 0.735 ACSE Height (m) 25.789 0.000 8.972 0.062 14.424 0.006 Branches/tree 9.939 0.041 3.121 0.538 11.420 0.022 Fruits/tree 123.963 0.000 40.505 0.000 26.571 0.000 Seeds (g) 9.601 0.048 7.804 0.099 9.079 0.059 ANLE Height (m) 8.500 0.014 5.956 0.114 0.050 0.822 Branches/tree 6.558 0.038 5.282 0.152 0.001 0.977 Fruits/tree 75.443 0.000 119.144 0.000 8.269 0.004 Seeds (g) 9.489 0.009 3.853 0.278 0.364 0.546 BAAE Height (m) 31.843 0.000 3.067 0.381 1.734 0.188 Branches/tree 10.290 0.016 7.874 0.049 7.874 0.319 Fruits/tree 119.856 0.000 4.844 0.184 3.016 0.082 Seeds (g) 14.203 0.003 2.129 0.546 1.111 0.292

Study species are: ALAM: Albizia amara, ACSE: Acacia senegal, ANLE: Anogeissus leiocarpus, BAAE: Balanites aegyptiaca

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Habitat Elevation

(b) (a) SP CP WNSSS Class 1Class 2Class 3Class 4Class 5 15 15

10 10

5 5 Height (m)

0 0

Number of branches 2 0 0 1234

(e) (f) 1200 1200 1000 1000 800 800 600 600 400 400

Number of fruits 200 200 0 0

(h) (g) 12 12 ) 10 (g 10 8 8 6 6 4 4 2 2 Weight of seeds 0 0 1234 ALAM ACSE ANLE BAAE Species Species

Fig. 4 Vegetative and reproductive traits of the four study spe- amara, ACSE: Acacia senegal, ANLE: Anogeissus leiocarpus, BAAE: cies in contrasting habitat types (left hand column) and elevation Balanites aegyptiaca. Habitat types are: SP sand plain, CP clay plain, classes (right hand column), indicating: tree height (a, b), number W wadi bed, NS north-facing slope, SS south-facing slope. Eleva- of branches per tree (c, d), number of fruits per tree (e, f), and dry tion classes are: 1 = 750–850 m a.s.l., 2 = 850–950 m a.s.l., 3 = 950– mass of 50 seeds (g, h). Study species are labelled as: ALAM: Albizia 1050 m a.s.l., 4 = 1050–1150 m a.s.l. and 5 = > 1150 m a.s.l

