Upland vegetation monitoring for the Blue River Landscape Study: Year 2 results

Steven A. Acker

Dept. of Forest Science

Oregon State University

Apr. 11, 2000

Outline

1. Results of measurements in 1999
   1. Patches sampled in 1999
   2. State of the data
   3. Estimated effort for data collection and quality control
   4. Pre-harvest stand conditions
      1. Live trees
      2. Tree regeneration
      3. Vascular plant species composition and cover
      4. Coarse woody debris
2. Discussion
   1. Relation of patches measured in 1999 to monitoring design
   2. Problems in data collection
   3. Produce regular reports

The objectives, design, and methods for upland vegetation monitoring for the Blue River Landscape Study were described in the report dated January 22, 2000. Results of measurements in 1998 were also described in that report.

I. Results of measurements in 1999

Patches sampled in 1999

Only Landscape Area 3 was represented in the timber sale included in the Blue River Landscape Study that was measured in 1999. Patches in two sale blocks were measured. Both blocks are situated in mature stands. One sale block was located entirely in the western hemlock zone; the other contained elements of both the western hemlock and Pacific silver fir zone. The administrative and ecological setting of the measured patches is summarized in Table 1.

State of the data

Data from 1999 have been typed into computer database files. The computerized data have been checked for completeness and logical errors. The data are archived in the Forest Science Data Bank at Oregon State University (study code = TV048).

Estimated effort for data collection and quality control

Field data were collected by a seasonal crew hired and supervised by personnel from the Blue River Ranger District. The work was performed in late August and early September. A total of 10 individuals recorded data in the field, over a period of 10 days. However, they were not all present on each day. Our best estimate is that 400 hours was expended on the fieldwork (10 days, 8 hours/day, an average of 5 people on the crew).

Data entry was carried out by student hourly workers under the supervision of Gody Spycher of the Dept. of Forest Science. Data entry required 20 hours.

Howard Bruner of the Dept. of Forest Science carried out quality control and archiving after data were entered. He was aided by Gody Spycher and myself. Howard spent 5 hours cleaning and archiving data. Preparation of this report required approximately 20 hours of my time.

Pre-harvest stand conditions

Live trees

Stand structure, tree species composition, and bole volume were generally similar for the two patches (Tables 2-5). Trees per ha, basal area, and average height of the 3 largest trees were slightly higher on Patch 21, while average diameter at breast height (DBH) was slightly higher on patch 40 (Table 2). The 95% confidence intervals (95%CI) for mature stands computed by Spies and Franklin (1991) from an extensive set of plots in natural stands of different seral stages provides a basis for comparison. Both patches were within the 95%CI for trees per ha, but exceeded the 95%CI for basal area.

Tree species composition was similar for the two patches from the perspective of relative basal area, but less so from the perspective of relative density (Tables 3 and 4). Douglas-fir and western hemlock accounted for more than 90% of basal area in both patches. Pacific silver fir accounted for one-quarter of the stems in patch 21, but only 1% in patch 40. Western redcedar comprised 10% of stems in patch 40 but was absent in patch 21.

Information from the Willamette National Forest Plant Association and Management Guide (Hemstrom et al. 1987) provides a standard for comparison of bole volumes on the sampled patches (Table 5). Hemstrom et al. (1987) computed total stand volume, to a 4-inch top, for the mature and old-growth stands they measured in the various plant associations. Table 5 includes total stand volume including top and stump, so values might be expected to be somewhat higher than those reported by Hemstrom et al. Each patch was compared to the most common plant association identified in the patch (i.e., western hemlock/vanilla leaf for patch 21, and western hemlock/dwarf Oregon grape for patch 40). For western hemlock/vanilla leaf, average total stand volume from Hemstrom et al. is 1343 m³/ha (standard error 220). For western hemlock/dwarf Oregon grape, average total stand volume is 1087 m³/ha (s.e. 108). Values for the sampled patches were compared to the average total stand volumes plus or minus 2 standard errors. Total stand volume on both patches exceeded the respective averages (Table 5). However, in both cases the difference was smaller than 2 standard errors.

