SLASH PINE SITE PREPARATION STUDY RESULTS AT AGE 11. Plantation Management Research Cooperative. Warnell School of Forest Resources

Transcription

1 SLASH PINE SITE PREPARATION STUDY RESULTS AT AGE Plantation Management Research Cooperative Warnell School of Forest Resources University of Georgia PMRC Technical Report 99- Prepared by L. V. Pienaar, B. D. Shiver, J. W. Rheney

2 P M R C SLASH PINE SITE PREPARATION STUDY RESULTS AT AGE This study was initiated in 979 in the lower coastal plain of southeast Georgia and north Florida. The objective of this long-term study was to develop site-specific yield prediction models for commonly used site preparation treatments, in conjunction with an early fertilizer application and complete control of competing vegetation. Four Soil Conservation Service (SCS) soil drainage classes are represented in this study, namely Nonspodic soils. ) poorly drained 2) somewhat poorly to moderately well drained Spodic soils. 3) poorly to moderately well drained with underlying argillic horizon 4) poorly to moderately well drained without underlying argillic horizon Five sites were selected in each of these 4 SCS soil drainage classes for a total of 20 separate installations, with a balance between spodosols and nonspodosols. Only 6 installations, 9 spodosols and 7 nonspodosols remain available for analysis. All installations were located in existing unfertilized non-old-field slash pine plantations over 20 years old. Each installation consists of 2 half-acre treatment plots. Total tree height was measured on a sample of dominant and codominant trees in the existing plantation and a site index was calculated for each potential treatment plot using a site index equation for site-prepared slash pine plantations in the lower coastal plain developed by

3 Newberry and Pienaar (978). The maximum allowable range of site indices over all plots in an installation was 5 ft. in order to insure some degree of homogeneity in site quality at each location. The range of site indices over the installations was from 55 to almost 80 ft. (base age 25 years). Existing plantations were harvested in 978. Treatment plots were siteprepared in 978/79 and were hand-planted during the 979/80 planting season with genetically improved slash pine seedlings grown in a single nursery. Seedlings were planted on an approximate 8' x 0' spacing with two seedlings planted approximately 2 ft. apart at each planting location. Surviving doubles were removed at the end of the second growing season to ensure a reasonably uniform stocking of about 545 trees per acre over all plots. One plot at one of the 6 installations has since been abandoned due to damage sustained during company operations. Eleven treatments were included at each installation with the 2th plot being used to duplicate one of the treatments 2 through as shown in Table. The control plot was planted after harvest without any further treatment. The chop was a single pass with a drum chopper, and the burn was a broadcast burn after the chopped brush had been allowed to dry for several weeks. Bedding was done by means of a double pass with a bedding harrow to insure a well-formed bed. The fertilizer was 250 pounds of di-ammonium phosphate (DAP) applied in a 4-ft. band on the rows at the beginning of the second growing season. The herbicide treatment was complete control of competing vegetation to establish the maximum yield increase attainable from complete competition control. Vegetation was sprayed with a 3% solution of Roundup prior to any site preparation. After pines were planted they were shielded when further applications of Roundup and Garlon were used as needed to maintain complete control until crown closure.

4 Table. Treatment definitions Treatment Action Control 2 Chop - Unfertilized 3 - Fertilized 4 Chop + Burn - Unfertilized 5 - Fertilized 6 Chop + Burn + Bed - Unfertilized 7 - Fertilized 8 Chop + Burn + Herbicide - Unfertilized 9 - Fertilized 0 Chop + Burn + Bed + Herbicide - Unfertilized - Fertilized

5 Each treatment plot was /2-acre with a /5-acre interior measurement plot. Every tree in each measurement plot was measured for dbh with a diameter tape and every other tree was numbered and measured for total height to the nearest ft. Every tree was examined for Cronartium stem cankers. Measurement plots have been measured and evaluated in this manner at ages 2, 5, 8 and. Results and Discussion. This designed study has a split-plot structure with soil groups representing whole plots, and was analyzed as such. Separate analyses were made of average tree height, basal area per acre, total volume per acre, and percent of trees with Cronartium stem cankers. Analysis of variance tables are in the Appendix. In all cases there were no significant differences in overall response between the two SCS soil classes in either the spodosols, or the nonspodosols. All analyses of variance and associated contrasts included in the Appendix were therefore based on only 2 soil groups; spodic soils represented by 9 installations, and nonspodic soils represented by 7 installations. Average Tree Height. ANOVA and contrast analysis results for average tree height at age are given in Table A. in the Appendix. Average height for spodosols over all treatments (3.3 ft.) was not significantly different from the nonspodosols (32.8 ft.). Treatment had a highly significant effect on average height and there was a highly significant interaction between soil group and treatment effects. tree height at age for the treatments by soil group. Table 2 shows average Figure provides histograms of average tree height for the different treatments and shows the difference in treatment effects on spodosols and nonspodosols. Contrast analyses indicated that chopping, bedding, fertilizer and herbicide all had highly significant effects on average height on nonspodic

6 Table 2. Average tree height at age for different treatments on spodosols and nonspodosols. Treatment # Spodosols (ft.) Nonspodosols (ft.)

