Unit-level changes over time

Change in the proportion of sample points with < 5% tree cover over the study period (1985-2020).

Change in the proportion of sample points with < 5% tree cover over the study period (1985-2020).

However, these declines in tree-less area do not appear to come at the cost of other land cover types:

In fact, over all 27 units from 1985-2020, there are only 18 instances of changes greater than 10% in mean cover (increase or decrease), six of which were tree increases, with only two instances of concurrent reductions in perennial grass & herb cover:

Indeed, most tree cover changes have been increases:

Distribution of sample points across all Great Plains NPS units by change in tree cover between 1985 and 2020.

Distribution of sample points across all Great Plains NPS units by change in tree cover between 1985 and 2020.

Changes within landscapes

There is nuance to where within NPS properties tree cover, and tree cover changes, occur most.

Firstly, substantial tree cover is primarily restricted to four ecological site groups.

Secondly, changes in tree cover on these four site groups vary from predominately steady over time (Badlands) to considerable increases (> 10% and > 25% on loamy sites).

Note that Badlands site groups occur only at Badlands NP and the three units of Theodore Roosevelt NP.

Distribution of sample points within ecological site classifications with substantial tree cover by change in tree cover between 1985 and 2020.

Distribution of sample points within ecological site classifications with substantial tree cover by change in tree cover between 1985 and 2020.

Proportion of each Great Plains NPS unit occupied by the four Ecological Site Groups with substantial tree cover.
unit Shallow Limy Loamy Badlands
Agate Fossil Beds 22 NA NA NA
Alibates Flint Quarries NA 34 8 NA
Amistad 34 NA 21 NA
Badlands 16 NA 27 24
Bent’s Old Fort NA NA 44 NA
Bighorn Canyon 40 13 NA NA
Capulin Volcano NA NA 31 NA
Chickasaw 35 NA 8 NA
Ft Laramie NA NA 10 NA
Ft Larned NA NA 71 NA
Ft U Trading Post 0 12 39 NA
Ft Union NA NA 100 NA
Homestead NA NA 81 NA
Knife River 7 NA 65 NA
LBJ NA NA 17 NA
Little Bighorn 33 NA NA NA
Nez Perce NA 24 69 NA
Palo Alto NA NA 17 NA
Salinas 49 NA 15 NA
San Antonio 3 4 75 NA
Sand Creek NA NA 40 NA
Scotts Bluff 17 65 NA NA
Tallgrass NA 41 55 NA
Teddy R’velt Elkhorn NA 2 61 22
Teddy R’velt North 4 1 16 50
Teddy R’velt South 0 20 10 58
Washita NA NA 56 NA