Panel 1: The chilean case (Contd.)

THE GENUS PROSOPIS AND ITS MANAGEMENT AT THE TAMARUGAL PAMPA (Contd.)

TABLE 12
Annual periodical average height gain of tamarugo by site location Basis: 20 plots, 13-year span

3.4.2 Mean Annual Growth According to Salinity and Depth of Water Table

Table 12 includes the mean height increment values found acording to salinity and depth of the water table.

It can be seen, from the above table, that mean annual growth decreases with age.

It is interesting to note, furthermore, that the two highest mean increment values correspond to plots with salt content of 3,000–3,500 mg/l in a groundwater table 2 m below the surface.

In light of the interest in determining some of the trends regarding height increment, data from 37 plots from the forestry survey were annexed to that from the permanent plots. These additional plots had been established at the Pintados deposit, ranked by water table depth and salinity. To center the analysis and to obtain a greater degree of accuracy in annual growth rate for the different ages, only ages from 8 to 15 years were considered.

The above data are detailed in Table 13 below, complemented with the health condition of the forest resource. This condition was assessed according to the following criteria:

1. Healthy tree

2. Affected by mild attack

3. Affected by medium attack

4. Severely attacked tree

5. Dead tree

This table includes also the values for the individual height variation within each plot, in percentage.

TABLE 13
Tamarugo Growth Rate According to Underground Water Table Depth and Salinity

The growth differences were ascertained to be statistically significant or casual by means of a variance analysis. The model used was totally randomized, with a repetition number different for each treatment, which in this case were the following water table depth ranges: 0–2 m; 2–4 m; 4–6 m; 6–8 m; and 8–10 m.

The results showed that there are significant differences (probability level 95%) in the annual average growth rate for sites with different water table depths.

Although sampling errors are slightly higher than commonly accepted, since the temporary sampling plots were established for a different purpose, some interesting conclusions may be derived therefrom:

1. The growth rate in the period under consideration (8–15 years) in terms of mean height, is significantly higher in sites with a water table depth of 0–4 m.
2. For ages over 15 years, growth rate differences in relation with water table depth are lower.
3. The growth rate for this species in the age range of 8–15 years, in places with water salinity between 1,000–3,500 mg/1 is not affected significantly.

3.5 Nutritional Survey

A marked variation range both for development and survival may be observed in the Prosopis tamarugo forests growing in the Pintados and Bellavista Salt Flats.

These variations are undoubtedly related to groundwater availability and physico-chemical features of the soil. Both factors are very important and interact to determine various conditions for the growth of the species.

Growth rate variations are related to groundwater table depth, availability of macro-and trace elements, salt concentrations and physical characteristics of the soil, but the degree of incidence of each of these factors in Tamarugo survival and growth rates, and fruit production, is unknown.

The Forestry Institute of Chile, in 1981, undertook a study intended to establish a correlation between the growth of the species and the presence and concentration of nutrients found by foliar analysis. A chemical analysis of soil samples was also made for all the sites selected for foliar analysis.

The relationship between mean growth and the concentration of a given nutrient at leaf level indicates the nutritional condition of the tree, with a potential for pinpointing the optimum levels of a given nutrient for growth and reflecting soil conditions.

The tamarugo plantations at the Pampa show no deficiency when observed as a whole, but, as previously stated, there is a great variation both among individuals and plantations. This may be an indication of different nutritional conditions among the trees.

A multiple regression analysis was used to determine the relationship between growth and foliar nutrient concentration, by means of a step-by-step algorithm which considered the independent variables —the nutrients contained in the leaves—, and the dependent variable, the mean annual height increment.

The data was processed at the Data Processing Center of the University of Chile (CEC), using a Statistical Package for the Social Sciences (SPSS).

3.5.1 Sectors Sampled

The sectors to be sampled were determined by means of stand grouping by age class. Each class was further divided according to height development. Last, groundwater table depth was also included as a variable. Basing on these parameters, 17 sites were selected for sampling (14 in young forests), within the Pintados and Bellavista Salt Flats. Samples from the native forests were also included.

Once the sites to be sampled had been established, their location was determined with the help of aerial photographs.

Three foliar samples were obtained from each sector, each containing leaves from 5 trees, and were analyzed for their N, P, K, Ca, Mg, Na, Cl, B, Fe, Cu, Mn, and Zn content, according to a method described by González et al (1973).

3.5.2 Findings

Table 14 shows the values obtained in the foliar analysis of tamarugo (September, 1981) for 14 young stands (8–15 years of age), with different mean annual height increment. The depth of the groundwater table is also included.

The more relevant findings and conclusions are as follows:

1. An interesting trend was observed in the relationship between the mean annual height increment rate (m/year) and the concentration of phosphorus (P) in the leaves (Fig. 5).

   This trend indicates better growth rates for concentrations ranging from 0.12–0.14% in the leaf.

