Introduction

Climate change affects all ecosystems, which already face many challenges and pressures (^{Nelson et al., 2009}). Deforestation is one of the actions that have more negative impact on the environment, in addition to threatening the cultural integrity and lifestyles of different communities that depend on forests for their livelihoods (^{Kanninen et al, 2007}). The decrease of forest cover favors biomass loss and land fragmentation and modifies the hydrological cycle, as well as the regime of temperature and precipitation, so that the native species of animals and plants remain vulnerable to adverse environmental conditions (^{Debinski and Holt, 2000}; ^{Cayuela, 2006}; ^{López, 2012}).

Fortunately, several reforestation programs to recover deforested areas have been installed in Mexico. However, evaluations reveal that survival is less than 60 %, due to various factors such as grazing, competition with native vegetation, fires and prolonged droughts (^{UANL, 2009}). The latter causes water stress which leads to changes in the physiology of plants and affects most of its vital functions, resulting in the loss of turgidness, reduction of the rate of cell expansion, decreased synthesis of cell wall and reduced protein synthesis; when the water shortage is severe cavitation of xylem elements, falling leaves, accumulation of organic solutes, wilting and plant death occurs (^{Moreno, 2009}).

Therefore, in the last 20 years scientific work has focused on the development of water-saving technologies in order to ensure the survival of the plants in the field because it is expected that the rainy season is to become more erratic as a result of climate change (^{Nelson et al, 2009}). Thus, the open cell phenolic foam is proposed as an alternative, as it is a synthetic resin capable of storing more than 40 times its own weight in water (^{Gardziella et al., 2000}), so it has been used as substrate in hydroponic cultures (^{Pilato, 1979}; ^{Cocozza and De Lucia, 1994}; ^{Coelho, 2010}).

Pinus leiophylla Schiede ex Schltdl. et Cham. is one of the most wdely distributed pine species in Mexico (^{Santillán, 1991}). It is considered a pioneer species, since it is able to establish itself in poor soils covered by volcanic lava (Eguiluz, 1978 in^{Musálem and Martínez, 2003}). Its wood is highly valued in different industries such as construction, paper and rural industries. However, its natural populations occupy the lowest in the pine forests, near the agricultural frontier, which have subjected it to excessive logging, which has drastically reduced its surface in certain areas (^{Musálem and Martínez, 2003}). Despite this, it is expected that due to the effects of climate change, its distribution range will increase 35.5 % (^{Arriaga and Gómez, 2004}) so it will be necessary to establish management plans for the establishment that include the changes in rainfall patterns.

Based on the above, the aim of this study was to evaluate survival, height and diameter at early stages of Pinus leiophylla plants by adding hydrated phenolic foam blocks at the time of planting in the field.

Materials and Methods

The trial was established in the community of San Sebastián in the Huasca de Ocampo municipality, Hidalgo State, which lies between 20°15'7.96" N and 98°31'3859" W. The altitude at the region ranges from 1 800 to 2 800 m; it has a climate of the Cw type, with an average annual temperature of 15 °C and an average annual rainfall of 752 mm (^{Chávez et al., 2001}). The precipitation and temperature conditions prevailing at the site during the evaluation period, August 2014 to February 2015 are described in Table 1.

Table 1 Precipitation and temperature prevailing in the study area during the August 2014 - February 2015 period. 

*Data taken from the Huasca de Ocampo´s weather station of INIFAP , located in the homonymous municipality.

One year- old plants were used, which were produced in a technified system, and that were delivered in packages of 15 individuals wrapped in thin plastic on the part of the root ball containing 170 cc volume each; also good care was taken in their transportation to the planting site; through a visual assessment, at the time of placing them, disease-free plants, with i of the woody stem with needles and fully developed fascicles were selected.

Plantation holes (30 x 30 x 30 cm) were made on the same date of transplantation; the extracted soil was divided in two parts in order that the surface portion containing more nutrients was deposited in the deepest part of the hole. The plants were placed in the center thereof with their respective treatment (so that the hydrated foam had the largest area of contact with the root ball). The holes were filled, and lumps or large rocks were removed to avoid macropores in the soil; in addition, the soil around the plant was slightly compacted with the feet (^{Conafor, 2013}). The plantation was established in real frame design with spacing of 3 x 3 m between plants and lines to obtain a density of 1 111 plants per hectare and with an experimental design of randomized complete blocks.

Five treatments at planting time (Table 2) were applied; each treatment consisted of three replications of 30 plants each, with a total of 90 individuals and 450 treatment plants throughout the experiment.

Table 2 Description of the treatments used in the study. 

The studied variables were: survival, and growth in height and diameter. Survival was evaluated visually by using the methodology of ^{Barchuk and Díaz (2000)}, which indicates that if the sample shows signs of wilting, lack of firmness and loss of characteristic color of the species, the plant is considered dead. Measurements were made every month for a period of six months, as it is the time when most plants die in the field (^{Sigala et ai, 2015}).