Tree regeneration

Density of seedlings and saplings was very low: only one seedling and no saplings were observed on the two sampled patches (Table 6). In patch 21, a total of 18, 1 m² quadrats were measured, while in patch 40 a total 24 quadrats were measured.

Vascular plant species composition and cover

A total of 84 species were recorded on the 14 patches sampled in 1998 (Table 7). These included 10 tree species, 26 shrub species, and 48 forb species. No identifications were attempted within the grass family. There was only one exotic species on the list (Lactuca muralis), though the unidentified grasses or Senecio may have included exotic species.

The two patches were similar with respect to diversity of vascular plant species and total understory cover. For both patches, average richness of vascular plant species was between 40 and 50 species per 0.1 ha plot (Table 8). The sum of cover of herbs, shrubs, and tree regeneration was 52% for block 21 and 43% for block 40. However, the distribution by stratum and species differed between the two blocks. In block 21 herbs and low shrubs accounted for most of the understory cover whereas tall shrubs and tree regeneration accounted for most of the understory cover in block 40. For block 21, the dominant species in the two strata were vanilla leaf and Pacific silver fir, respectively. In block 40, the dominant species were dwarf Oregon grape and vine maple (Table 8).

Coarse woody debris

Downed logs in the sampled patches represented the full range of decay states, with 5% in the least decayed state, class 1, 24% in decay class 2, 42% in decay class 3, 21% in decay class 4, and the remaining 9% in decay class 5. Nearly half the logs were Douglas-fir (48%), 44% were of unknown species, 7% were western hemlock, and 3% were other species. The majority of snags were of decay class 2 (63%), with 18% each in both decay classes 1 and 3, and 2% in decay class 4. No snags of the most decayed state, class 5, were recorded. Nearly all the snags were Douglas-fir (92%), 4% were of unknown species, and 4% were of other species.

Logs and snags were more abundant on patch 40 than on patch 21 (Table 9). Mass or volume of snags has not been computed due to complications imposed by missing data. Compared to the extensive survey of natural stands reported by Spies et al. (1988), the two patches had expected to high numbers of logs, while log mass was much higher than expected. In both patches the number of snags was lower than expected. For mature stands in the Oregon Cascades, Spies et al. (1988) reported means of 413 logs per ha (standard error 45), 23 Mg/ha mean log mass (s.e. 3), and 109 snags per per ha (s.e. 17).

The problems that prevented computation of volume and mass for snags concern snags with broken tops. Such snags require measurements of height and top diameter. The problem cases include no top diameter recorded, and no information recorded to compute height to the broken top. It should be possible to estimate the missing data using taper equations and other assumptions, given sufficient time to modify data summary programs. However, accurate measurements would be preferable.

II. Discussion

Relation of patches measured in 1999 to monitoring design

The basic design of this monitoring effort (see report of Jan. 22, 2000) consists of replicate forest patches within strata defined by common combinations of Landscape Area (harvest prescription), plant association, and seral stage. The design calls for at least 3 replicate patches in each stratum. Thus the patches added to the monitoring effort in 1999 represent an incomplete job for two reasons. The first is that only 2 patches representing Landscape Area 3 were measured. The patches measured prior to 1999 included only Landscape Areas 1 and 2, so adequate replication in Landscape Area 3 has not yet been achieved. The second problem concerns the dissimilarity of the environment of the two patches measured in 1999. From the assignment to plant associations using plot data, one patch occupies the most productive end of the gradient of sites in the western hemlock zone (block 21), while the other patch occupies the middle of that gradient. Thus it does appear reasonable to consider these 2 patches as replicates. If timber sales in subsequent years allow, it will be important to add patches in mature stands in Landscape Area 3 representing both moderate and high productivity sites in the western hemlock zone.

Problems in data collection

Many of the systematic problems in data collection that occurred in 1998 did not occur in 1999. Other problems did reoccur, but to a more limited extent than in the previous year. It is important to continue to communicate with field crews to prevent these problems.