   TABLE 14
   Foliar analysis for tamarugo (september) Mean values of foliar macro and micro nutrients by mean annual growth of various stands (INFOR 1981)

   Mean annual height gain (m/year)	Stand No	Age in 1981 (years)	Groundwa ter depth (m)		Mean values
   					Macro nutrients %							Micro nutrients p.p.m.
   					N	P	K	Ca	Mg	Na	Cl	B	Fe	Cu	Min	Zn
   0,24	169	13	12 y más		2,21	0,11	6,71	3,93	0,33	0,78	0,38	303,3	91,0	9,7	522,3	30,7
   0,24	166	13	6 –	12	2,04	0,07	0,81	3,11	0,40	0,96	0,96	319,7	96,0	22,7	359,3	59,0
   0,25	167	12	0 –	6	2,25	0,08	8,98	3,42	0,38	0,67	0,82	369,0	64,3	12,7	351,3	45,3
   0,45	7	8	6 –	12	2,47	0,09	0,79	2,77	0,27	0,38	0,82	384,0	94,7	94,7	17,3	45,0
   0,46	42	15	6 –	12	3,24	0,25	1,67	1,75	0,22	0,09	0,81	104,0	141,3	11,0	127,3	53,0
   0,55	44	12	6 –	12	2,79	0,18	1,26	2,08	0,30	0,13	0,55	157,3	94,7	12,3	236,3	40,0
   0,56	159	13	0 –	6	2,75	0,17	1,21	2,74	0,23	0,14	1,07	241,3	63,0	11,0	143,3	54,0
   0,64	148	10	0 –	6	2,83	0,18	1,39	2,13	0,20	0,11	0,87	164,0	90,0	12,3	185,3	50,0
   0,70	172	12	6 –	12	2,52	0,11	0,99	3,33	0,31	0,29	0,76	179,2	91,0	11,0	313,7	31,3
   0,72	136	9	0 –	6	2,75	0,14	1,11	2,40	0,25	0,31	0,63	290,3	64,3	13,3	252,7	33,0
   0,72	165	9	6 –	12	2,48	0,09	0,79	3,58	0,35	0,83	0,47	340,7	143,0	12,3	369,7	42,7
   0,75	150	14	0 –	6	2,64	0,12	1,10	2,64	0,25	0,35	1,44	384,0	58,7	19,0	184,0	39,7
   0,84	154	10	0 –	6	2,37	0,08	0,95	2,93	0,26	0,78	0,49	269,7	70,3	16,0	321,0	23,3
   0,88	163	12	6 –	12	2,54	0,13	1,18	2,35	0,16	0,26	1,04	274,7	49,7	15,0	146,0	37,0

   * Corresponds to same substratum as Stand No. 171.
   ** Corresponds to same substratum as Stand No. 43.

   From the above Table it can be drawn that there exists an inverse relationship between phosporus (P) and sodium (Na) in the leaves. Experiences with citrus trees have shown that plants with high-P-content micorrhizae have a lower content of Na in the leaves.

   A direct relationship is also observed between phosphorus (P) and nitrogen (N), i.e., a trend to rising concentration of one of these elements as the other's concentration increases. This may point out the importance of P in N fixation.

2. The concentration of the other elements is as follows:

   Boron (B)

   The content is extremely high, and it would be toxic for many plants, particularly fruit trees. No correlation is observed between boron content and growth rates (Jarrel 1982; Valdés 1982).

   Sodium (Na)

   The concentration range is very wide, with no correlation found between Na concentration and growth.

   Iron (Fe) and Copper (Cu)

   In most cases the contents of these elements can be rated as normal, as compared with some conifer species.

3. The study of the results of the multiple regression analysis shows that the correlation between growth and concentration is more marked in the cases of Mg, Zn, Mn, Na, Fe and K. These nutrients account for 91.6% of the behaviour of the dependent variable.

FIGURE 5

Trend of the mean annual height gain/% foliar P ratio in tamarugo.

Trend of the foliar N - P ratio in tamarugo.
7, 42, 44, 136, ...etc.: Stand No. (Basis: CORFO-INFOR 1981).

3.6 Fodder Production

The importance of this species as a fodder tree for livestock has prompted CORFO and INFOR to undertake several studies aiming at the determination of fruit and leaf yields.

3.6.1 Determining Fruit and Leaf Yield Rates

Fruit production in Tamarugo begins in the juvenile stage, at around 8 years of age (INFOR 1971). Usually the fruit is distributed evenly through the green canopy, with the distribution of the fruit on the ground equally uniform, except at the edge of the area beneath the crown, where pod density is higher (INFOR, 1964).

A trial intending to assess the yield of fruit and leaves was established by Frohlich (1977), where the production of 19 trees was controlled. Fruit and leaf collection reached 2.1 kg per square meter beneath the canopy.

Additionally, INFOR, in 1964, had carried out a preliminary survey by taking samples of fruit from the same trees, which at that time had ages ranging from 18 to 30 years. Average output was found to be 2.6–3.4 kg per square meter beneath the crown of 30-year-old trees, and 1.8 kg/sq.m. for 18-year-old trees. The composition was established at 50% fruit and 50% leaves, from where the mean fruit yield was concluded to be 1.2kg/sq.m.

