Early Growth of 11 Native and Three Alien Tree Species in Northeastern Mindanao, Philippines

: Early growth performances of 11 native tree species were investigated in three different sites in Mindanao, Philippines, to evaluate their adaptability and potential for plantation development. Three alien species were added to assess how native species could potentially compete with these alien species based on survival rate, diameter growth rate (DGR), and height growth rate (HGR). A year after planting, the native species common to all sites that obtained >80% survival rate were Casuarina equisetifolia L. Alstonia macrophylla Wall. ex. G.Don., Alstonia scholaris (L.) R.Br., and Parkia javanica (Lam.) Merr. and were comparable to an alien species Acacia mangium Willd. The species with the lowest survival rate (30%) across all sites was Duabanga moluccana Blume. Native species P. javanica , Eucalyptus deglupta Blume, and A. macrophylla all had a DGR of 34 mm year − 1 and were comparable with the alien species Schizolobium parahyba (Vell.) S.F.Blake with 38 mm year − 1 . However, the HGR of native species E. deglupta (245 cm year − 1 ) and Melia dubia Cav. (230 cm year − 1 ) were higher than an alien species S. parahyba (222 cm year − 1 ). No native species can compete with the DGR (52 mm year − 1 ) and HGR (384 cm year − 1 ) of A. mangium . Rainfall signiﬁcantly explained 13%–97% of DGR, HGR and survival rate of >70% of the species while air temperature explained about 17%–96% of the variations of similar variables. This early assessment provides a strong basis to better predict the early performances of native species in the Philippines. Through this, appropriate silvicultural intervention can be recommended towards improving the growth and survival of the native seedlings as alternative industrial tree plantation species in the country. ing to seedling growth. Our study and survival of native species silvicultural management intervention at an early stage to improve the growth and survival of native seedlings selected as alternative species for industrial tree plantation development in the Philippines.


Introduction
Foresters, environmental researchers, and tree farmers face challenges in revitalizing our native tree species in degraded forest lands in the quest to manage productive, profitable, and fully functional ecosystems. Decades ago, the Philippines was one of the major exporters of logs of native trees from natural stands [1]. However, as with many other Asian countries, it lost its forest cover rapidly through heavy logging, upland migration, and agricultural expansion [2][3][4]. As a result, the country faces timber shortages and relies on imports to meet a large proportion of its demand [5].
The Caraga region of the Northeastern Mindanao, Philippines is the major contributor to the logging industry. Dubbed as the Timber Capital of the country, the Caraga Region provides 58%-72% of the country's log requirement [4] due to social inclination to tree planting, favorable climate, and existing wood processing plants. However Table 1. The San Luis field trial site is within the Casilayan Softwood Development Corporation (CSDC) in San Luis, Agusan del Sur. The area was previously covered with wild A. mangium and was clear-cut for this study. The site topography was slightly sloping [8], and the elevation was 159 m a.s.l. The site has an average temperature of 26.12 • C and an average rainfall of 2152 mm. [24]. The Bislig site was established within the 3248-hectare Bislig Experimental Forest in Bislig, Surigao del Sur. This site has an elevation of 220 m a.s.l. with a moderately steep slope. The soil was unclassified mountain soil (BSWM Map Soil Classification) with heavy texture and reddish-brown color. The site has an average temperature of 26.3 • C and an average rainfall of 3458 mm. [24]. The Butuan field trial site was within the 100-hectare JAKA Inc. industrial tree plantation site. The area was previously planted with Gmelina arborea Roxb. ex Sm. Upon harvest, the vegetation cover succession was dominated with Imperata cylindirica (L.) P.Beauv. (cogon) and Saccharum spontaneum L. (Talahib) grasses. The terrain is moderately steep, with an elevation of 171 m a.s.l. The soil classification was Butuan loam which developed from the older alluvial terraces [25]. The average temperature of the Butuan site is 26 • C and it has an average rainfall of 2127 mm [24]. The three sites fall to a type II climate, according to the modified Coronas classification, which is characterized by the absence of a dry season but with a maximum rain period from November to February [24].