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8 soils. On spodic soils chopping and burning did not have any significant effect. On spodic soils an average difference between treatment means of approximately 2.6 ft. would be considered significant at the 95% confidence level. While chopping and chopping + burning had no significant effect, the fertilizer resulted in an increase of 3-4 ft. in average height, as did the bedding, and these effects were additive. The effect from complete competition control, without bedding, was almost 0 ft. in average height, and with bedding it resulted in an increase of 8 ft. With complete competition control the fertilizer effect was not significant. On nonspodosols an average difference between treatment means of approximately 2.5 ft would be judged significant. In this case there is a fairly consistent and constant additive effect on average height from chopping, from burning, from bedding, from competition control and from fertilizer, with the smallest effect from burning and the largest effect from competition control. Height Growth Anova and contrast analyses of average height growth from age 8 to are in Table A.2 in the Appendix. Table 3 shows the average height growth from age 8 to for the different treatments and for the two soil groups. Average height growth over all treatments for spodosols (8.9 ft.) was not significantly different from nonspodosols (9.4 ft.). The treatments had a highly significant effect on height growth, but there was no longer a highly significant interaction between treatments and the soil groups. Figure 2 provides histograms of average height growth for the treatments and the two soil groups. Contrast analyses indicated that chopping still had a significant effect on average height growth on nonspodosols. There were no significant added

9 Table 3. Average height growth from age 8 to for different treatments on spodosols and nonspodosols. Treatment # Spodosols ft. Nonspodosols ft

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11 effects from the burn, bed and herbicide treatments, but there was a significant fertilizer effect. On spodosols only the herbicide treatment had a significant added effect. The overall fertilizer effect was not significant, with the positive effect with chop and chop + burn treatments largely offset by the negative effect with bedding and herbicide treatments. Results indicate that the early treatment effects on average height are being maintained on nonspodosols, whereas the more intensive treatments continue to have a positive effect on height growth on spodosols. Average height growth curves from age 2 to are shown in Figure 3 for two of the treatments: #6, chop + burn + bed, and #0, CHOP + BURN + BED + HERB. These two treatments were chosen to illustrate the dramatic effect of competing vegetation on early height growth. While the difference in average height growth between treatments had declined by age, the curves were still diverging slightly. These two sets of curves also illustrate the interaction between treatments and soil groups. Nonspodosols performed better than spodosols with treatment #6, but spodosols benefited much more from the competition control of treatment #0, so that the situation was actually reversed with spodosols performing better than nonspodosols with treatment #0. Basal Area Per Acre Anova and contrast analyses of the basal area per acre at age are given in Appendix Table A.3. The average basal area on spodosols (65.22 sq. ft.) was not significantly different from nonspodosols (67.74 sq. ft.). Treatment effects were highly significant overall and also differed significantly between the two soil groups. Table 4 shows average basal area per acre at age for the different treatments by soil group, and Figure 4 displays the results in the form of histograms. On spodosols neither chopping nor chopping + burning had a significant effect on basal area per acre at age, but for both these treatments adding fertilizer had a significant positive effect, as did bedding, with the bedding

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13 Table 4. Average basal area per acre at age for different treatments on spodosols and nonspodosols. Treatment # Spodosols sq. ft./ac Nonspodosols sq. ft./ac