Fodder production was measured by INFOR in 1971 at the permanent plots it had established in 1964, placing 1-sq.m. trays under two specimens picked up at random in plantations over 6 years of age. The allocation of trays was as follows: 6–9 years old, 3 trays; 12–18 years old, 6 trays; 21 years and older, 9 trays. These were distributed beneath the canopy in three radii 120° apart, with one always placed in a northerly direction. Fruit and leaves were weighed separately for each collection, carried out in January, February, March, July, September and December.

Output records were made taking into consideration age, groundwater table depth, and salinity.

The CORFO SACOR Agricultural Society carried out a sampling in 1980 and 1981, aimed at establishing fruit and leaf yields for tamarugo and algarrobo. Trees were classified into three sizes: small, medium and large. Yield was established for each category. Trees under 3 m in height and 3 m in crown diameter were rated as small; medium sized ones ranged from 3–5 m in height, with crown radius up to 5 m; large trees were taller than 5 m and with crown radius exceeding 5 m.

25-cm-wide wooden canoes were used to collect the fruit, placed along the whole legth of the radii of the crown projection area; leaves were collected in the entire area of projection.

3.6.2 Fodder Yield Findings

According to the findings of the survey carried out by INFOR in 1971, fruit yield distribution is as follows: January, 15%; February, over 60%; and March, 16%. The remaining 5.7% is spread among the months of July, September and December.

As regards leaf production, most of the yield occurs from July through December, with 84.8% of the total. The remaining 15.2% was collected in January, February and March.

Table 15 includes the findings for fruit and leaf yields in kg per square meter from the afo-rementioned study, over a period of 12 months.

TABLE 15
Tamarugo Fruit and Leaf Yields in kg/m² Over a Period of 12 Months

The two figures per plot in some columns come from the two trees making up the sample.

The findings determined by the CORFO-SACOR Agricultural Society are computed individually for every tree, and are expressed in grams of dry matter.

The data included in Table 16 summarize the fodder production findings per year (1981 and 1982) for tamarugo and algarrobo.

TABLE 16
Fodder Yield Summary for tamarugo and algarrobo Pampa del Tamarugal

Source: SACOR Ltda. (CORFO, 1982).

The characteristics of each species are as follows:

Figure 6.

The analysis of the above Table shows that fodder production is significantly higher in trees rated as “large”. Great variability is also observed in the yearly output among the species, probably from features of the trees themselves, and/or from phytosanitary conditions. This difference is also observed within the same species, in the same age bracket and at the same place of planting.

The findings of both institutions reveal the need of further research to establish the fodder yield of each species with greater certainty.

4. REGENERATION AND FOREST MASS FORMATION

4.1 Natural Regeneration

Abundant natural regeneration —particularly of tamarugo— was observed during the course of research conducted in the area of La Tirana in 1981. This fact, undoubtedly, stems from the flood caused in 1977 by the Altiplanic winter. The assumption for this regeneration is that the fruit was carried by the water —and destroyed in the process—, with a subsequent mechanical scarification of the seed. Once the waters receded, seeds settled and began to germinate profusely.

The natural regeneration process, according to Lanino (1978), does not take place on soils with surfaced salt crust. This may be due to excessive salt concentration in the soil mix, barring seedling development.

The natural regeneration in the above mentioned area is very open and heterogeneous.

4.2 Artificial Regeneration

The method for establishing tamarugo and algarrobo plantations has remained practically unchanged since last century. In fact, Billinghurst (1893), in his memoirs, describes a very similar technique to what still remains in use:

a) The seeds to be used for plant production are obtained from seed orchards, collected directly from the ground. Clean seeds are obtained by grinding the fruit with a hand mill, and sieving and floating the milled material.

As germination is very irregular and slow, due to the hardness of the sclerenchymatic tissue, it is necessary to make the seed undergo a mechanical or chemical scarification process to improve germination. The latter process is more commonly used, with concentrated sulphuric acid. Acid treatment of the seed varies from 8 to 12 minutes (Carvallo 1970).

Seedlings are raised outdoors. Seeds are sown in pots with a 2:1 mixture of soil and sheep manure. Sowing time is irrelevant, influencing only development rates, slower when carried out in winter. Watering is done every 4–5 days; the seeds remain in the nursery 3 to 5 months.

b) Planting is performed by removing the salt crust manually or mechanically, and making a suitable preparation of the ground to store irrigation water. Planting pit dimensions are about 80 cm in diameter, depth according to thickness of the salt crust. The planting hole itself is dug inside this pit, 20 cm in diameter and 50 cm deep.

As the Pampa soils lack organic matter, a mix of soil and manure is added to the pit before planting, in equal proportion as the nursery mix (Carvallo 1970).

4.2.1 Irrigation

To help seedling root formation, it is necessary to perform some watering the first few months after planting. The number of waterings depends on underground water table depth and soil texture (Lamagdelaine 1972). An average estimate for the establishment period is 11 waterings (FAO/BID 1970). The amount of water per irrigation and pit is 10 liters, every 5–10 days.