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Rendiconti Lincei. Scienze Fisiche e Naturali (2018) 29:659–673 669 seeds (6.99 g/50 seeds) at low elevations (elevation class 4 Discussion 1) compared to 5 g/50 seeds at higher elevations (elevation class 4) (Fig. 4g, h). The mountainous landscape of Jebel Marra with its dif- For populations of A. leiocarpus, all of the study traits ferent habitat types, elevations, and aspects provide only were significantly influenced by habitat type, but not part of the explanation of diferences in the population by elevation or the interaction between habitat type and structure and the regeneration potential of the four tree elevation, except in the case of the number of fruits per species studied. It is also important to consider the efects tree, where the habitat type, altitude and their interaction of anthropogenic factors including burning grasslands, were all statistically significant (Table 3). The maximum clearing of trees and the patterns of shifting, and perma- height attained by A. leiocarpus trees was an average of nent cultivation (Ahmed 1982; Babikir 1988). In addition, 9.8 m in the Wadis (W) and in elevation class 2, while factors like altitude and habitat type are often interrelated the shortest trees of this species were 7.56 m high on as, obviously, the plains are at lower altitudes and the the North-facing slopes, and 6.83 m in elevation class 4 slopes are at higher altitudes. In general, species show- (Fig. 4a, b). Greatest branching (14 branches per tree) for ing higher values for a trait in the plains also have higher A. leiocarpus occurred in the plains, in elevation class 1; values for that trait at low altitudes. Conversely, where the least branching (11 branches/tree) was seen on the species showed higher values for a trait on the north- and North- and South-facing slopes; 10 branches/tree were south-facing slopes, they also showed higher values for found at elevation classes 4 and 5 (Fig. 4c, d). In terms of that trait at high elevations. the number of fruits per tree, highest fruit production was Land degradation in the region is well documented; seen in the plains (1002 fruits/trees) and in the elevation conversion of lands to agriculture has triggered changes classes 1 and 2 (954 fruit/tree). This contrasted with low not only in terms of the vegetation pattern but also because fruit production on the North-facing slopes (645 fruits/ tillage leads to soil erosion (Mohamed 2006; Lahmar tree) and at elevation class 3 (522 fruit/tree, Fig. 4e, f). A et al. 2011; FAO 2015; Hegazy et al. 2016). Fortunately, similar pattern was seen in terms of seed mass; the heavi- agricultural activities in the study area do not involve est seeds (1.8–1.9 g/50 seeds) were found in the plains complete clearing of trees, as the local people retain and and at elevation class 1 (1.74 g/50 seeds); and lighter protect large trees for harvest. In such a situation, natural seeds were found on plants growing on the North-facing regeneration is more readily achieved, and species, even slopes (1.21 g/50 seeds) and at elevation classes 3 and 4 those with low reproductive output, are still represented (1 g/50 seeds, see Fig. 4g, h). in the plant community. However, the selective clearing of Balanites aegyptiaca showed a significant effect of small trees produces an unstable size distribution, in that habitat type on all the study traits, but a significant effect younger cohorts are underrepresented; this threatens the of elevation for only one trait, the number of branches persistence of the species, as older, larger trees senesce per tree (Table 3, Fig. 4). The greatest average number and die. of branches/tree (12–13 branches/tree) was seen on the Clay Plains (CP) and at elevation class 1; in contrast, only 8 branches/tree were seen on the Northern Slopes and 5 4.1 The study species branch/tree were observed at elevation class 5 (Fig. 4c, d). In terms of tree height, however, trees were tallest (9.8 m) This study reveals some species-specifc traits that are in the Wadis (W) and at elevation class 4, whereas they unrelated to habitat, altitude or other interaction factors. only grew to 7.56 m on the NS and 7.4 m in elevation For example, from Fig. 4g, h, it is apparent that seeds of class 4 (Fig. 4a, b). The greatest number of fruits per tree A. leiocarpus are smaller (in terms of individual mass) was seen in plants growing in the Sandy Plains (SP, 918 than those of the other species, whatever the habitat, or fruits/tree) and at elevation class 1 (903 fruits/tree); low- altitude. Another generalization that can be made is that est fruit production was seen on the North-facing Slopes A. senegal has fewer fruits than the other species, whatever (NS) with 504 fruits/tree, and at elevation class 4 with the habitat or altitude (Fig. 4e, f). And in general, whatever 498 fruit/tree (Fig. 4e, f). The heaviest seeds in terms of the habitat or elevation, the two rosid species, A. leiocar- the mass of 50 seeds were produced on trees growing in pus and B. aegyptiaca are typically taller and have more the plains (8.78–9.1 g/50 seeds) and at elevation class branches than the two leguminous trees, A. amara and A. 1 (10.1 g/50 seeds). The lightest seeds (5.2 g/50 seeds) senegal (Fig. 4a–d). were found on trees growing on the North-facing Slopes, Albizia amara is more frequently observed in the fallow and at higher elevations (elevation class 4, with 4.9 g/50 lands (elevation classes 1 and 2) in the Sand Plains, and seeds (Fig. 4g, h). in the grazing land (elevation class 5). Awok et al. (2013)