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15 and fertilizer effects being additive. An average difference between treatment means of 9-0 sq. ft. would be judged significant at the 95% confidence level. The herbicide treatment (complete completion control) had the most dramatic effect with an increase of over 40 sq. ft. Both the bedding and fertilizer treatments had a diminished and non-significant effect on plots that received the herbicide treatment. On nonspodosols there is a more consistent additive effect from chopping, burning, bedding and competition control, with a somewhat less constant added fertilizer effect. The herbicide treatment had the highest added effect of just over 20 sq. ft., but not as dramatic as on the spodosols. On nonspodosols an average difference of about 8-9 sq. ft. would be judged significant. Total Stem Volume Per Acre. Individual stem volumes were calculated with a simultaneous total and merchantable standard volume equation (PMRC 985-5). Heights of trees that were not measured were estimated by means of an appropriate regression equation. Treatment effects on total stem volume at age are summarized in Table 5 for the two soil groups, and are displayed in the form of histograms in Figure 5. The average volume per acre over all treatments for spodosols (65 cu. ft.) was not significantly different from nonspodosols (24 cu. ft.). Analysis of variance and contrast analyses in Table A.4 parallel those for basal area per acre, and the same trends are apparent in Figure 4. Treatment effects were highly significant with the better treatments having 3 times the volume of the control, and a significant interaction between the treatments and the two soil groups. On spodosols chopping and chopping + burning did not effect total stem volume at age, but adding fertilizer did have a significant positive effect as did bedding, and the bedding and fertilizer effects appear to be additive, each contributing about 300 cu. ft. An average difference between treatment

16 Table 5. Average total volume per acre at age for different treatments on spodosols and nonspodosols. Treatment # Spodosols cu. ft. Nonspodosols cu. ft

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18 means of about 220 cu. ft./acre would be judged to be significant. An increase of about 900 cu. ft. resulted from the control of all competing vegetation and on these plots the bedding and fertilizer effects were less obvious and not significant. On nonspodosols, as in the case of basal area, there is a more consistent additive effect from chopping, burning, bedding, fertilizing and herbicide treatment. The greatest effect was due to competition control (about 500 cu. ft.), but not as dramatic as it was on spodosols. Cronartium Stem Infection. The percentage of the trees with one or more visible stem cankers was calculated for each measurement plot. Table 6 shows the average percentage of infected trees for each of the treatments on the two soil groups. The average infection rate on spodosols over all treatments (2%) was only half the infection rate on nonspodosols (24%), however, this difference was not significant given the high variability among treatments. Analysis of variance and contrast analyses of Cronartium stem infection at age appear in Table A.5. Treatment differences were highly significant, and treatment effects did not differ significantly on the two soil groups. The contrast analyses indicate that the herbicide treated plots, and in general, the treatments with the highest initial growth rates, had a significantly higher infection rate. Figure 6 shows the average infection rates for the treatments in the form of histograms for the two soil groups. Relevance to Current PMRC Yield Prediction System It is informative to use our current PMRC yield prediction system (PMRC 990-3) to predict per-acre basal area (BA) and total stem volume inside bark (TVIB) at age for the different treatment plots, and to compare these predictions with the observed basal areas and volumes (using the standard volume equation to calculate individual tree volumes). Table 7 shows the observed average basal area per acre for treatments -, as well as the average of the predicted basal areas for the plots that

19 Table 6. Average percent Cronartium stem infections at age for different treatments on spodosols and nonspodosols. Treatment # Spodosols % Nonspodosols %

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21 Table 7. Average observed and predicted basal area and volume per acre for different treatments at age. Treatment Basal Area (sq. ft.) Total Stem Volume (TVIB cu. ft.) # Plots Obs. Pred. Obs. Pred. Pred

22 received each treatment. For treatments -7 the basal area prediction equation does quite well. However, for all plots where competing vegetation had been eliminated, the basal areas are seriously underpredicted. Compared to less intensive treatments, this implies a different stem form and/or diameter distribution for these plots. The average volume inside bark as calculated with the standard volume equation is shown in the table as observed volume. The average predicted volume by the PMRC per-acre volume prediction equation, using the observed basal area as input, is shown as Pred., and the average predicted volume when the predicted basal area is used as input, is shown as Pred. 2. The volume prediction equation clearly performs satisfactorily for all treatments when the observed basal area is used in the prediction equation. When the predicted basal area is used, it seriously underpredicts the volume for treatments 8, 9, 0 and, which is understandable since the basal areas were seriously underpredicted. Basal area per acre is an input variable for the PMRC diameter distribution prediction system. We can generate two predicted diameter distributions; one with actual measured basal area as input, and one with predicted basal area from the PMRC basal area prediction equation using age, average dominant height and trees per acre as input variables. Figure 7 shows frequency histograms for a typical vegetation control plot. In most cases, if the actual basal area is provided, the actual distribution (Figure 7.a) and the predicted distribution (Figure 7.b) agree reasonably well. When the predicted basal area is used as input to the diameter distribution model for treatments 8- (Figure 7.c), the range of diameters is increased and the modal class is shifted to the left. In treatments 8- there are more uniformly large trees than on other plots with the same age, dominant height and trees per acre. Table 8 shows the average coefficient of variation (C.V.) for the different treatments, for the observed diameter distributions, as well as for the predicted distribution using the actual basal area, and for the predicted distribution using the predicted basal area. As the treatment intensity