Species Information
We evaluated eleven native tree species for their early growth field performances. We added three alien species for comparison purposes between the native trees and alien fast-growing trees. We based our selection of native tree species on a previous tree domestication study [18]. We collected the seeds mainly in different places in Mindanao except one species (Batino, Alstonia macrophylla Wall ex G.Don), which was collected in Palawan, Philippines. We sowed and raised the seeds in the Bislig Clonal Nursery of ERDB-FWRDEC, Maharlika, Bislig City. Taxonomic information is shown in Table 1. Scientific names and their authorships were obtained from Plants of the World Online (http://powo.science.kew.org, accessed on 21 June 2021).

Experimental Design, Establishment and Data Collection
We used a randomized complete block design (RCDB) in this study. The planting distance was 2 m × 2 m with 36 plants per species (six plants in rows and six plants in columns) and replicated five times (blocks). Each study measures 1.08 hectares. We eliminated the weeds and undesirable trees before planting and every two months thereafter. We outplanted the seedlings in the trial sites from August to November 2019. We applied complete fertilizer (14-14-14), which is a ratio, or equal percentages, of nitrogen (N), phosphorus (P), and potassium (K). We used 100 g for each plant every six months.

DGR, HGR, and Survival Rate Determination
The initial height (cm) and the diameter at ground level (dgl; mm) were obtained two months after outplanting. We performed subsequent measurements every six months. We used a vernier caliper to measure the dgl and a calibrated pole to measure the height. The total height and dgl were instantaneous data at the time of measurement. To avoid biases and inherent differences in scale between contrasting species at the time of planting, we standardized them using the relative annual growth rate, termed as diameter growth rate (DGR, mm year −1 ) for dgl and height growth rate (HGR, cm year −1 ) for height. These growth rates were calculated following the equation [26]: where W represents either dgl or height at t 1 at the beginning of the experiment and t 2 at the end of the experiment in an annual basis. Survival rate was calculated by counting the number of plants of each species that had survived divided by the number of plants originally planted of that species, expressed in percentage survival.

Climate Data Collection
We installed a Davis Vantage Pro2 automated weather monitoring station (AWMS) at each site to determine the micro-climatic condition, particularly the temperature and rainfall. We retrieved these climate data once a month.

Data Analysis
We used a two-way analysis of variance (ANOVA) with interaction effect to determine significant differences in survival rate, diameter-at-ground (dgl) level, and height growth rates at species and site levels and their interactions.
Local climatic variables (rainfall and air temperature) were plotted against survival rate, DGR, and HGR using the linear regression in the ggplot2 package. All analyses were processed in R version 4.0.3 (R Core Team, 2020) [27].

Species Level
Across all sites, the highest survival rate was attained by an alien species A. mangium (95%), although the survival rate of native species such as A. scholaris (93%), C. equisetifolia (93%), P. javanica (91%), and B. javanica (90%) were close and did not differ significantly (p > 0.05). The overall average survival rate across sites was 84%, yet other alien species such as S. macrophylla (82%) and S. parahyba (79%) fell below this average level. All native and alien species attained >75% survival rate except for D. moluccana, where only 30% of the planted seedlings survived (Figure 2).
In the Butuan site, the minimum survival rate was again observed in D. moluccana (23%) while the rest had >80% survival rate. The maximum survival percentage in the Butuan site was 98%, not only exhibited by A. mangium but also for A. scholaris, C. equisetifolia, P. javanica, and A. macrophylla ( Figure 3).
In the San Luis site, D. moluccana still had the lowest survival rate (39%), however this rate is high compared to its performances in the Bislig (29%) and Butuan (23%) sites (p < 0.05). The maximum 98% survival rate of A. scholaris, C. equisetifolia, P. javanica, B. javanica, and A. chinensis were relatively at par with A. mangium (99%) in the San Luis site. Alien species such as S. parahyba (82%) and S. macrophylla (79%) fell below the average survival rate of 86% for this site. Out of 14 species, 12 had >80% survival rate in the San Luis site (Figure 3).