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670 Rendiconti Lincei. Scienze Fisiche e Naturali (2018) 29:659–673 surveyed the forests of Jebel Marra, and found A. amara fuel-wood, the leaves and bark are used for tanning, and the growing on deep permeable soil with hilly topography at twigs provide a popular tea (Miehe 1986). 1300 to 1500 m above sea level (this corresponds to our In B. aegyptiaca, populations with unstable size distribu- elevation class 5). In the present study, the species showed tions were observed even in stands of natural vegetation. steady recruitment in all habitat types at diferent elevation This could, in part, be due to the harvesting of wood for fuel classes, with healthier populations found in the grazing and construction; however, the species is able to re-sprout lands followed by those in the Sand Plain habitats of the from woody stem bases after fre or heavy grazing (Adams fallow lands. 1967; Viswanatahan 1986; Hall 1992). This irregular pattern Populations of A. senegal were more frequent at the mid- of size distribution does not necessarily mean the potential dle altitudinal belts 2–4. The species had healthy populations persistence of the species is threatened, as B. aegyptiaca is a with stable age structures indicating continuous recruitment drought resistant species that is widely distributed in Africa in all land-use patterns and habitat types. This is similar and the Arabian Peninsula. The species shows considerable to the fndings of El Amin et al. (2015), who reported the intraspecifc phenotypic plasticity, and provides fruits and presence of the species, in Sudan, in various habitat types foliage in the dry season even in years with reduced rainfall across a wide range of rainfall and soil textures. The healthi- (Hall 1992; Hegazy et al. 2014). The species is also con- est populations were found in the grazing land followed by sidered as invasive in degraded lands, due to its low water the Sand Plains habitat type of the fallow lands. In terms of requirements (Miehe 1986). As Elfeel and Warrag (2011) altitude, the healthiest populations of A. senegal were found have pointed out, B. aegyptiaca is subjected to overgrazing in the frst and third altitudinal belts; however, the size distri- and intensive cutting to the extent that some trees look as bution was more unstable in other elevation classes, where though they are sufering from die-back; the selective clear- trees in the larger size classes were missing. The loss of large ing of other trees and grasses may be an additional indirect trees in the high altitudinal belts, where the vegetation is in a factor. The growth and reproductive traits of B. aegyptiaca more natural state, may be due to overgrazing and overhar- are negatively afected by the fact that the species has mul- vesting of this species as a source of “gum Arabic”. These tiple uses; the thorns are used for fencing, the fruits have sites are located in areas of Darfur that are relatively remote important medicinal value, and the fruits and leaves are and insecure, with frequent presence of hostile groups, in palatable to both wild and domestic animals (Hall 1992; Le contrast to the regularly harvested trees found within the Houérou 1980). cultivated areas (UNEP 2013b). The quality of gum Arabic is signifcantly afected by the surrounding land use; trees 4.2 Conservation considerations in cultivated lands are relatively protected and provide gum of higher quality than that from trees that are part of the Human interference and impacts have in many ways afected natural vegetation, that are subjected to grazing by livestock the vegetation and population characteristics of keystone (UNEP 2013b). Gum Arabic can be regarded as an impor- species in the region of Jebel Marra. Some species may tant cash crop, produced for export, as it is an important recover, while others may not, depending on their ability natural food additive used in soft drinks and confectionery, to regenerate from seed and clonal growth in the face of and as an ingredient of health foods and diabetic products harvesting, grazing, and land-clearing activities. These fac- (Couteaudier 2007; SIG 2012). tors, combined with regional changes in climate, are likely In the present study, Anogeissus leiocarpus was most to shape the population resilience potential of each species abundant in the fallow lands (on the plains) and at altitudi- in slightly diferent ways. nal belts 1 and 5. This result agreed with Awok et al. (2013) The disruption of traditional agricultural management who found the species on shallow soils and steep slopes in practices has created the fallow lands in the region; this dis- Jebel Marra region. Similarly, healthier populations of A. ruption may in fact facilitate recovery and resilience (A.H., leiocarpus were found in the grazing lands (on the south- personal observation). The potential for species recovery on facing slopes) followed by those on the fallow lands (the the fallow lands will depend on the species-specifc resil- plains). A more balanced size-class distribution was reported ience potential of the populations in terms of whether they at altitudinal belts 1 and 2, but populations at other altitudes will be able to restore a healthy population structure through showed irregular size distributions. This may be due to the juvenile recruitment over an extended period free of dis- higher sensitivity of seedlings to fre, as better recruitment turbance. This resilience potential depends mainly on the of the species was found in open savannas. Another factor regeneration capacity of the species. In this situation, many is that the species is quite efective at clonal growth, via factors are interacting, including seed dispersal mechanisms, rhizomes (Sobey 1978; Hennenberg et al. 2005). The likely seedling recruitment and the availability of “safe sites” suit- cause of the irregular size distributions of trees of this spe- able for germination (Hegazy and Lovett-Doust 2016; Can- cies is that its wood is harvested for construction and as a cellieri et al. 2017). Our data show that the two leguminous

