> weed <- read.csv(file.choose(), header=TRUE)
> weed.mod=aov(Density~Year+factor(Quadrant), data=weed)
> anova(weed.mod)
Analysis of Variance Table

Response: Density
                Df Sum Sq Mean Sq F value    Pr(>F)
Year             1 3444.5  3444.5  62.838 1.920e-07 ***
factor(Quadrat)  4 3439.8   859.9  15.688 7.909e-06 ***
Residuals       19 1041.5    54.8
---
Signif. codes:  0 ‘***’ 0.001 ‘**’ 0.01 ‘*’ 0.05 ‘.’ 0.1 ‘ ’ 1
> TukeyHSD(weed.mod)
  Tukey multiple comparisons of means
    95% family-wise confidence level

Fit: aov(formula = Density ~ Year + factor(Quadrat), data = weed)

$`factor(Quadrat)`
     diff        lwr        upr     p adj
2-1  11.2  -2.881403  25.281403 0.1604470
3-1  32.6  18.518597  46.681403 0.0000111
4-1   1.0 -13.081403  15.081403 0.9994923
5-1  12.0  -2.081403  26.081403 0.1180825
3-2  21.4   7.318597  35.481403 0.0017334
4-2 -10.2 -24.281403   3.881403 0.2299065
5-2   0.8 -13.281403  14.881403 0.9997901
4-3 -31.6 -45.681403 -17.518597 0.0000170
5-3 -20.6 -34.681403  -6.518597 0.0025251
5-4  11.0  -3.081403  25.081403 0.1727971

Warning messages:
1: In replications(paste("~", xx), data = mf) : non-factors ignored: Year
2: In TukeyHSD.aov(weed.mod) :
  'which' specified some non-factors which will be dropped
> weed <- read.csv(file.choose(), header=TRUE)
> weed.mod=aov(Density~Year+factor(Quadrant), data=weed)
> anova(weed.mod)
Analysis of Variance Table

Response: Density
                 Df Sum Sq Mean Sq F value    Pr(>F)
Year              1 3444.5  3444.5  62.838 1.920e-07 ***
factor(Quadrant)  4 3439.8   859.9  15.688 7.909e-06 ***
Residuals        19 1041.5    54.8
---
Signif. codes:  0 ‘***’ 0.001 ‘**’ 0.01 ‘*’ 0.05 ‘.’ 0.1 ‘ ’ 1
> TukeyHSD(weed.mod)
  Tukey multiple comparisons of means
    95% family-wise confidence level

Fit: aov(formula = Density ~ Year + factor(Quadrant), data = weed)

$`factor(Quadrant)`
     diff        lwr        upr     p adj
2-1  11.2  -2.881403  25.281403 0.1604470
3-1  32.6  18.518597  46.681403 0.0000111
4-1   1.0 -13.081403  15.081403 0.9994923
5-1  12.0  -2.081403  26.081403 0.1180825
3-2  21.4   7.318597  35.481403 0.0017334
4-2 -10.2 -24.281403   3.881403 0.2299065
5-2   0.8 -13.281403  14.881403 0.9997901
4-3 -31.6 -45.681403 -17.518597 0.0000170
5-3 -20.6 -34.681403  -6.518597 0.0025251
5-4  11.0  -3.081403  25.081403 0.1727971