Species Level
It is not surprising that alien species A. mangium attained the highest DGR (mean = 61 mm year -1 ) across all sites (Figure 4a). Following A. mangium were alien species S. parahyba and S. macrophylla with a DGR of 38 mm year -1 and 31 mm year -1 , respectively. Native species such as A. macrophylla, E. deglupta, P. javanica, and M. dubia, with DGR ranging from 32-35 mm year -1 , grew at rates close to that of S. parahyba and S. macrophylla. The species with the lowest DGR was attained by D. moluccana (14 mm year -1 ).
A. mangium also attained the highest average height growth (HGR = 406 cm year -1 , Figure 4b) followed by M. dubia (301 cm year -1 ). The average HGR of native species E. In the Butuan site, the minimum survival rate was again observed in D. moluccana (23%) while the rest had >80% survival rate. The maximum survival percentage in the Butuan site was 98%, not only exhibited by A. mangium but also for A. scholaris, C. equisetifolia, P. javanica, and A. macrophylla (Figure 3).
In the San Luis site, D. moluccana still had the lowest survival rate (39%), however this rate is high compared to its performances in the Bislig (29%) and Butuan (23%) sites (p < 0.05). The maximum 98% survival rate of A. scholaris, C. equisetifolia, P. javanica, B. javanica, and A. chinensis were relatively at par with A. mangium (99%) in the San Luis site. Alien species such as S. parahyba (82%) and S. macrophylla (79%) fell below the average survival rate of 86% for this site. Out of 14 species, 12 had >80% survival rate in the San Luis site (Figure 3).

Species Level
It is not surprising that alien species A. mangium attained the highest DGR (mean = 61 mm year −1 ) across all sites (Figure 4a). Following A. mangium were alien species S. parahyba and S. macrophylla with a DGR of 38 mm year −1 and 31 mm year −1 , respectively. Native species such as A. macrophylla, E. deglupta, P. javanica, and M. dubia, with DGR ranging from 32-35 mm year −1 , grew at rates close to that of S. parahyba and S. macrophylla. The species with the lowest DGR was attained by D. moluccana (14 mm year −1 ).

Species Level
It is not surprising that alien species A. mangium attained the highest DGR (mean = 61 mm year -1 ) across all sites (Figure 4a). Following A. mangium were alien species S. parahyba and S. macrophylla with a DGR of 38 mm year -1 and 31 mm year -1 , respectively. Native species such as A. macrophylla, E. deglupta, P. javanica, and M. dubia, with DGR ranging from 32-35 mm year -1 , grew at rates close to that of S. parahyba and S. macrophylla. The species with the lowest DGR was attained by D. moluccana (14 mm year -1 ).

Site-Species Interactions
Using the two-way ANOVA test with interaction effect, we found significant differences among blocks, sites, and species, as well as interactions between the sites and species in terms of DGR, HGR, and survival rate (p < 0.0001~p < 0.04, Table 2). The interaction between site and species was highly significant (p < 0.0001), which indicates that relationships between species and DGR, HGR, or survival rate depends on the site condition. This prompted us to dig into the sources of variations in species growth and survival as affected by any condition at the site. We used the available climatic data for each site and evaluated how these affect the DGR, HGR, and survival rates of the species as discussed in the succeeding sections.

Site-Species Interactions
Using the two-way ANOVA test with interaction effect, we found significant differences among blocks, sites, and species, as well as interactions between the sites and species in terms of DGR, HGR, and survival rate (p < 0.0001~p < 0.04, Table 2). The interaction between site and species was highly significant (p < 0.0001), which indicates that relationships between species and DGR, HGR, or survival rate depends on the site condition. This prompted us to dig into the sources of variations in species growth and survival as affected by any condition at the site. We used the available climatic data for each site and evaluated how these affect the DGR, HGR, and survival rates of the species as discussed in the succeeding sections. Table 2. Summary of two-way analysis of variance (ANOVA) of DGR, HGR, and survival rate. Degrees of freedom (DF), F-statistic (F), and P values (Pr) are shown for each of the block, site, and species and the interaction between site × species. Significant differences are shown by (*). Significance level: *, 0.05; **, 0.01-0.001; ***, <0.001.