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Rendiconti Lincei. Scienze Fisiche e Naturali (2018) 29:659–673 671 species, A. amara and A. senegal, have managed to maintain way, natural regeneration gradually transforms fallow lands a balanced and stable size distribution in the fallow lands— into treed savanna (HTS 1977). in marked contrast to the other two species. We can, therefore, distinguish two strategies of population resilience: (1) comparatively faster recovery of populations, in the case of 5 Conclusions A. amara and A. senegal which show healthy population structure in grazing and fallow land-use patterns and (2) For the four species studied here, population structure and slow recovery of populations in the case of A. leiocarpus aspects of resource allocation such as tree height, branch- and B. aegyptiaca, where we see unstable population struc- ing, fruit production, and average seed mass difer between ture in the fallow lands. It is worth noting that both groups the fallow lands (the sandy and clay plains and wadis where of plants have experienced the same pattern of disturbance, cultivation practices followed by abandonment of lands and times since last disturbance, but have responded difer- prevail), and the rough pasture lands (the north- and south- ently. Specifcally, the latter two species, A. leiocarpus and facing slopes where natural vegetation is consistently sub- B. aegyptiaca, have responded to direct injury from cutting jected to grazing). For all four species, growth, in terms of and overgrazing by clonal growth; sprouting new shoots vegetative (tree height and number of branches) and repro- from the damaged stem (Adams 1967; Viswanatahan 1986; ductive (number of fruits per tree and dry weight of seeds) Hall 1992; Hennenberg et al. 2005). Clearly, in terms of the traits is greater in the fallow lands, at lower altitudes. This usual markers of population resilience such as population pattern refects a common response on the past of these tree age- and size-structure recovery strategies that depend on species to the benefts of anthropogenic disturbance of the seed production, dispersal, and seedling recruitment, we see natural habitat. Human activities are directed to maximize greater resilience in populations in A. amara and A. senegal, production in the plains, by creating a better environment compared to A. leiocarpus and B. aegyptiaca. Meantime, on for plant growth and reproduction. For example, competition the rough grazing lands of the slopes (NS and SS), mature is reduced by the removal of seedlings and juveniles, and trees of the two rosids, A. leiocarpus and B. aegyptiaca, the addition of moderate grazing. However, from the per- although typically smaller in stature, branching and repro- spective of the populations of these four species, although ductive output than their counterparts on the plains, are sur- the removal of seedlings and juveniles improves the growth rounded by enough juveniles and seedlings to constitute a of the surviving larger trees, it has a detrimental efect on healthy population structure. population structure, since there are few juveniles available Populations of A. amara and A. senegal provide local- for future recruitment. In contrast, when human infuences ized nutrient enrichment through nitrogen fxation by their are removed, and cultivated lands are abandoned, there is symbiotic Rhizobium species, and safe sites for their seeds an opportunity for renewed recruitment of juveniles from to germinate. The prior availability (inoculum) of Rhizo- seed, increasing the resilience and likelihood of persistence bium symbionts allows relatively faster and more successful of the populations. recruitment of new individuals than is seen in the rosids, A. Distinctive population structures are seen in the fallow leiocarpus and B. aegyptiaca. The poor recruitment seen lands, where the leguminous trees, A. amara and A. senegal in the latter species may be due to poor germination and/ show greater potential for establishing stable populations or seedling recruitment due to intrinsic factors (seed viabil- than do the two rosids, A. leiocarpus and B. aegyptiaca, ity, dormancy) or extrinsic factors including the fact that given the same time interval since last disturbance (i.e., soil quality may be seriously degraded in the fallow lands, growing in the same sites). where the soil surface tends to become encrusted, prevent- It is interesting to refect that, while cultivation and man- ing seed germination for many species (Lahmar et al. 2011). aged grazing have not provided a stable resource base for the A strategy involving clearing of grasses in the fallow lands region’s people, they have signifcantly changed the vegeta- might facilitate seed germination and seedling recruitment tion map of the region. Some species have not been greatly for these latter species. A failure of natural regeneration, afected (they are showing good regeneration), while, for resulting in unstable size distributions has been reported for other species, anthropogenic disturbance has had a lasting other tree species in the study area or in the surrounding efect, and they are, today, showing a poor response in terms regions, and this will, in the long run, potentially threaten of regeneration through seedling recruitment. It is ironic their persistence and contributions to ecological functions that in some cases for these species, smaller, less produc- in the community (Adam and El Tayeb 2008; Hegazy et al. tive trees, but trees that were members of healthy popula- 2008; Kabiel et al. 2016a, b). In what was previously a natu- tions can be found in the rough upland grazing lands, while ral savanna, human activities have, in short, improved germi- larger more productive trees of the same species were found nation and establishment conditions for some species, while in cultivated or fallow lands, but, as a result of our current inhibiting the regeneration of others (Vetaas 1992). In this management practices, they were not surrounded by the

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672 Rendiconti Lincei. Scienze Fisiche e Naturali (2018) 29:659–673 juveniles that would assure the persistence of the species Hegazy AK, Hammouda O, Lovett-Doust J, Gomaa NH (2008) Popu- Moringa peregrina in these areas. lation dynamics of along altitudinal gradi- ent in the northwestern sector of the Red Sea. J Arid Environ 72:1537–1551 Hegazy AK, Kabiel HF, Al-Rowaily SL, Faisal M, Zayed K, Doma E (2014) Temporal genetic and spatial pattern variations within References and among Anastatica hierochuntica populations. Rend Fis Acc Lincei 25:155–166 Adam AA, El Tayeb AM (2008) A comparative study of natural Hegazy AK, Kabiel HF, Al-Rowaily SL, Lovett-Doust L, Al regeneration of Boswellia papyrifera and other tree species in Borki AS (2016) Plant communities and reproductive phe- Jebel Marra Darfur; Sudan. Res J Agric Biol Sci 4:94–102 nology in mountainous regions of northern Libya. 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