Problems with height measurements of live trees and snags were common in the data from 1998. In particular, many heights were recorded with such large angles to the top (>55 degrees) that the observations were discarded. In 1999, this problem still occurred but was not common. Eight height measurements for live trees (out of 136) were discarded due to excessive top angle. The crew is to be commended for indicating on the field sheet that for these heights, measured with the Impulse laser, it was not possible to view the tree tops at angles under 60 degrees. However, the data are still unusable. Procedures should be established for selecting alternate trees when the tops of trees initially selected for height measurements are not possible to view at an appropriate angle.

The use of 4- or 5-character acronyms for plant species ("Garrison codes"), though convenient, often generates some confusion when data are analyzed. Two common problems are neglecting to include the integer at the end of the acronym when necessary and recording an acronym that has the same sound, but a different spelling than the intended species. The 1999 crew eliminated nearly all such problems by writing the complete species name opposite each species code recorded on data sheets containing whole plot species lists. Future crews should be encouraged to continue this practice. There were a few apparent errors in which erroneous codes were recorded for species which were observed in 1x1 m quadrats but not recorded on the whole plot species list. In the future, crews should be reminded to check the quadrat and line intercept cover data forms against the whole plot species list before leaving a plot.

Produce regular reports

As mentioned in the report of Jan. 22, 2000, production of a report on each year’s data is a very valuable exercise which should be continued.

III. Literature cited

Hemstrom, M.A., S.E. Logan, and W. Pavlat. 1987. Plant association and management guide: Willamette National Forest. USDA Forest Service, Pacific Northwest Region, R6-Ecol 257-B-86. 312 p.

Spies, T.A., and J.F. Franklin. 1991. The structure of natural young, mature, and old-growth Douglas-fir forests in Oregon and Washington. Pp. 91-110 in L. Ruggiero, ed. Wildlife and vegetation of unmanaged Douglas-fir forests. Gen. Tech. Rep. PNW-GTR-285. USDA Pacific Northwest Research Station, Portland, OR.

Spies, T.A., J.F. Franklin, and T.B. Thomas. 1988. Coarse woody debris in Douglas-fir forests of western Oregon and Washington. Ecology 69: 1689-1702

Table 1. Summary of patches within which permanent plots were established in 1999 for monitoring upland vegetation for the Blue River Landscape Study.

^aDetermined separately for each plot.

Table 2. Stand structure of patches within which permanent plots were established in 1999. Standard errors in parentheses.

Table 3. Relative density (percent of total trees per hectare) for patches within which permanent plots were established in 1999.

^aSpecies codes: ABAM=Pacific silver fir; ABGR=grand fir; ABPR=noble fir; PSME=Douglas-fir; TABR=western yew; THPL=western redcedar; TSHE=western hemlock.

Table 4. Relative basal area (percent of total basal area) for patches within which permanent plots were established in 1999.

Table 5. Tree bole volume and biomass of patches within which permanent plots were established in 1999. Standard errors in parentheses.

^aScribner rule, to 6" top.

Table 6. Tree regeneration on patches within which permanent plots were established in 1999.

^aSpecies code: ABAM=Pacific silver fir.

^bThere are 4 size classes for seedlings, based on height: 1 (0 to 10 cm); 2 (10 to 25 cm); 3 (25 to 75 cm); 4 (75 to 136 cm). There are 5 size classes for saplings: 0 (0 to 0.9 cm DBH); 1 (1 to 1.9 cm DBH); etc.

Table 7. List of vascular plant species recorded on patches within which permanent plots were established in 1999.

Table 8. Vascular plant species richness, cover of herbs and low shrubs from 1 m² quadrats, and cover of tall shrubs and tree regeneration from line intercepts. Standard errors in parentheses.

^aCover computed by summing covers of all species in the group.

^bSee Table 7 for species acronyms.

Table 9. Coarse woody debris amounts on patches in which permanent plots were established in 1999. Standard errors in parentheses.