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24 Table 8. Average coefficient of variation (CV%) of dbh for the different treatments. Treatment # Observed Distribution Predicted with Observed Basal Area Predicted with Predicted Basal Area

25 increases, the CV decreases, which is indicative of relatively less variability and more peaked diameter distributions. The CV's for the observed distribution and the predicted distribution using the observed basal area match well, an indication that the PMRC diameter distribution prediction model produces the necessary peaked distributions when provided with the correct basal area. A statistical test (K-S test) was made to test the hypothesis that the predicted diameter distributions and the observed distribution are the same. Table 9 is a summary of the results. Only % of the predicted distributions differed significantly ( = 0.05) from the observed distributions when the diameter distribution prediction model is provided with the observed basal area. If the predicted basal area is used 4% of the predicted distributions differed significantly from the observed. In almost all cases there was a corresponding large error in estimating the basal area for fertilized and/or vegetation control plots. It is clear that when either observed or accurate basal area estimates are available, the current PMRC yield prediction system provides acceptable estimates of total per-acre volume and of the stand tables for all treatments. The current per-acre basal area prediction equation provides acceptable estimates for treatments -7, but not for treatments 8- where all competing vegetation had been eliminated with the herbicide treatment. Consequently, the per-acre volumes and stand tables are poorly estimated for treatments 8-. This problem can be resolved by providing a better estimate of basal area either by means of an inventory or by developing a prediction equation that reflects the treatment differences. As an example, separate basal area prediction equations for treatments -7 and 8- for the age data provided the estimates in Table 0.

26 Table 9. Results of K-S tests of differences in observed and predicted dbh distributions for different treatments. Treatment # Number of Distributions Observed BA # Sign Diff Predicted BA # Sign Diff Obs-Pred BA sq. ft./ac Total

27 Table 0. Average observed and predicted basal area using different equations for treatments -7 and 8-. Treatment # No. Plots Observed BA sq. ft. CV % Predicted BA sq. ft

28 APPENDIX

29 Table A.. ANOVA and Contrast Analyses for Average Height. SOURCE df SS MS F PROB OF GREATER F SOIL INST (SOIL) TRT SOIL x TRT TRT x INST (SOIL) REP (TRT & INST) CORR. TOTAL * * not additive due to unbalanced design CONTRAST SOIL df SS F PROB OF GREATER F FERT VS UNFERT HERB VS NO HERB BED VS NO BED BURN VS NO BURN CHOP VS CONTROL

30 TABLE A.2. ANOVA and Contrast Analyses for Average Height Growth from Age 8. SOURCE df SS MS F PROB OF GREATER F SOIL INST (SOIL) TRT SOIL x TRT TRT x INST (SOIL) REP (TRT & INST) CORR. TOTAL 90 * * not additive due to unbalanced design CONTRAST SOIL df SS F PROB OF GREATER F FERT VS UNFERT HERB VS NO HERB BED VS NO BED BURN VS NO BURN CHOP VS CONTROL

31 TABLE A.3. ANOVA and Contrast Analyses for Basal Area Per Acre at Age. SOURCE df SS MS F PROB OF GREATER F SOIL INST (SOIL) TRT SOIL x TRT TRT x INST (SOIL) REP (TRT & INST) CORR. TOTAL * not additive due to unbalanced design CONTRAST SOIL df SS F PROB OF GREATER F FERT VS UNFERT HERB VS NO HERB BED VS NO BED BURN VS NO BURN CHOP VS CONTROL

32 TABLE A.4. ANOVA and Contrast Analyses for Total Stem Volume Per Acre at Age. SOURCE df SS MS F PROB OF GREATER F SOIL INST (SOIL) TRT SOIL x TRT TRT x INST (SOIL) REP (TRT & INST) CORR. TOTAL * * not additive due to unbalanced design CONTRAST SOIL df SS F PROB OF GREATER F FERT VS UNFERT HERB VS NO HERB BED VS NO BED BURN VS NO BURN CHOP VS CONTROL

33 TABLE A.5. ANOVA and Contrast Analyses of Cronartium Stem Infection at Age. SOURCE df SS MS F PROB OF GREATER F SOIL INST (SOIL) TRT SOIL x TRT TRT x INST (SOIL) REP (TRT & INST) CORR. TOTAL * not additive due to unbalanced design CONTRAST SOIL df SS F PROB OF GREATER F FERT VS UNFERT HERB VS NO HERB BED VS NO BED BURN VS NO BURN CHOP VS CONTROL