Parameter
Source In terms of DGR-rainfall relationship, 43% of the species were sensitive to rainfall, although the sensitivity and the trajectory of the slope varied (R 2 = 0.16~R 2 = 0.92, Figure 6). Among them, E. deglupta, a fast-growing native species, was the most sensitive (R 2 = 0.92), with higher rainfall slowing down its DGR. Some of the species that benefited from the high rainfall amount were alien species such as A. mangium and S. macrophylla, but at a lower extent, with R 2 = 0.16 and R 2 = 0.19, respectively.
Similarly, the HGR of fast-growing native species E. deglupta, B. javanica, and A. scholaris (R 2 = 0.66~0.88) were highly affected by rainfall, although they exhibited different response trajectories. For example, high rainfall lowered the HGR of E. deglupta and B. javanica, and A. scholaris grew faster with high rainfall. In contrast, the HGR of the alien species S. macrophylla (R 2 = 0.17) were less likely affected by rainfall and the HGR of A. mangium was not affected at all (R 2 = 0.01, p > 0.05).
The survival rates of Terminalia foetidissima Griff., P. javanica, B. javanica, E. deglupta, and C. equisetifolia were very sensitive to rainfall (R 2 = 0.91~0.97). However, the survival of T. foetidissima and C. equisetifolia were high when rainfall was low and declined when it was the opposite. The survival of A. mangium was less sensitive to rainfall (R 2 = 0.16). The survival of D. moluccana, the slowest growing species with the lowest survival, was not at all affected by rainfall (R 2 = 0.01, p > 0.05).
T. foetidissima and C. equisetifolia were high when rainfall was low and declined when was the opposite. The survival of A. mangium was less sensitive to rainfall (R 2 = 0.16). Th survival of D. moluccana, the slowest growing species with the lowest survival, was not all affected by rainfall (R 2 = 0.01, p > 0.05).

The Response of DGR, HGR and Survival to Temperature
The temperature-DGR relationships were significant to only 36% of all the species. D. moluccana, the slowest growing native species, was mostly affected by temperature (R 2 = 0.76) indicating that high temperature environment induces greater diametric expansion of the species (Figure 7). Interestingly, the DGR of E. deglupta, a fast growing native species, was less sensitive to changes in temperature regime (R 2 = 0.17). The DGR of alien species such as A. mangium, S. macrophylla, and S. parahyba were not affected at all by changes in temperature (R 2 = 0.01, p > 0.05).

Species Level
Acacia mangium, a fast-growing tree from Indonesia, Papua New Guinea and Aus tralia, has been cultivated outside its native environment and introduced into humid trop ical lowland regions of Asia, South America and Africa over the last few decades [28]. I is a promising plantation species [2,29]. The survival rate of A. mangium is high and can reach >79% even 4 years after planting [29]. Thus, in the Philippines, many logging con cessionaires and private tree growers prefer A. mangium due to its short rotation period timber quality, marketability, and high survival rate [4,30], even though native species in the Philippines can also attain high survival rates comparable to A.mangium. For example our previous study showed that P. javanica and B. javanica achieved 80%-90% surviva rates 5 years after planting, which proved the ability of these native species to survive wel as that of A. mangium.
While all species at our study sites attained >75% survival rate, D. moluccana had the lowest survival tendency (~30%). Generally, D. moluccana thrives well near bodies of water In terms of HGR-temperature relationship, 35% of the species were highly limited by temperature, which was one of the most limiting factors on their height growth. However, the variance explained is only up to about 50% (R 2 = 0.16~0.55), indicating that factors other than temperature were driving the HGR of these species. The HGR of D. moluccana, a slow growing native species, was highly affected by temperature (R 2 = 0.54), whereas S. parahyba, an alien species, was the least affected (R 2 = 0.16).
In terms of survival rate-temperature relationships, the survival rates of all species were highly limited by temperature (R 2 = 0.10~0.96). T. foetidissima, M. dubia, and D. moluccana were highly affected by temperature, although the slope varied significantly even at a small temperature range (25~28 • C). Alien species such as S. macrophylla, A. mangium, and S. parahyba were among those species that were less likely to be affected by temperature (R 2 = 0.10~0.24).

Species Level
Acacia mangium, a fast-growing tree from Indonesia, Papua New Guinea and Australia, has been cultivated outside its native environment and introduced into humid tropical lowland regions of Asia, South America and Africa over the last few decades [28]. It is a promising plantation species [2,29]. The survival rate of A. mangium is high and can reach >79% even 4 years after planting [29]. Thus, in the Philippines, many logging concessionaires and private tree growers prefer A. mangium due to its short rotation period, timber quality, marketability, and high survival rate [4,30], even though native species in the Philippines can also attain high survival rates comparable to A.mangium. For example, our previous study showed that P. javanica and B. javanica achieved 80%-90% survival rates 5 years after planting, which proved the ability of these native species to survive well as that of A. mangium.
While all species at our study sites attained >75% survival rate, D. moluccana had the lowest survival tendency (~30%). Generally, D. moluccana thrives well near bodies of water such as perennial gullies and streams. Micro-climate, soil water, nutrient availability, and physical soil properties change strongly from gullies and stream ecosystems to open sites [31], posing very distinct barriers to the growth and survival of newly established D. moluccana. However, if this species is used as planting material in an undulating terrain plantation site near gullies and streams with a high groundwater table, D. moluccana may thrive well, which has been observed in East Kalimantan, Indonesia [32].
Overall, seedling mortality was low at the three sites. One plausible explanation for the low mortality rates in our sites is that seedlings were fertilized when planted and at two months post-planting to ensure establishment. Fertilization may have ameliorated nutrient stress initially, while the same does not apply for moisture stress as rainfall is not a limiting factor in all sites.

