After the whole-tree harvest of Watershed 5, periodic vegetation surveys were conducted to track the regrowth of total biomass, and to evaluate the changing species composition and nutrient status of the watershed.  Included here is a short summary of the results to date.

        1. Biomass
        2. Phytosociology
        3. Nutrients
        4. Methods
 
 
 

1. Biomass

         In the summer of 1999, we surveyed the vegetation on the watershed for the sixth time since it was clearcut in the fall of 1983 into the winter of 1984.  From each of these samples we have estimated the total amount of aboveground biomass on the watershed and can follow biomass accretion through time (see graph below).  The curve reflects what we might expect--something approaching exponential growth in these early years of forest regeneration.

        Watershed 6 (the adjacent reference watershed) was first surveyed in 1965, when the forest was about 55 years old.  Superimposing the Watershed 6 biomass onto the W5 graph, we can estimate what W5 may look like as the forest ages (see graph below).  The W5 forest will be 55 years old in the year 2039.  The bars between 2039 and 2071 on the graph below represent the calculated biomass (in grams/m²) of W6 between 1965 and 1997, and stand in as a representation of what W5 might look like if its long-term regrowth were similar to that of W6 after it was logged in the early 1900s.

 
 
 

2. Phytosociology

        Two standard phytosociological tables are included below for the live and dead stems from the 1999 plot surveys.  Beech has overtaken pin cherry as the most abundant species.  This is noteworthy in that we have watched beech proliferate in the understories of the uncut areas of the forest for the last 30 years.  Beech is apparently capable of proliferating in regenerating forests as well. As we might expect, sugar maple is not very abundant on W5.  The forest is clearly dominated by yellow and white birch, which together make up 42% of the stems.  Whereas there are no white birch on W6 below the top, it appears the W5 forest is going to be dominated by them for some time.

        Pin cherry dominated the W5 forest early on.  Most individuals of this shade intolerant species have by now been suppressed--over 70% of the dead stems are pin cherries.

Species     Basal    Rel. Density   Rel.  Freq.   Rel.  Importance 
             area     BA  # trees  dens.          freq.  Value
            m2/ha     %      /ha     %      %       % 
-----------------------------------------------------------------------------

   Beech          2.71    16.27  3693.37    25.14    87.13    16.45    19.28
   White birch    2.88    17.28  3446.90    23.46    78.22    14.77    18.50
   Pin cherry     4.95    29.74  2133.36    14.52    76.24    14.39    19.55
   Yellow birch   3.43    20.62  2800.08    19.06    83.17    15.70    18.46
   Striped maple  0.66     3.97   795.59     5.41    47.52     8.97     6.12
   Sugar maple    0.51     3.08   606.82     4.13    40.59     7.66     4.96
 
   Balsam fir     0.71     4.24   357.55     2.43    25.74     4.86     3.85
   Red maple      0.19     1.13   286.78     1.95    26.73     5.05     2.71
   Mt. ash        0.14     0.87   262.88     1.79    17.82     3.36     2.01
   Red spruce     0.13     0.77   108.98     0.74    15.84     2.99     1.50
   Aspen          0.17     0.99    88.19     0.60    14.85     2.80     1.47
   White ash      0.08     0.46    55.39     0.38     8.91     1.68     0.84
   Willow         0.06     0.34    24.56     0.17     2.97     0.56     0.35
   Mt. maple      0.01     0.08    17.72     0.12     1.98     0.37     0.19
   Black cherry   0.02     0.12    11.68     0.08     0.99     0.19     0.13
   Alt. Lv
   Dogwood        0.00     0.03     3.89     0.03     0.99     0.19     0.08


No of plots =  101 
Total BA    =  16.65
Tot density = 14694

Species     Basal   Rel. Density   Rel.  Freq.   Rel.  Importance 
             area    BA  # trees  dens.          freq.  Value
            m2/ha    %      /ha     %      %       % 
-----------------------------------------------------------------------------

   Pin cherry    1.17    80.85  1677.34    70.88    74.26    41.90    64.54
   White birch   0.09     6.46   203.08     8.58    27.72    15.64    10.23
   Beech         0.07     4.65   199.78     8.44    25.74    14.53     9.20
   Yellow birch  0.05     3.67    94.15     3.98    12.87     7.26     4.97
   Striped maple 0.03     1.81    86.61     3.66    14.85     8.38     4.62


   Sugar maple   0.01     0.70    43.32     1.83     8.91     5.03     2.52
   White ash     0.00     0.18    11.74     0.50     2.97     1.68     0.78
   Mt. maple     0.01     0.57     3.38     0.14     0.99     0.56     0.43
   Mt. ash       0.00     0.32    15.65     0.66     1.98     1.12     0.70
   Red maple     0.00     0.10     7.82     0.33     1.98     1.12     0.52
   Aspen         0.01     0.51    15.81     0.67     2.97     1.68     0.95
   Unknown       0.00     0.12     3.79     0.16     0.99     0.56     0.28
   Black cherry  0.00     0.06     3.89     0.16     0.99     0.56     0.26


No of plots =  101 
Total BA =     1.45 
Tot density =  2366

 
 

3. Nutrients

        Nutrient analysis of collected material was conducted for each sampling year.  By calculating total aboveground biomass by plant part (i.e. leaves and wood) for each species or group, and multiplying by the element concentration in that tissue, we arrived at a total aboveground nutrient amount for each of several elements for each year (see table below). As expected, the total amount of nutrients stored aboveground increases as the biomass increases.

         Saplings were not collected from plots, but we were able to opportunistically harvest about 150 saplings of various species from W5 in 1998.  These were analyzed for wood chemistry and the resulting concentrations were used to estimate nutrients in the 1999 sapling biomass.  Leaf concentrations by species were gleaned from the analysis of other trees at Hubbard Brook Experimental Forest.

 
 

4. Methods

        In each of the six sampling years, the herbaceous layer was surveyed in 100 1 x 1 meter plots scattered throughout the watershed.  Herbs and shrubs were clipped from the plots and collected to obtain biomass (dry weight) and nutrient concentration.  Spinulose wood fern and raspberries were collected separately, while most other herbs and other shrubs were pooled.  Trees less than 50 cm tall were also cut and collected--we refer to this size class as "seedlings", but it also includes stunted and suppressed saplings.  Pin cherry was collected separately, but all other "seedlings" were pooled.  Trees greater than 50 cm tall but less than 1.5 cm dbh were measured for diameter at the base and at breast height, but not clipped.  Their biomass was estimated using allometric equations developed from other trees in this size class at Hubbard Brook Experimental Forest.

        Once the trees began to reach diameters greater than 1.5 cm, a second sampling method was added to capture these larger trees.  All trees greater than 1.5 cm dbh were surveyed on a 1 meter wide strip along one edge of each of 100 of the 25 x 25 meter grid units.    (These plots are therefore 25 m² in area, except in cases where the plots were slightly longer or shorter due to drift of the corner poles over time.  The exact length of each plot was measured and recorded and used in the subsequent calculations.)  Species, vigor (live or dead), and dbh in cm was recorded for each tree.  Biomass of these trees was estimated with allometric equations developed at Hubbard Brook Experimental Forest for each tree species.

         Nutrient analysis involved grinding each sample in a Wiley mill, ashing a subsample overnight at 500 degrees C, dissolving in a 6 N nitric acid solution, and analyzing for various elements on an ICP spectrometer.  For woody plants, leaf and wood tissue were analyzed separately.

Web page created June 2000
by Ellen Denny and Thomas Siccama