The height and diameter growth was evaluated in all plants. It was measured by using the methodology of ^{Pereira (2014)}, which measures those dimensions from digital images; a Nikon Coolpix S2800 digital camera was used for this ending; for image processing, the ImageJ version 1.48 program was used. The photographs were taken in parallel to the plants at a distance of 50 cm, with a pre-set reference; height was considered from the base to the apical bud, and the diameter was measured at a height of 5 cm from the base of the plant.

The individual data per month for survival were subjected to an analysis by the Kaplan-Meier estimator. If there were any significant differences, the log-rank test was used to determine the most effective treatment.

The individual data of growth in height and diameter after six months were submitted to analysis of covariance, for which a generalized linear model was applied in version 7.0 Statistica statistical package; initial values height and diameter were used as covariates; when statistical differences (P ≤ 0.05) were verified, the multiple comparison test of Tukey for the purpose of identifying the fastest growing treatment plants in the field was made.

Results and Discussion

Survival

The Kaplan-Meier estimate indicates significant differences between treatments (P = 0.00004) on survival: control plants had a survival rate at 180 days (6 months) of 0.47, while plants with 616 cc and 462 cc phenolic foam have a ratio of greater survival than 0.7 (0.74 and 0.72 respectively) (Figure 1).

Figure 1 Survival curves from the Kaplan-Meier estimator for Pinus leiophylla Schiede ex Schltdl. et Cham. individuals with different treatments of cell phenolic foam. 

This implies that to establish a plantation under these conditions, control can lose more than 50 % of its members in less than six months; similar results have been reported by ^{Colpos (2008)}, ^{UANL (2009)}, ^{UACh (2010)} y ^{Coneval (2012)}. These results agree with those of ^{Bezerra et al. (2010)} and ^{Muller et al. (2012)}, which recorded a significant increase in survival by adding phenolic foam to Lactuca sativa L. plants and hybrids of Eucalyptus urophylla S. T. Blake and E. resinifera Sm. in up to 23 % and 22 %, respectively under greenhouse conditions.

The Log Rank analysis confirmed that plants with 462 and 616 cc foam have a higher survival regarding the 231 treatment plants and control. Plants with 308 cc phenolic foam only have significant differences with the control (P = 0.008); which had the lowest survival in the experiment with plants in blocks of 231 cc, since in both groups no significant difference (P = 0.46) are appreciated (Table 3).

Table 3 Results matrix for the Log-Rank analysis. 

Lower results than 0.05 and with an * mean that there are statistical significant differences between treatments.

It is observed that the plants with 462 cc, 616 cc foam and control kept 100 % survival after 30 days, which means that the transplant was performed properly. However, in plants with 231 cc and 308 cc foam, 1.1 and 2.2 % died, respectively, which suggests that planting errors remained as low as possible. Throughout the experiment, control was the group that had the lowest survival, with a marked decrease at 60 days (30 % less). Plants with 462 and 616 cc foam kept the highest tendency and maintained it throughout the experiment, with very similar survival rates, and they even shared the same percent at 120 days (80 %). Plants with 308 cc foam shared a similar behavior to that of plants with 462 and 616 cc. However, this behavior changed at day 150 after the transplant, in which their survival decreased dramatically (64 %) compared to plants with 462 and 616 cc foams (> 70 %) (Figure 2).

Figure 2 Survival (%) of plants of Pinus leiophylla Schiede ex Schltdl. et Cham. over time, with the application of blocks of different phenolic foam volume in strain at the time of planting. 

Height and diameter growth

The analysis of covariance for height growth showed significant differences (P ≤ 0.05) between treatments, which did not happen to the diameter (Table 4). Plants with 462 cc phenolic foam blocks had the greatest growth (16.5 cm). There was a difference of 6.6 cm relative to the control, which represents 40 % more growth in six months. This indicates that with the phenolic foam, the plant has moisture for a longer time, which favors its vital functions and can achieve a larger size. However, ^{Bezerra et al. (2010)}, ^{Espinoza (2010)} and ^{Muller et al. (2012)} indicate that the phenolic foam in Lactuca sativa has no effect in this sense, although the test was conducted in a greenhouse.

Table 4 Results of the analysis of covariance for growth in height and diameter of phenolic foam treatments in Pinus leiophylla Schiede ex Schltdl. et Cham. 

^a The degrees of freedom for each variation source are in parenthesis.

*Bars with different letters are statistically different.

Figure 3 Growth in height of Pinus leiophylla Schiede ex Schltdl. et Cham. plants with different treatments of blocks of phenolic foam after six months planted in the field. 

Conclusions

When adding the 462 and 616 cc cell phenolic foam at the time of planting of Pinus leiophylla the survival percentage increases significantly up to 26 % more in regard to the control plants after 180 days of their incorporation in the field. The first type also increased significantly the growth in height up to 6.6 cm in regard to control. However, there are no significant differences in diameter increment.

Conflict of interests

The authors declare no conflict of interests.

Contribution by autor

Abraham Palacios Romero: execution of the experiment, calculations and analysis of results; Rodrigo Rodríguez Laguna: original idea and statement of the research study, funding negotiations for the research, writing and review of the manuscript; Francisco Prieto García: data analysis and writing of the manuscript; Joel Meza Rangel: review of the manuscript; Ramón Razo Zárate: review of the manuscript; María de la Luz Hernández Flores: review of the manuscript.