Site Level
Our results showed that although A. mangium generally had high survival when planted in a wetter bioclimatic zone such as in the San Luis site, its survival can be lower in drier and sloping sites, such as the Bislig and Butuan sites. This lower survival of A. mangium in drier conditions in our study is consistent with the study of Hardie et al., 2018 [33].
The high survival rates of P. javanica, B. javanica, C. equisetifolia, A. macrophylla, and A. scholaris in our three study sites which were consistent with A. mangium, which demonstrates the potential of these native species to compare favorably with that of alien species under appropriate ecological conditions. Our previous species trial performed in Agusan del Norte, Philippines also showed a very high survival tendency of P. javanica [18] planted in sloping terrain with favorable climate, such as our present study sites. P. javanica is an agroforestry tree species in most tropical regions. In the Philippines, the tree can grow luxuriantly in the wild and in shifting agriculture lands [34]. P. javanica is a large tropical tree that grows well under full sunlight, although it also thrives well in cooler tropical conditions, making it an excellent candidate native species for plantation establishment. B. javanica, A. macrophylla, and C. equisetifolia belong to species that existed in old-growth and secondary forests in the Philippines but are now vulnerable to shifting cultivation and land-use change [3]. These species are used presently for assisted natural regeneration and many forest structure recovery efforts in the Philippines. It may still be too early to draw conclusions about the fate of P. javanica, B. javanica, and C. equisetifolia on this upland condition at its early stage of development. Long-term monitoring is needed to understand better the species adaptation of these native species.

Species Level
Among all native and alien species planted, A. mangium had the highest DGR and HGR. This is not surprising, because Acacia species are prime candidates as they are fastgrowing, even in poor soils [35,36], and can grow in high-light environments and vice versa under low-light conditions [37]. A. mangium was introduced as a plantation tree in the Philippines in the early 1980s to contribute to the timber industry alongside Falcataria moluccana [4]. However, it has become increasingly clear that some alien tree species used in industrial tree plantation development can cause major problems as invaders of natural and semi-natural or disturbed ecosystems [7,[37][38][39]. This species may accrue costs to the ecosystem that may far outweigh its benefits [36,38,40,41]. Thus, the use of native species has been increasingly promoted as an alternative for industrial tree plantation development in the Philippines.
Past studies in the Philippines reported that native species such as A. macrophylla, A. scholaris, P. javanica, B. javanica, and C. equisetifolia were used in reforestation efforts. These species were proven to help rapidly recover abandoned land areas left after shifting cultivation [3]. These were the same species that exhibited relatively higher DGR and HGR in our study sites, capable of competing with alien species such as A. mangium, S. parahyba, and S. macrophylla.

Site Level
Slow growing native species such as A. chinensis, D. moluccana, and T. foetidissima mostly thrive in a habitat different from our trial sites in Bislig, Butuan, and San Luis. They usually grow in wetland areas, along the coastal plains, and near streams. Difficulty in adapting to a new environment could cause high mortality rates and poor growing performances [16], such as what we observed in our study.
Many species with better DGR, HGR, and survival rates are found in upland forests similar to our study sites. These include C. equisetifolia, A. macrophylla, and P. javanica, among others. The growth of these species was comparable to that of other alien species such as S. macrophylla and P. parahyba. These native species that have the ability to grow comparatively with alien species should be monitored closely since they may have better chances of becoming alternative species for industrial plantation development.
Overall, height and diameter may not always be accurate predictors of performance after outplanting. Root system morphology and physiological status may also come into play [20]. Management interventions must then focus on attaining good growth patterns by avoiding weed competition and applying silvicultural and fertilizer treatments that ensure better structural form and growth of planted seedlings.

