Introduction

Does the non-masting red maple species exhibit muted dynamics compared to the masting sugar maple species? This question, asked by those at The Harvard Forest Long-Term Ecological (LTER) program, is trying to determine whether there is a slower rate of change in ecological communities between trees who exhibit non-masting and masting species. Non-masting seed output refers to the trees producing a consistent amount of seeds per each year and masting refers to irregular bursts of seeds, with some having higher amount, and others lower. These on and off years of masting affect the sap production during those times. Over time non-masting leaves create lower variability in a forest while masting leaves create higher variability.

Variable Description:
Maple Data Set

These variables come from the maple_seed_count, maple_sap, and maple_tap data sets.

Sap Weight Model: Sugar vs Red Maple Trees

The ANOVA model below shows Sugar_vs_Red. This model is displaying how fit the data is for the sap weight per each type of maple tree: red (ACRU) and sugar (ACSA).

## 
## Call:
## lm(formula = sap_wt ~ species, data = maple_sap)
## 
## Residuals:
##     Min      1Q  Median      3Q     Max 
## -4.1475 -2.2575 -0.5975  1.6225 19.8825 
## 
## Coefficients:
##             Estimate Std. Error t value Pr(>|t|)    
## (Intercept)  1.89603    0.09755   19.44   <2e-16 ***
## speciesACSA  2.26149    0.10379   21.79   <2e-16 ***
## ---
## Signif. codes:  0 '***' 0.001 '**' 0.01 '*' 0.05 '.' 0.1 ' ' 1
## 
## Residual standard error: 3.054 on 8389 degrees of freedom
##   (631 observations deleted due to missingness)
## Multiple R-squared:  0.05356,    Adjusted R-squared:  0.05345 
## F-statistic: 474.7 on 1 and 8389 DF,  p-value: < 2.2e-16

Results

When comparing the sap weight between only the species variable, ACSA weight slightly less than the ACRU species. Although this difference looks small, the small p-values for both are < 0.05 meaning these differences are significant.

(p<2e-16; ACSA) (p<2e-16; ACRU)

The fit for this model is very low (R2: 0.05345). A further investigation was made to determine the reasoning for this by using a histogram.

Sap Weight Histogram

These models show how well these data are fit to each other. The red color represent the Red Maple (ACRU) species and the teal color represent the Sugar Maple (ACSA) species.

Results

These plots show that the ACRU data has a significant amount less count and total sap weight than the ACSA data. This explains the low R-Squared value depicted in the ANOVA test above.

Date Model: Sugar Maples

The ANOVA model below shows sugar_maple. This model is displaying how fit the data is of the date of collection and the total count of that collection is for the sugar maple (ACSA) species.

## 
## Call:
## lm(formula = total.count ~ date, data = sugar_maple_seed)
## 
## Residuals:
##    Min     1Q Median     3Q    Max 
## -20.91 -16.68 -12.56  18.06  61.31 
## 
## Coefficients:
##               Estimate Std. Error t value Pr(>|t|)   
## (Intercept)  6.526e+01  2.339e+01   2.790  0.00574 **
## date        -3.293e-08  1.584e-08  -2.079  0.03877 * 
## ---
## Signif. codes:  0 '***' 0.001 '**' 0.01 '*' 0.05 '.' 0.1 ' ' 1
## 
## Residual standard error: 23.61 on 218 degrees of freedom
## Multiple R-squared:  0.01945,    Adjusted R-squared:  0.01495 
## F-statistic: 4.323 on 1 and 218 DF,  p-value: 0.03877

Results

When comparing the date and the total count of the sugar maple species, the total count showed significant, while the date showed statistically insignificant.

(p = 0.00574; total.count) (p = 0.03877; date) (R2 = 0.01495)

Discussion

Sap weight and species have statistical significance, but since there are such different numbers of each species accounted for, there isn’t a fair comparison to be made with these data above. The ANOVA test shows significance in both these tree species, and it also shows that the data isn’t fit to the null hypothesis. This means that these data likely align with an alternate hypothesis.

Total count has statistical significance, while date does not. Since these data are only a compilation of data points from sugar maple species, a fair comparison between the two maple species is unable to be made. Although the date is shown as an insignificant value, this is still important to know as it can be used later to determine whether that changes or not. Given the significance for the sugar maple tree in both sap weight and total.count, there is likely a correlation in the dynamics exhibited from this species.

Masting is an important ecological factor that helps enhance the reproductive efficiency of trees as well as having many important ecological impacts that trickle down the ecosystem. By creating an overabundance of seeds and fruit, the trees keep predators away, creating time for new trees to bury and flourish in surrounding areas. Given the lack of connection in these data, a more timely and organized experiment is needed to truly understand the impacts of everything being collected and researched by the LTER program. These data gave a great foundation for questions and further ecological investigation for those same researchers, or those interested in the subject after them.

Reference Joshua, R., Elizabeth, C., & Kristina, S. (2015). Data Portal - Metadata Viewer | Environmental Data Initiative (EDI). Edirepository.org. https://portal.edirepository.org/nis/metadataviewer?packageid=knb-lter-hfr.285.6