Climatic Factors Affecting the Growth and Survival of Native and Alien Species
Despite similar maintenance operations and silvicultural interventions applied in our sites, native and alien species' growth and survival differed due to the varying biological and environmental factors such as micro-climate, soil biota, nutrient availability, soil physical and chemical attributes, the quality of planting materials, topography, hydrology, pest and diseases, and weed competition, as well as the adaptation of the plants to the new environment [17,[42][43][44][45].
Accordingly, light is one of the key drivers for plant growth, coupled with soil moisture and temperature [46][47][48][49][50][51][52][53]. In our trial sites, we do not have solar radiation data, although we found that local rainfall and temperature drove the increase in DGR and HGR of most of the species. Our results suggest that if there is not much prolonged rainfall, and as well as longer dry days due to a slight increase in temperature, the planted species can attain optimum structural growth.
Rainfall and air temperature are not primarily a limiting factor for most alien species (A. mangium, S. macrophylla, and S. parahyba) in our study sites, indicating that their seedling growth and survival may be affected more by poor soil nutrients and soil health conditions, as reported by many authors [16,54,55].
Most fast-growing native species (e.g., E. deglupta and B. javanica) were less affected by temperature. E. deglupta are trees that take a wide range of physical forms and occupy a broad range of climatic and ecological niches [56]. Hughes et al. [57] reported that even in 1 • C to 2 • C annual mean temperature difference, the actual climatic tolerance of the eucalyptus species is wider, although questions arise as to level of tolerance of the species and its adaptability/plasticity in a future warmer climate. Nevertheless, our study revealed the tolerance of E. deglupta and other native species when subject to changing thermal conditions. However, we do not undermine the fact that temperature had positive and negative effects on tree growth through physiological processes (e.g., photosynthesis, respiration, absorption, translocation and transpiration) as evidenced on the contrasting slope of the line between the temperature and the DGR, HGR, and survival rates. Air temperature is usually confounded by light, CO 2 availability, soil temperature, soil moisture, and other environmental factors that all together affect the physiological and biological mechanisms in plants [58].
Temperature explained up to 76% of the variations in DGR in our study. Increased temperature enhances tree diameter [59,60], leading to a positive relationship between temperature and the DGR of most species. All sites received high rainfall each year (>2000 mm per year). An adequate soil moisture coupled with sufficient light intensity as in most of tropical ecosystems [43] but with a smaller degree of change in air temperature may have confounded and overshadowed the effect of temperature on the diameter growth of seedlings, thus a weaker relationship of DGR with air temperature.
The variance explained by the temperature-HGR relationship is only 16%-55%, indicating that other factors such as soil nutrients, topographical aspects, and other climatic factors individually or in combination may play a more significant role in the changes in height growth of the planted species.
We have only considered rainfall and temperature regimes as factors in the growth performances of the planted trees. However, we concur with the common notion that climate alone may not reflect seedling adaptations in our trial sites, but also the interaction of soil nutrients and soil fertility conditions with co-varying variables such as soil physical attributes, microbial activities, and root dynamics [47,53]. These compounding effects complicate our understanding of the growth dynamics of planted trees. The growth of planted trees is thus a complicated physiological and morphological mechanism that requires an in-depth investigation.

Conclusions
This early-stage assessment of some native and alien species in Northeastern Mindanao, Philippines, is important as an initial activity for long-term native tree species field trial and domestication efforts. Our results showed that some native species could potentially grow and survive at the rate closer to those fast-growing alien species. The genetic conservation of these species is of high importance as they can augment the diminishing log supply of the country and act as a refuge for the dwindling tropical forest biodiversity. Although it is too early to predict with certainty, our results reinforce the much-needed information on the early performances of native trees in the Philippines. Thus, prolonged monitoring is necessary so we can conclude with certainty the potentials of these native species for commercial use.
The diametric increment, height growth, and survival of native and alien species across all sites is related in part to differences in climatic condition (rainfall and temperature), although we firmly maintain that the relative importance of plant structural attributes, soil fertility/nutrients, and phenotypic variability are equally important. Therefore, in growth performance assessment, our result suggest that attention must be focused on environmental forcing, such as the positive impact of the future warmer climate on the rainfall-abundant environment or the negative impact of reduced rainfall and global warm-